1. Ribosomes and Protein Synthesis
13.2
3/18/2011

2. How Genes Are Expressed
DNA
TRANSCRIPTION
RNA
TRANSLATION
PROTEIN

3. Protein REVIEW Proteins are polymers of amino acids
Proteins are also called peptides or polypeptides because the amino acids that make them up are held together by peptide bonds
There are 20 different amino acids which make up all the proteins in living things
Different numbers & combinations = different proteins with individual properties

4. The Genetic Code
mRNA transcribed from DNA contains a code for making proteins
How is the mRNA genetic code of As, Us, Cs, and Gs “read” into a specific sequence of amino acids?
How can a code with only 4 letters contain instructions for 20 different amino acids?

5. Reading the Genetic Code of mRNA
The genetic code is read THREE letters at a time
Each “word” is three letters long and corresponds to one specific amino acid
Each of these three letter “words” is called a codon

7. How to Read mRNA Codons
Read the Genetic Code chart from the inside out
Start & stop codons
Think of as “punctuation”
Translation begins at start codon
AUG, the codon for methionine
Translation ends at one of three stop codons
UGA, UAA, UAG

9. Transfer RNA
Two sided: one side has anti-codon, the other is carrying an amino acid
tRNA anti codon matches mRNA codon

10. Protein Synthesis (Translation
During translation, or protein synthesis, the cell uses information from mRNA to produce proteins
The ribosomes of the cell read the instructions (the mRNA) and assemble the parts (the amino acids) into proteins

11. Steps of Translation Initiation Elongation Termination
Ribosome attaches to mRNA in the cytoplasm
Elongation
As each mRNA codon passes through the ribosome, the tRNAs bring the appropriate amino acid
One at a time, the ribosome attaches the amino acid from the tRNA to the growing chain of amino acids (this is forming the protein)
This “assembly line” continues until…
Termination
STOP codon reached, then…
mRNA and protein released from the ribosome