<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #ffffff;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      width: 100%;
      min-height: 100vh;
      padding: 10px;
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    .toolbar {
      display: flex;
      flex-wrap: wrap;
      justify-content: center;
      gap: 8px;
      margin-bottom: 8px;
    }

    .btn {
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      border-radius: 6px;
      padding: 6px 14px;
      font-size: 13px;
      font-weight: 600;
      color: #475569;
      cursor: pointer;
      transition: background 0.2s, color 0.2s, border-color 0.2s;
    }
    .btn:hover {
      background: #e2e8f0;
      color: #1e293b;
    }
    .btn.active {
      background: #0284c7;
      border-color: #0284c7;
      color: #ffffff;
    }

    .svg-container {
      width: 100%;
      max-width: 560px;
      height: auto;
    }

    svg {
      width: 100%;
      height: auto;
      display: block;
    }

    .pair-group {
      transition: opacity 0.3s ease;
    }
    .pair-group.dimmed {
      opacity: 0.18;
    }

    .h-bond {
      stroke: #64748b;
      stroke-width: 2.5;
      stroke-dasharray: 4 4;
      animation: bondPulse 3s infinite ease-in-out;
    }
    @keyframes bondPulse {
      0%, 100% { stroke-opacity: 0.7; }
      50% { stroke-opacity: 1; stroke-width: 3; }
    }
  </style>
</head>
<body>

  <div class="toolbar">
    <button class="btn active" id="btn-all" onclick="setMode('all')">Both Pairs</button>
    <button class="btn" id="btn-at" onclick="setMode('at')">A = T (2 bonds)</button>
    <button class="btn" id="btn-gc" onclick="setMode('gc')">G ≡ C (3 bonds)</button>
  </div>

  <div class="svg-container">
    <svg viewBox="0 0 540 330" preserveAspectRatio="xMidYMid meet">
      
      <g id="width-indicator">
        <line x1="85" y1="28" x2="455" y2="28" stroke="#0284c7" stroke-width="1.5" stroke-dasharray="3 3"/>
        <line x1="85" y1="20" x2="85" y2="36" stroke="#0284c7" stroke-width="2"/>
        <line x1="455" y1="20" x2="455" y2="36" stroke="#0284c7" stroke-width="2"/>
        
        <line x1="280" y1="22" x2="280" y2="34" stroke="#94a3b8" stroke-width="1.5"/>
        <text x="270" y="16" font-size="13" font-weight="700" fill="#0369a1" text-anchor="middle">Uniform Total Width: 3 Rings</text>
        <text x="175" y="44" font-size="12" font-weight="600" fill="#475569" text-anchor="middle">Purine (2 Rings)</text>
        <text x="370" y="44" font-size="12" font-weight="600" fill="#475569" text-anchor="middle">Pyrimidine (1 Ring)</text>
      </g>

      
      <g id="backbones" opacity="0.9">
        
        <line x1="50" y1="60" x2="50" y2="310" stroke="#94a3b8" stroke-width="6" stroke-linecap="round"/>
        <circle cx="50" cy="115" r="13" fill="#0284c7"/>
        <text x="50" y="119" fill="#fff" font-size="11" font-weight="700" text-anchor="middle">P</text>
        <circle cx="50" cy="245" r="13" fill="#0284c7"/>
        <text x="50" y="249" fill="#fff" font-size="11" font-weight="700" text-anchor="middle">P</text>
        <line x1="50" y1="115" x2="85" y2="115" stroke="#64748b" stroke-width="2"/>
        <line x1="50" y1="245" x2="85" y2="245" stroke="#64748b" stroke-width="2"/>

        
        <line x1="490" y1="60" x2="490" y2="310" stroke="#94a3b8" stroke-width="6" stroke-linecap="round"/>
        <circle cx="490" cy="115" r="13" fill="#0284c7"/>
        <text x="490" y="119" fill="#fff" font-size="11" font-weight="700" text-anchor="middle">P</text>
        <circle cx="490" cy="245" r="13" fill="#0284c7"/>
        <text x="490" y="249" fill="#fff" font-size="11" font-weight="700" text-anchor="middle">P</text>
        <line x1="455" y1="115" x2="490" y2="115" stroke="#64748b" stroke-width="2"/>
        <line x1="455" y1="245" x2="490" y2="245" stroke="#64748b" stroke-width="2"/>
      </g>

      
      <g id="pair-at" class="pair-group">
        
        <g transform="translate(85, 75)">
          
          <polygon points="30,0 75,0 100,35 75,70 30,70 5,35" fill="#ecfdf5" stroke="#059669" stroke-width="2.5"/>
          
          <polygon points="100,35 75,70 115,80 140,50 130,20" fill="#ecfdf5" stroke="#059669" stroke-width="2.5"/>
          <text x="52" y="32" font-size="19" font-weight="800" fill="#047857" text-anchor="middle">A</text>
          <text x="52" y="52" font-size="10.5" font-weight="700" fill="#059669" text-anchor="middle">Adenine</text>
        </g>

        
        <g>
          
          <rect x="242" y="72" width="58" height="20" rx="5" fill="#f8fafc" stroke="#cbd5e1" stroke-width="1.2"/>
          <text x="271" y="86" font-size="12" font-weight="700" fill="#334155" text-anchor="middle">2 bonds</text>
          <line x1="230" y1="105" x2="315" y2="105" class="h-bond"/>
          <line x1="230" y1="125" x2="315" y2="125" class="h-bond"/>
        </g>

        
        <g transform="translate(315, 75)">
          <polygon points="30,0 75,0 100,35 75,70 30,70 5,35" fill="#fef2f2" stroke="#dc2626" stroke-width="2.5"/>
          <text x="52" y="32" font-size="19" font-weight="800" fill="#b91c1c" text-anchor="middle">T</text>
          <text x="52" y="52" font-size="10.5" font-weight="700" fill="#dc2626" text-anchor="middle">Thymine</text>
        </g>

        
        <text x="270" y="172" font-size="13.5" font-weight="700" fill="#1e2945" text-anchor="middle">A = T (2 H-bonds)</text>
      </g>

      
      <g id="pair-gc" class="pair-group">
        
        <g transform="translate(85, 205)">
          
          <polygon points="30,0 75,0 100,35 75,70 30,70 5,35" fill="#eff6ff" stroke="#2563eb" stroke-width="2.5"/>
          
