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Metabolism is essential for life (Enzymes (Properties of Enzymes (Lowers…
Metabolism is essential for life
Metabolism
Catabolic
Breaks down of complex molecules to simplify them, usually releasing energy and often providing building blocks
Protein ---Enzyme---> Amino acid
Respiration is a catabolic process releasing energy which is used to synthesis proteins from amino acids
Anabolic
Brings about the biosynthesis of molecules from building blocks, this requires an input of energy
Amino acids ---Enzymes---> Proteins
Metabolic pathway
Anabolic and catabolic pathways are closely integrated and depend on each other
Anaerobic respiration in yeast is irreversible
Glucose ---> Carbon dioxide + Ethanol
Anaerobic respiration in mammals is reversible
Glucose <---> Lactic acid
Control of metabolic pathway
Glucose ---Enzyme A--->Intermediate 1<---Enzyme B--->Intermediate 2
Metabolic pathway is an enzyme controlled sequence reaction that change 1 metabolite into another
The conversion of glucose into Intermediate 1 is an irreversible step. As a result of this the glucose is kept at a low concentration in the cell to help promote continued glucose diffusion
If enzymes are not synthesised properly due to mutations, problems will occur in the pathway
Pathways often can be reversible and irreversible steps, this allows precise control during the pathways
Each step is controlled by an enzyme
If enzyme B doesn't work Intermediate 2 will build up and resulting in being toxic to the cell
Enzymes
Properties of Enzymes
Lowers the activation energy that is required for the chemical reaction to proceed
Speeds reactions up
Takes part in reactions but remains unchanged
Enzymes is specific to 1 substrate
Bringing the enzyme and substrate close together to allow a reaction to happen
Activation energy
Energy is required to initially break bonds for a reaction to happen
For a chemical reaction to happen is known as activation energy
Without an enzyme or catalyst the energy needed to start a reaction is very little resulting in the reaction being slow
With an enzyme or catalyst the energy required is a lot less and the reaction is quicker
Enzyme work by
Lowering the activation energy
Bringing the substrate close together to allow a reaction to happen
Induced fit model
The binding of the first substrate induces a physical conformation shift in the enzyme that then allows the second substrate to bind
The induced fit ensures the active site comes in close contact with the substrate increasing the chance of reaction taking place
The active site is a flexible structure and can alter it's shape the fit the substrate
Substrate binded onto Enzyme, it creates an enzyme-substrate complex, this then creates the product and enzyme
Substrate complex
The change in shape of the active site helps the reaction occur as it helps the substrate in the right way for the reaction it happen
When the reaction is complete the products have a low affinity for the active site and diffuse away
Substrate molecules have an high affinity for the active site of appropriate enzymes
Factors affecting enzyme activity
pH
Enzyme works within a range of pH depending on the type of enzyme
The pH that the enzyme works best is called the optimum pH
If the pH is too high, the enzyme will change shape and denature
Substrate concentration
Rate of reaction increase to a maximum when all active site are occupied
The enzyme concentration becomes a limiting factor
Temperture
If the temperature is too low the enzyme will denature and stop working
At optimum temperature energy works best
If the temperature is too high the enzyme will change shape and denature
Product concentration
Some metabolic reactions are reversible and the presence of the substrate of the removal of the product will drive the reaction in a particular direction
The accumulation of the product can inhibit an enzyme in the pathways and slow down the process
Regulating enzyme activity
Changing enzyme shapes (most effective)
Gene expression, switching on and off the genes that code for the enzymes
Keeping reactions (and enzymes) in compartments eg) Mitochondria or lysosomes
Controlling the number of enzymes molecules in a cell
At the level of enzymes action eg) Inhibitors
Membrane
Diffusion
Movement of water from high to low concentration, it is a passive process and moves down a concentration gradient
Osmosis
Movement of molecules from high to low concentration, it is a passive process and moves down a concentration gradient
Active transport
Movement of molecules across a concentration gradient, it is an active process and moves against a concentration gradient
Molecular transport
Membrane protein function
Enzymes - Some proteins in the membrane catalyse a specific protein
Structural support - Some proteins help maintain the shape of a cell
Channel (pore) protein - Allow large molecules and ions to pass through the membrane by passive transport
Carrier (pump) proteins - Bind to specific molecules or ion temporarily, enabling them to cross the membrane by active transport
Poison, Toxins and Venom
A poison is a substance that can impair function and damage the body, sometimes completly
Toxins in a poisonous substance produced by a living organism
Venom is a poisonous fluid secreted by certain snakes and scorpions
Inhibitors
Competitive inhibition
Competitive enzyme inhibitors work by having a similar shape to the substrate molecules
The inhibitors will fit into the active site therefore blocking the substrate attachment and decreasing the rate of reaction
This temporary and can be removed by increasing the substrate concentration
Adding more substrate increases the chance of a collision with an enzyme and a substrate, overcoming competitive inhibition
Non-competitive inhibition
By binding to a non active site it can cause a conformation change in the enzyme active site so it can no longer bind with the substrate
It may or may not be reversible
Non-competitive inhibitors binds to the enzyme to a non active site
It is not affected by increasing the substrate concentration
Enzymes can be inhibited by other "things" binding to them
Feedback inhibition
Some specific substrate are products in their self and can acts as inhibitors
Such inhibitors bind to enzyme at a specific site and modifies the active site if the enzyme
Self-regulating mechanism controls the activity of most enzymes that are involved in metabolic pathways
This prevents the binding of substrate molecules
Enzyme inhibitors reduce the rate of enzyme reaction by interfering with the enzyme in some way, this can by permanent or temporary