Cell Division Ppt

Genetic Information 

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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)

Mitosis 

http://www.johnkyrk.com/mitosis.html

Chromosome Structure 

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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)

Chromosome Number 

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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

Chromosome Number cont. 

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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)

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

Frequency of cell division 

Some cells do not divide after a certain age   

Liver cells Intestinal cells Nerve cells

Type of cell division 

Asexual

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Sexual

Asexual Reproduction   

Making of new cells by mitosis Offspring are exact replica of parent Only one parent 

Occurs in: 

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Unicellular organisms as a means of reproduction Lower plants and animals as a means of reproduction Most somatic cells of multi-cellular organisms

Asexual Reproduction 

Advantages     

Simple Fast Low energy output Large number of offspring Daughter cells are identical to parent cells

Asexual Reproduction 

Disadvantages 

No variation among offspring

Sexual Reproduction  

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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.

Sexual Reproduction 

Advantages 

Variation among offspring

Sexual Reproduction 

Disadvantages    

More complicated Must find mate High energy cost Fewer offspring (generally)

The Cell Cycle 

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The life of a eukaryotic cell is diagramed as a cell cycle A repeating sequence of growth and division 5 phases

The Cell Cycle 

Interphase : 3 phases 

G1 Phase:

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S Phase :

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G2 Phase:

The Cell Cycle 

Mitosis - NUCLEAR DIVISION -4 phases 

Prophase:    

Centrioles Spindle fibers Nucleolus Nuclear membrane

The Cell Cycle 

Metaphase 

Fibers push chromosomes to line up along the equator of the cell

The Cell Cycle 

Anaphase 

Fibers shorten and pull chromatids apart to opposite sides of the cell.

The Cell Cycle 

Telophase    

Spindle fibers Chromatids Nuclear membrane nucleolus

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