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Protein Synthesis and Genetic Code
Medical School Biochemistry
32
Biochemistry
Graduate
08/28/2011

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Term
How many start codons exist?
Definition
1, AUG
Term
How many stop codons exist?
Definition
3, UAA UGA UAG
Term
What is the Wobble-Hypothesis?
Definition
The Wobble Hypothesis is that, in many cases, the third codon is unecessary or "wobbly"
Term
How many codons for amino acids?
Definition
64
Term
What does it mean to say that the genetic code has no commas?
Definition
no breaks in the code, continues letters. This has important implication when you consider the reading frame; an insertion can shift the entire frame
Term
What is gene translocation?
Definition
When a piece of genetic code breaks from one chromosome and is added to another
Term
What is deletion?
Definition
loss of a segment of a chromosome
Term
What is a point mutation?
Definition
Small change (a few nucleotides) to a sequence of DNA
Term
What is Gene inversion?
Definition
Typically happen with DNA transposons, inversion is the act of flipping a sequence of DNA
Term
What is a dominant-negative mutation?
Definition
This is a mutation that codes for a protein that inhibits some function
Term
What is a conditional mutation?
Definition
A mutation that only has expression during specific conditions
Term
What is a gain-of-function mutation?
Definition
Mutation that causes more expression of protein than typical
Term
What is a loss-of-function mutation?
Definition
Mutation that causes less expression of protein then typical
Term
What is a lethal mutation?
Definition
mutation that leads to a death in the organism
Term
What is a null mutation?
Definition
Mutation that causes the protein to no longer work
Term
What are the two types of point mutations?
Definition
Transition and Transversion

Transition: exchange like for like (purine for purine or pyrimidine for pyrimidine)

Transversion: swaps nucleotide type
Term
What is a silent point mutation?
Definition
Point mutation that has no bearing on expression
Term
What is a frame-shift mutation?
Definition
A mutation that moves the entire reading frame (typically through addition or deletion of a nucleotide)
Term
What enzyme attaches amino acids to their particular tRNAs?
Definition
Amino acyl-synthetases
Term
Where does amino acid attachement occur on the tRNA?
Definition
on the 3' end, uses a CCA end for attachment
Term
What is an anticodon?
Definition
code on the tRNA that is complementary to the codon on the mRNA it matches too
Term
What drives the process of amino acid attachment to tRNA via synthetases?
Definition
ATP
Term
What is the ORF?
Definition
Open Reading Frame: The space on the mRNA that gets "read" by the tRNA's
Term
What is cap-binding complex, and of what is it composed?
Definition
Cap-binding complex is composed of EIF4G and EIF4E (among others). This is the complex that aids in translation
Term
What are the steps of translation?
Definition
1. Cap-binding complex joins the mRNA
2. Cap-binding complex is joined by EIF4B
3. 43S rRNA subunit is recruited
4. 60s and 43s join at the start codon
5. Protein synthesis begins (multiple 60s/40s complexes will attach at the start codon and continue coding
Term
What are the two sites for elongation of protein synthesis? How do they function?
Definition
A and P sites.

The A site recruits the incoming aminoacyl-tRNA.

The P site has the growing protein
Term
What enzyme catalyzes peptide-bond formation?
Definition
peptidyl transferase
Term
What promotes release of the protein from the ribosome?
Definition
RF (release factor)
Term
What is the action of Aminoglycosides such as Streptomycin?
Definition
Bind the bacterial 30s subunit and cause misreading of the the genetic code.

At high doses the aminoglycosides also inhibit initiation
Term
What is the action of tetracyclines?
Definition
Tetracyclines block the A spot so that new amino acids cannot be joined to the existing chain
Term
What is the action of Chloramphenicol?
Definition
Chloramphenical inhibits the formation of peptide bonds among amino acids by binding to the 50s Ribosomal subunit.

High levels of Chloramphenicol can disrupt mitochondrial translation
Term
What is the action of Erythromycin?
Definition
Erythromycin blocks peptide bond formation between amino acids by inhibiting the action of transferase
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