Key Area 1 - Metabolic Pathways Flashcards
What is ‘cell metabolism’?
Cell Metabolism refers to all the chemical reactions that take place inside living cells. Organisms must control their own metabolism to stay alive.
What are metabolic pathways?
Metabolic pathways are integrated (linked) and controlled pathways of enzyme-catalysed reactions within a cell. They start with a substrate and end with a product. These metabolic pathways can have reversible steps, irreversible steps and alternative routes.
What 3 things can metabolic pathways have?
Reversible steps
Irreversible steps
Alternative routes
What are anabolic reactions?
Anabolic reactions build up large molecules from small molecules.
Do anabolic reactions require energy or release energy?
Anabolic reactions require energy.
Give an example of an anabolic reaction.
Photosynthesis
Protein synthesis
DNA replication
What are catabolic reactions?
Catabolic reactions break down large molecules into smaller molecules.
Do catabolic reactions require energy or release energy?
Catabolic reactions release energy.
Give an example of a catabolic reaction.
Digestion
Respiration
Degradation of hydrogen peroxide
What is the function of protein pores embedded in the cell membrane?
Protein pores allow larger molecules and ions to be transported into or out of the cell. This is a passive process. Molecules and ions move from an area of high contraction to an area of low concentration.
What is the function of protein pumps embedded in the cell membrane?
Pumps recognise specific ions and transfer them across the cell membrane against the concentration gradient. This requires energy in the form of ATP.
Give 2 ways metabolic pathways are controlled.
Metabolic pathways are controlled by:
- The presence or absence of particular enzymes.
- The regulation of the rate of reaction of key enzymes.
Explain what is meant by the ‘induced fit’ model of enzyme activity.
When the substrate joins with an enzyme, the enzyme’s active site changes shape (slightly) to better fit the substrate after the substrate binds. This is called an induced fit. The induced fit ensures the active site is in contact with the substrates, increasing the chances of the reaction taking place.
Why do substrates bind to the active site?
The substrate molecule(s) have a high affinity (chemical attraction) for the active site.
What happens to the enzyme once the substrate binds?
Once the substrate binds, the enzyme’s active site changes shape slightly. The enzyme fits the substrates better and the activation energy is reduced.
Sketch a graph to show the effect of enzymes on activation energy.
Why do the products leave the enzyme?
The products have a low affinity (chemical attraction) for active site so they are released from the enzyme.
Draw a diagram to illustrate the induced fit model of enzyme activity.
Describe how the rate of enzyme controlled reactions is affected by substrate concentration.
The rate of enzyme reactions can be affected by the substrate concentration. As the substrate concentration increases the rate of reaction increases until all the active sites are occupied. At this point the enzyme is described as saturated.
Sketch a graph to illustrate the effect of increasing substrate concentration on the rate of reaction.
What is the ‘point of saturation’?
The point of saturation is the substrate concentration which results in all active sites being occupied.
What effect does the presence of a substrate have on the direction that a reversible reaction is driven in?
The presence of a substrate will drive the reaction towards the product in a reversible reaction.
What effect does the removal of a product have on the direction that a reversible reaction is driven in?
The removal of the product will drive the reaction towards the product in a reversible reaction.
What effect does an increase in the concentration of the product have on the direction of reversible reactions?
A build up of the product will drive a reversible reaction towards the substrates.
Name 3 types of enzyme inhibition.
Competitive inhibition
Non-competitive inhibition
Feedback inhibition
Describe how competitive inhibitors work.
Competitive inhibitors bind directly to the active site and prevent the substrate from binding. This can be reversed by increasing substrate concentration.
Explain why increasing the substrate concentration reversed the effect of competitive inhibitors?
At high substrate concentrations the ratio of substrate to inhibitor becomes high enough that the effect of the inhibitor is negligible.
Describe how non-competitive inhibitors work.
Non-competitive inhibitors bind away from the active site but change the shape of the active site preventing the substrate from binding. This cannot be reversed by increasing substrate concentration.
Sketch a graph to show the effect of competitive and non-competitive inhibitors on enzyme activity as substrate concentration increases.
Describe how feedback inhibition works.
Feedback inhibition occurs when the end product in the metabolic pathway reaches a critical concentration. The end-product then inhibits an earlier enzyme, blocking the pathway, and so prevents further synthesis of the end-product. Only when the end product concentration decreases will the pathway continue again.
