Translation

Question 1

What is translation

Answer 1

Process of converting mRNA into proteins

Question 2

What enzyme is responsible for translation?

Answer 2

ribosomes

Question 3

Where are ribosomes found in prokaryotes and eukaryotes?

Answer 3

Prokaryotes: cytosol
Eukaryotes: Endoplasmic reticulum

Question 4

What is codon?

Answer 4

Triplet of nt that encodes a particular amino acid

Question 5

What happens during the initiation stage in translation? (3)

Answer 5

• Small ribosome subunit binds RBS
• Finds “start codon” and tRNA-Met binds
• Large subunit binds

Question 6

What happens during the elongation stage of translation? (5)

Answer 6

1) tRNA enters A-site
2) Amino acid is transferred to tRNA in P-site
3) Ribosome moves 1 codon
4) Empty tRNA is released from E-site
5) Repeat.

Question 7

What happens during the termination stage in translation? (2)

Answer 7

• When the stop codon is reached, the release factor binds and the protein is released.
• Ribosome falls off

Question 8

What is tRNA?

Answer 8

tRNA is a type of RNA that carry a specific amino acid

Question 9

What is the difference between charged and uncharged tRNA?

Answer 9

charged tRNA: attached to an amino acid

uncharged tRNA: not attached to an amino acid

Question 10

What component of tRNA causes it to bind to a codon?

Answer 10

anti-codons

Question 11

What are ribosomes made up of?

Answer 11

rRNA and some proteins

Question 12

What is another possible start codon other than met?

Answer 12

GUG (rare though)

Question 13

What is post-translation modifications of translation?

Answer 13

Additional modifications of the polypeptide chain to become fully active, which is used in cell signalling

Question 14

What are the types of post-translation modifications of translation?

Answer 14

1) Structural changes

2) Addition of a chemical group

Question 15

What is a common structural PTM? What are the two common types?

Answer 15

The processing of precursor protein by peptide cleavage
Two common types:
1) Removal of signal peptide
2) Preprotein being cleaved into multiple subunits from a single polypeptide chain

Question 16

What is preprotein?

Answer 16

Protein with a signal peptide

Question 17

What is an example of a preproprotein?

Answer 17

Insulin

• Signal peptide is removed
• A, B, and C chains are cleaved into three pieces
• A and B link through disulfide bridges to form mature insulin

Question 18

What are the common functional groups that can be added for PTM? (5)

Answer 18

1) Phosphorylation
2) Glycosylation - often used in cell recognition and binding
3) Lipidation - addition of a lipid, often used in membrane anchoring
4) Addition of other small molecules - addition of an acetyl group or methyl group for example
5) Addition of a cofactor - addition of FAD to an enzyme for example

Question 19

What is the purpose of phosphorylation of protein after translation? (2)

Answer 19

• Used to control the function of a protein by changing the conformation of the protein
• Sometimes can be used as a tag to signal the cell to degrade a particular enzyme

Question 20

Which amino acids usually undergo phosphorylation?

Answer 20

• Serine, theonine, tyrosine or histidine side chain

- But also lysine, arginine, aspartic acid and glutamic acid residues

Question 21

What enzymes are used in phosphorylation and what do they do? (2)

Answer 21

1) Protein kinases - adds phosphate groups to a protein

2) Protein phosphorylations - remove phosphate groups from a protein.

Question 22

What is the typical co-substrate of phosphorylation?

Answer 22

ATP

Question 23

What is glycosylation and what does it affect?

Answer 23

• Glycosylation is the addition of sugars to a protein

- Affects protein folding and binding functions of a protein

Question 24

What are the types of glycosylation?

Answer 24

1) O-glycosylation : linked to the oxygen group of serine tyrosine or threonine
2) N-glycosylation : linked to the nitrogen group of an asparagine or arginine side chain

Question 25

What is ligand binding? What role does it play?

Answer 25

• A binding used in glycosylation

- Plays a role in cell signaling and cell adhesion

Question 26

What is an example of O-glycosylation?

Answer 26

ABO red blood cell types

red blood cells can have one of three types of sugars on their cell membrane proteins

Question 27

Which class organisms are N-glycosylation very common in?

Answer 27

• Common in eukaryotes
• Occurs widely in archaea
• Very rare in bacteria

Question 28

What are the steps of N-glycosylation?

Answer 28

1) core glycan is transferred to the protein (occurs in ER membrane)
2) glycan is trimmed and modified by different enzymes

Question 29

What is the biggest problem when manufacturing a human protein in a non human cell?

Answer 29

Glycosylation

• Different plant and animal species may have or lack particular glycosylation enzymes
• The final protein will be different if it needs to be glycosylated and glycosylation plays a major role in the function of that protein

Question 30

What is lipidation? What is it used for?

Answer 30

• It is the addition of a lipid group to a protein

- Often used for localizing proteins in the cell or organelle membranes since it creates a hydrophobic anchor

Question 31

What are the four common types of lipidation?

Answer 31

1) Addition of a C14:0 myristic acid group - myristolation (N-myri is irreversible)
2) Addition of a C16:0 palmitic acid group - palmitolation (S-palm is reversible)
3) Addition of a prenyl group - prenylation
4) Addition of a glycolipid group - glycosylphosphatidylinositol (GPI)

Question 32

What are the types of mutations? (4)

Answer 32

1) Silent - if non coding region is changed or if the codon is changed but the corresponding amino acid is the same
2) Missense - if protein sequence is changed
3) Nonsense - if codon is changed into a stop codon which shorten the protein
4) Frame shift - if 1 or 2 nt are deleted or inserted, so everything down the stream of the insertion will be shifted