1. From Gene to Protein
ie:
Transcription & Translation

2. Protein Synthesis: overview
One gene-one enzyme hypothesis
(Beadle and Tatum)
One gene-one polypeptide (protein) hypothesis
The linear sequence of DNA determines the sequence of Amino Acids
Transcription: synthesis of mRNA under the direction of DNA
Translation: actual synthesis of a polypeptide under the direction of mRNA
Difference in types of cells:
Prokaryotes- DNA not segregated from ribosomes. Transcription & Translation occurs in rapid succession
Eukaryotes- mRNA is modified and translocated to the cytoplasm for translation

3. The Triplet Code Xn = number of amino acids that can be coded for….
The genetic instructions for a polypeptide chain are ‘written’ in the DNA as a series of 3-nucleotide ‘words’ called….
Codons: the basic unit of genetic code
Don’t forget!
‘U’ (uracil) replaces ‘T’ in RNA
Xn = number of amino acids that can be coded for….
where X= # of bases ; n=bases per codon
For life on Earth: 43 = 64

4. Transcription:
Only one strand of DNA is transcribed: “The Template Strand”
RNA polymerase: pries DNA apart and hooks RNA nucleotides together from the DNA code
Promoter region on DNA: where RNA polymerase attaches and where initiation of RNA begins
Terminator region: sequence that signals the end of transcription
Transcription unit: stretch of DNA transcribed into an RNA molecule

5. Transcription continued…
Initiation~ transcription factors mediate the binding of RNA polymerase II to an initiation sequence (TATA box)
Elongation~ RNA polymerase continues unwinding DNA and adding nucleotides to the 3’ end.. Uses ATP this time!
Termination~ RNA polymerase reaches terminator sequence… signals the RNA polymerase to stop transcription and release the mRNA

6. Transcription: overview
See Campbell animations!!!
D:\bc_campbell_biology_7\0,7052, ,00.html

7. mRNA modification D:\bc_campbell_biology_7\0,7052,3117225-,00.html
1) 5’ cap: modified guanine; protection; recognition site for ribosomes
2) 3’ tail: poly(A) tail (adenine); protection; recognition; transport
3) RNA splicing: exons (expressed sequences) kept,introns (intervening sequences) spliced out; spliceosome
D:\bc_campbell_biology_7\0,7052, ,00.html

8. Translation
mRNA from nucleus is ‘read’ along its codons by tRNA’s anticodons at the ribosome
Each codon on the mRNA has a complimentary …
tRNA anticodon (nucleotide triplet)
Each tRNA has been previously linked to an amino acid using the enzyme…
“Aminoacyl-tRNA-synthetase”
Wobble: the ability of one tRNA to recognize 2-3 different mRNA codons. Example:
CC _ anticodon recognizes
GGC, GGA, GGG, and GGU but all code for Glycine.
“Redundancy not Ambiguity!”

9. Translation continued
Ribosome: made of rRNA) site of mRNA codon & tRNA anticodon coupling
P site holds the tRNA carrying the growing polypeptide chain
A site holds the tRNA carrying the next amino acid to be added to the chain
E site discharged tRNA’s

10. Translation continued
Initiation~ union of mRNA, tRNA, small ribosomal subunit; followed by large subunit
Elongation~ •codon recognition •peptide bond formation •translocation
Termination~ ‘stop’ codon reaches ‘A’ site
Polyribosomes: translation of mRNA by many ribosomes (many copies of a polypeptide very quickly)

11. Translation See Campbell/YouTube animations!!
D:\bc_campbell_biology_7\0,7052, ,00.html
this one is EPIC!

12. Mutations: genetic material changes in a cell
Point mutations….
Changes in 1 or a few base pairs in a single gene
Base-pair substitutions:
Silent mutations no effect on protein
Missense mutations ∆ to a different amino acid (different protein)
Nonsense mutations ∆ to a stop codon and a nonfunctional protein
Base-pair insertions or deletions:additions or losses of nucleotide pairs in a gene; alters the ‘reading frame’ of triplets~frameshift mutation
Mutagens: physical and chemical agents that change DNA. Examples include:
Radiation…or
Base Analogs
McGrawHill