the cell cycle
DESCRIPTION
CONSISTING OF INTERPHASE ,MITOTIC PHASE, & CYTOKINESIS. The Cell Cycle. The Mitosis Puzzle. Lay blank sheets lengthwise to each other and tape them together. Write Interphase, Prophase, Metaphase, Anaphase, & Telophase across the top of the sheet. - PowerPoint PPT PresentationTRANSCRIPT
The Cell CycleCONSISTING OF INTERPHASE ,MITOTIC PHASE, &
CYTOKINESIS
The Mitosis Puzzle
Lay blank sheet lengthwise .
Write Interphase, Prophase, Metaphase, Anaphase, & Telophase across the top of the sheet.
Cut out the cell diagrams and tape/glue them across the top under the appropriate phase label.
Arrange each description beneath the appropriate picture to describe the cellular changes of that phase.
Why do cells divide?• Bacteria cells & unicellular eukaryotic
organisms divide & produce an entire organism.
• Multi-cellular organisms: – Development -Growth -Repair
What do you get at the end of the cell cycle?
2 genetically identical daughter cells
Cellular Organization
PROKARYOTIC EUKARYOTIC
Approximately 2 m of DNA to
copy & be separated
Replication of so much DNA is manageable because of how DNA is packaged.
chromosomes
chromatin
Does the number of chromosomes in an organism determine how complex the
organism is?
Bat
Herring gull
Human
Crayfish
Fern
Reptiles
Dog
Organize the following organisms in order from complex to simple
Parts of a chromosome
THIS CHROMOSOME IS A DUPLICATED CHROMOSOME WITH 4 CHROMOSOMAL ARMS
The Cell Cycle• Interphase – Accounts for 90% of the cycle– Divided up into 3 subunits
The Cell Cycle• Mitotic phase– Includes both mitosis and cytokinesis– Usually the shortest part of the cell cycle.
and Cytokinesis
Mitotic Spindle• Begins to form during prophase & is complete during
metaphase
Starts here
Form from the breakdown of microtubules of the cytoskeleton
Not present in plant cells
What is the significance of the fact that chromosomes condense before they are moved?
WHICH OF THESE WOULD YOU RATHER ORGANIZE WITHOUT BREAKING?
CYTOKINESISANIMAL CELLS PLANT CELLS
BINARY FISSION
PROKARYOTES (BACTERIA & ARCHEA)
Evolution of Mitosis
A protein is thought to anchor the DNA to specific spot on membrane
Timing is everything!• The frequency of cell division varies with cell
type.– EX: human skin cells vs liver cells
• Some cells do not divide at all in a mature human.– EX: nerve cells and muscle cells
What was concluded?
Molecules present in the cytoplasm of cells in the S
or M phase control the progression of phases.
What Drives The Cell Cycle?
Hypothesis: -Each event in the cycle triggers the next.
CELL CYCLE CONTROL SYSTEM
THE G1 CHECKPOINT
The Cell Cycle Clock
• Maturation/Mitosis Promoting Factor (MPF) are regulatory molecules (mainly proteins)–Protein kinases and cyclins plus a
phosphate group
•Kinases are enzymes• Activate or inactivate other proteins by
phosphorylating them.•Give the go ahead signals at the G1 and G2
checkpoints.• Present in a constant concentration in a growing
cell, but are mostly inactive.• To be active they must attach to a cyclin (a
protein) = cyclin-dependent kinases, or Cdks
Cyclin and Kinases
Cyclin D triggers cells to move from G0 to G1 into S phaseCyclin E prepares the cell for DNA replication in S phaseCyclin A activates DNA replication inside the nucleus in S phaseCyclin B promotes the assembly of the mitotic spindle & other tasks in the cytoplasm to prepare for mitosis
Cyclins and cyclin-dependent kinases control the cell cycle.
After the MPF does its job the cyclin degrades. Why?
The cell would continue to divide even when not ready
In summary
• Internally:– The fluctuation of cyclin & cyclin-dependent
kinases seems to control the cell cycle internally using checkpoints to tell the cell to proceed or not
– The MPF complexes (cyclin + Cdk) initiates mitosis & can then go on to produce a cascade of other cell responses including phosphorylation of other proteins which:• Promotes fragmentation of nuclear envelope• Chromosome condensation and spindle formation
What about external factors?
