1. UNIT V - DNA & CELL DIVISION
Big Campbell – Ch 12, 13, 16
Baby Campbell – Ch 8,

2. I. ASEXUAL REPRODUCTION
Purpose
Unicellular Organisms
Multicellular Organisms

3. II. PROKARYOTIC ASEXUAL REPRODUCTION
Binary Fission
Asexual reproduction
Much shorter than euk cell cycle
Single chromosome replicates
Each copy begins moving to opposite ends of cell
Cell elongates
When bacterium is 2X original size, cell membrane pinches inward
Cell wall deposited
2 identical cells produces

4. III. EUKARYOTIC CELL DIVISION – THE CELL CYCLE
Can be divided into:

5. III. CELL CYCLE, cont Interphase
Portion of cell cycle in which cell is carrying out normal activities.
Approx 90% of normal cell cycle is spent in interphase.
DNA found in chromatin form
3 sub-phases

6. III. CELL CYCLE, cont Mitosis Nuclear division
Requires all the cells energy, resources
Last step is cytokinesis – splitting of the cell

7. III. CELL CYCLE, cont

8. III. CELL CYCLE, cont

9. III. CELL CYCLE, cont
Cytokinesis

10. III. CELL CYCLE, cont

11. IV. CONTROL OF THE CELL CYCLE
Internal Signals
Three major checkpoints in cell cycle G1 G2 M
Regulated by enzymes known as cyclin-dependent kinases or Cdks
Activated when bound to proteins known as cyclins
Kinase concentrations fairly constant; cyclin concentrations vary

12. IV. CONTROL OF THE CELL CYCLE, cont
External Signals
Growth Factors
Proteins released by certain cells that stimulate other cells to divide.
Cells stop dividing when growth factor is depleted.
Examples include erythropoetin, interleukin, pdgf

13. IV. CONTROL OF THE CELL CYCLE, cont
External Signals
Density-dependent Inhibition
Results from crowded conditions
When one cell touches another, cell division stops
Anchorage Dependence
Most cells must be in contact with solid surface to divide

14. IV. CONTROL OF THE CELL CYCLE, cont
Cell Cycle Out of Control = CANCER
Cancer cells do not respond to normal cell cycle controls
Apoptosis – Programmed cell death
Uncontrolled growth
Deprive normal cells of nutrients

15. IV. CONTROL OF THE CELL CYCLE, cont
Tumor – Mass of abnormal cells
Benign – Mass remains at original site
Malignant – Mass spreads to other parts of the body
Metastasis – Separation of cancer cells from tumor; travel through circulatory system

16. V. MEIOSIS Somatic Cells Body cells
Human somatic cells contain 46 chromosomes, 23 from mom, 23 from dad
2n or diploid
Matched pairs of chromosomes called homologous pairs. Each chromosome making up a homologous pair is known as a homologue. Both carry genes for same traits. The location of a gene on a chromosome is known as a locus.
44 Autosomes
2 Sex chromosomes
XX =
XY =

17. V. MEIOSIS, cont Gametes Egg and sperm cells Haploid or n
Contain 23 chromosomes
In fertilization, haploid (n) sperm fuses with haploid (n) egg → diploid (2n) zygote

18. V. MEIOSIS, cont Description of Meiosis
Special type of cell division that occurs to produce gametes
Occurs in ovaries, testes only
Involved specialized cells
DNA replicated once, cell divides twice
Produces 4 cells with ½ the original chromosome number
In humans,

19. V. MEIOSIS, cont

20. V. MEIOSIS, cont

21. V. MEIOSIS, cont
Nondisjunction – Failure of chromosomes to separate properly in meiosis

22. VI. GENETIC VARIATION

23. VI. GENETIC VARIATION, cont
Crossing Over
Further increases genetic variability
Occurs during prophase I when tetrads are forming
Piece of one sister chromatid breaks off & exchanges places with piece of sister chromatid of homologue
Known as chiasma
Occurs very frequently

24. VII. A COMPARISON OF MEIOSIS & MITOSIS

25. VIII. DNA – THE MOLECULE OF INHERITANCE
Chromosome
Single molecule of DNA wrapped in histone proteins. Proteins maintain chromosome structure & control DNA activity
Gene 25

