Lecture 4: DNA Replication

Question 1

What is the central dogma

Answer 1

DNA
(Transcription)
RNA
(Translation)
Protein

Question 2

What are the the three steps of DNA synthesis

Answer 2

-Initiation
-Elongation
-Termination

Question 3

When during the cell cycle does DNA replication occur

Answer 3

During the S phase

Question 4

What is the principle of semi conservative DNA replication

Answer 4

-DNA replication is fast and accurate
-Rarely has errors such as insertions or deletions
-The involvement of an older strand allows for proof reading as DNA synthesis occurs

Question 5

What are the 3 steps of DNA replication

Answer 5

1. DNA unwinds at the origin of replication
2. New Bases are dded to the complementary stand. One new strand is made in pieces
3. Primers are removed, new DNA nucleotides are put in place of primers and the backbone is sealed by DNA ligase

Question 6

What type of chromosomes to prokaryotes have

Answer 6

circular chromosomes
*DNA replication starts at one position in circular chromosome and works its way around the entire chromosome

Question 7

What speeds up DNA replication in prokaryotes

Answer 7

Many origins of replication.

Question 8

What enzyme unwinds DNA?

Answer 8

DNA Helicase

*It is a multi subunit enzyme that uses the energy of ATP Hydrolysis to break hydrogen bonds between base pairs

*It spins down the track of DNA

Question 9

_____________ prevents super coiling and promotes heathy strand separation

Answer 9

Topoisomerase

Question 10

What are the steps of DNA replication

Answer 10

1. The initiator protein binds to the double stranded DNA at the origin of replication and slightly unwinds the DNA
2. DNA helicase binds to the unwound DNA and continues the unwinding process.
3. DNA topoisomerase promotes strand separation by removing supercoils in from of DNA Helices. Since stranded DNA binding proteins (SSB) stabilize the stands of DNA, allowing the seperated strand to serve as templates. A replication fork is now evident
4. DNA primer binds to the leading strand template and synthesizes a short RNA primer that is complementary to DNA template
5. DNA polymerase III uses the RNA primer to initiate DNA synthesis by adding deoxyribonucleotides to its 3’ end. The leading strand requires only

Question 11

What does DNA polymerase install in the template strand

Answer 11

it installs a new dNTP in accordance with whatever is opposite the nucleotide it detects in the template strand
If it encounters a C it will install a G

Question 12

An _____________ is ejected during installation event this drives the unfavorable event forward

Answer 12

inorganic pyrophosphate

Question 13

Another enzyme _____________ immediately cleaves the PPI into two inorganic phosphates

Answer 13

inorganic pyrophaphatase

Question 14

DNA polymerase adds nucleotides in the __________________________ and the opposite strand travels in the _________________

Answer 14

5’ to 3’ direction
*DNA polymerase only works in this direction. The lagging stand is synthesize differently

3’ to 5’

Question 15

What are the steps of DNA synthesis of the lagging strand?

Answer 15

-DNA Polymerase III extends multiple RNA primers along the length of the strand. These little chunks of DNA are called Okazaki fragments.

-DNA polymerase enzymes must constantly start new ones in order to keep up with leading strand

Question 16

DNA is synthesize at which end of each primer to generate Okazaki fragments that grow

Answer 16

3’ end

Question 16

In which strand is DNA synthesis discontinuous and requires multiple RNA primers?

Answer 16

Lagging strand

Question 17

What enzyme links together adjacent Okazaki fragments.

Answer 17

DNA ligase.

Question 18

What are two major differences in Prokaryotic DNA and Eukaryotic DNA production

Answer 18

-Numerous different polymerases with specialized functions
-Much larger linear chromosomes vs smaller circular chromosomes in bacteria

Question 19

What is the function of Helices

Answer 19

Unwinds DNA at replication fork

Question 20

What is the role of single stranded binding proteins

Answer 20

-keeps single stranded DNA from reannealing
-Protects single stranded DNA from degradation by nuclease

Question 21

What is the function of DNA primase

Answer 21

synthesis RNA primers on leading and lagging strands

Question 22

What is the function of DNA polymerase

Answer 22

-installs new dNTP into the growing strand in 5’ –> 3’ direction

• 3’ –> 5’ exonuclease activity (to remove mismatched nucleotides)

-degrades RNA primers (DNA polymerase alpha only)

Question 23

What is the function of DNA ligase

Answer 23

it forces phosodiester linkages between adjacent dNMPs hybridizes on the same template strand

Question 24

What is the function of topoisomerases

Answer 24

nicks and re-ligate strand to mitigate supercoiling during replication

Question 25

What disease is a genetic deficiency of WRN gene –> believed to encode a DNA helices enzyme involved in Telomere lengthening?

-premature aging
-proof of concept that telomere shortening is highly correlated with aging process

Answer 25

Werner Syndrome

Question 26

Antibiotics block what?

Answer 26

Topoisomerase

Question 27

What do cancer chemotherapies target

Answer 27

etoposide block eukaryotic topoisomerase

Question 28

Prokaryotic cells do not have ________________

Answer 28

telomerase

Question 29

Origin of replication

Answer 29

-Prokaryotes: sinle
-Eukaryotes: multiple