Bioenergetics

Question 1

What is energy? Define calorie. What is a juole?

Answer 1

Definitions:
• Energy is the ability to do work – measured in
calories or joules (1cal = 4.184J)

• A calorie is the energy required to heat 1g of water by 1oC.
• A joule is the energy required to move a weight of 1N a distance of 1m

Question 2

Explain the first law of thermodynamics

Answer 2

First Law of Thermodynamics: Energy can neither be created or destroyed, only changed from one form to another

• Chemical reactions obey this law by releasing energy as heat (H) • The heat change is represented by DH and described as Enthalpy
In an open system (not in a cell)

• Reactions with a negative value of H, release heat to the surroundings
• EXOTHERMIC

• Reactions with a positive value of H, remove heat from the surroundings • ENDOTHERMIC

Question 3

Explain the second law of thermodynamics

Answer 3

Second Law of Thermodynamics: All chemical reactions have a tendency to proceed to a state of increased disorder

• Disorder change is represented by DS and described as Entropy

Reactions with a. Negative value of 🔼S are decreased in disirder

Reactions with positive value of 🔼S are increased in disorder

Question 4

What is Gibbs free energy?

Answer 4

The direction and extent to which a reaction occurs is determined by both laws: • Gibbs’ Free Energy (🔼G) = DH – T X 🔼S

• DH is the difference in chemical bond energy between reactants and products • DS is the change in entropy
• T is the temperature at which the reaction is occurring in Kelvins
• (temperature in Kelvins = oC = 273)

Question 5

Wwhat is Gibbs free energy in a cell?

Answer 5

The maximum amount of useful energy to do work that can be obtained from a reaction at constant temperature and pressure.

🔼G= 🔼Go + RTln (B)/(A)
Each biochemical reaction, from reactant to product, has a Standard Free Energy (DGo) which is calculated under standard conditions (described shortly)

Question 6

When does a reaction require energy?

Answer 6

Reaction is exergonic and proceeds spontaneously-🔼G is negative

Reaction is endergonic and does not proceed spontaneously- 🔼G is positive

Question 7

What happens when 🔼G is megative. Or positive ?

Answer 7

DG = negative, product has lower energy than reactant, reaction is exergonic and occurs spontaneously.

AB (reactants) (products)

DG = positive, product has higher energy than reactant, reaction is endergonic and does not occur spontaneously

🔼G of forward reaction = 🔼G of reverse reaction but opposite in sign

🔼G= 0, reaction is at equilibrium

Question 8

Calculate Standard Free Energy of a biochemical reaction

Answer 8

The Beginning of the reaction:
Reactants and Products are each at a concentration of 1M

At this tome [1]/[1]=0

Standard Free Energy (DGo) is the free energy change (DG) under standard reaction conditions
DGo’ is the standard free energy change at pH 7, when starting from Standard Conditions biology standard free energy changes are given as DGo’ values.

Question 9

What happebs to the reaction at equilibrium?

Answer 9

At equilibrium, the energy of the forward reaction is the same magnitude of the reverse reaction. Though in opposite directions (mathematically, one value will be positive and the other negative)

Each unique reactant/product pair has a specific ΔGo’ for us to use in biochemical calculations

Question 10

What are Keq and 🔼Go for a forward durection?

Answer 10

Keq>1

🔼Go= negative #

Question 11

When is the reverse reaction settings of Keq and 🔼Go?

Answer 11

Keq<1

🔼Go= possitive#

Question 12

What are Keq and 🔼Go at equilibrium?

Answer 12

Keq=1

🔼Go=0

Question 13

How us an unfavorable reaction made favorable?

Answer 13

1. Cellular concentrations of substrate and product can overcome a positive 🔼G
2. Thermodynamic coupling

Question 14

What shoukd be noted about 🔼Go?

Answer 14

DGo’ values for biochemical reactions in a pathway are also additive!

Question 15

What is the currency of energy?

Answer 15

The Free Energy released - is converted into chemical energy Adenosine triphosphate (ATP)

ATP is the universal energy currency of biological systems

Question 16

Explain the impact of ATP

Answer 16

ATP is classed as a high energy compound due to containing two phosphanhydride bonds between the g/b phosphate groups and b/a phosphate groups.

