Metabolism Flashcards
Define metabolism.
The process through which organisms acquire and utilise the free energy they need to carry out functions
What are the two main inputs for an organism?
Carbon and energy
What are the two ways that energy is generated?
- Absorption of light (photosynthesis)
- Oxidation reactions of reduced carbon compounds (exergonic)
Which output processes are endergonic?
- Assimilation of nitrogen
- Movement
- Transport processes
- Synthesis of biological molecules and growth.
What are the energy sources for:
- Photoautotrophs
- Photoheterotrophs
- Chemoautotrophs
- Chemoheterotrophs
-Photoautotrophs
>Light
-Photoheterotrophs
>Light
-Chemoautotrophs
>Inorganic substances
-Chemoheterotrophs
>Organic compounds
What are the carbon sources for:
- Photoautotrophs
- Photoheterotrophs
- Chemoautotrophs
- Chemoheterotrophs
-Photoautotrophs
>Carbon dioxide
-Photoheterotrophs
>Organic compounds
-Chemoautotrophs
>Carbon dioxide
-Chemoheterotrophs
>Organic compounds
What is the difference between autotrophs and heterotrophs?
- Autotrophs- get carbon from fixation of CO2 (“inorganic carbon”)
- Heterotrophs- get carbon from organic sources
- Ie autotrophs= inorganic carbon source, heterotrophs= organic carbon source
In metabolism, how is energy expressed?
Energy is expressed as Gibbs free energy, G
Can a reaction occur spontaneously if the Free energy increases?
Can a reaction occur spontaneously if the free energy decreases?
No, because an energy input is required.
Yes because the energy lost can be used in another process.
What is the relationship between exergonic and endergonic reactions?
- Exergonic reactions produce energy which organisms use to drive endergonic reactions through the synthesis of intermediates
- Intermediates such as ATP (energy in the form of chemical potential)
Why is ATP not thermodynamically stable under biological conditions?
The free energy change is negative under biological conditions.
Is ATP kinetically stable? How do we know this?
Yes. Because it has a very long half life (low rate of hydrolysis).
How can exergonic reactions that produce ATP occur spontaneously?
Because the combined reaction of ATP forming ADP and ADP forming ATP has an overall decrease in free energy.
What are endergonic reactions usually driven by?
Phosphoryl transfer from ATP (as the combined reaction still produces a decrease in free energy.
What factor determines how much ATP is produced/ required in a reaction?
The stoichiometry of the reaction determines this.
How are reduced cofactors a form of cellular energy?
Reduced cofactors are a form of cellular energy because they are used to produce ATP, such as NADH and FADH2
Which molecule helps maintain the levels of ATP? Use an equation to describe the mechanism through which this occurs. What is the enzyme that catalyses this reaction?
- GTP acts as a ‘buffer’ for the amount of ATP
- GTP + ADP ATP + GDP
- Nucelotide diphosphate kinase is the enzyme that catalyses this reaction.
How is creatine phosphate used as an energy store in muscles?
- Used as an energy store which generates ATP from ADP
- A phosphate from ATP is transferred to creatine to from creatine phosphate
By which other mechanisms can ATP be generated?
- Concentration gradients
- Electrical potentials from transporting ions across a membrane
-Provide the potential for ATP to be generated from these molecules going down their concentration gradients.
Why are metabolic pathways effectively irreversible?
Because a different route must be taken to reform what was broken down. This is because if it was reversible, no outcome would be generated as equilibrium would eventually be reached.
This is achieved by one of the steps having a large change in free energy, making the pathway effectively irreversible.
Name the 6 characteristics of metabolic pathways.
-Effectively irreversible
-Occur in specific
cellular locations
- Every metabolic pathway must have a committed first step
- Catabolic and anabolic pathways must differ (If this were not the case, degradative and biosynthetic pathways could not coexist).
- All metabolic pathways are regulated (all steps regulated)
- Cannot be considered as separate because they form component parts of the overall metabolism of the organism, despite being called separate for many purposes
