lab 7: cell division: mitosis and meiosis

Lab 7: Cell Division: Mitosis and Meiosis

Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cyclesAIM: Describe how the cell cycle is regulated.Are there molecular signals in the cytoplasm that regulate the cell cycle?

Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cyclesAIM: Describe how the cell cycle is regulated.Are there molecular signals in the cytoplasm that regulate the cell cycle?

Conclusion: The results suggest that molecules are present in the cytoplasm of cells in the S or M phase controlling the progression of phases.

What are these molecules you ask?

Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cyclesAIM: Describe how the cell cycle is regulated.The cell cycle clock: Cyclins and Cyclin-Dependent KinasesWhat is a cyclin-dependent kinase (cdk)?It’s a group of related

kinases (enzymes that phosphorylates molecules – usually proteins) that are activated by a group of proteins called cyclins. What is a cyclin?A group of proteins that are made in cycles (hence the name) and are allosteric activators of the cdk’s (activate them upon binding).Ex. “Cyclin B”

Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cyclesAIM: Describe how the cell cycle is regulated.

Expression of human cyclins throughout the cell cycle

Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cyclesAIM: Describe how the cell cycle is regulated.The cell cycle clock: Cyclins and Cyclin-Dependent KinasesGive an example:

Ex. “Cyclin B” (the cyclin in the figure to the right) begins to be made at the end of S phase and slowly increases in concentration throughout G2. When the concentration gets high enough, Cyclin B will bind to Cdk-1 (the Cdk shown in the diagram to the right), activating it.“Cyclin B” + Cdk-1 = MPF

MPF stand for maturation-promoting factor –(aka mitosis-promoting factor).

****All molecular binding (binding of two molecules) is concentration dependent.


Ex. MPF will activate mitosis at the G2 checkpoint by going around and phosphorylating a number of proteins including:1. Condensins

Proteins involved in condensing the chromosomes.

3. Proteins involved in microtubule spindle fiber formation4. Lamins

The proteins that hold the nuclear envelope together (nuclear lamina)

2. Histones – to condense DNA


How will the MPF complex be turned off?

High levels of MPF result in the phosphoylation of proteins that will degrade (break down) Cyclin-B - negative feedback

Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cyclesAIM: Describe how the cell cycle is regulated.All of the various cyclins and Cdk’s are part of the…

Cell Cycle Control System


Recall that mitotic cell division is regulated by Cyclin and Cdk’s (cyclin dependent kinases).

Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cyclesAIM: Describe how the cell cycle is regulated.Checkpoints of the Cell Cycle Control SystemThere are three major checkpoints:

A. G1 checkpoint- Passing G1 checkpoint = point of no return- Cell can halt at this checkpoint and remain there for their lifetime-external and internal signals required to pass this checkpoint-Growth Factor (external

signal) like PDGF (platelet derived growth factor), which stimulates division near a wound.- Enough nutrients/enzymes (internal)


B. The G2 checkpointEx) Is all the DNA replicated?Ex) Is the DNA too damaged from replication (too many mistakes made) to continue? If yes, apoptosis; if no, continue to mitosis.-Internal signals only

Checkpoints of the Cell Cycle Control SystemThere are three major checkpoints:


C. The M (metaphase) checkpoint

Ex) Are all the sister chromatids present and attached to microtubules and ready to be pulled apart?

-internal signals only

Checkpoints of the Cell Cycle Control SystemThere are three major checkpoints:

Chapter 12/13 - Cell Cycle, Meiosis, and Sexual cyclesAIM: Describe how the cell cycle is regulated.CheckpointsReview

Lectin- Highly specific carbohydrate-binding proteins- Present throughout natureEx) Concanavalin A

Jack Bean ConA – pdb code: 3CNA Jack Bean

- Promotes cell division in plant cell by binding to cell surface receptors that have been glycosylated with very specific polysaccharide chains.


What’s a Lectin?