          <polygon points="100,35 75,70 115,80 140,50 130,20" fill="#eff6ff" stroke="#2563eb" stroke-width="2.5"/>
          <text x="52" y="32" font-size="19" font-weight="800" fill="#1d4ed8" text-anchor="middle">G</text>
          <text x="52" y="52" font-size="10.5" font-weight="700" fill="#2563eb" text-anchor="middle">Guanine</text>
        </g>

        
        <g>
          
          <rect x="242" y="202" width="58" height="20" rx="5" fill="#f8fafc" stroke="#cbd5e1" stroke-width="1.2"/>
          <text x="271" y="216" font-size="12" font-weight="700" fill="#334155" text-anchor="middle">3 bonds</text>
          <line x1="230" y1="232" x2="315" y2="232" class="h-bond"/>
          <line x1="230" y1="245" x2="315" y2="245" class="h-bond"/>
          <line x1="230" y1="258" x2="315" y2="258" class="h-bond"/>
        </g>

        
        <g transform="translate(315, 205)">
          <polygon points="30,0 75,0 100,35 75,70 30,70 5,35" fill="#fffbeb" stroke="#d97706" stroke-width="2.5"/>
          <text x="52" y="32" font-size="19" font-weight="800" fill="#b45309" text-anchor="middle">C</text>
          <text x="52" y="52" font-size="10.5" font-weight="700" fill="#d97706" text-anchor="middle">Cytosine</text>
        </g>

        
        <text x="270" y="304" font-size="13.5" font-weight="700" fill="#1e2945" text-anchor="middle">G ≡ C (3 H-bonds)</text>
      </g>
    </svg>
  </div>

  <script>
    function setMode(mode) {
      document.querySelectorAll('.btn').forEach(b => b.classList.remove('active'));
      document.getElementById('btn-' + mode).classList.add('active');

      const at = document.getElementById('pair-at');
      const gc = document.getElementById('pair-gc');

      if (mode === 'all') {
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        gc.classList.add('dimmed');
      } else if (mode === 'gc') {
        at.classList.add('dimmed');
        gc.classList.remove('dimmed');
      }
    }
  </script>
</body>
</html>

DNA Structure: Nucleotides, Base Pairs, and the Double Helix

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #ffffff;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      width: 100%;
      min-height: 100%;
      padding: 10px 12px;
      user-select: none;
    }

    .controls {
      display: flex;
      gap: 6px;
      margin-bottom: 6px;
      flex-wrap: wrap;
      justify-content: center;
    }

    .btn {
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      border-radius: 20px;
      padding: 5px 14px;
      font-size: 13px;
      font-weight: 600;
      color: #475569;
      cursor: pointer;
      transition: all 0.2s ease;
    }

    .btn.active {
      background: #0284c7;
      border-color: #0284c7;
      color: #ffffff;
    }

    .svg-container {
      width: 100%;
      max-width: 540px;
      flex-grow: 1;
      display: flex;
      align-items: center;
      justify-content: center;
    }

    svg {
      width: 100%;
      height: auto;
      overflow: visible;
    }

    .backbone-line {
      stroke: #0284c7;
      stroke-width: 7px;
      stroke-linecap: round;
      transition: stroke 0.3s, opacity 0.3s;
    }

    .sugar-up {
      fill: #e0f2fe;
      stroke: #0284c7;
      stroke-width: 2px;
    }

    .sugar-down {
      fill: #fef3c7;
      stroke: #d97706;
      stroke-width: 2px;
    }

    .phosphate {
      fill: #f59e0b;
      stroke: #b45309;
      stroke-width: 1.5px;
    }

    .base-a { fill: #3b82f6; stroke: #1d4ed8; }
    .base-t { fill: #f97316; stroke: #c2410c; }
    .base-g { fill: #10b981; stroke: #047857; }
    .base-c { fill: #8b5cf6; stroke: #6d28d9; }

    .base-rect {
      stroke-width: 1.5px;
      rx: 4px;
      ry: 4px;
    }

    .base-text {
      fill: #ffffff;
      font-weight: 800;
      font-size: 14px;
      text-anchor: middle;
      dominant-baseline: central;
      font-family: inherit;
    }

    .h-bond {
      stroke: #64748b;
      stroke-width: 2.5px;
      stroke-linecap: round;
      stroke-dasharray: 2 4;
      transition: stroke 0.3s, stroke-width 0.3s;
    }

    .arrow-track {
      stroke-width: 3.5px;
      stroke-linecap: round;
      stroke-linejoin: round;
      fill: none;
      opacity: 0;
      transition: opacity 0.3s ease;
    }

    .arrow-left {
      stroke: #0284c7;
    }

    .arrow-right {
      stroke: #d97706;
    }

    .label-tag {
      font-size: 13px;
      font-weight: 700;
      fill: #1e2945;
      text-anchor: middle;
      font-family: inherit;
    }

    .sub-tag {
      font-size: 11px;
      font-weight: 600;
      fill: #64748b;
      text-anchor: middle;
      font-family: inherit;
    }

    .strand-dir {
      font-size: 12px;
      font-weight: 800;
      text-anchor: middle;
      font-family: inherit;
      opacity: 0;
      transition: opacity 0.3s ease;
    }

    .highlight-hbonds .h-bond {
      stroke: #e11d48;
      stroke-width: 3.5px;
    }

    .highlight-arrows .arrow-track,
    .highlight-arrows .strand-dir {
      opacity: 1;
    }
  </style>
</head>
<body>

  <div class="controls">
    <button class="btn active" id="btn-all" onclick="setMode('all')">Full Structure</button>
    <button class="btn" id="btn-antiparallel" onclick="setMode('antiparallel')">5′ ➔ 3′ Directions</button>
    <button class="btn" id="btn-bonds" onclick="setMode('bonds')">Hydrogen Bonds</button>
  </div>

  <div class="svg-container">
    <svg id="dna-svg" viewBox="0 0 460 360">
      <defs>
        <marker id="arrow-down" viewBox="0 0 10 10" refX="5" refY="5" markerWidth="6" markerHeight="6" orient="auto">
          <path d="M 0 0 L 10 5 L 0 10 z" fill="#0284c7" />
        </marker>
        <marker id="arrow-up" viewBox="0 0 10 10" refX="5" refY="5" markerWidth="6" markerHeight="6" orient="auto">
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      </defs>

      
      <line x1="88" y1="52" x2="88" y2="308" class="backbone-line" />
      <line x1="372" y1="52" x2="372" y2="308" class="backbone-line" style="stroke: #d97706;" />

