1. Protein Synthesis: An Overview
SBI 4UI – 5.2

3. Where is the DNA?
Cytoplasm?
Nucleus?
Outside the cell?

5. Central Dogma DNA is too important to leave the nucleus
Plus, there are only 2 copies of DNA in a somatic cell
Plus, ribosomes often need to make large amounts of protein
Plus, DNA would then have to reenter the nucleus
What to do?

6. Central Dogma Messenger RNA (mRNA) DNA is transcribed into mRNA
mRNA can travel to ribosomes to translate into polypeptide chains
This process in known as the central dogma of molecular genetics

7. Transcription
DNA  mRNA
Transcription is like making a carbon copy

8. Translation Ribosomes mRNA  amino acid sequences
Translation is like translating

9. Ribonucleic Acid DNA RNA Carries genetic information Deoxyribose sugar
Adenine pairs with thymine
Adenine pairs with uracil
Double stranded
Single stranded
Resides in nucleus
Resides in nucleus and cytoplasm

10. Messenger RNA Varies in length Intermediary between DNA and ribosomes
Like a blueprint for protein production
Contains codons

12. Transfer RNA
Delivery system of amino acids to ribosomes as they make proteins
Very short (70-90 base pairs)
Contains anticodons

14. Ribosomal RNA Central component of the ribosome Varies in length
Protein manufacturing machinery
Varies in length

16. Transcription Initiation Elongation Termination
RNA polymerase binds to the promoter
Elongation
Begins adding ribonucleotides  mRNA
Termination
“Stop” signal ends transcription and mRNA is released

17. Translation Initiation Elongation Termination
Ribosome recognizes a sequence on mRNA and binds to it
Ribosome moves along mRNA 3 nucleotides at a time (3 nucleotides = 1 amino acid)
Elongation
tRNA delivers appropriate amino acid
Termination
3 base nucleotide codes as “stop” signal and polypeptide is released

18. Genetic Code 20 amino acids, but only 4 bases
Triplet(3) of nucleotides = codon
43 = 64 possible combinations
Start codon signals initiation
Stop codon signals termination

20. To Do:
Section 5.2
Understanding Concepts #1-11