1. Cell Growth and Division
Chapter 10 -
Cell Growth and Division

2. This liver cell has almost completed the process of cell division
This liver cell has almost completed the process of cell division. During cell division, a cell splits into two roughly equal daughter cells (magnification: 11,500×).

3. 10-1 Cell Growth, Division, and Reproduction
Limits to Cell Size
What are some of the difficulties a cell faces as it increases in size?
The larger a cell becomes, the more demands the cell places on its DNA and the more trouble the cell has moving enough nutrients and wastes across the cell membrane.

4. Limits to Cell Size DNA Overload Exchanging Materials
As a cell grows in size, its DNA does not
“information crisis”
Exchanging Materials
getting food into and wastes out of the cell
Ratio of Surface Area to Volume
volume increases more rapidly than surface area

6. Division of the Cell
Before a cell becomes too large, it divides into two new “daughter cells”
This process is called “cell division”
Cell division solves all 3 problems

7. Solutions: DNA Overload Exchanging Materials
Before cell division occurs, the cell replicates (copies) all of its DNA so that each daughter cell will get a copy of genetic information
Exchanging Materials
Reduces cell volume
Ratio of Surface Area to Volume
Increases Surface Area to Volume Ratio

8. Cell Division and Reproduction
How do asexual and sexual
reproduction compare?
Reproduction (the formation of new individuals) is one of the most important characteristics of living things.

9. Asexual Reproduction Offspring are produced from a single parent cell
Simple, efficient, effective
Enables populations to increase in number very quickly
The two daughter cells are genetically identical to the parent cell (in most cases)
Exs. – Bacteria – Single-celled organisms

10. Sexual Reproduction
Offspring are produced by inheriting some of their genetic information from each parent cell
Involves the fusion of genetic information from two separate parent cells
Allows for genetic diversity in populations
The daughter cells are genetically different from the parent cell
Exs. – Most animals and plants

11. Comparing Methods of Reproduction
Asexual
Faster Reproduction
when conditions are right
Lack of Genetic Diversity

12. More Genetic Diversity
Sexual
Slower Reproduction
More Genetic Diversity
Able to survive changes in environmental conditions

13. Comparing Asexual & Sexual Reproduction
Parent Cells
Offspring

14. 10-2 The Process of Cell Division
Prokaryotic Chromosomes
Prokaryotes do not have a nucleus
Their DNA is found in the cytoplasm
Most Prokaryotes contain a single, circular DNA chromosome

15. Eukaryotic Chromosomes
DNA is contained in the nucleus
Chromosomes are made up of DNA and proteins.
Chromosomes are not visible except during division.
Before division, each chromosome is replicated (copied).

16. Chromosomes become visible at the beginning of cell division.
Each chromosome consists of two identical “sister” chromatids.
Each pair of chromatids is attached at an area called the centromere. Centromeres are usually located near the middle of the chromatids, some lie near the ends.

17. A Human Chromosome
This is a human chromosome shown as it appears through an electron microscope. Each chromosome has two sister chromatids attached at the centromere.

18. The Prokaryotic Cell Cycle
Takes place very rapidly under ideal conditions
DNA is replicated when bacteria reach a certain size
Cell Division begins when replication is complete

19. The 2 DNA molecules attach to different regions of the cell membrane
The cell is pinched inward, dividing the cytoplasm and chromosomes between the two new cells
This results in a form of asexual reproduction called binary fission

20. The Eukaryotic Cell Cycle
The cell cycle consists of 4 Phases:
G1, S, G2, and M.
The length of the cell cycle and the length of each phase depends on the type of cell.

21. Interphase – a period of growth between cell divisions
Divided into 3 parts:
G1 - Cell Growth
Cells do most of their growing in this phase
S – DNA Replication (Synthesis)
DNA is replicated (copied)
The cell contains 2 copies of its DNA
G2 – Preparing for Cell Division
Usually the shortest phase
When completed, cell division begins

22. M Phase – Cell Division Produces 2 identical daughter cells
Two Stages:
Mitosis- Division of the Nucleus
Cytokinesis – Division of the Cytoplasm

23. Events of the Cell Cycle
During the cell cycle, the cell grows, replicates its DNA, and divides into two daughter cells.

