Enzymes- biological catalysts

Enzymes- biological catalysts

1. ~Enzymes are called biological catalysts as they speed up metabolic reactions in living organisms ->affect structure & function within cells, tissues & organisms

   • *catalysts speed up chemical reactions & remain unchanged at the end of the reaction & remain unchanged at the end of the reaction, able to be used again
     • *a small amount of catalyst can catalyse the conversion of a large number of substrate molecules into product molecules
       • *number of reactions that an enzyme molecule can catalyse per sec, known as its turnover number

2. Why are enzymes so remarkable?

   • ~chemical catalysts usually need v.high temps, incr pressures & extremes of pH ->enzymes speed up metabolic reactions by up to 10^12 times at lower temps, often at neutral pH & normal pressures
     • ~enzymes are also More specific than chemical catalysts ->don't produce unwanted by-products & rarely make mistakes. ->cells in which they're made and/or act can also regulate their production & activity to fit the needs of the cell or organisms a the time

3. Enzyme structure determines function

   • ~the structure of enzymes enables them to carry out their functions
     • *enzymes to catalyse reactions they need help from cofactors
       • *instructions for making enzymes are encoded in genes ->if the gene has a mutation that alters the sequence of amino acids in the protein, then this may alter enzyme's tertiary structure & prevent it from functioning
         • *enzyme that catalyses a metabolic reaction is deficient, then a metabolic disorder results
           • *enzymes also catalyse the formation of the organism's structural components, such as collagen in the bone, cartilage, blood- vessel walls, joints & connective tissue. ->some genetic disorders cause malformations of connective tissue & can be very harmful (e.g. stone man syndrome)

4. The active site

   • ~enzymes are large molecules with a specific area, an indentation or clef on the surface of the molecule =Active Site. ->consists of just a few (often about 6 to 10) amino acids
   • *tertiary structure of the active site is crucial, as its shape is complentary to the shape of the substrate molecule
   • *each type of enzyme is highly specific in its function ->can only catalyse a reaction involving a particular type of substrate molecule that fits into its active site
   • *shape of the enzyme's active site, & hence its ability to catalyse a reaction, can be altered by changes in temp & pH ->as these affect the bonds that hold proteins in their tertiary structure

5. Where enzymes work

   • ~enzymes catalyse a wide range of intracellular as well as extracellular reaction
   • Intracellular enzymes
     • ->may be up to 1000 metabolic reactions going on at the same time, each being catalysed by a different enzyme ->some part of metabolic pathway
       • *each metabolic pathway in a living cell is one of a series of consecutive reactions, every step catalysed by a specific enzyme that produces a specific product
         • *various reactants & intermediates act as substrates for specific enzymes
         • *reactants, intermediates & products are known as metabolites
         • *some metabolic pathways, described as catabolic, metabolites are broken down to smaller molecules & release energy
         • *other metabolic pathways, described as anabolic, energy is used to synthesise larger molecules from smaller ones
         • *respiration & photosynthesis are examples of complex metabolic pathways, with many enzymes involved
     • ~>catalase is found in nearly all living organisms that are exposed to O2 ->very important enzyme ->protects cells from damage by reactive oxygen quickly breaking down hydrogen peroxide, a potentially harmful by-product of many metabolic reactions, to water & oxygen
       • *catalase consists of 4 polypeptide chains & contains a haem group with iron
         • *fastest- acting enzyme, having the highest turnover number known (6mn per sec)
           • *eukaryotic cells, catalyses is found inside small vesicles called peroxisomes
             • *when WBC ingest pathogens they use catalase to help kill the invading microbe
               • ~optimum pH for human catalase is around pH7 ->other species it varies &so does optimum temp

6. Extracellular enzymes

   • ~some enzymes are secreted from the cells where they are made & act on their substrates, extracellularl. ->fungi (e.g. bread mould mucor, release hydrolytic enzymes from their thread-like hyphae
   • ~in our digestive system many enzymes are secreted, from cells lining the alimentary canal, into the gut lumen ->extracellularly digest the lumen moles, such as proteins, lipids, carbohydrates & nucleic acids, found in food. ->products of digestion are then absorbed, via epithelial cells of the gut wall, into the bloodstream in order to be used for respiration, growth & tissue repair.
     • *amalyse is produced in the salivary glands, & acts in the mouth to digest the polysaccharide starch to the disaccharide maltose. ->also made in pancreas & acts to catalyse the same reaction in the lumen of small intestine
     • *trypsin is made in the pancreas, & acts in lumen of small intestine to digest proteins into smaller peptides by hydrolysing peptide bonds ->optimum pH between 7.5 & 8.5