Biology unit 1 A

• Water


  Liquid at normal temperatures, while other small molecules like CO2 and O2 are gas
• Features of water and its significance to life


  • Hydrogen bonding
  • Solvent
  • High surface tension and cohesion
  • High specific heat capacity
  • High latent heat of vaporisation
  • Density and freezing properties
• Hydrogen bonding


  The weak electrostatic intermolecular force between a partially positive hydrogen that is bonded to a partially negative oxygen and other polar molecules nearby
• Solvent


  Water is an effective solvent because of its polarity and so can form electrostatic interactions with other polar molecules and ions. Thus it is a transport medium and reagent for metabolic and other reactions in plant and animal cells
• Cohesion


  The attraction of one water molecule to each other. Water molecules have strong, cohesive forces due to hydrogen bonds, thus having high surface tension
• Specific heat capacity


  The amount of heat energy required to raise the temperature of 1 kg of water by 1 °C. Water has high SPC due to its hydrogen bonds
• Latent heat of vaporisation


  A measure of the heat energy needed to vaporise a liquid. Water has a high LHV due to its high SPC as H bonds need to be broken before water can be vapourised, cooling the surrounding environment
• Density and freezing properties


  Ice is less dense than water and floats on it, insulating water and preventing it from freezing, preserving aquatic life underneath it. Changes in the density of water with temperature causes currents, which helps to maintain the circulation of nutrients in the oceans
• Monosaccharides


  Made up of Carbon, Hydrogen, and Oxygen. They have the general formula Cn(H2O)n where n represents the number of carbon atoms. Due to their structure, they are able to be broken down quickly by living organisms to produce ATP energy

  
• Properties of Monosaccharides


  • Sweet
  • Soluble in water
  • They have an osmotic effect
  • Crystalline in nature
• Examples of Monosaccharides


  • α-glucose
  • Fructose
  • Galactose

  
• Disaccharides


  Form when two monosaccharides join in a condensation reaction. Condensation reaction is the process in which two OH groups of two monosaccharides eliminate 2 Hydrogen atoms and 1 Oxygen atom, releasing water and forming a glycosidic bond

  
• Disaccharides


  • Maltose (α-glucose + α-glucose)
  • Sucrose (α-glucose + Fructose)
  • Lactose (β-glucose + Galactose)

  
• Glycosidic bond


  The bond formed between the two monosaccharides in a disaccharide

  
• Hydrolysis reaction


  The process in which a water molecule is reintroduced into a glycosidic bond which breaks it

  
• Polysaccharides


  Made up of monomers joined together by glycosidic bonds in condensation reactions. They are macromolecules with a large molecular mass, formed from a large number of monomers, contain Glycosidic bonds between monomers, have no sweet taste, and are insoluble in water

  
• Components of starch


  • Amylose
  • Amylopectin

  
• Amylose


  • 1,4 glycosidic bonds, helical and more compact structure

  
• Amylopectin


  • 1,4 and α 1,6 glycosidic bonds, giving its branched structure

  
• Glycogen


  A Polysaccharide that is used for the storage of energy in animal cells and is also made from α glucose molecules. The structure of glycogen is very similar to that of amylopectin, but it is much more branched, allowing it to be hydrolysed rapidly

  
• Triglyceride


  Forms by the condensation of 3 fatty acid chains and one glycerol molecule, forming ester bonds. Fatty acid chains are long hydrocarbon chains with a carboxylic head. Glycerol is an alcohol-containing 3 OH groups

  
• Differences between unsaturated and saturated fatty acids

  • Unsaturated: At least 1 C=C double bond, contains bent chains (kinks), lower H:C ratio
  • Saturated: No C=C double bond, straight chain, higher H:C ratio

  
• Role of triglyceride


  Better energy reserves than carbohydrates as more CH bonds, acts as an insulator and provides buoyancy, a metabolic source of water as gives CO2 and H2O on oxidation in respiration
• Amino acids


