1. Cell Growth and Division
Chapter 5
Cell Growth and Division

2. Cell Cycle Interphase Mitosis G1 S G2 Prophase Metaphase Anaphase
Telophase

3. Stages of the cell cycle

4. G1 (Gap 1) The first stage of a cell’s life.
Cell carries out normal functions
increases to the mature size
Organelles increase in number
Longest stage of the cell’s life
Cell must “meet” the checkpoint

5. S (synthesis) DNA replication occurs
At the end of the stage, two complete and identical copies of DNA exist

6. G2 (Gap 2) The third stage Normal functions continue
More growth occurs
Cell must “meet” the checkpoint

7. M (mitosis) Fourth stage Two phases Mitosis Cytokinesis
Division of the cell nucleus and its contents
Cytokinesis
Divides the cell cytoplasm and its organelles
Results in two daughter cells with complete and identical sets of DNA

8. Why cells divide Grow and change Repair worn out parts
Replace dead cells

9. Cells divide at different rates
Due to age (cells divide faster and more often in developing children)
Due to wear-and-tear (cells in abrasive areas like the digestive tract will divide more often; lungs, liver and other organs divide only in response to injury or cell death)

10. Cells divide at different rates
Cells that divide rarely
Enter G0
Continue to function
Unlikely to divide

11. Cell size is limited
The ratio of cell surface area – to – volume limits cell size
Nutrients, oxygen, and other materials must DIFFUSE through the membrane to the inside of the cell
Diffusion is the method of transport of materials internally
If the cell increases in size, volume increases faster than surface area, so diffusion would NOT be efficient

12. Role of chromosomes Carry genetic material
Actively involved in protein production and DNA replication
Copied and passed to new generations

13. Chromosome structure
Normally exist as chromatin (long uncoiled thread loosely associated with histones)
Coil to form short, thick chromosomes before cell division
DNA is not active for cell functions when in coiled chromosome form

16. Histones are proteins DNA wraps around for organization (DNA + histones = chromatin)
Telomeres, at the end of each DNA molecule, are repeating sets of nucleotides that DO NOT form genes
They prevent chromosomes from attaching to each other
They help prevent the loss of genes

17. Interphase Busiest time of cell cycle
Make ATP, repair parts, excrete wastes
Make proteins, organelles, copy chromosomes
3 stages
G1-cell grows in size, produces protein
S-chromosomes are copied
G2-short growth period, organelles made

18. Mitosis Prophase First and longest phase
Chromatin coils into chromosomes (each has 2 halves called sister chromatids held together by a centromere)
Nucleus disappears
Nucleolus and nuclear envelope dissolve
Centrioles migrate to poles
Spindles form

19. Mitosis Metaphase Shortest phase
Chromosomes attach to spindles at centromere
Chromosomes line up at equator
Each chromatid attached to its own spindle (to make sure that each new cell gets one copy)

20. Mitosis
Anaphase
Sister chromatids pull apart at the centromere and separate
Spindles shorten

21. Mitosis Telophase Chromatids reach opposite poles
Chromosomes uncoil to form chromatin
Nucleolus reappears
Nuclear envelope reforms
Plasma membrane separates the two daughter cells

22. Division of cytoplasm (cytokinesis)
Occurs after telophase
In animals
Plasma membrane pinches the cell into 2 parts
In plants
A cell plate forms at the cell’s equator to separate the 2 cells
Two completed cells are identical to each other and to the original cell

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Plant Cell Undergoing Mitosis
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24. Results of mitosis Two new cells with identical chromosomes
Can now function as the original cell did

25. Control of the cell cycle
External factors
Cell-to-cell contact
Growth factors that bind to the outside of the membrane to stimulate growth or cell division
Hormones can stimulate certain cell types to grow and divide

26. Control of the cell cycle
Internal factors
Kinases
Enzymes that transfer phosphate (and energy) to a target molecule
Cyclins
Proteins
Control kinases
Made/released at certain times during the cell cycle

27. Control of the cell cycle
Apoptosis – programmed cell death
Internal and external signals activate genes that produce self-destructive enzymes
Targeted cell is recognized and “gobbled” up by the immune system
Cell parts/components are recycled

28. Cancer
Cancer – uncontrolled cell division; regulation of the cell cycle is disrupted
Tumors – disorganized clumps of cancer cells
-benign – cancer cells are clumped together; cured by removal
- malignant – tumor allows some cells to break away; carried through blood or lymph to other parts of the body to form more tumors

29. Cancer Tumors are harmful because
They steal nutrients and blood supply away from healthy tissue
They put pressure on surrounding tissues/organs
They can metastasize

30. Cancer
Caused by damage to specific genes that control protein production for cell-cycle regulation
Mutations caused by carcinogenes
Mutations are found in 2 types of genes
Oncogenes – accelerate the cell cycle
Cell-cycle “brakes”

31. Asexual reproduction
Production of offspring from one parent; offspring are genetically identical to the parent
Binary fission
Similar to mitosis
Occurs in prokaryotes (bacteria)

32. Binary fission Bacteria Do not have nuclei Do not have spindle fibers
Have one, circular-shaped chromosome

33. Binary Fission

34. Asexual reproduction Eukaryotes Some reproduce asexually using mitosis
It can be in many forms:
Budding
Fragmentation
Vegetative reproduction

35. Multicellular organisms
Levels of organization
Cells work together
Tissue-large groups of cells that carry out the same function
Organ-groups of tissues that work together
Organ systems-organs that carry out similar functions
Organism-groups of organ systems that help maintain homeostasis

36. Cell differentiation
Process in which cells become specialized for specific structures or functions
Only certain genes are expressed
The location of the cells in early embryonic development can determine how the cells differentiate
Vertebrate embryos have 3 layers
Outer layer becomes skin and nervous system
Middle layer becomes bones, muscles, kidneys
Inner layer becomes internal organs

37. Stem cells Unique body cells that can
1. divide and renew themselves for long periods of time
2. remain undifferentiated in form
3. differentiate into a variety of specialized cell types

38. Stem cells When stem cells divide they can
1. produce two more stem cells Or
2. produce one stem cell and one specialized cell

39. Stem cells Adult stem cells
Can be extracted, grown in the lab, and put back in the patient
Decreases transplant rejection
Avoids ethical issues of embryonic stem cells
Disadvantages
Few in number
Hard to isolate
Difficult to grow in culture

40. Stem cells Embryonic stem cells
Come from donated embryos grown in culture (usually result from in-vitro fertilization)
Can form any cells in the body
Disadvantages
Can be rejected by the patient’s immune system
Could grow unchecked producing a tumor
Ethical issues: obtaining the stem cells results in destruction of the embryo (life at conception?)