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A2 Biology (Unit 1: F214) > Respiration > Flashcards

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What is respiration?

The process whereby the chemical potential energy stored in complex organic molecules is used to make ATP in living cells.


What is metabolism?

All chemical reactions that occur inside living cells that form an essential part to its survival and the survival of the organism.


What are the two main types of reactions that make up metabolism?

1. Catabolism: The breakdown of larger molecules into multiple smaller molecules.
2. Anabolism: The build-up of smaller molecules into larger molecules.


What cellular processes require energy from respiration?

- Active transport of substances across a membrane against the concentration requires a lot of energy and is an essential process in living organisms. An example is the mechanism to maintain the resting potential of neurones using Na+/K+ pumps.
- Secretion by exocytosis requires energy and is the primary secretion mechanism for larger molecules.
- Endocytosis also requires energy.
- Some anabolic reactions such as protein synthesis and cellulose synthesis require energy.
- DNA replication and many processes that happen pre-cellular replication require energy.
- Movement involving the cytoskeleton, including flagella/undulipodia, cilia and microtubules all require energy.
- Muscular contractions also requires energy.
- Other types of metabolic reactions such as phosphorylation reactions that are vital for survival also require energy.
- Heat energy released by respiration is used to maintain constant core temperature in endotherms in order to maintain constant rates to enzyme-catalysed reactions.


Where does most energy in living things come from?

1. Most energy in living things originate as light energy from the sun.
2. Photoautotrophs (producers) carry out photosynthesis which converts light energy into chemical potential energy stored in large organic molecules such as carbohydrates.
3. These producers are then consumed by consumers that use respiration to break down these large organic molecules into small inorganic molecules, releasing the stored energy as heat and chemical energy stored in ATP.


What is the structure of ATP?

ATP (Adenosine Triphosphate) consists of an adenosine group (adenine bonded to a ribose sugar), bonded to 3 phosphate (phosphoryl) groups.


What is the role of ATP in living organisms?

- ATP is the universal energy currency in cells.
- It is used in all energy-requiring reactions as a source of energy in all organisms.
- It acts as an intermediate molecule between all energy-releasing processes and energy-requiring processes in a cell.


How does ATP store energy from respiration?

Respiration occurs in many small steps that release small amounts of energy each time. This energy is used to phosphorylate ADP into ATP, storing the energy, which can be hydrolysed in an energy-requiring reaction. However, ATP is never stored and rarely imported and each cell only has a small amount, so it needs to be regenerated rapidly by respiration in order to keep up in demand.


What are the 4 stages of aerobic respiration?

Common reaction:
1. Glycolysis - Occurs in cytoplasm.
Aerobic respiration only:
2. Link reaction - Occurs in matrix of mitochondria.
3. Krebs cycle - Occurs in matrix of mitochondria.
4. Oxidative phosphorylation - Occurs in cristae, folded inner mitochondrial membrane.


What are coenzymes?

Molecules that are not part of the enzyme but are required in order for an enzyme to function properly. This makes them cofactors to enzymes.


What coenzymes are involved in respiration?

1. NAD (Nicotinamide Adenine Dinucleotide).
2. FAD (Flavin Adenine Dinucleotide).
3. Coenzyme A.


Why are coenzymes involved in respiration?

During most stages of respiration, oxidation reactions occur whereby hydrogen atoms are removed by the process of dehydrogenation. These reactions are carried out by dehydrogenase enzymes. However, the reactions release hydrogen atoms which are particularly unstable and cannot exist on their own, so dehydrogenation reactions cannot occur. Coenzymes NAD and FAD combine with these H atoms to form reduced NAD and FAD. This ensures that dehydrogenation reactions can occur when catalysed by dehydrogenase enzymes, making them coenzymes to dehydrogenase. They also act as carriers of H atoms to the cristae where they are used in oxidative phosphorylation.


How many hydrogen atoms can one NAD molecule accept?



What is glycolysis?

The metabolic pathway where each glucose molecule is broken down into 2, 3 carbon pyruvate molecules.


Where does glycolysis take place?

In the cytoplasm of respiring cells.


Why is glycolysis known as the 'common' pathway?

It does not require oxygen and is the only reaction pathway that takes place both in aerobic and anaerobic respiration.


What are the stages in glycolysis?

1. 1 ATP molecule is hydrolysed to ADP and Pi. Pi attached to carbon-6 on glucose to form glucose 6-phosphate. This process is called phosphorylation.
2. Glucose 6-phosphate is converted to fructose 6- phosphate.
3. Another ATP molecule is hydrolysed and the Pi attaches to carbon-1 to form fructose 1,6-bisphosphate.
4. Energy released from ATP hydrolysis used to activate molecule to form hexose 1,6-bisphosphate to prevent molecule from leaving cell.
5. 2 ATP molecules are used to form hexose 1,6-bisphosphate.

