General Energy Metabolism in Cells

Question 1

Which tissues breakdown nutrients to release energy?

Answer 1

All tissues

Question 2

Which tissues synthesise cell components?

Answer 2

All tissues except mature erythocytes

Question 3

Which tissues store nutrients?

Answer 3

Liver, adipose tissues and skeletal muscle

Question 4

Which tissues can interconvert nutrients to other nutrients?

Answer 4

Liver, adipose tissue, kidney cortex

Question 5

Which tissues can excrete nutrients?

Answer 5

Liver, kidneys, lungs

Question 6

What four things does cell metabolism of nutrients provide?

Answer 6

1. ATP - for cell function and synthesis of components
2. Building block molecules
3. Organic precursors - that allow interconversion of building block molecules (e.g. acetyl-CoA)
4. Bio-synthetic reducing power - used in the synthesis of cell components (NADPH)

Question 7

Define catabolism

Answer 7

The breakdown of larger molecules into smaller ones - generally oxidative releasing large amounts of free energy (some of which is converted to ATP) and producing intermediary metabolites

Question 8

Define anabolism

Answer 8

The synthesis of larger molecules from smaller intermediary metabolites - usually reductive, requiring ATP from catabolism to drive the synthesis of cell components

Question 9

What does an oxidation reaction involve?

Answer 9

Addition of oxygen or removal of H+&e- or e-

Question 10

What does a reduction reduction involve?

Answer 10

Removal of oxygen or addition of H+&e- or e-

Question 11

Name the three major carrier molecules, in their oxidised (left) and reduced forms (right)

Answer 11

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

Question 12

NAD+,NADP+and FAD+ are complex molecules which contain components which cannot be synthesised in the body and therefore must be obtained from our diet. Name the vitamins which supply these components

Answer 12

NAD+ and NADP+ come from the vitamin niacin

FAD+ comes from the vitamin riboflavin

Question 13

Why must carrier molecules cycle between oxidative and reductive forms if cell function is to be maintained?

Answer 13

The total concentration of carrier molecules (oxidised and reduced) is constant, therefore if e.g. FAD+ is all in its oxidised state, reductive reactions that require FADH2 cannot occur

Question 14

Name the two types of reactions that serve to reoxidise reduced carrier molecules

Answer 14

1. Cell respiration - ETC (NADH&FADH2) which ultimately reduced O2 to H2O and the free E released –> ATP synthesis
2. Substrate reducing reactions - use NADH or FADH2

Question 15

NADPH is not used in the electron transport chain. What reactions require it?

Answer 15

Biosynthetic reactions involving reduction steps e.g. fatty acid and cholesterol synthesis

Question 16

In the cell what reactions can occur spontaneously?

Answer 16

Exergonic reactions

Question 17

What reactions do exergonic reactions facilitate?

Answer 17

They can provide energy to drive endergonic (energy requiring) reactions

Question 18

The energy change in a reaction represents the difference in energy between the products and reactants of a reaction. What is this energy change known as?

Answer 18

Enthalpy change (delta-H)

Question 19

What is the entropy of a reaction (delta-S)?

Answer 19

Entropy is a measure of the disorder of the products relative to the reactants.

Question 20

What does positive delta-S mean?

Answer 20

There is an increase in disorder in the products of a reaction compared to the reactants

Question 21

The energy released by an exergonic reaction (delta-H negative) is not all available for work, why?

Answer 21

Some of the energy may appear in the form of a decrease in entropy.

Question 22

What is the name of the energy that is available for work?

Answer 22

Free energy (Gibbs free energy):
d.G = d.H - T x dS

Question 23

What is noticeable about the free energy (delta-G) of a reaction which is spontaneous?

Answer 23

It’s negative

Question 24

What does a positive delta-G value for a reaction indicate?

Answer 24

The reaction requires an input of free energy to drive the reaction

Question 25

What is the standard free energy change (delta-G^o') of a reaction?

Answer 25

The free energy change (delta-G) of a reaction WHEN measured under standardised conditions: 25oC reactant and product concentrations: 1M pH 7.0

Question 26

Why is the actual free energy change that is seen in a cell different from that of the values of the standard free energy change?

Answer 26

In the conditions of a cell temperature is 37oC not 25oC and the concentration or reactants and products is never 1M

Question 27

Which molecule plays a major role in coupling the free energy release during catabolism of fuel molecules to the energy requiring activities of the cell?

Answer 27

ATP

Question 28

What is Pi?

Answer 28

Inorganic phosphate (mixture of HPO4^(2-) and H2PO4-)

Question 29

What is the chemical equation for the hydrolysis of ATP?

Answer 29

ATP + H2O --> ADP + Pi

Question 30

What is the phosphate bond in ATP known as and why?

Answer 30

"high energy of hydrolysis bond" because relatively large amount of energy are available during the hydrolysis of it

Question 31

Why is ATP a carrier of free energy and NOT a store?

Answer 31

There is limited amount of ATP and ADP in the cell and the concentration of ATP is only sufficient for a few seconds of energy requiring cellular activity. Therefore it must be rapidly resynthesised from ADP using free energy released from the catabolism of fuel molecules

Question 32

What is a high-energy signal?

Answer 32

Molecules that signal that the cell has adequate energy for its immediate needs and tends to activate anabolic pathways. This is an example of negative feedback

Question 33

What is a low-energy signal?

Answer 33

Molecules that signal that the cell has not got adequate energy for its immediate needs and activates catabolic pathways to produce more ATP

Question 34

List some high energy signals

Answer 34

ATP NADH NADPH FADH2

Question 35

List some low energy signals

Answer 35

``` ADP AMP NAD+ FAD NADP+ ```

Question 36

List the two reactions in glycolysis, in which the reactants are phosphorylated compounds with high energy of hydrolysis bonds and therefore are coupled to substrate level phosphorylation

Answer 36

1. Step 10: phosphoenolpyruvates + ADP --> pyruvate + ATP 2. Step 7: 1,3-bisphosphoglycerate + ADP --> 3-phosphoglycerate + ATP

Question 37

Write the chemical equation for the synthesis of the high energy bond in creatine phosphate

Answer 37

creatine + ATP --> creatine phosphate + ADP

Question 38

Write the chemical equation for the synthesis of ATP from creatine phosphate

Answer 38

creatine phoshpate + ADP --> creatine + ATP

Question 39

Which cardiac and skeletal muscle energy store is important in the first few seconds of vigorous muscle activity such as sprinting?

Answer 39

Creatine phosphate

Question 40

Why is the daily excretion of creatinine a useful indicator of skeletal muscle mass?

Answer 40

Creatinine is the product of non-enzymatic chemical changes of creatine and creatine phosphate (which happens at a constant rate). It has no function and is readily excreted via the kidneys in the urine. The rate of production of creatine is proportional to the concentration of creatine in the muscle and is related to skeletal msucle mass. Therefore increased excretion can be indicative of active muscle wasting

Question 41

Other than muscle wasting what can the excretion of creatinine in urine and the concentration in blood be an indicator of?

Answer 41

Kidney function - kidneys are normally very efficient at excreting creatinine, therefore a high creatinine concentration in blood and a low concentration in urine can indicate reduced kidney function