      
      <path d="M 40 70 L 40 280" class="arrow-track arrow-left" marker-end="url(#arrow-down)" />
      <text x="32" y="175" class="strand-dir" fill="#0284c7" transform="rotate(-90 32 175)">5′ ➔ 3′</text>

      <path d="M 420 280 L 420 70" class="arrow-track arrow-right" marker-end="url(#arrow-up)" />
      <text x="428" y="175" class="strand-dir" fill="#d97706" transform="rotate(90 428 175)">5′ ➔ 3′</text>

      
      <g>
        <text x="88" y="20" class="label-tag">5′ end</text>
        <text x="88" y="34" class="sub-tag">(Phosphate)</text>
      </g>
      <g>
        <text x="372" y="20" class="label-tag">3′ end</text>
        <text x="372" y="34" class="sub-tag">(Sugar-OH)</text>
      </g>

      
      <g id="row1">
        
        <circle cx="88" cy="52" r="10" class="phosphate" />
        <text x="88" y="52" fill="#fff" font-size="10" font-weight="900" text-anchor="middle" dominant-baseline="central">P</text>
        <polygon points="88,62 108,76 99,94 77,94 68,76" class="sugar-up" />
        
        
        <line x1="108" y1="76" x2="140" y2="76" stroke="#0284c7" stroke-width="2" />
        <rect x="140" y="62" width="60" height="28" class="base-a base-rect" />
        <text x="170" y="76" class="base-text">A</text>

        
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        <line x1="205" y1="81" x2="255" y2="81" class="h-bond" />

        
        <rect x="260" y="62" width="60" height="28" class="base-t base-rect" />
        <text x="290" y="76" class="base-text">T</text>
        <line x1="320" y1="76" x2="352" y2="76" stroke="#d97706" stroke-width="2" />

        
        <polygon points="372,94 352,80 361,62 383,62 392,80" class="sugar-down" />
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      <g id="row2">
        
        <circle cx="88" cy="118" r="10" class="phosphate" />
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        <polygon points="88,128 108,142 99,160 77,160 68,142" class="sugar-up" />

        
        <line x1="108" y1="142" x2="140" y2="142" stroke="#0284c7" stroke-width="2" />
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        <text x="170" y="142" class="base-text">G</text>

        
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        <line x1="205" y1="149" x2="255" y2="149" class="h-bond" />

        
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        <text x="290" y="142" class="base-text">C</text>
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      <g id="row3">
        
        <circle cx="88" cy="184" r="10" class="phosphate" />
        <text x="88" y="184" fill="#fff" font-size="10" font-weight="900" text-anchor="middle" dominant-baseline="central">P</text>
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        <line x1="108" y1="208" x2="140" y2="208" stroke="#0284c7" stroke-width="2" />
        <rect x="140" y="194" width="60" height="28" class="base-c base-rect" />
        <text x="170" y="208" class="base-text">C</text>

        
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        <line x1="205" y1="208" x2="255" y2="208" class="h-bond" />
        <line x1="205" y1="215" x2="255" y2="215" class="h-bond" />

        
        <rect x="260" y="194" width="60" height="28" class="base-g base-rect" />
        <text x="290" y="208" class="base-text">G</text>
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        <circle cx="372" cy="184" r="10" class="phosphate" />
        <text x="372" y="184" fill="#fff" font-size="10" font-weight="900" text-anchor="middle" dominant-baseline="central">P</text>
      </g>

      
      <g id="row4">
        
        <circle cx="88" cy="250" r="10" class="phosphate" />
        <text x="88" y="250" fill="#fff" font-size="10" font-weight="900" text-anchor="middle" dominant-baseline="central">P</text>
        <polygon points="88,260 108,274 99,292 77,292 68,274" class="sugar-up" />

        
        <line x1="108" y1="274" x2="140" y2="274" stroke="#0284c7" stroke-width="2" />
        <rect x="140" y="260" width="60" height="28" class="base-t base-rect" />
        <text x="170" y="274" class="base-text">T</text>

        
        <line x1="205" y1="269" x2="255" y2="269" class="h-bond" />
        <line x1="205" y1="279" x2="255" y2="279" class="h-bond" />

        
        <rect x="260" y="260" width="60" height="28" class="base-a base-rect" />
        <text x="290" y="274" class="base-text">A</text>
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        <polygon points="372,292 352,278 361,260 383,260 392,278" class="sugar-down" />
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        <circle cx="372" cy="308" r="10" class="phosphate" />
        <text x="372" y="308" fill="#fff" font-size="10" font-weight="900" text-anchor="middle" dominant-baseline="central">P</text>
      </g>

      
      <g>
        <text x="88" y="334" class="label-tag">3′ end</text>
        <text x="88" y="348" class="sub-tag">(Sugar-OH)</text>
      </g>
      <g>
        <text x="372" y="334" class="label-tag">5′ end</text>
        <text x="372" y="348" class="sub-tag">(Phosphate)</text>
      </g>

      
      <text x="230" y="348" class="sub-tag" font-weight="700" fill="#475569">Sugar-Phosphate Backbone</text>
    </svg>
  </div>

  <script>
    function setMode(mode) {
      const svg = document.getElementById('dna-svg');
      const btnAll = document.getElementById('btn-all');
      const btnAnti = document.getElementById('btn-antiparallel');
      const btnBonds = document.getElementById('btn-bonds');

      btnAll.classList.remove('active');
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        svg.classList.add('highlight-hbonds');
      } else {
        btnAll.classList.add('active');
      }
    }
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
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      background: transparent;
      font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
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      display: flex;
      flex-wrap: wrap;
      gap: 5px;
      justify-content: center;
      width: 100%;
      max-width: 420px;
      margin-bottom: 2px;
      z-index: 10;
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      appearance: none;
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      background: #0284c7;
      color: #ffffff;
      border-color: #0284c7;
      box-shadow: 0 1px 4px rgba(2, 132, 199, 0.35);
    }

    /* Stage Area */
    .stage {
      position: relative;
      width: 100%;
      max-width: 390px;
      aspect-ratio: 410 / 355;
      display: flex;
      align-items: center;
      justify-content: center;
      touch-action: pan-y;
      cursor: grab;
    }
    .stage:active {
      cursor: grabbing;
    }
    svg {
      width: 100%;
      height: 100%;
      overflow: visible;
      display: block;
    }

