1.6 metabolic pathways Flashcards
State the meaning of metabolic pathways
A metabolic pathway is a series of integrated (linked) and controlled enzyme-catalysed reactions within a cell.
Identify the three types of step that can be part of a metabolic pathway.
reversible steps
irreversible steps
alternitive route
Identify the two types of reactions that take place within metabolic pathways
Reactions within metabolic pathways can be anabolic or catabolic.
Describe the two types of reactions that take place within metabolic pathways
Anabolic reactions build up large molecules from small molecules and require energy. Catabolic reactions break down large molecules into smaller molecules and release energy.
Explain how metabolic pathways are controlled by genes.
Each step in a metabolic pathway is controlled by the presence or absence of a particular enzyme. Since enzymes are made of protein and protein production is controlled and regulated by the genes, the presence or absence of a particular enzyme in a metabolic pathway is determined by the gene code. Therefore, expression of the gene code regulates the reaction rate of key enzymes in the metabolism.
Describe the term induced fit
The induced fit model of enzyme action is called ‘induced fit’
Describe what induced fit means
The active site of an enzyme binds to its specific substrate it changes the shape of its active site slightly to ensure that the fit between the two is an exact match.
how does induced fit happen
due to chemical interactions between the enzyme and substrate
State the effect of an enzyme on the activation energy of a reaction.
The presence of an enzyme attached to its substrate via its active site will lower the activation energy needed for the reaction.
Why are enzymes described as catalysts in term of the enzyme effect of activation energy
if the enzyme is present and the activation energy is lowered, then less energy is needed to initiate the chemical reaction and so it is more likely to take place i.e. faster than it would without the enzyme.
Explain the meaning of the term ‘high affinity’
Substrate molecules have high affinity for the active site of their specific enzyme. This means that there is a strong chemical attraction between the substrate and its specific active site.
Explain the meaning of the term low affinity
The product of a chemical reaction has a low affinity for the active site of the specific enzyme that helped to produce it. This means that as soon as the product is made there is no longer a chemical attraction and so it exits the active site of the enzyme to make way for another substrate molecule with high affinity to bind.
State the effect of substrate and product concentration on the direction and rate of a reaction
Some steps in metabolic pathways are reversible. The relative concentrations of the substrate/product for these reaction steps will drive the reaction in a particular direction at a particular rate
Describe the effect of increasing the substrate concentration on the reaction rate of an enzyme-controlled reaction.
As the substrate concentration of an enzyme-controlled reaction is increased, the reaction rate will increase until the enzyme concentration becomes the limiting factor and then as the substrate concentration is increased beyond this point, the reaction rate will remain constant.
Identify the three types of enzyme inhibition.
Competitive
non competitive
feedback
compare competitive and non competitive in terms of enzyme activity
Competitive and non-competitive inhibitors both reduce the activity of an enzyme, but they work in different ways.
compare competitive and non competitive in term of binding (competitive)
Competitive inhibitors bind at the active site of the enzyme preventing the substrate from binding.
compare competitive and non competitive in term of binding
Non-competitive inhibitors bind to the enzyme but
away from the active site (at a site called the allosteric site) and this changes the shape of the active site preventing the substrate from binding.
Compare competitive and non competitive in terms of reversible or irreversible
Competitive inhibition can be reversed but non-competitive inhibition cannot be reversed by increasing substrate concentration.
Describe feedback inhibition of enzymes.
Feedback inhibition occurs when the end-product in a metabolic pathway increases to a critical concentration. At this point, the end-product then becomes an inhibitor of an enzyme earlier in the same pathway, creating a blockage and so preventing further synthesis of the end-product.
What is a respriotiremeter
A respirometer is a piece of apparatus that forms a sealed unit that can be used to measure the oxygen uptake of a respiring organism over a given period of time.
What does a repritoremeter do?
The sealed unit contains a known volume of air. As the organism respires it uses up oxygen and releases carbon dioxide.
What is contained in a respriotiremeter
A respirometer contains sodium hydroxide or soda lime pellets to absorb carbon dioxide.
What happens to the total volume of air in a repriotiremeter
A respirometer contains sodium hydroxide or soda lime pellets to absorb carbon dioxide.
How do you measure the amount of oxygen used up
This decrease in the volume of air (oxygen used up) is measured because the level of coloured liquid in a capillary tube will move upwards to fill the space where the oxygen has been used up and this movement of the coloured liquid can be measured per unit time.
what is the metabolic rate of an organism
The metabolic rate of an organism is the sum total of all the metabolic reactions taking place within its cells and this is measured as the quantity of energy used in a given period of time
Why are indirect measures needed
energy use is difficult to measure directly and so indirect measures relating to respiration rate are often used as an indicator of metabolic rate.
What are the three indirect measures
-Measurement of oxygen uptake (using a respirometer or an O2 probe)
-Release of carbon dioxide (CO2 monitors / probes)
-Release of heat (thermometer / temperature probe)