24. Mitosis
Mitosis – the part of cell division during which the nucleus divides.
  Biologists divide the events of mitosis into four phases:
prophase
metaphase
anaphase
telophase
Mitosis may last anywhere from a few minutes to several days.

25. Prophase Longest phase Chromosomes become visible
Centrioles move to opposite sides of the nucleus
Spindles form
Nuclear membrane
breaks down

26. Metaphase Lasts only a few minutes
Chromosomes line up in the center of the cell
Microtubules connect the centromere to the spindles

27. Anaphase
Centromeres joining sister chromatids separate to become individual chromosomes
Chromosomes move apart
Ends when chromosomes are at the poles of the spindle.

28. Telophase Chromosomes begin to fade into a tangle of dense material
Nuclear envelope reforms
Spindle breaks apart
Nucleolus becomes visible
Last phase of mitosis

29. Cytokinesis Last phase of the M phase Division of the cytoplasm occurs
Cell plate is formed in plants

30. 10-3 Regulating the Cell Cycle
Controls on Cell Division
Cells grown in the lab will continue to divide until they come into contact with other cells. Then they stop growing.
If you remove cells, the cells will divide again until they touch other cells.
This shows that controls on cell growth and division can be turned on and off.

31. Cell Growth

32. The Discovery of Cyclins
For many years, biologists searched for a signal that would regulate the cell cycle – something that would tell cells when it was time to divide, replicate their chromosomes, or enter another phase of the cell cycle.
In the 1980’s, a protein was discovered that when injected, would cause a nondividing cell to form a mitotic spindle.
They named this protein Cyclin.

33. Cyclins are proteins that regulate the timing of the cell cycle.
Scientists have discovered a family of cyclins that regulate the timing of the cell cycle in eukaryotic cells.

34. Cell Cycle Regulation

35. Regulatory Proteins
The cell cycle is controlled by regulatory proteins both inside and outside the cell.
Internal Regulators – proteins that monitor and respond to events inside the cell.
Examples:
Making sure the a cell does not enter mitosis until its chromosomes have replicated
Preventing a cell from entering anaphase until the spindle fibers have attached to the chromosomes

36. External Regulators Examples:
proteins that respond to events outside the cell.
Can direct the cell to speed up or slow down their cell cycles.
Examples:
Growth Factors
Stimulate the growth and division of cells
Important during embryonic development and wound healing

37. Cell Growth and Healing

38. Apoptosis A process of programmed cell death
Once triggered, a cell undergoes a series of controlled steps leading to its self-destruction:
The cell and its chromatin shrink
Then parts of the cell’s membranes break off
Neighboring cells then quickly clean up the cell’s remains

39. Apoptosis plays a key role in development by shaping the structure of tissues and organs in plants and animals.
Example – the embryonic development of a mouse’s foot
The space between the toes is caused by cell death through Apoptosis
When Apoptosis does not occur as it should, a number of diseases can result
Examples: Cell loss in AIDS and Parkinson’s disease from too much Apoptosis

40. Apoptosis

41. Cancer: Uncontrolled Cell Growth
Cancer is a disorder in which body cells lose the ability to control cell growth and division
Cancer cells do not respond to the signals that regulate the growth of most cells.
As a result, most cancer cells divide uncontrollably.

42. Cancer cells form a mass of cells called a tumor
Not all tumors are cancerous
Some tumors are benign, or noncancerous
A benign tumor does not spread to surrounding healthy tissue or to other parts of the body.

43. Cancerous tumors are malignant
Malignant tumors invade and destroy surrounding healthy tissue
As cancer cells spread:
They absorb the nutrients needed by other cells
Block nerve connections
Prevent organs from functioning properly
This disrupts the delicate balances of the body, and life-threatening illness results

45. Lung Cancer

46. What Causes Cancer?
Cancer is caused by defects in the genes that regulate cell growth and division
Sources of defects:
Smoking or chewing tobacco
Radiation exposure
Defective genes
Viral Infection

47. All cancers have one thing in common The control over the cell cycle has broken down.
Many cells have a defect in the gene p53. This gene normally stops the cell cycle until all of the chromosomes have properly replicated.
Cells lose the information they need to be able to respond to the signals that normally control cell growth.

