NM - Overview of Metabolism Flashcards
Define ‘metabolism’.
It made up of a series of enzyme reactions within cells for converting
fuel molecules into ‘useful energy’.
Metabolism is the process of breaking down food molecules into building blocks of biosynthesis via catabolic pathways, and then using them to form the many molecules that form the cell through anabolic pathways.
What is the difference in where the reactions mostly occur between catabolism and anabolism?
Catabolism: mitochondrial
Anabolism: mostly in the cytosol
Outline the difference between oxidation and reduction.
When you oxidise a compound, you generate energy, and when you reduce a compound, you need energy.
Oxidation is taking electrons away, and reduction is adding them. This often happens with hydrogen ions, so we call reduction ‘hydrogenation’, and oxidation ‘dehydrogenation’.
If you go from a single bond to a double bond, that is also an oxidation.
Alkanes are at the lowest oxidation state, so it is a very good fuel.
What does integration of pathways have to do with metabolism?
The pathways of glycolysis and TCA cycle act together to convert glucose to CO2.
There is high integration of these pathways.
What happens to substances that go through glycolysis, beta-oxidation and transamination?
They all end up as a substance called acetate.
What happens to acetate in the TCA or Krebs cycle?
Acetate is further oxidised to carbon dioxide, and we transfer the equivalent of hydrogens to so called cofactors, so we have half the energy, which is converted to ATP in the third stage.
How does glucose get through the mitochondrial double membrane?
The fatty acids and glucose are taken up through the cellular membrane. We can see a glucose transporter, but we also have a fatty acid transporter.
The glucose is broken down to pyruvate in the cytosol, and it is transferred to the mitochondria, where the other two pathways take place, Krebs/TCA cycle and oxidative phosphorylation.
How do fatty acids get through the mitochondrial double membrane?
Fatty acids are transported with proteins through the membrane. Albumin delivers it, and fatty acids binding (FAB) proteins that take it up inside and transport it. The fatty acids are transported through the double membrane into the mitochondria.
Describe ATP.
Full name: adenosine triphosphate
It is the energy currency in the cell. It is chemically stable at pH 6-9.
It has structural features that are recognised by specific proteins, enxymes, etc.
Hydrolysis of ATP gives us ADP + Pi + H+.
List some functions of ATP.
- used directly in cell motility and contraction
- used in Na+ / K+ pumps, active transport systems & metabolic control
- used in metabolism to add Pi to metabolic intermediates
(when we add phosphate, we give the glucose a charge, which allows the cell to hold on to the glucose, so that it can initiate a series of reactions to start breaking down this glucose)
Describe the rate and direction of enzymatic reactions.
The rate of a biochemical reaction is dependent on enzyme activity.
The direction (equilibrium) of a reaction is dependent on the properties of the chemical molecules themselves.
What is the difference between exothermic and endothermic reactions?
If a reaction generates energy, it is called exothermic.
If it uses energy, it is called endothermic.
What is delta G?
Delta G is the free energy in a reaction.
A reaction occurs spontaneously when delta G is less than 0.
List some ways in which the rate of an enzymatic reaction.
- by altering the availability of the substrate, (e.g. by increasing the transport system into the cell)
- by increasing the amount of enzyme present in the cell, by increasing the rate of transcription from the gene in DNA into mRNA)
- the interconversion of ‘active’ & ‘inactive’ forms of key enzymes
- allosterism
Describe the interconversion of active and inactive forms of enzymes.
By simply phosphorylating an enzyme, we can activate it.
These enzymes are usually called kinases.
There are also enzymes called phosphatases which do the opposite, and remove a phosphate group from a molecule, rendering it inactive.
