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Introduction to Human Genetics Chapter One What is DNA? • Deoxyribonucleic Acid: – String of nucleotides • Nucleotides made up of three parts: OH ON – HO-CH2 -O – + P – O- = + O N OH deoxyribose (a sugar) phosphate cyclic amine (base) Nucleotide N – O- – P – O-CH2 = O OH -O N O- – DNA N – -O P – O-CH2 N = Specific Bases O N – O – -O P – O-CH2 N = O – O – -O P – O-CH2 = O O Sugar-Phosphate Backbone (negatively charged) N N The Five Bases • • • • A = Adenine T = Thymine G = Guanine C = Cytosine • RNA only: – U = Uracil (replaces T) Structures of Bases Pyrimidines O NH2 O CH3 N N N N N N T U C NH2 Purines O N N N N N N A NH2 N N G O- – DNA T – -O P – O-CH2 = O – O A – -O P – O-CH2 = O – O – -O P – O-CH2 = O O Sequence of DNA is order of the bases attached to backbone C Double Helix • Sugar-Phosphate backbone is on outside • Bases are inside - Hydrogen-bonding to opposing base on opposite strand • Forming Base Pairs Base Pairing • Experiments showed: 1. Two strands were always same distance apart 2. Percentages of A always matched T, and G always matched C • Therefore… 1. A Purine must always be base paired to a Pyrimidine 2. A = T, and G == C 3. Strands must be complementary Summary of DNA • String of Nucleotides • deoxyribose Sugar-Phosphate backbone • 4 Bases: – A, G are Pyrimidines – T, C are Purines –A=T –G= =C • Two complementary strands (double helix) Central Dogma dog·ma P Pronunciation Key (dôg ma) n. pl. dog·mas or dog·ma·ta 1. A doctrine or a corpus of doctrines relating to matters such as morality and faith, set forth in an authoritative manner by a church. 2. An authoritative principle, belief, or statement of ideas or opinion, especially one considered to be absolutely true. Central Dogma DNA Transcription RNA Translation Protein Transcription RNA polymerase Double Stranded DNA “Promoter” opens initiation elongation termination single stranded mRNA Translation ...AGAGCGGAATGGCAGAGTGGCTAAGCATGTCGTGATCGAATAAA... AGAGCGGA.AUG.GCA.GAG.UGG.CUA.AGC.AUG.UCG.UGA.UCGAAUAAA MET.ALA.GLU.TRP.LEU.SER.MET.SER.STOP 4 Nucleotides 20 amino acids 1 base codon - 41 = 4 possible amino acids 2 base codon - 42 = 16 possible amino acids 3 base codon - 43 = 64 possible amino acids Translation amino acid tRNA single stranded mRNA } Codon (3 bases) The Genetic Code UUU UUC UUA UUG CUU CUC CUA CUG AUU AUC AUA AUG GUU GUC GUA GUG Phe Leu Leu Ile Met Val UCU UCC UCA UCG CCU CCC CCA CCG ACU ACC ACA ACG GCU GCC GCA GCG Ser Pro Thr Ala UAU UAC UAA UAG CAU CAC CAA CAG AAU AAC AAA AAG GAU GAC GAA GAG Tyr Stop His Gln Asn Lys Asp Glu UGU Cys UGC UGA Stop UGG Trp CGU CGC Arg CGA CGG AGU Ser AGC AGA Arg AGG GGU GGC Gly GGA GGG Translation Note: Actually a different tRNA for each different codon Proteins • Protein Sequence = order of the amino acids Sequence Structure Function Central Dogma Summary • • • • • • DNA is in the nucleus of each cell DNA encodes for RNA (transcription) RNA encodes for Proteins (translation) DNA and RNA are made of nucleotides Protein is made of amino acids A protein’s function is determined by it’s structure, which is determined by it’s sequence • Therefore…DNA encodes protein function What is a gene anyway? • A gene is a small piece of DNA • It begins with a promoter – This is region of sequence that tells RNA polymerase “start here” – Also regulates amount of mRNA that is made • Includes Introns and Exons – Introns are removed during transcription – Exons are the parts of the sequence that become mRNA • Also, gene has regulatory regions Gene Structure mRNA protein One gene = one protein • Only not really: – Splice variants = form different proteins – Different alleles = different versions of the same protein – Polymorphisms; may change protein sequence or regulation of protein – Mutations may destroy a protein, or change it’s normal function or expression Genetic variance: • Allele: Alternative form of one gene, usually form same protein, with slight changes, but same function • Polymorphism: Usually a silent change (something that doesn’t affect the protein), that is often common in population • Mutation: A change in the DNA sequence that will change the protein’s function or regulation, usually in a detrimental way Sequence vs. Expression • Genetic variances can affect: – Sequence of the gene • May change the sequence of the protein • May be “silent” – Level the gene is expressed • Amount of protein that will be made – Where a gene is expressed • What cell type • What tissue • What time point in development Chromosomes • Chromosomes can carry thousands of genes – Made of DNA and proteins • Human have 22 pairs of autosomal chromosomes – 1 is the largest, 22 is the smallest • Humans have 1 pair of sex chromosomes – XY is male, XX is female – X inactivation in females How are genes inherited? • Genes are carried in the DNA • DNA is condensed into chromosomes • Each individual has two copies of every chromosome • Sex cells (sperm or eggs) each have one copy of every chromosome • Mating leads to one copy of every chromosome coming from one parent and other copy coming from the other parent – Variances are mixed in offspring Traits • Any distinguishing feature that can be measured – Quantitatively (ex. height, weight) – Qualitatively (ex. disease status) • Inherited Traits – Completely genetic • Non-inherited Traits – Completely Environmental • Complex Traits – Partially Genetic, partially environmental Complex Traits • Disorder that is proven heritable, yet has no clear mode of inheritance – Doesn’t follow Mendel’s laws • More than one gene • Interaction between genes • Interaction between gene(s) and environment Why Common Complex Disorders and Rare Mendelian Disorders? • Evolution can act upon a single detrimental gene – negative selection • Gene functions that are good for some things, but can be harmful in excess – ex: rational fear vs. anxiety disorders • Normal alleles only predisposing – other mutations/environment present Genotype vs. Phenotype • Genotype = combination of alleles individual is carrying – Genes (which versions) • Phenotype = measurable traits individual shows – Final Product Applications: • Selection – First use of genetics – What are some examples? • Evolution – Tracing origins • Forensics – What are some examples? • Medical Care – Studying, treating, curing diseases Next Class: • Read Chapter Three • Homework – Chapter One Problems; – Review: 1, 2, 4 – Applied: 3, 4, 11, 14