Protein Synthesis Flashcards
(19 cards)
Explain how synthesis of polypeptide is coded for by DNA
Each amino acid in a polypeptide is coded for by a triplet in the DNA molecule
Genes undergo transcription to form mRNA with a base sequence complementary to a section of DNA
During translation, the sequence of bases in mRNA is converted into a specific sequence of amino acid
Each mRNA codon undergoes complemtary base pairing with the anticodon of a specific aminoacyl-tRNA carrying. Specific amino acid
Explain why the genetic diode is a triplet code ?
There are only 4 ribonucleotide ashes to specify 20 amino acids
Being a triplet code, can produce 64 possible codons to provide sufficient codons to specify all the amino acids needed for translation
Describe initiation of transcription
General transcription factors bind to the promoter at the TATA box
Recruits RNA polymerase onto promoter forming transcription initiation complex
DNA double helix unwinds as H bonds between complementary bases in the doublhelix break
What is the direction of transcription ?
3’ to 5’ of template strand
(3’ end needed to add ribonucleotide triphosphate)
Describe elongation of transcription
Free ribonucleotide triphospahte complementary base pair with the DNA bases on template strand
RNA pol catalyses formation of phosphodiester bond between adjacent RNA nucleotides
RNA pol moves in the 3’ to 5’ direction of the template strand
Describe termination of transcription
Terminator sequence codes for polyadenylation signal
Signal recruits certain proteins to cleave the RNA transcript 10-35 nucleotides down from the polyadenylation signal
Post transcriptional modification
What direction does translation occur in ?
5’ to 3’ of mRNA
N-terminus to C-terminus of growing polypeptide
Decsiobre preparation of translation
Amino acid binds to tRNA forming aminoacyl tRNA
Catalysed by aminoacyl tRNA synthase
Describe initiation of translation
Initiator tRNA binds to small unit stabalioised by initiation factors
This complex binds to 5’ UTR of mRNA via RNA binding site
Moves downstream till the start codon, AUG
Anticodon of amicoacyl tRNA complementary base pairs with starts codon
Large subunit binds to form translation initiation complex, with energy form GTP hydrolysis
What amino acid does initiator tRNA carry ?
Methionine
Describe elongation of translation
Coreespondnig amicoacyl tRNA for the next codon binds at the A site via complementary base pairing of its anticodon and the codon at A site
Peptide bond forms between amico acid on P site and aminos acid on A site catalysed by peptidyl transferase.
Ribosome moves down 3 codon in the 5’ to 3’ direction of the mRNA
Free tRNA on E site released
Coreepsonfing aminoacyl tRNA binds to codon on A site via complemtary base pairing with its anticodon
Describe termination of translation
Ribosome reaches stop codon , UAA/UAG/UGA
A site accepts release factor which caused addition of water too the polypeptide hydrolysing the bond between amicoacid and tRNA on the P site.
Polypeptide released through the tunnel in large subunit
Describe how the correct amino aicid is joined to tRNA
There is 20 aminoacyl tRNA synthase 1 for each amino acid
Specific amino acid binds to the active site of aminoacyl tRNA synthase
Specific tRNA with specific anticodon coresponding to the amino aicid enters the ative site
Aminoacyl tRNA synthethase catalyses formation of covalent bond between amino acid and 3’ end of the tRNA
Compare transcription and translation
Location:
- nucleus
- ribosomes
Key enzymes:
- RNA polymerase
- aminoacyl tRNA and peptidyl trasferase
Products:
- mRNA
- polypeptide
Monomers:
- RNA nucleotides
- amino acid
Bonds between monomers:
- phosphodiester
- peptide
When does transcription and translation occur ?
Many ribosomes can translate 1 single mRNA simultaneously
Both trsnacription and translation can occur simultaneously
Sickle cell anaemia is a results of what mutation
Results of single base-pair substation
Describe sickle cell anaemia
Base pair substitution of A with T
Hydrophobic valine replaces hydrophilic glutamic acid resulting in change in 3D conformation in haemoglobin
Descreases solubility of deoxygenated HbS and at low oxygen, hydrophobic area of different HbS will stick together
Can phenotype remain the same is one remaining copy of the normal gene left ?
Yes, able to produce enough functional protein
Ribosome consists of subunits containing ribosomal rRNA, where is rRNA synthesised ?
In nucleolus
Complexed with protein from cytoplasm
Subunits exported to cytoplasm via nuclear pores