    /* Base legend */
    .legend {
      display: flex;
      justify-content: center;
      gap: 14px;
      margin-top: 1px;
      font-size: 11.5px;
      font-weight: 600;
      color: #475569;
    }
    .legend-item {
      display: flex;
      align-items: center;
      gap: 4px;
    }
    .swatch {
      width: 10px;
      height: 10px;
      border-radius: 2px;
    }

    /* Dynamic Callouts */
    .callout-text {
      font-size: 10.5px;
      font-weight: 700;
      fill: #0f172a;
      letter-spacing: 0.1px;
    }
    .callout-sub {
      font-size: 9px;
      font-weight: 500;
      fill: #64748b;
    }
    .term-label {
      font-size: 12px;
      font-weight: 800;
      text-anchor: middle;
      dominant-baseline: central;
      transition: opacity 0.3s ease;
    }
  </style>
</head>
<body>

  
  <div class="controls">
    <button class="btn active" id="btn-all" onclick="setMode('all')">Overview</button>
    <button class="btn" id="btn-backbone" onclick="setMode('backbone')">Backbone</button>
    <button class="btn" id="btn-bases" onclick="setMode('bases')">Base Pairs</button>
    <button class="btn" id="btn-terminals" onclick="setMode('terminals')">5' &amp; 3' Ends</button>
  </div>

  
  <div class="stage" id="stage">
    <svg id="dna-svg" viewBox="-205 -178 410 356"></svg>
  </div>

  
  <div class="legend" id="legend">
    <div class="legend-item"><div class="swatch" style="background:#0284c7;"></div>A (Adenine)</div>
    <div class="legend-item"><div class="swatch" style="background:#f59e0b;"></div>T (Thymine)</div>
    <div class="legend-item"><div class="swatch" style="background:#10b981;"></div>G (Guanine)</div>
    <div class="legend-item"><div class="swatch" style="background:#ec4899;"></div>C (Cytosine)</div>
  </div>

  <script>
    const SVG_NS = "http://www.w3.org/2000/svg";
    const svg = document.getElementById('dna-svg');

    // DNA Geometry Constants
    const NUM_RUNGS = 21;
    const TOTAL_TURNS = 2;
    const RADIUS = 56;
    const HEIGHT = 310;
    const Y_START = -HEIGHT / 2;
    const Y_STEP = HEIGHT / (NUM_RUNGS - 1);
    const ANGLE_STEP = (TOTAL_TURNS * 2 * Math.PI) / (NUM_RUNGS - 1);
    const MINOR_OFFSET = 2.25;

    // Base pair types (A-T, G-C, T-A, C-G)
    const PAIRS = [
      { b1: 'A', c1: '#0284c7', b2: 'T', c2: '#f59e0b' },
      { b1: 'G', c1: '#10b981', b2: 'C', c2: '#ec4899' },
      { b1: 'T', c1: '#f59e0b', b2: 'A', c2: '#0284c7' },
      { b1: 'C', c1: '#ec4899', b2: 'G', c2: '#10b981' },
      { b1: 'A', c1: '#0284c7', b2: 'T', c2: '#f59e0b' },
      { b1: 'C', c1: '#ec4899', b2: 'G', c2: '#10b981' },
      { b1: 'G', c1: '#10b981', b2: 'C', c2: '#ec4899' },
      { b1: 'T', c1: '#f59e0b', b2: 'A', c2: '#0284c7' },
      { b1: 'A', c1: '#0284c7', b2: 'T', c2: '#f59e0b' },
      { b1: 'G', c1: '#10b981', b2: 'C', c2: '#ec4899' },
      { b1: 'C', c1: '#ec4899', b2: 'G', c2: '#10b981' },
      { b1: 'T', c1: '#f59e0b', b2: 'A', c2: '#0284c7' },
      { b1: 'A', c1: '#0284c7', b2: 'T', c2: '#f59e0b' },
      { b1: 'G', c1: '#10b981', b2: 'C', c2: '#ec4899' },
      { b1: 'T', c1: '#f59e0b', b2: 'A', c2: '#0284c7' },
      { b1: 'C', c1: '#ec4899', b2: 'G', c2: '#10b981' },
      { b1: 'A', c1: '#0284c7', b2: 'T', c2: '#f59e0b' },
      { b1: 'G', c1: '#10b981', b2: 'C', c2: '#ec4899' },
      { b1: 'T', c1: '#f59e0b', b2: 'A', c2: '#0284c7' },
      { b1: 'C', c1: '#ec4899', b2: 'G', c2: '#10b981' },
      { b1: 'A', c1: '#0284c7', b2: 'T', c2: '#f59e0b' }
    ];

    let currentMode = 'all';
    let rotAngle = 0;
    let isDragging = false;
    let startX = 0;

    function setMode(mode) {
      currentMode = mode;
      document.querySelectorAll('.btn').forEach(b => b.classList.remove('active'));
      const activeBtn = document.getElementById(`btn-${mode}`);
      if (activeBtn) activeBtn.classList.add('active');
      render();
    }

    // Touch & Mouse Drag to Rotate
    const stage = document.getElementById('stage');
    stage.addEventListener('mousedown', e => { isDragging = true; startX = e.clientX; });
    window.addEventListener('mousemove', e => {
      if (!isDragging) return;
      const dx = e.clientX - startX;
      rotAngle += dx * 0.015;
      startX = e.clientX;
      render();
    });
    window.addEventListener('mouseup', () => isDragging = false);

    stage.addEventListener('touchstart', e => {
      if (e.touches.length === 1) {
        isDragging = true;
        startX = e.touches[0].clientX;
      }
    }, { passive: true });
    window.addEventListener('touchmove', e => {
      if (!isDragging || e.touches.length !== 1) return;
      const dx = e.touches[0].clientX - startX;
      rotAngle += dx * 0.015;
      startX = e.touches[0].clientX;
      render();
    }, { passive: true });
    window.addEventListener('touchend', () => isDragging = false);

    function createSVGEl(type, attrs = {}) {
      const el = document.createElementNS(SVG_NS, type);
      for (const [k, v] of Object.entries(attrs)) {
        el.setAttribute(k, v);
      }
      return el;
    }

    function render() {
      svg.innerHTML = '';

      const bbOpacity = (currentMode === 'bases') ? 0.2 : 1;
      const baseOpacity = (currentMode === 'backbone' || currentMode === 'terminals') ? 0.18 : 1;

