c1.2 cell respiration Flashcards
how do we get energy?
living organisms require energy to perform and maintain life processes such as movement, nutrition and excretion. this energy is released by the process of cell respiration. energy released during the reactions of respiration is transferred to the molecule of adenosine triphosphate (ATP).
what is ATP?
ATP is a small and soluble molecule that provides a short term store of chemical energy that cells can use (such as in facilitated diffusion). it is vital in linking energy requiring and energy yielding reactions. ATP is described as the universal energy currency, as it can be reused.
the hydrolysis of ATP can be carried out quickly and easily with just one enzyme. a useful quantity of energy is released from the hydrolysis of one ATP molecule. it is relatively stable at cellular pH levels.
what life processes are reliant on ATP?
anabolic reactions; moving molecules during active transport; enabling movement of the entire cell; moving cell components, such as chromosomes, within the cell. organisms require a constant supply of ATP because much of the energy is lost to the surroundings as heat.
how is ATP used as energy?
ATP is readily converted to ADP and a phosphate ion (Pi), during which energy is released. molecules such as glucose and fatty acids are used as short-term stores of energy, while glycogen, starch and triglycerides act as long-term storage molecules of energy.
how is energy transferred between ATP and ADP?
when ATP is hydrolysed, ADP and Pi are produced. as ADP forms, free energy is released that can be used for processes within a cell (like DNA synthesis).
organisms cannot build up large stores of ATP, which means the cells must make ATP as and when they need it. ATP is formed when ADP is combined with an inorganic phosphate group. this is an energy requiring reaction - water is released as a waste product (condensation reaction).
what is cellular respiration?
cell respiration is the controlled release of energy from organic compounds to produce ATP. its purpose is to release energy in usable forms from chemical energy stored in food. respiration is a catabolic process and glucose is the main respiratory fuel used in cells (lipids and proteins can also be used but they must undergo several changes).
why do enzymes control respiration?
organic food substances contain a lot of chemical energy. this energy cannot be released in one, uncontrolled step as it would cause cell damage and tissue death. enzymes control the release of energy through a series of chemical reactions which results in the production of ATP.
what are the different types of respiration?
there are two forms of respiration, depending on the oxygen availability of the cell: aerobic and anaerobic. aerobic is the process of breaking down a respiratory substrate in order to produce ATP using oxygen, whilst anaerobic takes place in the absence of oxygen.
what is aerobic respiration?
complete oxidation of glucose; requires oxygen; high ATP yield (approx 36 molecules); carbon dioxide as a waste product; water as a by-product; cytoplasm + mitochondria
glucose + oxygen → carbon dioxide + water
what is anaerobic respiration?
incomplete oxidation of glucose; doesn’t require oxygen; low yield of ATP (2 molecules); lactic acid as a product (or ethanol and carbon dioxide); cytoplasm
glucose → lactic acid (or ethanol and carbon dioxide in plants)
what variables affect the rate of respiration?
how metabolically active the cell is; size of the organism; the oxygen supply; supply of respiratory substrates; temperature; pH
how can you use a respirometer to measure oxygen consumption in respiration?
respirometers are used to measure and investigate the rate of oxygen consumption during respiration in organisms. the experiments usually require live organisms, such as seeds or invertebrates. there are many different designs of respirometers, though they all have certain features in common: a sealed container, alkaline solution (for co2), and a capillary tube.
the organisms respire aerobically and the co2 they release is absorbed by the alkali. this reduces the air pressure and the capillary tube fluid moves towards the organisms, allowing gas uptake to be measured.
what are oxidation and reduction?
oxidation is the loss of electrons and hydrogen, the gain of oxygen, and the release of energy.
reduction is the gain of electrons and hydrogen, the loss of oxygen and the absorption of energy.
what are electron carriers?
respiration involves a group of molecules called electron carriers which accept and donate their electrons. NAD and FAD are both coenzymes (and oxidising agents) which serve as links between redox reactions. these electron carriers are used to transport the electrons they have gained to other reactions in respiration.
what is glycolysis?
glycolysis is the first stage of respiration that takes place in the cytoplasm of the cell. it results in the production of two pyruvate, net two ATP (overall four ATP), and two reduced NAD.
what are the steps of glycolysis?
phosphorylation: glucose is activated by phosphorylation from two ATP to form fructose-1,6-biphosphate. this makes the 6C molecule less stable and more reactive
lysis: fructose-1,6-biphosphate splits into two molecules of triose phosphate
oxidation: hydrogen is removed from each molecule of triose phosphate to form two reduced NAD
ATP formation: phosphates are transferred from the immediate substrate molecules to form four ATP through substrate linked phosphorylation
how is pyruvate converted to lactate in anaerobic respiration?
