biological molecules

Cards (68)

  • Fibrous proteins have regular, repetitive sequences of amino acids enabling them to form fibres, have a relatively long, thin structure, are insoluble in water, are metabolically inactive, often have structural roles within an organism, and examples include collagen and keratin.
  • Collagen is a fibrous protein with a triple helix structure, made up of three polypeptide chains, forms cross-links between adjacent collagen molecules, contributing to its strength, provides mechanical strength, is found in cartilage and connective tissues, bones, tendons, skin and artery walls, plays a crucial role in wound repair and tissue regeneration.
  • Keratin is a fibrous protein and has a helical structure, forming intermediate filaments, is tough and resistant to wear and tear, insoluble in water, rich in sulphur-containing amino acids, giving it strength and stability, as it forms disulfide bridges between cysteine residual groups, as well as hydrogen bonds, is the main component of hair, nails, and the outer layer of skin, providing protection against mechanical damage, contributes to the waterproofing of skin and feathers, as an impermeable barrier to water, preventing entry of water-borne pollutants.
  • Elastin has a coiled structure and is more flexible than collagen, contains cross-links that allow it to stretch and recoil, provides elasticity to tissues, allowing them to return to their original shape after being stretched, is predominantly found in lungs, arteries, bladder, and skin, allowing them to inflate/deflate, withstand high pressure, hold urine, and stretch around bones.
  • Globular proteins have molecules of a relatively spherical shape, are soluble in water, often have metabolic roles within organism, have hydrophobic R groups turned inwards, hydrophilic groups on the outside, are more reactive to changes in pH, examples include haemoglobin and insulin.
  • Haemoglobin is a globular protein with a quaternary structure, consists of four polypeptide chains, contains iron-containing heme groups, is soluble in water, easily affected by temperature and pH, binds with oxygen in the lungs, carrying oxygen from lungs to tissues and organs, also helps transport carbon dioxide from tissues to the lungs, acts as a buffer, helping to maintain the pH of blood.
  • Insulin is a globular protein with two polypeptide chains linked by disulfide bridges, is soluble in water, binds to glycoprotein receptors on the outside of muscle and fat cells, stimulating increased uptake of glucose from blood, increasing rate of consumption of glucose, reducing overall blood glucose levels, also stimulates increased glycogen synthesis and storage in liver and muscles.
  • Pepsin is a protease enzyme, functions optimally in an acidic environment, typically in the stomach, is initially secreted as pepsinogen, which is activated to pepsin by the acidic conditions in the stomach, is made up of a single polypeptide chain of 327 amino acids, has a symmetrical tertiary structure, held together by hydrogen bonds and 2 disulphide bridges, has only 4 basic R groups and 43 acidic R groups, is so stable in acidic conditions, as there are fewer basic groups to react with H+ ions, so little effect on enzyme’s structure and shape.
  • Water has a tendency to stick to itself (“cohesion”) because it easily forms hydrogen bonds.
  • At any point, a large percentage of water molecules are hydrogen bonding with several neighbors.
  • Surface Tension is a property of water in which water molecules are attracted to each other by hydrogen binding, allowing the molecules to move together.
  • Cholesterol is used to make bile for digestion.
  • Plants contain a cholesterol derivative (has a double bond, where cholesterol has none).
  • Cholesterol ensures cell surface membranes are fluid.
  • Water also has a tendency to stick to other polar objects (“adhesion”), which is why we describe polar objects as hydrophilic (they are miscible with water).
  • Non-polar objects (such as hydrocarbons, or oils) are hydrophobic as they cannot dissolve and are repelled by water.
  • Water adheres weakly to a waxy surface, but strongly to itself, forming a rounded water bead instead of a puddle.
  • Capillary Action is the combination of cohesion, adhesion and surface tension, and occurs because adhesion to the walls of a vessel is stronger than the cohesion between the water molecules.
  • The liquid sticks to the walls then pulls other molecules up behind it, then climbs higher, like a rock climber.
  • If the diameter of the tube is too big, the molecules cannot climb the walls.
  • Polysaccharides are polymers of monosaccharides.
  • Homopolysaccharides are polysaccharides made out of one type of monosaccharide.
  • Heteropolysaccharides are polysaccharides made out of more than one type of monosaccharide.
  • Polysaccharides are good energy stores because they contain 1-4 glycosidic bonds, are polymers of glucose, and can also be respired to release energy.
  • Polysaccharides are usually branched, which can be used for faster release of glucose, as enzymes can work simultaneously on multiple branches.
  • Polysaccharides are insoluble, will not affect water potential, and cannot diffuse into or out of cells.
  • Polysaccharides are very compact yet large, making them efficient methods of energy storage, maximising the amount of energy stored.
  • Polysaccharides are insoluble because they are big, and regions which could hydrogen-bond with water are hidden away inside the molecule.
  • The centre of the bilayer is hydrophobic, so water cannot pass through, making the bilayer a semi-permeable barrier.
  • Phospholipids can also form micelles, balls with tails inside and heads outside.
  • Phospholipids can form a bilayer, and make up 20-80% of all membranes in animal and plant cells.
  • Membrane is more solid, so less substances can pass through freely.
  • Fatty acids: a hydrocarbon chain with a carboxyl group (-COOH), which ionises into H+ and -COO(-)
  • Phospholipids contain a charged phosphate head (PO4 (3-) ion), a glycerol and 2 fatty acids.
  • Inside and outside the membrane is an aqueous solution, therefore the phosphate heads point outwards, and the fatty acid tails face inwards.
  • Glycerol molecule: an alcohol with 3 hydroxyl groups (-OH)
  • In water, phospholipids form a monolayer, with heads in water and tails sticking up out of water.
  • Polyunsaturates tend to kink, and they cannot pack closely or crystallise as the kinks push the molecules apart slightly, making them more fluid, so they are often liquids at room temp.
  • Saturated fats - have no C=C double bonds
  • R groups are any groups in which a carbon or hydrogen atom is attached to the rest of the molecule