GENE TO PROTEINTranscription and Translation

DNA determines your unique characteristics. A Review…

• DNA is the instructions for making proteins.• Proteins play a big role in everything you do and

determine most of your characteristics

Examples of Proteins

Hormones

Pigments

Muscle

Fibers

Enzymes

Cytoskeleton

Carrier Molecules

Membrane

Channels

Antibodies

Connective

2 Stages

Transcription• DNA mRNA

Translation• mRNA Protein

mRNA? What’s that?

DNA mRNA• Uracil replaces Thymine

• DO NOT say A turns into U. A codes for U• The DNA does not become or mutate into the

RNA

DNA nucleotide codes for RNA nucleotideAdenine (A) Uracil (U)Thymine (T) Adenine (A)Guanine (G) Cytosine (C)Cytosine (C) Guanine (G)

Transcription

• The enzyme RNA polymerase builds an RNA strand complementary to the DNA

The following diagram shows the strands of DNA unwinding and RNA nucleotides being added…

This diagram just shows how the RNA strand breaks off

from the DNA template…

Where Does Transcription Begin?• At the promoter (for our simulations the

TATAA box)• Proteins called

transcription factorshelp RNA Polymerasebind to the DNA

Prokaryotes vs. Eukaryotes

Prokaryotes• No nucleus• Transcription and

translation happen relatively simulataneously

Eukaryotes• Transcription in nucleus• mRNA edited before

translation (beyond our scope)

• mRNA leaves nucleus for translation

Translation

• The mRNA serves as instructions for assembling a protein

How?• The sequence of mRNA nucleotides

determines the order of amino acids in the protein

• Every 3 nucleotides (codon) codes for one amino acid

So the process basically works like this….

Remember Amino Acids?

Order of Amino Acids Determine Protein Structure

Due to

Side Chains

Translation Details

• Occurs in the ribosome in both prokaryotes and eukaryotes• mRNA brings the code from

transcription• tRNA carries in amino acids one by

one• Protein is assembled

There are 3 different types of RNA:• fold differently =• different functions

1. MESSENGER (mRNA): carries message2. TRANSFER (tRNA): carries amino acids in

translation3. RIBOSOMAL (rRNA): makes up parts of the

ribosomes which are the sites of protein synthesis

How Does the tRNA “know” Which Amino Acid to Bring?

• The anticodon on the tRNA is complementary to the codon on the mRNA

Hydrogen bonds

More Realistic View

The Start and Stop CodonsStart Codon• Begins translation• Always AUG• So Met is always the

first amino acid

Stop Codon• DOES NOT code for

an amino acid• Stops translation

1. mRNA attaches to a RIBOSOME at start codon

Start Codon

2. As ribosome moves, anti-codon tRNA complimentary base pairs to codon.

3. amino acid dropped off. Amino Acids

tRNA

Anticodon

*This is how the DNA instructions are followed & appropriate placement of the amino acids is accomplished creating the correct protein.

4. The process continues until a stop codon is reached.

5. The protein is then released from the ribosome.

To make the process of translation faster and to make many copies of a protein, multiple ribosomes can move along mRNA at

once looking something like this…

Review

DNA: AGCGCTATAAGCTACGCGCAGCATTmRNA: CGAUGGCGUCGUAAtRNA: UACCGCAGC

Protein Met-Arg-Ser

Promoter

Start CodonStop Codon

Rapid Review• Transcription makes mRNA based on the DNA–Occurs in nucleus–Begins at promoter

• Translation assembles protein based on mRNA code–With help of tRNA in ribosome–Begins at start codon. Ends at stop codon

• The structure and shape of the protein depends on the DNA sequence

Keep in mind…• Genes don’t code for

traits• They code for proteins

(or parts of proteins) that can affect traits

• i.e. they can code for a protein that makes eyes blue

• Differences in DNA determine differences in proteins = differences in physical traits.

Transcription Animation

• http://www.hhmi.org/biointeractive/dna/DNAi_transcription_vo2.html

Basic Translation Animation

• http://www.youtube.com/watch?v=1PSwhTGFMxs• http://www.hhmi.org/biointeractive/dna/DNAi_tra

nslation_vo1.html

Detailed Translation Animation

• http://www.hhmi.org/biointeractive/dna/DNAi_translation_vo2.html