Mitosis Animations

Mitotic Cell Division

(http://www.youtube.com/watch?v=NR0mdDJMHIQ&feature=related)

The Stages of Mitosis

 (http://www.youtube.com/watch?v=VGV3fv-uZYI)

Mitosis

(http://www.youtube.com/watch?v=ATlUv-AGhEU&feature=related)

3.24c Mitosis (3)

Notes


Process of Mitosis


-------------- START OF MITOSIS ---------------

1. Interphase (resting state) = nucleus visible, but chromosomes are not

2. Prophase = Break down of nuclear membrane (nucleus breaks down)-> chromosome visible as a 'pair of chromatids'

3. Pro-metaphase = Inside cell (no nucleus remains), network of protein molecules (spindle/fibres) extends from one pole of the cell to the other:
-> Pair of chromatids join onto protein fibre in centre (via centromere)

4. Metaphase = Pair of chromatids joined onto protein fibre in 'spindle' via centromere.
-> Chromosomes are arranged in the 'equator' of cell

5. Anaphase = 'spindle' fibre shortens -> splits pair of chromatids in opposite directions

6. Telophase = Two nuclei form at opposite ends of the cell, around the seperated chromatids.

--------------------- END OF MITOSIS -----------------------

(7.) Cyto-Kinesis (not regarded as part of mitosis) = Cell begins to move inward dividing cytoplasm in half -> Membrane fuses across equator = Two cells each containing a chromosome (same as parental cell)

-> Human: 23 pairs undergo mitosis at the same time

(http://www.ba-education.com/dna/mitosis.jpg)

3.24b Mitosis (2)

Notes


Mitosis - creating identical 'daughter' cells requires 'DNA replication'

-> Process: Each chromosome undergoes copying process -> Identical copy with identical genes & alleles
---> Takes place inside nucleus (unobservable) = Interphase of cell cycle

-> Two copies held together by centromere (structure around central region) = referred to as 'pair of chromatids'

3.24a Mitosis (1)

Notes


Mitosis = form of cell division -> growth, by increase in number of cells

Outline
Cell, with nucleus -> Diploid number (2N) number of chromosomes (human 2N = 46 chromosomes/cell)

-> Mitosis = cell divides into two, each with 1 diploid nucleus (identical/'daughter' cells):
  --> same number of chromosomes
  --> same set of chromosomes = same chromosome found in copy nucleus

3.16 DNA and Genetic Information

Notes


Chromosomes -> Gene loci

---> Double helix structure (DNA), interwoven parallel helixes

------> Outside sections = 'sugar phosphate backbone'
------> Inside contains 'base pairs' = Adenine (A) <--> Thymine (T), Cytosine (C) <--> Guanine (G) which hold two sides of the 'backbone' together
------------> Base pairs order (right side of helix structure): GENE
(R) (L)

A  T
C  G
T  A
G  C
A  T
A  T
C  G
C  G
A  T
G  C
C  G

Gene inside nucleus = order of bases & number of bases -> codes for construction of protein in cytoplasm -> organism characteristics

3.14 Recall that a nucleus of a cell contains chromosomes on which genes are located

Notes

Chromosome = genetic information within a cell

Typical cell -> Nucleus -> Chromosomes -> DNA (double helix structure) -> Repeating structure known as 'Gene'

Gene = instructions for construction of a protein which define organism characteristics
-> Different organisms contains different number of chromosomes, humans = 46 per cell.

Chromosomes operate in homologous pairs (X,Y), based upon LENGTH of chromosomes (similar lengths will operate together)
-> Identical genes located at identical postion on the chromosomes - known as the gene loci
   -> 2 versions of each gene for 1 characteristic, known as alleles

3.15 Understand that a gene is a section of a molecule of DNA

Notes


DNA - Deoxyribonucleic acid = Double-helix structure
 ->Nucleus
   --> Gene - carries information (characteristics) of organism, individual genes for:
      ---> Blood group (animal)
      ---> Petal colour (plant)
      ---> Etc.

Nucleus, Gene (genetic information) -- passed to Cytoplasm --> Cytoplasm, Protein
 - Protein controls production of characteristic 


Below (http://publications.nigms.nih.gov/thenewgenetics/images/ch1_dnagenes.jpg)
 -> Diagram of DNA relative to cell structure

3.1 Differences in Sexual and Asexual Reproduction

Notes


Sexual

-> Identifiable: Distinguish between male/female
-> Meiosis (gamete cell division): 1/2 total number of adult chromosomes in gamete cells
-> Produce 'gamete' cells (male - sperm / female - egg)
-> Fertilisation: gamete cells fuse together (male / female cells fuse together - 23 x 2 = 46)
-> Variation: Populations of individual sexually reproducing species show broad amount of variations

Asexual

-> NOT Identifiable
-> Mitosis / binary fission: 20 chromosome cell -- divides --> 20 x 2 chromosome cells
-> NO Gamete cells produced
-> NO Fertilisation: no gamete cells = no cell fusion = no fertilisation
-> Small variations: identical population (clones)


*Question: What factors affect whether a species will be a sexually or asexually reproducing animal? What are the advantages/disadvantages of each method, that lends itself to particular circumstances (e.g. Scarce populations of species in an area, therefore asexual would be more advantageous)?