3.9 - The Ribosome & Translation

Question 1

What are the 3 parts of the ribosome?

Answer 1

-** A site**: accepts the amino acid from the tRNA so that they can be added to the growing polypeptide chain
- P site: hold the polypeptide chain in placeas more amino acids are added
- E site: the “exist” site; where discharged tRNA are released

Question 2

What are rules of the ribosome?

Answer 2

1) holds mRNA and tRNA in place so codons can be read
2) catalyzes information of polypeptides between amino acids
3) determinds where transitions start & end

Question 3

What part of the ribosome holds the mRNA?

think subunit

Answer 3

the small ribosome subunit
(binds to mRNA first)

Question 4

What part of the ribosome allows tRNA to enter?

Answer 4

the large ribosomal subunit

Question 5

What direction is the mRNA read in?

Answer 5

5’ to 3’ ends

Question 6

What are the 4 steps of translation?

similar to transcription

Answer 6

1) initiation
2) elongation
3) termination
4) protein folding

Question 7

Describe initation.

Genetics: transcription, ribosome

Answer 7

• ribosome small subunit binds to 5’ cap of the mRNA transcript
• ribosome moves along the mRNA and reads the codons
• nothing starts until the start codon is read
• the start codon begins in the P site

Question 8

Describe elongation.

Genetics: transcription, ribosome

Answer 8

• the second codon is now in the A site
• the tRNA delivers the correct amino acid in the protein sequence & a poly peptide bond is formed between the met and the 2nd amino acid
• the ribosome shifts one codon over. The tRNA that carried met is released, while the 2nd amino acid takes its spot in the P site
• tRNA is released in the E site
• the next/third amino acid is brought to the A site & another peptide bond is formed between the 2nd and 3rd amino acid
• continues until stop codon is reached

Question 9

Describe termination.

Genetics: transcription, ribosome

Answer 9

• when a stop codon is reached, the process of elongation stops
• a protein called the release factor recognizes that that the stop codon is reached
• this causes the ribosome to fall apart & disassemble which releases the mRNA and the polypeptide chain

Question 10

Describe the protein folding step.

Genetics: transcription, ribosome

Answer 10

• the newly released polypeptide chain begins to fold into its protein
• the protein is transported to to where it is required

Question 11

In the process of translation (occurs in the ribosome), which part is stationary, & which part moves?

Answer 11

stationary: mRNA
moving: ribosome