Respiratory Substrates Flashcards
0
Q
Explain the difference in relative energy levels in carbohydrates
A
- stores of glycogen in animals and starch in plants can be hydrolysed to glucose
- fructose and galactose (monosaccharides) can also be changed to glucose
- theoretically up to 94 mol ATP per glucose molecule is produced but the actual yield is about 38 mol (40% efficient)
- the remaining energy is released as heat to maintain the optimum body temperature
1
Q
What is a respiratory substrate?
A
It is an organic substance that can be broken down in respiration to release energy
2
Q
Explain the difference in relative energy levels in proteins
A
- Excess amino acids are deaminated, the rest become glycogen or fat which are stored
- respired during prolonged exercise, fasting and starvation
- some converted to pyruvate or acetate and is carried to the Krebs cycle
- some enters the Krebs cycle directly
- the number of hydrogen atoms per mol of protein accepted by NAD is higher than the number accepted by every mol of glucose so more energy is released
3
Q
Explain the difference in relative energy levels in lipids
A
- especially important in muscles
- triglycerides are hydrolysed by lipase to fatty acids and glycerol
- glycerol can be converted to glucose, but fatty acids cannot
- fatty acids are a source of many protons for oxidative phosphorylation (more protons = more ATP)
- in the mitochondrion matrix each fatty acid is broken down to 2-carbon acetyl groups, these then combine with CoA (requires energy from hydrolysis of ATP)
- this forms reduced NAD and reduced FAD
- acetyl groups are released and enter the Krebs cycle where 3 NADH, 1 FADH and 1 ATP are formed for each acetate
- NADH is reoxidised during oxidative phosphorylation producing large amounts of ATP by chemiosmosis
4
Q
What are the mean energy values of the respiratory substrates?
A
- carbohydrates –> 15.8 kJ/g
- lipids –> 39.4 kJ/g
- proteins –> 17.0 kJ/g
5
Q
How do you calculate the respiratory quotient?
A
Vol of CO2 produced (per unit time)
—————————
Vol of O2 produced
- if glucose is used RQ = 1
- if another substance is used RQ is usually less than one
