3.24c Mitosis 3

understand that division of a diploid cell by mitosis produces two cells which contain identical sets of chromosomes.

INTERPHASE

-in a microscope we would see the nucleus as a spherical structure- you would not see the chromosomes.

-DNA replication occurs.

PROPHASE

- the first sign which shows that a cell is entering the process of mitosis and cell division is when we see the break down of the nucleus membrane.

-the chromosomes become visible as a pair of chromatids- in pairs.

LATE PROPHASE

-the nucleus is gone.

-network of protein molecule- called spindle (each one is a fibre)- extend from pole of the cell to the other.

-the chromosomes pair (the pair of chromatids) will move towards the spindle and will join onto one of the spindle fibres.

METAPHASE

-pair of chromatids are attached to the spindle fibre.

-the chromosomes are in the middle- arranged across the equator of the cell.

ANAPHASE

-the spindle fibre shortens- the pair of chromatids are moving apart and they move to the pole of the cells.

-separation of the pair of the chromatids.

TELOPHASE

-end of mitosis.

-the nucleus begins to reform around the chromosomes at either end of the cell- will be the new nucleus of the new cell.

-the formation of 2 nuclei at opposite ends of the cell.

CYTOKINESIS

-cell split into two- not part of mitosis.

-cell begins to move inwards to divide cytoplasm in half- membrane fuse across equator to form the two cells.

-the new cells each contain a chromosome which is the same as the parental cell.

MITOSIS

P- appear

M-middle

A- apart

T- two

3.24b Mitosis 2

understand the division of a diploid cell by mitosis produces 2 cells which contain identical sets of chromosomes

-cell divides to form 2 cells and when you look inside the nuclei they will have the same number of chromosomes and the same number of sets.
-DNA replication- each chromosomes undergoes a copying process to form an identical copy of itself and is held by a structure called a centromere.
-they are now called a 'pair of chromatids'
-process of DNA replication takes place inside the nucleus while the nucleus is still intact, you cant see the process- it is called the interphase of the cell cycle.

3.24a Mitosis 1

understand that division of a diploid cell by mitosis produces two cells which contain identical sets of chromosomes.
-mitosis is a form of cell division.
-cell division results in growth and growth occurs by an increase in the number of cells.

-diagram shows a normal cell with its nucleus.
-the number of chromosomes in this nucleus is known as the diploid number (can be shown as [symbol] 2n)
- humans: 2n = 46
- cats: 2n = 38
-in the process of mitosis the cell will divide into 2 cells, each with a nucleus.
-if you look inside the nucleus you will find that each of these cells will have a diploid nucleus- the cells are identical-sometimes described as daughter cells.
-identical in 2 ways:

• same number of chromosomes
• they have the same set of chromosomes- if we choose one chromosome from the nucleus of one cell you will find an identical version of that chromosome in the other cell (there have been 2 sets produced)

3.16 DNA and Genetic information

describe a DNA molecule as two strands coiled to form a double helix, the strands being linked by a series of paired bases: adenine (A) with thymine (T) and cytosine (C) with guanine (G)
-first chromosome- likely to contain thousands of genes.
-gene loci -> double helix and appear to be parallel.
-double helix -> known as 'sugar phosphate backbone'
-in the centre there is a group of molecules called bases
-there are 4 different type of base called adenine, thymine, cytosine and guanine.
-in the molecule the bases are holding together the 2 helices.
-they are held together by pairing of the 2 (A-T) and (G-C) this is as known as base pairs. (always found in DNA)
-base pairs are gluing together one side of the DNA double helix with the other.
-order of the base on the right side of DNA is A, C, T, G, A, A, C, C, A, G. this is the order of the bases. this order is called the GENE.

-gene is inside a nucleus- order of bases (ATGC)

-number of bases- construction of protein in the cytoplasm- gives the characteristic.

question- why are the base pairs arranged A-T and G-C? 

3.15 Genes

understand that a gene is a section of a molecule of DNA.
-photo below shows a DNA.
-one section is a gene- it carries the information which forms the characteristic of the organism. it could be the blood group or it could be the petal colour in a flower.
-genes are located in the nucleus
-information is passed to the cytoplasm and in the cytoplasm, that genetic information is formed into the protein, protein controls the production of the characteristics.
-information flows the gene (in nucleus) to the protein (in cytoplasm)

question- can there be different size genes? eg. would the size of a gene which forms the characteristics of a blood group be bigger/smaller than the one which forms the characteristics of the petal of a flower?

3.14 Chromosomes

recall that the nucleus of a cell contains chromosomes on which genes are located.
-chromosomes are genetic information within a cell.
-typical cell will have a nucleus, and if you open the nucleus up you will find a number of chromosomes.
-a chromosome is composed of a molecule called DNA (DeoxyriboNucleic Acid), this forms a shape known as the double helix.

-sections of the molecules are called genes

-one chromosome will have many genes possibly thousands of genes.

-each gene carries the information for the construction of a protein.

-protein gives us the characteristics associated with the genes eg. blood group.

-different organisms have different numbers of chromosomes. 

• cat- 38 chromosomes.
• chicken- 78 chromosomes
• chimpanzees- 42 chromosomes.
• human- 46 chromosomes

-chromosomes are known to work in pairs- homologous pairs.

-the homologous nature is based on the length of the chromosomes.

-the 2 arrows on the diagram above is the gene loci. if you go to the same position on the homologous pair you find the same gene (gene loci)

-there is 2 versions of each gene for one characteristic. (alleles)

question- is the number of chromosomes in human males and females the same?

3.1 Sexual and Asexual Reproduction

describe the difference between sexual and asexual reproduction

sexual reproduction
-sex, can identify if male or female.
-produce cells called gametes. sperm: male & egg: female (plants- sperm is known as pollen grain, egg is known as pollen grain)
-meiosis- the type of cell that produces gametes. effect- half the total adult number of chromosomes in the gamete cell. (in humans the total number of chromosomes is 46 per cell, however in gametes the total number is 23 per gamete cell) the process of reducing 46 from 23 is called (cell division) meiosis.
-process of fertilisation. gamete cells (sperm cells from male) and egg cells from female fuses together.
-variation- board. many differences in individuals of the sexual reproduction population.

assexual reproduction
-no sex, can not be determined if male or female.
-does not produce gametes
-no meiosis only mitosis in eukatyotic cells/ binary fission in prokaryotic bacterial cells, in this process the number of cells (chromosomes) are maintained constantly. eg. if there is 20 cells will divide to produce 2 cells each with 20 chromosomes, they are identical.
-no gametes, no cell fusion so no fertilisation
-small amount of variation due to mutation, but they are mostly identical= clone.

question- what is the difference between mitosis and meiosis?