      // Compute 3D points
      const rungs = [];
      for (let i = 0; i < NUM_RUNGS; i++) {
        const theta1 = rotAngle + i * ANGLE_STEP;
        const theta2 = theta1 + MINOR_OFFSET;
        const y = Y_START + i * Y_STEP;

        const p1 = { x: RADIUS * Math.cos(theta1), y: y, z: RADIUS * Math.sin(theta1) };
        const p2 = { x: RADIUS * Math.cos(theta2), y: y, z: RADIUS * Math.sin(theta2) };

        rungs.push({
          idx: i,
          p1,
          p2,
          midZ: (p1.z + p2.z) / 2,
          pair: PAIRS[i % PAIRS.length]
        });
      }

      // 1. Render Back-Segments of Strands (z < 0)
      renderRibbonSegments(rungs, true, bbOpacity);

      // 2. Render Base Pairs (sorted by Z depth)
      const sortedRungs = [...rungs].sort((a, b) => a.midZ - b.midZ);
      sortedRungs.forEach(rung => {
        const { p1, p2, pair } = rung;
        const mx = (p1.x + p2.x) / 2;
        const my = (p1.y + p2.y) / 2;

        const g = createSVGEl('g', { opacity: baseOpacity, style: 'transition: opacity 0.25s;' });

        // Strand 1 Base
        g.appendChild(createSVGEl('line', {
          x1: p1.x, y1: p1.y, x2: mx, y2: my,
          stroke: pair.c1, 'stroke-width': (currentMode === 'bases' ? 5.5 : 4),
          'stroke-linecap': 'round'
        }));

        // Strand 2 Base
        g.appendChild(createSVGEl('line', {
          x1: mx, y1: my, x2: p2.x, y2: p2.y,
          stroke: pair.c2, 'stroke-width': (currentMode === 'bases' ? 5.5 : 4),
          'stroke-linecap': 'round'
        }));

        // Hydrogen Bond Center Notch / Dot
        const hBondColor = (currentMode === 'bases') ? '#ffffff' : '#ffffffdd';
        g.appendChild(createSVGEl('circle', {
          cx: mx, cy: my, r: (currentMode === 'bases' ? 2 : 1.3),
          fill: hBondColor
        }));

        svg.appendChild(g);
      });

      // 3. Render Front-Segments of Strands (z >= 0)
      renderRibbonSegments(rungs, false, bbOpacity);

      // 4. Mode-Specific Annotations & Callouts
      if (currentMode === 'all') {
        renderGrooveCallouts();
      } else if (currentMode === 'backbone') {
        renderBackboneCallouts();
      } else if (currentMode === 'bases') {
        renderBasePairCallouts();
      } else if (currentMode === 'terminals') {
        renderTerminalLabels(rungs);
      }
    }

    function renderRibbonSegments(rungs, isBack, opacity) {
      const strand1Color = '#3b82f6';
      const strand2Color = '#8b5cf6';

      for (let i = 0; i < rungs.length - 1; i++) {
        const rA = rungs[i];
        const rB = rungs[i + 1];

        // Strand 1 segment
        const z1Avg = (rA.p1.z + rB.p1.z) / 2;
        if ((isBack && z1Avg < 0) || (!isBack && z1Avg >= 0)) {
          const depthAlpha = 0.5 + 0.5 * ((z1Avg + RADIUS) / (2 * RADIUS));
          svg.appendChild(createSVGEl('line', {
            x1: rA.p1.x, y1: rA.p1.y, x2: rB.p1.x, y2: rB.p1.y,
            stroke: strand1Color,
            'stroke-width': 7,
            'stroke-linecap': 'round',
            opacity: opacity * depthAlpha,
            style: 'transition: opacity 0.25s;'
          }));
        }

        // Strand 2 segment
        const z2Avg = (rA.p2.z + rB.p2.z) / 2;
        if ((isBack && z2Avg < 0) || (!isBack && z2Avg >= 0)) {
          const depthAlpha = 0.5 + 0.5 * ((z2Avg + RADIUS) / (2 * RADIUS));
          svg.appendChild(createSVGEl('line', {
            x1: rA.p2.x, y1: rA.p2.y, x2: rB.p2.x, y2: rB.p2.y,
            stroke: strand2Color,
            'stroke-width': 7,
            'stroke-linecap': 'round',
            opacity: opacity * depthAlpha,
            style: 'transition: opacity 0.25s;'
          }));
        }
      }
    }

    function renderGrooveCallouts() {
      const g = createSVGEl('g', { id: 'groove-callouts' });

      // Major Groove bracket (Right side)
      const mjY1 = -82, mjY2 = 8;
      const rx = 74;
      g.appendChild(createSVGEl('path', {
        d: `M ${rx} ${mjY1} L ${rx+11} ${mjY1} L ${rx+11} ${(mjY1+mjY2)/2} L ${rx+18} ${(mjY1+mjY2)/2} L ${rx+11} ${(mjY1+mjY2)/2} L ${rx+11} ${mjY2} L ${rx} ${mjY2}`,
        stroke: '#0284c7', 'stroke-width': 1.5, fill: 'none', 'stroke-linecap': 'round', 'stroke-linejoin': 'round'
      }));
      const mjText = createSVGEl('text', { x: rx + 24, y: (mjY1+mjY2)/2 - 3, class: 'callout-text' });
      mjText.textContent = 'Major Groove';
      const mjSub = createSVGEl('text', { x: rx + 24, y: (mjY1+mjY2)/2 + 10, class: 'callout-sub' });
      mjSub.textContent = 'Wide gap';
      g.appendChild(mjText);
      g.appendChild(mjSub);

      // Minor Groove bracket (Left side)
      const mnY1 = 28, mnY2 = 82;
      const lx = -74;
      g.appendChild(createSVGEl('path', {
        d: `M ${lx} ${mnY1} L ${lx-11} ${mnY1} L ${lx-11} ${(mnY1+mnY2)/2} L ${lx-18} ${(mnY1+mnY2)/2} L ${lx-11} ${(mnY1+mnY2)/2} L ${lx-11} ${mnY2} L ${lx} ${mnY2}`,
        stroke: '#8b5cf6', 'stroke-width': 1.5, fill: 'none', 'stroke-linecap': 'round', 'stroke-linejoin': 'round'
      }));
      const mnText = createSVGEl('text', { x: lx - 24, y: (mnY1+mnY2)/2 - 3, class: 'callout-text', 'text-anchor': 'end' });
      mnText.textContent = 'Minor Groove';
      const mnSub = createSVGEl('text', { x: lx - 24, y: (mnY1+mnY2)/2 + 10, class: 'callout-sub', 'text-anchor': 'end' });
      mnSub.textContent = 'Narrow gap';
      g.appendChild(mnText);
      g.appendChild(mnSub);

      svg.appendChild(g);
    }

    function renderBackboneCallouts() {
      const g = createSVGEl('g', { id: 'backbone-callouts' });
      
