DNA Structure
What are the three parts of a nucleotide?
Sugar, phosphate, base
What enzyme unzips the DNA double helix?
Helicase
What are cyclins and Cdks?
Proteins that regulate the cell cycle
Mitosis creates ___ cells.
Two identical cells
What’s a proto-oncogene’s normal job?
Promotes normal cell growth/division
Which bases pair together in DNA?
A–T, G–C
What enzyme builds the new DNA strand?
DNA polymerase
What happens when cyclin binds Cdk?
Forms an active complex that advances the cell cycle
Meiosis creates ___ cells.
Four genetically different cells
What happens if a proto-oncogene mutates into an oncogene?
Cell division is overstimulated
What type of bond connects the bases?
Hydrogen bonds
What enzyme glues Okazaki fragments together?
DNA ligase
What limits Cyclin-Cdk activity?
Cyclins degrade at specific times or are blocked by checkpoint proteins
What happens during crossing over?
Homologous chromosomes exchange DNA
What’s the role of tumor suppressor genes?
Stop cell division when needed
What bond connects nucleotides along one strand?
Phosphodiester bond
What does primase do?
Lays down RNA primers
What phase does p53 stop the cell in?
G₁ phase
In what phase does crossing over occur?
Prophase I
What happens if p53 is nonfunctional?
DNA damage isn’t stopped → mutations accumulate
What does “5′ to 3′” mean?
Nucleotides connect from the 5′ phosphate to the 3′ hydroxyl of the next sugar
Why is the lagging strand made in fragments?
DNA polymerase only builds 5′ → 3′, so it works in short pieces opposite the fork
What does p21 do?
Blocks Cyclin-Cdk complexes when DNA is damaged
Why is meiosis important for sexual reproduction?
Increases genetic diversity & halves chromosome number
What happens if p21 is nonfunctional?
Checkpoint fails → uncontrolled division