Translation

• Translation takes the “message” carried by mRNA and turns it into proteins

• This happens in the ribosomes (protein factories)

Steps in translation

• mRNA leaves the nucleus and travels to the ribosome

• The bases in mRNA are read in groups of 3 (codons)

• Each codon specifies a particular amino acid• There are 64 codons and 20 amino acids, so

some codons code for the same amino acid

• The codon (triplet) is recognized by a tRNA molecule. The tRNA has an anticodon on one end that base pair matches the mRNA codon.

• On the other end is an amino acid• Each tRNA brings the appropriate amino acid

to the ribosome where it is attached by a peptide bond to the previous amino acid

• The tRNA then releases the amino acid and goes back to the cytoplasm to pick up another one

• The chain continues until a stop codon is read and then the protein is released to go do its job

Summary• mRNA is the messenger—it carries the message

“blueprint” made from the DNA to the ribosome• The ribosome (made of rRNA) is the factory—it

builds the protein according to the blueprints• The tRNA is the truck that brings the amino acid to

the ribosome—each truck only brings one kind of amino acid

• The protein is the product the factory makes and when it is built, it gets shipped out to do its job-make muscle, hair, be an enzyme, an antibody, collagen etc.

Mutation effects

• Point mutation-one base pair swapped—may or may not make a difference

• Insertion or deletion-all codons from that point forward are messed up and the protein is nonsense

• Ex: The cat ate the rat• Point mutation: The cat ate the bat• Insertion: The cat tat eth era t• Deletion: The caa tet her at

The t that goes right here is missing

Gene expression

• Not all of your genes are being used all the time at the same rate

• We only want to use the genes we need at the time

• They are “expressed” only when needed

Introns and Exons

• We have lots of “junk” DNA that does not code for proteins

• After transcription spliceosomes cut out the non-coding portions of the mRNA molecule and reassemble it before it is translated. That way only the useful part is made into a protein.

• The coding part of the genome are the exons• The non-coding part of the genome are the

introns (removed before translation)• Some scientists think the extra DNA give us

more genetic flexibility for evolution