ENZYMES AND CELL PROCESSES

ENZYMES
1. enzymes are proteins
2. act as biological catalysts
  1. controlling speed of chemical reactions in all organisms
    1. increasing rate of chemical reactions
      1. without enzymes, metabolism would take place too slowly for life to exist
3. are specific
  1. 1 enzyme catalyses only 1 type of reaction
4. each enzyme has a particular shape determined by sequence of amino acids
  1. active site of an enzyme corresponds that of the substance it catalyses
    1. the 'lock and key model'
      1. in the way a key fits into a particular lock, the substrate fits into the active site of the enzyme
        as the enzyme and substrate fit together,
        chemical bonds are formed or broken
5. not consumed or broken down in reactions
  1. i.e. 1 enzyme molecule can be reused at a fast rate
    1. e.g. peroxidase in liver cells can catalyse breakdown of several million hydrogen peroxide molecules per min
6. shape maintained by weak H bonds.
  1. susceptible to denaturing at high temp
    1. as H bonds break, active site shape changes
      1. enzyme unable to function
ENZYME ACTIVITY: FACTORS
1. Temperature
  1. warmer the temp, faster the enzymes catalyse the reaction
    1. at low temp, both enzyme and reactants move slowly
      1. i.e. low kinetic Energy
      2. less successful collisions between enzymes' active site and substrate
        a slow ROR
        as temp increases, both reactant and enzyme gain more kinetic energy
        move faster and more successful collisions -> faster ROR
        at high temp, enzyme active site changes shape (denatures)
        substrate can no longer fit into active site
        enzyme is unable to function
        ROR decreases
        (ROR= rate of reaction)
2. Substrate concentration
  1. low substrate conc: less substrate
    1. less chance of enzyme active site and substrate collisions
      1. slow ROR
  2. as substrate conc increases, more substrate is present
    1. more chance of successful collisions with enzyme active site
      1. faster ROR
  3. at high substrate concentration
    1. other factors will become limiting factors
      1. ROR wont increase and levels off
      2. e.g. enzyme conc, temperature
3. pH
  1. enzymes work best at a specific pH
    1. if pH is outside the range for an enzyme it denatures
      1. substrate can then no longer fit and no longer acts as a catalyst
        ROR decreases
    2. e.g. amylase=7 pepsin=1~2
4. Co-factors
  1. assist in catalysis
    1. small inorganic ions or vitamins- coenzymes
  2. necessary when only weak bonds form between enzyme and substrate
    1. co-enzyme acts as a bridge, locking enzyme and substrate more tightly together
5. Inhibitors
  1. substances that prevent enzymes catalysing reactions
    1. poisons
  2. can take over active site of enzyme
    1. stop substrate from binding to active site
  3. bonding to another part of enzyme
    1. altering shape of active site
      1. can no longer bind to substrate
        usually temporary
PHOTOSYNTHESIS
1. occurs in chloroplasts of plant cells
2. process which plants produce GLUCOSE from CARBON DIOXIDE and WATER in presence of light Energy and chlorophyll
3. carbon dioxide + water ---------------> glucose + oxygen
  1. light E and chlorophyll on the arrows
4. 6CO2 + 6H2O -------------> C6H12O6 + 6O2
5. Light Phase
  1. occurs in grana
  2. electrons in chlorophyll are excited by solar E striking them
    1. passed along series of carrier molecules and synthesises ATP from ADP
      1. electrons return to chlorophylll
        water is split to Hydrogen has and oxygen gas
6. Dark phase
  1. light independent reaction
  2. occurs in stroma
  3. CO2 and H enter a complex biochemical cycle
    1. are rearranged to form C6H12O6 (glucose) as a final product
  4. ATP used to run the cycle
7. Glucose Produced
  1. stored as insoluble starch in cells of roots
  2. used in respiration
  3. used to make other needed organic chemicals
    1. e.g. fats, amino acids
8. Importance of Photosynthesis
  1. converts solar E into chemical E as organic molecules
    1. plants= autotrophs, producers
      1. i.e. self feeders
      2. starting point of food chains.
