4- Proteins (gene regulation & protein synthesis) Flashcards
what do codons and anti-codons each consist of?
3 nucleotides
in translation, (A) of tRNA molecules pair with (B) of mRNA molecules
(A) anticodons
(B) codons
what does degenerate mean? (in context of proteins and genetic code)
one codon sequence can code for multiple amino acids
what does unambiguous mean?
each codon only codes for one amino acid
why does there need to be a specific start reading frame sequence?
because if wasn’t specific start - you wouldn’t know what amino acids are there as bases could be any order
what are the sources of energy for translation?
ATP & GTP
what steps of translation require a specific set of protein factors?
- initiation of protein synthesis
- elongation of protein synthesis
- termination
what is function of aminoacyl-tRNA synthetases?
it binds (attaches) amino acids to their corresponding tRNA molecule (highly specific)
what is ratio of aminoacyl-tRNA synthetases to amino acids?
at least one per amino acid
what is rough idea of aminoacyl-tRNA synthetases steps?
- ATP provides energy for covalent bond
- enzyme catalyses reaction joining activated amino acid & tRNA (very specific)
- charged tRNA delivers appropriate amino acid to join elongating polypeptide product
what are the 3 tRNA binding sites on ribosomes?
A = aminoacyl (first site amino acid arrives at on ribosome)
P = peptidyl (middle site, also could be “processing”)
E = exit
what provides energy for initiation?
GTP is hydrolysed to provide energy
what does GTP energy allow to happen in initiation?
small ribsosomal subunit bind to 5’ end of mRNA (which is capped)
=this helps protect RNA and acts as recognition site for ribosome
what is the start codon of translation initiation and what is the process?
AUG is the start codon, it moves along mRNA until it reaches AUG, the special initator tRNA recognises the pattern as has UAC anticodon base pairs (which is methionine)
=movement requires ATP hydrolysis
what is the only code for methionine?
AUG (UAC anticodon)
what site is initiator tRNA located?
in P site (peptidyl)
describe the start of the elongation process
elongation factor (EF-1a) brings the next amino-acyl tRNA(charged tRNA carrying an amino acid) to the A site (aminoacyl site) and anticodon base pairs with codon
what is GTP required for in elongation process?
it’s hydrolysed to provide energy for the release of elongation factor from tRNA
what does the second elongation factor do?(translation)
regenerates the first elongation factor to pick up the next aminoacyl-tRNA (starting process again)
what is the name of
a) 1st elongation factor
b) 2nd elongation factor
a) EF-1a
b) EF-bg
what catalyses the petide bond formation between amino acids ?
peptidyl transferase
what sites of the ribosome are the peptide bonds formed?
in the P (peptidyl) and A (aminacyl) sites
- peptide now located in A site
what moves ribosome along mRNA in translocation and by how much?
elongation factor (EF2) moves the ribosome - by 1 triplet
where does an “empty” tRNA move?
it moves to E site (exit) where it leaves and becomes reloaded with an amino acid
where does tRNA with growing peptide move through sites i.e what order?
from A to P site then to E. leabing A site free for next aminoacyl-tRNA
when does termination occur?
when A site of ribosome encounters a STOP codon
what are examples of stop codons that cause termination?
-UAA
-UAG
-UGA
why does a stop codon stop the translation of the protein?
because no aminoacyl-tRNA base pairs with stop codon
what happens after stop codon is detected in termination?
- release factor (RF) binds to stop codon - due to energy from GTP hydrolysis
- finished protein cleaved off tRNA
- components rRNA, tRNA and mRNA dissociate from one another so whole process starts again with small subunit being bound by IF ready for translation of new protein
what direction is translation?
from 5’ to 3’ (the polypeptide chain gets longer at 3’ end)
what are point mutations?
change in single base DNA
what is result of missense mutations?
results in change of amino acid sequence which can change protein function
what are nonsense mutations?
creates new termination code which changes length of protein due to premature termination
what are silent mutations?
change in base makes no change in amino acid sequence due to degeneracy of genetic code so no effect on protein function
what is frameshift mutation?
addition or deletion of single base or 2 which changes reading frame of translation of protein so affects all proteins that come after that
what are chromosomal mutations?
affect larger proportions of genome
examples:
1. deletions
2. duplications
3. inversions
4. translocations
what are the steps for the completed protein after translation?
- targeting
- modification
- degredation
what happens in targeting process of finished protein?
-protein moves to final destination
(many possible locations within a cell)
final destination depends on presence of specific amino acid sequences within the translated proteins
what is the modification stage of the finished protein?
-post translational modification
= addition/removal of further chemical groups
what is degredation step of finished protein?
-unwanted or damaged proteins have to be removed
what are the proteins made by free ribosomes (they’re in the cytoplasm) destined for?
-cytosol
-nucleus
-mitochondria
(translocated post translationally)
what are proteins made by bound ribosomes (on RER) destined for?
-plasma membrane
-ER
-golgi apparatus
-secretion
(translocated co-translationally = as they’re moving)
what are some examples of post translational modification?
- glycosylation = addition and processing of carbohydrates in ER and golgi (adding sugars important for targeting & recognition)
- formation of disulfide bonds in ER
- folding and assembly of multisubunit proteins in ER
- proteolysis = specific proteolytic cleavage in ER, golgi & secretary vesicles to allow fragments to fold into different shapes
5.added phosphate groups after shape of protein
