Chapter 22: Carbohydrate Metabolism

Glycogenolysis

________ is the biochemical pathway for breakdown of glycogen to free glucose.

Protein

________ is also broken down into amino acids that can be used to generate energy.

→Glycolysis

________ is the first of two sequential, catabolic pathways leading to ATP synthesis as a result of electron transfer.

Cori cycle converts

The ________ lactate into pyruvate, the substrate for gluconeogenesis, a pathway that makes glucose from non- carbohydrate molecules (lactate, amino acids, and glycerol) beginning with pyruvate.

aerobic oxidation

For ________ to proceed, pyruvate first moves across the outer mitochondrial membrane from the cytosol where it was produced.

Nutrients

________ are absorbed through millions of tiny projections (the villi) in the intestinal lining and transferred into the bloodstream.

amino acids

The pyruvate necessary for gluconeogenesis may come not only from glycolysis but also from ________ or glycerol from lipids.

muscle cells

In ________, glucose 1- phosphate immediately enters glycolysis at step 2.

ATP

Through a series of metabolic oxidations, the energy stored in glucose is converted to ________ energy and used to power other reactions within the cell.

UTP

________ is a high energy compound similar to ATP.

Lactate

________ is oxidized to pyruvate by another pathway when oxygen is available.

Cori cycle

The ________ is essentially a recycling pathway.

sufficient oxygen

When ________ again becomes available, lactate is recycled back to pyruvate in muscle cells or to glucose via the Cori cycle in liver cells.

Hyperglycemia

________ occurs when there is higher than normal blood glucose concentration.

Hypoglycemia

________ occurs when there is lower than normal blood glucose concentration.

Glycogenesis

________ is the biochemical pathway for synthesis of glycogen, a branched polymer of glucose.

Glycolysis

________ is a series of 10 enzyme- catalysed reactions that converts a glucose molecule into two pyruvate molecules and in the process yields two ATP molecules and two NADH molecules.

Digestion

________ entails the physical grinding, softening, and mixing of food, as well as enzyme- catalysed hydrolysis of carbohydrates, proteins, and fats.

Epinephrine

________ accelerates the breakdown of glycogen, but primarily in muscle tissue, where glucose is used to generate energy needed for quick action.

ADP

The production of ATP by transfer of a phosphate group to ________ from another molecule is called substrate- level phosphorylation.

→Yeast

________ is an organism with a different pathway for pyruvate; it converts pyruvate to ethanol under anaerobic conditions.

UDP

________ serves as a carrier for glucose.

conversion of glucose

The ________ to pyruvate is a central metabolic pathway in most living systems.

bloodstream moves

The ________ lactate from muscle cells to liver cells; it is oxidized to pyruvate by lactate dehydrogenase.

→When cells

________ are well supplied with glucose, excess glucose is converted to other forms for storage: into glycogen, the glucose storage polymer, by the glycogenesis pathway, or into fatty acids by entrance of acetyl- CoA into the pathways of lipid metabolism rather than the citric acid cycle.

stable blood glucose concentration

A(n) ________ is vital for proper functioning of the body.

Fats

________ are our largest energy reserve, but adjusting to dependence on ________ for energy takes several days because there is no direct pathway for generating glucose from the fatty acids in ________.

Pyruvate

________ is the substrate for an 11- step series of reactions in the gluconeogenesis pathway; the final product is glucose, which is exported to tissues dependent on glucose but lack the gluconeogenesis pathway.

absence of oxygen

Microorganisms often must survive in the ________ and thus have evolved numerous anaerobic strategies for energy production, generally known as fermentation.

→Acetyl CoA delivers

________ acetyl groups to the citric acid cycle for oxidation, with the energy captured transferred through the electron transport system, resulting ultimately in the formation of ATP.

Dehydration Enolase

STEP 9: ________ catalyses the dehydration of 2- phosphoglycerate to phosphoenolpyruvate, the second energy- providing phosphate of glycolysis.

Cleavage Aldolase

STEP 4: ________ catalyses cleavage of the bond between carbons 3 and 4 in fructose 1, 6- bisphosphate.

products of digestion

The ________ are mostly small molecules that are absorbed from the intestinal tract.

aerobic conditions

Under ________, NADH is continually re- oxidized to NAD+ during electron transport under anaerobic conditions, electron transport slows and so does the production of NAD+.

