Gene Expression

What is gene expression?

How DNA makes proteins

What are the two steps to gene expression?

transcription and translation

Transcription

DNA—→ RNA

Translation

RNA—→Protein

What did Archibald propose?

Proposed Genes make enzymes affect traits.

Beadle and Tatum’s Experiment

Used bread mold to show that each gene makes one enzyme.

Transcription Basics

A—>U, T—>A,C—→G,G—>C.

Template Strand

Used to make RNA

Coding Strand

same as mRNA but T is replaced by U.

Translation Basics

Uses mRNA to build a protein chain from amino acids.

Every 3 RNA bases(codon)

one amino acid

AUG

start Codon

UAA,UAG,UGA

stop Codons

Reading Frame

mRNA must be read in groups of three bases for the correct protein.

RNA Polymerase

makes RNA from DNA during transcription. 

Promoter

where RNA polymerase binds

TATA Box

helps start transcription

Three steps of Transcription

Initiation, Elongation, and termination

Initiation

Start at promoter

Elongation

build RNA

Termination

Stop and Release RNA

introns

removed(noncoding)

Exons

kept(coding)

Alternative Splicing

One gene can make multiple proteins by using different exon combinations.

tRNA Function

Transfer RNA brings amino acids to the ribosome during translation.

Aminoacyl-tRNA Synthetase

This enzyme connects each tRNA to its correct amino acid.

Wobble Effect

The third base of a codon can change without affecting the amino acid. 

Ribosome Structure

Have two parts: small and large subunits made of tRNA and proteins.

Ribosome Sites

A site, P site, E site

A site

holds new tRNA

P site

holds growing chain

E site

tRNA exits

Translation steps

Initiation, Elongation, Termination

Initiation

start at AUG

Elongation

chain grows

Termination

stop codon ends process

Protein Folding

New proteins fold into their 3D shape right after translation.

Protein Targeting

Proteins can stay in the cytoplasm, go to the ER, or be secreted.

Polyribosomes

Many Ribosomes can read the same mRna at once

Prokaryotes

transcription and translation happen together.

Eukaryotes

separate( nucleus vs cytoplasm)