Cell Cycle

Cell Division Notes

Mitosis and Cell DIvision produces two identical daughter cells

The goal of mitosis and cell division is growth, repair, and development.

Ratio of Surface Area to Volume


  • A ratio is a comparison

    • Surface area/Volume

  • Volume = l x w x h


6:1

3:1

2:1


We want a higher ratio of surface area to volume


The greater the SA/V ratio, the easier it is for the cell to exchange materials


Cell Size and Material Exchange


The larger a cell grows the surface area/volume ratio decreases, which makes cells less efficient at…


  • Moving enough nutrients in

  • Moving waste materials out


The Cell Cycle and Mitosis


The cell cycle is divided into two halves


  • Interphase: period of the cell cycle between cell divisions

  • M phase: Period of time when mitosis and cell division occurs


Parts of Interphase


G1 Phase (Gap 1)

  • Growing

  • Synthesize new proteins and organelles

  • Doing their jobs

  • Longest phase of cell cycle

S Phase (Synthesis)

  • Chromosomes (DNA) are replicated

  • Key proteins associated with replication are made (centromeres)

G2 Phase (Gap 2)

  • Shortest of the 3 phases of interphase

  • Organelles and molecules for cell division are produced (centrioles)

  • Check-up phase before mitosis


Chromatin

Chromatin: A complex of DNA and proteins in the cell nucleus that condenses to form chromosomes during cell division

Chromosomes: Condensed chromatin

Chromosomes Replication

During the cell cycle (before division can take place) chromosomes are replicated to form an identical copy of itself

Two identical copies of a chromosome are called

  • “Sister” chromatids” - a replicated chromosome

  • Centromere - the protein where the chromatids of a chromosome are attached

Chromosomes

Different organisms have different numbers of chromosomes

  • Human cells - 46

  • Fruit Fly Cells - 8

  • King Crab Cells - 206

Prokaryotes have one circular chromosome and replicate via binary fission

Mitosis

  • Prophase

    • Chromatin condenses into chromosomes

    • Nucleoli and nuclear envelope break down

    • Spindle fibers grow from centrioles

    • Centrioles migrate to opposite poles of cell

  • Metaphase

    • The chromosomes are lined up at the equator of the cell

    • The spindle fibers from each centriole are attached to the centromeres of the chromosomes

    • The nuclear membrane has disappeared

  • Anaphase

    • The centromeres split, and the sister chromatids separate as each is pulled to an opposite pole

  • Telophase

    • The chromosomes become longer, thinner, and less distinct

    • New nuclear membranes form

    • The nucleolus reappears

    • Cell division is nearly complete

Cytokinesis

  • Cytoplasmic division and other changes exclusive to nuclear division that are part of mitosis or meiosis

Regulating the Cell Cycle

Internal Regulation:

-Cyclins

CDK’s (Cyclin Dependent Kinases

External Regulation:

  • Growth Factors HGH

    • Platelet Driven Growth Factors

    • Produced by platelet blood cells

- Density-Dependent Inhibition

-Anchorage-Dependent Inhibition

Density-Dependent Inhibition: No more space to reproduce (stops when they contact other cells)

Anchorage Dependence: To divide they must be anchored to a substratum (Bones or other sorts of tissue)

Cancer Cells

  • Free of both density-dependent inhibition and anchorage dependence

  • Divide excessively and invade other tissues because they are free of the body’s control mechanisms

How do cells know when to divide or not?

Internal Regulators - the proteins that respond to events inside the cell

Cyclins - Control the activation of enzymes

CDK’s - Cyclin dependent kinases - enzymes that control the cell cycle

External Regulators - Proteins that respond to events outside of the cell are called external regulators

  • Growth factors are among the most important external regulators

    • Molecules found on the surfaces of neighboring cells often have an opposite effect, causing cells to slow down or stop their cell cycles

Cancer

Tumor - a mass of cancer cells

  • Benign tumor - a tumor that does not invade it's surrounding tissue or spread around the body

  • Malignant tumor - a tumor that may invade it's surrounding tissue or spread around the body

Cancer has many causes:

  • Smoking

  • Radiation

  • Viral infections

  • Genetics

The common threat in all cancers is that control over the cell cycle has broken down

Over 50 percent of cancer cells have a defect in the p53 gene (anti-oncogne)

Proto-Oncogene

When proto-oncogenes get mutated, cancer usually follows

Oncogenes:

  • Proto-oncogene = ras

  • Oncogene = mutated ras

  • Always activated

  • Always stimulating

  • Proliferation

P53 Antioncogene

  • P53 is a tumor suppressor gene found mutated in about half of human cancers

  • It encodes a gene regulatory protein that is activated by damaged DNA and is involved in blocking further progression of the cell cycle

Cancer Treatments

  • Surgery: Remove the tumor

  • Radiation: Kill the cancer through radiation

  • Hormone Therapy

  • Chemotherapy

  • Targeted Therapy

Cell Growth Vs Development

Growth and Repair

  • New daughter cells divide from existing cells to form identical cells

Development

  • Stem cells

  • New daughter cells divide from existing cells, but changes occur to form new types of cells

    • Blood

    • Bones

    • Skin

    • Nervous

Differentiation - process of stem cells changing into specific cell types

Stem Cells

  1. Totipotent (omnipotent) - can become entire organism (first four divisions after fertilization)

  2. Embryonic Stem Cells

  1. Pluripotent - can differentiate into nearly all cells / not full organism

  • Inner cells mass from blastocyst (4-5 days after fertilization)

3. Adult Stem Cells

  1. Multipotent - a number of cell types

  2. Oligopotent - a few cell types

  3. Unipotent - one cell type

4. Induced Pluripotent Stem Cells

  1. Created in lab settings. Adult somatic cells (usually skin cells) are reverted back to pluripotent form via treatment

Asexual Reproduction - reproduction through mitosis or binary fission

  • Fast reproductive rate but little variation (2 identical daughter cells)

Sexual Reproduction

  • Reproduction through the production of gametes (sperm and eggs) by the process of Meiosis. Slower Reproductive rates, but increased variation