Biochemistry - Carbohydrate Metabolism

Metabolic Pathways

Metabolism of macronutrients namely, carbohydrates, fats, proteins, and nucleic acids

Metabolism

Comprises of catabolism and anabolism

Catabolism

Breakdown

Anabolism

Building up

Carbohydrates

Will be converted to simple sugars mainly in the form of glucose

Proteins

Will be converted into amino acids

Fats

Will be converted to fatty acids and glycerol

Acetyl-CoA

Will proceed to citric acid cycle to produce ATP and carbon dioxide

Glucose-6-phosphate

Glucose will be converted into?

Pyruvate

The end product of glycolytic pathway

Lactate

The end product in anaerobic conditions or in the red blood cells

Liver

Organ that plays a major role in metabolism

Lactate

Will be the end product of glucose metabolism in the erythrocytes

Mitochondrion

The site for gluconeogenesis and TCA cycle

Acetyl-CoA

Pyruvate will go into mitochondria to be converted to?

Beta-oxidation

Occurring in the cytoplane in the mitochondrion then convert into acetyl-CoA and ketone bodies

Mitochondrion

Site for Gluconeogenesis, Beta-oxidation of fatty acids, Ketogenesis, Citric acid cycle

Liver

All the major pathways will take place in the?

Liver

The only organ that is the site for ketogenesis or ketone body formation

Glucokinase

Enzyme that is very special to the liver

Fatty acid

Major source of energy for heart is?

Hormone-sensitive lipase

Enzyme that is very specific to adipose tissue

Fatty acids

Major energy source of resting muscles will be?

Kidneys

Aside from liver, this organ will also contribute to gluconeogenesis (about more than 30%)

Phosphoenolpyruvate carboxykinase

The enzyme for gluconeogenesis

Glucose

During the Fed state, the main substrate that is present in the liver will be?

Glucose and Triacylglycerol

The major product that is being exported in the liver are?

Ketogenesis

The liver is the only organ that is the site for your?

Glucokinase

The specialized enzymes that are present in the liver will be?

Glycolysis and citric acid cycle

In the brain, you have the major pathways such as

Glucose

The main substrate of the brain is glucose as it is an obligate user of?

Amino acids and ketone bodies

In prolonged starvation, your brain will use?

Lactate

The major product exported by the brain is ________ and the end products of neurotransmitter metabolism.

Beta-oxidation and citric acid cycle

The major pathways in the heart are?

Lipoprotein lipase

The specialized few enzymes of the heart will be?

Electron transport chain

This is very active in the heart.

Adipose Tissue

Non-esterified fatty acids or free fatty acids and the glycerol are exported to the liver

Free fatty acids

The major energy source of resting muscles will be the?

Glycolysis

During intense activity or fast acting activity, the major energy source is?

Beta-oxidation

In slow-twitch muscles, ____________ occurs to break down free fatty acids, which are used as a source of energy for resting muscles.

Gluconeogenesis

Notable for the kidneys is

Glucose

The major products exported in kidneys will be

Glycerol kinase

Enzyme present in kidneys but only in minimal amount

Phosphoenolpyruvate carboxykinase

This is also present in the kidneys, which is the main enzyme for gluconeogenesis.

Erythrocytes

Notable pathway is the anaerobic glycolysis.

Embden Meyerhoff Pathway

Glycolysis is also called as?

Glycolysis

A catabolic pathway used by all cells to extract energy from glucose. Glucose is a substrate that undergoes a catabolic pathway.

Anaerobic

In patients with myocardial infarction, glycolysis is?

Glyceraldehyde-3-phosphate dehydrogenase

Under anaerobic conditions, the NADH generated by this enzyme accumulates.

Lactate dehydrogenase

To prevent glycolytic inhibition, _____________________ will convert pyruvate to lactate, regenerating NAD+ for use in glycolysis, specifically as a substrate for the glyceraldehyde-3-phosphate dehydrogenase reaction.

Pyruvate dehydrogenase

Pyruvate then enters the mitochondria, where it is processed by ________________ to form acetyl-CoA.

A. To regenerate reducing equivalents for pyruvate dehydrogenase

NAD+ used in glycolysis must be regenerated in order for glycolysis to continue.

A. To regenerate reducing equivalents for pyruvate dehydrogenase

B.To provide a cofactor for hexokinase

C. To maintain redox balance in the cell

D. Because it is needed to metabolize pyruvate to acetaldehyde

Glucokinase

Enzyme present only into organs: the liver and pancreas

Hexokinase

Enzyme found in muscles and other tissues

Hexokinase

Enzyme for this reaction: Glucose → Glucose-6-phosphate (G6P). First ATP investment step in glycolysis

Phophoglucose Isomerase (Phosphohexose Isomerase)

Enzyme for this reaction: G6P → Fructose-6-phosphate (F6P). Prepares glucose for phosphorylation & division. Also used in gluconeogenesis which converts F6P back to G6P

Phosphofructokinase-1 (PFK-1)

Enzyme for this reaction: F6P → Fructose-1,6-bisphosphate (F1,6BP). Second ATP investment step in glycolysis

Magnesium ion

This reaction: F6P → Fructose-1,6-bisphosphate (F1,6BP) requires this as it is an ATP-dependent reaction.

Phosphofructokinase-1 (PFK-1)

The primary regulatory enzyme of glycolysis.

