1. Cellular Reproduction and the Cell Cycle

2. What do all cells require to survive?
A complete set of genetic instructions
– produce required molecules
– direct life processes
Genetic instructions are coded in
the DNA of cells

3. Why do cells divide?
Growth
Repair
Development

4. Cell Cycle Activities of a cell from one cell division to the next
– Cell grows, adding more
cytoplasmic constituents
Why?
– DNA is replicated
Why?
– cell divides into two identical
daughter cells

5. Essential Features of Cell Division
Transmit a complete copy of
genetic information (DNA)
Transmit materials necessary for
cell to survive and use genetic
information

6. Two Fundamental Types of Cells
(organisms):
Prokaryotic
Eukaryotic

7. Prokaryotic Cell
no nucleus – genetic material
(DNA) in cytoplasm
no membrane-bound organelles
cell division is called binary fission
example: bacteria

8. Prokaryotic Cell Cycle
Prokaryotic chromosome a circular loop
chromosome attaches to one point
on plasma membrane
chromosome is replicated
– replicated chromosome attached
to plasma membrane at a different
nearby point

9. cell elongates – new plasma
membrane is added between
between chromosomes, pushing
them towards opposite ends of cell
plasma membrane grows inward
at middle of cell
parent cell is divided into two
identical daughter cells

10. Cell wall
Plasma membrane
Chromosome

13. Eukaryotic Cell
membrane-bound organelles, including
a nucleus
genetic material (DNA) contained within
the nucleus
cell division of somatic cells called
mitotic cell division
examples: fungi, protists, plants,
animals

14. Chromosomes
In Eukaryotic cells, the genetic information that is passed from generation to the next is carried by chromosomes.
Chromosomes:
threadlike structure within the nucleus containing the genetic information that is passed from one generation of cells to the next.
Each cell has a specific number of chromosomes
Fruit flies = 8 chromosomes
Humans = 46 chromosomes

15. Chromosomes Chromosomes are not visible in cells until cell division
Prior to cell division the DNA and protein molecules that make up the chromosomes are spread throughout the nucleus.
During cell division the chromosomes condense into compact, visible structures.
Chromosomes are copied before cell division and consist of identical “sister” chromatin.

16. Chromosomes A
Centromere B
Sister chromatids

17. Limitations on Cell Growth
If a cell is larger then it demands more on the cell’s DNA.
DNA Overload:
When a cell is small the information stored in the DNA is able to meet the cells needs, but as a cell increases in size the DNA in not copied so there is an “information crisis”.
It will also have trouble moving enough nutrients and wastes across the cell membrane.
Exchanging Materials:
The rate at which exchange occurs depends on the surface area of the cell, which is the total area of the cell. A cells waste production depends on the amount used by the cell. When a cell is larger it is producing a higher number of waste and exchanges waste for nutrients at a lower number.

18. Division of the Cell
Before a cell gets too large, and begins undergoing problems, a cell will divide forming 2 daughter cells in cell division.
Cell division solves the problem of increasing size by reducing cell volume. Each daughter cell has an increased ratio of surface area to volume, allowing efficient exchange of materials with the environment.

19. Before Cell Division Cells Replicate:
Prior to cell division a cell will make copies of its DNA.
This replication solves the problem of information storage because each daughter cell will have their own complete set of genetic information.
Cell division also solves the problem of increasing size by reducing cell volume, which allows for efficient exchange of materials with the environment.

20. The Cell Cycle Cell Cycle:
Series of events that cells go through as they grow and divide
During the cell cycle, a cell….
grows
prepares for division
divides to form 2 daughter cells which begin their own cell cycle

21. The Cell Cycle 4 phases of the Cell Cycle M Phase: S Phase:
Mitosis and cytokinesis
S Phase:
Chromosome replication or synthesis
G1 and G2 Phase:
“Gap” phases, occur between M and S Phase
Period of intense growths and activity

22. The Cell Cycle
A: G1 Phase
B: S Phase
C: G2 Phase
D: M Phase

23. Events of the Cell Cycle
Interphase:
G1, S, and G2 Phase
G1 Phase:
Cells do most of their growing. The cells will increase in size and synthesis new proteins and organelles.
S Phase:
Chromosomes are replicated and the synthesis of new DNA molecules takes place. Key proteins associated with the chromosomes are also synthesized.
G2 Phase:
Shortest of the 3 phases. Organelles and molecules required for cell division are produced

24. Events of the Cell Cycle
After the cell has gone through the 3 phases of Interphase the cell will be ready to go through M Phase (cell division).

