Enzymes, Digestion And Excretion Flashcards
What are enzymes?
Enzymes are biological catalysts, globular proteins, and can catalyze intracellular or extracellular reactions. They have specificity, with an active site complementary to a specific substrate to form enzyme-substrate complexes. Enzymes are sensitive to denaturation due to temperature and pH.
What is a metabolic pathway?
A metabolic pathway is an enzyme-catalyzed cascade of reactions.
How do enzymes lower activation energy?
Enzymes destabilize bonds in reactants to make them more reactive, thereby lowering the activation energy.
What is the induced fit hypothesis?
The induced fit hypothesis suggests that the enzyme’s active site can change shape slightly after substrate binding, undergoing conformational changes. This replaces the earlier ‘lock and key’ hypothesis.
How is enzyme activity investigated?
Enzyme activity is investigated by measuring the rate at which product is formed or reactants are used up.
What factors affect enzyme activity?
- Temperature: Enzymes have an optimum temperature. At too low a temperature, the rate of reaction (RoR) is too slow due to fewer collisions and lower energy collisions. At too high a temperature, denaturation occurs, breaking the bonds holding the tertiary structure together and permanently damaging the active site.
- pH: Enzymes have an optimum pH. Extreme pH levels can cause denaturation by weakening hydrogen and ionic bonds.
- Enzyme concentration: As enzyme concentration increases, the RoR increases. However, if substrate concentration is low, enzyme concentration can become a limiting factor.
- Substrate concentration: Similar to enzyme concentration, substrate concentration increases RoR, but once all active sites are saturated, a plateau occurs, and enzyme concentration becomes the limiting factor.
What are reversible inhibitors?
Regulatory in metabolic pathways. Non-competitive inhibitors bind to a separate active site on regulatory enzymes (e.g., end-product inhibition of PFK in respiration). 2 types:
- Competitive inhibitors: Similar in shape to the substrate and bind to active sites, forming an enzyme-inhibitor complex. Increasing substrate concentration reduces their effect.
- Non-competitive inhibitors: Bind to a separate site on the enzyme, changing the shape of the active site or deforming the enzyme-substrate complex.
What are irreversible inhibitors?
Irreversible inhibitors form permanent covalent bonds with one of the groups vital for catalysis to occur. Examples include arsenic, cyanide, and mercury. These inhibit neurotransmitter, requiring the production of new enzymes for translation and transcription, which is a slow process.
What are cofactors?
Cofactors are inorganic ions that stabilize enzymes or may participate in reactions at the active site. An example is chlorine in amylase.
What are coenzymes?
Coenzymes are organic cofactors that can be either permanent or temporary. They carry electrons and chemical groups to aid in catalysis.
Which vitamins are part of the B group and what do they do?
- Pantothenic acid: Forms coenzyme A.
- Nicotinic acid: Forms NAD.
- B1 (Thiamine): Forms FAD.
What is the process of digestion and absorption?
Large, insoluble molecules are broken down into smaller molecules that can pass through the cell membrane. These smaller molecules are used to release energy or build other molecules for growth and repair.
What are the main parts of the human digestive system?
- Mouth: Teeth chew food to increase surface area for enzyme action; carbohydrate digestion occurs here, and salivary glands release amylase enzymes to form a bolus.
- Oesophagus: Food passes into the stomach by peristalsis of muscular walls.
- Stomach: Protein digestion occurs here, and hydrochloric acid lowers the pH to provide optimum conditions for proteases and to unravel proteins. It can also kill microbes.
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Small intestine:
- Duodenum: Carbohydrate, lipid, and protein digestion occurs using enzymes secreted by the pancreas and small intestine.
- Jejunum + Ileum: Absorption of digested molecules into the bloodstream and absorption of water. The walls are lined with villi. Smooth muscular walls contract in peristalsis.
- Large intestine: Absorbs water, vitamins, and minerals.
How are carbohydrates digested?
- In the mouth and small intestine: Amylase made in the pancreas, salivary glands, and small intestine hydrolyzes starch into maltose. Membrane-bound disaccharidases, such as maltase and lactase, embedded in the microvilli membrane of epithelial cells in the small intestine, further break down carbohydrates into monosaccharides.
How are proteins digested?
- In the stomach: Endopeptidases hydrolyze peptide bonds between protein molecules to form smaller protein chunks.
- In the small intestine: Pancreatic fluid, containing endopeptidases and exopeptidases, breaks bonds at the end of polypeptide chains to form dipeptides. Dipeptidases in the small intestine hydrolyze peptide bonds between dipeptides to form amino acids by hydrolysing peptide bonds, which can be absorbed.
