Protein Synthesis

Central Dogma

DNA → RNA → Protein

Function of DNA

Stores genetic information

Function of RNA

Carries instructions to make proteins

DNA Sugar

Deoxyribose

RNA Sugar

Ribose

DNA Bases

A, T, C, G

RNA Bases

A, U, C, G

Where does DNA stay?

Nucleus

Can RNA leave the nucleus?

Yes

Types of RNA

mRNA, tRNA, rRNA

Transcription

DNA → mRNA

Where does transcription occur?

Nucleus 1

Enzyme used in transcription

RNA polymerase

Direction RNA is built

5′ → 3′

Base pairing during transcription

A-U, T-A, C-G, G-C

Promoter

DNA sequence where transcription starts

TATA box

Common eukaryotic promoter sequence

Termination (transcription)

RNA polymerase reaches terminator and releases mRNA

RNA Processing occurs in

Eukaryotes only

5′ cap function

Protects mRNA and helps ribosome attach

Poly-A tail function

Stability and export from nucleus

Introns

Noncoding regions removed from mRNA

Exons

Coding regions kept in mRNA

RNA splicing

Removal of introns and joining of exons

Codon

Group of 3 mRNA bases

Start codon

AUG (methionine)

Stop codons

UAA, UAG, UGA

Genetic code is redundant

Multiple codons can code for same amino acid

Genetic code is not ambiguous

Each codon codes for only one amino acid

Translation

mRNA → Protein

Where does translation occur?

Ribosome

tRNA function

Brings amino acids to ribosome

Anticodon

tRNA triplet that matches mRNA codon

rRNA function

Forms ribosome

A site

tRNA with new amino acid enters

P site

Holds growing protein chain

E site

tRNA exits ribosome

Initiation (translation)

Ribosome binds mRNA at start codon

Elongation (translation)

Amino acids added one at a time

Termination (translation)

Stop codon reached, protein released

Mutation

Change in DNA sequence

Silent mutation

No change in amino acid

Missense mutation

Different amino acid

Nonsense mutation

Early stop codon

Frameshift mutation

Insertion or deletion shifts reading frame