Unit 2 KA1 Flashcards
Metabolism
The thousands of integrated biochemical reactions that occur within a living cell.
Metabolic pathways
Integrated sequences of chemical reactions within cells.
Each step is controlled by a different enzyme.
They contain reversible and irreversible steps and alternative routes.
Anabolic (synthesis) reactions
Build up large molecules from small ones.
Require energy.
eg. protein synthesis
Catabolic (degradation) reactions
Break down large molecules into smaller ones, releasing energy.
eg. respiration, digestion (starch to maltose using amylase)
Fluid mosaic model
Describes the structure of cell membranes - a double layer (bilayer) of phospholipids with proteins floating in it.
The cell membrane is the boundary of the cell, and controls entry and exit of materials.
Many of the proteins are enzymes.
Organelles
Compartments inside cell, which are made of membrane.
They are the sites of specific chemical reactions. eg. mitochondria (respiration)
Internal cell membranes containing enzymes, provide a large surface area for reactions.
Membrane proteins
Globular proteins which act as channels, pores, pumps, enzymes, receptors and antibodies.
Diffusion
The movement of particles from a high to a low concentration along a concentration gradient.
Small molecules pass between the phospholipids, larger or charged particles need a channel protein or pore.
Active transport
The movement of molecules and ions from a low to a high concentration, against the concentration gradient.
Requires ATP and a specific carrier protein in the membrane.
Multi-enzyme complex
A group of enzyme molecules embedded in a membrane, which catalyse the steps of a metabolic pathway in a specific order for maximum efficiency.
Activation energy
The energy required to start a reaction, by breaking the bonds in the reactants.
Enzymes
Globular protein molecules that act as biological catalysts.
They reduce the activation energy required to start a reaction, so that it can occur rapidly at cell temperature.
They take part in a reaction but are unchanged at the end.
Active site
The area on the surface of an enzyme molecule where the substrate binds.
Enzyme and substrate are complementary, so fit together exactly, making enzymes specific for their particular substrate.
Induced fit
Proteins are flexible molecules, so when the substrate enters the active site of an enzyme, it changes shape slightly to fit the substrate better.
Affinity
Attraction.
Substrate molecules have a high affinity for the active site of an enzyme.
Products have a slightly different shape, don’t fit as well into the active site and are released.
Products have a low affinity for the active site.
Orientation of reactants
When 2 or more substrates enter the active site of an enzyme (during an anabolic reaction), they need to be the correct way up for the reaction to proceed.
The shape of the active site will determine how the substrates align themselves.
Factors affecting enzyme action
Temperature, pH
Enzyme concentration, substrate concentration
Inhibitors
Denatured
Extremes of temperature or pH affect the bonds that maintain the 3D shape of an enzyme.
If the bonds are disrupted, the shape of the enzyme changes, affecting the shape of the active site.
The substrate no longer fits in and the enzyme is said to be denatured.
Effect of increasing substrate concentration on an enzyme controlled reaction.
The rate of an enzyme controlled reaction will increase with increasing substrate concentration, until all active sites are saturated and the reaction rate levels out.
Control of metabolic pathways
Metabolic pathways can be controlled by :
1) Controlling gene expression
2) Using inhibitors to reduce the activity of enzymes that are continually expressed.
Competitive inhibitors
Compete with the substrate for the active site of the enzyme, as they have a similar shape to the substrate.
They block the active site so that the substrate can’t fit in.
The reaction rate can be increased by increasing substrate concentration.
Non-competitive inhibitors
Do not have a similar shape to the substrate.
Attach to an area away from the active site, which alters the shape of the enzyme, and therefore the shape of its active site. The substrate can no longer fit in and the rate of reaction decreases.
If the inhibitor is removed, the effect is reversed.
Increasing the substrate concentration will have no effect.
Feedback (end product) inhibition
Inhibition of an enzyme early in a metabolic pathway which prevents further synthesis of the product.
If the end product starts to run out, the effect is reversed.
It is an example of negative feedback control.
