BBOL- Genetic Code and Protein Synthesis Flashcards
1
Q
What are the features of the genetic code?
A
- Non-overlapping triplet
- redundant
- Defined start (AUG)
- Defined stop (UAA,UAG,UGA)
- Universal
- Degenerate
- Open reading frame (btwn start and stop)
2
Q
Where does translation occur?
A
- Ribosome (made up of protein and ribosomal RNA)
- Subunits one come together when they bind to mRNA during protein synthesis
- Eukaryotic bigger than prokaryotic
3
Q
What are activated amino acids associated with?
A
- Soluble RNA molecule, RNA, tRNA, is the adaptor between mRNA and amino acids
4
Q
Describe transfer RNA (tRNA)*
A
- Each cell contains many different tRNAs (75-95 nucleotides)
- Contains many modified bases
- Clover-leaf structure- D arm, TA-arm and anticodon loop
- All have CCA at one end
- Contains a number of non-standard nucleotides
5
Q
What is a wobble?*
A
- 61 codons require tRNAs with matching anticodons but humans only have 48 different tRNAs
- 3rd base in anticodon can pair with several nucleotides- wobble base
6
Q
Describe the activation of amino acids*
A
- Before translation can begin
- Done by aminoacyl-tRNA synthetases- 1 for each amino acid
- Couples right amino acid to right tRNA
- Coupling requires energy- stored in ester bond between tRNA and amino acid
- Process highly accurate
7
Q
What are the key components of translation?*
A
- Intermediate between DNA and protein- mRNA
- Amino acid protein building blocks
- Transfer mRNA adaptor molecules
- Aminoacyl-tRNA synthetases enzyme to link tRNA to amini acid
- Ribosome site
8
Q
What are the 3 steps to protein synthesis in a ribosome?*
A
- Initiation- initiation complex formed where ribosome bound mRNA start site and initiator tRNA annealed to initiator codon and bound to ribosome
- Elongation- addition of further amino acids forming polypeptides
- Termination- recognition of end of ORF and release of polypeptide
9
Q
Why is rRNA critical to ribosomes?*
A
- For ribosome function
- rRNA responsible for overall structure, ability to position tRNAs on mRNA and catalytic activity in forming covalent bonds (ribozyme not enzyme)
- tRNA sites are designated to Ribosome RNA binding sites (A-, P- and E- sites)
- No more than 2 sites occupied at the same time
10
Q
Describe eukaryotic initiation*
A
- Initiation factor binds to initiator aminoacyl tRNA-Met-tRNAMet
- Forms complex with small ribosomal unit and binds to the start of mRNA
- Proceeds downstream until AUG
- Large ribosomal unit binds with initiatior aminoacyl tRNA in the P site
11
Q
Describe elongation*
A
- Right aminoacyl tRNA enters A site, peptidyl-synthetase activity of ribosome links amino acid to polypeptide chain via a peptide bond
- Leaves empty tRNA in P site, new peptidyl tRNA in A site
- Ribosome moves forward, empty tRNA moves from P to E and peptidyl- tRNA from A to P (facilitated by another elongation factor and GTP)
- Empty tRNA leaves E site
12
Q
Describe termination*
A
- Elongtion continues until stop codon
- Release factor binds at A site, another release factor breaks ester bond between peptide and tRNA
- Ribosome dissociates for new cycle
13
Q
Bacterial vs Eukaryotic translation*
A
- Initiator tRNA carries methionine (Met) and prokaryotes use modified methionine (fMet)
- Bacterial initiation needs recognition of ribosomal binding sequence in mRNA (no 4-CAP mark to start), bacterial ribosomes start at middle and b-mRNAs are often polycistronic
- Both bacterial and eukaryotic translation use similar protein initiation, elongation and release factors
14
Q
What are polysomes?*
A
Multiple ribosomes bind and translate a single mRNA simultaneously to speed up protein production
15
Q
Describe antibiotic function against bacterial protein synthesis*
A
- Competition with tRNA for A site- tetracyclines
- Induce misreading of mRNA- aminoglycosides
- Inhibition of peptidyl transferase- chloramohenical
- Inhibit translocation- erythromycin
