1. Replication / Cell Division Notes Chapter 10 and 11

3. Maurice Wilkins and Rosaline Franklin - 1952 • Photographed DNA using x-rays (crystallography) • Showed a wide, tightly coiled molecule with a helix shape

4. James Watson and Francis Crick - 1953 • Used Franklin’s DNA x-ray to determine structure of DNA • DNA’s shape • Double helix • 2 strands • Rungs (nitrogen bases)

5. DNA

6. DNA Structure • Shape – double helix • Location – chromosomes contain DNA • Found in nucleus of eukaryotic cells • Length – long • E. coli – 4,639,221 base pairs or 1.6mm long • 1 m of DNA in each Eukaryotic cell

7. Nucleotides • Nucleotide consists of: • 5-carbon sugar – deoxyribose • Phosphate group • One of 4 nitrogen bases • Adenine • Thymine • Guanine • Cytosine

8. Nitrogen Bases • Base pair rule • Adenine always pairs with thymine • A:T • Guanine always pairs with cytosine • G:C • Adenine and guanine are purines • Thymine and cytosine are pyrimidines • Bases are held together by hydrogen bonds (weak)

9. DNA Structure

10. DNA Replication • Process by which DNA is copied • DNA reproduces prior to cell division • Steps • DNA double helix unwinds and unzips • Enzymes break H2 bonds between bases, separating 2 strands • Each parent strand of DNA serves as a template for each new strand • New strands are assembled from free nucleotides • DNA polymerase matches the bases on parent strand creating new double helixes

11. Replication

12. Why Cells Divide • Cell size • Maintain large surface area to volume ratios to transport materials easily • Minimum • DNA • Protein • Internal structures to survive and reproduce • Maximum • Obtain adequate nutrients • Dispose of wastes

13. Why Cells Divide • Growth • Result of cells producing new cells by cell division • Differentiation – when cells develop into specialized shapes • Repair • Regeneration • Replace dead cells • Skin cells replace every 28 days

14. Why Cells Divide • Reproduction • Asexual – offspring prod. by 1 parent • Ex. Bacteria, protists, plants and some animals • Cell division (mitosis) replicates chromosomes of one parent cell • Offspring are genetically identical to parent • Gives rise to diploid daughter cells (2N) • Sexual – offspring have combination of genetic material from 2 parents • Cell division (meiosis) results in offspring genetically different from parents • Results in 4 haploid (N) cells

15. How Do Cells Divide? • Cell cycle – period from beginning of 1 cell division to beginning of the next cell division • 2 parts • Growth • Preparation • Cell divides in 2 stages • Mitosis (nuclear division) • Cytokinesis is (cytoplasm division)

16. Cell Cycle Pg. 245

17. Interphase • Part of cell cycle that occurs between divisions • Longest part of cell cycle – 90% of time • Stages • G1 or gap 1 – 1st stage • Characterized by growth and development • S or synthesis – 2nd stage • Chromosomes in nucleus replicate forming 2 identical structures called sister chromatids • Sister chromatids are visible as cell division begins • Joined together at a point called a centromere • Chromatin – thin, fibrous form of DNA and protein that make up a chromosome

18. Phases of Mitosis • Prophase – 1st phase • Chromosomes condense and sister chromatids visible • Nuclear membrane and nucleolus break and disappear • Spindle fibers (from cytoskeleton) attach to centromere & begin to move sister chromatids toward center of cell

19. Phases of Mitosis • Metaphase – 2nd phase • Chromosomes pull to center of cell and line up on the metaphase plate

20. Phases of Mitosis • Anaphase – 3rd phase • Centromeres divide, spindle fibers pull chromatids apart and towards separate poles (ends) • Once separated, the chromatids are 2 identical sets of daughter chromosomes

21. Phases of Mitosis • Telophase – 4th phase • 2 daughter nuclei are formed • Nuclear envelope forms around each set of chromosomes • Chromosomes uncoil to form chromatin • Animal cells – each new nucleus has a pair of centrioles outside its nuclear envelope

22. Phases of Mitosis • Cytokinesis – cytoplasm divides • Begins during telophase as daughter nuclei form • Animal cell • Cell membrane at the center of parent cell folds inward = cleavage furrow • Furrow develops and 2 distinct cells with complete membranes are formed • Plant cell • Membrane fragments fuse to form a cell plate between the 2 new nuclei • A new cell wall forms between the membranes of the cell plate • A complete cell wall that divides the 2 daughter cells is formed

23. Cytokenesis

24. Regulating Cell Cycle • Cyclins • Proteins found in dividing cells • Regulate timing of cell cycle in eukaryotic cells • Figure 10-7 • Internal regulators – proteins that respond to events inside cell • External regulators – proteins that respond to events outside the cell • Cancer cells do not respond to either external or internal signals that regulate the growth of most cells

25. Meiosis • Before meiosis • A diploid cell replicates its chromosomes • It will now consist of 2 sister chromatids joined by a centromere

26. Phases of Meiosis • Meiosis I • Prophase I – each homologous pair of chromosomes attach to one another and equals 4 sister chromatids called tetrad • Metaphase I – chromosomes move to the center of the cells • Anaphase I – chromosomes are pulled to the poles • Telophase I – 2 daughter cells are formed that are haploid and consist of 2 sister chromatids • Each daughter cell now undergoes Meiosis II

27. Phases of Meiosis • Meiosis II • Prophase II – sister chromatids begin to move to the center of the cell • Metaphase II – centromeres split in middle of cell • Anaphase II – individual chromosomes are pulled to the poles • Telophase II – 4 haploid daughter cells result • (2 from each Meiosis I daughter cell)

28. Phases of Meiosis • Cytokenisis • In human males • All 4 haploid nuclei form sperm • In human females • Only 1 haploid nuclei forms an egg • The other 3 nuclei receive almost no cytoplasm and do not form gametes

29. Meiosis Overview

30. Regulating the Cell Cycle • Proteins found in dividing cells • Regulate timing of cell cycle in eukaryotic cells • Internal regulators – proteins respond to events inside • External regulators – proteins respond to events outside cell • CDKs • Involved in regulation of transcription of mRNA • Target for anti-cancer treatment

31. Genes and Cancer • Causes of cancer • Mutations that change the genes that control cell growth and specializations • Can be inherited • Environmental factors • Combination of genetic and envir.

32. Oncogene • A gene that causes a cell to become cancerous • Caused by a mutation in a growth factor gene • Caused by a DNA replication error • Multiple copies of a single growth factor gene • Caused by a change in a gene’s location

33. Cancers Linked to Deletion Mutations

35. Environmental Factors • Mutagens – factor in the envir. that can cause mutations • Radiation • Chemicals (tobacco prod.) • Carcinogen – agent that causes or tends to cause cancer by replacing or changing DNA • Tars • Chemicals in smoked meat • Viruses • Radiation (UV – sunlight) • Drugs • Coal tars (hair dyes)

36. Karyotype • Picture of homologous pairs of chromosomes • Can show a various abnormalities • Nondisjunction – when chromosomes fail to separate during meiosis • Can result in too few or too many chromosomes