Ch. 15 Flashcards
The one gene, one enzyme hypothesis is based on the work of
Beadle and Tatum
Protein are polymers consisting of amino acids linked by ____ bonds. Amino acid sequence is it’s ____ structure.
Peptide bonds
Primary structure.
There are ___ amino acids total.
4 components?`
20
Amino group, Carboxyl Group, Hydrogen, Radial Group (Side chain)
Codon
3 nucleotides = 1 amino acid
Nirenberg and Matthaei’s Homopolymers
If you create it with use one base (ex: UUUUUUUU) and all you get is phenylalanine, than that’s what it is
Nirenberg and Leder’s use of tRNA
tRNA bring amino acids to ribosome. tRNAs have anti-coons with complimentary sequence to the codon (how they bring the appropriate amino acid) .
When mRNA with GUU added, tRNA bound to valine
Neirenberg’s random copolymer
RNAs of 2-3 different basses, which would produced a certain number of proteins. Proportions decide which bases go with what.
There are ___ possible codons, ___ stop codons, and thus, ___ SENSE codons (encode amino acids) .
64
3 stop
61 sense
Why is this code a degenerate code?
Because it has multiple physical states that have equivalent meanings. Amino acid maybe specified by more than one codon.
Synonymous codons
Codons that specify the same amino acid
Many differ only in the third position
Initiation Codon
AUG (met)
Termination codons
UAA, UAG, UGA
How do you explain that most organisms posses from about 30-50 different tRNAs, yet there are only 20 different amino acids in proteins?
Isoaccepting tRNAs: Different tRNAs that accept the same amino acid but have different anticodons.
Wobble hypothesis
1st two nucleotides bind via Watson-and Crick rules.
HOWEVER, 3rd base pairs weakly (wobble)- allows some tRNAs to pair with more than one codon on mRNA, thus 30-50 tRNAs can pair with 61 sense codons.
Wobble Rules: C G A U I (inosine)- modified bases found in tRNA
C- only with G G- C, wobbles U A- only with U U- A, wobbles G I- A, U or C
Through wobble, a single ______ can pair with more than 1 ______.
A) codon; anticodon
B)Group of three nucleotides in DNA; codon in mRNA
C) tRNA; amino acid
D) anticodon; codon
d. Anticodon, codon
Reading Frame/Nonoverlapping
Although Reading frame can be read different ways, in nonoverlapping, single nucleotide may not be included in more than one codon (genetic code nearly always like this)
How does one establish the correct reading frame?
Initiator codon
AUG (methionine)
Bacteria: initial amino acid is formylmethionine; unformulated methionine thereafter in the polypeptide (internal)
Eukaryotes: all methionine unformulated
What do we mean by “the universality of the code”?
Each codon specifies the same amino acid in all organisms (generally)
Translation
Amino acids are assembled into protein.
- Binding of amino acids to tRNAs
- Initiation
- Elongation
- Termination
The binding of amino Acids to tRNA involves
1. Aminoacyl-tRNA synthetases and
2. tRNA charging
What is charging?
Charging is the act of binding the amino acid to the tRNA
What determines the specificity between an amino acid and its tRNA
Individual aminoacyl-tRNA synthesis (enzymes)
There are exactly ___ different aminoacyl-tRNA synthetase in a cell.
20, one for each amino acid.
Amino Acids bind to which part of tRNA? A) anticodon B) DHU arm C) 3' end D) 5' end
C) 3’ End
