Metabolism Flashcards
Metabolism
“The whole range of biochemical processes that occur within a living organism.”
Functions of metabolism
- providing energy for cells via high energy electrons with a negative redox potential
- providing reductive power for anabolic processes via high energy electrons
- providing carbon to build cellular components
Where does all energy come from?
the sun
- the gas in plasma formed in the sun goes through fusion, creating energy for plants
- this allows for plants to synthesise macromolecules including glucose and oxygen (photosynthesis)
- catabolic reaction
- macromolecules oxidised to produce ATP
- ATP can then drive biosynthetic reactions
- as long as there is oxygen in the sun, the energy transfer is continuous
What is this energy used for?
- With energy from the sun, plants can synthesise macromolecules
- This is an example of a catabolic pathway, in which the macromolecules are oxidised to produce ATP
- This ATP can then go on to drive biosynthetic reactions
Which two types of reactions make up metabolism?
Catabolism and anabolism
Catabolism
- Large complex organic molecules are broken down into smaller molecules
- Degradative
- Oxidative (mostly oxygen is lost)
- Energy released (ATP)
- there is energy bonds being broken and so there must be energy being liberated
- Converging (all protein and fat is made into carbon dioxide)
Anabolism
- Small molecules are constructed to for larger complex organic molecules
- disordered to ordered
- Biosynthetic
- Reductive
- Requires energy
- Diverging
Oxidation - reduction reactions
- redox (electrons are transferred from one molecule to another)
- OIL RIG (Oxidation is loss, reduction is gain)
- As one molecule is oxidised (loses an electron), another is reduced (gains an electron) and so are called a ‘redox pair’
- reduced compound is called a reducing agent because it causes the reduction of compound B
- oxidised compound is called oxidising agent as it causes oxidation of compound A
- oxidised compound becomes reduced
- reduced compound becomes oxidised
Most reduced state of carbon
Methane
Most oxidised state of carbon
Carbon Dioxide
The steps of glucose oxidation
- change in free energy, if this decreases then will become oxidised and energy will be released
- The activation energy is reduced so that the reaction can occur at the optimum temperature of 37° C
- The released free energy is reduced – this can be coupled to endergonic reactions and does not damage the cell
- Convenient control points are provided
- Can be integrated with other cellular metabolism
- the first few stages the energy is increased, decreasing the stability of the bonds
Electron flow in chemotrophs
- chemotrophs obtain the energy of other cells
- Organic compounds, such as carbohydrates, amino acids and lipids, are oxidised to release high energy electrons
- Organic cofactors act as electron carriers
- NAD+ + 2H+ is reduced to NADH + H+
- FAD + 2H+ is reduced to FADH2
- A terminal electron acceptor is reduced aerobically: O2 → H2O
- the electron acceptor is oxygen which is reduced to water
Enzymes
- Proteins
- Biological catalysts that facilitate the conversion of a substrate into a product
- Often require co-enzymes, e.g. ATP
- Are present in most chemical reactions in cells
- The name of an enzyme is derived from its substrate and its action: substrate action-ase
Oxidoreductase
- all enzymes catalysing oxido-reductions
- e.g. alcohol dehydrogenase
Transferases
- transfer a group onto a substrate
- e.g. UMP kinase
Hydrolases
- catalyse the hydrolysis of various bonds
- e.g. aminoacyl-tRNA hydrolase
Lyases
- cleave C-C, C-O, C-N and other bonds by other means than by hydrolyses or oxidation
- e.g. pyruvate decarboxylase
Isomerases
- catalyse changes within one molecule
- e.g. DNA topoisomerase
Ligases
- catalyse the joining of two molecules with concomitant hydrolysis of the diphosphate bond in ATP or a similar triphosphate
- e.g. DNA ligase (ATP)
Enzyme which transfers phosphate groups
- kinase
- e.g phosphofructokinase
Enzyme which rearranges the molecule
- isomerase
- e.g. isomerase
Enzyme which makes a molecule from parts
- synthase
- e.g. ATP synthase
Enzyme which removes hydrogen
- dehydrogenase
- e.g. isocitrate dehydrogenase
Enzyme which removes phosphate from a protein
- phosphatase
- e.g. dual specificity phosphatase
Oxidation states of carbon
- depending on what the carbon atom is joined to, it can be in a reduced or oxidised state
- general rule: the smaller the compound the more oxidised and lower free energy
- alkane (fats) > alcohol (carbohydrates) > aldehyde > carboxylic acid > carbon dioxide (final product of metabolism)
Is it possible to get all 94 glucose molecules from a cell?
Yes, but not in nature.
To get all 94 glucose molecules from a cell, it would require combustion which is not possible, this is too much energy being applied to the cell and would cause unwanted reactions, damage, breaks, stable bonds to break.
