3.24 c - Mitosis

background information:

INTERPHASE

in a microscope nucleus would be seen as a spherical structure, would be unable to see chromosomes -- this is the interphase. this is when DNA replication occurs. 

PROPHASE

nucleus membrane breaks down - prophase 

chromosomes become visible - visible as a pair of "chromatids"  (two copies) 

LATE PHROPHASE

cell division proceeds - network of protein molecules (spindle and spindle fibres)

late phrophase - chrmosome pair will move towards spindle and join onto one fibre

METAPHASE

pair of chromatids are attached to spindle fibre by centromere. 

characteristic - chromosomes are arranged across the middle. the 'equator' of the cell. 

ANAPHASE 

spindle fibre shortens pulling chromatids in different directions 

pair of chromatids move apart to the poles of the cell 

separation of the pair of chromatids 

TELOPHASE

end of mitosis 

nucleus begins to reform around the chromosomes at either end of the cell

new nucleus of two new cells 

formation of two nucli at opposite ends of the cell 

CYTOKINESIS

cell splits into two - not part of mitosis! 

cell begins to move inwards to divide cytoplasm in half. - membrane fuses across equator to produce two cells 

they each contain a chromosome that is the same as the parental cell 

P - aPpear

M - Middle

A - Apart

T - Two

Cytokinesis is NOT part of Mitosis 

3.24 b - Mitosis

detail of mitosis: 

first cell has to copy its chromosomes in order for the two split cells to have he same number of chromosomes and same sets 

-  this is DNA replication (copy chromosomes) 

- DNA replication - each chromosomes undergoes copying process. held together by centromere. 

- they are now a 'pair of chromatids' 

- takes place in the nucleus while it is still intact - interphase of the cell cycle 

3.24 a - Mitosis

mitosis - cell division --> growth/increase in number of cells

Outline of process:

- begin with cell - with nucleus. 

- number of chromosomes in the nucleus - diploid number (2n) 

- for humans 2n = 46

- for cats 2n = 38

- mitosis - cell divides into two cells, each with nucleus, each cell has a diploid nucleus - these cells are identical/daughter cells

- identical because 1. Same number of chromosomes. 2. same set of chromosomes 

How are the copies of chromosomes made? and how are they separated? 

3.16 - DNA and Genetic information

first Chromosome - 1000's of genes. 

- gene loci --> double helix - parallel

- double helix --> 'sugar - phospate backbone'

- in the center, group of molecules called bases 

- Adenine, thymine, cytosine and guanine 

- in the molecule they are holding together the two helisis 

- pairing between A-T and G-C - base pairs (ALWAYS in DNA) 

- order of the bases on right side A, C, T, G, A, A, C, C, A, G --> this is the gene 

- Gene in the nucleus - order of the bases (ATGC) 

                                       - number of the bases 

this constructs a protein in the cytoplasm - gives characteristic 

Question: Why are the base pairs always arranged as  A-T and G-C? 

3.15 - Genes

Photo is a molecule of DNA - Double helix shape 

One section is a Gene 

- This gene carries the information of the characteristic of the organsim 

could be: a blood group or a petal colour on a flower 

- Genes are located in the nucleus 

- information passed to cytoplasm 

- then transformed into protein 

- this protein controls the characteristic 

information flows from gene (nucleus) to protein (cytoplasm) 

Question: Are the number of genes affected by your gender?

3.14 - Chromosomes

- 1.

- chromosomes - genetic information within a cell 

- in the nucleus - number of chromosomes. 

- chromosomes - composed of DNA (double helix shape) 

- Sections of the DNA are Genes, poissibly 1000s of genes 

- genes carries information for the construction of a protein 

- protein --> characteristic of the gene. e.g. blood

2. 

- different organisms have different number of chromosomes 

Cat has 38, Chicken has 78, Chimpanze has 42 and humans have 46 

chromosomes per cell 

3. 

- chromosomes operate in pairs - homologus pairs

- homologus nature depends on the length of the chromosomes 

- position pointed out is the Gene Loci. on both homologus pairs the gene is the same at this point 

- 1 version on each so in total 2 versions of each gene for one characteristics. They are called Alleles 

Question: Why do we all have different chromosomes/genes? 

3.1 - Sexual and Asexual reproduction

Sexual reproduction 

show:

- sex - (male or female) 

- produce Gametes. In male (sperm). In female (egg). In plant (sperm is pollen and egg is ovule)

- Type of cell division - Meiosis - half's the total no. of chromosomes in the gamete cell. 

- fertilisation. gametes cells fuse together

- Variation - broad differences

Asexual Reproduction

show:

- sex - none

- no gametes 

- no meiosis only mitosis and binary fission 

- no cell fusion so no fertilisation 

- Small variation. but when enlarged, identical (clone)

question: since sexual reproduction is a lot more common, when and what would use asexual reproduction?