Download Unit 2 Review: Molecular Genetics

Unit 2 Review: Molecular Genetics
DNA Discovery and Structure
-several experiments to demonstrate DNA is the hereditary material
-structure deduced by Watson and Crick, using X-ray diffraction, base proportions
-anti-parallel strands, base pairing (purine to pyrimidine), double helix with sugarphosphate backbone, 5' (phosphate) to 3' (sugar) direction
DNA Replication
-needed for cell division, growth, tissue repair
-strands separate by breaking the hydrogen bonds
-each strand acts as a template for the new DNA strand (semi-conservative)
-DNA helicase unwinds the double helix, single-stranded binding proteins prevent the
strands from reannealing, DNA gyrase swivels the DNA to relieve tension
-multiple replication forks occur, because DNA is too large
-RNA primers anneal to starting region
-DNA polymerase III adds nucleotides to the 3' (OH) end
-leading and lagging strands, Okazaki fragments
-DNA polymerase I removes RNA primers, replaces with DNA
-DNA ligase binds fragments together
-polymerase I & III act as proofreaders, removing mismatched nucleotides to avoid errors
Protein Synthesis
-various experiments used to link DNA to the production of proteins
-DNA too valuable to leave nucleus, other problems with direct translation
-mRNA needed to carry code to ribosomes (single stranded, has uracil)
-transcription -initiation by promoter region (A's and T's)
-elongation of mRNA by RNA polymerase
-termination at stop sequence, mRNA leaves nucleus, to ribosomes
-translation -initiation by start codon (AUG) and 2 ribosomal subunits
-elongation of polypeptide by tRNA bringing amino acids
-terminates at stop codon
Control Mechanisms
-42,000 human proteins, needed at specific times in different locations, and amounts
-gene regulation controlled at four different levels:
-transcriptional- transcription factors turn genes on/off
-post-transcriptional- introns removed from mRNA, exons spliced together
-translational- rate/frequency of translation, degradation of mRNA
-post-translational- add functional groups, move around, forms 3D shape
-prokaryotes used as examples:
-lactose digestion- produces β-galactosidase enzyme, lactose acts as inducer,
inhibiting Lac1 repressor =>positive regulation
-tryptophan production- tryptophan activates repressor, preventing the production
of enzymes needed to synthesize tryptophan
Mutations
-errors in DNA sequence that can be inherited, have no or negative effect
-types: silent, missense, nonsense, substitution, deletion, insertion, frameshift, point,
translocation, transposable elements, inversion
-causes: exposure to radiation, mutagenic agents, pesticides, spontaneous (polymerase)
-can lead to cancer, genetic diseases like cystic fibrosis
Comparing Eukaryotes/Prokaryotes
-prokaryotes: no nucleus, coupled transcription-translation, 1 csome, diff. methionine
-eukaryotes: transcription in nucleus, translation in cytoplasm, no operators, have introns,
5' cap on mRNA, many csomes
Chromosome Structure
-DNA must be packed tightly to fit in nucleus (1.8m long)
-double helix is wrapped around histones to form nucleosomes, which are coiled into
chromatin fibres, which are then supercoiled
-individuals have microsatellites (random repeats, non-coding) that make them unique
-some can cause diseases (Huntington’s)
-also for protection during division, degradation (telomeres, centromeres)
Biotechnology
-Restriction Endonucleases-enzymes that cut DNA in specific locations (sticky or blunt)
-Methylases- protect certain DNA, to prevent cutting by restriction enzymes
-Ligases- join two fragments of DNA together, ends must be cut by same enzyme
-Gel Electrophoresis- separation of DNA fragments based on size, forms band pattern
-Plasmids- used to insert desired genes into bacterial DNA for expression (insulin)
-Transformation- put plasmid into bacteria, antibiotic resistance gene confirms transfer
-Genetic Engineering- alter DNA, causing organisms to make products useful to humans
-Polymerase Chain Reaction- produce multiple copies of DNA strand (forensics)
-Restriction Fragment Length Polymorphism- link DNA to individual based on different
DNA fragment lengths (microsatellite regions), bands read by radioactive probes
-DNA sequencing- dideoxy nucleotides stop DNA replication, fragments separated on
gel, sequence read using radioactivity, X-ray film (four tubes)
Applications
-medical: early diagnosis, treatment, prevention; genetic screening, gene therapy
-agricultural: transgenic crops, yield increase, pest/pesticide resistance
-forensics: DNA fingerprinting (PCR, RFLP), use microsatellite regions, DNA databases
Review Questions:
p320 # 17, 18, 21, 22
p324 # 13, 19, 21, 23, 24, 28, 30, 32a-d, 34, 37a,d, 44, 46