biological molecules

• The chemical elements found in carbohydrates are carbon, oxygen and hydrogen.
• The chemical elements found in lipids are carbon, oxygen and hydrogen.
• The chemical elements found in proteins are carbon, oxygen, hydrogen, nitrogen and sulfur.
• The chemical elements found in nucleic acids are carbon, oxygen, hydrogen, nitrogen and phosphorus.
• Properties of water:

  • Metabolic importance
  • High heat capacity
  • Heat of vaporization
  • Cohesive and adhesive properties
  • Useful as a solvent
• Water is a polar molecule as the oxygen atoms are slightly negatively charged and the hydrogen atoms are slightly positively charged.
• Water is used or formed in many metabolic reactions such as condensation and hydrolysis:

  • ATP + H₂O -> ADP + Pᵢ + energy (a bond is broken and water is made so this is hydrolysis)
  • ADP + Pᵢ + energy -> ATP +H₂O (a bond is formed and water is released so this is condensation)
• Monomer are single subunits, e.g. amino acids, nucleotides and monosaccarides.
• Polymers are formed by combining monomers using covalent bonds, e.g. protein, DNA, starch.
• Products of condensation:

  • Amino acids produce proteins
  • Two monosaccarides produce a disaccaride
  • Many disaccarides produce a polysaccaride
  • Fatty acids and monoglycerides produce lipids
• Examples of monosaccarides (simple sugars):

  • Glucose
  • Galactose (found in milk)
  • Fructose (found in fruit)
• Glucose is a hexose sugar with the chemical formula C₆H₁₂O₆
• During cellular respiration, the energy released from glucose helps to make adenosine triphosphate (ATP)
• Aplha- and beta- glucose are isomers. The carbon atoms are numbered from 1-6 and the OH groups are in a different orientation are C₁

  
• Hexose sugars have six carbons in their structure, e.g. glucose
• Pentose sugars have five carbons in their structure and are monosaccarides, e.g. ribose
• Disaccarides are formed by the condensation reaction of two monosaccarides
• Examples of disaccarides:

  • glucose + glucose -> maltose
  • glucose + fructose -> sucrose
  • glucose + galactose -> lactose
• Polysaccarides are made of two or more monosaccarides joined by glycosidic bonds. They can be branched or unbranched and may contain different types of monosaccarides.
• Examples of polysaccarides:

  • starch
  • glycogen
  • cellulose
  • chitin
• Glycosidic bonds are formed when -OH groups from neighbouring monosaccarides undergo a condensation reaction to form an O-link between the two monosaccarides, releasing water.
• Starch:

  • Main energy storage material in plants
  • Stored in seeds
  • Broken down into glucose when energy is needed
  • Does not change the water potential in a cell because it's insoluble
• Starch is made up of amylopectin and amylose, which are both alpha-glucose polysaccarides.
• Amylopectin is a highly branched chain of alpha-glucose monomers. The branched structure means that enzymes can easily access the glycosidic bonds so the glucose molecules can be quickly released when needed.
• Amylose is a linear chain of alpha-glucose monomers with a helical structure because of the way the monomers are joined. This means the strands can pack closely together, making it good for storage.
• Glycogen is formed by condesation reactions of alpha-glucose molecules and is the main energy storage material in animals. It can be thought of as the animals equivalent of starch.
• Glycogen is highly branched so glucose can be quickly released when blood glucose levels decrease (glycogenolysis).
• Glycogen is a good storage molecule because it is so compact.
• Cellulose is a long, unbranched, linear chain of beta-glucose linked by glycosidic bonds.
• Microfibrils are strong fibres that are made of many cellulose chains held together by hydrogen bonds.
• Cellulose is the most abundant natural polymer. It makes up the walls of plant cells and can offer structural support due to the microfibrils.
• Triglycerides are a type of lipid that are mainly used as energy storage molecules.
• Triglycerides are formed by the condensation of three fatty acids and one glycerol. Esther bonds form between the glycerol and fatty acids, releasing one molecule of water per bond.
• Fatty acids have long hydrocarbon tails with four to thirty-six carbons (most have twelve to eighteen). Glycerol links to the central carbon atom.
• Energy is released from triglycerides when they break down and they contain double the energy per gram as carbohydrates do.
• Phospholipids are a type of lipid that forms a bilayer. They are formed of a phosphate group, glycerol backbone and fatty acid chains. The membrane has both a hydrophobic (fatty acids) and hydrophilic (modified phosphate group) section. This means it is amphipathic.
• Proteins are made up of amino acids.
• Amino acids are made of a central carbon (alpha carbon) with four other bonds:

  • NH₂ (amino group)
  • COOH (carboxyl group)
  • H (hydrogen atom)
  • R (side group)
• The R group is different in every amino acid and determines how it interacts and bonds with other amino acids.
• Polypeptides are made of amino acid monomers joined by peptide bonds. There is an amino acid terminal at each end of the chain:

  • N-terminal (amine terminal)
  • C-terminal (carboxyl terminal)