  2. photosynthesis by plants accounts for increase in level of O2 in atmosphere
    1. O2 is essential for aerobic respiration
    2. (as O2 is a waste product of Photosynthesis)
RATE OF PHOTOSYNTHESIS
1. Temperature
  1. increasing temperature increases R.O.Photosynthesis up to an optimum temp
    1. when temp increases too far above optimum temp,
      1. enzymes controlling photosynthesis denature and can no longer catalyse reaction
        therefore photosynthesis ceases
2. Light Intensity
  1. increasing light intensity increases R.O.Photosynthesis up to a maximum
    1. above this maximum/limit, further increase in light intensity will have no further effect on R.O.P
      1. because either
        (i) light absorbing pigments are saturated
        (ii) other factors becoming limiting factors
        e.g. conc of CO2 or temperature
3. CO2 concentration
  1. increasing CO2 conc increases R.O.P up to a maximum
    1. above this maximum/limit, further increase in CO2 conc has no further effect on photosynthetic rate
      1. due to other limiting factors
        e.g. temperature, light intensity
4. because 3 factors combine to determne R.O.P
  1. R.O.P can alter if one of the other factors change
ADAPTATIONS OF THE PLANT
1. Adaptations of Chloroplasts
  1. grana have large S.A to absorb light, maximising Photosynthesis
  2. stoma is clear to allow light to pass through to grana, maximising Photosynthesis
  3. oval in shape
    1. increase S.A : Vol ratio so it can take in more CO2 and H2O faster
      1. faster rate of diffusion
        maximising Photosynthesis
2. Adpatations of the Leaf
  1. waxy cuticle and epidermal layer is clear
    1. so that maximum light can penetrate to palisade layer
      1. maximising photosynthesis
  2. thin and flat
    1. reduce distance for gases and substances to diffuse through stomata to photosynthesising cells
  3. thin
    1. allows light to pass through
  4. flat
    1. maximises S.A exposed to light
  5. air spaces in spongy mesophyll
    1. allows gases to diffuse faster to photosynthesising cells
  6. palisade cells
    1. richly supplied with chlorophyll
    2. on upper surface of leaf to capture light
    3. packed tightly
RESPIRATION
1. process that occurs in mitochondria of all living cells, breaking down glucose to produce ATP to be utilised for cell processes
2. GLUCOSE + OXYGEN -----------------> CARBON DIOXIDE + WATER + ENERGY
3. C6H12O6 + O2 ---------------> CO2 + H20 + ENERGY
4. Aerobic Respiration
  1. requires oxygen for complete breakdown of glucose to CO2 H2O and Engergy in the form of ATP and heat
  2. Gylcolysis
    1. occurs in cytoplasm (no oxygen required)
      1. changes glucose -----> pyruvate
        produces 2 molecules of ATP
    2. Krebs cycle
      1. occurs in matrix (requires oxygen)
        pyruvate + O2 ----> CO2 + H+ ions
        (CO2 is released as a waste product)
        H+ ions enter the electron transfer chain and 2 ATP molecules are produced
      2. Electron transfer
        occurs in cristae (requires oxygen)
        H+ ions passed along chain releasing Energy
        34~36 ATP molecules produced
5. carried out actively in cells with high E demands
  1. e.g. muscle cells- contract and release - need ATP therefore have high no. of mitochondira
  2. e.g. kidney tubules reabsorb nutrients (glucose) in filtrate using ATP through active transport therefore have high no. of mtochondria
CELL DIVISION
1. DNA (deoxyribonucleic acid) : large molecule in chromosomes that carries genetic info
  1. double helix shape
  2. each strand is made of many repeating units = nucleotides
  3. bas pairs held together by weak H bonds
    1. base pairing rule (A=T) (G=C)
  4. 2 strands are anti parallel
    1. 3' -> 5' and 5' -> 3'
2. DNA Replication
  1. essential so that chromosomes are copied and give same genetic code to every new cell made
  2. occurs prior to cell division
  3. 1 identical DNA molecules are produced
  4. semi-conservative
    1. 1 side of final DNA strand = original
      1. other side is new
  5. Factors affecting DNA Replication
    1. controlled by enzymes
      1. any factor affecting enzymes affects rate of DNA replication
        i.e. temp, amount of nucleotides, amount of enzymes
    2. plants grow more in spring
      1. warm and unlimited resources
    3. animals grow more at certain stages of their life cycle
      1. e.g. foetus or at young
  6. during interphase
3. 1. DNA molecule unzipped by DNA helicase breaking H bonds b/w complementary base pairs
  1. 2. nucleotides from within nucleus used to produce new strand of DNA
    1. 3. as DNA unzipps, DNA polymerase adds new nucleotides to 3' end of original strand producing a continuous strand
      1. 4. DNA polymerase only adds to nucleotides to 3' end of original strand
        DNA polymerase must work from the replication down the strand producing Okazaki fragments
        5. Okazaki fragments bonded by enzyme ligase to form a continuous strand
        6. 2 identical complete DNA molecules twist into a helix
4. Mitosis
  1. cell division process producing 2 genetically identical cells for growth and repair
    1. so that same cell functions and processes continue
  2. Mitosis is rapid when:
    1. new cells are forming during periods of growth
      1. e.g. zygote, embryo, infant and young organism or plants coming our of periods of dormacy
    2. repairing after tissue damage
      1. e.g. dermis of skin dividing rapidly to form replacement cells
    3. in the bone marrow
      1. constantly producing red blood cells

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