Concept 9.6: Glycolysis and the citric acid cycle connect to many other metabolic pathways Flashcards
We obtain most of our calories in the form of fats, proteins, and carbohydrates such as .
sucrose and other disaccharides, and starch, a polysaccharide
Glycolysis can accept a wide range of carbohydrates for
catabolism.
In the digestive tract, starch is hydrolyzed to glucose, which can then be broken down in the cells by
glycolysis and the citric acid cycle
The digestion of disaccharides, including
sucrose, provides glucose and other monosaccharides as fuel for respiration.
Many of the amino acids are used by the organism to build
new proteins.
Amino acids present in excess are converted by enzymes to intermediates of
glycolysis and the citric acid cycle
Before amino acids can feed into glycolysis or the citric acid cycle, their amino groups must be removed, a process called
deamination.
The nitrogenous waste is excreted from the animal in the form of
ammonia (NH3), urea, or other waste products.
can also harvest energy stored in fats obtained either from food or from fat cells in the body.
Catabolism
After fats are digested to glycerol and fatty acids, the glycerol is converted to
glyceraldehyde 3-phosphate, an intermediate of glycolysis.
breaks the fatty acids down to two-carbon fragments, which enter the citric acid cycle as acetyl CoA.
beta oxidation
NADH and FADH2 are also generated during beta oxidation; they can enter the electron transport chain, leading to further
ATP production.
Not all the organic molecules of food are destined to be oxidized as fuel to make
ATP.
Compounds formed as intermediates of glycolysis and the citric acid cycle can be diverted into anabolic pathways as precursors from which the cell can synthesize the
molecules it requires.
humans can make about half of the 20amino acids in proteins by modifying compounds siphoned away from the citric acid cycle; the rest are .
“essential amino acids” that must be obtained in the diet
these anabolic, or biosynthetic, pathways do not generate ATP, but instead
consume it.
Basic principles of supply and demand regulate the
metabolic economy.
If there is a surplus of a certain amino acid, for example, the anabolic pathway that synthesizes that amino acid from an intermediate of the citric acid cycle is
switched off.
The most common mechanism for this control is feedback inhibition:
The end product of the anabolic pathway inhibits the enzyme that catalyzes an early step of the pathway
The cell also controls its
catabolism
f the cell is working hard and its ATP concentration begins to drop, respiration
speeds up.
When there is plenty of ATP to meet demand, respiration
slows down
Phosphofructokinase is an allosteric enzyme with receptor sites for specific
inhibitors and activators
It is inhibited by
ATP and stimulated by AMP (adenosine monophosphate)
