2.1.4 Enzymes Flashcards
What are enzymes
- Proteins that act as biological catalysts for intracellular and extracellular reactions to determine structure and function
- Affects metabolism of cells and organisms
- Specific tertiary structure determines shape of active site complementary to specific substrate
- Formation of enzyme substrate complexes lowers activation energy of metabolic reactions
Give an example of an enzyme that catalyses intracellular reactions
Catalase: decomposition of hydrogen peroxide which causes oxidative stress into water + oxygen
Give 2 examples of enzymes that catalyse extracellular reactions
Amylase: carbohydrate catalyses digestion of starch to maltose in saliva and small intestine lumen
Trypsin: pancreatic endopeptidase catalyses hydrolysis of peptide bonds in small intestine
Explain the induced fit model of enzyme action
- Shape of active site is not directly complementary to substrate and is flexible
- Conformational changes enables ESC to form when substrate absorbs
- This puts strain on substrate bonds, lowering activation energy
- Bonds in EPC are weak so product desorbs
Explain the lock and key model of enzyme action
- Suggests that active site has rigid shape determined by tertiary structure so is only complementary to 1 substrate
- Formation of ESC lowers activation energy
- Bonds in EPC are weak so product desorbs
Name 5 factors that affect the rate of enzyme controlled reactions
- Enzyme concentration
- Substrate concentration
- Concentration of inhibitors
- pH
- Temperature
How does substrate concentration affect rate of reaction
- Given that enzyme concentration is fixed, rate increases proportionally to substrate concentration
- The rate levels off when maximum number of ESC form at any given time
How does enzyme concentration affect rate of reaction
- Given that substrate is in excess rate increases proportionally to enzyme concentration
- Rate levels off when maximum number of ESC form at any given time
How does temperature affect the rate of reaction
- Rate increases as kinetic energy increases and peaks at optimum temperature
- Above optimum, ionic and hydrogen bonds break and active site is no longer complementary to substrate (denaturation)
How does pH affect rate of reaction
- Enzymes have a narrow pH range
- Outside the range H+ and OH- ions interact with hydrogen bonds and ionic bonds (denaturation)
How do competitive inhibitors work
- Bind to active site since they have a similar shape to substrate
- Temporarily prevents ESC from forming until released
- Increasing substrate concentration decreases their effect
How do non competitive inhibitors work
- Bind at allosteric binding site
- Trigger conformational change of active site
- Increasing substrate concentration has no impact on their effect
What is end product inhibition
- One of the products of a reaction acts as a competitive or non competitive inhibitor for an enzyme involved in the pathway
- Prevents further formation of products
What are irreversable inhibitors
- Heavy metal ions cause disulphide bonds in tertiary structure to break
- Bind to enzymes by strong covalent bonds
What are reversible inhibitors
- May be competitive or non competitive
- Binds to enzyme temporarily
- ESC can form after the inhibitor is released
Define metabolic poison
- Substance that damages cells by interfering with metabolic reactions
- Usually an inhibitor
Give some examples of some metabolic poisons
Respiratory inhibitors include:
- Cyanide: non competitive and irreversible
- Malonate: competitive
- Arsenic: competitive
How do medicinal drugs act as inhibitors
- Penicillin: non competitive inhibitor of transpeptidase to prevent formation of peptidoglycan cross links in bacteria cell wall
- Ritonavir: inhibits HIV protease to prevent assembly of new virons
What are inactive precursors in metabolic pathways
- To prevent damage to cells, some enzymes in metabolic pathways are synthesised as inactive precursors
- One part of the precursor acts as an inhibitor
ESC forms when its removed
What are cofactors
Non protein compounds required for enzyme activity
- coenzymes
- inorganic cofactors
- prosthetic groups
What are coenzymes
- Organic cofactors
- Dont bind permanently
- Often transport molecules or electrons between enzymes
- Frequently derived from water soluble vitamins
What are inorganic cofactors
- Facilitate temporarily binding between substrate and enzyme
- Often metal ions
- e.g. Cl- is the cofactor for amylase
What are prosthetic groups
- Tightly bound cofactors act as a permanent part of enzymes binding site
- e.g. Zn2+ for carbonic anhydrase
