Practice Questions

Question 1

What is the status of regulatory factor binding to the lactose operon promoter when E coli is grown in media containing both lactose and galactose?

Answer 1

Neither LacI nor CAP is bound

LacI repressor only binds when no lactose present; CAP only binds when no glucose present - ‘hunger’ signal

Question 2

What is the difference between euchromatin and heterochromatin in regards to acetylation and methylation?

Answer 2

E: high histone acetylation, low DNA methylation, H3-K4 methylation
H: low histone acetylation, high DNA methylation, H3-K9 methylation

Question 3

How do steroid hormone receptors stimulate gene expression?

Answer 3

by binding enhancer sequences and recruiting chromatin remodeling proteins

Question 4

What are the two parts of a tRNA that are required for codon recognition and AA attachment, respectively?

Answer 4

Codon recognition: Anticodon loop - contains sequence that will base pair to codon in mRNA; determines AA

AA attachment: 3’ CCA end - not transcribed but added after processing; is essential for aminoacylation that is addition of tRNA

Question 5

What is aminoacylation?

Answer 5

The process by which AAs are attached to tRNAs

• aminoacyl tRNA synthesases (20 of them) recognize anticodon and other structural features of tRNAs –> add the appropriate AA (requires ATP)
• fidelity is carefully controlled

Question 6

How are incorrectly aminoacylated tRNAs prevented from being used during translation?

Answer 6

if an incorrect AA starts to bind to the synthesis site of the enzyme, the exiting site will evolve to have a higher affinity for that AA, will cleave that AA, and tRNA released so it can start over

Question 7

What are the components of a mammalian ribosome?

Answer 7

60S (contains 3 RNAs that interact with about 49 proteins)
40S (contains 1 RNA that interacts with about 33 proteins)
- ribosome made mostly of RNA

S = measure of velocity through a gradient

Question 8

Why is the ribosome considered a ribozyme?

Answer 8

a ribozyme is a piece of RNa that can perform a catalytic reaction just like a protein
in the ribosome, peptide formation occurs without the contribution of any protein

Question 9

What are the 3 tRNA binding sites in the ribosome?

Answer 9

1. A (aminoacyl) site: initial tRNA binding site for next codon
2. P (peptidyl) site: peptide bond formation
3. E (exit) site: tRNA release

Question 10

What factors bind the 5’ cap, initiator tRNA, and cap binding protein?

Answer 10

respectively: eIF4E, eIF2, eIF4G