DNA Replication: Chapter 14

DNA gyrase

relieves torque (force causing cell to rotate)

primers for DNA polymerase

short segments of RNA about 10 nucleotides long.

leading strand

the strand that is synthesized continuously from an initial primer

lagging strand

the strand that is synthesized discontinuously with multiple priming events

Initiation - replication begins Elongation - new strands of DNA are synthesized by DNA polymerase Termination - replication is terminated

three stages of DNA replication?

helicase

unwinds double helix

nucleotide, sugar, nitrogenous base (T,A,G,C)

what do nucleotides consist of?

2 strands of nucleotides bound together by hydrogen bonds

what does a double helix contain?

Something to copy (DNA parental molecule) something to do the copying (enzymes) building blocks to make the copy (nucleotide triphosphate)

what three things are required for DNA replication?

5' to 3'

which way does a DNA strand elongate?

because it can only add nucleotides to the end of an existing chain that is base-paired with the template strand.

why can't DNA polymerase initiate synthesis of a polynucleotide (DNA/RNA) ?

Specific repair Targets a single kind of lesion in DNA and repairs only that damage Nonspecific Use a single mechanism to repair multiple kinds of lesions in DNA

2 categories of DNA repair?

Recognition of damage Removal of the damaged region Resynthesis using the information on the undamaged strand as a template

3 steps of excision repair?

photolyase

Absorbs light in visible range Uses this energy to cleave thymine dimer

DNA primase

RNA polymerase that makes RNA primer RNA will be removed and replaced with DNA Add new bases to 3′ end of existing strands Synthesize in 5′-to-3′ direction Require a primer of RNA

C

The beta subunit of DNA polymerase III (also known as the beta clamp) has which of the following functions in DNA synthesis? A) Adds nucleotides to the 3' end of the growing DNA strand. B) Adds nucleotides to the 5' end of the growing DNA strand. C) increases the processivity of DNA polymerase III

DNA polymerase can only add nucleotides to an existing polymer

Why is the enzyme primase required for DNA replication?

DNA polymerase I

erase primer and fills gaps

single-strand binding protein

a protein that keep the unpaired template strands apart during replication.

DNA gyrase (Topoisomerase II)

a protein that relieves the twisting up stream of the replication fork.

helicase

a protein that untwists and separates the template DNA strands at the replication fork

primase

an DNA dependant RNA polymerase, links 5 to 10 ribonucleotides that are complementary to the DNA template into a primer for DNA Pol III.

mutagen

any agent that increases the number of mutations above background level

false

can DNA gyrase (topoisomerase) cut only a single strand of the double helix?

topoisomerase 1

cut single stand of the double helix, pass the other strand through the cut and reseal the break, to minimize tension.

topoisomerase 2

cuts both strands of a double strand DNA, passes another double strand through the break, and then reseals the break. Can remove supercoiling two twists at a time, to create a relaxed circle.

telomerase

enzyme makes telomere section of lagging strand using an internal RNA template (not the DNA itself)

macromolecular assembly

Enzymes involved in DNA replication form a ____

thymine dimers

Covalent link of adjacent thymine bases in DNA

ATP

DNA gyrase required supercoiled DNA as one substrate. What is the other required substrate?

pol I

E.coli polymerase that Acts on lagging strand to remove primers and replace them with DNA

pol II

E.coli polymerase that is Involved in DNA repair processes

pol III

E.coli polymerase that is the Main replication enzyme

replication fork

Partial opening of helix forms ____

telomeres

Specialized structures found on the ends of eukaryotic chromosomes Protect ends of chromosomes from nucleases and maintain the integrity of linear chromosomes Gradual shortening of chromosomes with each round of cell division

photorepair

Specific repair mechanism For one particular form of damage caused by UV light

causes a change in shape

The DNA Helicase uses ATP to unwind the double helix. ATP binding and hydrolysis does what to the enzyme?

an area of DNA undergoing replication

The replication fork is ________________

3' end

To where on the strand does the DNA polymerases add the nucleotides?

torsional strain

Unwinding DNA causes _____

primer

What is required to start a new strand of DNA?

DNA polymerase III

Which enzyme is responsible for the the addition of nucleotides to the new DNA strand?

C

Which of the following enzymes does not require ATP to function? A) Helicase B) DNA Ligase C)DNA Polymerase

DNA clamp (sliding clamp)

is a protein fold that serves as a processivity-promoting factor in DNA replication. it binds DNA polymerase and prevents this enzyme from dissociating from the template DNA strand. increases the number of nucleotides that the polymerase can add to the growing strand per association event.

DNA ligase

joins the end of DNA segments; DNA repair

single-stranded binding protein

stabilizes single stranded regions

linear multiple origins of replication

structure of Eukaryotic replication?

DNA polymerase III

synthesizes DNA

rimase

synthesizes RNA primers