Chapter 4: Enzymes :> Flashcards
What is a catalyst?
- A catalyst is a substance that speeds up the rate of a chemical reaction without altering itself at the end of the reaction.
What are biological catalysts?
- Biological catalysts are substances that are found in living things and are made out of protein.
- They can also alter the rate of chemical reactions without changing themselves at the end of the reactions.
(E.g.) One example of a biological catalyst is an enzyme, like a biological molecule.
How can enzymes change or speed up chemical reactions?
- Enzymes can change or speed up chemical reactions by lowering the activation energy of a chemical reaction.
- Activation energy is the energy needed to start a chemical reaction.
- When an enzyme is present, it speeds up the reaction by lowering the activation energy.
- Thus, the rate at which the products are formed is increased.
What is an activation energy?
- Activation energy is the energy needed to start a chemical reaction.
How many groups can enzyme-catalysed reactions be classified in?
- Enzyme-catalysed reactions can be classified into 2 groups:
1. Anabolic reactions in which complex substances are synthesised from simpler ones.
(simpler –> complex)
2. Catabolic reactions in which complex substances are broken into simpler ones.
(complex –> simpler)
What are the examples of enzyme-catalysed reactions?
- Synthesis of complex substances:
- Special enzymes in the cytoplasm build up proteins from amino acids.
- Enzymes are involved in the synthesis of glucose from carbon dioxide and water during photosynthesis. (Photosynthesis equation: Carbon dioxide + Water — (sunlight +chlorophyll) –> Oxygen + Glucose) - Breaking down of complex substances:
- Enzymes such as digestive enzymes break down large molecules in food into smaller ones which are soluble in water and can pass through the cell membrane.
- Certain enzymes break down large molecules that are toxic, into smaller and safer ones.
(E.g.) Hydrogen peroxide is produced during some chemical reactions in plant and animal cells, but this is toxic to the cells.
(E.g.) Catalyse breaks down hydrogen peroxide from water and oxygen.
(E.g.) Catalyse is abundant in the blood and liver of mammals.
- Various enzymes break down glucose to release energy, carbon dioxide, and water in cellular respiration.
What are the enzymes that are involved in the breaking down of glucose to release energy, carbon dioxide, and water during cellular respiration?
- During glycolysis (the first stage of cellular respiration that takes place in the cytoplasm of cells), glucose is broken down into two molecules of PYRUVATE.
(E.g.) Dehydrogenase: - It oxidises glucose by stripping 2 electrons from it and transferring them to a coenzyme called NAD+.
(E.g.) Pyruvate dehydrogenase:
- It helps in the conversion of pyruvate, which is transported into the mitochondria and is then converted into acetyl-CoA.
(E.g.) Isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, and succinate dehydrogenase:
- Enzymes that are found in the citric acid cycle which takes place in the mitochondrial matrix.
- During this stage, acetyl-CoA is broken down into carbon dioxide and water, thus releasing energy during this process.
(E.g.) ATP synthase:
- During oxidative phosphorylation, it takes place in the inner mitochondrial membrane.
- During this stage, the energy that is released from previous stages is used to generate ATP.
What are the examples of digestive enzymes?
(Digestive enzymes aid in the digestion and breaking down of substances)
1. Carbohydrase:
Function: To digest carbohydrates.
(E.g.) (A) Amylase digests starch into maltose.
(B) Maltase digests maltose into glucose.
(C) Sucrase digests sucrose into glucose and fructose.
(D) Lactase digests lactose into glucose and galactose.
- Protease:
Function: To digest proteins.
(E.g.) (A) Pepsin digests proteins into polypeptides.
(B) Trypsin digests proteins into polypeptides.
(C) Peptidases digest polypeptides into amino acids. - Lipase:
Function: To digest fats (lipids)
(E.g.) (A) Steapsin digests lipids into glycerol and fatty acids.
What are substrates?
- Substrates are substances that enzymes act on.
What is an active site and what are the substances that can fit into it?
- An active site is where a substrate fits into, which are also depressions on the surface of an enzyme.
How are enzymes specific in their action?
- Enzymes are highly specific in their action.
- Each chemical reaction is catalysed by a unique enzyme, and this specifically is due to the enzyme’s 3D shape.
- Thus, this means that only a substrate with a shape complementary to that of the enzyme’s active site can fit into the active site.
What is the lock-and-key hypothesis?
- According to the lock-and-key hypothesis, the enzyme is like a lock and the substrate is like a key.
What is an enzyme-substrate complex and how is = it formed?
- An enzyme-substrate complex is created when a substrate binds to the active site of an enzyme.
Why do chemical reactions occur at the enzyme’s active site?
- Chemical reactions occur at the enzyme’s active site to convert the substrate into products.
What is the mode of action of an enzyme?
(Enzyme changes shape light as the substrate binds themselves together)
- The substrate enters the active site, but it is not fully connected to the enzyme.
- Enzyme-substrate complex.
- Enzyme-product complex.
- Products leave the active site.
