Introduction to Metabolism Flashcards
(29 cards)
What is metabolism?
What is exergonic and what is endergonic?
Defined as the overall process through which living systems acquire and utilise the free energy they need to carry out their various functions
Living systems: Couple the exergonic (energy producing) reactions to the endergonic (energy requiring) process = Maintains the living state
What are the two main inputs for organisms?
Energy and carbon
Main requirements needed for synthesis of biological molecules
What chemical reactions generate energy for higher animals and plants?
Higher animals: Oxidation of reduced carbon compounds such as sugars and fats
Plants: Absorption of light= Photosynthesis
What are some examples of exergonic processes?
Nutrient oxidation: Oxygen is added to organic compounds to form nitrates, sulphates, CO2
Photosynthesis: Carbon dioxide needed for organic compounds, light, water for inorganic compounds and forms oxygen
What are some examples of endergonic processes?
1) Assimilating nitrogen and other elements needed for growth
2) Transport processes, maintaining intracellular environment
3) Movement and other processes which needs motility
4) Synthesis of biological molecules, growth
What is the difference between autotrophs and heterotrophs? What are some examples of each?
Autotrophs: Obtain carbon by fixation of carbon dioxide (inorganic carbon)
Example:
Photoautotrophs: Light as energy source and carbon dioxide as carbon source
Chemoautotrophs: Inorganic substances as energy source and carbon dioxide as carbon source
Heterotrophs: Obtain carbon from organic sources
Photoheterotrophs: Light as energy source and organic compounds as carbon source
Chemoheterotrophs: Organic compounds as energy source, organic compounds as carbon source
What is energy given as?
In metabolism, energy is expressed as Gibbs Free Energy (symbol G)
Free energy changes are usually standardised to a fixed amount= 1 mole
Free energy changes are given the units ΔG mol^-1
Remember: Free energy has to decrease for a process to occur spontaneously= Energy lost in process can be used in another process or wasted as heat BUT even if it is negative, does not tell us about the kinetics
What is the equation linking ΔG to Keq?
–ΔG° = RT ln Keq
Normally use ΔG°’ indicating biological standard conditions
How can you link metabolism with coupling of exergonic and endergonic reactions?
Metabolism is about linking processes that have -veΔG (exergonic, energy generating) to processes that have +ve ΔG (endergonic, energy requiring)
Normally require the use of intermediates such as adenosine triphosphate (ATP) which are used to store energy in the form of chemical potential- ATP hydrolysis has high negative standard free energy to ADP
The energy store can then be used to drive other processes
How stable is ATP?
ATP not stable thermodynamically due to -ΔG
BUT is stable kinetically= process is slow at solutions at pH=7.0
What is ATP able to do?
Able to both transfer phosphosryl groups to other molecules + Accept phosphoric groups from other molecules
Phosphoryl transfer by ATP drives endergonic reactions
Why are reduced cofactors so important?
Oxidation of reduced carbon compounds generates reduced cofactors such as NADH and NADPH which are a form of cellular energy as they are used to produce ATP
Apart from ATP, what are the other energy stores which living cells use?
1) Chemical potential in the form of other energy storage compounds e.g. GtO and creatine phosphate which are formed using ATP to drive synthetic reactions
Creatine phosphate: ATP must be replenished by sung this to produce ATP as cells only maintain minimal reserves of ATP + It can be resynthesised from ATP
2) Stored nutrients e.g. starch, oil which also act as chemical potential and are synthesised in situ using ATP
3) Concentration gradients which can be used to generate ATP
4) Electrical potential as a result of ion transport across membranes= Can then be used to generate ATP
These energy storage methods are all interconvertible with ATP
What are metabolic pathways?
Series of consecutive enzyme-catalysed reactions that produce specific products
DO NOT NEED TO KNOW PATHWAY IN DETAIL= Need to understand the mechanisms and how the pathways are controlled
What is catabolism?
Degradation= Nutrients and cell constituents are broken down exergonically to simple common intermediates
Generates ATP
What is anabolism?
Biosynthesis= In which biological molecules are synthesised endergonically from simpler components
Uses ATP as energy
What are the 3 stages of complexity of metabolism?
LOOK AT DIAGRAM IN BOOK
What are characteristics of metabolic pathways?
1) Effectively irreversible
2) Catabolic and anabolic pathways must differ
3) First committed step
4) Regulated
5) Occur in specific cellular locations
6) Pathways form component parts of the overall metabolism of the organism
Why are metabolic pathways effectively irreversible?
1):
A step in the pathway will have a large change in free energy (approx >50kJ mol^-1)
Flow of material through pathway will only occur at a significant rate in that direction due to irreversible step
Why must catabolic and anabolic pathways differ?
Would not be able to co-exist if they were the same
If two metabolites are interconvertible:
Pathway from first to second MUST DIFFER in at least one step in pathway of second to first e.g. the step that is large in free energy
Allows independent control of the two processes
What is the first committed step?
Steps where there is a small change in standard free energy are reversible
Early in each pathway, generally an irreversible (exergonic) reaction that commits the intermediate it produces to continue down the pathway
Why are metabolic pathways regulated?
To allow a living organism to respond to changes in its environment
Most readily regulated by making the step which is irreversible the rate limiting step for the pathway
What are the specific cellular locations which metabolic pathways in eukaryotic cells occur?
Eukaryotic cells: A series of membrane-bound subcellular compartments
Membranes= Impermeable to most metabolites= diffusion is prevented
Spatial separation of processes
What process takes place in the cytosol?
Glycolysis
