1. Genes and Protein Synthesis
Chapter 7

2. One Gene-One Polypeptide Hypothesis
DNA contains all of our hereditary information
Genes are located in our DNA
~25,000 genes in our DNA (46 chromosomes)
Each Gene codes for a specific polypeptide

3. Main Idea
Central Dogma
Francis Crick (1956)

4. Overall Process Transcription Translation DNA to RNA
DNA molecule
Gene 1
Gene 2
Gene 3
DNA strand
TRANSCRIPTION
RNA
Polypeptide
TRANSLATION
Codon
Amino acid
Transcription
DNA to RNA
Takes place inside nucleus
Translation
Assembly of amino acids into polypeptide
Takes place in cytoplasm

5. Key Terms RNA transcription TATA box Introns, Exons mRNA, tRNA, rRNA
Initiation, Elongation, Termination
TATA box
Introns, Exons
mRNA, tRNA, rRNA
Translation
Ribosome
Codon
Amino Acids
Polypeptide

6. DNA
RNA
Double stranded
Single stranded
Adenine pairs with Thymine
Adenine pairs with Uracil (A with U)
Guanine pairs with Cytosine
Guanine pairs with Cytosine (C with G)
Deoxyribose sugar
Ribose sugar
Remember!! When transcribing DNA to RNA, T from DNA pairs with A for RNA and A from DNA pairs with U for RNA

7. DNA to Protein Protein is made of amino acid sequences 20 amino acids
DNA molecule
Gene 1
Gene 2
Gene 3
DNA strand
TRANSCRIPTION
RNA
Polypeptide
TRANSLATION
Codon
Amino acid
Protein is made of amino acid sequences
20 amino acids
How does DNA code for amino acid?

8. Genetic Code Codon AA are represented by more than one codon
Three letter code
5’ to 3’ order
Start codon (AUG/methionine)
3 Stop codons
AA are represented by more than one codon
61 codons that specify AA
4³ = 64 minus 3 stop codons = 61

9. Amino acids

10. Transcription DNA to RNA Occurs in nucleus Three process Initiation
RNA polymerase
DNA of gene
DNA to RNA
Occurs in nucleus
Three process
Initiation
Elongation
Termination
Promoter
DNA
Terminator
DNA
Initiation
Elongation
Termination
Growing RNA
Completed RNA
RNA polymerase

11. Initiation RNA polymerase binds to DNA Binds at promoter region
TATA box
RNA polymerase unwinds DNA
Transcription unit
Part of gene that is transcribed
Transcription factors bind to specific regions of promoter
Provide a substrate for RNA polymerase to bind beginning transcription
Forms transcription initiation complex

12. Elongation RNA molecule is built Primer not needed 5’ to 3’ direction
RNA polymerase
Primer not needed
5’ to 3’ direction
Template strand is copied
3’ to 5’ DNA
Coding strand
DNA strand that is not copied
Produces mRNA
Messenger RNA
DNA double helix reforms

13. Termination
RNA polymerase recognizes a termination sequence – AAAAAAA (polyadenylation)
Nuclear proteins bind to string of UUUUUU on RNA
mRNA molecule releases from template strand

15. Post-Transcriptional Modifications
Pre-mRNA undergoes modifications before it leaves the nucleus
Poly(A) tail
Poly-A polymerase
Protects from RNA digesting enzymes in cytosol
5’ cap
7 G’s
Initial attachment site for mRNA’s to ribosomes
Removal of introns

16. Splicing the pre-mRNA DNA comprised of Spliceosome Exons Introns
sequence of DNA or RNA that codes for a gene
Introns
non-coding sequence of DNA or RNA
Being researched for code responsible for different splicing arrangements
Spliceosome
Enzyme that removes introns from mRNA

17. Splicing Process
Spliceosome contains a handful of small ribonucleoproteins
snRNP’s (snurps)
snRNP’s bind to specific regions on introns

18. Alternative Splicing
Increases number and variety of proteins encoded by a single gene
~25,000 genes produce ~100,000 proteins

19. Translation Takes place in cytoplasm mRNA to protein
Ribosomes read codons
tRNA assists ribosome to assemble amino acids into polypeptide chain

20. tRNA Contains Are there 61 tRNA’s to read 61 codons? triplet anticodon
amino acid attachment site
Are there 61 tRNA’s to read 61 codons?

21. tRNA: Wobble Hypothesis
First two nucleotides of codon for a specific AA is always precise
Flexibility with third nucleotide
Aminoacylation
process of adding an AA to a tRNA
Forming aminoacyl-tRNA molecule
Catalyzed by 20 different aminoacyl-tRNA synthetase enzymes

22. Ribosomes Translate mRNA chains into amino acids
Made up of two different sized parts
Ribosomal subunits (rRNA)
Ribosomes bring together mRNA with aminoacyl-tRNAs
Three sites
A site - aminoacyl
P site – peptidyl
E site - exit

23. Translation process Three stages Initiation Elongation Termination 1
Codon recognition
Amino acid
Anticodon
A site
P site
Polypeptide 2
Peptide bond formation 3
Translocation
New peptide bond
mRNA movement
mRNA
Stop codon
Three stages
Initiation
Elongation
Termination

24. Initiation Reading frame is established to correctly read codons
Ribosomal subunits associate with mRNA
Met-tRNA (methionine)
Forms complex with ribosomal subunits
Complex binds to 5’cap and scans for start codon (AUG) (scanning)
Large ribosomal subunit binds to complete ribosome
Met-tRNA is in P-site
Reading frame is established to correctly read codons

25. Elongation Amino acids are added to grow a polypeptide chain
A, P, and E sites operate
4 Steps

26. Termination A site arrives at a stop codon on mRNA
UAA, UAG, UGA
Protein release factor binds to A site releasing polypeptide chain
Ribosomal subunits, tRNA release and detach from mRNA

27. polysome a b
What molecules are present in this photo?
Red object = ?

28. Review What is a gene? Where is it located?
What is the main function of a gene?
Do we need our genes “on” all the time?
How do we turn genes “on” or “off”?