Cell Continuity
Cell Continuity
Cell continuity is the ability of cells to divide and survive from one generation to the next.
3 steps to form a new cell
— Produce materials it will need
— Grows larger
— Reproduces to form a new cell
Ø When dividing = Chromatin forms a numbers of clearly distinguishable Chromosomes
Ø Chromosomes are in pairs in diploid cell, called homologous pairs.
Ø Homologous chromosomes are pairs of chromosomes that posses the same genes, in the same positions.
Ø Diploid is symbolised as ‘2n’ and total no. of chromosomes in cell is given as 2n=46 in humans
Ø In diploid cells, 1 chromosome from the homologous pair comes from the mother and the other comes from the father.
Cell continuity is the ability of cells to divide and survive from one generation to the next.
3 steps to form a new cell
— Produce materials it will need
— Grows larger
— Reproduces to form a new cell
Ø When dividing = Chromatin forms a numbers of clearly distinguishable Chromosomes
Ø Chromosomes are in pairs in diploid cell, called homologous pairs.
Ø Homologous chromosomes are pairs of chromosomes that posses the same genes, in the same positions.
Ø Diploid is symbolised as ‘2n’ and total no. of chromosomes in cell is given as 2n=46 in humans
Ø In diploid cells, 1 chromosome from the homologous pair comes from the mother and the other comes from the father.
Mitotic Cell Cylce
- Interphase: Period between division
- Mitosis:
- Cell divides
Longest phase in cell cycle = 90% of a cells life is in interphase
DNA been copied.
o The total DNA content goes from 2n to 4n
Cell organelles been copied
o .This is to ensure that each of the two new cells receives copies of all the organelles (so it can function).
Mitosis is division of the nucleus to produce two daughter nuclei containing identical sets of chromosomes.
Stage 1: Prophase
Stage 2: Metaphase
Stage 3: Anaphase
Stage 4: Telophase
Stage 1: Prophase
![Picture](/uploads/2/6/9/0/26900109/78515.png)
• Each chromosome appears as a duplicated strand: Sister chromotids.
• Centrioles migrate to each end of the cell and fibres appear in cytoplasm
• Nuclear membrane starts to break down.
• Centrioles migrate to each end of the cell and fibres appear in cytoplasm
• Nuclear membrane starts to break down.
Stage 2: Metaphase
![Picture](/uploads/2/6/9/0/26900109/2521993.png)
• Chromosomes thicken even more
• Chromosomes line up across the centre of cell
• Fibres attach to chromosomes at centromers (Each sister chromotid has 2 fibres attached, 1 from each side of the cell)
• Chromosomes line up across the centre of cell
• Fibres attach to chromosomes at centromers (Each sister chromotid has 2 fibres attached, 1 from each side of the cell)
Stage 3: Anaphase
![Picture](/uploads/2/6/9/0/26900109/7499577.png)
• Fibres contract, sister chromatids are pulled apart
• Each daughter chromosome is pulled to opposite end of cell.
• Hence, identical set of genes pulled to each end of the cell.
• Each daughter chromosome is pulled to opposite end of cell.
• Hence, identical set of genes pulled to each end of the cell.
Stage 4: Telophase
![Picture](/uploads/2/6/9/0/26900109/4963168.png)
• Nuclear membrane forms around each of the 2 sets of chromosomes
• Chromosomes elongate within each nucleus to chromatim
Mitosis is complete
• Chromosomes elongate within each nucleus to chromatim
Mitosis is complete
Cell divides/Cytokinesis
Original cell divides to form 2 cells
Functions of Mitotic cell division
In Unicellular Organisms
Method of reproduction eg. Amoeba. Reproduction that does not involve the joining of 2 cells is called asexual reproduction.
In Multicellular Organisms
Produces new cells, not new individuals
Responsible for growth & renewal and repair of cells
Method of reproduction eg. Amoeba. Reproduction that does not involve the joining of 2 cells is called asexual reproduction.
In Multicellular Organisms
Produces new cells, not new individuals
Responsible for growth & renewal and repair of cells
Functions of Meiotic cell division
2 functions in Multicellular Organisms
Allows sexual reproduction without increasing the number of chromosomes in the offspring
Allows new combinations of genes
Allows sexual reproduction without increasing the number of chromosomes in the offspring
Allows new combinations of genes
Cancer
Rate of cell division (mitosis) is carefully controlled.
Sometimes a cell or group of cells lose the ability to control the rate of cell division.
They form a mass of cells called a tumour which can be benign or malignant.
Cancer is a group of disorders in which certain cells lose their ability to control both the rate of mitosis and the number of times mitosis takes place.
Sometimes a cell or group of cells lose the ability to control the rate of cell division.
They form a mass of cells called a tumour which can be benign or malignant.
Cancer is a group of disorders in which certain cells lose their ability to control both the rate of mitosis and the number of times mitosis takes place.
Benign tumours
Benign means kind, they are not life threatening and do not invade other tissues. Eg warts, skin tags.
Cells stop dividing after some time
Cells stop dividing after some time
Malignant tumours
Uncontrolled multiplication of abnormal cells
Malignant tumours (cancers) invade other cells and move around the body
Movement of these cells called Metastasis.
Malignant cancer cells divide indefinitely.
Malignant tumours (cancers) invade other cells and move around the body
Movement of these cells called Metastasis.
Malignant cancer cells divide indefinitely.
Causes of Cancer
Caused when normal genes are altered to form cancer-causing genes called oncogenes.
Brought about by cancer causing agents called carcinogens eg cigarette smoke, asbestos fibres, ultraviolet radiation and some viruses
Most cancers can be cured with Radiation (burn out cancer), Chemotherapy (Chemicals slow down mitosis) and surgery
Brought about by cancer causing agents called carcinogens eg cigarette smoke, asbestos fibres, ultraviolet radiation and some viruses
Most cancers can be cured with Radiation (burn out cancer), Chemotherapy (Chemicals slow down mitosis) and surgery