1. Cell Biology
Unit Seven

2. The Cytoskeleton
The cytoskeleton is a series of tubules and filaments that have a variety of functions:
~ determine cell shape
~ organelle attachment
~ provide cell movement
~ provide organelle movement
~ spindle formation

3. The Cytoskeleton
The tubules and filaments of the cytoskeleton are comprised of protein and are divided into three categories:
~ microtubules
~ microfilaments
~ intermediate filaments

4. The Cytoskeleton
Microtubules are hollow tubes that are the largest of the three components
In cross section they appear as thirteen subunits (protofilaments) made of globular protein units called tubulin

5. The Cytoskeleton

6. The Cytoskeleton
Microtubules are the major component of the cytoskeleton, centrioles, flagella & cilia

7. The Cytoskeleton
Microfilaments are solid protein polymers found in muscle cells
There are thin microfilaments (actin) and thick microfilaments (myosin)
These microfilaments produce muscle cell contractions

8. The Cytoskeleton

9. The Cytoskeleton
Intermediate filaments are solid protein polymers found in several different forms
They comprise part of the cytoskeleton and aid in the positioning of organelles

10. The Cytoskeleton
Intermediate filaments confer most of the mechanical strength of the cytoskeleton

11. Flagella and Cilia
Microtubules form the skeleton of flagella and cilia
The pattern is a 9+2 arrangement of microtubules that is covered with the cell membrane
There are nine pair of microtubules that surround two singles

12. Flagella and Cilia
The paired microtubules have ATPase attached which provides the energy needed for movement
The movement is thought to be created by sliding

13. Flagella and Cilia

14. Centrioles
Centrioles are bundles of microtubules that are arranged in nine triplet sets
In animals there are two per cell, set perpendicular to each other
Centrioles form the centrosome which produce microtubules for use in the cell

15. Centrioles
Centrioles separate during cell division producing the spindle (spindle fibers)
Cilia & flagella grow from centrioles that have migrated to the plasma membrane
Two of each of the triplet sets will begin to grow, forming the pairs of microtubules in these strucuture

16. Centrioles

17. DNA Replication
DNA replication occurs during the S phase of interphase in preparation for cell division
It is semi-conservative, meaning each strand of the original acts as a template for a new strand

18. DNA Replication DNA replication occurs in two stages:
+ synthesis of nucleotides
+ synthesis of new DNA
strands

19. DNA Replication DNA nucleotides are synthesized in the cytoplasm
They are first synthesized with ribose, then converted to deoxyribose
They are then transported into the nucleus for DNA replication

20. DNA Replication
DNA replication occurs in the nucleus under the direction of several enzymes
Synthesis always occurs in the 5’→3’ direction with the addition of nucleotides on the 3’ end

21. DNA Replication

22. DNA Replication

23. DNA Replication

24. The Characteristics and Functions of Cell Division (Mitosis)
Begins with a diploid cell & ends identical diploid cells
Occurs for growth, repair & replacement

25. The Characteristics and Function of Meiosis
Production of gametes
Begins with a diploid sex cell & ends with non-identical haploid gametes
Assures correct chromosome numbers in offspring

26. Interphase G1 – organelles double S – DNA replicates
G2 – proteins produced

27. Mitosis
Prophase
Metaphase
Anaphase
Telophase

29. Plant Mitosis

30. Cytokinesis

31. Significance of Cell Division
Cell division (mitosis) is an efficient process that assures the correct number of chromosomes will be found in the new daughter cells

32. Significance of Cell Division
Chromosome number is a critical characteristic in determining a species and the viability of an organism
Correct chromosomes numbers are essential for successful fertilization events

33. Significance of Cell Division
In animals, increasing or decreasing chromosome numbers has deleterious effects
In plants, the increase in the number of chromosomes can lead to polyploidy

34. Significance of Cell Division
Cellular homeostasis is maintained by a number of factors:
+ cell size
+ nutrient availability
+ DNA damage
+ growth factors
+ cell population density

35. Significance of Cell Division

36. Significance of Cell Division
Surface to volume ratio determines the maximum size a cell can obtain
The amount of nutrients available is a factor in the rate of growth
Growth factors such as cyclins, Cdks and hormones influence the speed and amount of cell growth

37. Significance of Cell Division
The density of cells also controls cell growth – loss of cells stimulates cell division, adequate numbers of cells inhibit the process

38. Cancer
Cell division is orchestrated by proteins and hormones so that growth and division is controlled
Cancer cells are normal body cells that are transformed. In this transformed state, they ignore the controls of cell division and multiply unchecked

39. Cancer
Normally, the immune system destroys these cancer cells, but some may escape destruction and then form a tumor
A tumor is a mass of cancer cells found within otherwise normal tissue

40. Cancer
A tumor is said to be benign if the cancer cells remain within the tumor. These can usually be removed through surgery
A malignant tumor contains cancer cells that are invasive, meaning they spread to other tissues. A person with a malignant tumor is said to have cancer

41. Cancer
Remember - cell division is orchestrated by proteins and hormones so that growth and division is controlled
Oncogenes are those that initiate cell division, but in an accelerated and exaggerated process

42. Cancer
Tumor suppressor genes are those that prevent cell division and promote normal cell death
If tumor suppressor genes are altered, inactivated or removed the result can be cancer

43. Cancer
Cancer can occur through genetic abnormalities, activating oncogenes and/or inactivating tumor suppressor genes
Environmental influences can also affect the activity and inactivity of these genes

44. Cancer Environmental influences include: ~ diet ~ exercise
~ sun exposure
~ smoking
~ altering of DNA

45. Meiosis
Meiosis is the cell division process by which gametes are produced
It occurs only in sex cells that are found in the gonads

46. Meiosis
The process goes through two meiotic divisions – meiosis I and meiosis II

47. Meiosis
Homologous chromosomes

48. Meiosis

49. Meiosis

50. Meiosis

51. Meiosis vs. Mitosis

52. Spermatogenesis

53. Oogenesis