7.3 Translation [HY]

Question 1

How does mRNA transcript leave the nucleus after its created and processed?

Answer 1

• Nuclear Pores

Question 2

Translation

Answer 2

• a complex process that requires mRNA, tRNA, ribosomes, amino acids, and energy in the form of GTP.

Question 3

Ribosome

Answer 3

• composed of proteins and
  rRNA. In both prokaryotes and eukaryotes, there are large and small subunits; the subunits only bind together during protein synthesis.

Question 4

What are the 3 binding sites in the ribosome for tRNA?

Answer 4

• the A site (aminoacyl), P site (peptidyl), and E site (exit)

Question 5

What is replication and the direction?

Answer 5

DNA → DNA = replication: new DNA synthesized in 5′ → 3′ direction

Question 6

What is transcription and the direction?

Answer 6

DNA → RNA = transcription: new RNA synthesized in 5′ → 3′ direction (template is read 3′ → 5′)

Question 7

What is translation and direction?

Answer 7

RNA → protein = translation: mRNA read in 5′ → 3′ direction

Question 8

What’re the ribosomal subunits?

Answer 8

• ribosomal subunits created are the 60S and 40S subunits; these subunits join during protein synthesis to form the whole 80S ribosome.

Question 9

3 stages of translation?

Answer 9

• initiation, elongation, and
  termination

Question 10

Initiation

Answer 10

• The small ribosomal subunit binds to the mRNA
• In prokaryotes, the small
  subunit binds to the Shine–Dalgarno sequence in the 5′ untranslated region of the mRNA
• In eukaryotes, the small subunit binds to the 5′ cap structure.
• The charged initiator tRNA binds to the AUG start codon through base pairing with its anticodon within the P site of the ribosome
• The large subunit then binds to the small subunit, forming the completed
  initiation complex. This is assisted by initiation factors (IF) that are not permanently associated with the ribosome.

Question 11

Elongation

Answer 11

• During elongation, the ribosome moves in the 5′ to 3′ direction along the mRNA, synthesizing the protein from its amino (N-) to carboxyl (C-) terminus.

Question 12

Peptide bond

Answer 12

• formed as the polypeptide is passed from the tRNA in the P site to the tRNA in the A site
• requires peptidyl transferase, an enzyme that is part of the
  large subunit.
• GTP is used for energy during the formation of this bond

Question 13

Elongation factors (EF)

Answer 13

• assist by locating and recruiting aminoacyl-tRNA along with GTP, while helping to remove GDP once the energy has been used.

Question 14

How are secreted peptides such as hormones and digestive enzymes moved?

Answer 14

a signal sequence directs the ribosome to move to the endoplasmic reticulum (ER),
so that the protein can be translated directly into the lumen of the rough ER

Question 15

Termination

Answer 15

• When any of the three stop codons moves into the A site, a protein called release factor (RF) binds to the termination codon, causing a water molecule to be added to the polypeptide chain. The addition of this water molecule allows peptidyl transferase and termination factors to hydrolyze the completed polypeptide chain from the final tRNA. The polypeptide
  chain will then be released from the tRNA in the P site, and the two ribosomal subunits will dissociate.

Question 16

Glycosylation

Answer 16

• addition of oligosaccharides as proteins pass through
  the ER and Golgi apparatus to determine cellular destination

Question 17

Prenylation

Answer 17

• addition of lipid groups to certain membrane-bound enzymes

Question 18

Carboxylation

Answer 18

addition of carboxylic acid groups, usually to serve as calcium-binding sites

Question 19

Posttranslational Processing

Answer 19

• The nascent polypeptide chain is subject to posttranslational modifications before it will become a functioning protein
• In peptides with signal sequences, the signal sequence must be cleaved if the protein is to enter the organelle and accomplish its function.

Question 20

Chaperones

Answer 20

the main function of which is to assist in the protein-folding process