Glucose

________ is the preferred energy source for brain and blood cells and must be supplied.

Digestion

________ is the the breakdown of food into small molecules.

muscle cells

In ________, this occurs when there is an immediate need for energy, while in liver cells, it occurs when blood glucose is low.

Amino acids

________ can enter the citric acid cycle for oxidation to energy or can be used to synthesize glucose in liver cells via the gluconeogenesis pathway.

Lactate

________ is a normal product of glycolysis in red blood cells and in muscle cells during vigorous exercise.

Digestion

________ begins in the mouth, continues in the stomach, and concludes in the small intestine.

→When cells are well supplied with glucose, excess glucose is converted to other forms for storage

into glycogen, the glucose storage polymer, by the glycogenesis pathway, or into fatty acids by entrance of acetyl-CoA into the pathways of lipid metabolism rather than the citric acid cycle

STEP 1

Phosphorylation Glucose is carried in the bloodstream to cells, where it is transported across the cell membrane into the cytosol

STEP 2

Isomerization The enzyme glucose 6-phosphate isomerase converts glucose 6-phosphate (an aldohexose) to fructose 6-phosphate (a ketohexose)

STEP 3

Phosphorylation A second energy investment is made as phosphofructokinase converts fructose 6-phosphate to fructose 1,6-bisphosphate by reaction with ATP in an exergonic reaction

STEP 4

Cleavage Aldolase catalyses cleavage of the bond between carbons 3 and 4 in fructose 1,6-bisphosphate

STEP 5

Isomerization Triose phosphate isomerase catalyses the conversion of dihydroxyacetone phosphate to glyceraldehyde 3-phosphate

STEP 6

Oxidation Glyceraldehyde 3-phosphate from both steps 4 and 5 is oxidized to 1,3-bisphosphoglycerate by glyceraldehyde 3-phosphate dehydrogenase

STEP 7

Phosphorylation Phosphoglycerate kinase transfers a phosphate group from 1,3-bisphosphoglycerate to ADP

STEP 8

Isomerization Phosphoglycerate mutase catalyses the isomerization of 3-phosphoglycerate to 2-phosphoglycerate

STEP 9

Dehydration Enolase catalyses the dehydration of 2-phosphoglycerate to phosphoenolpyruvate, the second energy-providing phosphate of glycolysis

STEP 10

Phosphate Transfer Pyruvate kinase transfers a phosphate group from phosphoenolpyruvate to ADP forming pyruvate and ATP in a highly exergonic, irreversible reaction

Step 1

Phosphoglucomutase isomerizes glucose 6-phosphate to glucose 1-phosphate

Step 2

Pyrophosphorylase attaches glucose 1-phosphate to uridine triphosphate (UTP) producing uridine diphosphate (UDP)-glucose in a reaction driven by the release of inorganic pyrophosphate

Step 3

Glycogen synthase adds UDP-glucose to a glycogen chain, lengthening the chain by one glucose unit and freeing UDP in the process

Step 1

Glycogen phosphorylase simultaneously hydrolyzes a-1, 4 glycosidic bonds and sequentially phosphorylates glucose units

Step 2a

Phosphoglucomutase isomerizes glucose 6-phosphate to glucose 1-phosphate

Step 2b

In liver cells, glucose 6-phosphatase hydrolyzes glucose 6-phosphate to glucose that moves out of the liver to blood stream to raise blood sugar levels

Step 1

In an energetically expensive step, pyruvate carboxylase adds CO2 to pyruvate forming oxaloacetate

Step 2

In a second energetically expensive step, phosphoenolpyruvate carboxylase removes CO2 from oxaloacetate while adding a phosphate group from guanosine triphosphate (GTP) (similar to ATP) producing phosphoenolpyruvate and guanosine diphosphate (GDP)

Steps 3-8

In reversible reactions, the same set of enzymes as found in glycolysis steps 4-9 convert phosphoenolpyruvate to fructose 1,6-bisphosphate via the same intermediates found in glycolysis

Step 9

In a one-way reaction, fructose 1,6-bisphosphatase hydrolyzes fructose 1,6-bisphosphate to fructose 6-phosphate

Step 10

In a one-way reaction, phosphohexose isomerase changes fructose 6-phosphate into glucose 6-phosphate

Step 11

In a one-way reaction, glucose 6-phosphatase hydrolyzes glucose 6-phosphate to glucose