Energy reaction in cells

Question 1

Define Metabolism

Answer 1

Metabolism is the set of processes which derive energy and raw materials from food stuffs and use them to support repair, growth and activity of the tissues of the body to sustain life

Question 2

Where do reactions in metabolic pathways occur

Answer 2

– Some metabolic pathways occur in all cells
– Others are restricted to some cell types
– Some may be further restricted to compartments within cells

Question 3

What are the different points in the metabolic pathway

Answer 3

– Start points
– Intermediates (metabolites)
– End points
– Interconnections

Question 4

What are the two types of the metabolic pathway, and what do each do?

Answer 4

• Catabolic pathways
  – Break down larger molecules into smaller ones
  (intermediary metabolites)
  – Release large amounts of free energy
  – Oxidative – release H atoms – ‘ reducing power’ - that generates ATP
• Anabolic pathways
  – Synthesise larger important cellular components
  from intermediary metabolites
  – Use energy released from catabolism (ATP)
  – Reductive (i.e. use H released in catabolism)

Question 5

What is Isothermal

Answer 5

Humans are isothermal - can not use heat energy for work

Question 6

What are all cellular activities an expression of

Answer 6

All cellular activities are expressions of chemical reactions in which chemical bonds are broken or formed

Question 7

What is Exergonic and Endergonic difference

Answer 7

• Exergonic - release energy
• Endergonic - require energy

Question 8

Exergonic Reaction

Answer 8

Exergonic reaction:
* ∆G < 0
* Energy released

Question 9

Endergonic Reaction

Answer 9

Endergonic reaction:
* ∆G > 0
* Requires energy input

Question 10

In a metabolic pathway is the ∆G negative or positive

Answer 10

the ∆G must be negative overall

Question 11

How is energy released from chemical bond

Answer 11

Chemical bond energy of fuel molecules is released by oxidation reactions

Question 12

What is Oxidation

Answer 12

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

Question 13

What is redox

Answer 13

All oxidation reactions accompanied by a reduction
reaction, known as REDOX REACTIONS

Question 14

What happens to the electrons and protons when fuel molecule is oxidised

Answer 14

When fuel molecules are oxidised, electrons and protons are transferred to carrier molecules

Question 15

What are the MAJOR carrier molecules

Answer 15

Major carrier molecules / Oxidised form. / Reduced form
Nicotinamide adenine dinucleotide. / NAD+ / NADH + H+/
Nicotinamide adenine dinucleotide phosphate / NADP+ / NADPH + H+ /
Flavin adenine dinucleotide. / FAD. / FADH2. /

Question 16

What is the conc of ‘oxidised and reduced’ carriers

Answer 16

Total concentration of ‘oxidised and reduced’ carriers is constant - cycle between oxidative and reductive processes.

Question 17

What is the ∆G for
ATP + H2O –> ADP + Pi
ADP + H2O –> AMP + Pi

Answer 17

∆Go’ = -31 kJ.mole-1
∆Go’ = -31 kJ.mole-1

(energy stored within the phosphate bond)

Question 18

What is the ∆G for
ADP + Pi –> ATP + H2O

Answer 18

∆Go’ = +31 kJ.mole-1

Question 19

what is Energy released in exergonic reactions used to drive

Answer 19

ADP + Pi ——–> ATP

Question 20

How is energy flow controlled

Answer 20

ATP is stable in the absence of specific catalysts
Enables flow of energy to be controlled

Question 21

Facts about ATP turnover

Answer 21

• At any moment in time, the human body contains ~250 g ATP
• ATP energy currency is constantly turning over
• Turnover body weight in ATP each day

Question 22

What is the high energy signals

Answer 22

High energy signals
Activate anabolic pathways
ATP NADH NADPH FADH2

Question 23

What is the low energy signals

Answer 23

Low energy signals
Activate catabolic pathways
ADP, AMP NAD+ NADP+ FAD

Question 24

What is Adenylate Kinase (myokinase)

Answer 24

Enzyme that converts
2ADP —> ATP + AMP

Switched on when ATP levels are dropping

Question 25

What does a boost in AMP trigger

Answer 25

AMP increases ATP generation by glycolysis

Question 26

What does AMP and ADP activate

Answer 26

AMP (and ADP) is also an important activator of
AMP dependent kinase
that regulates gene expression switching from anabolic to catabolic pathways

(anabolic - switches of with elevated AMP)
(catabolic - switched on with elevated AMP levels)

Question 27

What happens when puppy of energy exceeds demand

Answer 27

When supply exceeds demand, energy is most often stored in the form of polymer macromolecules of fuel molecules, e.g. glycogen, triglyceride

Question 28

What is creatine phosphate used for

Answer 28

Creatine + ATP <——> Creatine Phosphate + ADP

Uses Creatine Kinase Enzyme

• When ATP concentrations ([ATP]) are high, creatine phosphate is formed
• If ATP concentration falls suddenly, the reaction reverses providing short term boost to [ATP]

Question 29

What is Creatine Kinase (CK)
What is it used for

Answer 29

Creatine Kinase (CK) - a marker of muscle damage

• Creatine kinase is made up of two subunits – M and B – and because it is a cytosolic enzyme will appear in blood soon after cell damage.
• 3 Different isoform combinations are possible – MM, BB and MB.
• CK-MB used to be used as a marker for cardiac muscle damage (e.g. myocardial infarction – but it is not very specific and has been superseded by cardiac specific troponin tests)
• CK activity is still a sensitive serum marker for any condition that causes myocyte damage and is used routinely for patients with suspected muscle injury or unexplained muscle weakness (myopathy).

Question 30

What is Creatinine

Answer 30

Creatinine is a Breakdown product of creatine (and creatine phosphate)

• Produced by a spontaneous reaction at a constant rate
  – unless muscle is wasting

Question 31

What is creatinine used for clinically

Answer 31

• Excreted via kidneys
• Used to assess kidney function
• Creatinine excretion per 24h is proportional to muscle mass of the individual
  – Provides a measure of muscle mass
• Creatinine concentration in urine is a marker of urine dilution
• Can be used to estimate true urinary loss of many substances – E.g. hormones in pregnancy