4.1.2 Cell division

4.1.2.1 Chromosomes

• Chromosomes are the genetic information in nucleus
• They affect the make-up of the cell
• They determines which proteins are made

• DNA is packaged in chromosomes
• Chromosome are made up of coiled up DNA sections
• The DNA must not be tangled

• DNA makes up genes
• Genes = sequences of DNA
• Genes code for certain characteristics
• Each chromosome has many genes

Chromosomes in Pairs

• Chromosomes come from biological parents
• Each cell has 23 pairs of chromosome
• One copy of each set from the father and one copy from the mother
• Chromosomes are found in pairs

• If they are not paired, it could lead to genetic disease
• Many genetic diseases are as result of chromosome pairing problems e.g. Down’s Syndrome – extra 21st chromosome

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4.1.2.2 Mitosis and the cell cycle

Cell Cycle

• The cell cycle is how cells duplicate and divide
• Cells divide to replace dead cells for growth or repair
• The length of the cell cycle varies between organisms
• Hair follicles, blood, skin and digestive system lining divide fast, and have a very quick cell cycle

• Interphase – cell are ready to divide, the cell grows, DNA duplicates, organelles are made
• Metaphase – genetic material separates, the cell is ready to divide into two daughter cells
• Cytokinesis – the cytoplasm and cell membrane split into two daughter cells

DNA Replication

• The cell grows to form two copies of each chromosome
• This cell now has double the DNA
• Each cell will eventually get the normal share of DNA

Making Organelles

• Organelles are produced so the cell now has double the organelles
• There is an increase in mitochondria number for energy
• There is also an increase in ribosomes for protein synthesis
• The cell grows, with the cell surface membrane extending and the cytoplasm grows too

Mitosis

• Chromosomes line up on equator (middle of the cell)
• Chromosomes are pulled to opposite poles (sides) of the cell
• Chromosomes are pulled apart by spindle fibres
• Membranes form around the chromosomes to become two new nuclei

Cytokinesis

• Division of the cytoplasm and cell membranes to surround the new nuclei are formed
• This final stage of the cell cycle involves the formation of new cells

Mitosis for Growth

• Cells are constantly growing and dividing
• Mitosis allows this with the formation of identical daughter cells
• Important for all eukaryotes cells as they are needed to grow

Mitosis for Development

• Replacing skin cells – skin cells damaged constantly, replaced by dividing cells underneath the surface
• Growth of organism
• Asexual reproduction – single-celled organisms reproduce to produce two daughter organisms

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4.1.2.3 Stem cells

Types of Stem Cells

• A stem cell is an undifferentiated cell
• It has the ability to differentiate and form a specialised cell
• It can divide by mitosis to form a tissue of stem cells
• Then different cell clusters can differentiate to many tissues of different specialised cells
• This is how the human body develops from a single embryonic stem cell

Embryonic Stem Cells

• Stem cells in embryos are known as embryonic stem cells
• Embryonic stem cells are found in early embryos
• They are completely undifferentiated
• They can be used to turn into any type of cell

Adult Bone Marrow Stem Cells

• Stem cells can be found in the bone marrow, teeth and other areas
• These cells cannot differentiate into any type of cells (like embryonic stem cells)
• They can only differentiate into predetermined cells, such as some blood cells (i.e. red blood cells and white blood cells)

Plant Stem Cells

• Stem cells are found in plant meristems
• These cells can differentiate to form any type of plant cell
• They are present throughout the lifespan of the plant

• Stem cells from meristems can be used to prevent extinction
• These cells can be harvested from plants that are threatened by extinction
• These plants can then be grown in favourable conditions, as clones of the original plant, to keep these rare plants in existence

Stem Cells to Treat Diabetes

• Patients with diabetes suffer from a lack of insulin, and have high blood glucose levels
• Stem cells can be made that can produce insulin, for insulin injections
• Used to treat those who suffer from diabetes (type I)

Stem Cells to Treat Paralysis

• Stem cells can be differentiated to form nerve cells
• These cells are used to treat those who suffer from the nerve damage that causes certain types of paralysis

Therapeutic Cloning

• Immune rejection is an issue in medical treatment
• There is a risk of the recipient’s immune system rejecting the  ‘foreign’ cells
• The use of therapeutic cloning can reduce the risk of rejection

• Therapeutic cloning uses stem cells from the patient
• An embryo is produced, to have the same genetical material as the patient, and the stem cells are extracted
• These cells should not be rejected by the patient’s immune system as they have the same genetic material as the patient

Ethical Debate