26. VIII. DNA, cont Genome All of an organism’s DNA
Provides working instructions for cell through ______________________
Must be copied prior to cell division 26

27. IX. DISCOVERY OF DNA
Early 1900s – Scientists determined genes determined inherited characteristics. Also realized chromosomes were composed of DNA & protein.
Griffith (1928) – Studied 2 strains of bacteria. Determined pathogenicity could be transferred when living non-pathogens were exposed to remains of dead pathogens.
Avery (1944) – Identified “transforming substance” as DNA 27

28. IX. DISCOVERY OF DNA, cont
Hershey & Chase (1952)
Used bacteriophage with labeled phosphorus, sulfur
Tested bacterial cells, supernatant following exposure
Proved it was the DNA component that was injected into host cell and used to make new virus particles. 28

29. IX. DISCOVERY OF DNA, cont
Rosalind Franklin (late 1950s) – Produced x-ray crystallography image of DNA; “borrowed” by Watson & Crick
Watson & Crick
Realized DNA was a helix composed of 2 nucleotide strands
Franklin suggested backbone of DNA was composed of alternating sugar-phosphate molecules
Watson & Crick determined interior of DNA was made up of paired N-bases
Eventually deduced bases always paired a specific way
Chargaff – Chemically proved the same base-pairing rules that Watson & Crick proved structurally 29

30. X. A CLOSER LOOK AT DNA Monomers of DNA Nucleotides Composed of
Pyrimidines
Purines 30

31. X. A CLOSER LOOK AT DNA, cont
Structure of DNA
Each strand of nucleotides held together with
Double helix
2 nucleotide strands are antiparallel
Each strand has a 3’ end (terminus) and a 5’end; named for carbon on deoxyribose 31

32. X. A CLOSER LOOK AT DNA, cont
Base Pairing 32

33. XI. DNA REPLICATION DNA Replication
Prior to cell division, DNA must be replicated
Occurs during _____ or ________________ phase of mitosis, meiosis
Known as semiconservative model of replication
Meselson-Stahl Experiment 33

34. XI. DNA REPLICATION, cont.
Chromatids
Two identical DNA molecules
Result of replication
Term is only used when identical DNAs are physically attached; described as one chromosome made up of two sister chromatids
Centromere – Site where sister chromatids are most closely attached 34

35. XI. DNA REPLICATION, cont.
Steps of Replication:
DNA helicase unwinds the DNA double helix
Replication begins at specific points on the DNA molecule known as origins of replication. The Y-shaped region where new strands of DNA are elongating are called replication forks 35

36. XI. DNA REPLICATION, cont.
As DNA is “unzipped”, single-strand binding proteins hold the DNA open
A topoisomerase relieves tension creating by unwinding of DNA by making cuts, untwisting, & rejoining the nucleotide strand.
DNA polymerase can only add nucleotides to an already-existing strand so an RNA primer is synthesized to get replication going 36

37. XI. DNA REPLICATION, cont.
DNA polymerases add complementary nucleotides to each side of the DNA molecule.
DNA polymerase can only add nucleotides to the 3’ end of the growing strand, so the daughter DNA is synthesized 5’ – 3’, which means parental DNA is “read” _______________.
This means only one side of the DNA (3’ – 5’) molecule can be replicated as a continuous strand. Known as the leading strand. 37

38. XI. DNA REPLICATION, cont.
Synthesis of lagging strand
To synthesize the other new strand of DNA, DNA polymerase must work away from the replication fork. Leads to synthesis of short pieces of DNA known as Okazaki fragments.
DNA ligase binds fragments together to form a continuous strand of nucleotides.
Proofreading & Repair
DNA Polymerase proofreads nucleotides as they are added 38

39. XI. DNA REPLICATION, cont.
An Overview of Replication 39

40. XI. DNA REPLICATION, cont.
Telomeres
5’ ends of daughter strands cannot be completed because DNA polymerase can only add nucleotides to the 3’ end
Results in shorter and shorter DNA molecules with jagged ends
To protect genetic integrity, ends of chromosomes do not contain genes – instead there are nucleotide sequences known as telomeres
Contain nucleotide repeat sequences
Telomeres shorten each time cell divides - limits the number of times a cell can divide; thought to protect organism from cancer
Telomerase – Enzyme produced by stem cells, cancer cells that restores telomere length 40