12. Energy and Respiration Flashcards
From where can living organisms obtain a continuous source of energy?
Chemical potential energy from nutrient molecules, or the absorption of light energy.
How is photosynthesis important to living organisms?
Photosynthesis converts light energy into chemical potential energy - it provides an energy supply and usable carbon compounds.
Why is having a source of carbon important?
Carbon is found in all biological macromolecules, which are essential to living organisms.
Autotrophs can use an inorganic source of carbon (CO2), but heterotrophs need a ready-made organic supply.
How can organic compounds be used in living organisms?
Building blocks for other, more complex organic molecules essential to the living organism, or as a representation of the chemical potential energy that can be released when they are broken down in respiration. This energy can be used to do work.
What are some examples of work in a living organism?
- Anabolic reactions (the synthesis of complex substances from simpler ones, eg. polysaccharides from monosaccharides).
- Active transport (eg. sodium-potassium pump).
- Mechanical work (eg. movement of cilia and flagella, amoeboid movement, movement of vesicles through cytoplasm).
- Bioluminescence and electrical discharge.
How do different organisms maintain a constant body temperature?
Ectotherms use thermal energy from their external environment to warm their bodies.
Endotherms (mammals, birds) use thermal energy released from metabolic reactions within their bodies, to maintain a temperature above that of their surroundings when necessary. Constant body temperature is also maintained through negative feedback loops.
What must happen in order for work to be done?
Energy-requiring reactions must link with energy-yielding reactions.
What is a multi-step reaction?
In a multi-step reaction, a series of elementary steps lead to an overall reaction. In each step, a small amount of the reaction’s total energy is released. They allow precise control of the reaction via feedback mechanisms and they allow optimal energy usage - if all energy were available at once then much of it would be wasted.
Give an example of a multi-step reaction.
An example is the respiration equation (the complete oxidation of glucose in aerobic conditions). It releases 2870kJ of energy.
Why can’t glucose react ‘naturally’?
Glucose, although energy-rich, is quite stable due to its high activation energy. The activation energy in living organisms can be overcome through the use of enzymes (which lower the activation energy by providing an alternate pathway for the reaction), or through the phosphorylation of glucose.
How is energy from respiration harnessed?
Rather than the energy released from each step being harnessed directly to be used in work, a more flexible method occurs where energy-yielding reactions in all organisms produce the universal intermediary molecule, ATP. ATP is used for all the energy-requiring reactions in the cell.
What is the structure of ATP?
Three phosphate groups, the last one bonded to a ribose sugar, the sugar bonded to an adenine nitrogenous base.
How much energy is released in the hydrolysis of ATP?
When the first and second phosphate groups are removed (ATP -> ADP and ADP -> AMP), 30.5kJ/mol are released. When the last phosphate group is removed, only 14.2kJ/mol are released. The two outer bonds are therefore considered ‘high-energy’, but this should be avoided as the energy released doesn’t come simply from the breaking of bonds, but from the changes in chemical potential energy in all parts of the system.
All of these reactions are reversible. Water is added and an inorganic phosphate group removed.
What are some key features of ATP?
It is easily hydrolysed and therefore has a high interconversion rate (ATP and ADP). This is useful to the cell as energy can easily be made available and restored. It is small and water-soluble, making it very easy to transport within the cell.
Energy data around the usage of ATP.
A resting human can use about 40kg per day, but at any one time there are only about 5g of ATP. During strenuous exercise, the rate of breakdown can reach 0.5kg/min.
What is the difference between an energy storage and energy currency molecule?
An energy storage molecule can be a short-term (glucose, sucrose) or long-term (glycogen, starch, triglyceride) store of chemical potential energy for the cell. An energy currency molecule, like ATP, is an immediate donor of energy to the cell’s energy-requiring reactions. Rather than using multiple different intermediates, the cell ‘trades’ in ATP.
Why are energy transfers inefficient?
At different stages in a multi-step reaction, the energy available may not correspond with / exceed the energy required. Many energy-requiring reactions do not use all the energy released by the hydrolysis of ATP -> ADP. The excess is lost as thermal energy. Some will always be released as thermal energy during energy transfers.
How does the sodium-potassium ion pump work?
The pump is a transmembrane protein that has binding sites for Na ions and ATP on the inner end, and K ions on the outer end. It acts as an ATPase, hydrolysing ATP to ADP to release energy. This energy is used in the active transport of Na and K ions. The protein changes shape to pump 3 Na out and 2 K in for each molecule of ATP. This creates a potential difference across the membrane (inner more - than outside).
Some diffusion down a conc. gradient will occur, but it is easier for K to leave than for Na to enter, so this p.d. is actually made stronger.
What is an example of the p.d. in a living organism?
The resting potential of a nerve cell. It is specialised to exaggerate this difference.
Around 50% of the ATP in a resting mammal is devoted to maintaining the ionic content of a cell.
Describe the structure of a mitochondrion.
Filamentous/rod-shaped organelle, 0.5-1um diameter. Can change shape.
Double membrane, outer is slightly more permeable to small molecules. Inner has infoldings (cristae) to increase surface area, more metabolically active mitochondria have longer, more densely packed cristae. Inner membrane studded with ATP synthase (9nm), attached by stalks.
Intermembrane space has lower pH than matrix (high H ion concentration from e- transport chain).
Matrix contains circular DNA, 70S ribosomes, enzymes needed for link reaction and Krebs cycle.
How is the energy needed for ATP synthesis made available?
By reorganising chemical bonds in respiration (chemical potential energy) and by using electrical potential energy via chemiosmosis.
What is respiration in basic terms?
A reaction in which organic molecule are used as fuel. The main fuel is glucose but some cells can also respire fatty acids, glycerol or amino acids. The organic molecules are broken down in multi-step reactions to release chemical potential energy, which can then be harnessed to synthesise ATP.
