1. PROTEIN SYNTHESIS

2. Learning Outcomes
B7 Demonstrate an understanding of the process of protein synthesis
State roles of DNA, mRNA, tRNA and ribosomes
Explain the processes of transcription and translation
Determine the sequence of amino acids for a DNA sequences using a table of mRNA codons

3. DNA, Chromosomes and Genes
Each chromosome contains many genes
Each gene contains many base pairs (3000 is average)
Each gene carries the code for one specific polypeptide

4. The Central Dogma of Genetics
DNA 
RNA
Protein

6. The Genetic Code
How many possible combinations of 3 can you make using A,T,C,G?

7. THE GENETIC CODE
sequence of nucleotide bases in DNA determines the sequence of amino acids in a polypeptide
Triplet code - 3 bases for one amino acid (ex. AAG,GTC, etc.)
code is redundant - more than one triplet can code for the same amino acid

8. Proteins
Recall that polypeptides are chains of amino acids, and a protein can contain several polypeptides
A typical protein contains amino acids
All proteins are made up of only 20 different amino acids

9. RNA How is RNA different from DNA?
3 types of RNA are involved in Protein synthesis

10. Types of RNA mRNA (messenger RNA) copies the code from DNA
rRNA (ribosomal RNA) is part of the ribosomes
tRNA (transfer RNA)carries amino acids to the ribosomes

11. mRNA Each group of 3 mRNA nucleotides is called a codon
Each codon codes for a specific amino acid

12. tRNA
Each tRNA molecule has a 3-base anticodon which is complementary to a mRNA codon
Also has a binding site for a specific amino acid

14. rRNA A complex molecule that makes up the structure of a ribosome
Binds to tRNA and mRNA

16. PROTEIN SYNTHESIS Protein synthesis consists of two stages –
Transcription (in the nucleus)
Translation (at ribosomes)

17. TRANSCRIPTION Takes place in the nucleus Part of DNA strand unzips
mRNA nucleotides attach to DNA strand, forming a complementary strand (enzyme – RNA polymerase)
mRNA detaches from the DNA strand
DNA zips back together
mRNA can now carry the instructions out of the nucleus

18. mRNA & DNA Base Pairing:
U pairs with A
A pairs with T
G pairs with C
C pairs with G

21. RNA processing Not all of the DNA is part of a gene
Introns are pieces that are not part of the gene
Exons are the parts that make up the gene (expressed)
Intron sections of mRNA are removed by ribozymes (RNA enzymes )

22. Translation
Takes place outside the nucleus, at ribosomes (attached to ER or free in the cytoplasm)
Takes place in 3 stages:
Initiation
Elongation
Termination

23. 1. Initiation
Ribosomal subunits attach to mRNA strand at the “Start” codon
2 codons of mRNA are in the ribosome at a time

25. 2. Elongation
As each mRNA codon binds to the ribosome, a tRNA with the complementary anticodon brings the correct amino acid
As amino acids are delivered to the ribosome, they are joined by peptide bonds forming a growing chain
Sequence of codons determines the primary structure
Ribosome moves along the mRNA one codon at a time

27. 3. Termination
When the “Stop” codon is reached, the ribosome detached from the mRNA and the polypeptide is released
The new polypeptide may now enter the ER for modification

30. Mass Production of Proteins
Many ribosomes may move along the same mRNA strand (polyribosome), producing many copies of the polypetide