L10: Protein Synthesis Flashcards
Proteins are polymers of what?
Amino Acids
What two molecules ensure the correct assembly sequence of DNA?
tRNA and mRNA
What is deacylated or uncharged tRNA?
tRNA molecule which has had its amino acid removed
What do you call a tRNA molecule bound to a growing polypeptide chain?
Peptidyl tRNA
What shape is tRNA
Clover
What are the two ends of the chain referred to as?
3’ and 5’
Which end has an amino acid attached to it?
3’
What bond is used to attach the amino acid?
Ester Bond
What causes the clover shape of the molecule?
Intramolecular base-pairing
Does tRNA have a codon or an anticodon?
Anticodon
What is a codon?
Base triplet in mRNA (three bases that code for an amino acid)
Does each amino acid have a unique codon that codes for it’s synthesis?
No. Multiple codons can code for each amino acid.
e.g the following all code for serine UCA UCC UCG UCU
Which bases in the codon are the most crucial for coding?
The first two
Why is it important for multiple codons to code for the same amino acid?
It gives tolerance against mutations. If one of the bases is changed, there is a chance it will still produce the correct amino acid
How many amino acids can only be coded by one codon?
Just two - Tryptophan and methionine. Fortunately, tryptophan this is abundant in our diet
How many amino acids are coded for by 4 or more codons
Leucine Valine Glycine Serine Proline
What are the start codons?
Just AUG (also codes for methionine)
What are the stop codons?
UAG, UAA, UGA
What are the Hydrophobic amino acids?
Valine, Leucine, Isoleucine, Methionine, Proline
What are the basic amino acids?
Histidine, Arginine, Lysine
BASICally, Shallow HAL has a POSITIVE message
What are the acidic amino acids?
Glutamic Acid, Aspartic Acid
ACID and Glue Always have NEGATIVE effects
What are the sulphuric amino acids?
Cysteine, Methionine
SULPHUR Creates Malodours
What are the amide amino acids?
Asparagine, Glutamine
AMID us Are Ghosts
What are the aromatic amino acids?
Phenylalanine, Tyrosine, Tryptophan
AROMATIC People Try Tripping
What are the nucleophilic amino acids?
Serine, Threonine, Cysteine
What are the alcohol amino acids?
Serine, threonine
ALCOHOL is a SERIous THREat
When reading a DNA sequence and using the mRNA codon table, to determine the amino acids formed, what is the first step?
You have to work out the matching base pair sequence. So A becomes U, T becomes A, G becomes C and C becomes G.
What is transcription?
DNA -> RNA
What is translation?
RNA -> Protein
Where does transcription take place?
Nucleus
Why does transcription take place in the nucleus?
DNA is too big to leave, therefore its sequence is transcribed onto a strand of mRNA, which is small enough to leave through the nuclear pores
Which molecule unzips the DNA strands?
Helicase
After its coding, the mRNA is premature and requires additional steps. Outline the sequence required to mature the mRNA
- Add 5’ phosphorylated 7-methyl guanosine cap
- Add 3’ poly-A-tail
- Splice off introns
Which end is given a cap?
5’
What is the 5’ cap made from?
Phosphorylated 7-methyl guanosine
Which enzyme adds the phosphorylated 7-methyl guanosine cap to the 5’ end of the pre-mRNA?
Guanyltransferase
What are the three main functions of the 5’ cap?
- Ensures exportation of mRNA from nucleus
- Prevents degradation of mRNA by 5’ exonucleases
- Promotes translation
What sequence signals the cleavage of the mRNA?
AUAAAA at the 3’ end
What is done after cleaving the 3’ end of the mRNA?
200 adenosine residues are added as a tail
Which enzyme cleaves the 3’ end?
Endonuclease
Which enzyme adds the poly-A tail?
Poly-A-polymerase
What are the three main functions of the poly-A-tail?
- Protect mRNA from 3’ exonucleases
- Ensures export of mRNA from the nucleus
- Terminates translation
Why is splicing necessary?
During transcription, unused base sequences (introns) are formed. These introns need to be cut out
How can a single gene code for many different proteins?
Splicing variations will lead to different codon sequences
Describe a mature strand of mRNA
5’ cap - 5’ UTR - Start Codon - Coding Region - Sop Codon - 3’ UTR - 3’ Poly-A-Tail
What two subunits form a ribosome?
60S and 40S
In translation, what happens in the initiation phase?
Ribosome binds to 5’ end of mRNA, aminoacylated tRNA carrying methionine hydrogen bonds to the AUG start codon
In translation, what happens during the elongation phase?
Addition of amino acids to the growing polypeptide chain as aminoacylated tRNAs are matched to the sequence. Peptidyl transferase forms covalent peptide bonds between amino acids
What is a peptide bond?
Bond formed by dehydration synthesis. Bonds amino acids together. Carboxyl group and amino group joined and water is released.
In translation, what happens during the termination phase?
Stop codon is reached and the ribosome separates (40S and 60S) and releases the polypeptide
Once synthesised, what else needs to be done to make the protein functional?
Secondary, tertiary, and quaternary structure must be acquired through folding and assembly
What causes Sickle Cell Anaemia?
Mutation that means Glutamic Acid is replaced with Valine
What happens to blood cells in Sickle Cell Anaemia?
Haemoglobin crystallises and causes a sickle shaped. These cannot carry oxygen and get stuck in blood vessels
What are the clinical consequences of Sickle Cell Anaemia?
Tissue ischaemia - causes pain and infarction
Immunity to malaria
How do you contract Sickle Cell Anaemia?
It is inherited or caused by a mutation in your own DNA
Why is Sickle Cell Anaemia common in Sub-Saharan Africa?
It provides protection against malaria, and so has been passed on through natural selection
