biology 3201 unit 2a notes mitosis - tina mcdonalds science 2018-01-22آ human sperm or egg cells...
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Biology 3201 Unit 2A Notes
Somatic cell: refers to a body cell; anything not a germ (sex) cell
Cell cycle: a continuous sequence of cell growth and division
The cell cycle consists of two main stages
1. Interphase – growth phase; includes G1, S phase, and G2
G1 (gap 1): cell carries out metabolic activities and prepares for cell division
S phase: DNA is replicated
G2 (gap 2): centrioles replicate and cell prepares for division
2. Division stage – includes mitosis and cytokinesis; ( PMAT) Mitosis and cytokinesis are the
two shortest events in the cell cycle.
Cytokinesis - separation of the cytoplasm and the formation of two new daughter cells;
cytokinesis occurs after telophase of mitosis
Mitosis – division of the cell’s nucleus where the daughter cells receive the exact number of
chromosomes and genetic makeup as the parent cell
Different cells have different timing for their cells cycles; some take longer than others to go
through their cycle, and they also spend different amounts of time in each stage.
Parent cell – the original cell that divides during mitosis to form two new daughter cells
Daughter cells – the cells produced during mitosis of a parent cell
Why is mitosis important? In order for an organism to grow, repair, and maintain its function new cells are needed to
replace old ones. Each cell that undergoes mitosis produces 2 new cells. Mitosis allows the
regeneration of damaged tissue (like cuts) and to replace worn out cells (like red blood cells)
- New cells are needed for growth maintenance and repair -cells can regenerate damaged tissues (cuts) -cells that do not function properly must be replaced -cells die (blood cells) -chromosome number must be maintained.
eg. Humans 46 chromosomes in somatic cells
When human somatic cells undergo mitosis, a parent cell replicates to produce a daughter cell
with the same number of chromosomes. Mitosis ensures that the same amount of genetic
information in each type of cell. Mitosis and cell division occur in many somatic (body) cells.
New cells are exact copies of previously existing cells. This occurs because of DNA stored in the
TERMS TO KNOW:
Chromatin: the long strands that form chromosomes and contain DNA, RNA and various
proteins. Found in the nucleus of cells.
Chromosome: condensed chromatin structure formed when cells replicate (divide) (see fig.
14.6, p. 462)
Chromatid: one half of a
chromosome. Two sister
chromatids are joined by a
centromere to form a
Centromere: is a region of DNA
typically found near the middle of
a chromosome where two
identical sister chromatids come
closest in contact
Centriole: A centriole is a barrel-
shaped cell structure involved in
the organization of the mitotic
spindle and in the completion of
Human somatic cells have 46 chromosomes (22 pairs plus the sex chromosomes). Before
mitosis, the parent cell has 46 chromosomes. After mitosis, the daughter cells each have 46
http://en.wikipedia.org/wiki/DNA http://en.wikipedia.org/wiki/Chromosome http://en.wikipedia.org/wiki/Sister_chromatids http://en.wikipedia.org/wiki/Cell_structure http://en.wikipedia.org/wiki/Mitotic_spindle http://en.wikipedia.org/wiki/Mitotic_spindle http://en.wikipedia.org/wiki/Cytokinesis
The stages of mitosis : Prophase
Chromatin coils and thickens forming chromosomes
Chromosomes are composed of two sister chromatids held together by a centromere. Each sister chromatid is a genetic copy of the other. (Identical DNA)
Because of this, each daughter cell receives a full set of parent genes
The nuclear membrane disappears
Centrioles made up of microtubules migrate to opposite ends of the cell.
Spindle fibres (also made of microtubules) form between the two centrioles Metaphase:
Spindle fibres attach to centromere of the replicated chromosome.
Chromatids are guided to the cell’s equator (spindle fibres from one pole attach to one chromatid and spindle fibres from the other pole attach to the other chromatid)
Centromere splits apart and chromatids are pulled to opposite poles of the cell by spindle fibres
Chromatids are pulled apart as a result of a shortening of microtubules Telophase :
Chromatids have reached two opposite poles
Chromatids are now a single , non-replicated chromosome
Chromosome now begins to unwind and becomes less visible
Spindle fibres are not needed so they break down and disappear
Nuclear membrane forms around each new set of chromosomes which are at the opposite ends of the cell
This is defined as the separation of the cytoplasm and the formation of two new daughter cells.
cytoplasm and all its contents divides between the two halves of the cell.
In animal cells an indentation of the membrane between two daughter cells forms and deepens.
In plant cells , a new cell wall and membrane form and separate the newly formed nuclei.
Lab: “Observing the cell cycle in plant and animal cells”- Pg 466-467
Mutations affecting cell division
Permanent change in the DNA of an organism
Can occur spontaneously or by certain compounds, radiation, etc.
Mutations that occur in parent cells are passed on to daughter cells
Most mutations I somatic cells are not important because those daughter cells can be
replaced by normal cells
However, if a mutation affects a gene (DNA) which controls cell division, cancer can
result (uncontrolled rapid growth of cells)
Radiation and chemotherapy: Cancer cells divide more rapidly than any other type of body cells. Therefore , anything that interferes with cell division will affect cancer cells more than healthy cells. This is the basis for radiation and chemotherapy. Radiation therapy:
Directs radiation such as x-rays are gamma rays at the affected part of the body.
Usually treated two to three times per week
Internal radiation therapy involves placing radioactive material next to the cancerous growth
Generally radiation therapy works by damaging the chromosomes in a cell. Then it cannot divide.
Healthy cells are also damaged but many are able to repair themselves.
Goal of radiation therapy is to focus the radiation on the diseased part of the body and avoid affecting healthy tissue.
Usually used on localized cancerous tumours such as on the skin ,breast , larynx , and cervix.
May include one or more types of drugs depending on the patient and the cancer.
May be used in conjunction with radiation or on its own.
Some drugs attack dividing cells as they divide or prevent cells from dividing
Chemotherapy affects the entire body and is usually used to treat cancers that are spread throughout the body such as leukemia.
Unfortunately, healthy cells are affected
Side effects of radiation and chemotherapy: Radiation: Skin inflammation and fatigue Specific side effects depending on location of treatment eg: brain - hair loss testicular cancer - sterility Chemotherapy: Hair loss, nausea, diarrhea For both treatments, side effects usually last only for the duration of the treatment. However ,sterility can be permanent. Treatments are particularly harmful to body cells that divide quickly, such as bone marrow cells, skin cells ,hair cells , cells in the GI tract and cells of the reproductive system. What is the goal of cancer research? Find treatment that affects cancerous cells and leaves healthy cells unharmed.
A zygote (fertilized egg) contains chromosomes from both parents but does not contain double the number of chromosomes found in each body cell. This happens because of meiosis which produces haploid cells called gametes. Gametes are haploid (h) which means that they contain one copy of each type of chromosome that the diploid (2n) contains. The first part of meiosis reduces the number of chromosomes from diploid to haploid. This is referred to as reduction division. Human sperm or egg cells contain 22 autosomes and 1 sex chromosome. Autosomes - not directly involved in sex determination.
Phases of meiosis : Meiosis is similar to mitosis, but there is an extra set of phases for each stage. Prophase I
Each pair of homologous chromosomes (carry genes for same information) become aligned.
Replicated homologous pairs are called tetrads.
One copy of a homologous chromosome came from one parent (egg) and one from the other parent (sperm).
Mothers chromosome - maternal origin Fathers chromosome- paternal
*note - homologous chromosomes are like a pair of shoes; same characteristics but not identical Although homologous chromosomes contain the same genes, they may have different forms of these genes called alleles. Alleles determine how a gene is exp