Cell Growth & Division

1. Cell Growth & Division Biology  Pearland ISD

2. Cell Division • There are 2 main reasons cell divides: • The cell has more trouble trying to move nutrients and wastes across the cell membrane. • The larger a cell becomes, the greater the demand it puts on its DNA. • Bottom line – cells need to be replaced

3. Cell Cycle • The sequence of growth and division of a cell • An average cycle may be 22 hours • Three general periods: • resting phase • growth phase • division phase

4. G0 (Resting phase) • Non-dividing, differentiated state. • Most human cells are in G0 phase. • Liver cells: • Generally in G0, but can be “called back” to cell cycle by external cues. • Nerve & muscle cells: • Highly specialized. • Arrested in G0 & can never divide.

5. Interphase (Growth phase) • Most of the cell’s life is spent in interphase • Longest phase –(90% of cell’s growth) Centrioles – help to organize cell division Chromatin – DNA bound protein within the nucleus

6. Interphase (Growth phase) New DNA is formed during 3 phases: G1 – 1st period of growth 1. Increase in size. 2. Makes new proteins and organelles. S – DNA is synthesized or replicated 1. Chromosomes are replicated. 2. New DNA molecules are made. G2 – final cell growth 1. Shortest phase 2. Prepares cell for mitosis

7. S-Phase of the Cell Cycle Synthesis

8. 50 µm DNA • Genetic information = genome. • Packaged into chromosomes. • During the S phase, the chromosomes enter a relaxed state that allows the enzyme DNA polymerase to access the DNA double helix inside each chromosome.

9. Copying DNA Coil DNA into compact chromosomes Copying & Packaging DNA • When cell is ready to divide… • Copy DNA first, then… • Coil up doubled chromosomes like thread on a spool… • Now move DNA around cell without having it tangle & break.

10. DNA & Chromosomes • The DNA in a eukaryotic cell is organized into several linear chromosomes, whose organization is much more complex than the single, circular DNA molecule in a prokaryotic cell. • All eukaryotic cells store genetic information in chromosomes. • Most eukaryotes have between 10 and 50 chromosomes in their body cells. • Human cells have 46 chromosomes. • 23 nearly-identical pairs

11. Chromosomes A structure inside the cell’s nucleus containing long, tightly-coiled strands of DNA wrapped around proteins.

12. Structure of Chromosomes • Chromosomes are composed of a complex of DNA and protein called chromatinthat condenses during cell division. • DNA exists as a single, long, double-stranded fiber extending chromosome’s entire length. • Each unduplicated chromosome contains one DNA molecule, which may be several inches long.

13. Chromosomes Maternal set of chromosomes (n = 3) 2n = 6 Paternal set of chromosomes (n = 3) Two sister chromatids of one replicated chromosome Centromere Two non-sister chromatids in a homologous pair Pair of homologous chromosomes (one from each set)

14. Pair of sister chromatids Chromosomes Centromere (DNA that is hidden beneath the kinetochore proteins) • The centromereis a constricted region of the chromosome containing a specific DNA sequence, to which is bound 2 discs of protein called kinetochores. Kinetochore proteins One chromatid (dark blue) One chromatid (light blue)

15. Chromosomes • In a diploid cell, the chromosomes occur in pairs. • The 2 members of each pair are called homologous chromosomes or homologues. • In a cell in which DNA synthesis has occurred all the chromosomes are duplicated and thus each consists of two identical sister chromatids.

16. Chromosomes • Non-homologous chromosomes: • Look different. • Control different traits. • Sex chromosomes: • Are distinct from each other in their characteristics. • Are represented as X and Y. • Determine the sex of the individual, XX being female, XY being male.

17. Chromosome Duplication • In preparation for cell division, DNA is replicated and the chromosomes condense. • Each duplicated chromosome has two sister chromatids, which separate during cell division.

18. 0.5 µm A eukaryotic cell has multiplechromosomes, one of which is represented here. Before duplication, each chromosomehas a single DNA molecule. Chromosomeduplication(including DNA synthesis) Centromere Once duplicated, a chromosomeconsists of two sister chromatidsconnected at the centromere. Eachchromatid contains a copy of the DNA molecule. Sisterchromatids Separation of sister chromatids Mechanical processes separate the sister chromatids into two chromosomes and distribute them to two daughter cells. Sister chromatids Centrometers

19. Non-sister chromatids Centromere Duplication Sister chromatids Sister chromatids Two Unduplicated Chromosomes Two Duplicated Chromosomes Chromosome Duplication • Because of duplication, each condensed chromosome consists of 2 identical chromatidsjoined by a centromere. • Each duplicated chromosome contains 2 identicalDNA molecules (unless a mutation occurred), one in each chromatid. • Homologous chromosomes are made up of sister chromatids joined at the centromere.

