unit 10: gene expression

central dogma

explain flow of genetic information (DNA --> mRNA --> protein)

gene expression

process DNA directs synthesis of proteins

steps of gene expression

1. transcription

2. translation

codon

unit of 3 nucleotides that codes for 1 amino acid

mRNA

messenger RNA complementary to a gene

tRNA

transfer RNA carrying amino acid and matching it with codons in mRNA

rRNA

read/match mRNA codon and tRNA anticodon

where does transcription occur?

nucleus

transcription

use DNA as template to copy genes into mRNA transcripts that can leave the nucleus (DNA --> mRNA)

RNA polymerase

primary transcription enzyme

promotor

where RNA polymerase binds initiating transcription

terminator

signals RNA polymerase to detach, terminates transcription

steps of transcription

1. Initiation

2. Elongation

3. Termination

Initiation

-RNA polymerse recognizes and binds to promotor

-RNA polymerase seperates strands of double helix

Elongation

• RNA polymerase use DNA template to build mRNA molecule (5' --> 3')

in what direction is mRNA built?

5'--> 3'

termination

-RNA polymerase reaches terminator sequence in RNA

• mRNA released

translation

protein synthesis usng mRNA transcript to build amino acid sequence

start codon

AUG methionine

stop codon

UAA, UAG, UGA STOP

anticodon

tRNA sequence complementary to mRNA codon.

peptide bond

covalent bond between amino acids

where does translation occur?

cytoplasm and ribosomes

stages of translation

1. Initiation

2. Elongation

3. Termination

Initiation Translation

• mRNA bind to rRNA

• ribosome scan mRNA transcript for start codon

• tRNA carries methionine to ribosomes

Elongation Translation

• ribosome scans codon from start to stop codon

• create peptide bonds between amino acids

Termination Translation

• stop codon read by rRNA

• release of polypeptide chain from ribosome

mutation

change sequence of nucleotides

features of mutations

spontaneous and induced

spontaneous

mistakes in DNA replication

induced

caused by outside factors

point mutations

mutations that change a single nucleotide in DNA

base-pair substitution

replace ment of one nucleotide with another

types of substitution mutations

1. silent

2. missense

3. nonsense

silent mutations

substitution to the 3rd nucleotide (no affect on amino acid)

wobble position

3rd nucleotide in a codon providing extra protection from mutations

missense mutation

substitutes 1st or 2nd nucleotide (changes one amino acid)

nonsense mutations

substititues 1st or 2nd nucleotide creating a STOP (protein truncation)

protein truncation

shortened form of the protein

frameshift mutation

change in reading frame of mRNA

2 types of frame mutation

1. insertions

2. deletions

insertions

nucleotide randomly added to the nucleotide sequence (change in every amino acid downstream)

deletions

nucleotide randomly removed from the nucleotide sequence (change in every amino acid downstream)