Energy Metabolism

Question 1

Catabolism

Answer 1

The breakdown of molecules into smaller molecules
- glycolysis
- glycogenolysis
- releases energy
Generates ATP, NADH, requires complex molecules

Question 2

Anabolism

Answer 2

The synthesis of molecules from smaller molecules
- protein synthesis
- gluconeogenesis
- requires energy
Requires ATP, NADH & precursor molecules

Question 3

Delta G key concepts

Answer 3

Reactions with a large neg delta G will be essentially irreversible in a cellular environment due to the large amount of energy needed
Delta G values are additive so reactions can be coupled to enable an otherwise unfavourable reaction to proceed
Neg delta G indicates the reaction will proceed in the forward direction and the product has a lower energy state than reactants

Question 4

3 phases of cellular respiration

Answer 4

Oxidation of fuel molecules to produce Acetyl co-A (glycolysis)
Acetyl co-A is fed into the TCA cycle to produce CO2 with electrons being transferred to carrier molecules (krebs cycle)
Electron carriers pass electrons through the ETC and eventually to O2 where the energy is conserved as ATP (ETC)

Question 5

Glucose and cellular energy

Answer 5

Most tissues can use fatty acids to generate energy required for cellular functions
The brain has an absolute requirement for glucose as source of energy because it has very low glycogen levels.
Red blood cells also depend on glucose because they do not have mitochondria.
Highly energy intensive.

Question 6

Glycemic index

Answer 6

How quickly levels of glucose in the blood change after food.
Regulated by insulting and glucagon.
Free glucose present in plasma is approx 80mg/100ml and approx 20g of free glucose available in the blood. When food is consumed approx 50-100g of free glucose, so glucose is rapidly taken up by tissues, decreases in glucose a production by liver. Therefore spoke in blood glucose is only a small indication of the extra glucose added to the system.

Question 7

Control of glucose in the blood

Answer 7

Cells of small intestine absorb glucose- diet glucose is released from the liver (glycogen)
Insulin promotes glycogen production (liver), promotes use of glucose for energy (muscle), promotes uptake of glucose for lipids (fat cells) and decreases blood glucose levels

Glucagon promotes release of glucose from liver glycogen and increased blood glucose levels.

Question 8

Glucose uptake by red blood cells

Answer 8

Transport via GLUT1 occurs at 50,000 times the U catalysed rate.
There is a conformational change in GLUT 1 upon glucose binding.
The GLUT1 transporter is reversible so it depends on the inside to outside concentration gradient for glucose as to which way it will be pumped. The transporter will function to restore the glucose equilibrium in and outside the cell.

Question 9

NAD/NADP+

Answer 9

Derived from the vitamin niacin found in many foods. Acts as electron carriers- accepts a hydride ion - 2 electrons, 1 proton

Vitamin B3 niacin deficiency results in dermatitis, dementia and diarrhoea

Question 10

FAD /FMN

Answer 10

Derived from the vitamin riboflavin, act as electron carriers (1 or 2 electrons) often found tightly bound to an enzyme

Question 11

Glycolysis

Answer 11

Breakdown of glucose into pyruvate and H2O to produce energy and reducing equivalents (NADH)
Glucose + 2NAD+ 2 ADP + 2Pi –> 2NADH + 2H + 2H2O + 2 pyruvate
Can be divided into two phases:
- preparatory phase (requires energy) - 6C to 2x 3C and uses 2ATP, steps 1-5
- pay off phase (releases energy) - pyruvate, produces 4ATP net:2ATP, steps 6-10

Question 12

Fate of pyruvate (aerobic)

Answer 12

• 1X 6C
• 2X 3C (2 pyruvate)
• Produces 2 CO2 and 2 Acetyl CoA (2X2 C) in citric acid cycle
• 4X1 carbon and 4H2O

Question 13

Fate of pyruvate (conversion to lactate)

Answer 13

Low oxygen levels in muscle due to vigorous exercise, ATP levels drop preventing normal energy production via the TCA cycle and oxidative phosphorylation (due to lack of oxygen)

Glucose - 2 pyruvate (anaerobic) - 2 lactate
Fermentation to lactate in vigorously contracting muscle, in erythrocytes, in some other cells and in some microorganisms
In plants becomes ethanol
NAD+ is regenerated

Question 14

Glycolysis summary

Answer 14

10 step reaction pathway
3 essentially irreversible steps which are highly regulated (1, 3 and 10)
2 phases- preparatory (energy input) and payoff (energy output)
Key enzymes are hexokinase, phosphofructokinase, and pyruvate kinase
2 NADH molecules produced in glycolysis (6)
2 ATP molecules produced in glycolysis (7, 10)
Some tissues depend entirely on glycolysis for their brain, erthrocytes

Question 15

Non glucose carbs entering glycolytic pathway

Answer 15

Broken down into monosaccharides and disaccharides and then all into monosaccharides which are directly taken up my cell

Question 16

Fructose intolerance

Answer 16

Caused by a deficiency of F1P aldolase (splitting enzyme)

Patients accumulate F1P in liver: this uses up Pi , can’t make ATP. ATP levels decrease, cannot maintain ion pumps etc. cells swell and lyse, can lead to liver damage.

Question 17

Gluconeogenesis

Answer 17

Glucose synthesis from non-carbohydrate sources (ie. Pyruvate, lactate, glycerol- 3C compounds)

• takes place predominantly in the liver, and glucose produced is passed into the blood stream for delivery to other tissues
• use many of the glycolytic enzymes (but in reverse)
• has 3 bypass reaction
• irreversible steps in glycolysis need to be avoided (large negative standard free energy change)
• gluconeogenesis is a anabolic pathway- requires energy (it is expensive)
• major precursor for glucose is pyruvate

Question 18

Bypass reaction 1

Answer 18

2 enzymes required 
Pyruvate taken up into mitochondria, acted on by enzyme 
Pyruvate formed into PEP 
Make NADH in cytosol 
First regulatory step
- ATP and GTP used to make one super energy rich PEP 
- net loss of one ATP per cycle 
Futile cycle if not controlled

Question 19

Bypass reaction 2

Answer 19

In cytosol

Particular compounds blocked so use alternative pathways

Question 20

Bypass reaction 3

Answer 20

Proteins devoted to removal of glucose and phosphate in the cell