Transcription

The Central Dogma• DNA

• Transcription

• RNA

• Translation

• Proteins

GOAL• Use DNA to make a Protein– Step 1: Replicate DNA– Step 2: Transcribe DNA into RNA – Step 3: Translate RNA into a protein

• Where does this happen?– Step 1: Nucleus– Step 2: Nucleus– Step 3: Cytoplasm

Ribosomes

replication

transcription

translation

RNA vs. DNADNA• Sugar: Deoxyribose• Bases: A,T,C,G• Double Stranded

RNA• Sugar: Ribose• Bases: A,U,C,G• Single Stranded

RNA• Stands for: Ribonucleic Acid• Three Types:

1. mRNA• Carries the message from the DNA to

the ribosome2. tRNA• Brings amino acids from the

cytoplasm to the ribosome3. rRNA• Makes up part of the ribosome

Transcription Basics• Process of taking DNA and turning it

into RNA• Uses enzymes: Chemical Reaction• Happens in the nucleus

Transcription• Starts because of an enzyme called RNA

polymerase• This enzyme starts to unwind the DNA at

the start of a gene• Nucleotides pair with ONE strand of DNA• RNA Polymerase (enzyme) bonds them

togetherstart site

nucleotides

RNA Polymerase

DNA molecule

Transcription • DNA winds back up• mRNA detaches and leaves the

nucleus

mRNA

Transcription vs Replication Similarities

• Both involve enzymes • Both pair the matching bases

together• Happens in the nucleus

Transcription vs Replication Differences

Transcription• Only copies ONE

gene

• Only copies ONE side

• A will match with U instead of T

• Final Product: mRNA

Replication• Copies the ENTIRE strand• Copies BOTH sides• A will match with T

• Final Product: Same thing you started with (DNA)

Translation

Goal of Translation• Convert mRNA into amino acids that

will end up building a protein

• Proteins are polymers of amino acids

Amino acids are coded by mRNA base sequences.

• Codons are three letters words• There are 64 different codons• Each word means (translates) into ONE of the

AMINO ACIDScodon formethionine (Met)

codon forleucine (Leu)

CodonsReview: Codon=3 nucleotides that are read together.

If this is the strand of mRNA:

UCGCACGGUThe codons are:

UCG-CAC-GGU

How many codons are there?

3

• The genetic code matches each codon to its amino acid or function.

• There are 20 Amino Acids

Amino acids are linked to become a protein • An anticodon is a set of three nucleotides that is

complementary to an mRNA codon.• An anticodon is carried by a tRNA.

Your TurnStrand of mRNA:AUGCGUACCUUAUAA

What are the codons?AUG-CGU-ACC-UUA-UAA

What are the anticodons?UAC-GCA-UGG-AAU-AUU

– tRNA carries amino acid to ribosome– ribosome forms bonds between the

amino acids.

Important Notes• Start: ALWAYS start with codon AUG–What amino acid will you always start

with?–Methionine (AUG)

• End: ALWAYS end with a STOP–Which codons will that be?– UAA, UAG, UGA