      // Pointer to Strand 1
      g.appendChild(createSVGEl('line', {
        x1: -105, y1: -65, x2: -62, y2: -65,
        stroke: '#3b82f6', 'stroke-width': 1.5, 'stroke-dasharray': '3,3'
      }));
      g.appendChild(createSVGEl('circle', { cx: -62, cy: -65, r: 2.8, fill: '#3b82f6' }));
      const t1 = createSVGEl('text', { x: -110, y: -61, class: 'callout-text', 'text-anchor': 'end' });
      t1.textContent = 'Sugar-Phosphate';
      const s1 = createSVGEl('text', { x: -110, y: -49, class: 'callout-sub', 'text-anchor': 'end' });
      s1.textContent = 'Strand 1';
      g.appendChild(t1);
      g.appendChild(s1);

      // Pointer to Strand 2
      g.appendChild(createSVGEl('line', {
        x1: 105, y1: 45, x2: 62, y2: 45,
        stroke: '#8b5cf6', 'stroke-width': 1.5, 'stroke-dasharray': '3,3'
      }));
      g.appendChild(createSVGEl('circle', { cx: 62, cy: 45, r: 2.8, fill: '#8b5cf6' }));
      const t2 = createSVGEl('text', { x: 110, y: 49, class: 'callout-text' });
      t2.textContent = 'Sugar-Phosphate';
      const s2 = createSVGEl('text', { x: 110, y: 61, class: 'callout-sub' });
      s2.textContent = 'Strand 2';
      g.appendChild(t2);
      g.appendChild(s2);

      svg.appendChild(g);
    }

    function renderBasePairCallouts() {
      const g = createSVGEl('g', { id: 'base-callouts' });

      // Hydrogen bonding pointer
      g.appendChild(createSVGEl('line', {
        x1: 0, y1: -78, x2: 0, y2: -32,
        stroke: '#0f172a', 'stroke-width': 1.5, 'stroke-dasharray': '3,3'
      }));
      g.appendChild(createSVGEl('circle', { cx: 0, cy: -32, r: 3, fill: '#0f172a' }));

      const pill = createSVGEl('rect', {
        x: -56, y: -102, width: 112, height: 23, rx: 11.5,
        fill: '#ffffff', stroke: '#cbd5e1', 'stroke-width': 1.2
      });
      const t = createSVGEl('text', { x: 0, y: -87, class: 'callout-text', 'text-anchor': 'middle' });
      t.textContent = 'Hydrogen Bonds';
      
      g.appendChild(pill);
      g.appendChild(t);
      svg.appendChild(g);
    }

    function renderTerminalLabels(rungs) {
      const g = createSVGEl('g', { id: 'terminal-labels' });

      const topRung = rungs[0];
      const botRung = rungs[rungs.length - 1];

      // Strand 1: 5' (top) -> 3' (bottom)
      drawEndBadge(g, topRung.p1.x, topRung.p1.y - 14, "5'", '#3b82f6');
      drawEndBadge(g, botRung.p1.x, botRung.p1.y + 14, "3'", '#3b82f6');

      // Strand 2: 3' (top) -> 5' (bottom) [Antiparallel]
      drawEndBadge(g, topRung.p2.x, topRung.p2.y - 14, "3'", '#8b5cf6');
      drawEndBadge(g, botRung.p2.x, botRung.p2.y + 14, "5'", '#8b5cf6');

      // Antiparallel Indicator badge
      const antiPill = createSVGEl('rect', {
        x: -56, y: 147, width: 112, height: 22, rx: 11,
        fill: '#f8fafc', stroke: '#cbd5e1', 'stroke-width': 1.2
      });
      const antiText = createSVGEl('text', { x: 0, y: 162, class: 'callout-text', 'text-anchor': 'middle' });
      antiText.textContent = 'Antiparallel Strands';
      g.appendChild(antiPill);
      g.appendChild(antiText);

      svg.appendChild(g);
    }

    function drawEndBadge(parent, x, y, text, color) {
      const circle = createSVGEl('circle', {
        cx: x, cy: y, r: 11.5,
        fill: color, stroke: '#ffffff', 'stroke-width': 1.5,
        style: 'filter: drop-shadow(0 1px 3px rgba(0,0,0,0.2));'
      });
      const lbl = createSVGEl('text', {
        x: x, y: y,
        fill: '#ffffff', class: 'term-label'
      });
      lbl.textContent = text;
      parent.appendChild(circle);
      parent.appendChild(lbl);
    }

    // Initial render
    render();
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      color: #1e2945;
      background: #ffffff;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100%;
      padding: 12px 10px;
      user-select: none;
    }

    .controls {
      display: flex;
      gap: 6px;
      flex-wrap: wrap;
      justify-content: center;
      width: 100%;
      max-width: 420px;
    }

    .btn {
      appearance: none;
      border: 1px solid #e6e6e6;
      background: #f8fafc;
      color: #1e2945;
      padding: 5px 12px;
      border-radius: 999px;
      font-size: 13px;
      font-weight: 600;
      cursor: pointer;
      transition: background 0.2s ease, color 0.2s ease, box-shadow 0.2s ease;
    }

    .btn:active {
      transform: translateY(1px);
    }

    .btn.active {
      background: #1e2945;
      color: #ffffff;
      border-color: #1e2945;
      box-shadow: 0 2px 6px rgba(30, 41, 69, 0.25);
    }

    .diagram-svg {
      width: 100%;
      max-width: 420px;
      height: auto;
      display: block;
      margin: auto 0;
    }

    .part-group {
      cursor: pointer;
      transition: opacity 0.3s ease;
    }

    .dimmed {
      opacity: 0.22;
    }

    .carbon-badge {
      font-family: system-ui, sans-serif;
      font-size: 13px;
      font-weight: 700;
      fill: #1e2945;
    }

    .part-label {
      font-family: system-ui, sans-serif;
      font-weight: 700;
      text-anchor: middle;
      pointer-events: none;
    }

