DNA & Genetics

1. DNA & Genetics

2. DNA Replication Errors and Mutations • Error rates • in bacteria 3 errors per 100,000 bases copied • every generation of cells would have 1,000 faulty proteins • Proofreading and error correction • after DNA polymerase replicates strand, a smaller polymerase proofreads it and makes corrections • results in only 1 error per 1,000,000,000 bases copied • Mutations - changes in DNA structure due to replication errors or environmental factors • some cause no effect, some kill cell, turn it cancerous or cause genetic defects in future generations

3. DNA Function • Serves as code for protein synthesis, cell replication and reproduction • Gene - sequence of DNA nucleotides that codes for one polypeptide • Genome - all the genes of one person

4. Translation of mRNA Flow Chart

5. DNA & Peptide Formation

6. Cell Cycle • G1 phase, the first gap phase • normal cellular functions • S phase, synthesis phase • DNA replication • G2 phase, second gap phase • preparation for mitosis • replicates centrioles, synthesizes enzymes for cell division • M phase, mitotic phase • nuclear and cytoplasmic division • G0 phase, cells that have left the cycle

7. Functions of Mitosis • Embryonic development • Tissue growth • Replacement of old and dead cells • Repair of injured tissues

8. Mitosis: Prophase • Chromatin supercoils into chromosomes • Nuclear envelope disintegrates • Centrioles sprout microtubules, mitotic spindle • Centrioles move to poles

9. Metaphase Chromosome

10. Mitosis: Metaphase • Chromosomes line up on equator • Spindle fibers attach to centromere • Asters anchor centrioles to plasma membrane

11. Mitosis: Anaphase • Centromeres divide • Spindle fibers pull sister chromatids to opposite poles of cell

12. Mitosis: Telophase • Chromatin uncoils • Nuclear envelopes form • Mitotic spindle breaks down

13. Cytokinesis • Division of cytoplasm • Myosin pulls on actin in the membrane skeleton • Causes crease around cell equator called cleavage furrow • Cell pinches in two

14. Timing of Cell Division Cells divide when: • Cells large enough • DNA replicated • Adequate supply of nutrients • Growth factor stimulation • Open space in tissue Cells stop dividing when: • Loss of growth factors or nutrients • Contact inhibition

15. Cancer • Tumours • abnormal growth, when cells multiply faster than they die • oncology is the study of tumors • Benign • connective tissue capsule, grow slowly, stays local • potentially lethal by compression of vital tissues • Malignant • unencapsulated, fast growing, metastatic (causes 90% of cancer deaths)

16. Causes of Cancer • Carcinogens - estimates of 60 - 70% of cancers from environmental agents • chemical • cigarettes, food preservatives • radiation • UV radiation,  particles,  rays,  particles • viruses • type 2 herpes simplex - uterus, hepatitis B - liver

17. Mutagens • Trigger gene mutations • cell may die, be destroyed by immune system or produce a tumor Defenses against mutagens • Scavenger cells • remove them • Peroxisomes • neutralize nitrites, free radicals and oxidizing agents • Nuclear enzymes • repair DNA • Tumor necrosis factor (TNF) destroys tumors

18. Cancer Genes • Oncogenes • mutated form of proto-oncogenes • sis oncogene causes excessive production of growth factors • stimulate neovascularization of tumor • ras oncogene codes for abnormal growth factor receptors • sends constant divide signal to cell • Tumor suppressor genes • inhibit development of cancer • damage to one or both removes control of cell division

19. Effects of Malignancies • Displaces normal tissue, function deteriorates • rapid cell growth of immature nonfunctional cells • metastatic cells different tissue origin • Block vital passageways • respiratory or vascular • Diverts nutrients from other tissues • tumors have high metabolic rates • causes weakness, fatigue, emaciation, infection

20. Chromosomes • Karyotype • chart of chromosomes at metaphase by size, structure • Homologous chromosomes • 2 chromosomes in each pair, 1 from each parent • autosomes (22 pairs) • sex chromosomes (X and Y) • Germ cells - sperm and egg cells, haploid • Somatic cells - all other cells, diploid

21. Genes and Alleles • Gene loci • location of gene on chromosome • Alleles • two homologous chromosomes have same gene at same locus, may be different forms of gene • Dominant allele • produces normal, functional protein • Recessive allele • when both alleles are recessive produces abnormal protein or no protein

22. Genetics of Earlobes • Genotype • alleles for a trait (DD) • Phenotype • trait that results • Dominant allele (D) • expressed with DD or Dd • Dd parent ‘carrier’ of recessive gene • Recessive allele (d) • expressed with dd only Punnett square

23. Multiple Alleles, Codominance, Incomplete Dominance • Gene pool • collective genetic makeup of whole population • Multiple alleles • more than 2 alleles for a trait • such as IA, IB, i alleles for blood type • Codominant • both alleles expressed, IAIB = type AB blood • Incomplete dominance • phenotype intermediate between traits for each allele

24. Polygenic Inheritance • 2 or more genes combine their effects to produce single phenotypic trait, such as skin color

25. Pleiotropy • Single gene causes multiple phenotypic traits, as in sickle-cell disease

26. Sex-Linked Inheritance • Recessive allele on X, no gene locus for trait on Y, so hemophilia more common in men

27. Penetrance and Environmental Effects • Penetrance • % of population to express predicted phenotype • Role of environment • brown eye colour requires phenylalanine from diet to produce melanin, the eye pigment

28. Alleles at the Population Level • Dominance and recessiveness of allele do not determine frequency in a population • Some recessive alleles, blood type O, are the most common • Some dominant alleles, polydactyly, are rare

29. Recombinant DNA Technique