Protein Synthesis

Beadle and Tatum

proposed one gene one enzyme hypothesis

Nature of Genes current hypothesis

one gene, one polypeptide

Central Dogma of Molecular Biology

DNA -> RNA -> Protein

Transcription

the flow of information from DNA to RNA

Translation

flow of information from RNA to protein

4 nucleotides in DNA

Adenine, Thymine, Guanine, Cytosine

4 nucleotides in RNA

Adenine, Uracil, Guanine, Cytosine

Codon

set of 3 nucleotides that specifies a particular amino acid

Reading frame

the series of nucleotides read in sets of 3

Stop codons

3 codons in the genetic code to terminate translation

Start codon

the codon used to signify the start of translation

Template strand

strand of the DNA double helix used to make RNA

Coding strand

strand of DNA that is complementary to the template strand

RNA ploymerase

the enzyme that synthesizes RNA from the DNA template

Transcription/translation proceeds through

initiation, elongation, termination

Transcription initiation

RNA polymerase identifies where to begin transciption

Transcription elongation

RNA nucleotides are added to the 3' end of the new RNA

Transcription termination

RNA polymerase stops transcription when it encounters terminators in the DNA sequence

Translation initiation

mRNA, tRNA, and ribosome come together

Translation elongation

tRNAs bring amino acids to the ribosome for incorporation into the polypeptide

Translation termination

ribosome encounters a stop codon and releases polypeptide

Messenger RNA (mRNA)

carries the information from DNA that encodes proteins

Ribosomal RNA (rRNA)

a structural component of the ribosome

Transfer RNA (tRNA)

carries amino acids to the ribosome for translation

Synthesis of RNA transcription is

5' to 3'

DNA template strand reads

3' to 5'

addition of a 5' cap, addition of a 3' poly-A tail, removal of non-coding sequences (introns)

In eukaryotes, the primary transcript must be modified by:

aminoacyl-tRNA synthetases

add amino acids to the acceptor arm of tRNA

anticodon loop

contains 3 nucleotides complementary to mRNA codons

tRNA binding sites

A site, P site, E site

A site

binds the tRNA carrying the next amino acid to attach to the growing chain

P site

binds the tRNA attached to the growing peptide chain

E site

binds the tRNA that carried the amino acid it just attached

Stop codon

elongation continues until the ribosomes encounters a ____

Point mutations

alter a single base

Nonsense mutations

create stop codon

Frameshift mutations

caused by insertion or deletion of a single base