    .chem-label {
      font-family: system-ui, sans-serif;
      font-weight: 600;
      text-anchor: middle;
      pointer-events: none;
    }
  </style>
</head>
<body>

  <div class="controls" id="btnGroup">
    <button class="btn active" data-part="all">All Parts</button>
    <button class="btn" data-part="phosphate">Phosphate</button>
    <button class="btn" data-part="sugar">Sugar</button>
    <button class="btn" data-part="base">Base</button>
  </div>

  <svg class="diagram-svg" viewBox="0 0 460 300" aria-label="DNA Nucleotide Structure">
    
    <g stroke="#94a3b8" stroke-width="4" stroke-linecap="round" stroke-linejoin="round">
      
      <line x1="88" y1="92" x2="135" y2="128" />
      
      <line x1="135" y1="128" x2="158" y2="175" />
      
      <line x1="282" y1="175" x2="330" y2="175" />
    </g>

    
    <g class="part-group" id="group-phosphate" data-name="phosphate">
      <circle cx="68" cy="76" r="46" fill="#fef3c7" stroke="#f59e0b" stroke-width="3" />
      <text x="68" y="70" class="part-label" fill="#92400e" font-size="12">Phosphate</text>
      <text x="68" y="85" class="part-label" fill="#92400e" font-size="12">Group</text>
      <text x="68" y="105" class="chem-label" fill="#b45309" font-size="13">PO₄³⁻</text>
    </g>

    
    <g class="part-group" id="group-sugar" data-name="sugar">
      
      <polygon points="220,132 282,175 258,245 182,245 158,175"
               fill="#ffedd5" stroke="#f97316" stroke-width="3.5" stroke-linejoin="round" />
      
      
      <circle cx="220" cy="132" r="12" fill="#ffffff" stroke="#f97316" stroke-width="2.5" />
      <text x="220" y="136" class="chem-label" fill="#ea580c" font-size="12">O</text>

      <text x="220" y="196" class="part-label" fill="#c2410c" font-size="12">Deoxyribose</text>
      <text x="220" y="212" class="part-label" fill="#c2410c" font-size="12">Sugar</text>

      
      
      <circle cx="135" cy="128" r="11" fill="#fff7ed" stroke="#ea580c" stroke-width="2" />
      <text x="135" y="132" text-anchor="middle" class="carbon-badge">5′</text>

      
      <circle cx="158" cy="175" r="11" fill="#fff7ed" stroke="#ea580c" stroke-width="2" />
      <text x="158" y="179" text-anchor="middle" class="carbon-badge">4′</text>

      
      <circle cx="182" cy="245" r="11" fill="#fff7ed" stroke="#ea580c" stroke-width="2" />
      <text x="182" y="249" text-anchor="middle" class="carbon-badge">3′</text>

      
      <circle cx="258" cy="245" r="11" fill="#fff7ed" stroke="#ea580c" stroke-width="2" />
      <text x="258" y="249" text-anchor="middle" class="carbon-badge">2′</text>

      
      <circle cx="282" cy="175" r="11" fill="#fff7ed" stroke="#ea580c" stroke-width="2" />
      <text x="282" y="179" text-anchor="middle" class="carbon-badge">1′</text>
    </g>

    
    <g class="part-group" id="group-base" data-name="base">
      <rect x="330" y="135" width="112" height="80" rx="10"
            fill="#e0f2fe" stroke="#0284c7" stroke-width="3" />
      <text x="386" y="170" class="part-label" fill="#0369a1" font-size="13">Nitrogenous</text>
      <text x="386" y="188" class="part-label" fill="#0369a1" font-size="13">Base</text>
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DNA as a Polymer and Double Helix Structure

Nucleotides and Complementary Base Pairing

The Human Genome and Genetic Material Organisation

How the Genetic Code Directs Protein Synthesis

Non-Coding DNA and Gene Regulation

The Human Genome Project and Medical Advances

Interactions Between Genome and Environment

science

DNA and the Human Genome

What Is DNA? The Molecule of Heredity

Nucleotides: The Building Blocks of DNA

The Sugar-Phosphate Backbone of DNA

The Four Nitrogenous Bases: A, T, G, and C

Base Pairing Rules and the Double Helix

How DNA Stores Genetic Information

The Genetic Code: Codons and Amino Acids

From Nucleotide Sequence to Protein to Trait

Scientific Explanations for the Origin of DNA

DNA Structure and the Genetic Code

Chargaff's Rules and Hydrogen Bonding in DNA

Comparing DNA and RNA Structures and Functions

Transcription: Synthesizing mRNA from a DNA Template

Translation: Protein Synthesis at the Ribosome

Universal Biochemical Code as Evidence for Evolution

DNA Structure, the Universal Genetic Code, and Protein Synthesis

Historia del descubrimiento del material genético

Nucleótidos: bloques de construcción de los ácidos nucleicos

El modelo de doble hélice del ADN y reglas de Chargaff

Enlaces químicos y estabilidad de la molécula de ADN

Antiparalelismo y orientación 5' a 3' de las hebras

Empaquetamiento del ADN: histonas, cromatina y cromosomas

Estructura molecular y empaque del ADN

What Is Gene Expression?

