The cell cycle
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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.

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The Cell Cycle

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The cell cycle

CONSISTING OF INTERPHASE ,MITOTIC PHASE, & CYTOKINESIS

The Cell Cycle


The mitosis puzzle

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.

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

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

What do you get at the end of the cell cycle?

2 genetically identical daughter cells


Cellular organization

Cellular Organization

PROKARYOTIC

Approximately 2 m of DNA to copy & be separated

EUKARYOTIC


Replication of so much dna is manageable because of how dna is packaged

Replication of so much DNA is manageable because of how DNA is packaged.

chromatin

chromosomes


Does the number of chromosomes in an organism determine how complex the organism is

Does the number of chromosomes in an organism determine how complex the organism is?

Organize the following organisms in order from complex to simple


Parts of a chromosome

Parts of a chromosome

THIS CHROMOSOME IS A DUPLICATED CHROMOSOME WITH 4 CHROMOSOMAL ARMS


The cell cycle1

The Cell Cycle

  • Interphase

    • Accounts for 90% of the cycle

    • Divided up into 3 subunits


The cell cycle2

The Cell Cycle

  • Mitotic phase

    • Includes both mitosis and cytokinesis

    • Usually the shortest part of the cell cycle.

and Cytokinesis


Mitotic spindle

Mitotic Spindle

  • Begins to form during prophase & is complete during metaphase

Form from the breakdown of microtubules of the cytoskeleton

Not present in plant cells

Starts here


The cell cycle

What is the significance of the fact that chromosomes condense before they are moved?


The cell cycle

WHICH OF THESE WOULD YOU RATHER ORGANIZE WITHOUT BREAKING?


Cytokinesis

CYTOKINESIS


Binary fission

BINARY FISSION

PROKARYOTES (BACTERIA & ARCHEA)


Evolution of mitosis

Evolution of Mitosis

A protein is thought to anchor the DNA to specific spot on membrane


Timing is everything

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


The cell cycle

What Drives The Cell Cycle?

Hypothesis:

-Each event in the cycle

triggers the next.

What was concluded?

Molecules present in the cytoplasm of cells in the S or M phase control the progression of phases.


The cell cycle

CELL CYCLE CONTROL SYSTEM


The cell cycle

THE G1 CHECKPOINT


The cell cycle clock

The Cell Cycle Clock

  • Regulatory molecules (mainly proteins)

    • Protein kinases and cyclins


The cell cycle

Protein Kinases & Cyclin

  • 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


The cell cycle

The fluctuating activity of MPF (M-phase-promoting factor)

MPF triggers the cell’s passage past the G2 checkpoint into M phase.

Starts in late S phase. It is protected from degradation so it accumulates

Cdk is recycled.

During anaphase, degradation terminates M phase

Promotes mitosis


Cyclins and cyclin dependent kinases control the cell cycle

Cyclins and cyclin-dependent kinases control the cell cycle.


In summary

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


The cell cycle

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.


The cell cycle

EXTERNAL FACTORS ON CELL DIVISION:

DENSITY-DEPENDENT INHIBITION


In summary1

In summary

  • Externally:

    • Growth factors secreted from the endocrine glands or platelet 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

When do cells fail to divide?

Note: there are more than 50 growth factors

If essential nutrients are missing.

If growth factors ( protein released by certain cells to stimulate other cells to divide) are missing.

How does a cell divide “wrong”?

Let’s look at a cell gone wrong in the video Non disjunction or non segregation in Mitosis


The cell cycle

LOSS OF CELL CYCLE CONTROLS

  • Cancer cells to 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


The cell cycle

MALIGNANT VS BENIGN TUMOR

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

What does it mean if the cancer has metastasized?


Differentiation of human 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

What are stem cells?

What do you know about stem cell research?

WHAT SIDE DO YOU FALL ON???

LET’S READ AN ARTICLE!!!


Embryonic 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.


The cell cycle

TOTIPOTENT VS PLURIPOTENT VS MULTIPOTENT

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.

Multipotentcells 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

Stem Cells –video on youtube


The cell cycle

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.


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