Week 13 — Readings & Resources · DNA Structure & Replication

Course: Introduction to Biology — General Biology I (BIOL 101) · Silver Oak University (fictional sample) · Prof. Castellano
Objective covered: Objective 7 — Describe the structure of DNA and explain how it is copied (semiconservative replication and the replication enzymes).

How to use this page

Everything here is a link to an external resource — open it in your browser, the same way you'd open a YouTube link. Nothing needs to be downloaded.

This week's load is deliberately light: 2 short videos + 2 short readings, grouped by the ideas from the lecture, plus two optional free interactives. Watch or read one item per group and you're ready for the quiz; do all of them and you'll be very comfortable. Total time is roughly 35–45 minutes if you do everything, far less if you pick one per group.

Order that matches the lecture: ① the structure of DNA (double helix, base pairing) → ② Chargaff's rule → ③ how DNA is copied (semiconservative replication & the enzymes).

A habit to start now: before you trust any biology claim — in these resources or anywhere — ask the questions from class: Does A really pair with that base? Is replication semiconservative or conservative? Do these base percentages add to 100%?

① The Structure of DNA · the double helix and base pairing

Maps to Lecture Segments 2–4. DNA is a double helix with a sugar-phosphate backbone and antiparallel strands; the bases pair A–T and G–C through hydrogen bonds, so the two strands are complementary.

Video — "DNA, Chromosomes, Genes, and Traits: An Intro to Heredity" (Amoeba Sisters)
🔗 https://www.youtube.com/watch?v=8m6hHRlKwxY
Why it earns the click: a friendly ~8-minute tour that shows the double-helix structure, the sugar-phosphate backbone, and how DNA, genes, and chromosomes relate — the exact "what is a gene physically made of?" picture we built in class (watch from the DNA Structure chapter at ~3:25).
⏱ ~8 min

Reading — "DNA Structure and Sequencing" (OpenStax Biology 2e, Ch. 14)
🔗 https://openstax.org/books/biology-2e/pages/14-2-dna-structure-and-sequencing
Why it's assigned: the cleanest plain-language version of the double helix, the four bases (A, T, G, C), complementary base pairing, the antiparallel strands, and the Watson/Crick/Franklin/Wilkins history we covered — free to read online, no account needed. (Read the structure section; the Sanger-sequencing part at the end is optional enrichment.)
⏱ ~12 min

② Chargaff's Rule & the Base-Pairing Logic

Maps to Lecture Segment 3. Because every A is paired with a T and every G with a C, %A = %T and %G = %C — so one base percentage gives you all four. (This is the small calculation on the quiz, the assignment, and the lab.)

Interactive — "Build a DNA Molecule" (Learn.Genetics, University of Utah)
🔗 https://learn.genetics.utah.edu/content/basics/builddna
Why it earns the click: a hands-on builder where you snap nucleotides together using the A–T, G–C rule and watch complementary base pairing hold the two strands into a double helix — exactly the structure→copying logic from class, and it even explains how base pairing keeps copying accurate.
⏱ ~8 min

③ How DNA Is Copied · semiconservative replication & the enzymes

Maps to Lecture Segments 5–6. The cell unzips the helix and uses each old strand as a template, so every copy is half old, half new (semiconservative); helicase unzips, DNA polymerase adds the complementary bases, and ligase seals.

Video — "DNA Replication (Updated)" (Amoeba Sisters)
🔗 https://www.youtube.com/watch?v=Qqe4thU-os8
Why it earns the click: an ~8-minute walkthrough of replication that names the key enzymes — helicase, DNA polymerase, and ligase, shows the antiparallel strands, and explains the semi-conservative model. Exactly Segments 5–6. (It also mentions extra detail like leading/lagging strands, which is beyond what we test — focus on the three enzymes and "half old, half new.")
⏱ ~8 min

Reading — "Basics of DNA Replication" (OpenStax Biology 2e, Ch. 14)
🔗 https://openstax.org/books/biology-2e/pages/14-3-basics-of-dna-replication
Why it's assigned: lays out why the double-helix structure "immediately suggests" a copying mechanism, defines semiconservative replication against the conservative and dispersive alternatives, and describes the Meselson–Stahl experiment that settled it — free to read online.
⏱ ~10 min

Optional one-stop references (free online)

• Khan Academy — DNA structure & replication. A free unit with short articles and videos on DNA structure, base pairing, and replication. A good place to return to all term.
  🔗 https://www.khanacademy.org/science/ap-biology/gene-expression-and-regulation/dna-and-rna-structure
• OpenStax Biology 2e — "Historical Basis of Modern Understanding" (Ch. 14). The story of how scientists figured out that DNA — not protein — is the genetic material (Griffith, Avery, Hershey–Chase), if you want the backstory to this week.
  🔗 https://openstax.org/books/biology-2e/pages/14-1-historical-basis-of-modern-understanding

Pick-one quick path (≈16 min total)

In a hurry? Do exactly these two and you'll be ready for the quiz:
1. Watch "DNA Replication (Updated)" (group ③) — it covers the enzymes and semiconservative copying.
2. Skim the structure section of "DNA Structure and Sequencing" (group ①) for the double helix and the A–T, G–C rule, and try one round of "Build a DNA Molecule" (group ②) for the base-pairing logic.

Heads-up (links rot): these point to outside sites that occasionally move or rename pages. If a link ever fails, tell Prof. Castellano and use the OpenStax or Khan Academy references above in the meantime.