Protein SynthesisStep 2: Translation

ReviewProtein Synthesis: The process by

which the message of DNA is used to make proteins

Step 1: Transcription◦Takes place in the nucleus◦Changes DNA to mRNA◦Base Pairs: A-U and C-G

Step Two: Translation “to decode ordecipher the meaning of” Now that our mRNA

molecule has been made, it’s time for its message to be made into a protein sequence.

How does the mRNA sequence translate into an amino acid sequence?

Step Two: TranslationProblem:

◦There are 20 different amino acids.

◦There are 4 RNA bases.phe ile val pro ala his asn asp cys arg

leu met ser thr tyr gln lys glu trp gly

A T C G

Step 2: TranslationTranslation in 3 steps:

1. mRNA leaves the nucleus and finds a ribosome in the cytoplasm

2. tRNA brings amino acids to the ribosome

3. rRNA joins the amino acids together by matching the codes between mRNA and tRNA

Ribosome

(rRNA)

tRNA

Step Two: TranslationWatch this simplified animation:http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swf

Watch the more complex animation!

http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a3.html

Step Two: Translation1. So how do you exactly go about

determining what protein your cells are going to make?

2. FIRST, divide the mRNA sequence into codons.

◦ Codons are three-base sections of mRNA:

AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA

Step Two: Translation2. Since each 3-letter combination

“codes” for an amino acid, you need to figure out what amino acid matches up with each codon:

?

AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA

Use a Codon Chart!

Step Two: Translation2. Since each 3-letter combination

“codes” for an amino acid, you need to figure out what amino acid matches up with each codon:

met

AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA

?

Step Two: Translation2. Since each 3-letter combination

“codes” for an amino acid, you need to figure out what amino acid matches up with each codon:

met

AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA

Important Codons/Amino Acids!

Codon Amino Acid

Signal

AUG Methionine

START

UAA None STOP

UAG None STOP

UGA None STOP

Ribosome

(rRNA)

tRNA

How does tRNA know where to go?tRNA has an anticodon that

coordinates with the codon on mRNA

Anti-codon

Anti-codon and

codon pair up!

RECAP:1. DNA is transcribed

into mRNA in the nucleus.

2. The mRNA leaves the nucleus and enters the cytoplasm.

3. The protein is translated from the mRNA sequence using tRNA and amino acids.