Genetics Exam 2-Ch11 DNA Replication

The DNA mutants fell into two groups when shifted to the nonpermissive temperature:

1. Some showed a rapid arrest These genes encoded enzymes needed for replication of the DNA; 2. Other mutants completed their current round of replication but could not start another.Encoded genes needed for initiation of replication

DNA polymerases possess two unusual features:

1. They synthesize DNA only in the 5' to 3' direction 2. They cannot initiate DNA synthesis

DNA Replication: ___ pairs with __, and ____ pairs with ____ during synthesis of a new strand.

A pairs with T and G pairs with C

Which of the following enzymes of bacterial DNA replication removes RNA primers and fills in gaps with DNA? A) DNA polymerase I B) DNA polymerase III C) Primase D) DNA ligase

A) DNA polymerase I

True or False, DNA polymerases cannot initiate DNA synthesis. A) True B) False

A) True

Which of the following subunits of the DNA Polymerase III holoenzyme from E. coli is responsible for synthesizes DNA? A) α B) Β C) ε D) θ

A) α

Origins of replication in Saccharomyces cerevisiae are termed:

ARS elements (Autonomously Replicating Sequence).They are about 50 bp in length. They have a high percentage of A and T; ARS consensus sequence (ACS), ATTTAT (A or G)TTTA

Three types of DNA sequences in oriC are functionally significant:

AT-rich region DNA A boxes GATC methylation sites

A type of _______mutant is a temperature-sensitive (ts) mutant

conditional

T1 termination sequence (ter sequence) stops ________ forks

counterclockwise

Two DNA pol III proteins act in concert to replicate both the leading and lagging strands The two proteins form a ___ ____ _____that moves as a unit toward the replication fork

dimeric DNA polymerase

Proofreading Mechanisms: DNA replication exhibits a high degree of ______

fidelity; Mistakes during the process are extremely rare (DNA pol III makes only one mistake per 108 bases made)

DNA replication is the process by which the _____ _____ ___ _______

genetic material is copied; The original DNA strands are used as templates for the synthesis of new strands

The origin of replication in E. coli is termed ________

oriC (origin of Chromosomal replication)

DNA synthesis begins at a site called _______ __ ____________

origin of replication

Replication begins with assembly of the ____ ______

prereplication complex (preRC); consists of at least 14 different proteins

DNA helicase and primase are physically bound to each other to form a complex called the ______that leads the way at the replication fork

primosome

DNA pol I

removes the RNA primers and fills the resulting gap with DNA

Mammalian cells contain well over a dozen different DNA polymerases. Four: alpha (a), delta (d), epsilon (e) and gamma (g) have the primary function of ___________ DNA

replicating;

The primosome is physically associated with two DNA polymerase holoenzymes to form the _______

replisome

Okazaki fragments

small fragments of DNA (1000-2000 nucleotides) synthesized by RNA primers used by DNA pol III

On the opposite side of the chromosome to oriC is a pair of ______ __________

termination sequences called ter sequences; These are designated T1 and T2

The protein _______ binds to the ter sequences.

tus (termination utilization substance); tus bound to the ter sequences stops movement of the replication forks

Reasons why fidelity is high in DNA replication include:

1. Instability of mismatched pairs; 2. Configuration of the DNA polymerase active site; and 3. Proofreading function of DNA polymerase

Proofreading of bacterial DNA polymerase III occurs in which direction? A) 5' to 3' B) 3' to 5' C) Bidirectional D) None of the above; DNA polymerase III is incapable of proofreading

B) 3' to 5'

True or False, hemimethylation of bacterial GATC sites promotes initiation of DNA replication. A) True B) False

B) False

True or False, most bacterial chromosomes contain telomeres. A) True B) False

B) False

Which of the following eukaryotic DNA replication enzymes removes RNA primers? A) DNA polymerase III B) Flap endonuclease C) Telomerase D) Primase

