Cells, Tissues, Organs & DNA
Cells - Single units of life. They are the building blocks of all living things. All cells contain: DNA and organelles. A group of the same type of cell work together to form a tissue.Organelles are different parts of a cells's structure. They do different jobs within the cell and work together to allow the cell to perform a specific function.Tissues - Salivary gland cells = a salivary gland. It's function is to secrete saliva. Nerve cells = a neuron(e). It's function is to conduct electrical impulses. Blood cells = blood for transport e.g. transporting nutrients. Bone cells = bone marrow/bone for support.Organs -Different groups of cells work together to form an organ. Each organ peforms different jobs to allow the human body to survive. Lung = gas exchange (by respiration and expiration) Stomach = digestion of vital nutrientsKidney = excretion + vital controlling of water balance. DNA - a very large molecule shaped like a twisted ladder. The shape is a double helix.Long strands of DNA make up chromosomes. These are found in the nucleus of a cell.Animal cells - have: cytoplasm (where most chemical reactions take place), a nucleus (contains genetic information), ribsomes (where protien synthesis takes place) and a cell membrane (controls movement into & out of the cell. Plant cells: cell wall (strengthens the cell), a permanent vacuole (helps support the cell) & chloroplasts (absorb light energy to make food).
Mitosis & Meiosis
Mitosis is a type of cell division. Mitosis occurs wherever more cells are needed. It produces two new cells that are identical to each other, and to the parent cell. The process of growth and division is called the cell cycle.The cycle starts as the number of organelles - the different parts of the cell - increases. This is to ensure that each of the two new cells receives copies of all the organelles.Before a cell divides, its chromosomes are copied exactly. The DNA molecule is made of two strands. As each of the two strands separate, new strands are made alongside each of them, making two new copies.
Meiosis - Meiosis is a different kind of cell division. It is used to produce male and female gametes. A human body cell contains 46 chromosomes arranged in 23 pairs. The gametes are sperm or eggs, and only contain half as many chromosomes (23). This is why meiosis is sometimes called reduction division.At fertilisation, the nuclei of the sperm and an egg join to form the zygote. The zygote contains 23 pairs of chromosomes - 23 single chromosomes from the sperm, and 23 single chromosomes from the egg, thereby creating the correct number of 46 chromosomes for all body cells. It also means the zygote contains a complete set of chromosomes from each parent.
Fertilization, Variation and Genes
Fertilization = Male gamete (sperm) + female gamete (egg) = zygote (a single-body cell) Gametes only have 1/2 of the number of chromosomes as the parent cell so the zygote has a full set. Pair of chromosomes = 1 from mum + 1 from dad. The zygote divides by mitosis to produce an embryo. The embryo divides by mitosis to eventually be a big grown up adult (1-2-4-8-16-32 etc.)
Variation -Meiosis & sexual reproduction produce variation between parents & their kids. When the gametes fuse, genetic info from 2 people is combined. Per gene, 1 parent's alleles are passed on.Each kid can have a different combination of the parent's alleles = kids with different characteristics.
Genes - on the chromosomes in each cell nucleus. Genes control growth & development in organisms & the development of charcteristics like eye colour.
Genetic Code, Controlling Growth & Development
Genetic code - genes control characteristics by providing instructions for the production of proteins. The instructions are top-secret, and are written in a code, made up of 4 bases which hold the 2 strands of DNA molecule together. The bases always pair the same way; Adenine (A) pairs with Thymine (T) & Cytosine (C) pairs with Guanine (G).
Controlling Growth & Development - DNA is too large to leave the nucleus. The genes stay inside the nucleus but protein production is outside the nucleus, in the cytoplasm. Information stored in the genes has to be transferred into the cytoplasm. 1) the relevant section of DNA is unzipped. 2) Instructions are copied onto smaller moleclules called messenger RNA(mRNA) 3) The mRNA leave the nucleus and carry the instructions to the ribsomes. 4) The ribsomes follow the instructions to make the relevant protein.
The sequence of bases in a gene determines the order in which amino acids are joined together to make a particular protein. A group of 3 base pairs codes for 1 amino acid in a protein chain called the triplet code. There are 20 different amino acids that can be made. The structure of the protein depends on the amino acids that make it up. 1) DNA unravels at the correct gene 2) A copy of the coding strand is made to produce mRNA 3) The mRNA copy moves from the nucleus into the cytoplasm. 4) The triplet code is decoded by the ribsomes. 5)Amino acids are joined together to form a protein (called polypeptide)
Development of new organisms & Stem cells
Development of new organisms - Up to the 8 cell stage, all cells in a human embryo: are unspecialized and can turn into any type of cell. These cells = embryonic stem cells. After the 8 cell stage, the cells in the embryo become specialized and form different types of tissue. The cells contain the same genes, but many genes are not active because the cell only produces the proteins it needs to carry out its role.
Stem Cells - Stem cells could potentially be used to help treat diseases and disorders and/or repair damage to various tissues. There are 3 sources of stem cells; 1) embryos 2) blood from the umbilical cord 3) adult stem cells. Only the embryonic stem cells are completeley unspecialised and can be used to form any cell type. In therapeutic cloning 1) the nucleus is removed from an egg cell and replaced with a nucleus from 1 of the patients' cellls. 2) The egg cell is then stimulated so that it starts to divide (as if it were a zygote) 3) At the 8 cell stage, cells can be removed as they are still unspecialised.
Adult stem cells will only produce cells of a certain type. e.g. cells for creating blood in bone marrow have to be encouraged to grow more of that type of cell by reactivating (switching back on) inactive genes in the nuclei. Advantage= the replacement tissue can be taken from the patient so the patient's immune system won't reject the transplant.