20. DNA Replication • Replication begins when helicase enzymes unzip various locations along the chromosome, separating the two complementary strands of DNA. • DNA polymerase molecules read each original, or template, strand and synthesize new DNA strands containing complementary genetic information. • Each replicated double helix consists of a template strand and a new strand in a process called semiconservative replication.

21. Copying DNA • A dividing cell duplicates its DNA. • Creates 2 copies of all DNA. • Separates the 2 copies to opposite ends of the cell. • Splits into 2 daughter cells. • But the DNA stays loosely wound in the nucleus. • If you tried to divide it like that, it could tangle & break. DNA Cell Nucleus

22. Organizing & Packaging 4 chromosomesin thisorganism DNA has been “wound up” DNA in chromosomes in everyday “working” cell. DNA Cell Cell Nucleus Nucleus DNA in chromosomes in cell getting ready to divide

23. Organizing & Packaging Nucleosome Chromosome DNA Double Helix Coils Supercoils Histones

24. DNA Synthesis • Matching base pairs allows DNA to be easily copied.

25. Base Pairs • Base-pairing rules • A binds with T • (AU if DNA-RNA hybrid) • G binds with C

26. DNA Synthesis: Replication • DNA starts as a double-stranded molecule with matching bases (A:T, C:G) • Then, it unwinds and unzips…

27. DNA Replication • Strands “unzip” at the weak hydrogen bonds between bases. Replication Fork

28. Enzymes DNA polymerase Adds new bases Replication DNA basesin nucleus DNA polymerase

29. DNA Replication • Build daughter DNA strand. • Use original parent strand as “template”. • Add new matching bases. • Synthesis enzyme = DNA polymerase. DNA Polymerase

30. DNA polymerase DNA polymerase New Copies of DNA • Get 2 exact copies of DNA to split between new cells.

31. Double-strandedHuman Chromosomes Ready for Mitosis

32. DNA Must be Duplicated… Chromosomes in Cell DNA in Chromosomes 4 single-stranded chromosomes Cell Duplicated Chromosomes Nucleus Duplicated Chromosomes Cell 4 double-stranded chromosomes

33. Terms to know • Chromosome – contains genetic information (DNA) passed from one generation to the next • Spindle – microtubule that helps separate chromosomes A – centromere: center of chromosome B – chromatids: two identical “sister” parts of the chromosome

34. Following Interphase .. MITOSIS

35. Mitosis Takes place within the nucleus of the cell.

36. Mitosis (Division phase) 4 Phases: (PMAT) • Prophase • Metaphase • Anaphase • Telophase

37. 4 phases that blend from one to another

38. Prophase • 1st and longest phase of mitosis • Chromatin become chromosomes • Chromatids are joined by centromere • Nucleus disappears • Centrioles migrate to poles • Spindles are formed

39. Metaphase • 2nd phase of mitosis • Chromosomes meet in the middle of cell • Pulled by spindles • Each chromosome is attached to top of spindle

40. Anaphase • 3rd phase of mitosis • Centromeres are split apart • Chromatids are pulled apart and begin to drift to opposite poles

41. Telophase • Final phase of mitosis • Begins when chromatids reach poles • New nucleus starts to form • Chromosomes start to unwind • Spindles disappear • Cytoplasm begins to divide

42. Each daughter cell has an identical set of chromosomes Cytokinesis • Cytoplasm pinches in half

44. CellCycle G0 phase resting

45. When Cells Don’t Stop … Cancer

46. Cancer • Cancer is a disorder where the cell has uncontrolled growth. • Cancer cells do NOTrespond to regulators. • This causes the cells to form masses called tumors, which can damage surrounding tissues.

49. Cancer Development Cancer develops only after a cell experiences ~6 key mutations (“hits”). • Unlimited growth • Turn ON growth promoter genes. • Ignore checkpoints • Turn OFFtumor suppressor genes. • Escape apoptosis • Turn OFF suicide genes. • Immortality = unlimited divisions • Turn ON chromosome maintenance genes. • Promotes blood vessel growth • Turn ON blood vessel growth genes. • Overcome anchor & density dependence • Turn OFF touch-sensor gene.

50. Cancer Triggers • Mutations in cells can be triggered by: • UV radiation • Chemical exposure • Radiation exposure • Heat • Cigarette smoke • Pollution • Age • Genetics