Unit 1 - Metabolic Pathways Flashcards
What are Metabolic Pathways?
Metabolic pathways are integrated and controlled pathways of enzyme-catalysed reactions within a cell
What categories are Metabolic Pathways divided into?
- Catabolism
- Anabolism
Describe Catabolism
Catabolic pathways breakdown complex molecules to simple molecules
This (usually) releases energy
Describe Anabolism
Anabolic pathways involve the biosynthesis (build up) of complex molecules from simpler molecules
This requires energy
What does the use of irreversible steps in metabolic pathways mean?
After that point substrates cannot be converted back and are committed to continuing on the pathway
Describe reversible steps in metabolic pathways
Reversible steps are important if too much of a substrate builds up
It allows it to be converted back to the previous substrate
Some products of metabolism in the body are potentially toxic, this can prevent toxicity
When do you use alternative routes in metabolic pathways?
When substrates are plentiful or in short supply
What is the result of Alternative routes in metabolic pathways?
This can conserve energy, (or prevent the build-up of toxic intermediate products).
What controls metabolic pathways?
The presence or absence of particular enzymes
What is activation energy?
An initial input of energy to start a reaction
Describe the effect of enzymes on activation energy
Enzymes reduce Ea, this conserves energy
What is Enzyme Specificity?
Enzymes only work with one type of substrate
The substrate fits exactly into the active site
Name the chemical attraction between substrate and enzyme
Affinity
Describe an Induced Fit in Enzymes
The active site is flexible and slightly alters its shape when the substrate enters
This close fit ensures the active site is in very close contact with the substrate
End products are released because there is low affinity with the active site.
The enzyme will return to its original conformation.
Describe Substrate Orientation
In a reaction with 2 or more substrates, the shape of the active site ensure they are held in the correct position
This weakens the chemical bonds
This reduces Ea required to get reactants to ‘transition state’
Define the Transition State in terms of enzyme activity
Transition state is where the structure is no longer a substrate but not yet a product
To function efficiently enzymes must have…
- Suitable temperature
- Appropriate pH
*Adequate supply of substrate
Talk about Substrate Concentration in terms of Rates of Reaction
Substrate concentration refers to the relative number of substrate molecules present that could bind to an available enzyme.
At low concentrations, the rates of reaction in a cell are low because there are too few substrate molecules to bind to active sites of enzymes.
An increase in substrate concentration means that there will be more substrate to bind to active sites therefore reaction rate will increase.
This trend will continue until all of the active sites are occupied. At this point, enzyme concentration becomes a limiting factor and rates of reaction will plateau.
What are the 3 types of Enzyme inhibition?
- Competitive inhibition
- Non-competitive inhibition
- End-product inhibition
Describe Competitive Inhibition
Competitive inhibitors compete with a substrate for the active site of an enzyme
These inhibitors are a similar structure to the substrate so can block an active site
Describe Non-Competitive Inhibition
Non-competitive inhibitors become attached to a non-active (allosteric) site on an enzyme
This alters the shape of the enzyme and in turn the active site
Describe Allosteric regulation
If the allosteric site is occupied by an activator (regulatory molecule) the enzyme will be in an active form
If occupied by a non-competitive inhibitor, the enzyme will change shape
Describe End product inhibition
When the end product of an enzyme catalysed reaction builds up it can bind to an enzyme found earlier within the pathway.
This slows down the conversion of A to B, and in turn regulates the whole pathway, preventing wasteful conversion of substrates and accumulation of products
