Translation Flashcards
What is translation
Process of converting mRNA into proteins
What enzyme is responsible for translation?
ribosomes
Where are ribosomes found in prokaryotes and eukaryotes?
Prokaryotes: cytosol
Eukaryotes: Endoplasmic reticulum
What is codon?
Triplet of nt that encodes a particular amino acid
What happens during the initiation stage in translation? (3)
- Small ribosome subunit binds RBS
- Finds “start codon” and tRNA-Met binds
- Large subunit binds
What happens during the elongation stage of translation? (5)
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.
What happens during the termination stage in translation? (2)
- When the stop codon is reached, the release factor binds and the protein is released.
- Ribosome falls off
What is tRNA?
tRNA is a type of RNA that carry a specific amino acid
What is the difference between charged and uncharged tRNA?
charged tRNA: attached to an amino acid
uncharged tRNA: not attached to an amino acid
What component of tRNA causes it to bind to a codon?
anti-codons
What are ribosomes made up of?
rRNA and some proteins
What is another possible start codon other than met?
GUG (rare though)
What is post-translation modifications of translation?
Additional modifications of the polypeptide chain to become fully active, which is used in cell signalling
What are the types of post-translation modifications of translation?
1) Structural changes
2) Addition of a chemical group
What is a common structural PTM? What are the two common types?
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
What is preprotein?
Protein with a signal peptide
What is an example of a preproprotein?
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
What are the common functional groups that can be added for PTM? (5)
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
What is the purpose of phosphorylation of protein after translation? (2)
- 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
Which amino acids usually undergo phosphorylation?
- Serine, theonine, tyrosine or histidine side chain
- But also lysine, arginine, aspartic acid and glutamic acid residues
What enzymes are used in phosphorylation and what do they do? (2)
1) Protein kinases - adds phosphate groups to a protein
2) Protein phosphorylations - remove phosphate groups from a protein.
What is the typical co-substrate of phosphorylation?
ATP
What is glycosylation and what does it affect?
- Glycosylation is the addition of sugars to a protein
- Affects protein folding and binding functions of a protein
What are the types of glycosylation?
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
What is ligand binding? What role does it play?
- A binding used in glycosylation
- Plays a role in cell signaling and cell adhesion
What is an example of O-glycosylation?
ABO red blood cell types
red blood cells can have one of three types of sugars on their cell membrane proteins
Which class organisms are N-glycosylation very common in?
- Common in eukaryotes
- Occurs widely in archaea
- Very rare in bacteria
What are the steps of N-glycosylation?
1) core glycan is transferred to the protein (occurs in ER membrane)
2) glycan is trimmed and modified by different enzymes
What is the biggest problem when manufacturing a human protein in a non human cell?
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
What is lipidation? What is it used for?
- 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
What are the four common types of lipidation?
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)
What are the types of mutations? (4)
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
