Chapter 10 - Expression of Genetic Information

Question 1

RNA Polymerase

Answer 1

transcribes DNA into RNA

Question 2

Which polymerase requires a primer with a free 3’-OH group to initiate chain elongation?

Answer 2

DNA polymerase

Question 3

Pribnow Box (prokaryotic)

Answer 3

TATAAT (-10 region) and TTGACA (-35 region)

Question 4

Hogness Box (eukaryotic)

Answer 4

TATA box (-25 region) and CAAT box (-75 region) upstream from the +1 site; the CAAT box may or may not be present

Question 5

What are some general stop signals?

Answer 5

GC-rich region followed by an AT-rich region on the DNA template

Question 6

What is unique about the terminator sequence of E. coli?

Answer 6

to end protein synthesis, there is a base-paired hairpin sequence on the newly synthesized RNA strand

Question 7

Base-Paired Hairpin Sequence

Answer 7

region of RNA sequence that’s rich in G and C, then a sequence of four or more U residues (poly-U tail)

Question 8

Rho-independent termination

Answer 8

once hairpin pairing occurs, RNA polymerase pauses; uracil and adenine that are still annealed to each other (RNA-DNA hybrid) are unstable and RNA chain will dissociate from RNA polymerase and DNA duplex

Question 9

Rho-dependent termination

Answer 9

involves rho protein, a hexameric protein of 46 kd subunits and has ATPase activity to allow it to specifically bind newly synthesized single-stranded RNA and pull itself towards the replication bubble where it will dislodge RNA polymerase from the DNA template

Question 10

RNA Polymerase I

Answer 10

transcribe rRNA

Question 11

RNA polymerase II

Answer 11

transcribes mRNA

Question 12

RNA polymerase III

Answer 12

transcribes tRNA

Question 13

RNA polymerase holoenzyme

Answer 13

four subunits alpha2, Beta, Beta’, and sigma

Question 14

What is the accuracy of replication and transcription?

Answer 14

DNA polymerase enzymes edit and there are repair enzymes; roughly 10^10 bases will be replicated before an error is made that is not caught. RNA polymerase does not edit and do not have repair systems, so errors occur one in every 10^4 or 10^5 transcribed bases

Question 15

What inhibits RNA polymerase?

Answer 15

actinomycin D (binds to double stranded DNA and prevents RNA polymerase from using it as a template for transcription)

Question 16

Enhancer Sequences

Answer 16

typically far away from promoter region, can be up or downstream, can even be within gene itself

Question 17

What is the purpose of 5’ capping of RNA?`

Answer 17

protects 5’ end from degradation and enhances stability of RNA molecule

Question 18

What is the purpose of 3’ polyadenylation of RNA?

Answer 18

250 adenine residues from ATP are added to the free 3’ end of the RNA polymer to form poly-A tail to protect from nucleases and phosphatases

Question 19

Shine-Dalgarno Sequence

Answer 19

about 10 nucleotides upstream from initiating codon is this purine-rich sequence of bases; responsible fro binding mRNA to the 16s subunit

Question 20

What is required to make a protein?

Answer 20

20 aminoacyl-tRNAs, each attached to correct tRNA, mRNA that contains codons that specify protein sequence desired, ribosomes, initiation factors, elongation and termination factors, and GTP as an energy source

Question 21

Puromycin

Answer 21

binds at the A-site and acts as an analog of an aminoacyl-tRNA, thus preventing other aminoacyl-tRNAs from entering the A-site

Question 22

Helicase

Answer 22

catalyze unwinding

Question 23

How can proofreading via 3’ –> 5’ exonuclease activity occur?

Answer 23

DNA polymerase I and III have 3’–>5’ exonuclease activity

Question 24

DNA Ligase

Answer 24

catalyze the formation of a phosphodiester bond between 3’ hydroxyl at one end of replaced DNA strand and 5’-phosphate of previously synthesized DNA strand

Question 25

Mutagens

Answer 25

external agents that can cause mutations and also increase the possibility of mutations occurring

Question 26

Base Analog Mutagen

Answer 26

can easily substitute for a naturally occurring base in DNA like 5-bromouracil replacing thymine

Question 27

Chemical Mutagen

Answer 27

Nitrous acid (HNO2) can cause deamination of cytosine to uracil: a transition mutation occurs

Question 28

Ultraviolet (UV) Radiation Mutagens

Answer 28

if two pyrimidine residues like thymine are adjacent to each other, energy in UV radiation (about 260 nm) can link them together; thymine dimers inhibit DNA replication

Question 29

Restriction Enzymes (Restriction Endonucleases)

Answer 29

recognize specific sequences in DNA polymers and cleave that DNA at those sites