reduced NAD transfers its hydrogens to pyruvate to form lactate, allowing NAD to be reoxidised in the absence of oxygen and pyruvate formation can continue. pyruvate is reduced to lactic acid - pyruvate is the final hydrogen acceptor and lactate can be metabolised
how is lactate metabolised in anaerobic respiration?
lactate can either be oxidised back to pyruvate, which is then channeled into the krebs cycle, or converted to glycogen for storage in the liver. the oxidation of lactate needs extra oxygen, which explains why animals breathe deeper and faster after exercise.
how is alcoholic fermentation in yeast cells useful?
in bread making, flour, yeast and water are mixed and kneaded together to form dough. in a warm environment, the yeast breaks down the starch in flour and then anaerobically respires to rise the dough. baking kills the yeast, evaporates the ethanol and leaves air pockets where carbon dioxide bubbles were in the rising dough.
what is the metabolic pathway of alcoholic fermentation?
in the alcoholic fermentation pathway, reduced NAD transfers its hydrogens to ethanal to form ethanol. pyruvate is decarboxylated to ethanal, producing carbon dioxide. then ethanal is reduced to ethanol - ethanal is the hydrogen acceptor and ethanol is a waste product.
what is the link reaction?
the link reaction takes place in the matrix of the mitochondria. it is called the link reaction because it links glycolysis to the krebs cycle.
pyruvate + NAD + CoA → acetyl CoA + carbon dioxide + reduced NAD
what are the steps of the link reaction?
oxidative decarboxylation: carbon dioxide is removed to produce a 2C molecule. this 2C molecule is then oxidised to produce an acetyl compound and reduced NAD.
enzymes: the acetyl compound is combined with coenzyme A to form acetyl CoA.
what is the krebs cycle?
the krebs cycle takes place in the matrix of the mitochondria. per glucose molecule, the krebs cycle produces: 4 carbon dioxide, 2 ATP, 6 reduced NAD, 2 reduced FAD
what are the steps of the krebs cycle?
1: acetyl CoA is accepted by oxaloacetate (4C compound) to form citrate (6C compound).
2: citrate is decarboxylated to a 5C compound and carbon dioxide is released. citrate is also dehydrogenated, which forms reduced NAD.
3: 5C compound undergoes a decarboxylation and a dehydrogenation, releasing carbon dioxided and forming reduced NAD. a phosphate is transferred from one of the intermediates to ADP, forming ATP.
4: two more dehydrogenations occur in a double oxidation step. this reduces NAD and FAD, regenerating oxaloacetate.
what is the electron transport chain?
the electron transport chain is made up of a series of redox reactions that occur via membrane proteins embedded into the inner mitochondrial membrane. the chain is used to transport electrons and move protons across the membrane. electron carriers are positioned close together, which allows the electrons to pass from carrier to carrier.
what are the steps in the electron transport chain?
energy is transferred when a pair of electrons is passed to the first carrier in the chain - this converts reduced NAD back to NAD. hydrogen ions (protons) are created when electrons are removed from hydrogen atoms. as electrons are transported along the electron carriers, energy is released in a controlled manner - this energy is used to form ATP. oxygen acts as the final electron acceptor in the chain and forms water.
how is a proton gradient useful?
electrons are given to the ETC. protons are released when the electrons are lost. the carrier proteins pump these protons across the cristae into the intermembrane space, creating a proton gradient. returning the protons down the gradient back into the matrix releases the energy required for ATP synthesis.
what is chemiosmosis?
the movement of electrons through the ETC causes a proton gradient. protons that have built up in the intermembrane space can only pass through the membrane by facilitated diffusion through ATP synthase. as protons move through ATP synthase, it catalyses the phosphorylation of ADP, generating ATP. this process is called chemiosmosis.
what is the final electron acceptor in the electron transport chain?
the final link in the ETC is oxygen and is referred to as the final electron acceptor. oxygen is reduced by the electrons and, when combined with protons from the matrix, forms water.
why is oxygen necessary in respiration?
if oxygen is not present to accept electrons, reduced NAD and FAD won’t be oxidised and there will be no further hydrogen transport. the ETC will stop and ATP won’t be formed, meaning cells can’t carry out any more reactions.
what are lipids like as respiratory substrates?
energy storage: lipids have a higher energy content per gram than carbohydrates
source of metabolic water: oxidation produces a higher volume of metabolic water than carbohydrates
solubility in cells: insoluble thereby doesn’t affect the osmotic properties of cells
ability to be broken down: hydrolysed less easily than carbohydrates, so energy is transferred slower
