The genetic code (L15) Flashcards
What are the 3 stop codons
UAG, UGA, UAA
What are the 3 types of point mutations?
Give a disease example for each
Silent: single base change that codes for same AA
Missense: single change that codes for diff AA (eg sickle cell anemia)
Nonsense: single change that codes for STOP codon (eg beta-thalessemia)
What are the 3 types of mutations?
Give a disease example for each:
Point: a single base change
Insertion: Addition of one or more bases (eg Tay Sachs)
Deletion: A loss of one or more bases (eg cystic fibrosis)
What is the difference b/w human nuclear genome and mitochondrial genome w/ respect to:
- Gene density
- Introns
- Percentage of coding DNA
Nuclear __; Mitochondrial __
- 1/40k bp; 1/450 bp
- Frequently found in most genes; absent
- 3%; 93%
What is the difference b/w homoplasmy and heteroplasmy?
Which is more likely?
Homoplasmy: When all copies of a mitohondrial genome is identical in a cell;
Heteroplasmy: When there is a mixture of 2 or more mitochondrial genotypes (more likely)
tRNA contains an AA at what end?
At its 3’ end.
NOTE: the AA is always bound to the 3’ end like so: 5’-…CCA-(AA)-3’; CCA is always present
If an mRNA codon reads:
5’-…AUG…-3’
How will the tRNA anticodon read?
It binds on top like: 3’-…UAC…-5’
BUT usually we write it 5’>3’ so that would look like:
5’-…CAU…-3’
How does Inosine contribute to the wobble hypothesis?
Give an example w/ Alanine
NOTE: Inosine is the nucleoside but hypoxanthine is the base
The hypothesis is that there is allowable variation for the 3rd base in the mRNA codon for the same AA.
This is b/c Inosine is a nucleoside found in tRNA that can base pair w/ U,C,or A.
Example: Thus the allowable codons for alanine are 5’-GC(U,C,A,G)-3’. The first 3 options b/c the anticodon can be 3’-CG(I)-5’. The 4th option b/c there is a tRNA that carries Ala w/ the anticodon 3’-GCG-5’ (remember inosine won’t bp w/ G)
If the first base of the anticodon on tRNA is:
- C
- A
- U
- G
- I
What is the 3rd base on the mRNA codon?
REMEMBER: 5’-XX_-3’ is 3rd codon, 5’-_XX-3’ is first codon (ie always in relation to 5’>3’)!
mRNA 3rd base would be:
- C: G
- A: U
- U: A or G
- G: U or C
- I: U, A, or C
ie U, G, and I are flexible bases for tRNA anticodon 1st bases
Describe the formation of aminoacyl-tRNA
- The amino acid is activated by reacting w/ ATP releaseing PPi resulting in Enzyme-[aminoacyle-AMP]
- The A of the 5’-…CCA-3’ of the 3’ end of the tRNA attack the AA-AMP to form a diester bond w/ the AA and AMP will be released resulting in the
aminoacyl-tRNA
NOTE: The enzyme that facilitates this is aminoacyl-tRNA synthetase which will bind to the acceptor stem AND the anticodon loop of the tRNA to do this.
How does Streptomycin and other aminoglycosides work to inhibit protein synthesis (usually used to fight bacteria)?
Inhibits initiation and causes misreading of mRNA (prokaryotes)
How does Tetracycline work to inhibit protein synthesis (usually used to fight bacteria)?
Binds to 30S subunit and inhibits binding of aminoacyl-tRNAs (prokaryotes)
How does Chloramphenicol work to inhibit protein synthesis (usually used to fight bacteria)?
Inhibits the peptidyl transferase activity of the 50S ribosomal subunit (prokaryotes)
How does Cyclohexamide work to inhibit protein synthesis (usually used to fight bacteria)?
Inhibits peptidyl transferase activity of the 60S ribosomal subunit (eukaryotes)
How does Erythromycin work to inhibit protein synthesis (usually used to fight bacteria)?
Binds to the 50S subunit and inhibits translocation (prokaryotes)
