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14 Cards in this Set

  • Front
  • Back

Why do plants, animals and microorganisms need to respire?

All reactions that take place within organisms are known collectively as metabolism. Metabolic reactions that build large molecules are described as anabolic and those that break large molecules into smaller ones are catabolic. Metabolic processes that need energy inc:


•Active transport- much of an organism’s energy is used for this


• Secretion- large molecules made in some cells are released by exocytosis


• Endocytosis- bulk movement of larger molecules into the cell


• Metabolic reactions- synthesis of large molecules from smaller ones eg. proteins from Amino Acids,steroids from cholesterol, cellulose from β-glucose. These are all anabolic


• Replication of DNA and synthesis of organelles before a cell divides


• Movement


o Bacterial flagella


o Eukaryotic cilia and undulipodia


o Muscle contractions


• Activation of chemicals e.g. phosphorylation of glucose

Describe the structure and role of ATP

Describe the structure and role of ATP

ATP is a phosphorylated nucleotide which is found in both prokaryotic and eukaryotic cells. Each molecule consists of adenosine (adenine and ribose sugar) plus 3 phosphate groups. ATP can be hydrolysed to ADP & Pi (inorganic phosphate), releasing 30.6kJ energy per mol. So energy is immediately available to cells in small amounts that won't damage the cell or be wasted. The energy released from ATP hydrolysis is an immediate source of energy for biological processes such as DNA replication or protein synthesis.

What is the importanceof coenzymes in respiration?

Coenzymes aid in the oxidation and reduction of reactions. NAD combines with the Hydrogen atoms and takes them to the mitochondrial membrane where they can belater split into hydrogen ions and electrons for the election transport chain. It is used in glycolysis, the Krebscycle and anaerobic respiration. Coenzyme A carries acetate groups either from the link reaction, or that have been made from fatty acids oramino acids onto the Krebs cycle.

Outline the process of glycolysis

Glycolysis occurs in the cytoplasm. Process:


•Glucose is a hexose sugar (6C).


•One ATP molecule is hydrolysed & the phosphate group released is attached to the glucose molecule at carbon 6.


• Glucose 6-phosphate is changed to fructose 6-phosphate.


• Another ATP molecule is hydrolysed & the phosphate group released is attached to the fructose 6-phosphate at carbon 1. This activated hexose sugar is now fructose 1,6-biphosphate.


•The hexose sugar is activated by the energy release from the hydrolysed ATP molecules.


•It now cannotleave the cell and is known as Hexose-1,6-biphosphate.


It is split into two molecules of Triose phosphate


• Two hydrogen atoms are removed from each Triose Phosphate, which involves dehydrogenaseenzymes.


• NAD combines with the Hydrogen atoms to form reduced NAD


• Two molecules of ATP are formed- substrate level phosphorylation


• Four enzyme-catalysed reactions convert each triose phosphate molecule into a molecule of pyruvate.


• Two more molecules of ATP are formed, so there is a net gain of two ATP.State that, during aerobic respiration in animals, pyruvate is actively transported into mitochondria.


In aerobic respiration, pyruvate is actively transported into the mitochondria.

How does the structire of mitochondria enable them to carry out their function?

How does the structire of mitochondria enable them to carry out their function?

The Matrix:


1. Enzymes that catalyse the stages of aerobic respiration (highly-concentrated mixture of hundreds ofenzymes).


2. Molecules of coenzyme NAD.


3. Oxaloacetate - the 4-carbon compound that accepts acetate from the link reaction.


4. Mitochondrial DNA, some of which codes for mitochondrial enzymes and other proteins.5. Mitochondrial ribosomes where the proteins are assembled.


The Inner Membrane:


1. different lipid composition than the outer layer (Impermeable to most small ions, including protons(or else aerobic respiration would stop if damaged))


2. Is folded into many cristae to give a large surface area.


3. Has embedded on it many electron carriers and ATP synthase enzymes.


4. high protein-to-phospholipid ratio.


The Outer Membrane: It contains proteins, some of which form channels or carriers that allow the passage of moleculessuch as pyruvate. Other proteins in this membrane are enzymes

Outline the Link reaction

Link reaction occurs in the matrix. Pyruvate dehydrogenase removes hydrogen atoms from pyruvate. Pyruvate decarboxylase removes a carboxyl group, which eventually becomes CO2, from pyruvate. The coenzyme NAD accepts the hydrogen atoms. CoA accepts the acetate to become Acetyl CoA. The function of CoA is to carry acetate to Krebs cycle.

Outline the process of The Krebs cycle

The Krebs cycle occurs in the matrix.


1. Acetate is offloaded from CoA and joins with Oxaloacetate (4C compound) to form citrate (6C compound).


2. Citrate is decarboxlyated (1 molecule of CO2 removed) and dehydrogenated (a pair of H's removed) to form a 5C compound.


a. The hydrogen atoms are accepted by NAD, which become reduced & take them to the Electron Transport Chain


b. The Carboxyl group becomes CO2.


