UNIT 1: DNA STRUCTURE AND REPLICATION (9)

Relaxed, 'beads on a string' form of DNA during interphase

Chromatin

Proteins that DNA wraps around in chromatin

Histones

Tightly condensed DNA visible during cell division

Chromosome

One of the two identical copies of a replicated chromosome

Chromatid (sister chromatid)

Structure that holds sister chromatids together

Centromere

Why does DNA stay loose (chromatin) during interphase?

So enzymes can reach genes for transcription and replication

Why does DNA condense into chromosomes before division?

So it can be moved and divided without tangling or breaking

In which phase of the cell cycle does DNA replication occur?

S phase (synthesis) of interphase

Why is DNA replication called semi-conservative?

Each new DNA molecule has one OLD strand and one NEW strand

The two DNA strands run in opposite directions. This is called ___.

Antiparallel

Sites where replication begins

Origins of replication — Why: Humans have thousands so replication goes fast.

Enzyme that unwinds DNA by breaking hydrogen bonds between bases

Helicase

Y-shaped region where the strands separate

Replication fork

Proteins that keep the separated strands from snapping back together

Single-strand binding proteins (SSBPs)

Enzyme that makes the short RNA primer

Primase — Why: Hook: PRIMase makes the PRIMer.

Why is a primer needed?

DNA polymerase can't start a strand from scratch; it can only add onto an existing strand

Enzyme that adds DNA nucleotides to build the new strand

DNA polymerase

DNA polymerase builds new DNA in which direction?

5' → 3'

New strand built continuously toward the fork

Leading strand

New strand built in short pieces away from the fork

Lagging strand

Short DNA pieces on the lagging strand

Okazaki fragments

Enzyme that seals gaps between Okazaki fragments

DNA ligase — Why: Hook: Ligase Locks the gaps.

Enzyme that makes RNA (not DNA)

RNA polymerase — Why: Distractor in replication questions.

DNA polymerase checking and fixing its own errors

Proofreading

Uncorrected errors in the DNA sequence

Mutations