48. Treatments for Cancer
When a cancerous tumor is located, it can often be removed by surgery
Example – Melanomas (skin cancer)
Cancer cells grow rapidly so they must copy their DNA quickly.
This makes them vulnerable to damage from radiation

49. Chemical compounds that would kill cancer cells (or at least slow their growth) are used in chemotherapy.
Great advances in chemotherapy has made it possible to cure some forms of cancer.
However, because chemotherapy compounds target rapidly dividing cells, they also interfere with cell division in normal, healthy cells.

50. Chemotherapy produces some serious side effects in some patients
Researchers are searching to find highly specific ways in which cancer cells can be targeted for destruction while leaving healthy cells unaffected
Cancer is a serious disease. It is a disease of the cell cycle and conquering it will require a deeper understanding of the processes that control cell division

52. 10-4 Cell Differentiation
From One Cell to Many
How do cells become specialized for different functions?
Multicellular organisms start life as just one cell
Living things pass through a developmental stage called an embryo from which the adult organism is gradually produced

53. During the development process, an organism’s cells become more and more differentiated and specialized for particular functions

54. Differentiation
Differentiation is the process by which cells become specialized
During the development of an organism, cells differentiate into many types of cells
A differentiated cell has become different from the embryonic cell that produced it
The cell is specialized to perform certain tasks
Exs. – contraction, photosynthesis, protection

55. Mapping Differentiation
The process of differentiation determines a cell’s ultimate identity
In some organisms, a cell’s role is determined at a specific point in development
Each time an organism develops, the process is the same

57. Differentiation in Mammals
In mammals and other organisms, cell differentiation is a flexible process that is controlled by a number of interacting factors in an embryo
Adult cells generally reach a point at which their differentiation is complete (they can no longer become other types of cells)

58. How are all of the specialized, differentiated types of cells in the body formed from just a single cell?
Such a cell is called “totipotent”
It is literally able to do everything and to develop into any type of cell in the body

59. Stem Cells What are Stem Cells?
Stem cells are unspecialized cells from which differentiated cells develop
They are at the base of a branching “stem” of development from which different cell types form
They have the potential to develop into other cell types

60. Human Development
After about 4 days of development, a human embryo forms into a blastocyst, a hollow ball of cells with a cluster of cells inside called the inner cell mass
Even at this early stage, the cells of the blastocyst begin to specialize.

61. The cells of the inner cell mass are pluripotent
Pluripotent cells can develop into most (but not all) of the body’s cell types

62. Embryonic Stem Cells
These are pluripotent cells found in the early embryo
These cells can be grown in culture and coaxed to differentiate into nerve cells, muscle cells, and even into sperm and egg cells

64. Typically, stem cells of a given organ or tissue produce only the types of cells that are unique to that tissue
Examples:
Adult stem cells in bone marrow can develop into several different types of blood cells
Stem cells in the brain can produce neurons (nerve cells)

66. Adult Stem Cells
These are groups of cells that differentiate to renew and replace cells in the adult body
They have limited potential and are called multipotent, meaning that they can develop into many types of differentiated cells

68. Potential Benefits
Stem cells offer the potential benefit of using undifferentiated cells to repair or replace badly damaged cells and tissues
Stem cells may have an important impact on human health
Stem cells may be able to repair the cellular damage of some conditions such as:
Heart muscle cells following a heart attack
Brain cell damage caused by a stroke
Paralysis from spinal cord injuries

69. Ethical Issues
Human embryonic stem cell research is controversial because the arguments for it and against it both involve ethical issues of life and death
Most techniques for harvesting embryonic stem cells cause the destruction of the embryo
Unlike embryonic stem cells, adult stem cells have raised few ethical questions as they can be obtained from the body of a willing donor

70. In the future, it may be possible to address these concerns with a technological solution
Recent experiments suggest that it may be possible to extract a small number of embryonic stem cells without damaging the embryo itself
Other experiments have shown that it is possible to reprogram adult cells by switching “on” a few genes, causing them to function like embryonic stem cells

71. In this way, there would be no need to involve embryos at all
It could also make it possible to tailor specific therapies to fit the needs of each individual patient
If successful, methods like these might allow research to go forward while avoiding any destruction of embryonic life