High energy phosphate bonds due to the large electrostatic repulsive forces.

Hydrolysis of ATP to ADP releases a large amount of energy, DGo’ = -30.5 kJ/mol

Hydrolysis of ADP to form AMP has DGo’ = -32 kJ/mol Hydrolysis of AMP to form
Adenosine has DGo’ = -14 kJ/mol

Question 17

Explain the impact of ATP hydrolysis

Answer 17

At each hydrolysis step inorganic phosphate is release, which is stable due the process electron resonance.

ATP hydrolysis provides the energy required to allow the body to perform reactions that would otherwise be thermodynamically unfavorable:

Glucose + ATP— > Glucose-6-phosphate + ADP
🔼Go’= -17.9 kJ/mol

In reality the energy released from ATP hydrolysis as heat cannot be directly transferred into energy requiring reactions.

Cellular enzymes directly transfer the phosphate group from ATP onto a reactant to produce a metabolic intermediate:
Phosphate Group Transfer

Question 18

What stimulates energy oroduction and usage of ADP + Pi?

Answer 18

Respiration

Carbohydrates

Lipid

protein

Question 19

What stimulates energy utilisation ?

Answer 19

Biosynthesis

Muscle contraction

Active transport

Thermogenesis

Question 20

What is energy state and charge?

Answer 20

Cells with a high ATP/low ADP concentrations are said to be in a high energy state
and have a high capacity for work.

Cells with a low ATP/high ADP concentration are said to be in a low energy state
and have a low capacity for work.

Cells maintain an energy charge of 0.8-0.9

Adenylate kinase: phosphotransferase enzyme, catalyzes the interconversion of adenine nucleotides (ATP, ADP, and AMP).

Adenylate kinase plays an important role in cellular energy homeostasis

Question 21

Whwt are high energy compounds?

Answer 21

Compounds whose hydrolysis reactions have a negative DGo’ and lead to the release of a significant amount of free energy.
Are mainly phosphate and thioesters compounds.

High in order:
PEP

Phosphocreatine

1,3-b8sphosphoglycerate

Succinyl CoA

Pyrophosphate (PPi)

Acetyl Coenzyme A

Low energy compounds

Glucose-1-P

Fructose-6-P

Glucose-6-P

Question 22

What is group trabsfer potential?

Answer 22

DGo’ of hydrolysis can also be termed the Group-transfer potential

Compounds with higher DGo’ of hydrolysis than ATP can be used to form ATP
ATP can supply the free energy to form compounds with lower DGo’ of hydrolysis

Question 23

What is Succinyl CoA?

Answer 23

Thioester compound formed by linking the reactant of interest to Co-enzyme A

High energy intermediate to drive anabolic reactions and the generation of ATP or other triphosphate nucleotides. Also used in the transfer of acyl groups e.g. lipid oxidation and the TCA cycle.

Question 24

How is Succinyl CoA forned?

Answer 24

Succinyl-CoA formed from a-ketoglutarate and the energy release from the conversion of succinyl-CoA to succinate is used in a substrate phosphorylation producing GTP.

Drives TCA cycle in the forward direction

Question 25

What is Acetyl CoA?

Answer 25

Acetyl CoA plays a central role in metabolism.

DGo’ for Acetyl CoA hydrolysis is -31.3 kJ/mol – provides energy to drive TCA cycle in a forward direction

Question 26

What is the metabolic role of NADPH?

Answer 26

The metabolism of energy–rich molecules like glucose results in the release of electrons which are accepted by various co-enzymes e.g. NAD+

Transfer of electrons to NAD+ generates NADH and a proton, H+.

Electrons are passed from NADH to O2 in the process of oxidative phosphorylation leading to generation of ATP.

May also be used in oxidation reactions of alcohols and aldehydes.

Question 27

How does NADP+ differ from NAD+?

Answer 27

NADP+ differs from NAD+ by the presence of a phosphate group.

Transfer of electrons to NADP+ generates NADPH

Question 28

When is NADPH produced?

Answer 28

NADPH is generated by the Pentose Phosphate pathway not the TCA cycle.

NADPH is not used for ATP generation but to provide electrons for biosynthetic and detoxification pathways.