Flashcards in Translation_Molecules Deck (61):
What carries out translation?
What is translation?
Protein synthesis when there is a conversion of RNA code to AA code
What does mRNA get translated by?
2) rRNA and proteins
3) peptide bond formation catalysed by rRNA (not protein enzyme)
What is translation regulated by?
How does miRNA regulate translation?
suppress growth inhibitor -> too much miRNA
Can you go directly from protein to RNA?
No can't use it to transfer information to RNA directly
What structures are visible under a microscope?
mRNA (gets stained)
A sequence of 2 bases can specify what?
4^2 (16) AA
4^3 (64) AA
Why can a single base in the mRNA not specific an AA in a polypeptide?
mRNA has only four bases but polypeptides contain 20 AA
What are codons?
a sequence of three bases on the mRNA codes for an AA
What direction does the ribosome read the codon?
5' -> 3' direction
What happens when the ribosome moves along the mRNA in the 5' -> 3' direction?
It synthesises the polypeptide in the amino -> carboxyl terminal direction
What are the properties of genetic code?
2) nonoverlapping and "commaless"
4) Contains 61 AA coding codons and the three stop codons UAA, UAG, UGA
What does it mean that the genetic code is colinear
sequence of AA in the polypeptide from amino end to carboxyl end, corresponds exactly to the sequence of their codons in the mRNA, read form 5' -> 3'
What does it mean the genetic code is non overlapping and "commaless"
Codons are aligned without overlapping and without empty spaces in between. Each base belongs to only one codon.
What does it mean the genetic code is degenerate
More than one codon can code for an AA
What does it mean that the genetic code is unambiguous?
Each codon specifies one and only one AA
What does it mean that the genetic code is universal?
With the minor exception of the start codon AUG, the code is identical in prokaryotes and eukaryotes
What breaks the properties of genetic code?
Synthesising mRNA could make a new protein.
1) poly U -> poly Phe
2) poly C -> poly Pro
3) poly random (U,small amount of C) -> Phe, Pro, Ser and Lys
4) poly (AU) -> Ile-Tyr-Ile-Tyr-...
What is the start codon?
What is the stop/termination/nonsense codon?
What is the exception that slightly doesn't follow the genetic code in the human body?
When you silent a codon, which position is normally silenced
the third position
What does AUG also code for?
What are the two types of mutations?
1) Point mutation
2) Frameshift mutation
What are examples of point mutations and what are they?
Silent mutations - degenerate positions
Missense mutations - change AA
Nonsense mutations - create stop codon
Change stop codon tonne stop - "read through mutations - get a longer protein
What does point mutations do?
Change one base
What is frame shift mutation?
insert or delete 1,2,4,5,7 etc bases -> random with respect to protein
What happens during silent mutation?
Normally no phenotypic change
Can alter splicing causing disease and cancer
How is silent mutations detected by?
DNA sequencing or mRNA sequencing (can't see by sequencing protein or AA)
What are examples of silent mutations?
SNP (single nucleotide polymorphism)
Codon usage in bacterial and virus genomes not random
What is an example of missense mutation
- Sickle cell anaemia
- GAA -> GUA OR
- GAG -> GUG at codon 6
- hundred other globin mutations known
What is an example of nonsense mutation?
- imbalance in globin production or absence of one globin
- e.g. AAG -> UAG at codon 17 of beta globin (beta thalassemia)
- entire globin gene missing
What happens in alpha thalassaemia?
4 copies of alpha globin gene
- 2 on each chromosome 16
- deletion of 1 - 4 copies causes disease
- also "read through" mutation of stop codon -> abnormally long alpha globin chains
How many transfer RNA are there?
Approx 50 per organism, one or more for each AAA
How many tRNA syntheses are there?
- attach 1 AA to one tRNA
Each tRNA recognises how many codons?
1 or 2 codons
- modified nucleotide at the 3rd position and can recognise at the silent position
What do ribosome need to do?
1) Bind to mRNA
2) Recognise start of coding sequence
3) Move along coding sequence
-> read RNA, codon by codon from 5' -> 3'
-> Add amino acids to protein chain from N terminus to C terminus
-> need an "adaptor" molecule which is tRNA
When reading nucleotype what happens?
need to use another nucleic acid/nucleotype because H bonding is completely specific
What are the features of tRNA?
1) Approximately 70 nucleotide long
2) AA attached at 3' end
3) All end in CCA
What type of structure does the tRNA have?
Clover leaf structure
What is Gm and what does the Gm AA read in tRNA
What is the codon recognised by?
What are the prominent features of tRNA?
1) Modified nucleotides
2) Methylated bases
What are the two subunits of ribosome?
What does S stand for?
Svedberg unit: centrifugation size
What does the small subunit contain (in humans)?
1) 34 proteins
2) one RNA -> SSU or 18S rRNA
What does the large subunit contain (in humans)?
1) 50 proteins
2) 3 RNA
- LSU or 28S rRNA
- 5.8 S and 5S
Looking in atomic detail, when does the 2 subunits attach?
Attach to each other on a mRNA to carry out translation other than that they don't attach
Prokaryotes have what type of ribosome?
- small (30S) and large (50S)
What does the small subunit bind to?
What does the large subunit bind to?
Eukaryotes have what type of ribosome?
- small (40S) and large (60S) subunit
What happens during translation?
1) Start with Met at first AA
2) Add AAs in order specified by codons (in frame)
3) Stop at stop codon
4) Post translational modification
What happens during translation?
Ribosomes need to be positioned correctly
What is Shine-Dalgarno sequence?
Ribosomal binding site in bacteria, generally located around 9 - 10 nucleotide away from the AUG codon
In humans, where is first AUG sometimes?
What does the Shine-Dalgarno sequence do?
RNA sequence helps recruit the ribosome to the messenger RNA (mRNA) to initiate protein synthesis by aligning the ribosome with the start codon.
What is the ribosomal binding site rich in?
A /G rich region about 10 bases upstream of the start codon
What is the codons for mixed spel-xbal restriction site?