Example of a growth factor is PDGF (platelet-derived growth factor)
PDGF is required for the division of fibroblasts (a type of connective tissue)
Triggers a transduction pathway allowing the cells to pass the G1 checkpoint & divide.
An injury can instigate this growth factor to help heal a wound.
MORE EXTERNAL FACTORS ON CELL DIVISION:
DENSITY-DEPENDENT INHIBITION (in culture)
In summary
• Externally:– Growth factors secreted from the endocrine
glands or blood cells are present– A substrate to attach to is needed– Density of neighboring cells are a factor– Receptors (on outside of cell that’s dividing) are
needed to receive each of the cell signals mentioned above.
When do cells fail to divide?If essential nutrients are missing.
If growth factors ( protein released by certain cells to stimulate other cells to divide) are missing.
Note: there are more than 50 growth factors
Let’s look at a cell gone wrong in the video Non disjunction or non segregation in Mitosis
How does a cell divide “wrong”?
What is the definition of cancer?
• The unregulated cell division of an organism’s cell
LOSS OF CELL CYCLE CONTROLS
Cancer cells do not follow the normal signals that regulate the cell cycle.• They don’t stop dividing even when there are no growth factors present.• Can continue dividing indefinitely in culture with ample nutrients.
• EX: HeLa cells of 1951
MALIGNANT VS BENIGN TUMOR
What does it mean if the cancer has metastasized?
Have too few genetic & cellular changes to survive elsewhere.
Have genetic & cellular changes that enable the cells to spread to new tissues & impair functions of organs = cancer
Cancer most often results from mutations in genes
• Proto-oncogenes: they often code for proteins that stimulate cell division, prevent cell differentiation or regulate programmed cell death (apoptosis).
• Tumor suppressor genes- produce proteins that signal cells when they are getting too crowded.
How does someone “get cancer”?• It can be triggered by:– Carcinogens- Substances and environmental exposures that
can lead to cancer • Teratogens-Any agent that can disturb the development of an embryo
or fetus. Teratogens may cause a birth defect in the child. Or a teratogen may halt the pregnancy outright. The classes of teratogens include radiation, maternal infections, chemicals, and drugs.
– Viruses: ex: HPV (human papilloma virus) causes cervical cancer & EBV (Epstein Barr virus) is associated with Hodgkin’s lymphoma, and gastric cancer.
– Aging: ex: breast cancer increases the older you get
How can we kill cancer cells?
• Radiation• Chemotherapy– CDKs are considered a potential target for anti-
cancer medication. – If it is possible to selectively interrupt the cell cycle
regulation in cancer cells by interfering with CDK action, the cell will die.
– Targets fast dividing cells
Differentiation of Human Cells
A zygote starts development by dividing over and over until you get a few dozen
identical cells. These cells are embryonic stem cells.
What are stem cells?
Embryonic Stem Cells• Cells that start to take different development paths to become
specialized cells, such as blood stem cells, which means they can no longer produce any other type of cell.
Can give rise to any and all tissues in the body
they can differentiate into some, but not all, cell types.
Totipotent cells can form all the cell types in a body, plus the extra-embryonic, or placental cells.
Embryonic cells within the first couple of cell divisions after fertilization are the only cells that are totipotent.
Pluripotent cells can give rise to all of the cell types that make up the body; embryonic stem cells are considered pluripotent.
Multipotent cells can develop into more than one cell type, but are more limited than pluripotent cells; adult stem cells and cord blood stem cells are considered multipotent
TOTIPOTENT VS PLURIPOTENT VS MULTIPOTENT
Stem Cells Video
To generate cultures of specific types of differentiated cells—heart muscle cells, blood cells, or nerve cells, for example—scientists try to control the differentiation of embryonic stem cells. They change the chemical composition of the culture medium, alter the surface of the culture dish, or modify the cells by inserting specific genes.
What side of stem cell research do you fall?