Chapter 4 - Enzymes Flashcards
What are enzymes?
Biological catalysts.
They are globular proteins that interact with substrate molecules causing them to react at faster rates without the need of harsh environmental conditions.
What are the roles of enzymes in reactions?
- anabolic (building up) reactions required for growth are catalysed by enzymes.
- energy is released from large organic molecules in metabolic pathways consisting of many catabolic (breaking down) reactions. These are also catalysed by enzymes.
- catalyse digestion.
- metabolic reactions can only happen as a result of control and order imposed by enzymes.
What is metabolism?
The sum of all the different reactions and reaction pathways happening in a cell/organism. These reactions maintain normal function.
What is activation energy and Vmax?
-Activation energy is the minimum energy required for a reaction to start.
-Enzymes can only increase the rates of a reaction up to a certain point called the Vmax.
It is the maximum rate of the enzyme-catalysed reaction.
What is an active site?
An area within the tertiary structure of an enzyme that is complimentary to the shape of a specific substrate molecule.
Explain the lock and key hypothesis.
Only a specific substrate will fit the active site of an enzyme.
- when the substrate is bound to the active site an enzyme-substrate complex is formed.
- substrate(s) react and the product(s) is formed in an enzyme-product complex.
The product is then released, leaving the enzyme unchanged.
- R-groups within the active site form temporary bonds with the substrate. These put strain on the bonds within the substrate, which helps the reaction along.
Explain the induced-fit hypothesis.
Suggests that the active site of the enzyme actually changes shape slightly as the substrate enters.
- initial interaction = weak, but these weak interactions rapidly induce changes to the enzyme’s tertiary structure.
- these changes strengthen binding, putting strain on the substrate.
- this can weaken bonds in the substrate and therefore lowering the activation energy.
What are intracellular enzymes?
- enzymes that act within cells.
- the synthesis of polymers from monomers requires enzymes.
- enzyme catalase ensures hydrogen peroxide (toxic product of many metabolic pathways) is broken down to oxygen + water quickly, preventing accumulation.
What are extracellular enzymes?
Enzymes released from cells to work outside the cell.
- enzymes are released to break down large nutrient molecules into smaller molecules in digestion.
- in some organisms (eg.fungi) they work outside the body.
- single celled and multi-cellular organisms rely on these enzymes to make use of polymers for nutrition.
- single celled organisms release them into their immediate environment. They break down large molecules into small molecules which are absorbed by the cell.
- enzymes involved in human digestion = amylase + trypsin.
Digestion of starch.
Starch is digested in two steps.
1.starch polymers partly broken down into maltose (disaccharide) by enzyme amylase.
Amylase is produced by salivary glands and pancreas. Released into mouth and small intestines.
2.maltose broken down into glucose (monosaccharide) by enzyme maltase which is present in small intestine.
Glucose is small enough t be absorbed by the cells lining in digestive system and then absorbed into bloodstream.
digestion of proteins?
Trypsin = protease, a type of enzyme that catalyses the digestion of proteins into smaller peptides, which can then be broken down into amino acids by other proteases.
- trypsin is produced in the pancreas and released as pancreatic juice into small intestine, where it acts on proteins.
- amino acids produced by action of protease are absorbed by the cells lining in digestive system and then into bloodstream.
Explain the effect of temperature on enzyme activity.
temperature increases= particles have more kinetic energy= more frequent successful collisions= increase in the rate of reaction.
However, temperatures that are too high cause enzymes to denature:
High temps= bonds vibrate more= bonds strain + break = change in tertiary structure = enzyme denatures .
When an enzyme denatures, the active site changes shape, therefore substrate is unable to bind to it.
What is the temperature coefficient?
Q10 is a measure of how much the rate of reaction increases with a 10C rise in temp.
For enzyme controlled reactions = usually 2.
Meaning Rate doubles with 10C increase.
What is optimum temperature?
The temperature at which an enzyme has the highest rate of activity.
-varies differently in different organism types.
- optimum temp of enzymes in humans = 40*C
Once the enzymes have denatured above the optimum temp, the decrease in rate is very rapid.
- Q10 no longer applies once enzymes have denatured.
- the decrease in rate below the optimum temperature is not as rapid as enzymes haven’t denatured, they are just less active.
What are the features of enzymes in different environments?
Cold:
-more flexible (especially active site)
-less stable than enzymes at higher temperatures. (Due to flexibility)
- small temperature change denatures them.
Hot: (thermophiles)
- more stable due the the increased no. of bonds in tertiary structures. (More hydrogen bonds and sulfur bridges)
-shapes are more resistant to change as the temperature rises.
