biological molecules

as biology module 1

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Globular - roll up to form balls, usually soluble, usually have metabolic roles, e.g enzymes found in all organisms, plasma proteins and antibodies found in the blood of mammals. Haemoglobins quaternary structure consists of four polypeptide subunits, two alpha cahins and two beta chains. The four subunits form one water soluble globular protein. A specialised part of each polypeptide called the haem group, a prosthetic group, contains an iron ion. the haem group is responsible for the colour. An oxygen molecule can bind to the to the iron in the haem group, one haemoglobin can bind to four oxygen molecules.

Fibrous - form fibres, usually insoluble, usually have structural roles, e.g collagen found in bone and cartilage, keratin found in hair and fingernails. Collagen is a fibrous protein made up of three polypeptide chains wound around each other. each of the three chains is a coil made up of around 1000 amino acids. hydrogen bonds form between the chains giving strength. Strength is increased as each collagen molecule forms covalent bonds with the collagen molecules next to it resulting in a collagen fibril, many fibrils form a fibre. collagen provides mechanical strength e.g in the walls of arteries, tendons connecting skeletal muscles to bones, cartilage, bones, connective tissue.

Quaternary structure refers to the fact that some proteins are made up of more than one polypeptide subunit joined together.

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Lipids are a diverse group of chemicals that dissolve in organic solvents suchas alcohol but not water. They perfrom a number of functions - a source of energy, energy storage, biological membranes, insulation, protection, some steroid hormones. Lipids are insoluble in water.

Triglycerides - consist of one glycerol molecule bonded to three fatty acid molecules. A condensation reaction betweenthe acid group of a fatty acid molecule and one of the OH groups of the glycerol molecule forms a covalent bond, a water molecule is also produced. The new bond is an ester bond. They are hydrophobic as the charges are evenly distributed around the molecule. This means that hydrogen bonds cannot form with water molecules so they do not mix easily.

Phospholipids - similar to triglyceride except the third fatty acid is not added instead a phosphate group is. The phosphate head is hydrophilic and the tails are hydrophobic.

Cholesterol is a small molecule made from four carbon based rings. It is hydrophobic so can sit between tails and regulate membrane fluidity. Testosterone, oestrogen and vitamin D are made from cholesterol. In bile it can stick together to form gallstones, atherosclerosis in blood vessels.

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*Solvent - metabolic processesin all organisms rely on chemicals being able to react together in solution - 70-95% of cytoplasm is water. Dissolved chemicals take part in processes such as respiration and photosynthesis. *Liqiud - The movement of materials around organisms, both in cells and on a large scale in multicellular organisms , requires a liquid transport medium - blood in animals and the vascular tissues in plants use water as a liquid transport medium. *Cohesion - water molecules stick to each other creating surface tension. cohesion also makes long, thin water columns strong and difficult to break - transport of water in the xylem relies on water molecules sticking to each other as they are pulled up the xylem in the transpiration stream. some organisms make use of surface tension to walk on water. *Freezing - water freezes forming ice on the surface. water beneath the surface becomes insulated and less likely to freeze - polar bears live in an environment of foating ice packs. lakes tend not to freeze completely so aquatic organisms are not killed as temperature drops. *Thermal Stability - large bodies of water have fairly constant temperatures, evaporation of water can cool surfaces by removing heat - oceans provide a relatively stable environment in terms of temperature. Many land based organisms use evaporation as a cooling mechanism. *Metabolic - water takes part as a reactant in some chemical processes - water molecules are used in hydrolysis reactions and in the process of photosynthesis.

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Bethany Cunningham


Great, clear information!

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