DNA & Genetics

Define DNA polymer of 2 polynucleotide chains that coil around each other to form a double helix What does DNA carry? Genetic information What are polynucleotides composed of? Nucleotides What are nucleotides composed of? Nitrogenous base, a pentose sugar and a phosphate group What are the 2 DNA strands held together by? Strong covalent bonds What bonds hold nitrogenous bases together? Hydrogen bonds Why are DNA strands antiparallel? Run in opposite directions Why do DNA strands twist? Protect the bases inside it & prevent them from being damaged by the environment How many bonds are between C-G? 3 hydrogen bonds How many bonds are between A-T? 2 hydrogen bonds The more C-G bonds in a piece of DNA... The more energy required to denature it When you read the message on 1 strand, What does it mean by DNA strands are you know the message on the other side complementary? (Not identical) What is Chargaff's rule? A=T and G=C (All together should add up to 100%, e.g gA = 30%, T = 30%, G = 20%, C =2 0%) What is chromatin? Complex of DNA What supports chromatin structure? Histones What is chromosomes? Threadlike structures in the nucleus made of proteins and a single molecule of DNA What is the centromere? Constriction point, dividing chromosome into 2 sections of an arms 1/6 Draw a chromosome and label it What is the purpose of chromosomes? To package huge amounts of DNA into the restricted nucleus What is a telomere? Regions of short repetitive DNA What are telomeres linked with? Ageing and Cancer Protection What is a gene? Section of DNA providing instructions for one protein molecule What are chromosomes made of? Genes What is DNA replication? Produces two identical replicas of one original DNA Which phase is DNA copied during interphase? S (synthesis) stage What are the requirements for DNA replication? - Original DNA template - Free DNA nucleotides - Replication enzymes - Primers Draw the semi-conservative theory (Include Messelson and Stahl's light and heavy nitrogen testing) Draw the conservative theory Draw the dispersive theory How do you measure DNA density? Using density gradient centrifugation 2/6 What are the three steps of replication? 1. Initiation 2. Elongation 3. Termination What must happen before replication can occur? DNA must be unzipped How is the double helix unwound? Breakage of weak hydrogen bonds What is DNA helicase? Enzyme that unzips DNA When the DNA strands separate, what shape does it form? A Y shape, know as the replication fork Which strand does DNA progress (synthesise) in? Only progresses in the 5' to 3' end, (though is directional in both strands) What is attached to the 5' end strand? A phosphate group What is attached to the 3' end strand? A hydroxyl group What is 5' and 3' end also known as? Leading strand, is continuous What is 3' to 5' end also known as? Lagging strand, discontinuous How is an okazaki fragment formed? RNA primer is extended by DNA polymerase What is the purpose of DNA primase? Synthesises RNA primers What is the purpose of DNA polymerase? Adds nucleotides to leading and lagging strands. (Also proofreads new DNA strand) What is the purpose of topoisomerase? Unwinds and rewinds DNA to stop the DNA from becoming supercoiled What is the purpose of exonuclease? Group of enzymes that remove nucleotide bases from the end of the DNA chain What is the purpose of DNA ligase? Facilitates joining of DNA strands by forming phosphodiester bonds Define transcription DNA into mRNA Describe initiation of transcription - Transcription Factor IID (TFIID) binds to the TATA box via the TATA Binding Protein (TBP) 3/6 - 5 more transcription factors & RNA polymerase combing around TATA box to form a transcription-initiation complex Describe elongation in transcription - Nucleotides are added to mRNA strand (added at the 3' end) - RNA polymerase moves along the DNA template from 3' to 5' Describe termination in transcription In bacteria: Polymerase stops transcription at the end of the terminator & mRNA can be translated without further modifications In eukaryotes: mRNA needs to be modified before translation take places Define translation RNA to protein What is the start codon? AUG (MET/methionine) Describe initiation of translation - Aminoacyl tRNA synthase catalyses bonding between specific tRNA & amino acids - Peptidyl transferase connects A & P site by forming a peptide bond during elongation phase - GTP used as energy source Describe elongation of translation. Amino acids are brought and added to the mRNA by tRNA one by one growing a polypeptide chain Describe termination of translation Stop codon in mRNA is recognised by protein release factor & the translational apparatus comes apart, releasing a completed polypeptide chain How are mRNA codons read? from 5' to 3' What do mRNA codons specify? Order of amino acids in a protein from N -terminus to C - terminus What happens if damage/alterations to DNA are not quickly repaired? Results in mutations 4/6 Define mutations Permanent alteration/change in a DNA sequence that are propagated through cellular generations What are somatic mutations? Occur in somatic ells and only affect the individual in which the mutation arises What are germ-line mutations? Alter gametes & passed to the next generation What are missense mutations? Change in 1 DNA base pair resulting in substation of 1 amino acid for another What are nonsense mutations? Point mutation which results in a premature stop codon (nonsense stop codon) in a transcribed mRNA What is the result of a nonsense mutation? A truncated (shortened), incomplete & usually nonfunctional protein. What are insertion mutations? Addition of another nucleotide Removes a nucleotide Smaller deletions - remove one or a few What are deletion mutations? (mention base pairs in a gene small and larger deletions) Larger deletions - remove an entire or several neighbouring genes What are duplication mutations? Piece of DNA is abnormally copied one or more times What are frameshift mutations? Addition or loss of DNA bases, changing a genes reading frame What is a reading frame? 3 bases that code for one amino acid What agents damage DNA? Radiation Chemicals in the environment What does DNA replication stress cause? Insertions/Deletions, resulting in mismatch repair What does oxygen radicals, ionising radiation and chemotherapeutics cause? Single strand DNA breaks resulting in base-excision repair What does polyaromatic hydrocarbons and UV light cause? DNA adducts and IntRAstrand crosslinks, resulting in nucleotide-exci5/6 sion repair, transcription-couple/ global genome repair Double strand DNA breaks and IntERstrand crosslinks, resulting in ds DNA break repair, homologous recombination/non-homologous end joining What does ionising radiation & chemotherapeutics cause? 6/6