Protein Synthesis Flashcards
Steps of DNA Transcription
1) RNA Poly separates strands
2) RNA P pairs up free nucleotides to the DNA of template strands by H-bonds.
3) RNA P links nucleotides together by covalent bonds between sugars and phosphates.
4) mRNA Strand seperates.
5) DNA rewinds
Role of H-bonding in transcription
- Can easily be broken to separate RNA strand.
- G-C have 3 h-bonds, A-T have 2 h-bonds, contributres to complementary base pairing.
How do cells specialize?
They transcribe only the genes that code for specific polypeptides, showing characteristics.
Translation
The synthesis of a polypeptide by tRNA that is complementary to codons that code for specific amino acids in ribosomes.
Overview of roles in translation:
1) mRNA binds to small subunit, contains codons which code for 1 AC.
2) 2 tRNA attach to large subunit, contains anticodon with corresponding AC.
3) Aminoacids in tRNA are bonded by peptide linkage.
The genetic code properties:
- A codon has 3 bases, creating a greater number of different codons, enough for 20 amino acids.
- Degenerate: one AC can be coded for more than 1 codon.
- Universality: all 64 codons have the same meaning in cells of all organisms.
Outline the steps in translation:
1) tRNA binds to a site, p site has chain made so far and e site is vacant.
2)Bond is made between a site amino acid and p site amino acid catalysed by ribosomal RNA»_space; Polypeptide is transferred to a site.
3) Ribosome moves 3 bases towards 3’ end, p tRNA moves towards e site, a to p site, a site vacant.
4) t site tRNA detaches and exits, next tRNA at a site binds.
How many codons indicate when the translation should end:
three stop codons
What is the start codon and for what amino acid does it code?
methionine , AUG
Mutation
Change in base sequence of DNA
what gene codes for the beta polypeptide of haemoglobin?
HBB
Explain the genetic cause of sickle cell disease:
- sixth amino acid changes adenine to thymine (CAC > CTC), transcribes mRNA to GUG codon instead of GAG, a tRNA with the anticodon CAC for valine binds, hemoglobin with valine (hydrophobic) creates sickle cells.
In what direction does transcription occur?
5 to 3
In what direction does translation occur
5 to 3 bardo
promotor
section of DNA that is a promotor where RNA Polymerase binds, start of a gene.
What do repressor proteins do?
Bind to promotor and prevent transcription.
Transcription Factors
Proteins that bind to promoter sites to promote or prevent RNA P from binding and inhibit transcription.
Outline the roles of non-coding DNA:
- Regulating gene expression: promoters or protein binding sites promote/repress, which is important for transcription.
- introns; roles in mRNA processing
- telomeres: prevents parts of important genes from being lost during replication.
- transcribing these genes produces tRNA for translation and ribosomal RNA.
What are the two types of post-transcriptional modification:
adding extra at the ends of transcript nucleotides or removal of nucleotides
3 types of modification
- five prime cap; contains three Ps, guanine and an extra methyl group, stabilizes mRNA, prevents digestion by nuclease enzymes.
- poly A tail, makes translation stop (prevents digestion and stabilises polypeptide).
- introns are removed, remaining exons are spliced together.
How is translation started?
1) tRNA with anticodon AUG binds.
2) small subunit and initiator tRNA attach to 5’ and move along the mRNA until they reach the start codon.
3) tRNA anticodon and codon pair up at P site.
4) A large subunit binds to a small unit.
5) tRNA binds to A site.
6) A peptide bond is formed between the amino acids.
A, P, E site stand for
amino acyl, peptidyl, exit
What are the main types of protein modification?
- changes to side chains of amino acids.
- folding into tertiary stricture.
- excising part of the polypeptide.
- combining polypeptides to form Q protein.
how is preproinsulin (110 AC) modified into insulin?
- protease in the rER lumen removed 24 AC sequences from the N-terminal»_space; proinsulin
- folded, 3 S-S bonds are created to stabilize the tertiary structure.
- proteases in Golgi remove 33 AC seq by breaking peptide bonds between lysine and arginine at 2 positions.
- 2 AC are removed from the C-terminal of the B chain, to create insulin with 51 AA.
Proteasomes
organelles that digest specific proteins
how do proteasomes digest proteins
- they recognize proteins marked by ubiquitin at either end.
- polypeptide is folded and fed into central chamber.
- active sites of proteasomes digest it into amino acids.
What is ‘spliced’ mRNA?
Mature mRNA
Promoter
Binding site for RNA Polymerase
Alternative Splicing
Different exons can be spliced together to produce variants of a polypeptide from a single gene.