Aldolase

Enzyme for this reaction: F1,6BP → Glyceraldehyde-3-phosphate (G3P) + Dihydroxyacetone phosphate (DHAP)

Triose phosphate isomerase

Enzyme for this reaction: DHAP → G3P

Glyceraldehyde-3-Phosphate Dehydrogenase

Enzyme for this reaction: G3P → 1,3-Bisphosphoglycerate (1,3-BPG). NAD⁺ → NADH (1 per G3P, so 2 NADH total)

Phosphoglycerate Kinase

Enzyme for this reaction: 1,3-BPG → 3-Phosphoglycerate (3-PG)

Substrate-level phosphorylation

Phosphoglycerate kinase and pyruvate kinase produces 2 ATP per G3P through?

Phosphoglycerate mutase

Enzyme for this reaction: 3PG → 2-Phosphoglycerate (2PG)

Enolase

Enzyme for this reaction: 2PG → Phosphoenolpyruvate (PEP)

Pyruvate Kinase

Enzyme for this reaction: PEP → Pyruvate

Krebs Cycle

In aerobic conditions: Pyruvate enters?

Lactate

In anaerobic conditions: Pyruvate is converted to?

Iodoacetate and fluoride

Very important inhibitors of glycolysis

D. Fructose-1,6-Biphosphate

The immediate product of the reaction catalyzed by phosphofructokinase 1 in glycolysis is:

A. Glucose-6-Phosphate

B. Glucose-1-Phosphate

C. Fructose-6-Phosphate

D. Fructose-1,6-Biphosphate

D. Pyruvate dehydrogenase

Which of the following is not an enzyme of glycolysis

A. Glucokinase

B. Pyruvate Kinase

C. Enolase

D. Pyruvate dehydrogenase

B. Phosphoglycerate mutase

The following are irreversible steps of glycolysis, except which one?

A. Hexokinase/ Glucokinase

B. Phosphoglycerate mutase

C. Phosphofructokinase

D. Pyruvate kinase

False

[TRUE/ FALSE]: ATP is formed by oxidative phosphorylation.

False

[TRUE/ FALSE]: A molecule of pyruvate is formed from the oxidation of one glucose molecule.

False

[TRUE/ FALSE]: Pyruvate kinase is the rate limiting enzyme of glycolysis

True

[TRUE/ FALSE]: Two molecules of ATP are used in the beginning of the pathway.

Glycero-3-Phosphate Shuttle and Malate-Aspartate Shuttle

What are the shuttles that NADH use in aerobic pathways?

Anaerobic Glycolysis

The NADH is therefore oxidized to NAD in the cytosol by reduction of pyruvate to lactate.

B. Lactic acid

The end product of glycolysis in exercising muscle and red blood cells is:

A. Pyruvic acid

B. Lactic acid

C. Acetic acid

D. Acetoacetic acid

Pyruvate

Lactate released from cells that undergo anaerobic glycolysis is taken up by other tissues (primarily the liver, heart, and skeletal muscle) and oxidized back to?

Cori Cycle

The cycling of the lactate and pyruvate substrates is called?

B. Lactic Acid

The end product of glycolysis in exercising muscle and red blood cells is:

A. Pyruvic Acid

B. Lactic Acid

C. Acetic Acid

D. Acetoacetic Acid

A. Lactate is taken up by the liver for synthesis of glucose

What is achieved by the ‘Cori Cycle’ which involves metabolism of lactate?

A. Lactate is taken up by the liver for synthesis of glucose

B. Metabolic alkalosis is prevented by removing lactate from the blood

C. Lactate is removed from the blood as it inhibits glycolysis in the erythrocyte.

D. Lactate is used by the muscle for fuel.

Hepatic Fetor

Ammonia smell on the patients could indicate death

Lactic Acidemia

Lactic acid accumulates in blood to levels that significantly affect the pH (less than 7.2)

Lactic acidosis

Generally results from a greatly increased NADH/NAD+ ratio in tissues. The increased NADH concentration prevents pyruvate oxidation in the TCA cycle and directs pyruvate to lactate

Bisphosphoglycerate shunt

A “side reaction” of the glycolytic pathway in which 1,3-bisphosphoglycerate is converted to 2,3-bisphosphoglycerate (2,3-BPG)

Hexokinase, Phosphofructokinase, Pyruvate Kinase

What are the three irreversible steps in glycolysis?

Contraction

Glycolysis in skeletal muscle provides ATP primarily to power?

Ratio of ATP to AMP

The primary control of muscle glycolysis is the energy charge of the cell

Phosphofructosekinase (PFK)

Most important control site in the mammalian glycolytic pathway. The rate limiting enzyme. The activity of the enzyme increases when the ATP/AMP ratio is lowered.

C. Phosphofructokinase-1

Which of the following is the major regulatory enzyme in glycolysis?

A. Hexokinase

B. Pyruvate Kinase

C. Phosphofructokinase-1

D. PEP Carboxylase

Hexokinase

Catalyzes the first step of glycolysis and is inhibited by its product, glucose-6-phosphate. The inhibition of PFK leads to the inhibition of this

A. Hexokinase

Which of the following glycolytic enzymes is inhibited by its product?

A. Hexokinase

B. Enolase

C. Pyruvate Kinase

D. Mutase

Pyruvate Kinase

Controls the efflux from this pathway. ATP allosterically inhibits PK to slow glycolysis when the energy charge of the cell is high.

Alanine

Also inhibits PK — to signal that building blocks are abundant.

Glucokinase

The enzyme primarily responsible for phosphorylating glucose in the liver

High

Glucokinase phosphorylates glucose only when glucose is abundant because it has a _______ (high/low) Km for glucose.

A. High Km and High Vmax

Which of the following best describes the kinetics of glucokinase?

A. High Km and High Vmax

B. Feedback inhibition by glucose-6-phosphate

C. Low Km and Low Vmax

D. None of the above