Lysis of hexose 1,6-bisphosphate:
6. Hexose 1,6-bisphosphate splits into 2 molecules of triose phosphate.

Oxidation of triose phosphate:
7. Dehydrogenase enzymes oxidise each triose phosphate molecule by removing 2 hydrogen atoms from each.
8. Hydrogen atoms combine with NAD molecules to form reduced NAD.
9. ADP and Pi are recombined to form ATP in a process called substrate level phosphorylation.
10. 2 triose phosphate molecules are converted to 2 oxidised intermediate compounds, with the formation of 2 ATP and 2 reduced NAD molecules.

Conversion of triose phosphate to pyruvate:
11. A series of 4 enzyme catalysed reaction convert the intermediate compound into a pyruvste molecule.
12. A further 2 ATP molecules are formed through substrate level phosporylation.
13. 2 intermediate molecules are converted to 2 pyruvate molecules with the formation of 2 ATP molecules.


What is the overall process of glycolysis?

Glucose + 2 x NAD + 2 x ATP ---> 2 x pyruvate + 2 x reduced NAD + 4 x ATP


What is the net gain in ATP through glycolysis?



What types of cells have many mitochondria?

Cells that characteristically have high energy requirements. Including muscle cells, brain cells, ciliated epithelial cells and PCT epithelial cells.


What is the structure of a mitochondrion?

- All mitochondria are enclosed by 2 phospholipid membranes surrounding it in an envelope. An outer membrane and an inner membrane.
- The outer membrane is smooth whereas the inner membrane is folded into cristae to maximise surface area.
- Space between outer and inner membrane called the intermembrane space.
- Matrix surrounded by the inner membrane and is of a gel-like consistency, containing lipids, proteins, enzymes, ring of DNA and mitochondrial ribosomes.


How is the matrix adapted to its function?

- Matrix is site of link reaction and Krebs cycle.
- Contains the appropriate enzymes to catalyse these reactions.
- Contains a lot of NAD.
- Oxaloacetate present in number to accept acetate molecules into the Krebs cycle from link reaction.
- DNA coding for vital proteins required by mitochondria,
- Ribosomes to manufacture proteins inside the mitochondria itself.


How is the outer membrane adapted to its function?

- Contains carrier proteins that only allow certain molecules to enter and leave mitochondria, controlling movement of substances.
- Enzymes to catalyse certain reactions.


How is the inner membrane adapted to its function?

- Inner membrane site of oxidative phosphorylation.
- Folded into cristae to maximise surface area.
- H+ pumps for active transport of H+ ions during chemiosmosis.
- Contains many cofactors and enzymes that form part of the electron carrier chain.
- Many ATP synthase to manufacture ATP from ATP synthase.
- Different composition to outer membrane and is impermeable to small ions.


What is the structure of ATP synthase molecules?

- Proton channel part embedded into the inner membrane and allows H+ ions to pass from intermembrane space into matrix.
- Headpiece attached to an axel (stalk) which allows for free rotation.
- Kinetic energy from the H+ ions flowing down concentration into the matrix through proton channel drives rotation of headpiece which allows ADP to join with Pi to form ATP.


Where does the link reaction occur?

In the matrix of the mitochondria.


What are the steps in the link reaction?

1. Dehydrogenation/decarboxylation - Pyruvate decarboxylase removes one CO2 molecule per pyruvate molecule. Pyruvate dehydrogenase oxidises pyruvate by dehydrogenation, with NAD acting as the hydrogen acceptor. The pyruvate (3C) becomes an acetate molecule (2C).
2. Acetate molecule binds onto coenzyme A (CoA) to form acetyl coenzyme A and is carried into the Krebs cycle.


What is the overall equation for the link reaction?

2 pyruvate + 2 CoA + 2 NAD ---> 2 acetyl CoA + 2 CO2 + 2 reduced NAD


Where does the Krebs cycle take place?

In the matrix of the mitochondria.


What are the stages in the Krebs cycle?

1. The acetate is transferred from the acetyl CoA onto a 4C oxaloacetate compound to form a 6C citrate compound.
2. Citrate is decarboxylated and dehydrogenated by enzymes, one molecule of NAD accepts the hydrogen atoms from dehydrogenation to form reduced NAD. A 5C intermediate compound is formed, as well as CO2.
3. the 5C compound is further decarboxylated and dehydrogenated, producing another CO2 molecule and reducing an NAD to reduced NAD, as well as a 4C compound.
4. The 4C compound is changed into another 4C compound through a series of reactions which results in a molecule of ADP being phosphorylated to ATP through substrate-level phosphorylation.
5. The 4C compound is further dehydrogenated, with FAD acting as the electron acceptor to form a molecule of reduced FAD.
6. 4C compound further dehydrogenated to form oxaloacetate and a molecule of NAD is reduced.
7. Oxaloacetate ready to accept more acetyl CoA molecules to repeat cycle.