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Cells and Organs

Cells are the basic units of life.

Groups of celss works together to from tissues.

Groups of tissues work together to from organs.

Example organs: Eyes, lungs, ears, heart, stomach, skin

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How a baby is made

A stem cell- a unspecialised cell that can develop into other cells. Adult stem cells have a limitted range. Embryonic stem cells have a full range.

How a baby is made:

Fertilisation --> fertilised egg cell (zygote) --> the zygote splits for the first time --> 8 cell stage still has embryonic stem cells --> cells continue to grow and divide but now are becoming specialised and start forming differnt tissues --> at 12 weeks the embryo becomes a fetus --> a baby is born

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Mitosis occurs in the reproduction of a cell. It produces clones with no genetic variation. You end up with 2 cells.

Each chromosome has an identical copy attached to it. The membrane around it breaks down.

The chromosomes move to the center of the cell. Proteins release spindles untangle and pull apart the chromosome pairs.

The chromosome copies seperate to opposite ends of the cell. New nuclear membranes form.

There is cell growth to make up for the rest of the organelles and the chromosomes are copied. The whole cell then splits and the cycle is continued

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Difference between plants and animals

Plants have rings of dividing cells in the stem tips, roots, buds and leaves to increase their size. These are called meristems. The new cells produced from meristems are also unspecialised. These can go on to form xylem of phloem tissues within the plant organs (bud, root, stem and leaf)

Animals have stem cells which can divide into new specialised cells. Eg. when a newts leg gets bitton off stem cells go too the stump and re grow a leg. This is because newts stem cells stay unspecialised throughout their lives.

When gardeners take cuttings they are clones of the original plants. Plants can clone themselves but humans can't

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You have two copies of each chromosome.

Just before cell divison, copies of the gentetics information are made. So each chromosome is doubled.

In meiosis the cell devides twice, so four gamates are formed. In the first division, the doubled chromosomes pair up and line along the center of the cell

The chromosomes move apart and begins to split

Two cells are made and the process repeats. 

The cells produced only contain 23 chromosomes. This is important because during fertilisation they will join will anouther 23 chromosomes to make a unique set of DNA

Haploid = half the amount

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There are four special molecules, called bases, that make up your DNA

  • Adenine (A)
  • Thymine (T)
  • Guanine (G)
  • Cytosine (C)

A always pairs with T (AT)

C always pairs with G (CG)

DNA has a double helix structure. Basics links the two helixes together.

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Protein is made up of amino acids.

There are 20 kinds of amino acids in protein

Amino acids can be joined in any order along the chain, so thousands of different kinds of protein are possible.

The sequence of amino acid, fixes the shape. The shape gives the protein it's chemical properties.

The order of the bases in a gene is the genetic code for the production of a protein. For every 3 bases you get an amino acid ( the triplet code).

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Protein Synthesis

DNA is a long double helix.

An enzyme (DNA helicase) unzips the DNA 

MRNA is a small section of DNA that is small enough to fit through the holes of the nucleus membrane. MRNA has Uracyle (U) instead of Thymine (T).

The genes do not leave the nucleus but a meassenger (RNA) is produced to carry the genetic information to the cyctoplasm.

The MRNA travels to the Rhibosome. 

Here it is read 3 bases at a time. 3 bases= an amino acid.

The amino acids join together to make proteins.

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Gene switching

In an unspecialised cell all genes are switched on

In a specialided cell some genes are switched off. Eg. In a hair cells certain genes are switched off making it a hair cell or in a salivery gland cell anouther combination of genes are switched off making it a salivery gland cell. This is because a cell only needs to make the specific protein it needs.

In carefully controlled conditions of the cloning of mammels it is possible to reactiviate genes that have been switched off in the nucleus of a body cell to form cells of all tissue types.

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