cell division ppt
DESCRIPTION
Class lecture notes presented on powerpoint. Material is intended for middle school through high school and can be adjusted as needed. Topics covered include; structure of a chromosome, chromosome number, mitosis, and the cell cycle.TRANSCRIPT
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Genetic Information
Genetic information is carried on genes
A gene is… 1 molecule of DNA contains
thousands of genes DNA=chromatin when the cell is not
dividing (not visible under a microscope)
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Mitosis
http://www.johnkyrk.com/mitosis.html
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Chromosome Structure
DNA (chromatin) replicates at during cell division preparation = 2 identical chromatids
2 chromatids coil, condense and join together at the centromere = chromosome (now visible under a microscope)
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Chromosome Number
Every species has a characteristic # of chromosomes
Chromosomes occur in pairs (code for same info – one from ea. Parent) = homologous pairs
A cell that contains both members of the homologous pair are called diploid – 2N
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Chromosome Number cont.
A cell that contains only one member of the homologous pair is called haploid – 1N
In humans: Diploid number is 46 (somatic cells) Haploid number is 23 (gametes)
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Frequency of cell division
Varies drastically among different cell types Bacteria – every 20 minutes Human embryo - 15-20 minutes Human skin – every 2 weeks Liver cells – approx. every 18 months
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Frequency of cell division
Some cells do not divide after a certain age Liver cells Intestinal cells Nerve cells
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Type of cell division
Asexual
Sexual
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Asexual Reproduction Making of new cells by mitosis Offspring are exact replica of parent Only one parent
Occurs in: Unicellular organisms as a means of
reproduction Lower plants and animals as a means of
reproduction Most somatic cells of multi-cellular
organisms
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Asexual Reproduction
Advantages Simple Fast Low energy output Large number of offspring Daughter cells are identical to parent
cells
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Asexual Reproduction
Disadvantages No variation among offspring
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Sexual Reproduction
Making of new gametes by meiosis Involves the combining of gametes
from 2 different parents Gametes fuse to form a zygote
(fertilized egg) Chromosome number in gametes is
1N to ensure constant chromosome number on future generations.
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Sexual Reproduction
Advantages Variation among offspring
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Sexual Reproduction
Disadvantages More complicated Must find mate High energy cost Fewer offspring (generally)
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The Cell Cycle
The life of a eukaryotic cell is diagramed as a cell cycle
A repeating sequence of growth and division
5 phases
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The Cell Cycle
Interphase : 3 phases G1 Phase:
S Phase :
G2 Phase:
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The Cell Cycle
Mitosis - NUCLEAR DIVISION -4 phases Prophase:
Centrioles Spindle fibers Nucleolus Nuclear membrane
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The Cell Cycle
Metaphase Fibers push chromosomes to line up
along the equator of the cell
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The Cell Cycle
Anaphase Fibers shorten and pull chromatids apart
to opposite sides of the cell.
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The Cell Cycle
Telophase Spindle fibers Chromatids Nuclear membrane nucleolus
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The Cell Cycle
Cytokinesis: CYTOPLASM DIVISION Not a phase of mitosis
Cytoplasm and organelles separate Usually begins in early anaphase Cytoplasm pinches in In plant cells, a new cell wall is formed
between the 2 new cells – cell plate
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