General Interview Questions - Cells and Energy

How is energy captured by cells?

What is that energy used for?

How is energy stored in cells?

The laws of thermodynamics state that energy cannot be created or destroyed and that entropy increases, yet living cells are highly structured systems -- how is that possible? do cells break the laws of thermodynamics?

How does a catalyst effect a chemical reaction?

When a system is at equilibrium, what does that mean? Are cells at equilibrium?

What do you learn when you know the equilibrium constant of a reaction?

What is the role of electron in the capture and transfer of energy between molecules?

What happens to an electron when it passes through an electron transport chain?

How is energy stored in chemical gradients used by cells?

Describe the role of ATP in the energy economy of the cell?

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General importance
1.The cell is the basic unit of life. The free form of viruses, virions, are not alive, they are ametabolic. To replicate a virus must invade and parasitize a cell.
2.Cells are bounded systems of interacting chemical reactions. The rates of these reactions are controlled by catalysts (enzymes and ribozymes).
New. Metabolism is the sum of all of the chemical reactions that occur within a particularly living system.  
3.Cells are non-equilibrium systems that depend upon the continual influx of energy and the export of entropy.
4.Living organisms obey all of the laws of thermodynamics.
5.When a molecule is reduced electrons are added to it. Oxidation is the opposite, it involves the the removal of electrons.
6.The addition of electrons to a molecule increases its free energy.
7.Under the conditions that normally exist within a cell, energy can be stored by reducing molecules and released upon their oxidation.
8.The rate of a reaction reflects the step in the reaction with the highest activation energy. This step is the the rate limiting step.
9.Catalysts act to reduce the activation energy of a reaction.
10.It is possible to couple, through common intermediates, reactions that are energetically favorable with those that are energetically unfavorable, so that energetically unfavorable reaction occurs to a significant extent.
11.The equilibrium constant of a reaction reflects the concentration of reactants and products when the reaction reaches equilibrium. The equilibrium constant does not provide an estimate for the time it takes for the reaction to reach equilibrium.
12.Biological catalysts are either proteins (enzymes), RNAs (ribozymes) or macromolecules complexes (e.g. the ribosome and the splicesome) that contain both polypeptides and RNAs.
13. The energy of visible light can be captured by cells using pigments, associated with proteins, that absorb these wavelengths of light.
14. When light is absorbed by a molecule, an electron moves into a higher energy state. The electron is said to be excited. When the electron relaxes this energy can excite an electron in another molecule, be emitted as a photon (fluorescence) or transformed into molecular motion (heat).
15. An electron transport chain (ETC) is a series of membrane proteins.
16. As an excited electron moves through an electron transport chain, the components of the electron transport chain undergo sequential oxidation and reduction.
17. As electrons move through an electron transport chain, H+s are pumped across a membrane, generating a H+ gradient.
18. Adenosine triphosphate (ATP) is a major storage form of chemical energy within cells.
19. ATP can be generated from adenosine diphosphate (ADP) and phosphate as H+s move through the membrane-protein ATP synthase, an enzyme.
20. The hydrolysis of ATP into ADP and phosphate can be used to generate ion gradients across membranes.
21. A non-equilibrium situation, for example the existence of a high concentration of protons on one side of a membrane and a low concentration on the other, provides an opportunity for cells to capture energy to do metabolic work.

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