3. The 5C compound is decarboxylated and dehydrogenated to form a 4C compound & another reduced NAD.


4. The 4C compound is changed into another 4C compound. ADP is phosphorylated to produce a molecule of ATP. This is substrate-level phosphorylation.


5. The second 4C compound is changed into a third 4C compound and a pair of hydrogen atoms areremoved, reducing the coenzyme FAD.


6. The third 4C compound is further dehydrogenated to regenerate oxaloacetate. Another molecule of NAD is reduced.

Outline the process of oxidative phosphorylation

• The final stage of aerobic respiration involves electron carriers embedded in the mitochondrial membranes


• The membranes are folded into cristae, which increases the surface area for electron carriers and ATPsynthase enzymes.


• Oxidative phosphorylation is the formation of ATP by the addition of an inorganic phosphate to ADP inthe presence of oxygen.


• As protons flow through ATP synthase, they drive the rotation part of the enzyme and join ADP to Pi tomake ATP


• The electrons are passed from the final electron carrier to molecular oxygen, which is the final electronacceptor.


• Hydrogen ions also join, so oxygen is reduced to water

Outline the process of chemiosmosis

1. Reduced NAD and FAD donate hydrogens, which are split into protons and electrons, to the electroncarriers.


2. The protons are pumped across the inner mitochondrial membrane using energy released from thepassing of electrons down the electron transport chain.


3. This builds up a proton gradient, which is also a pH gradient, and an electrochemical gradient


4. Thus, potential energy builds up


5. The hydrogen ions cannot diffuse through the lipid part of the inner membrane, but can diffuse throughATP synthase- an ion channel in the membrane. The flow of hydrogen ions is chemiosmosis.


Oxygen is the final electron acceptor in aerobic respiration.

Explain why the theoretical maximum yield of ATP per molecule of glucose is rarely, if ever, achieved in aerobic respiration?

The maximum yield for ATP is rarely reached as:


• Some hydrogens leak across the mitochondrial membrane


o Less protons to generate the proton motive force


• Some ATP is used to actively transport pyruvate into the mitochondria


• Some ATP is used to bring Hydrogen from reduced NAD made during glycolysis, into the cytoplasm, intothe mitochondria.

Evaluate the experimental evidence for the theory of chemiosmosis

• Researchers isolated mitochondria and treated them by placing them in a solution with a very lowwater potential.


• This meant that the outer membrane ruptured, releasing the contents of the intermembrane space.


• If they further treated these mitoblasts (mitichondria stripped of their outer membrane) with a strong detergent, they could release the contents of thematrix.


• This allowed them to identify the enzymes in the mitochondria, and to work out that the link reactionand Krebs cycle occurred in the matrix, whilst the enzymes for the electron transfer chain wereembedded in the mitochondrial membrane.


• Electron transfer in mitoblasts did not produce ATP, so they concluded that the intermembrane spacewas also involved


• ATP was also not made if the mushroom-shaped parts of the stalked particles were removed from theinner membrane of the intact mitochondria.


• ATP was also not made in the presence of oligomycin, an antibiotic which is now known to block theflow of protons through the ion channel part of ATP synthase.


• In the intact mitochondria


o The potential difference across the membrane was -200mV, being more negative on the matrixside than on the intermembrane space side.


o The pH of the intermembrane space was lower than that of the matrix.

Explain why anaerobic respiration produces a much lower yield of ATP than aerobic respiration.

This is because only glycolysis occurs. The electron transport chain cannot occur, as there is no oxygen to act as thefinal electron acceptor. This means that the Krebs cycle stops, as there are no NAD- they are all reduced.This prevents the link reaction from occurring. Anaerobic respiration takes the pyruvate, and by reducing it,frees up the NAD, so glycolysis can continue, producing two molecules of ATP per glucose molecule respired.

Compare and contrast anaerobic respiration in mammals and in yeast

Mammals


1. Pyruvate combines with a hydrogen which is provided by reduced NAD, this forms lactate and oxidisedNAD


2. it involves the enzyme lactate dehydrogenase and is refered to as the lactate pathway


3. Oxidised NAD can go back to accepting hydrogen from glucose, and so Glycolysis can continue


Yeast


1. Pyruvate is converted to ethanal which involves decarboxalation as CO2 is released.


2. Ethanal combines with hydrogen from reduced NAD to form ethanol, catalysed by alcoholdehydrogenase


3. oxidised NAD can continue to go back and accept hydrogen from glucose, so glycolysis can continue

Define respiratory substrate and explain the difference in relative energy values of carbohydrate, lipid and protein respiratory substrates

An organic substance that can be used in respiration. The higher the number of hydrogen atoms per mole, the higher the relative energy value, as more NADmolecules can be reduces & used in the Electron Transport Chain. Lipids have the most, followed byproteins, and then carbohydrates.