  Only differ in the R-groups/ variable side chains and will always contain an amine group (basic), carboxyl group (acidic) and a hydrogen atom attached to the central carbon atom

  
• Peptide bond


  Formed by condensation between 2 amino acids, forming a dipeptide. Many amino acids that join together by peptide bonds form a polypeptide. Peptide bonds are broken when hydrolysed into amino acids

  
• Structures of proteins


  • Primary structure
  • Secondary structure
  • Tertiary structure
  • Quaternary structure

  
• Primary structure


  • The sequence of amino acids held together by polypeptide bonds in a polypeptide chain

  
• Secondary structure


  • The structure of a protein molecule resulting from the regular coiling or folding of the chain of amino acids. α-helix: the polypeptide chain twists into a regular spiral and is maintained by hydrogen bonds between the (-NH) group of one amino acid and the (CO-) group. β-pleated sheet: the chain is not tightly coiled and lies in a looser, straighter shape

  
• Tertiary structure


  • The precise folding and coiling of alpha-helices and beta-pleated sheets of an amino acid chain. They are held together by hydrogen bonds between a wide variety of R-groups, disulfide bridges between two cysteine molecules, ionic bonds between R groups containing amine and carboxyl groups, and hydrophobic interactions between non-polar R groups

  
• Quaternary structure


  • The three-dimensional arrangement of two or more polypeptides, or a polypeptide and a non-protein component such as haem, in a protein molecule. The polypeptide chains are held together by bonds in the tertiary structure

  
• Globular proteins


  Curl up into a spherical shape with their hydrophobic regions pointing into the centre of the molecule and hydrophilic regions pointing outwards. They are soluble in water, e.g. enzymes and haemoglobin
• Haemoglobin


  A globular protein that has a quaternary structure with 4 polypeptide chains, 2 α-globin and 2 β-globin chains, each connected by disulfide bridges. Each chain has one prosthetic haem group containing an iron atom that reversibly binds to an oxygen molecule. Oxyhaemoglobin is bright red when the haem group is combined with oxygen. Otherwise, it is purplish. Haemoglobin is an example of a conjugated protein

  
• Fibrous proteins


  Form long strands, are insoluble in water and have structural roles, e.g. collagen, hair, nails
• Collagen


  A fibrous protein that is made up of three polypeptide chains in a helical structure held together by hydrogen bonds where each polypeptide chain is made up of a repeating sequences of the amino acids glycine, hydroxyproline and proline

  
• Diffusion


  In small organisms, diffusion is sufficient for gaining nutrients and excreting waste due to the short distance of diffusion between the deepest part of the organism and the outside, the high SA:V ratio allowing for fast diffusion, and the low metabolism usually found in small organisms
• Mass transport


  Larger organisms are unable to rely solely on diffusion due to their low SA:V ratio. Thus, to overcome their limitations, they have a transport system that carries substances by mass flow from one part of the body to another, and they increase the surface area of parts of the body involved in an exchange with the environment, e.g. Alveoli. Features of mass transport include a medium of transport (e.g. blood), a system of vessels, a pump, and a way to ensure substances moved in the right direction
• Mammalian circulatory system


  A closed double circulation. This is because blood passes through the heart twice in one circulation of the body (pulmonary circuit and systemic circuit), contained inside blood vessels. Advantages include maintaining different pressures to the lungs and the rest of the body, and maximising the rate of diffusion by sending deoxygenated blood to the lungs and sending oxygenated blood to the rest of the body
• Components of blood


  • Plasma
  • Leukocytes (white blood cells)
  • Platelets
  • Erythrocytes (red blood cells)
• Adaptations of red blood cells


  • Biconcave, allowing for a greater surface area to volume ratio to carry oxygen
  • No nucleus nor mitochondrion, allowing more space for haemoglobin
  • Small diameter to allow it to squeeze through capillaries
• Haemoglobin (Hb)


  A red oxygen-carrying pigment found in RBCs and is a globular protein. It is made of 4 polypeptide chains each containing an iron ion