2.1.2 - biological molecules

• water has a high surface tension
• water is incompressible
• water is a solvent for chemical reactions in the body
• water has a high latent heat of vaporisation
• water has cohesion between molecules
• water being incompressible is important to organisms as it provides turgidity to plant cells. it also

  provides a hydrostatic skeleton for small animals
• ice floats on water because it is less dense than water. hydrogen bonds between molecules hold ice in an open lattice structure further away form eachother.
• ice floating on water is important for organisms as it traps an insulating layer of water underneath so aquatic organisms can survive and acts as a habitat
• waters high surface tension is important because it slows water loss due to transpiration stream.

  allows water to rise high in narrow tubes so there is less pressure on roots.

  allows some insects to skim across the surface of water
• water is an important solvent for organisms as it is polar so dissolves and transports charged particles involved in cell reactions
• The high specific heat capacity and latent heat of water is important as it acts as a temperature buffer which enables substances to resist fluctuations in core temperature to maintain optimum enzyme activity
• high specific heat capacity and latent heat of water is important because when water evapourates from the skin it gives as cooling affect to lower body temperature for thermoregulation
• Waters high boiling point means that animals have a stable water temperature and less energy is spent on temperature control.
• Ice floats on water so the water below doesn’t freeze allowing organisms to move under water
• Water has adhesion to other molecules and surfaces
• A monomer is the smaller units that join together to form larger molecules
• Examples of monomers are:

  monosaccharides

  amino acids

  nucleotides
• A polymer is the molecules formed when many monomers join together
• In condensation reactions, a chemical bond forms between 2 molecules and a molecule of water is produced
• In hydrolysis, a water molecule is used to break a chemical bond between two molecules
• The elements found in carbohydrates and lipids are:

  carbon

  hydrogen

  oxygen
• The elements found in proteins are:

  carbon

  hydrogen

  oxygen

  nitrogen

  sulfur
• Alpha and beta glucose are both hexose monosaccharides with a ring structure
• Alpha glucose has a hydrogen above carbon one and a hydroxyl group below carbon one
• Beta glucose has a hydroxyl group above carbon one and a hydrogen below carbon one
• Alpha glucose is small and soluble so is easily transported around the blood stream
• alpha glucose has a complementary shape to enzymes for glycolysis
• Ribose has a hydroxyl group above carbon one and a hydrogen below carbon one
• Ribose is a pentose monosaccharide with a ring structure
• 1-4 or 1-6 glycosidic bonds form when monosaccharides react
• 2 monosaccharides together forms a disaccharide.

  Multiple monosaccharides form a polysaccharide.
• Maltose is a disaccharide formed from a condensation reaction between alpha glucose and alpha glucose
• Sucrose is a disaccharide formed by a condensation reaction between glucose and fructose
• starch is a storage polymer of alpha glucose in plant cells. it is insoluble so has no osmotic effect on cells. it is large so it does not diffuse out of cells
• Starch is made from amylose and amylopectin
• Amylose is made from alpha 1-4 glycosidic bonds. it is a helix shape with intermolecular hydrogen bonds and is very compact
• Amylopectin is made from 1-4 and 1-6 glycosidic bonds. It is branched with many ends for hydrolysis into glucose
• Cellulose is a polymer of beta glucose and gives rigidity to plant cell walls as it prevents cells from bursting when turgid.
• Cellulose is made of 1-4 glycosidic bonds. it is a straight chain unbranched molecule. alternate glucose molecules are rotated 180 degrees. the hydrogen bond crosslinks between parallel strands form microfibrils which give high tensile strength
• Chains of cellulose form hydrogen bonds between them to form beta pleated sheets