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Updated Apr 5, 2026

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2 pages

Comprehensive Study Guide for Unit 2: DNA

Ari

@emoxramen

DNA and the cell cycle are fundamental to understanding how... Show more

# UNIT 2 DNA AND CELL CYCLE STUDY GUIDE

History of DNA
- Chargaff's Rule - Base Pair Rule (30:30:20:20)
- Watson and Crick - Found the stru

DNA Structure and Replication

DNA carries the genetic instructions for all living organisms. Scientists like Watson, Crick, and Franklin discovered its famous double helix structure, while Chargaff established the base pair rule (30:30:20:20) showing that DNA's bases pair in predictable ways.

The DNA molecule has a "backbone" made of deoxyribose sugar and phosphate groups, with "rungs" formed by nitrogenous bases. Each DNA strand runs in opposite directions (antiparallel), with one strand running 5' to 3' and the other 3' to 5'. A complete nucleotide consists of a nitrogenous base, deoxyribose, and a phosphate group.

DNA replication begins when an enzyme called helicase unzips the DNA strands. Single-stranded binding proteins hold the DNA open while RNA primase and primers mark where replication should begin. DNA polymerase then builds new complementary strands. The leading strand (5'-3') is built continuously, while the lagging strand (3'-5') is created in fragments called Okazaki fragments, which are later joined by ligase.

Remember this! The Hershey-Chase experiment proved that genetic information is stored in DNA, not proteins - a revolutionary discovery that changed our understanding of genetics forever.

Mutations and Cell Cycle

Mutations are changes in the coding sequence of a gene that can either help organisms adapt or make survival more difficult. Point mutations include silent mutations (no effect on the protein), missense mutations (changed protein), and nonsense mutations (premature stop in protein production). Frameshift mutations occur through insertions (adding bases) or deletions (removing bases), which shift how the genetic code is read.

The cell cycle begins with interphase, which includes G1 (organelle replication), S (DNA replication), and G2 (final checks). DNA exists as loose chromatin when not dividing, but condenses into chromatids during division. After replication, the chromosome consists of two sister chromatids joined at the centromere, where kinetochore proteins later connect to spindle fibers.

Mitosis has four main phases: Prophase (nuclear membrane dissolves, DNA condenses), Metaphase (chromosomes align in middle), Anaphase (sister chromatids separate), and Telophase (nuclear membrane reforms). The process concludes with cytokinesis, where the cell physically divides into two identical daughter cells.

Fascinating fact! Your body replaces millions of cells every day through mitosis - that's why you can heal cuts and grow new skin cells without even thinking about it!

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Biology

•

Updated Apr 5, 2026

•

2 pages

Comprehensive Study Guide for Unit 2: DNA

Ari

@emoxramen

DNA and the cell cycle are fundamental to understanding how life works at its most basic level. This guide explores the structure and replication of DNA, genetic mutations, and the process by which cells divide to create new cells -... Show more

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DNA Structure and Replication

Remember this! The Hershey-Chase experiment proved that genetic information is stored in DNA, not proteins - a revolutionary discovery that changed our understanding of genetics forever.

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Improve your grades

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Mutations and Cell Cycle

Fascinating fact! Your body replaces millions of cells every day through mitosis - that's why you can heal cuts and grow new skin cells without even thinking about it!