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. DNA

DNA• 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 Turn

Strand 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