The Central Dogma: DNA to RNA to Protein

Types of RNA: Messenger, Transfer, and Ribosomal

Transcription: Making RNA from a DNA Template

RNA Processing: Splicing Introns and Exons

Translation: The Ribosome Reads mRNA

Transfer RNA and Amino Acid Delivery

Building a Polypeptide Chain

Modeling Protein Synthesis Step by Step

Gene Regulation: How Cells Control Expression

Gene Expression and Protein Synthesis

Key Terms in Genetics: Alleles, Genotype, and Phenotype

Predicting Genotype and Phenotype Ratios

Sex Determination and Sex Chromosomes

Inherited Disorders: Cystic Fibrosis and Polydactyly

Analysing Family Pedigree Charts

Embryo Screening and Gene Therapy Ethics

Polygenic Inheritance and Complex Traits

Monohybrid Inheritance and Genetic Crosses

Modelo semiconservativo de la replicación del ADN

Enzimas clave en la replicación: helicasa y ADN polimerasa

Mecanismos de corrección de errores y fidelidad replicativa

Diferencias estructurales y funcionales entre ADN y ARN

El genoma y la organización de la información hereditaria

Aplicaciones biotecnológicas del conocimiento del ADN

Replicación del ADN y función genética

El dogma central de la biología molecular

Transcripción génica: síntesis de ARN mensajero

Maduración y procesamiento del ARN en eucariotas

El código genético universal: codones y aminoácidos

ARN de transferencia y los ribosomas en la traducción

Fases de la traducción: iniciación, elongación y terminación

Plegamiento y estructura tridimensional de las proteínas

Funciones biológicas de las proteínas: estructurales y enzimáticas

Expresión génica: del ADN a las proteínas funcionales

Principles of DNA Sequencing: Sanger Chain Termination

High-Throughput Next-Generation Sequencing Technologies

Sequencing Genomes of Microorganisms and Pathogens

The Human Genome Project and Computational Genomics

Bioinformatics and Comparative Genomics in Evolution

Predicting Amino Acid Sequences and Proteomes from DNA

Non-Coding DNA, Alternative Splicing, and Proteomic Complexity

Genome Sequencing Projects and Proteomics

Amino Acid Structure, Zwitterions, and R-Group Diversity

Peptide Bond Synthesis and Polypeptide Polarity

Primary Protein Structure and Covalent Sequencing

Secondary Conformations: Alpha-Helices and Beta-Sheets

Tertiary Structure Folding and Intramolecular Bonds

Quaternary Architecture and Conjugated Proteins

Comparing Globular and Fibrous Proteins: Haemoglobin and Collagen

The Biuret Assay for Protein Detection

Protein Structure, Bonding, and Functional Diversity

Amino Acid General Structure and R-Group Diversity

Peptide Bond Formation and Dipeptide Synthesis

Primary Structure of Proteins and Polypeptide Chains

Secondary Structure: Alpha-Helices and Beta-Pleated Sheets

Tertiary Structure and Intramolecular Bonding Interactions

Quaternary Structure and Prosthetic Groups in Proteins

Globular versus Fibrous Proteins: Structure and Properties

Collagen and Haemoglobin as Exemplar Protein Models

Biochemical Testing for Proteins: The Biuret Test

Protein Structure, Function, and Testing

Continuous and Discontinuous Variation

Causes of Variation: Genetic, Environmental, and Combined

How Mutations Arise and Influence Phenotypes

Mutations in Protein Structure and Enzyme Active Sites

Calculating Percentages, Means, and Probability in Variation

Variation, Mutations, and Phenotypic Effects

Mutaciones puntuales y sus consecuencias en las proteínas

Inserciones, deleciones y cambio en el marco de lectura

Enfermedades genéticas moleculares: el caso de la hemoglobina

Regulación de la expresión génica en células diferenciadas

Mutaciones, enfermedades genéticas y regulación génica

Darwin's Theory of Evolution by Natural Selection

Comparing Darwin and Lamarckian Evolution

Speciation and Reproductive Isolation

Alfred Russel Wallace and Warning Colouration

Tracking Changes in Allele Frequency Over Time

Natural Selection and Evolutionary Change

Nucleotide Structure and Phosphodiester Bonding

DNA Double Helix and Complementary Base Pairing

RNA Structure: mRNA, tRNA, and rRNA

Semi-Conservative DNA Replication and Polymerase Action

The Meselson-Stahl Experiment: Evidence for Semi-Conservative Replication

Features of the Genetic Code: Triplet, Degenerate, and Universal

Eukaryotic Transcription and Pre-mRNA Processing

Ribosomal Translation and Polypeptide Synthesis

Gene Mutations and Protein Tertiary Structure

Nucleic Acids, Genetic Coding, and Protein Synthesis

Evidence for Evolution: The Fossil Record

Causes of Extinction and Mass Extinction Events

Case Study: Antibiotic Resistance in Bacteria

Linnaean Classification and Binomial Naming

Carl Woese and the Three-Domain System

Interpreting Evolutionary Trees

Evidence for Evolution and Classification Systems

Nucleotide Structure: Pentose, Phosphate, and Nitrogenous Base

DNA Double Helix Structure and Antiparallel Strands

RNA Structure and Comparison with DNA

Messenger RNA, Transfer RNA, and Ribosomal RNA

ATP Structure and Energy Release via Hydrolysis

ATP Synthesis and Phosphorylation of Metabolites

Semi-Conservative DNA Replication Mechanism

Experimental Evidence for Semi-Conservative Replication: Meselson and Stahl

Nucleic Acids, ATP, and DNA Replication

The Genetic Code: Triplet, Degenerate, and Universal Nature

Genes, Loci, Exons, and Non-Coding Introns

Transcription in Eukaryotes: Pre-mRNA Synthesis

Post-Transcriptional Modification and Splicing of Pre-mRNA

Translation: Ribosomal Assembly and tRNA Codon Recognition

Polypeptide Elongation and Termination During Translation

Gene Mutations: Substitutions, Insertions, and Deletions

How Mutations Alter Protein Tertiary Structure and Function

Protein Synthesis, Gene Expression, and Mutation

Selective Breeding in Plants and Animals

Risks and Limitations of Selective Breeding

Principles of Genetic Engineering

Main Stages in Genetic Engineering and Bacterial Vectors

Genetically Modified Crops and Recombinant Insulin

Benefits, Risks, and Ethics of Gene Technology

Cloning Techniques in Plants and Animals

Mathematical Analysis in Genetics and Biotechnology

Selective Breeding and Genetic Technology

DNA Nucleotides: The Building Blocks of Genetic Code

Purines vs Pyrimidines: Two Categories of Nitrogenous Bases

The DNA Sugar-Phosphate Backbone

Antiparallel Orientation of DNA Strands

How the DNA Sequence Specifies Organism Traits

Genes as Protein-Coding Instructions

Connecting Genotype to Phenotype

DNA Components and Genetic Information

DNA vs RNA: A Structural Comparison

Scientific Hypotheses for the Origin of DNA

Evaluating Evidence for DNA's Origins

Identifying Patterns in Experimental Data

DNA in Context: RNA, Origins, and Data Analysis

Gene Expression: How the Same DNA Makes Different Cells

RNA Molecules in Gene Expression: mRNA, tRNA, and rRNA

RNA Splicing: Removing Introns, Keeping Exons

Codons and the Genetic Code

tRNA's Role in Protein Synthesis

Polypeptide Chain Assembly: Building Proteins

Controlling Gene Expression in Cells

Comparing Gene Regulation in Prokaryotes and Eukaryotes

OGS.10.GVE.1

OGS.10.GVE.1

Aligned learning resources

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