Each group of 3 consecutive nucleotides in RNA is called a _______
Mutation that does not change the amino acid.
Mutation that changes amino acid in the protein with vastly different function.
Example of disease caused by missense mutation
Sickle Cell Anemia On 6th codon in the allele of the gene for human β-globin (HBB), a subunit of adult hemoglobin.
GAG (Glu) to GTG (Val)
Negatively charged hydrophilic to hydrophobic
Codon changes into a stop codon causing premature chain termination.
Nonsense Mutation (null mutation)
Protein either degraded or formed as a truncated version.
What mutation causes Duchenne Muscular Dystrophy (DMD) and Becker Muscular Dystrophy?
Nonsense mutations in the dystrophin gene lead to partially or non-functional dystrophin protein.
Out of frame deletions cause DMD.
In frame cause BMD (truncated forms)
Deletion or insertion where one or more nucleotides are deleted or inserted into the open reading frame.
Out of frame causes change in the codon sequence and consequently alteration in the amino acid sequence
E.g. Duchenne Muscular Dystrophy, beta thalassemia
Components of mRNA
- Codons (present in coding region)
- 7-methylguanosine cap at the 5′ end
- Poly(A) tail at the 3′ end.
What makes up the structure of tRNA?
Set of 3 consecutive nucleotides that pair with mRNA.
3’ CCA terminal region which binds the amino acid that matches the corresponding codon.
How are amino acids bound to tRNA "ativated"?
Catalyzed by enzymes called aminoacyl tRNA
synthetases which help to add AMP to COOH end of amino acids.
Units of Eukaryotic Ribosomes in size.
Units of prokaryotes in size
What does the A site of a ribosome do?
mRNA codon exposed to receive aminoacyl tRNA, except the met tRNA
What does the P site of a ribosome do?
Where aminoacyl tRNA is attached.
What does the E site do?
Location occupied by empty tRNA before exiting ribosome
How do Eukaryotes identify the start of translation?
mRNA 5’ cap, 3’ poly-A tail, the Kozak sequence and an ATP-dependent mRNA scan
mRNA molecules also contain signals that define the beginning of there polypeptide chain
How do Prokaryotes identify the start of translation?
Shine Dalgaro sequence or AGGAGG
What are the initiation factors mentioned in eukaryotic translation?
What is an intiator tRNA?
Bound to GTP and attaches to P site of small subunit
Codon is AUG (codes for methione)
N-formylmethioninyl tRNA in
prokaryotes and methioninyl tRNA in eukaryotes
What happens when the initiator tRNA's GTP is hydrolyzed in initiation?
The large subunit binds to DNA and translation begins
What are the steps of elongation in translation?
The incoming aminoacyl tRNA is attached to a GTP-bound elongation factor.
Loading of an aminoacyl tRNA anticodon so it base pairs at the A site with codon
Loading accompanied by GTP hydrolysis and release of factor from aminoacyl tRNA
How is the peptide bond formed between the A and P site in elongation?
Catalyzed by peptidyl transferase.
What are the stop codons?
UAA, UAG and
What is a Release Factor?
Promote the release of a complete protein from tRNA
Bind to A site of ribosome containing the stop codon
and cleaves the ester bond between the C terminus of
the polypeptide and the tRNA.
Catalyze the addition of water instead of AA
Large ribosomal subunit leaves with hydralyzation of GTP
At the very end of translation, what fuels the dissociation of the ribosomal complex?
Prokaryote Elongation inhibitors
Streptomycin - 30s (30s and 50s association)
Tetracycline - 30s (aminoacyl-tRNA to complex)
Chloramphenicol -peptidyl transferase
Clindamycin and erythromycin - 50s (translocation of ribosome)
What is erthromycin used to treat?
Inhibits peptidyl transferase
Toxin from Streptomyces griseus: inhibits peptidyl transferase (euk.)
From Corynebacterium diphtheriae: inactivates GTP-bound eEF-2, interfering with ribosomal translocation (euk.)