C1.1 Enzymes Flashcards
(17 cards)
C1.1.1 Enzymes as catalysts
A catalyst:
* increases the rate of a chemical reaction
* is not changed by the reaction
* can catalyse a reactions many times
Enzymes = biological catalysts. They are made by living cells to speed up biochemical reactions.
Substrate(s) + enzyme(s) → product(s)
C1.1.2 Role of enzymes in metabolism
Almost all metabolic reactions are catalysed by an enzyme. Enzymes catalyse specific/group (of) reaction.
This allows organisms to control metabolism, as making more/less of an enzyme, cells control rate of a reaction.
C1.1.3 Anabolic reactions
Anabolic reactions use energy from ATP to produce macromolecules from monomers. They are condensation reactions.
- protein synthesis (translation) by ribosomes
- photosynthesis
C1.1.3 Catabolic reactions
Catabolic reactions break down larger molecules into smaller ones, releasing energy. This energy can be captured by coupling the reaction to ATP synthesis.
* digestion of food
* cell respiration
C1.1.4 Enzymes as globular proteins with an active site for catalysis
- Enzymes are globular proteins.
- substrate(s)+ active site shape and chemical properties match each other.
Active site amino acids are often apart in the PP but brought together by folding. 3D structure = crucial; alteration may change AS + prevent catalysis.
C1.1.5 Interactions between substrate and active site to allow induced-fit binding
The substrate binds, altering bond angles and lengths of S + AS in induced-fit binding.
Changes to substrate(s) make it easier for bonds within them to break/form.
Product(s) detach, active site to return to its original state and repeats the catalytic cycle.
C1.1.6 How do substrate-active site collisions occur?
Substrates and enzymes move randomly. When close enough to interact, the E’s chemical properties attract S to AS. Substrate–active site collision occurs = binding.
Happens more w/ higher substrate/enzyme concs or inc temperature.
C1.1.6 How does molecular motion vary between substrates and enzymes?
- In cytoplasm: both are dissolved = free to move. Often, substrate is smaller, moves more.
- Substrates = large, don’t move much. Enzyme moves in relation to substrate (transcribe DNA).
- Enzymes embedded in membranes = immobilized. Substrate does the movement.
C1.1.7 Relationships between the structure of the active site, enzyme–substrate specificity and denaturation
This is called Enzyme–substrate specicity allows specific binding. Enzyme’s 3D shape is determined by AA interactions, affected by heat/acidity. AS changes can prevent substrate catalysis + denaturation.
C1.1.8 Effects of temperature on the rate of enzyme activity
Liquid is heated→particles gain kinetic energy. Enzyme + substrate molecules move quicker, collision chance increases.
Heating enzymes = bonds to vibrate more, increasing chance of bond breakage. Alters active site → denaturation.
C1.1.10 Effect of enzymes on activation energy
Enzymes lower activation energy by binding to the substrate and weakening its bonds, which makes it easier to reach the transition state. The yield stays the same.
C1.1.11 Intracellular and extracellular
enzyme-catalysed reactions
Intracellular: made by free ribosomes in the cytoplasm, catalyse metabolic reactions e.g. glycolysis.
Extracellular (exoenzymes): made by ribosomes on the rER. Break down macromolecules into monomers that can be absorbed (digestive system).
C1.1.12 Generation of heat energy by the reactions of metabolism
Products have less energy than reactants -> converted to heat.
Birds + mammals use metabolic heat to maintain a body temperature above environment + raise their metabolic rate when basal metabolism isn’t enough.
- Involuntary muscle contractions = shivering, raises the core temperature.
- Brown fat tissue. Many mitochondria that carry out uncoupled respiration (no ATP).
C1.1.14 Allosteric sites and non-competitive inhibition
The binding and unbinding of the allosteric site causes the enzyme to change conformation, allowing the activity of an enzyme to be regulated. It either activates or prevents catalysis.
C1.1.15 Competitive inhibition as a consequence of an inhibitor binding reversibly to an active site
Structurally similar to the substrate so they can bind to the active site, preveting catalysis. Not converted into products = bound longer.
Inhibition = greater if conc. of the inhibitor increases.
If there are many more substrates than inhibitors, substrates almost always arrive at the active site first.
C1.1.16 Regulation of metabolic pathways by feedback inhibition
The end product of a pathway inhibits the first enzyme by binding to its allosteric site, changing its shape and stopping catalysis. This prevents excess production. If the end product is too low, the pathway remains active.
E.g. Threonine->isoleucine pathway, isoleucine inhibits enzyme threonine
C1.1.17 Mechanism-based inhibition as a consequence of chemical changes to the active site caused by the irreversible binding of an inhibitor
Irreversible inhibitors bind permanently, often forming a covalent bond. Heavy metals (mercury, lead) binds to –SH groups in cysteine. Some mechanism-based inhibitors, like penicillin, are used by organisms to kill others.
