Translation

Question 1

What is the primary enzyme used in translation?

Answer 1

Ribosome

Question 2

What is the template used for translation?

Answer 2

mRNA

Question 3

What are the subunits assembled during translation?

Answer 3

Amino acids

Question 4

What are the two subunits that make up a ribosome?

Answer 4

Large and small subunits. Both are made of at least one RNA and lots of proteins

Question 5

What does tRNA do during translation?

Answer 5

It reads the mRNA sequence and brings the right amino acid to be added next. They are physically bound to an amino acid that corresponds to the codon on the mRNA

Question 6

How are tRNAs recycled?

Answer 6

After leaving the ribosome, they go to the tRNA synthetase and it binds to the anticodon and attaches another amino acid to the tRNA

Question 7

How many tRNA-synthetases are in a cell?

Answer 7

20, one for each amino acid

Question 8

What defines the beginning and end of translation?

Answer 8

The start and stop codons

Question 9

Are the start codons always at the very beginning of an mRNA transcript?

Answer 9

No, most of the time it isn’t. It will be further downstream so there will be a 5’ untranslated region on the mRNA

Question 10

Are the stop codons always at the very end of an mRNA transcript?

Answer 10

No. There will be an untranslated region 3’ of the stop codon

Question 11

How does translation initiation occur in prokaryotes?

Answer 11

1. The small ribosomal subunit recognizes and binds to the ribosome binding site
2. The small subunit slides along the mRNA until it finds an AUG
3. The small subunit recruits tRNA and the large ribosomal subunit and translation begins

Question 12

How does the ribosome recognize the ribosome binding site?

Answer 12

Complementary base pairing with rRNA

Question 13

Why is an mRNA able to encode more than one polypeptide in prokaryotes?

Answer 13

There are multiple ribosome binding sites along the transcript. The polypeptide that gets produced will depend on which ribosome binding site the ribosome binds to

Question 14

In eukaryotes, what needs to happen before the small subunit can bind to the mRNA transcript?

Answer 14

Eukaryotic initiation factors need to bind to the 5’ cap, the polyA tail, and to each other to circularize the mRNA. Then the small subunit gets recruited

Question 15

Where does the small ribosomal subunit bind in eukaryotes?

Answer 15

At the 5’ end

Question 16

How does the small ribosomal subunit determine which AUG is a start codon and which AUG is just a methionine in eukaryotes?

Answer 16

Eukaryotes use the scanning mechanism, so they start at the 5’ end and scan until it finds an AUG. The first AUG the small subunit finds will be the start codon

Question 17

Why is the mRNA circularized?

Answer 17

It makes it easier to reload the ribosomes and translate multiple times, reusing the mRNA to make more proteins

Question 18

Can a eukaryotic mRNA encode multiple polypeptides like in prokaryotes?

Answer 18

No, because of the scanning mechanism there will always be only one start codon. The ribosome won’t bind anywhere but the 5’ end

Question 19

What is the A site in the ribosome?

Answer 19

The aminoacyl tRNA site. It is where the tRNA with the next amino acid will bind with complementary base pairing between the codon and anticodon

Question 20

What is the P site in the ribosome?

Answer 20

The peptidyl tRNA site. The growing peptide chain is physically bound to the amino acid on the tRNA coming in from the A site

Question 21

What is the E site in the ribosome?

Answer 21

The exit site. The peptide chain is transferred to the next tRNA and the tRNA in this site leaves the ribosome and go to a tRNA synthetase

Question 22

How do we know that it’s the rRNA that is catalyzing the formation of peptide bonds and not the proteins?

Answer 22

If the large ribosomal subunit is treated with a protease, it can still catalyze the formation of peptide bonds

Question 23

What are the steps in translation elongation?

Answer 23

1. The tRNA comes into the A site and complementary base pairs to the codon
2. The tRNA moves into the P site
3. The growing peptide chain is transferred to the amino acid carried by the tRNA
4. The tRNA moves into the E site
5. The tRNA is detached from its amino acid
6. the tRNA leaves the ribosome to be reloaded by a tRNA synthetase

Question 24

How is translation terminated?

Answer 24

A release factor binds to a stop codon in the A site and hydrolyzes the bond between the tRNA in the P site and the amino acid it is attached to. The protein, ribosome, mRNA, and tRNA all dissociate

Question 25

What is a polyribosome?

Answer 25

An mRNA with a lot of ribosomes attached and translating

Question 26

How are transcription and translation coupled in prokaryotes?

Answer 26

Translation can begin as soon as a ribosome binding site is available, even while the RNA is still being transcribed

Question 27

Why do transcription and translation need to stay separate in eukaryotes?

Answer 27

Organelles, there’s membranes in the way. Transcription occurs in the nucleus and translation occurs in the cytoplasm. This ensures that the mRNA gets all modifications before it is translated