DNA Replication Preview

Question 1

What is the Direction of DNA replication?

Answer 1

Unidirectional: replication growth at two starting points
Unidirectional growth of double strands from 1 starting point
Bidirectional growth at one starting point

Question 2

Where Does DNA replication begin

Answer 2

For DNA, replication begins at specific places that is easy for initiator proteins to bind to and then replication forks bind to keep the strands separated

Question 3

What happens at replication forks

Answer 3

Replication fork is asymmetrical and the leading strand is continuously replicate DNA and lagging strand discontinuously replicates DNA

Question 4

What is a simplified process of DNA replication

Answer 4

1. Separate strands
2. Synthesize
3. Proofread

Question 5

What function does initiator proteins have DNA replication for bacteria?

Answer 5

Initiator proteins bind to origin of replication
helps DNA helicase (catalyzes and breaks hydrogen bond of strands

Question 6

What unwinds DNA?

Answer 6

DNA helicase binds to origin and reads the strands from a 5’ to 3’ on the lagging strand

Question 7

What follows DNA helicase

Answer 7

Single strand binding proteins that keep the strands separated

Question 8

Primase

Answer 8

makes the rna primer

Question 9

RNA primer

Answer 9

Short sequence of RNA complementary to the template strand

Question 10

In which direction does primase move

Answer 10

It reads the template strand in the 3’ -5’ direction

Question 11

Describe the process and function of primase

Answer 11

Following single strand building proteins, primase attaches to the template strand and moves in a 3’-5’ direction. While it moves, incoming nucleotides are brought in and primase joins them together and eventually the primase will make rna primer

Question 12

DNA polymerase

Answer 12

After RNA primers do the job of placing nucleotides, DNA polymerase comes in and start synthesizing new copies of DNA and adds on 3’ end

Question 13

Helper of DNA polymerase

Answer 13

DNA polymerase needs help sticking on DNA strand and a sliding clamp comes and does this job

Question 14

How are the Okazaki fragments on the lagging strand linked

Answer 14

Ligand seals the nick by using ATP to attach 2 phosphates and then AMP is released

Question 15

The unwinding problem

Answer 15

When helicase is unwinding the DNA strand there is a lot of tension that creates circular shapes, topoisomeres fixes that

Question 16

Shortening on the 5’ end

Answer 16

This is a problem for the lagging strand because the primase doesn’t do a good job of putting a primer on the very end so there is sequence information missing.
This happens because when the primer is removed DNA polymerase does not add onto the 5’ end

Question 17

What is the solution to the shortening

Answer 17

Telomere has RNA template and through reverse transcriptase (RNA—DNA), DNA is added onto the new strand to and after the telomere is removed there will still be a gap but it doesn’t matter because it is all repeated sequences

Question 18

3’-5’ exonuclease

Answer 18

Removes disincorporated nucleotides

Question 19

What are the two sites present on DNA polymerase

Answer 19

It has a polymerizing site and editing site

Question 20

Strand-directed mismatch repair

Answer 20

When a newly synthesized DNA strand has an error, there are two enzyme involved in fixing this problem
First there is MUTs, this recognized the messed up geometry and MUTL looks for the nick to fix the problem and removes the mismatch so DNA synthesis can put in the proper match

Question 21

How can DNA be damaged

Answer 21

Radiation, Oxidation, heat, chemicals

Question 22

How can radiation lead to alterations in DNA

Answer 22

Catalyzes two covalent bonds between pyrimidines, making a pyrimidine dimer

Question 23

Fill in the blank. There can also be spontaneous damage to DNA by _________ and __________

Answer 23

Depurination (Loss of adenine/guanine) and deamination (cytosine into uracil)

Question 24

What are the two mechanisms for DNA repair

Answer 24

BER (base excision repair): removes the uracil and places the appropriate cytosine

NER(nucleotide excision repair): removes a large section of sequence and DNA ligase and polymerase puts in the appropriate sequence

Question 25

DNA repair of broken strands

Answer 25

1. Nonhomogolous which is quick . IT removes some of the nuclei acids through nucleuses and then sealed by ligase
2. Homogolous: Processed by recombination specific nuclear and puts back together by undamaged DNA as template