Lecture Notes Beginning Week 9-End ‘

Question 1

What are the mechanisms of DNA replication?

Answer 1

Unwinding of the DNA strands- Initiation of Replication- Elongation of the DNA strands being replicated-Termination of Replication

Question 2

Origins of replication are associated with a _____.

Answer 2

Bubble

Question 3

Each replication bubble has _____ replication forks.

Answer 3

2

Question 4

Which order of strands are continuous?

Answer 4

From the origin of replication, 3’ to 5’ strands are continuous.

Question 5

Define Replication Fork

Answer 5

A y-sharped region of the replicating DNA where the parental DNA strands are being unwound and the replication of DNA takes place.

Question 6

Define Origin of Replication

Answer 6

A region of DNA that has specific nucleotide sequences where the DNA replication begins.

Question 7

Define Helicases

Answer 7

Enzymes that untwist the double helix at the replication forks, separating the 2 strands and making them available as templates.

Question 8

Which enzyme is responsible for releasing the tension in DNA strands?

Answer 8

Topoisomerase.

Question 9

Define Topoisomerase

Answer 9

An enzyme that breaks, swivels, and rejoins the DNA strands. During the replication of DNA, this enzyme helps relieve the strain in the double helix ahead of the replication fork. T-BSR

Question 10

Define Single Strand Binding Proteins

Answer 10

Proteins that bind to the unpaired DNA strands during DNA replication, stabilizing them and holding them apart while they serve as templates for the synthesis of the complementary DNA strands.

Question 11

Define Primase

Answer 11

AN RNA Polymerase that joins RNA nucleotides to make the primer using the parental DNA strands as a template.

Question 12

Define DNA Polymerase III

Answer 12

A complex of enzymes that catalyzes the elongation of new DNA by adding nucleotides to the 3’ end of an existing chain. In elongates in the 5’ to 3’ direction and READS in the 3’ to 5’ direction.

Question 13

What is an important thing to note about DNA Polymerase III?

Answer 13

It can only add nucleotides to the free 3’ end of a sequence of nucleotides and CANNOT do it by itself. It needs the primase enzyme to add a sequence of ribonucleotides.

Question 14

The _____ end has to be free to allow for further binding.

Answer 14

3’

Question 15

What is the bond formed between the carbon ends and the phosphate groups of another nucleotide?

Answer 15

Phosphodiester Bond

Question 16

What happens to the phosphates in the phosphate group when DNA polymerase allows for the binding of nucleotides?

Answer 16

2 inorganic phosphates get released in the cytoplasm and the nuclear matrix.

Question 17

_____ must be removed; this is done by _____.

Answer 17

Primers-DNA Polymerase I

Question 18

Define DNA Polymerase I

Answer 18

An enzyme that removes and replaces the RNA primer.

Question 19

Define Ligase

Answer 19

An enzyme that ligates the ends of DNA molecules.

Question 20

What is the main difference between leading strands of DNA and lagging strands of DNA?

Answer 20

The main difference is that the leading strand is continuous and the lagging strand is in Okazaki fragments.

Question 21

Define Okazaki Fragments

Answer 21

Short of sections of DNA. Formed at the time of discontinuous synthesis of the lagging strand during replication of DNA.

Question 22

What is meant by the proofreading activity of DNA polymerase?

Answer 22

Polymerase has the ability to check each nucleotide against the template soon after it is added to the growing strand. In real life, we find 1 in 10 million mistakes.

Question 23

How do mismatched nucleotides evade DNA polymerase proofreading?

Answer 23

They evade proofreading or occur after DNA replication because of the exposure of cells to things such as chemical carcinogens and UV light.

Question 24

How is the mismatched nucleotide problem fixed?

Answer 24

Thymine Dimer distorts the DNA molecule
A nuclease enzyme cuts the damaged DNA strands at two points.
DNA polymerase fills the gap.
DNA ligase seals the remaining nick.

Question 25

How many enzymes aid in the fixing of nucleotide mismatching? What is a defect in these enzymes associated with?

Answer 25

We have about 130 enzymes. Defects of one of these enzymes is associated with colon cancer.

Question 26

What happens in the process of chromatin packing ?

Answer 26

Proteins called histones allow for the wrapping of strands to make nucleosome beads. The beads pack together. The domains further loop and get more and more condensed.

Question 27

What histones are available to us? What histones do the nucleosome contain?

Answer 27

H1, H2A, H2B, H3, H4 ate available to us.

H2A,H2B,H3,H4 are contained in the nucleosome (2 of each).

Question 28

Which histone is not present in the histone octamer? Where is it located?

Answer 28

H1; it is attached near the nucleosome.

Question 29

What are histone modifications?

Answer 29

Methylation of Histones leads to the condensation of DNA and PREVENTS transcription of genes.

Acetylation of Histones leads to the decondensation of DNA and ALLOWS for the transcription of genes.