25. What is Mitotic Cell Division?
Division of somatic cells
(non reproductive cells) in
eukaryotic organisms
A single cell divides into two
identical daughter cells
(cellular reproduction)
=> Maintains chromosome ploidy of cell

26. Ploidy – refers to the number of pairs of
chromosomes in cells
haploid – one copy of each
chromosome
– designated as “n”
diploid – two copies (= pair) of each
chromosome
– designated as “2n”

27. Each species has a characteristic
number of chromosomes:
Prokaryotes – one chromosome
Crayfish – 200 chromosomes
Human – 46 chromosomes
=> 23 pairs of chromosomes

28. Diploid organisms receive one
chromosome from female parent
(= maternal) and one chromosome
from male parent (= paternal)
A “matched” pair of maternal and
paternal chromosomes are called
homologues

29. Structure of a eukaryotic chromosome
unreplicated chromosome
arm
centromere

30. Prior to cell division: chromosomes (DNA) are replicated (duplicated)
duplicated chromosome
– attached at their centromeres
– as long as attached, known as
sister chromatids
duplicated
chromosome

31. daughter
chromosomes
sister
chromatids

32. Eukaryotic Cell Cycle
2 major phases:
Interphase (3 stages)
– DNA uncondensed (= chromatin)
Mitotic cell division (4 stages)
– DNA condensed (= chromosomes)

33. Mitotic Cell Division
2 major processes:
mitosis – nuclear division
=> preserves diploid number of
chromosomes
cytokinesis – cytoplasmic division
=> cell divides into two daughter cells

34. Mitosis
4 phases:
1st – Prophase (3 major events)
2nd – Metaphase
3rd – Anaphase
4th – Telophase and Cytokinesis

35. Prophase
3 major events
i) chromosomes condense
ii) spindle fibers form
iii) chromosomes are captured by
spindle

36. Chromosomes Condense
Recall that chromosomes were
duplicated during interphase
=> each chromosome consists of
2 sister chromatids attached to
each other at the centromere

37. Mitotic Spindle Forms
spindle fibers are specialized
microtubules
spindle fibers radiate out from
centrioles, forming the “aster”
centrioles occur in pairs, and are
duplicated during interphase

38. one pair of centrioles migrates to
one pole of cell, the other pair
migrates to opposite pole of cell

39. Spindle Captures Chromosomes
When spindle fibers are fully formed
nuclear envelope disintegrates and
nucleolus disappears
Spindle fibers attach to chromosomes
at the kinetochore, a structure located
at the centromere

40. other spindle fibers do NOT attach
to chromosomes, but retain free
ends that overlap at cell’s equator
=> “free spindle fibers”
function of spindle fibers is to
organize division of sister chromatids
into daughter cells

41. chromatin
nucleolus
nucleus
centrioles
condensing
chromosomes

42. chromosomes align along equator of the cell, with one
Metaphase
chromosomes align along
equator of the cell, with one
kinetochore facing each pole
centrioles
spindle fibers
chromosomes

43. Anaphase
sister chromatids separate
spindle fibers attached to
kinetochores shorten and pull
chromatids poleward
free spindle fibers lengthen and push
poles of cell apart

44. V-shaped chromatid
free spindle fibers

45. Telophase
spindle fibers disintegrate
nuclear envelopes form around both
groups of chromosomes
chromosomes revert to their extended
state
nucleoli reappear

46. Telophase chromosomes decondensing pinching of cell
nuclear envelope
reforming
nucleolus reappears
pinching of cell
membrane at equator

47. Cytokinesis occurs, enclosing each daughter nucleus into a separate cell

48. Cytokinesis
Animal cells:
– microfilaments attached to plasma
membrane form a ring around
equator of cell
– ring contracts, like a drawstring,
dividing the cytoplasm

49. Plant cells:
– stiff cell wall makes pinching
impossible
– Golgi complex buds off vesicles
filled with carbohydrate
– vesicles line up at equator and
fuse, producing a structure
called the cell plate
– cell plate becomes new cell wall
between the two cells

50. Mitotic Cell Division
Functions:
Growth, maintenance, repair of body
tissues
Forms the basis of
Asexual Reproduction

51. Cell Cycle Regulators
Internal Regulators: proteins that respond to events inside the cell
Cyclin: protein that regulates the timing of the cell cycle in eukaryotic cells
Many other proteins have been discovered that also assist in the cell cycle timing.
There are also proteins that check the cell before it can enter into the next part of the cell cycle.
Ex: A cell cannot enter mitosis until the chromosomes are replicated.

52. Cell Cycle Regulators
External Regulators: proteins that respond to events outside the cell
External regulators direct cells to speed up or slow down the cell cycle.
Growth regulators: stimulate the growth and division of the cell.

53. Uncontrolled Cell Growth
Cell growth is constantly regulated to prevent uncontrolled cell growth.
Cancer: disorder in which some of the body’s own cells lose the ability to control growth.
Cancer cells do not respond to the signals that regulate the growth in most cells. This constant growth causes masses call tumors.

54. Uncontrolled Cell Growth
What causes the loss of growth control?
Cancer cells have a defect in a gene called p53, which halts the cell cycle until chromosomes have been properly replicated.
Damage to p53 causes the cell to lose the information needed to respond to signals that ensure orderly growth.