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Transcript
N5 Revision Cell Biology Cell structure Animal Cell Ribosomes Cell membrane Nucleus Cytoplasm Mitochondrion Cell structure Cell structure Fungal Cell (yeast) Cell structure Bacterial Cell DNA Cytoplasm Plasmids Ribosomes Cell wall Cell membrane Functions Transport Double layer of phospholipid Proteins Protein channel (Pore) Some proteins allow molecules to pass through them easily – PORES Some proteins are responsible for active transport of molecules Diffusion • Diffusion is defined as; The movement of a molecules down a concentration gradient from a high concentration to a lower concentration. • Diffusion is an example of passive transport; Passive transport is the movement of molecules down a concentration gradient from a high concentration to a lower concentration, and does not require energy for it to take place. Active transport • Active transport is; The movement of molecules and ions against a concentration gradient, from a region of low concentration to a region of high concentration. • Active transport requires energy for membrane proteins to move molecules and ions against the concentration gradient. • For example, nerve cells need to pump sodium out and potassium in. Producing new cells Stages • Chromosomes are replicating • Chromosomes shorten and thicken so they are now visible • Chromosomes line up at the equator and spindle fibres attach at the centromere • Chromatids are pulled apart to opposite sides of the cells • Nucleus reforms in each new daughter cell and cytoplasm divides DNA and the production of proteins The structure of DNA is known as a double helix. It has a 2 sugar phosphate back bones with pairs of complementary bases held together. DNA code DNA carries the genetic code to make proteins. This code is the order of the bases on the DNA molecule. The bases are adenine, thymine, cytosine and guanine. The DNA molecule is too important to carry the code from the nucleus to the ribosome where proteins are made, so a copy is made. This copy is messenger RNA (mRNA). It carries a complementary copy of the code to the ribosome. The sequence of the bases determines the order of the amino acids, which makes the protein . Different proteins are coded for by different strands of DNA, so their order of amino acids is different. Types of proteins Because of the different order of amino acids making up the protein their shape is often different. The shape of a protein is different for different types of proteins; Structural – structural proteins in the body are keratin found in hair and nails and collagen which makes skin elastic. Hormones – these are chemical messengers that travel in the bloodstream. Antibodies - these are Y-shaped molecules which will bind to foreign cells allowing our immune system to destroy them. Enzymes Enzymes are another type of protein in the body. They are biological catalysts They speed up chemical reactions in the body and are unchanged in the process. They work by binding to the substance they are going to work on (substrate) and holding it in the active site. The active site The active site must have a complementary shape to the substrate if they are going to fit together. For this reason enzymes are specific like a lock and key. Enzyme activity At low temperatures, enzyme activity is low as the substrate and the enzyme are moving so slowly they don’t get to meet very often to work. As the temperature increases so does enzyme activity, however, at high temperatures, the enzyme’s shape is altered, meaning the active site no longer matches the substrate shape. The enzyme is denatured. The temperature that the enzyme’s activity is the highest is known as the optimum temperature. Enzyme activity Enzymes are also sensitive to changes in pH. There will also be an optimum pH, and either above or below this, will cause the enzyme to denature. Genetic engineering Bacteria have plasmids which can be removed and altered in genetic engineering. We can add a human gene to the plasmid and then after inserting it back into the bacteria, have this genetically modified organism produce a new substance for us. Insulin is produced in this way. 3. Plasmid extracted 1.Chromosome extracted and gene identified 2. Gene cut out by a special enzyme 5. Gene inserted into plasmid and sealed by an enzyme 6. Plasmid inserted into bacterial host cell 7. Genetically modified bacterium grows and multiplies 8. Gene protein produced by duplicates of plasmid 4.Plasmid cut open by a special enzyme Photosynthesis Photosynthesis is a two-stage process. Stage 1 – Light Reactions Stage 2 – Carbon fixation Light reactions Light energy is trapped by the chlorophyll in chloroplasts. The light energy is used to split water into hydrogen and oxygen and make ATP. The ATP and hydrogen are used in the second stage but oxygen diffuses out of the cell. Carbon fixation Carbon fixation is where hydrogen and carbon dioxide are joined together to make glucose. Enzymes are essential in this stage. The glucose can be used for respiration immediately or it can be stored as starch or used to make cellulose for cell walls. Fermentation When no oxygen is present in the cell, fermentation occurs. In plants, Glucose pyruvate ATP ethanol + CO2