L17: Translation Part 2

Question 1

What is the tRNA made up of?

Answer 1

RNA bases (G, C, A, U)

Question 2

Describe the anti-codon.

Answer 2

• anti-parallel

- complementary to the codon on the mRNA`

Question 3

What is the start codon and its anti-codon

Answer 3

• mRNA: 5’-A-U-G-3’
• tRNA anti-codon: 3’-U-A-C-5’
• amino acid: methionine (Met)

Question 4

Describe ribosomes in a structural sense.

Answer 4

• bacterial and eukaryotic ribosomes are made up of different proteins (subunits) and ribosomal RNA (rRNA)

Question 5

Describe ribosomes in a functional sense.

Answer 5

• they translate in the same manner
• a piece of rRNA catalyzes the peptide bond
• there are hundreds to thousands of ribosomes in the cytosol

Question 6

What are the translation steps in bacteria?

Answer 6

• Step 1: Ribosome binds to the mRNA
• Step 2: a second ribosome binds after ribosome 1 has moved downstream
• Step 3: a third ribosome binds as #1 and #2 are moving along the mRNA downstream

Question 7

What is the direction of the ribosome in bacterial cells?

Answer 7

The ribosome moves from 5’ end of the mRNA to the 3’

Question 8

What are two examples of environmentally regulated genes?

Answer 8

• mal operon and lac operon

Question 9

What does it mean if a gene is regulated?

Answer 9

• bacterial cells only need to synthesize the proteins in the mal and lac operon if those sugars are present

Question 10

What are the 3 levels of gene regulation?

Answer 10

• Transcriptional
• Translational
• Posttranslational

Question 11

Are all genes always expressed?

Answer 11

• no! some genes are always expressed while the expression of others are regulated.

Question 12

What are constitutively expressed genes?

Answer 12

• a gene that is expressed all the time because its gene product is needed all the time
• (i.e. rRNA, tRNA, RNA pol, ribosomal proteins, aminoacyl tRNA synthetases (enzymes)

Question 13

What are environmentally-regulated genes?

Answer 13

• a gene whose expression level is linked to a condition in the environment
• (i.e. nutrient availability, mal and lac operons)

Question 14

What is the regulation of gene expression critical to?

Answer 14

• it is critical to the efficient use of resources, and thus survival

Question 15

Are constitutively regulated/expressed genes always made at the same level?

Answer 15

no! gene products of constitutively expressed genes are not needed in the same amounts in cells

Question 16

what are common control mechanisms of constitutively gene products?

Answer 16

1) Promoter “strength” (how effectively RNA pol and transcription factors bind to the promoter)
- this determines how frequently transcription is initiated
- this determines how many RNA molecules are made

2) mRNA half-life can effect
- how quickly the mRNA is degraded after it is made
- the longer the mRNA lasts, the more proteins can be translated per unit time
- only applies to protein-encoding genes i.e. mRNA
- recall that tRNA and rRNA are stable RNA and not degraded as mRNA!

Question 17

What is an operon?

Answer 17

• operons share a promoter and termination sequence but have multiple coding regions
• one mRNA is produced yet multiple proteins are translated - called polycistronic mRNA

Question 18

What does basal mean?

Answer 18

• base, minimal

- As in basal gene expression, basal transcription levels

Question 19

What is positive regulation?

Answer 19

• regulatory protein binds a region by the promoter (operator) and increases transcription
• regulatory protein is called the “activator” protein (i.e. MaIT)

Question 20

What is negative regulation

Answer 20

• regulatory protein binds to a region by the promoter (operator) and decreases transcription
• regulatory is a “repressor” protein (i.e. Lacl)