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Lecture 17

BMS1021:Cells, tissues and organisms: Lecture 17, 18 & 19

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Biomedical Sciences
John Bertram

Lecture 17: Water: - Polar - Forms hydrogen bonds between water molecules - A Calorie is defined as the amount of heat that causes 1g of water to change its temperature by 1 degree Celsius - High heat capacity equivalent to about 4.2 J gram-1 ºC-1 - Due to the strength of the hydrogen bond, it takes a lot of energy to break the bonds. - - Ice has a low density as the hydrogen bonds are more stable - The ice lattice that forms when water freezes forces water molecules further apart than they are in liquid water - Ice thus firms at the SURFACE of ponds and lakes, allowing life to continue underneath - Water is the principal SOLVENT for materials within cells. - Water readily dissolves polar molecules and is an excellent solvent for ionic compounds such as salts A molecule with both hydrophobic and hydrophilic regions is termed amphipathic Buffers in biological systems: Buffers are a mixture of a weak acid and it’s conjugate base, working best when both are present in equal amounts. They resist changes in pH caused by addition of H+ or OH-, due to a balancing act between the two dissociation equations: - Human blood is maintained at pH7.4 (7-7.8) This is vital for Oxygen carrying capacity as Haemoglobin’s Oxygen binding curve is pH dependant Lecture 18: Carbohydrates: - Polysaccharides Monosaccharides join up via glycosidic linkages Starch: - Starch is a homopolysaccharide made entirely from glucose - major energy storage sugar in plants - two forms, amylose and amylopectin - It is stored as granules inside the chloroplasts of plant cells Glycogen: - Glycogen is an animal polysaccharide, also a polymer of glucose - it is stored inside cells (mainly liver and muscle) as insoluble granules Polysaccharide chitin is one of the main components of the cell walls of fungi and the exoskeleton of crustaceans Bacterial cell wall is made of a complex polysaccharide bound to protein known as peptidoglycan Glycoproteins: - Protein chains with covalently bound sugar chains - Aid in communication and as markers on the cell Proteins: - function as enzymes in cellular metabolism - provide structural support - hormones are proteins - R
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