1. Cell Growth and Replication

2. Why Do Cells Divide Instead of Just Growing Bigger and Bigger?
The cell's DNA would no longer be able to serve the increasing needs of the growing cell.
The cell has more trouble moving enough nutrients and wastes across the cell membrane.
Larger cells have a smaller ratio of surface area to volume.

3. Prokaryotic vs. Eukaryotic
Prokaryotic Cell Division:
Simple matter of separating the contents of the cell into two parts.
Eukaryotic Cell Division:
Cell Cycle

4. Eukaryotic DNA Prokaryotic DNA
Located in the nucleus in the form of chromatin/ chromosomes
located in the cytoplasm
Have a single circular DNA molecule (usually referred to as the cell's chromosome)

5. Eukaryotic Cell Cycle
Cell Cycle - Series of events that cells go through as they grow and replicate.
Interphase - Period of the cell cycle between cell divisions (consists of S, G1, and G2 phase)
M Phase –Mitosis (division of the cell nucleus) Cytokinesis (division of the cytoplasm)

6. Cell Cycle- Interphase
G1 Phase – Period of intense growth before DNA replication
S Phase – DNA (chromosome) replication takes place, still little cell growth
G2 Phase – Period of more growth and final preparations before cell starts dividing.

7. G1 = making the key decision of whether the cell should divide, delay division, or enter a resting stage.
G0 = resting stage (Liver cells, for instance, enter mitosis only around twice a year.)
The G1 checkpoint is where eukaryotes typically arrest the cell cycle if environmental conditions make cell division impossible or if the cell passes into G0 for an extended period. In animal cells, the G1 phase checkpoint is called the restriction point
There are 3 “checkpoints” that allow the cells to continue moving through the cell cycle.

8. What do all of these have in common?
growth from an infant to an
adult
2) repairing or replacing damaged
issues/organs
3) cancer

9. Is Mitosis Asexual or Sexual?!??

10. Asexual Reproduction = Mitosis
Asexual Reproduction - Reproduction of genetically identical cells to the parent cell without the fusion of gametes; not necessary to have two parents
Examples include:
Single-celled organisms
Source of new cells when a multicellular organism grows and develops (skin cell, liver cell)

12. Four Phases of Mitosis
Prophase - Chromosomes visible/centrioles; nuclear envelope disappears
Metaphase – Centriole go to opposite ends of the cell; spindle fibers emerge from the centrioles; chromosomes line up in middle of cell
Anaphase - Sister chromatids are pulled to opposite ends of cell
Telophase - Chromosomes condense back to chromatin and nuclear envelope reappears
(The four phases are followed by Cytokinesis)

13. Four Phases of Mitosis

14. Cytokinesis Usually occurs at the same time as telophase.
Cytokinesis - The division of the cytoplasm itself.

15. Cytokinesis: Plant vs. Animal Cells
The cell membrane is pinched into two nearly equal parts = cleavage furrow.
Plant Cells:
A structure known as the cell plate forms midway between the divided nuclei and gradually develops into a separating membrane.
A cell wall then begins to appear in the cell plate.

16. What Phase Of the Cell Cycle Is It?B C D E F

17. What Phase Of the Cell Cycle Is It?B C
Anaphase D E F

18. What Phase Of the Cell Cycle Is It?B C
Anaphase
Telophase D E F

19. What Phase Of the Cell Cycle Is It?B C
Anaphase
Telophase
Cytokinesis D E F

20. What Phase Of the Cell Cycle Is It?B C
Anaphase
Telophase
Cytokinesis D E F
Interphase

21. What Phase Of the Cell Cycle Is It?B C
Anaphase
Telophase
Cytokinesis D E F
Interphase
Metaphase

22. What Phase Of the Cell Cycle Is It?B C
Anaphase
Telophase
Cytokinesis D E F
Interphase
Metaphase
Prophase

23. Lets take a deeper look at what DNA is before we learn how it replicates...
Deoxyribonucleic Acid (DNA) - The material inside the nucleus that carries all the genetic information
Responsible for determining all organism’s traits
Eye color, body structure, and cellular enzyme production

24. The Components of DNA
DNA is a long molecule made up of repeating individual units called nucleotides
Nucleotides are made up of three parts:
Sugar
Phosphate Group
Nitrogenous Base

25. Nucleotides Put Together = DNA3’ 5’ 3’ 5’

26. Nitrogenous Bases DNA contains four nitrogenous bases: Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)

27. Complimentary Bases [A] = [T] [G] = [C]
Chargaff discovered that there were always equal amounts of A & T. And equal amounts of C & G in cells.
Adenine pairs with Thymine, and Guanine pairs with Cytosine
The complimentary bases are held together by weak hydrogen bonds.
(No matter what organism it is!!!!)
[A] = [T]
[G] = [C]

28. Purines and Pyrimidines
Purines have two rings in their structures.
Adenine and guanine belong to this group
Pyrimidines have one ring in their structure.
Cytosine and thymine belong to this group

29. Structure of DNA Phosphate Group & Deoxyribose Sugar Nitrogenous Bases
Form the backbone or sides of the ladder.
Nitrogenous Bases
Form the “rungs” of the ladder or middle of the molecule.

