Figure: Connection of Amino Acids to Glucose Metabolism Pathways: The carbon skeletons of certain amino acids (indicated in boxes) are derived from proteins and
can feed into pyruvate, acetyl CoA, and the citric acid cycle
.
Can amino acids enter TCA cycle directly?
Hence,
all amino acids through transamination/deamination reactions can be converted into intermediates of TCA cycle, directly
or via conversion to pyruvate or acetyl-CoA (Figure 5).
What enters the Kreb cycle?
Pyruvate Oxidation Pyruvate enters the mitochondrion from the cytoplasm. becomes attached to the remaining carbon atoms, creating
acetyl–CoA
, which then enters the Krebs cycle.
What goes into the Krebs cycle and what comes out?
This process is called the Krebs cycle. The Krebs cycle consumes pyruvate and produces three things:
carbon dioxide, a small amount of ATP, and two kinds of reductant molecules called NADH and FADH
.
What amino acids enter the TCA cycle?
These are the so-called “glucogenic” amino acids.
De-aminated alanine, cysteine, glycine, serine, and threonine
are converted to pyruvate and can consequently either enter the citric acid cycle as oxaloacetate (an anaplerotic reaction) or as acetyl-CoA to be disposed of as CO
2
and water.
How do proteins enter the respiratory pathway?
Amino acids which are the precursors of proteins enter the respiratory pathway
via krebs cycle
.
How do proteins fats and sugars enter TCA cycle?
The fatty acids from fats connect with glucose catabolism
through acetyl CoA
. The amino acids from proteins connect with glucose catabolism through pyruvate, acetyl CoA, and components of the citric acid cycle.
How do lipids enter the respiratory pathway?
Fats are usually required as energy source, so
the fat reserves are mobilized, moved out of adipose tissue, and broken down into glycerol and fatty acids in the liver by the process of lipolysis
. This glycerol is thus connecting link between fats and respiratory pathway.
How amino acids enter the cell?
The transport of amino acids into the cytoplasm occurs
via functionally and biochemically distinct amino acid transport systems
that have been defined on the basis of their amino acid selectivities and physico-chemical properties.
Can carbohydrates proteins and fats enter the four metabolic pathways?
This happens because
all of the catabolic pathways for carbohydrates, proteins, and lipids eventually connect into glycolysis and the citric acid cycle pathways
. Metabolic pathways should be thought of as porous; that is, substances enter from other pathways, and intermediates leave for other pathways.
Can protein be converted to carbohydrates?
Dietary protein is used to replace proteins which were previously broken down and used by the body. Extra protein does not get stored. Instead,
excess amino acids get converted to carbohydrate or fat
.
How galactose and fructose enter the glycolytic pathway?
In the liver,
galactose is converted to glucose-6-phosphate
in order to enter the glycolytic pathway. Fructose is converted into glycogen in the liver and then follows the same pathway as glycogen to enter glycolysis.
Where do amino acids enter cellular respiration?
Glycolysis: Sugars, glycerol from fats, and some types of amino acids can enter cellular respiration
during glycolysis
. Pyruvate oxidation: Some types of amino acids can enter as pyruvate.