B) Flap endonuclease

Which of the following eukaryotic DNA polymerases elongates Okazaki fragments? A) DNA polymerase α B) DNA polymerase γ C) DNA polymerase δ D) DNA polymerase ε

C) DNA polymerase δ

Which of the following eukaryotic DNA polymerases is used to replicate mitochondrial DNA? A) Alpha (α) B) delta (δ) C) Gamma (γ) D) Epsilon (ε)

C) Gamma (γ)

Which of the following statements about both bacterial and eukaryotic DNA replications is FALSE? A) DNA replication in bacteria and eukaryotes is a semiconservative process B) DNA replication is bidirectional in both eukaryotes and bacteria C) Both bacterial and eukaryotic DNA replication involve more than one DNA polymerase D) DNA replication proceeds from multiple origins of replication in eukaryotes and bacteria

D) DNA replication proceeds from multiple origins of replication in eukaryotes and bacteria

In E. coli there are five proteins with polymerase activity:

DNA pol II, IV and V function in DNA repair and replication of damaged DNA; DNA pol I and III function in DNA replication; DNA pol I-Composed of a single polypeptide, Removes the RNA primers and replaces them with DNA; DNA pol III Responsible for most of the DNA replication, Composed of 10 different subunits, The a subunit catalyzes bond formation between adjacent nucleotides (DNA synthesis), The other 9 fulfill other functions; The complex of all 10 subunits is referred to as the DNA pol III holoenzyme

DNA replication is initiated by the binding of _______________

DnaA proteins to the DnaA box sequences

DNA Polymerase III is a ___________Enzyme

Processive; This processive feature is due to several different subunits in the DNA pol III holoenzyme

DNA polymerases catalyzes the formation of a covalent (ester) bond between the:

Innermost phosphate group of incoming deoxyribonucleoside triphosphate; AND 3'-OH of the sugar of the previous deoxynucleotide

The two new daughter strands are synthesized in different ways:

Leading strand and Lagging strand

___ ______ _____have telomeres at both ends; The term telomere refers to the complex of telomeric DNA sequences and bound proteins

Linear eukaryotic chromosomes

Other preRC proteins include ___ ________; Binding of ______ completes DNA replication licensing and the origin becomes capable of initiating DNA synthesis

MCM Helicase; Binding of at least 22 additional proteins is required to initiate synthesis during S phase

Leading strand:

One RNA primer is made at the origin; DNA pol III attaches nucleotides in a 5' to 3' direction as it slides toward the opening of the replication fork

An important part of the preRC is the____ _______ _____ (a six-subunit complex that acts as the initiator of eukaryotic DNA replication)

Origin recognition complex (ORC)

Lagging strand:

Synthesis is also in the 5' to 3' direction-However it occurs away from the replication fork; Many RNA primers are required; DNA pol III uses the RNA primers to synthesize small DNA fragments (1000 to 2000 nucleotides each)-These are termed Okazaki fragments after their discoverers

_____contains protein and RNA that is complementary to the DNA sequence found in the telomeric repeat that allows the telomerase to bind to the 3' overhang

Telomerase

What ends bacterial DNA replication?

The two replication forks eventually meet at the opposite side of the bacterial chromosome

DNA polymerases

are the enzymes that catalyze the attachment of nucleotides to synthesize a new DNA strand

Synthesis of DNA proceeds _____________ around the bacterial chromosome

bidirectionally

Bacterial DNA polymerases may vary in their subunit composition; However, they all have the same type of ____ _____

catalytic subunit; cannot initiate DNA synthesis. Problem is overcome by the RNA primers synthesized by primase

DNA ligase

catalyzes the formation of a phosphodiester bond

Finally DNA ligase covalently links the two daughter strands DNA replication often results in two intertwined molecules Intertwined circular molecules are termed ______.These are separated by the action of topoisomerase

catenanes

T2 termination sequence (ter sequence) stops ________ forks

clockwise