You are performing mitosis. Where is this occurring?

1
You are performing mitosis.Where is this
occurring?

• Describe what is happening.

2
Mitosis

• Nuclear division plus cytokinesis
• produces two identical daughter cells
• Part of cell cycle

3
Cell Cycle

• Set of events in cell growth and division into
  two daughter cells.
• Some cells cease to divide and are not considered
  to be part of the cell cycle.
• Examples are Cells from the heart, eye, and N.S.
  
• Cell cycle duration
• 8 minutes in some embryos
• as long as one year in liver
• Most mammalian cells about 24 hours.

4
Cell Cycle
5
Stages of Cell Cycle

• G1 Gap 1
• S Synthesis when DNA is replicated
• G2 Gap 2
• M Mitosis when chromosomes separate and
  cytokinesis occurs

6
G1

• Cells grow in size
• Produces RNA and synthesize protein
• Cells may become quiescence - no longer
  proliferating
• Cells maintain themselves
• An important cell cycle control mechanism
  activates (G1 Checkpoint)
• It ensures that everything is ready for DNA
  synthesis.

7
S phase - synthesis

• Cell replicates genetic material
• A family of enzymes make an exact replica of the
  DNA.
• In human cells, just 6-hours are needed to
  replicate 46 chromosomes
• totalling six billion nucleotides, kept in exact
  sequence as parental DNA
• A mistake mutation

8
G2 Phase

• Cell continues to grow and produce new proteins.
• At the end of this gap is a control checkpoint
  (G2 Checkpoint) to determine if the cell can
  enter M (mitosis) and divide.

9
M Phase - Mitosis

• Cell growth and protein production
• All of the cell's energy is focused on the
  complex and orderly division into two similar
  daughter cells.
• Mitosis lasts one to two hours.
• There is a Checkpoint in the middle of mitosis
  (Metaphase Checkpoint) that ensures the cell is
  ready to complete cell division.

10
Regulation of the cell cycle

• How cell division (and thus tissue growth) is
  controlled is very complex.
• Errors can lead to uncontrolled cell growth
  which is how tumors are formed
• The passage of a cell through the cell cycle is
  controlled by proteins in the cytoplasm.

11
Control of cell cycle
12
Main proteins in animal cells

• Cyclins
• Levels rise and fall with the stages of cell
  cycle.
• G1 cyclin (cyclin D)
• S-phase cyclins (cyclins E and A)
• mitotic cyclins (cyclins B and A)

13
cyclin dependent kinase

• Cdks
• G1 Cdk (Cdk4)
• S-phase Cdk (Cdk2)
• M-phase Cdk (Cdk1)
• Their levels in the cell remain fairly stable,
  but each must bind the appropriate cyclin (whose
  levels fluctuate) in order to be activated.
• They add phosphate to protein
• They are the major control switches for the cell
  cycle, causing the cell to move from G1 to S or
  G2 to M.

14

• MPF
• Maturation Promoting Factor
• triggers progression through the cell cycle

15

• p53
• Protein blocks the cell cycle if the DNA is
  damaged
• If the damage is severe this protein can cause
  apoptosis (cell death).

16
p27

• a protein that binds to cyclin and cdk blocking
  entry into S phase.

17
Steps in Mitosis

• Interphase, prophase, prometaphase, metaphase,
  anaphase, and telophase.

18
Interphase

• Stages G1, S, and G2 of the cell cycle.
• The cell preparing for mitosis
• Chromosomes are not clearly visible

19
Interphase

• At start of S (synthesis) stage, each chromosome
  is composed of one coiled DNA double helix
  molecule, which is called a chromatid.
• At the end of this stage, each chromosome has two
  identical DNA double helix molecules, and
  therefore is composed of two sister chromatids
  (joined at the centromere).
• During S phase, the centrosome is also
  duplicated.

20
Chromosome two chromatids
21
Prophase

• Chromatin in the nucleus begins to condense and
  becomes visible in the light microscope as
  chromosomes.
• The nucleolus disappears.
• Centrioles begin moving to opposite ends of the
  cell and fibers extend from the centromeres.
• Some fibers cross the cell to form the mitotic
  spindle.

22
Prophase
23
Prometaphase

• The nuclear membrane dissolves, marking the
  beginning of prometaphase.
• Proteins attach to the centromeres creating the
  kinetochores.
• Microtubules attach at the kinetochores and the
  chromosomes begin moving.

24
Prometaphase
25
Metaphase

• Spindle fibers align the chromosomes along the
  middle of the cell nucleus.
• This line is referred to as the metaphase plate
• helps to ensure each new nucleus will receive one
  copy of each chromosome.

26
Metaphase
Metaphase plate
Metaphase plate
27
Anaphase

• Paired chromosomes separate at the kinetochores
• Chromatids move to opposite sides of the cell.

28
Anaphase
29
Telophase

• Chromatids arrive at opposite poles of cell.
• New membranes form around the daughter nuclei.
• The chromosomes disperse.
• The spindle fibers disperse.
• Cytokinesis begins.

30
Telophase