Enzymes Flashcards
Catabolic-
Anabolic-
-large molecules broken into smaller ones releasing energy
-energy used to synthesise large molecules from smaller ones
Intracellular enzymes examples
-DNA polymerase
-helicase
-gyrase
-ligase
Catalase
-intracellular
-breaks down hydrogen peroxide into water and oxygen
-4 polypeptide chains, one haem group
-found inside vesicles
- WBC ingest pathogens, they use catalase to kill it
Extracellular enzymes examples
-Amylase- produced in salivary glands and acts in mouth to digest starch to maltose
-Trypsin- made in pancreas acts in small intestine to digest proteins into smaller peptides by hydrolysing peptide bonds
Prosthetic groups
-permanently bound by covalent bonds
eg. carbonic anhydrase has zinc ion permanently bound to active site
Inorganic ions/cofactor
-ions not permanently bound
-presence of ions my temporarily bind to substrate or enzyme to ease formation of enzyme-substrate complexes
eg. Cl- temporarily binds to amylase as a cofactor
Coenzymes
-small organic non-protein molecules that bind temporarily to active site
-coenzymes are chemically changed during the reaction
eg. NAD or coenzyme A
Lock and key hypothesis
-substrate and enzyme have kinetic energy and constantly moving
-if substrate successfully collides with enzyme, enzyme-substrate complex forms as active site complementary to substrate
-substrates broken down (catabolic) or built up (anabolic) forming enzyme product complex
-product now leaves active site
-enzyme is now able to form another ES complex
Induced fit hypothesis
-active site has complementary shape to substrate
-but when binds with substrate, slight changes to R groups on amino acids mean the active site molds around substrate
-this forms an enzyme-substrate complex which is held by non-covalent bonds eg. H bonds, van der waals etc
-substrate is converted into product producing enzyme-product complex
-as product has different shape to substrate, it detaches from active site
Effect of temperature on enzymes (optimum)
-both substrate and enzyme gain kinetic energy
-increases rate of successful collisions
-increases rate of formation of ES complexes, therefore increasing rate of EP complexes formed
-at enzymes optimum, the rate of reaction is at its max.
Effect of too much heat on enzymes
-enzymes are vibrating more
-this can break weak bonds eg. H bonds that hold the tertiary structure together
-shape of active site begins to change, so substrate doesn’t fit in so well, decreasing ROR
-as more heat applied, active site is changed permanently so no longer complementary to substrate
-enzyme is denatured
-produces a graph where ROR slowly increases to optimum and decreases rapidly afterwards
Temperature coefficient
rate of reaction at (T + 10)°C / rate of reaction at T°C
-for enzyme controlled reactions, rate doubles for every 10°C rise in temperature up to 40°C
Buffer-
-something that resists changes in pH eg. chemicals in blood that accept or donate H+ to minimize changes in pH
Effect of pH on enzymes
-H bonds and ionic forces hold tertiary structure of enzymes
-excess H ions interfere with H bonds and ionic forces, changing shape of active site, decreasing ROR
-H ions also alter charges of active site, as more protons cluster around negative groups, interfering with the binding of substrate
-produces a symmetrical graph with optimum pH as the highest ROR
Effect of changing substrate concentration
-as conc. increases, rate increases
-because more ES complexes can form, meaning more products can form
-adding more substrate molecules to increase rate won’t increase it past a certain point
-this is because all active sites are occupied with substrates
-produces a graph that rises quickly and then plateaus
