9/28/20171Course Business• Nisarg’s new office hours:– Mon. 3:30-4:30pm office hour– Mon. 4:30-5:30pm study hour29/28/201729/19/17Genetics: The Biology of Variation & Inheritance3Today’s Objectives(What Darwin did not know!)• DNA: What it is and what it does• Mendelian genetics:– How is genetic variation achieved?– How is it passed to future generations?49/28/20173Do NOT Panic5When in doubt about how much to learn given the detail in the textbook, use this lecture as a guide.We are learning what you need to know of genetics to understand evolutionary theory, not to become a geneticist or biochemist.Where is DNA and what does it do?69/28/20174Cell Biology• cell membrane• cytoplasm• nucleus– genetic material• other genetic material7Cell Biology• cell membrane• cytoplasm• nucleus– genetic material• other genetic material89/28/20175Cell Biology• cell membrane• cytoplasm• nucleus– genetic material• other genetic material9Cell Biology• cell membrane• cytoplasm• nucleus– genetic material• other genetic material109/28/201762 types of cells:• Somatic cells– Contain the full compliment of chromosomes (in humans, 23 pairs)• Gametes– Egg– Sperm– Contain only one of each of the 23 chromosomes112 types of cells:• Somatic cells• Gametes (sex cells)– Egg (produced in female humans while she is still a fetus in the womb)– Sperm (produced by human adult males continually)129/28/20177DNA• What is DNA?– Nucleotides form a chain:• phosphate and sugar backbone• Nucleotide bases: adenine, thymine, cytosine, guanine• Two strands twist around each other forming a double helix13SPASPASPGSPTSPCSPGSTPSTPSCPSAPSGPSCP• 2 complementary strands of DNA join at the bases which form weak bonds to create the double stranded DNA molecule• adenine thymine • cytosine guanine149/28/20178Any questions so far?15Reproduction of cells is accomplished through cell divisionWhy do cells need to reproduce?169/28/20179Functions of DNA: 1. Replicates Itself17• Error rate of 1 per billion base pairs.• Human genome has 3 billion, thus 3 errors per cell division.What do you call a replication error when it happens in a developing sperm or egg cell?DNA coils into Chromosomes before cell division189/28/201710Replication during Mitosis: generates duplicate cells- cell division for somatic cells- results in two identical daughter cells- diploid condition is retained19Replication during Meiosis: produces haploid gametes- cell division for gametes- results in four haploid daughter cells209/28/201711Some definitions…• DNA: deoxyribonucleic acid; moleculeresponsible for carrying genetic information• Chromosomes: discrete structures containing nuclear DNA; 23 pairs (46) in humans; nuclear=DNA in cell nucleus (eukaryotic organisms)• Homologous – 1 each from mother & father21• Gene: sequence of DNA that carries info for protein synthesis at a particular location (locus, plural loci) on a chromosome.• Allele: alternate forms of a gene• Diploid: full complement of chromosomes; somatic cells• Haploid: half set of chromosomes; gametesCrossover (recombination) during meiosis: exchange of genetic material between homologous chromosomesFM229/28/201712Crossover (recombination) during meiosis: exchange of genetic material between homologous chromosomesFM23Why is crossover (recombination) important?249/28/201713FMCrossover produces new combinations of (variation among) allelesGene contributingto eye colorGene contributing to hair color25Functions of DNA: 2. Protein Synthesis269/28/201714Proteins are amino acid chains….Examples hormones acting as messengers; enzymes speeding up reactions; antibodies fighting foreign invaders; structures in muscles, hair, ligaments, fingernails, the lens of your eyeIf there is a job to be done in the molecular world of our cells, usually that job is done by a protein.A protein hormone which helps to regulate your blood sugar levels27Two Steps in protein synthesis: transcription & translation289/28/201715Transcription: synthesis of mRNA from DNA• DNA molecule “unzips” between bases• Messenger RNA (mRNA) molecule is built by adding free-floating RNA nucleotides to the DNA strand• mRNA strand then breaks away and DNA zips up29RNA• Different from DNA– Single-stranded molecule– Contains a different sugar (ribose, instead of deoxyribose)– Uses the base URACIL instead of THYMINE (AU in RNA, not AT); other bases the same• Integral part of protein synthesis309/28/20171631Translation: synthesis of an amino acid sequence from the mRNA template• Every three mRNA bases (codon) is matched with its Transfer RNA (tRNA) anti-codon• Each tRNA anti-codon is attached to an amino acid.• Thus, mRNA strands are translated into tRNA to create amino acid chains.329/28/201717Protein FunctionOnly 20 Different Amino Acids, differing only in the beige partThe protein’s function is a result of the 3D shape of its unique 2D (linear) combination of amino acids33Introns and Exons34• Introns: grey• Exons: different colors9/28/201718Regulatory Sequences• Example of the production of lactase• Repressor region– Example: Bound in presence of glucose• Activator region– Example: Bound in presence of lactose– Transcription happens when activator bound and repressor unbound35Gene Regulation and Cell Differentiation• All cells have the same DNA code• Cell differentiation?– Gene expression• Ex: neurons• Ex: eye formation on fly antennae (Pax6 gene)369/28/201719Epigenetics (Evolutionary Developmental Genetics)37Questions?389/28/201720ALA#3:What is the appropriate sequence of events in protein synthesis? a) DNA transcribed to mRNA; mRNA translated to amino acids by tRNA in cell nucleus; Folding of amino acid polypeptide chain creates the protein. b) RNA transcribed to DNA; DNA leaves cell nucleus; DNA translated to an amino acid sequence in the ribosome; Folding of amino acid polypeptide chain creates the protein. c) DNA transcribed to mRNA; mRNA leaves cell nucleus; mRNA translated to amino acids by tRNA in the ribosome; Folding of amino acid polypeptide chain creates protein. d) DNA leaves cell nucleus; DNA transcribed to mRNA in the ribosome; mRNA translated to amino acids by tRNA in the mitochondrion; Folding of amino acid polypeptide chain to create protein. e) DNA transcribed to tRNA; tRNA leaves cell nucleus; Folding of amino acid polypeptide chain creates protein; tRNA
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