30. The Shape of DNA
DNA looks like a “twisted ladder” called a Double Helix.

31. Discovering DNA
Rosalind Franklin - Used X-ray diffraction; Showed the X-shaped pattern of DNA (helix shape)
Watson and Crick – Two scientists that discovered the double helix shape in 1953

32. Chromosome
Genes
Long, continuous single piece of DNA, contains many genes
Sequence of DNA that codes for a protein and thus determines a trait

33. Chromosomes
In eukaryotic cells, the genetic information that is passed on from one generation of cells to the next is carried by chromosomes.
The cells of every organism have a specific number of chromosomes
The cells of fruit flies have 8 chromosomes.
Human cells have 46 chromosomes.
Carrot cells have 18 chromosomes.

34. Chromosomes
Well before cell division, each chromosome is replicated, or copied.

35. Chromosomes
Each chromosome consists of two identical “sister” chromatids.
When the cell divides, the “sister” chromatids separate from each other.
One chromatid goes to each of the two new cells.

36. Chromosomes
Each pair of chromatids is attached at an area called the centromere.

37. Chromosome Structure DNA molecules are surprisingly long
The chromosome of the prokaryote E. coli, which can live in the human colon, contains 4,639,221 base pairs!
Analogy: Imagine trying to pack a 300-meter length of rope into your school backpack!
DNA must be dramatically folded and tightly packed to fit within the cell

38. Cell Cycle- Interphase
G1 Phase – Period of intense growth before DNA replication
S Phase – DNA (chromosome) replication takes place, still little cell growth
G2 Phase – Period of more growth ; organelles replicate; final preparations before cell starts dividing.

39. Cell Cycle – M Phase (cell division)
Cell Division - The process by which a cell divides into two new “daughter” cells.
M Phase –Mitosis (division of the cell nucleus) Cytokinesis (division of the cytoplasm)
Before cell division occurs, the cell replicates, or copies, all of its DNA.
Each daughter cell gets one complete set of genetic information.

40. What does the DNA look like?
CHROMATIN
CHROMOSOMES
What does the DNA look like?
Present in what stage of the cell cycle?

41. Interphase Cell Divison (M Phase)
CHROMATIN
CHROMOSOMES
What does the DNA look like?
Present in what stage of the cell cycle?
Interphase
Cell Divison (M Phase)

42. DNA Replication
Before a cell divides, it duplicates its DNA via a process called DNA Replication
During the S phase of cell division
Ensures that each resulting cell will have a complete set of DNA molecules
Result: Two identical DNA molecules (each DNA molecule has one original strand and one new strand)

43. How DNA Replication Occurs
Step 1:
Helicase, an enzyme, “unzips” the DNA molecule
Hydrogen bonds between the base pairs are broken
Result = 2 separated strands of DNA

44. How DNA Replication Occurs
Step 2: A replication fork is formed.

45. How DNA Replication Occurs
Step 3: Free floating nucleotides pair up with complimentary bases
Each strand of DNA serves as a template, or model, for the new strand
DNA Polymerase – Enzyme that joins individual nucleotides to produce a DNA molecule and also “proofreads” each new DNA strand

47. You Try It!
What is the complimentary DNA strand if the original DNA strand is AGTCTA?

48. You Try It! Complimentary Strand: TCAGAT
What is the complimentary DNA strand if the original DNA strand is AGTCTA?
Original Strand: AGTCTA
Complimentary Strand: TCAGAT

49. If a meerkat’s parent skin cell contained 34 chromosomes; after cell division how many chromosomes would each of the meerkat’s daughter skin cells contain?
17 chromosomes
34 chromosomes
68 chromosomes
None because skin cells don’t go through cell division

50. If a meerkat’s parent skin cell contained 34 chromosomes; after cell division how many chromosomes would each of the meerkat’s daughter skin cells contain?
17 chromosomes
34 chromosomes
68 chromosomes
None because skin cells don’t go through cell division
Asexual reproduction produces cells that are genetically identical to their parents for reasons of growth, repair and replacement.

51. Regulating the Cell Cycle
Not all cells move through the cell cycle at the same rate.
Cell growth and cell division are controlled.
Cyclins are proteins that regulate the timing of the cell cycle in eukaryotic cells.
G1 – 0-5 hrs
S – 6-8 hrs
G2 – 2-5 hrs
Mitosis – 1 hr

53. Regulating the Cell Cycle
If cells are placed in a petri dish containing food:
Cells will grow until they come in contact with other cells then they stop growing.
If cells are removed from the center of the dish:
The cells bordering the open space will begin dividing until they have filled the empty space.

54. Regulating the Cell Cycle
This occurs in an injury as well:
If a cut in the skin or a break in a bone occurs, cells at the edges of the injury are stimulated to divide rapidly.
When the healing process nears completion, the rate of cell division slows down.

55. Cancer
Cancer - Disorder in which some of the body's own cells lose the ability to control growth.
Cancer cell divide uncontrollably and form masses of cells (tumors)
Cancer cells may spread throughout the body:
Disrupts normal activities and causes serious medical problems or even death

56. There are many reasons that cells can divide and grow out of control:
There are many reasons that cells can divide and grow out of control: * exposure to environmental causes (such as carcinogens or ultraviolet (UV) radiation from the sun) *nutritional deficiencies * genetic causes *some infections (All of these will result in DNA mutations)