4 - Energy Reactions in Cells

Question 1

What happens to nutrients in food when they enter the GI tract (overview - no specific details)?

Answer 1

Absorbed into the bloodstream and then absorbed into the tissues. Can be utilised to produce energy or other molecules, interconverted or stored.

Question 2

What are the two main types of metabolic pathway?

Answer 2

Catabolic and anabolic pathways

Question 3

What is a catabolic pathway?

Answer 3

• Breaks down large molecules into smaller ones
• Releases large amounts of energy
• Oxidative - releases H+ (reducing power)

Question 4

What is an anabolic pathway?

Answer 4

• Synthesis of larger cellular components
• Uses energy from catabolism (ATP)
• Reductive (uses H+ released from catabolism)

Question 5

What are the products of catabolic metabolism?

Answer 5

• Building block materials (sugars, amino acids and fatty acids) used in turnover, growth and repair
• Organic precursors (Acetyl CoA) for interconversion
• Biosynthetic reducing power (NADH, NADPH)
• Energy for cell function (ATP)

Question 6

Energy is the capacity to do work. What forms of work does the cell have to do?

Answer 6

• biosynthetic work (synthesis of components)
• transport work (ion gradients and nutrient uptake)

Specialised functions:

• mechanical work (muscle contraction)
• electrical work (nerve impulses)
• osmotic work (kidney)

Question 7

Which nutrient group has the highest energy content per gram?

• carbohydrates
• fat
• protein

Answer 7

Fat has the highest (37 kJ/g or 9 kcal/g)

Carbs (17 kJ/g or 4 kcal/g)
Protein (16 kJ/g or 4 kcal/g)

Question 8

What factors make up the energy requirement of the body?

What is the daily energy requirement of the body in the average person?

Answer 8

• Basal metabolic rate (energy required at rest)
• Activity (muscular work - skeletal and heart)
• Specific dynamic action of food (energy cost of ingestion, digestion and absorption)

2000 - 2500 kcal per day

Question 9

Why can humans not use heat energy to do work?

Answer 9

Humans are isothermal - the body temperature is constant and cannot be used in metabolism

Question 10

What are the two types of energy change in chemical reactions?

Answer 10

• Exergonic (release of energy)

- Endergonic (require energy)

Question 11

What is an exergonic reaction?

Answer 11

• A reaction that releases energy
• Occur spontaneously as they don’t require energy
• Change in Gibbs free energy (ΔG) is negative (energy released)

Question 12

What is an endergonic reaction?

Answer 12

• A reaction that requires energy
• Not spontaneous as they need energy input
• Change in Gibbs free energy (ΔG) is positive (energy required)

Question 13

Why can standard free energy change (ΔG) not be used for cells?

Answer 13

Standard free energy is measured at 25oC, 1atm pressure and 1M concentration of reactants and products.

This is not relevant to cells (37oC, mM concentrations at highest, pH7).

Question 14

What is a redox reaction?

Answer 14

Chemical bond energy is released by oxidation reactions. All oxidation reactions are coupled with reduction reactions (REDOX REACTIONS).

Question 15

What happens to electrons in oxidation and reduction?

Answer 15

Oxidation involves removal of electrons (or H+ + e-)

Reduction involves gain of electrons (or H+ + e-)

Question 16

When fuels are oxidised, electrons and proton are transferred to H-carrier molecules (which are reduced). Name the 3 major carrier molecules.

Answer 16

Nicotinamide adenine dinucleotide (NAD+)
Nicotinamide adenine dinucleotide phosphate (NADP+)
Flavin adenine dinucleotide (FAD)

Question 17

What are the reduced forms of the 3 major H-carrier molecules?

Answer 17

NAD+ –> NADH + H+
NAPH+ –> NADPH + H+
FAD –> FADH2

Question 18

The total concentration of oxidised and reduced carriers is …………..

Answer 18

Constant

Question 19

The nicotinamide group of NAD+ and NADP+ is produced from which essential vitamin?

Answer 19

Niacin (vitamin B3 derivative)

Question 20

FAD+ contains which vitamin?

Answer 20

Riboflavin (B2)

Question 21

How do reduced carriers drive energy-requiring activities?

Answer 21

• Driectly - e.g. use of NADPH in biosynthesis

- Indirectly - e.g. NADH coupled to production of ATP in the electron transport chain

Question 22

In ATP, removal of each phosphate group incurs what ΔG?

Answer 22

-31 kJ/mol

Negative ΔG = energy released

Question 23

ATP is an energy carrier, why can ATP not store energy long-term?

Answer 23

There is a limited concentration of ADP for formation of ATP. Only enough for a few seconds. So ADP ATP must cycle rapidly.

Only a carrier, not a store!

Question 24

What are high energy signals in cells? What metabolic pathway type do they activate?

Answer 24

ATP, NADH, NADPH, FADH2

Activate anabolic pathways to use energy

Question 25

What are low energy signals in cells? What metabolic pathway type do they activate?

Answer 25

ADP, AMP, NAD+, NADP+, FAD+

Activate catabolic pathways to release energy

Question 26

When supply of energy exceeds demand, energy is stored in polymer macromolecules of the fuels. Give two examples of these polymers.

Answer 26

Glycogen

Triglycerides

Question 27

Skeletal muscle needs to increase activity quickly, so needs a high energy reserve. What molecule is used for this?

Answer 27

Creatine phosphate (phosphocreatine)

Question 28

What enzyme catalyses the formation of phosphocreatine from creatine? Where does the added phosphate come from?

Answer 28

Creatine kinase

ATP

Question 29

Phosphocreatine is formed when [ATP] is ……….., if [ATP] ……………… suddenly the reaction reverses

Answer 29

High, decreases

Question 30

Creatine kinase is a marker for ………. …………

What isoform of CK is found in heart muscle?

Answer 30

Myocardial infarction (appears in blood after a few hours)

CK-MB (other isoform is CK-MM)

Question 31

Spontaneous breakdown of creatine and phosphocreatine forms ……………., which is excreted via the …………

It is a useful clinical marker or ………. ……. and ……… ……….

Answer 31

Creatinine, kidneys

Muscle mass (excretion of creatinine is proportional) and urine dilution