Lesson 3: DNA Replication Key Terms

mutation rate

the rate at which changes (mutations) occur in DNA sequences

germ cells

a cell in the germ line of an organism, which includes the haploid gametes and their specified diploid precursor cells. Germ cells contribute to the formation of a new generation of organisms

somatic cells

diploid cells that make up the rest of your body

DNA polymerase

enzyme that synthesizes DNA by joining nucleotides together using a DNA template as a guide

replication fork

Y-shaped region of a replicating DNA molecule; the point at which the two strands of the parent DNA helix are being separated and the daughter strands are being formed

leading strand

one of the two newly synthesized strands of DNA found at a replication fork. The leading strand is made by continuous synthesis in the 5′-to-3′ direction

lagging strand

one of the two newly synthesized strands of DNA found at a replication fork. The lagging strand is made in discontinuous lengths that are later joined covalently

Okazaki fragments

short DNA segments synthesized discontinuously on the lagging strand during DNA replication, later joined to form a continuous strand

RNA primer

short stretch of RNA synthesized on a DNA template. It is required by DNA polymerases to start their DNA synthesis

DNA primase

enzyme that synthesizes a short strand of RNA on a DNA template, producing an RNA primer for DNA synthesis

proofreading

error-correcting activity of DNA polymerase that ensures newly synthesizes DNA strand is as accurate as possible

DNA ligase

enzyme that joins the ends of two strands of DNA together with a covalent bond to produce one continuous DNA strand using ATP

DNA helicase

unwinds the double helix ahead of the fork using ATP

single-strand DNA-binding proteins

protein that binds to the single strands and prevents helical structures from re-forming while DNA is being replicated

sliding clamp

ring around DNA that keeps polymerase from falling off

clamp loader

uses ATP to open and close the clamp around the DNA

strand-directed mismatch repair

a proofreading system that removes DNA replication errors missed by the DNA polymerase proofreading exonuclease; detects DNA helix distortion and then excises the mismatch in the newly synthesizes strand specifically

DNA topoisomerase I and II

I nicks one strand to relieve supercoiling, no ATP needed; II passes one DNA duplex through a break in another (uses ATP)

origin recognition complex

large protein complex that is bound to the DNA at origins of replication in eukaryotic chromosomes throughout the cell cycle

histone chaperones

protein that binds free histones, releasing them as they are incorporated into newly replicated chromatin

telomerase

enzyme that elongates the telomere sequences in DNA

initiator protein (DnaA/ORC)

binds the origin, opens the A/T-rich DNA to start replication

helicase loader (DnaC/Cdc6+Cdt1)

loads helicase onto origin in an active form

MutS/MutL (or eukaryotic homologs)

mismatch repair, distinguishes new strand from olds

Shelterin

protects telomere ends; helps form T-loop