GCD Chapter 13 Exam 2

translation

synthesis of cellular proteins from the mRNA

Garrod

discovered relationship between genes and protein

Beadle and Tatum

One gene One enzyme theory

One gene one enzyme

each gene codes a single, specific enzyme

One gene one enzyme theory experiment

proposed that a mutation in a gene that caused a defect in an enzyme

needed for synthesis of an essential molecule would prevent the strain from growing on minimal medium

genetic code

nearly universal, allows for the translation from mRNA(nucleotides) to proteins (amino acids)

codon

sequence of bases in mRNA in groups of 3

start codon

AUG. defines the reading frame of an mRNA

Sequence of codons

defines the sequence of the polypeptide

stop codons

end translation

the genetic code is degenerate

more than one codon can specify the same amino acid

wobble base

the degenerate base of the codon that can change. 3rd base

How does degeneracy help tRNA

allows less types because one tRNA can recognize multiple codons

Francis Crick

suggested role of tRNA in translation

Relationship between t and m RNA

mRNA codons are recognized by tRNA which carry the correct amino acid to the site of polypeptide synthesis

anti codon

codon on tRNA that binds to mRNA codon

aminoacyl-tRNA synthetase

catalyzes attachment of amino acids to 3 end of tRNA. 20 different types, one for each amino acid

charged tRNA

once the amino acid is attached to the tRNA

site of translation in bacteria and eukaryotes

ribosome

Ribosome discrete sites

A (aminoacyl) is the entry site, P (peptidyl) is the holding site, and E is the exit site

stages of translation

initiation, elongation, termination

Initiation

binding of mRNA, tRNA, and ribosomal subunits

Initiation in bacteria

tRNA carries a modified methionine. A ribosomal binding site compliments a short region of rRNA

Initiation in eukaryotes

tRNA carries a non-modified methionine. Cap at 5 end is active in initial binding of mRNA to ribosome. mRNA scans for AUG start site

shine dalgarno sequence

ribosomal binding site in bacterial mRNA thst recruits the subunit to the correct start codon

16S rRNA

forms the core of ribosomal subunit that has anti shine dalgarno sequence. Pairing with mRNA shine dalgarno to form start site

Elongation

adding amino acids one at a time to the polypeptide chain

A charged tRNA in elongation

binds to A site

enzyme peptidytransferase

catalyzes bond between amino acid and polypeptide change in A

Ribosomal translocation

translocates one codon to the 3 side, uncharged tRNA is released from E, repeated untill stop codon

Termination

occurs when stop codon is reached

Release factors

recognized by stop codons. One in eukaryotes, multiple in prokaryotes

where does RF bind

site A. polypeptide is released from P site followed by tRNA

Transcription and translation in bacteria

can occur simultaneously due to the lack of a nucleus

cytosol

where translation occurs in eukaryotes