AS LEVEL- Biology- Biological molecules (2)

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  • Biological molecules (2)
    • Lipids (C, H, O)
      • Triglycerides (Macromolecule)
        • Structure; 1 glycerol molecule, 3 fatty acids, fatty acids are joined to glycerol by an ester bond
        • Fatty acids can be saturated or unsaturated
          • Saturated fatty acids don't have any double bonds between their carbon atoms. The fatty acid is 'saturated' with hydrogen
          • Unsaturated fatty acids have at least one double bond between carbon atoms, which causes the chain to kink
        • Triglycerides contain ester bonds
          • 1) Triglycerides are synthesised by the formation of an ester bond between each fatty acid + the glycerol molecule
          • 2) Each ester bond is formed by a condensation reaction (water is released)
          • 3) The process by which triglycerides are synthesised is called esterification
          • 4) Triglycerides break down when the ester bonds are broken. Each ester bond is broken in a hydrolysis reaction (water is used up)
        • Structure to function; Triglycerides have high chemical energy content of bonds so bonds are broken down to release large quantities of energy. Triglycerides  are insoluble so it doesn't  affect the water potential of cells which  means it has no impact on osmosis.
        • Cholesterol
          • Structure to function; Cholesterol has a small size + flattened shape so it allows cholesterol to fit between the phospholipid molecules in the membrane. They bind to the  hydrophobic  tails of the  phospholipids causing them to pack more closely together so this makes the membrane less fluid + more rigid
      • Phospholipids (Macromolecule)
        • Structure; Phospholipids are modified triglycerides that contain P as well as C + O. One of the fatty acid chains of a triglyceride is replaced with an inorganic phosphate group. The phosphate group is hydrophilic (attracts water) + the fatty acid tails are hydrophobic (repels water)
        • Structure to function; Phospholipids have hydrophilic heads + hydrophobic tails so it forms a bilayer for membrane formation so separates the aqueous environment outside the cell + cytoplasm
    • Proteins (C, H, O, N, S)
      • Amino acids
        • Structure; A carboxyl group + an amino group attached to a C atom. There's also a R group that's different for each amino acid
      • Peptide bond
        • 1) Amino acids are linked together by peptide bonds to form dipeptides + polypeptides
        • 2) A molecule of water is released during the reaction- it's a condensation reaction
        • 3) The reverse of this reaction adds a molecule of water to break the peptide bond- it's a hydrolysis reaction
      • Levels of protein structure
        • Primary
          • This is the sequence of amino acids in the polypeptide chain. Different proteins have different sequences of amino acids in their primary structure. A change in just one amino acid nay change the structure of the whole protein
        • Secondary
          • The polypeptide chain doesn't remain flat + straight. Hydrogen bonds form between nearby amino acids in the chain. This makes it automatically coil into an alpha helix or fold into a beta pleated sheet- this is the secondary structure
        • Tertiary
          • The coiled or folded chain of amino acids is often coiled + folded further. More bonds form between different parts of the polypeptide chain. For many proteins made from a single polypeptide chain, the tertiary structure forms their final 3D shape
            • 1) Hydrophobic + Hydrophilic Interactions- *Interactions between polar + non- polar R groups *Hydrophobic (water repelling) R-groups 'clump' together in the centre *Hydrophilic (water attracting) R-groups are more likely to be pushed to the outside
            • 2) Hydrogen Bonds- *Forms between slightly positive hydrogen atoms + other slightly negative atoms on different R groups *Weakest bond
            • 3) Ionic Bonds- *Attraction between oppositely charged R groups *Stronger than hydrogen bonds
            • 4) Disulfide Bonds- *Covalent bonds *Strongest * Only forms between R groups that contain a S atom (Cysteine + Methionine)
        • Quaternary
          • Some proteins are made of several different polypeptide chains held together by bonds. The quaternary structure is the way these polypeptide chains are assembled together. eg. haemoglobin is made of 4 polypeptide chains, bonded together. For proteins made from 1 polypeptide chain the quaternary structure is the protein's final 3D shape
      • Types of proteins
        • Globular
          • *Usually  spherical  *Compact  *Water soluble *Hydrophilic R groups are pushed to the outside of the protein with hydrophobic R groups sheielded in the centre of the protein. This means the hydrophilic R groups interact with water in the aqueous environment
          • Eg. Insulin- Hormone secreted by the pancreas. It's involved in regulating  the blood  glucose levels. Its solubility is important as it means it can be transported in the blood to the tissues. An insulin molecule  consists of 2 polypeptide chains, which are held together by disufide  bonds
        • Conjugated
          • *Globular protein with a non- protein component attached called a prosthetic group *Proteins without a prosthetic group are called simple proteins *Prosthetic groups can either be lipids, carbohydrates, disulfide ions (cofactor)
          • Eg. Haemoglobin- Carries oxygen around the body in red blood cells. Made from 4 polypeptide chains so has a quaternary structure (2 alpha + beta subunits) + each subunit has a haem grouo. A haem group contains iron which oxygen binds to
          • Eg. Catalase- Enzyme that catalases the reaction between hydrogen peroxide into water + oxygen. It has a quaternary  structure + 4 haem groups
        • Fibrous
          • *Long *Strong *Insoluble as they have high proportions of amino acids with hydrophobic R groups *Limited range of amino acids including amino acids with smaller R groups

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