Replication and Transcription

Question 1

DNA replication is semiconservative , what does that mean?

Answer 1

when a new double strand is made, it has one strand from the original DNA and one newly made strand.

Question 2

what is replication governed by?

Answer 2

group of proteins called the replisome.

Question 3

where does replication start?

Answer 3

towards the middle at a site called origin of replication. a eukaryotic chromosome has multiple origins but a prokaryotic circular chromosome has one single origin

Question 4

what happens from the origin of replication?

Answer 4

two replisome proceed in opposite directions along the chromosome making replication bidirectional.

Question 5

what is the point where the replisome is attached to the chromosome?

Answer 5

replication fork

Question 6

DNA helicase is part of the replicasome, what does it do?

Answer 6

unwinds DNA

Question 7

what about DNA polymerase?

Answer 7

it makes new DNA but it cannot initiate a strand from two nucleotides, it can only add nucleotides to an existing strand. so primate comes in ( its RNA polymerase) , it makes a RNA primer approximately 10 ribonucleotides long to start a strand.

Question 8

in which direction does DNA polymerase read strand?

Answer 8

in 3’ to 5’ and it makes a new strand in a 5’ to 3’ direction.

Question 9

what is downstream?

Answer 9

5’- 3’

Question 10

what is upstream?

Answer 10

3’- 5’

Question 11

the beginning of transcription is called initiation - where a group of proteins called initiation factors find a promoter on the DNA strand and assemble transcription initiation complex which includes the RNA pol. A promoter is a sequence of DNA it designates the beginning point for transcription.

Answer 11

The most commonly found sequence of a promoter recognized by RNA pol sequence is called the consensus sequence- variation from this sequence causes RNA pol to bind less tightly and less often to the promoter, which leads to those genes being transcribed less frequently.

Question 12

what does the RNA pol do after it binds to the promoter?

Answer 12

it unzips the DNA helix creates a transcription bubble. NEXT , complex switches to elongation mode.

Question 13

what happens in elongation?

Answer 13

RNA pol only transcribes 1 strand of the DNA nucleotide sequence into a complementary RNA . the one strand that is transcribed is called the template strand or (-) antisense strand. the other strand, called the coding strand or (=) sense strand, it protects its partner against degradation. THE CODING STRAND WILL RESEMBLE THE DNA

Question 14

in what direction does RNA pol move?

Answer 14

like DNA pol it moves in 3-5’ and makes a new RNA strand in 5’ -3’. transcription is way slower than DNA replication. RNA pol also does not have proofreading mechanism, so the rate of errors is a lot higher.
errors in RNA are not passed on to progeny.

Question 15

what is the end of transcription called?

Answer 15

termination- which needs a special sequence so that the pol can break off the DNA.

Question 16

At which levels are genes activated or inactivated?

Answer 16

at the level of transcription! via proteins called activators and repressors.

Question 17

where do activators and repressors bind?

Answer 17

they bind to DNA close to the promoter, and either activate or repress the activity of the RNA polymerase.
activators and repressors are often allosterically regulated by small molecules such as cAMP.

Question 18

what is the primary function of gene regulation in prokaryotes?

Answer 18

respond to env changes. changes in gene activity are a response to the concentration of specific nutrients in and around the cell.

Question 19

what is polycistronic mRNA?

Answer 19

several genes are in one transcript. - SEEN IN PROKARYOTES

Question 20

monocistronic mRNA?

Answer 20

one gene per transcript - seen in eukaryotes.

Question 21

what is the operon?

Answer 21

genetic unit that has operator, promoter and genes that contribute to single prokaryotic mRNA. ex would be the lac operon

Question 22

lac operon

Answer 22

codes for enzymes that allow Ecoli to import and metabolize lactose when glucose is not present in sufficient quantities. low glc levels will lead to high cAMP levels. cAMP binds to and activates CAP (catabolite activator protein). activated CAP binds to a CAP site which is located adjacent to the promoter. promoter is now activated and allowing formation of an initiation complex and subsequent transcription and translation of 3 proteins. the operator is also a regulator site, it allows for the lac repressor protein to bind. this repressor protein is inactivated by the presence of lactose in cell.

Question 23

what happens when the lac repressor protein binds to the operator in the absence of lactose?

Answer 23

that will prevent the transcription of the lac genes. lactose can only induce transcription when glucose is not present!

Question 24

what are enhancers?

Answer 24

short, non coding regions of DNA found in eukaryotes. their function is similar to activators and repressors but they act from a much greater distance from the promoter