B3a - Molecules of Life

Cells
1. Nucleus - contains the genetic information and controls what the cell does. It has a membrane extending from it, onto which ribosomes are attached.
2. Cytoplasm - where most chemical reactions take place, it may contain mitochondria which is where most energy is released in respiration.
3. Cell membrane - controls movement into and out of the cell.
4. Mitochondria - place of respiration, provide energy for the life process. Liver and muscle cells have particularly large numbers of mitochondria because they have a high energy requirement.
DNA
1. The nucleus of each cell contains a complete set of genetic instructions called the genetic code.
2. Information is carried by genes on chromosomes, which are long coils of a chemical called DNA.
3. The genetic code controls cell activity and, consequently, some characteristics of the organism.
4. A DNA molecule is made up of two strands coiled around each other in a double helix.
5. The genetic code is in the form of a chemical code made up of four bases.
6. These bases bond together in pairs forming the links which hold the two strands of DNA together.
7. Each gene in a DNA molecule contains a different sequence of bases. The bases code for the structure of different proteins that are needed for the growth and repair of cells.
8. Proteins are made in the cytoplasm. The code, carried in DNA, is in the nucleus. As DNA does not leave the nucleus, a copy needs to be made and transferred to the cytoplasm.
9. DNA controls cell function by controlling the production of proteins, some of which are enzymes
Watson and Crick
1. This highly specialised structure was first put forward in 1953 by James Watson and Francis Crick. They used data from cyrstallography experiments performed by Rosaland Franklin. The data from her experiments helped Watson and Crick develpo a model that fitted the data. The model showed two chains wound as a double helix and other data indicated that the bases occured in pairs.
2. The structure fitted the data so perfectly that it was accepted almost immediately. Watson and Crick were awarded the nobel prize for medicine in 1962 for thier discovery of the structure of DNA. Thier discovery is considered the most important biological work of the last century. It led to an explosion of scientific advances including genetic engineering and mapping the human genome.
Bases in DNA
1. The four bases in DNA are A, C, G, T. A always bonds with T and C always bonds with G on opposite strands of the DNA molecule. This is complimentary base paring.
2. Proteins are made up of chains of amino acids. The cell uses the amino acid from food to construct them. When a cell needs to produce proteins of a particular type, certain genes will be switched on. These genes and their resulting proteins determine the characteristics of the cell.
Protein Synthesis
1. The sequence of bases in a gene represents the order in which the cell should assemble amino acids to make a protein.
2. A group of three bases represent one amino acid in a protein chain. Each protein has a different shape and function.
3. Proteins are synthesised by structures called ribosomes. These are too small to be seen under a light microscope. The are located in the cytoplasm.
4. In order for the DNA code in the nucleus to be translated as a new protein by the ribosomes, a 'messenger' molecule needs to travel from the nucleus into the cytoplasm and then become attached to a ribosome. The molecule is called mRNA
5. 1. mRNA constructed from DNA template in nucleus.... 2. mRNA carries code from original DNA into the cytoplasm and becomes attached to a ribosome.... 3. Ribosome'translates' the code on mRNA and constructs a sequence of amino acids.... 4. Amino acids linked together as a long chain protein, which is released from the ribosome to carry out it's function.

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B3a - Molecules of Life

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