Grade 12 Genetics in a Nutshell

History


10. In 1952, Hershey and Chase discovered that DNA is the hereditary information not protein.

• conducted an experiment with bacteriophage: phage tagged with radioisotopes, 32P in DNA and 35S in protein

9. In 1953, Watson and Crick discovered the double helical structure of DNA.

• with the help from the x-ray image of DNA retrieved by Franklin, they were able to figure out the width of the DNA, 2nm, and the arrangement of nitrogenous bases
• purines can only bind with pyrimidines and this explained the Chargaff's rules

DNA Structure

8. DNA consists of many nucleotides which are made up of phosphate, sugar, and base.

• nitrogenous bases: Adenine=Thymine, Guanine(triple bond)Cytosine
• sugar + nitrogenous base => Glycosyl bond (intra), sugar + phosphate => phosphodiester (intra), nucleotides + nucleotides => hydrogen bond (intermolecular)

DNA Replication

7. DNA uses semiconservative method to replicate. One old strand and one newly made strand.

6. Enzymes and proteins carry out the job of replication. => Helicase, Single-Strand Binding Protein, gyrase, primase, DNA polymerase III, DNA polymerase I, ligase

• 5' to 3' elongation!!!
• leading strand / template can code for a continuous complimentary strand, lagging strand has Okazaki Fragments 

video of the process: http://www.youtube.com/watch?v=teV62zrm2P0

Transcription

5. Messenger RNA is transcribed from the template strand of a gene.

• transcription factors aka TFs (proteins) bind to the promotor region (TATA box)
• then RNA polymerase binds to TFs creating transcription initiation complex
• RNA polymerase II conduct elongation 
• transcription process stops after transcribing the terminator sequence, AAUAA

Video: http://www.youtube.com/watch?v=SMtWvDbfHLo&feature=relmfu

4. pre-mRNA is modified after transcription in eukaryotic cells

• 5' => 5' cap of guanine. protect form hydrolytic enzymes and signal for ribosomes
• 3' => poly(A) tail. same as 5' cap and also export mRNA from the nucleus
• RNA splicing => cut introns and join extrons to form mRNA molecule with only coding sequence
• snRNA + proteins = snRNPs + other proteins + pre-mRNA => spliceosome 

Translation

3. initiation: mRNA, tRNA with amino acid, two ribosomal subunits join together

2. Elongation

• codon recognition: elongation factor => hydrogen bonding between mRNA codon under A site with anticodon of tRNA
• peptide bond forms with polypeptide in P site and the amino acid in the A site
• translocation: tRNA with polypeptide is moved from A site to P site by ribosome and the tRNA that was previously in P site is now in E site and then leaves the ribosome

1. Termination

• release factor enters A site then hydrolyzes the bond between polypeptide and its tRNA then translation complex disassembles