role of ATP in living cells

Question 1

what is metabolism?

Answer 1

integrated set of enzymatic reactions compromising both anabolic and catabolic reactions

Question 2

what is anabolism?

Answer 2

synthesis of complex molecules from simpler ones

Question 3

what is catabolism?

Answer 3

• breakdown of energy rich molecules into simpler ones

- energy released if ‘captured’ as adenosine triphosphate (ATP) and stored for later used in anabolic reactions

Question 4

what is energy required for?

Answer 4

• motions
• transport
• biosynthesis of essential metabolites
• thermoregulation

Question 5

what is ‘free energy’?

Answer 5

• cells are isothermal systems
• heat flow cannot be used as a source of energy (heat can only do work when it passes to an area or an object at a lower temperature)
• free energy is acquired from nutrient molecules

Question 6

what’s Gibbs free energy?

Answer 6

energy capable of doing work at constant temperature and pressure

Question 7

what is enthalpy?

Answer 7

the heat content of the reacting system

Question 8

what is entropy?

Answer 8

the randomness or disorder in a system

Question 9

what is coupling of reactions?

Answer 9

an endergonic reaction can be driven in the forward direction by coupling it to an exergonic reaction through a common intermediate

Question 10

what are the key facts/features of ATP?

Answer 10

• adenosine triphosphate
• ATP provides lots of the free energy required for anabolism
• ATP is the energy currency of the cell
• achieved by phosphate group transfer
• Gibbs free energy: the energy derived from the oxidation of dietary fuels to generate ATP
• energy is conserved as ATP and is transducer into useful work

Question 11

what are ATP/ADP Mg2+ complexes?

Answer 11

• ATP in the cytosol is present as a complex with magnesium ions
• magnesium ions with the oxygen of the triphosphate chain making it susceptible to cleavage in the phosphoric transfer reactions
• magnesium ion deficiency impairs virtually all metabolism

Question 12

what is substrate level phosphorylation (SLP)?

Answer 12

• formation of ATP by phosphate group transfer from a substrate to ADP
• known as SLP to distinguish form respiration-linked phosphorylation
• respiration linked phosphorylation involves membrane-bound enzymes and transmembrane gradient of protons and requires oxygen

Question 13

what are enzymes?

Answer 13

• biological catalysts that accelerate the rate of chemical reactions
• creates new pathway for the reactions by lowering the activation energy
• don’t affect Gibbs free energy

Question 14

what are cofactors?

Answer 14

non-protein molecules necessary for enzyme activity

Question 15

what are coenzymes/cosubstrates?

Answer 15

have loose association with their enzyme and diffuse between enzymes carrying electrons

Question 16

what are prosthetic groups?

Answer 16

• non protein cofactors that is covalently bonded to the enzyme
• not released as part of the reaction
• acts as a temporary store for electrons or intermediates

Question 17

how doe redox reactions and coenzymes/prosthetic groups interlink?

Answer 17

• major redox coenzymes/prosthetic groups involved in transduction of energy from dietary foods to ATP: NAD+/FAD/FMN
• electrons are transferred from dietary material to these carriers —> coenzymes are reduced
• in each case 2 electrons are transferred but the number of H+ moved varies

Question 18

rowdies nicotinamide adenine dinucleate (NAD+) work?

Answer 18

• NAD+ and NADP+ accept pairs of electrons to form NADH or NADPH
• it is the nicotinamide that is the functional part of the molecule

Question 19

how are the redox coenzymes re-oxidated?

Answer 19

• recycling NADH and FADH2 via the respiratory chain in the mitochondria
• this is coupled to ATP synthesis: process of oxidative phosphorylation

Question 20

what are the 2 possible fates of pyruvate?

Answer 20

• under aerobic conditions: oxidation and complete degradation
• in hypoxic conditions: it can be reduced to lactate

Question 21

in aerobic conditions describe the one fate of pyruvate

Answer 21

• conversion to acetyl-CoA for oxidation and complete degradation
• in the mitochondria
• glycolysis occurs in the cytosol (can occur in the presence or absence of oxygen)
• —-> pyruvate is transported into the mitochondria for complete oxidation

Question 22

how is pyruvate transported into the mitochondria?

Answer 22

• occurs via a specific carrier protein embedded in the mitochondria membrane in aerobic conditions
• pyruvate undergoes oxidative phosphorylation by the pyruvate dehydrogenase complex to form acetyl CoA: pyruvate + CoA + NAD+ —–> acetyl CoA + CO2 + NADH + H+
• reaction is irreversible and is the link between glycolysis and the citric acid cycle

Question 23

what are the 9 intermediates of TCA cycle?

Answer 23

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1) Acetyl CoA
2) citrate
3) Isocitrate
4) a-ketoglutarate
5) succinyl CoA
6) succinate
7) fumarate
8) malate
9) oxaloacetate

Question 24

how is the TCA cycle regulated?

Answer 24

flow of carbon atoms from pyruvate into and through the TCA cycle is tightly regulated at 2 levels:

1) conversions of pyruvate to acetyl-CoA
2) entry of acetyl-CoA into theTCA cycle

Question 25

what are the products of glycolysis and the TCA cycle?

Answer 25

• glycolysis: pyruvate and NADH

- TCA cycle: 3 NADH, 1 FADH2, 1 GTP (ATP)

Question 26

what are the 2 shuttles that transfers electrons from NADH into the mitochondria?

Answer 26

1) glycerol-3-phosphate shuttle especially prevalent in brain and muscle
2) malate-aspartate shuttle in liver and heart

*both shuttles act to regenerate NAD+ and make 1.5 or 2.5 moles of ATP