Unit 1.6 Metabolic Pathways Flashcards
What is cell metabolism
The product of all the biochemical reactions that take place in a living cell
What are metabolic pathways
Integrated & controlled pathways of enzyme-catalysed reactions within a cell
The 2 types of metabolic pathways
Catabolic reactions & Anabolic reactions
What do catabolic reactions do
Break down large molecules into smaller molecules and release energy
What do anabolic reactions do
Build up large molecules from small molecules and requires energy
2 examples of catabolic reactions
1- Aerobic respiration
2- Breakdown of starch by amylase: starch —> maltose
2 examples of anabolic reactions
1- protein synthesis
2- Synthesis of starch by phosphorylase: glucose-1-phosphate —> starch
What are the 2 types of steps a metabolic pathway could have
Reversible & irreversible
What type of pathway can bypass steps
Alternative pathways
What happens in reversible reaction
The substrate is converted into the product as long as the concentration of the reactant (substrate) is relatively higher than the product
What happens if the concentration of the reactant decreases in a reversible reaction
The reaction will proceed in the opposite direction
What do enzymes work to keep in a reversible reaction
An equilibrium- to maintain a balance of the starting reactants & products
What happens in the irreversible steps of a metabolic pathway
Once the substrate has turned into a product it cannot change back to a substrate
What do alternative routes in metabolic pathways allow
Certain steps in a pathway to be bypassed
What is metabolic rate
The quantity of energy consumed by an organism per unit of time
What can metabolic rate be measured by
Oxygen consumption, CO2 production & energy production in the form of heat
What are metabolic pathways controlled by
The presence or absence of particular enzymes
& the regulation of the rate of reaction of key enzymes
What are enzymes
Biological catalysts that speed up the rate of a reaction but remain unchanged after the reaction has taken place
What is activation energy
The energy needed to either make or break chemical bonds in the reactant chemicals (enzyme substrates)
What are reactant chemicals
Enzymes / substrates
How does an enzyme speed up a reaction
By lowering the activation energy
What is an active site
A region on the surface of an enzyme where the substrate binds
What is enzyme specificity
The shape of the active site means only a substrate with a complementary shape can bind to the active site
What does it mean if a substrate has a higher affinity for an enzyme
The substrate is specific/complementary to the enzyme
What is induced fit
When the active site on the enzyme changes shape to better fit the substrate after the substrate binds
What does induced fit increase the chance of
A reaction taking place
How does induced fit increase the chance of a reaction
By ensuring the active site comes into very close contact with the molecules of the substrate
What does induced fit cause to happen after the reaction takes place
The subsequent products now have a low affinity for the active site allowing them to leave the active site
What happens once enzymes have absorbed sufficient energy
Chemical bonds break & the reactants reach an unstable transition state
What happens as you increase substrate concentration
More enzyme/substrate complexes can form- this speeds up the rate of reaction
What happens once the enzyme is no longer in excess
The number of complexes is at a maximum, the rate of reaction levels off & remains constant no matter how much more substrate is added
How can you increase the rate of reaction once substrate concentration is at its maximum
Increase enzyme concentration
What are enzyme inhibitors
Chemicals that slow down or stop an enzyme-controlled reaction
2 types of inhibitors
Competitive & Non-competitive
What do competitive inhibitors do
Bind at the active site, so are competing with the substrate. This prevents substrate from binding
Can competitive inhibition be reversed- if so, how?
Yes, by increasing substrate concentration
What do non-competitive inhibitors do
Bind at the enzyme- not at the active site.
This causes the shape of active site to be altered & substrate molecules can no longer bind to the active site
Can non-competitive inhibition be reversed
No
When does feedback inhibition occur
When the end product in the metabolic pathway reaches a critical condition. It then inhibits an earlier enzyme, blocking the pathway & preventing further synthesis of the end product
What effect will increasing the substrate concentration have on a normal enzyme reaction
Increase the reaction
What effect will increasing the substrate concentration have on a reaction with a competitive inhibitor present
Increase the reaction
What effect will increasing the substrate concentration have on a reaction with a non-competitive inhibitor present
No effect