Ex) Concanavalin A

Jack Bean ConA – pdb code: 3CNA Jack Bean


After the procedure you should see this for both the lectin-treated (experimental) and untreated (control) groups:


Root Tip Interphase Mitotic Total

1 78 21 100

2 92 35 127

3 64 15 79

Total 234 71 306


1 84 32 116

2 102 44 146

3 91 39 130

Total 277 115 392

Untreated (Control)

Lectin-Treated (Expt)

Data from one group:



1 78 21 100

2 92 35 127

3 64 15 79

Total 234 71 306


1 84 32 116

2 102 44 146

3 91 39 130

Total 277 115 392

Untreated (Control)


Percentage of cell in interphase =

234/306*100=76.5 %We now know to expect that in a standard onion plant, 76.5% of the cells will be in interphase….

Therefore, if we have 392 total cells, we expect, if standard, 392*.765 to be in interphase =

300 cells – expected value



1 84 32 116

2 102 44 146

3 91 39 130

Total 277 115 392


300 cells in interphase – expected value Therefore 92 cells in mitotic phase – expected value

Interphase Mitotic Phase

Observed 277 115

Expected 300 92

Now calculate the chi2 and determine a p-value…


Interphase Mitotic Phase

Observed 277 115

Expected 300 92

Now calculate the chi2 and determine a p-value…

= (277-300)2/300 + (115-92)2/92

= 529/300 + 529/92= 1.76 + 5.75= 7.51

DOF = # groups – 1 = 2 -1 = 1

P < .01There is less than 1% probability that there is no difference (null hypothesis). Therefore, there is >99% that there is a difference and therefore the data supports the alternative hypothesis.



Hela cell karyotype Normal cell karyotype


Hela cell karyotype


HPV – Human Papillomavirus-most common STD- Infects genital areas as well as mouth and throat- Nearly everyone gets it at some point in their lives- 90% of cases fought off by immune systom and no symptoms arise.- The other 10%:

- Genital Warts- Cervical Cancer

*Nearly all cases of cervical cancer are caused by HPV!!!


How does HPV cause cancer?

- HPV is a small DNA virus- Ligand/receptor interactions allow virus access to cell.- Genome of virus enters nucleus by unknown mechanism- Between 10 and 200 copies are inserted into persons nuclear DNA.- Protein E6 and E7 are the major oncogenic (cancer causing) proteins

- “E” stands for early because the gene is transcribed early in the viral life cycle. “L” for late.

HPV genome - ~8000bp


Why are E6 and E7 oncogenic?

Both p53 (guardian angel) and pRb are tumor suppressor proteins.

E6 functions by ubiquitinating p53Recall that adding the

small protein ubiquitin to a protein targets it to be degraded by the proteosome!


p53

p53 (“the guardian of the genome”) bound to an enhancer region of DNA

- Transcription factor

“53” because its apparent mass is 53kDa or 53,000Da or 53,000amu.

- Turns on genes that code for proteins having to do with DNA repair, cell cycle arrest and apooptosis.

- Goes to work when the cell is in bad shape (DNA damage, etc…)- Like batman


pRb

pRb (Retinoblastoma Protein)

- Inhibits cell cycle progression at G1 checkpoints- Binds and inhibits transcription factors that want to turn on genes and push the cell into S phase.

- Named such because if you both copies are mutated early in life you will get retinoblastoma (cancer of the eye’s retina)

pRb is inactivated when it is phosphorylated by CDK/cyclin!!

Lab 7: Cell Division: Mitosis and Meiosishttp://www.youtube.com/watch?v=pOROHmEmqmU

Focus on meiosis part

mailto:http://www.youtube.com/watch?v=pOROHmEmqmU




lab 7: cell division: mitosis and meiosis

Documents

cell cycle clock

cell division

sexual cyclesaim

cyclin b4 growing cells

cyclindependent kinasesgive

cyclin b cdk

cyclindependent kinaseswhat

cytoplasm of cells