10: Ribosomes and Prokaryotic TX Termination

Question 1

In prokaryotes, what are the two types of transcription terminators?

Answer 1

Intrinsic (rho-independent)
Rho-dependent (extrinsic)

Question 2

What are the two components of intrinsic terminators?

Answer 2

Dyad symmetry and a string of T’s in the DNA sequence

Question 3

Intrinsic terminators form a secondary structure in the mRNA necessary for termination. What is its name?

Answer 3

A stem-loop or hairpin structure

Question 4

What comes after the stem-loop/hairpin in newly transcribed RNA that is terminated intrinsically?

Answer 4

A string of U’s

Question 5

In intrinsically-terminated RNA, what exists between areas exhibiting dyad symmetry?

Answer 5

A 7-nucleotide spacer

Question 6

In intrinsic termination, what affect does the hairpin have on RNA polymerase?

Answer 6

It makes RNA polymerase pause

Question 7

In intrinsic termination, what causes RNA polymerase to fall off the DNA?

Answer 7

A string of weak U:A basepairs

Question 8

What is the first step in rho-dependent TX termination?

Answer 8

The rho-utilization (rut) site in the DNA is transcribed in the RNA

Question 9

Where does the rho protein bind in rho-dependent TX termination?

Answer 9

The rho-utilization (rut) site

Question 10

In what direction does the rho protein move in rho-dependent TX termination?

Answer 10

Toward the 3’ end of the RNA (toward RNA polymerase)

Question 11

How does the rho protein terminate transcription (last step in termination)?

Answer 11

The rho protein causes the RNA to dissociate from DNA either by pushing RNA polymerase or pulling RNA (unknown which)

Question 12

What are the two parts of a ribosome?

Answer 12

Large (50S) subunit and small (30S) subunit

Question 13

In what direction do ribosomes translate mRNA?

Answer 13

From 5’ to 3’, from the protein N-terminus to C-terminus

Question 14

Can multiple ribosomes translate the same gene at the same time?

Answer 14

Yes

Question 15

In prokarotes, ribosomes can start translating an mRNA even before RNA pol has finished transcribing it.
Why is this not true in eukaryotes?

Answer 15

In eukaryotes, TX & TL take place in different locations (TX in nucleus & TL in cytoplasm)

Question 16

Why don’t prokaryotic cells fill up with too much mRNA and protein? (2 reasons)

Answer 16

1. Cell divison: cells need enough RNA and protein to divide quickly
2. Degradation: mRNA and proteins have limited lifespans

Question 17

In prokaryotes, on what part of mRNA does translation start?

Answer 17

Ribosome binding site (RBS)

Question 18

What two things are together sufficient to initiate prokaryotic translation?

Answer 18

RBS consensus sequence + start codon AUG

Question 19

Where are rRNAs found?

Answer 19

In the ribsosomal subunits

Question 20

How does the 3’ end of the 16S rRNA allow ribosome binding?

Answer 20

It basepairs with the RBS consensus sequence

Question 21

Could a change to the RBS be a null mutation, hypermorph, or both?

Answer 21

Both - null if the RBS was deleted, hypermorph if it increased the match of RBS sequence to the consensus