DNA

What is DNA’s role in the cell?

Stores hereditary information

Directs development (biochemical, anatomical, physiological traits)

What are chromosomes made of?

DNA and protein

Why did scientists initially think genes were proteins?

proteins are more complex and variable than DNA

What is transformation?

change in genotype/phenotype from uptake of foreign DNA

What did Griffith discover (1928)?

Dead pathogenic bacteria can transform harmless bacteria

What did Avery, McCarty, and MacLeod prove?

DNA is the transforming (genetic) material

Hershey-Chase experiment conclusion?

DNA (not protein) enters bacteria and controls viral replication

What are nucleotides made of?

Nitrogenous base + sugar + phosphate

What are Chargaff’s rules?

A = T, G = C

Base composition varies by species

Who discovered DNA structure? Describe DNA structure,

Watson & Crick (with Franklin’s X-ray data)

Double helix

Antiparallel strands

Sugar-phosphate backbone

Base pairing rules

A ↔ T (2 H-bonds)

G ↔ C (3 H-bonds)

What are the 3 replication models?

Semiconservative (correct)

Conservative

Dispersive

Direction of DNA synthesis?

Always 5′ → 3′

What enzyme builds DNA?

DNA polymerase

Why is a primer needed?

DNA polymerase needs a 3′ OH group to start

What makes RNA primers?

primase

Leading vs Lagging strand

Leading: continuous

Lagging: discontinuous

What are Okazaki fragments? What enzyme joins fragments?

Short DNA fragments on lagging strand

DNA ligase

DNA helicase function

Unwinds DNA (breaks H-bonds)

SSB proteins function

Keep strands separated

Topoisomerase function

Relieves twisting tension

Where does replication begin?

Origins of replication

What are telomeres? Why do telomeres shorten? What does telomerase do? Why are telomeres important?

they are repeating DNA at chromosome ends

No primer for final lagging strand so they shorten

they extends telomeres (active in germ & cancer cells)

important as they prevent gene loss and linked to aging

DNA replication error rate

~1 in 1 billion nucleotides

What is proofreading?

DNA polymerase removes incorrect bases

What is mismatch repair?

Fixes errors after replication

What causes thymine dimers?

UV radiation

What is nucleotide excision repair?

Removes damaged DNA and replaces it

What is Xeroderma Pigmentosum (XP)? Why does XP occur?

Genetic disorder → extreme UV sensitivity

High cancer risk

Defective DNA repair enzymes

How is DNA damage linked to cancer?

Mutations accumulate → uncontrolled cell growth