1. AP Biology Crosby High School
From Gene to Protein
AP Biology
Crosby High School

2. George Beadle and Edward Tatum
Neurospora Crassa
Exposed to radioactive X-rays
Created mutations in enzymatic pathways
Exposed to specific nutrients
Would not grow in absence of some nutrients

3. Beadle and Tatum Experiment

4. Transcription and Translation
DNA  RNA
Nucleic acid to nucleic acid
Template produces primary transcript
Modified to mRNA and exported to ribosome
RNA  Protein
Nucleic acid to amino acid
Occurs at ribosome
Creates primary structure of protein

5. DNA  RNA  PROTEIN

6. Genetic Code Based on Triplet code
Allows for 64 combinations
Only 20 amino acids
Three nucleotide bases makes a codon
Codons complementary to template strand
Some redundancy in third base
Must be in the proper reading frame

7. The Genetic Code

8. Cracking Genetic Code Poly U placed in tube with ribosomes AUG Stop
Produced only Phenylalanine (UUU)
AUG
Start
Methionine
Stop
UAA
UAG
UGA

9. Universal Genetic Code
Almost Identical in all life
Differences
Paramecium
Mitochondria

10. Transcription Three steps Binding and Initiation Elongation
RNA Polymerase II attaches at promoter
Elongation
RNA Polymerase II adds nucleotide bases creating mRNA
Termination
RNA Polymerase detaches at terminator

11. Binding and Initiation
Transcription factors
Recognize the promoter
Bind before RNA Polymerase
Transcription Initiation Complex
RNA Polymerase
TATA box
Promoter sequence
25 nucleotides upstream

12. Elongation Adds to 3’ end of RNA strand 60 nucleotides / second
Multiple transcriptions

13. Termination Prokaryotic Eukaryotic
Recognizes a STOP codon and terminates transcription
Eukaryotic
Recognizes a STOP codon and continues downstream
AAUAAA sequence terminates transcription

14. Eukaryotic Cells Modify RNA
Alteration of mRNA ends
5’ cap: modified GTP
Protects mRNA from degradation
“Attach Here”
poly (A) tail: adenine nucleotides
Prevent degradation

15. RNA Splicing Genetic “Cut and Paste”
8k nucleotides copied for 400 a.a.
Introns and Exons
Introns
Noncoding segments (Intervening sequences)
Regulatory roles
Allows for crossing over w/o affecting coding sequence
Exons
Expressed segments

16. RNA Splicing (cont.) snRNPs: Spliceosome
snRNA of snRNP recognizes splice site
Spliceosome
snRNP and other proteins
Cut out Introns
Fuse Exons

17. Transfer RNA Ends: Structure fits Function Specific amino acid
Anticodon
Structure fits Function
80 nucleotides long
U can bind with A or G (wobble)
Inosine binds with U,C, or A
Aminoacyl-tRNA: bonds a.a. to correct tRNA

18. Ribosomes Consist of proteins and rRNA Large and Small subunits
Structure
Binding site for mRNA
3 sites for tRNA
E: Exit site
P: Peptidyl –tRNA site (Peptide)
A: Aminoacyl – tRNA site (Acceptor)

20. Initiation Small ribo. subunit binds to mRNA
Bacteria: rRNA subunit binds to AUG
Euk.: rRNA subunit binds to 5’cap
Translation begins at AUG
Large ribo. Subunit attaches to complete translation Initiation complex
Initiator sits in P site

21. Elongation Codon Recognition: Peptide bond formation: Translocation:
Codon of mRNA H-bonds to tRNA anticodon
Attaches to the A site
Peptide bond formation:
rRNA of Large ribo. Subunit forms peptide bond between P and A site
Translocation:
Each tRNA moves to the next site
E site exits

22. Termination
Encounters a STOP codon
Binds a release factor

23. Mutations Changes in genetic material of the cell Point mutations:
chemical changes to just one base pair
Sickle-cell results from a point mutation in gene for Hemoglobin
Mutagens: Create mutations
Physical: Mutagenic radiation
Chemical

24. Types of Point Mutations
Substitution: replace one pair w/ another
Silent mutations: no affect
Missense mutations: Makes sense but codes incorrectly
Nonsense mutations: results in a STOP codon
Insertion and Deletion
Usually result in a frameshift mutation

25. Point Mutations