5.7.8: Energy values of different respiratory substrates Flashcards
Besides carbohydrates, which biological molecules can also provide respiratory substrates?
lipids and proteins
Why is the monosaccharide glucose the chief respiratory substrate?
Some mammalian cells, for example brain cells and red blood cells can only use glucose for respiration.
How do animals and some bacteria store carbohydrate?
Animals and some bacteria store carbohydrate as glycogen, which can be hydrolysed to glucose for respiration
How do plant cells store carbohydrate?
Plant cells store carbohydrate as starch, and this can be hydrolysed to glucose for respiration.
-How can disaccharides be used in respiration?
Disaccharides can be digested to monosaccharides for respiration.
-How can monosaccharides such as fructose and galactose be used in respiration?
Monosaccharides such as fructose and galactose can be changed, by isomerase enzymes, to glucose for respiration.
How can lipids be used as respiratory substrates?
Triglycerides are hydrolysed by lipase to glycerol and fatty acids. Glycerol can then be converted to triose phosphate and respired.
Describe fatty acids
- Fatty acids are long-chain hydrocarbons with a carboxylic acid group.
- Hence, in each molecule, there are many carbon and hydrogen atoms and very few oxygen atoms.
Why do fats produce more ATP than an equivalent mass carbohydrate?
-These molecules are a good source of protons for oxidative phosphorylation, and so fats produce more ATP than an equivalent mass carbohydrate.
How do the products of fat digestion enter the Krebs cycle?
Step 1:
- With the aid of some energy from the hydrolysis of one molecule of ATP to AMP, each fatty acid is combined with coenzyme A.
How do the products of fat digestion enter the Krebs cycle?
Step 1: With the aid of some energy from the hydrolysis of one molecule of ATP to AMP, each fatty acid is combined with coenzyme A.
Step 2:
- The fatty acid-CoA complex is transported into the mitochondrial matrix,where it is broken down into two-carbon acetyl groups, each attached to CoA.
How do the products of fat digestion enter the Krebs cycle?
Step 2: The fatty acid-CoA complex is transported into the mitochondrial matrix,where it is broken down into two-carbon acetyl groups, each attached to CoA.
Step 3:
- This beta-oxidation pathway generates reduced NAD and reduced FAD.
How do the products of fat digestion enter the Krebs cycle?
Step 3: This beta-oxidation pathway generates reduced NAD and reduced FAD.
Step 4:
- The acetyl groups are released from CoA and enter the Krebs cycle by combining with the four-carbon oxaloacetate.
For every acetyl group oxidised in the Krebs cycle, how many molecules of NADH, FADH and ATP are made?
- 3xNADH
- 1xFADH
- 1xATP, by substrate level phosphorylation
Where are excess amino acids, released after the digestion of proteins deaminated?
In the liver
What does the deamination of amino acids involve?
The removal of the amino group and its subsequent conversion to urea that is removed via the kidney.
What happens to the rest of the amino acid molecule after deamination?
-The rest of the amino acid molecule, keto acid, enters the respiratory pathway as puryvate, acetyl CoA or a Krebs cycle acid such as oaxaloacetate acid.
What happens during fasting, starvation, prolonged exercise, when insufficient glucose or lipid are available for respiration?
- Protein from muscle can be hydrolysed to amino acids which are then respired.
- These amino acids may be converted to pyruvate or acetate and enter the Krebs cycle.
When is most of the ATP produced during aerobic respiration made?
During oxidative phosphorylation
Why do respiratory substrates with more hydrogen atoms generate more ATP per molecule of substrate?
-The greater the availability of protons for chemiosmosis, the more ATP can be produced.
Therefore, the more hydrogen atoms are in a molecule of respiratory substrate, the more ATP can be generated per molecule of substrate.
Why is more oxygen needed for the respiration of substrates with a high proportion of protons?
-As the protons (hydrogen ions) ultimately combine with oxygen atoms to form water, the greater the proportion of hydrogen atoms in a molecule, the more oxygen will be needed for its respiration.
What is the formula for calculating the respiratory quotient, RQ, for different respiratory substrates?
RQ= CO2 produced/O2 consumed
ratio, so, no units
Respiratory substrate:
Glucose
C6H12O6+6O2–>6CO2+6H2O
calculate RQ
6/6 = 1
Respiratory substrate:
Palmatic acid (fatty acid)
C15H31COOH+23O2–>16CO2+16H2O
calculate RQ
16/23 = 0.7
