Carbohydrate Metabolism (1)

Flashcards about carbohydrate metabolism, glycolysis, and gluconeogenesis.

What are the major macronutrients in most human diets?

Carbohydrates, making up more than 60% of our foods.

What are the primary monosaccharides absorbed from the jejunum?

Mainly glucose, galactose, and fructose.

What type of passive transport is involved in glucose uptake?

Facilitated transport, which requires a carrier or transporter protein but no energy.

Which glucose transporters are the most significant?

GLUT 1-4.

What is the function of GLUT-1 & 3?

Maintaining a basal constant rate of glucose uptake in most tissues.

What tissues respond to insulin by increasing glucose uptake?

Skeletal muscle, cardiac muscle, and adipose tissue.

What are the four metabolic fates of glucose listed?

Oxidation, Glycogenesis, Lipogenesis, provision of other compounds.

What is Glycolysis?

The oxidation (breakdown) of one molecule of glucose (6C) into two molecules of pyruvate (3C) in the presence of oxygen, or two molecules of lactate (3C) in the absence of oxygen.

Where does Glycolysis occur?

In the cytosol of every cell in our body.

What are the two phases of Glycolysis?

Energy utilization phase (I) and Energy recovery phase (II).

How many ATPs are consumed during the Energy utilization phase of Glycolysis?

2 ATPs.

What does Glycolysis require to produce NADH?

NAD.

What two shuttles are required to transfer the reducing power of NADH to the mitochondria?

Glycerol-3-phosphate shuttle and Malate aspartate shuttle.

What enzyme catalyzes the reoxidation of NADH to NAD under anaerobic conditions?

Lactate dehydrogenase (LDH).

Name the three regulatory KEY enzymes that catalyze the irreversible steps of glycolysis

Hexokinase/Glucokinase, Phosphofructokinase-1 (PFK-1), and Pyruvate Kinase

Which enzyme is the most important regulatory enzyme in glycolysis?

Phosphofructokinase-1 (PFK-1).

What is MODY?

Maturity-onset diabetes of the young. Insufficient amounts of glucose are trapped in the pancreatic beta cells due to only one faulty copy of the glucokinase enzyme, leading to an insufficient increase in insulin secretion

How is glycolysis regulated according to the energy requirements of the cell?

High levels of AMP (activates glycolysis) and high levels of ATP (inhibits glycolysis).

What is the net gain of ATP molecules under anaerobic state?

2 ATP molecules (4 ATP produced – 2 ATP utilized = 2 ATP).

What is the net gain of ATP molecules under aerobic state?

7 ATPs

What is the only source of ATP in erythrocytes ?

Glycolysis is the only source of ATP by substrate level oxidative- phosphorylation (No mitochondria)

How much ATP is produced from complete oxidation of one mole of glucose under aerobic conditions?

32 ATPs.

What is pyruvate converted to under aerobic conditions?

Acetyl CoA, catalyzed by pyruvate dehydrogenase (PDH).

What vitamin derivatives are required by pyruvate dehydrogenase?

TPP, FAD, Lipoate, NAD, and COASH

What does Pyruvate Dehydrogenase Deficiency lead to?

Accumulation of pyruvate which leads to its conversion to lactate, resulting in lactic acidosis.

What condition results from a Pyruvate Kinase Deficiency?

The most common (95%) deficient Enzyme in inherited hemolytic anemia

What enzyme catalyzes the conversion of pyruvate to lactate?

Lactate dehydrogenase enzyme.

What does lactate dehydrogenase allow?

Allows glycolysis to proceed in the absence of oxygen by regenerating sufficient NAD+ for another cycle.

What enzyme catalyzes the conversion of pyruvate to oxaloacetate?

Pyruvate carboxylase.

What enzyme catalyzes the conversion of pyruvate to alanine?

Aminotransferase enzyme.

Define Gluconeogenesis

The formation of glucose from non-carbohydrate substances during fasting.

Which organs primarily carry out gluconeogenesis?

The liver and, to a lesser extent, the kidneys.

What are the gluconeogenic key enzymes substituting the glycolytic key enzymes?

Glucose 6-phosphatase, Fructose 1,6-bisphosphatase, Pyruvate carboxylase, and Phosphoenolpyruvate carboxykinase

Name the gluconeogenic substrates

Lactate, Glycerol, Glucogenic amino acids and Odd chain Fatty acids

Why does even chain fatty acid oxidation never give glucose?

Because pyruvate dehydrogenase reaction is irreversible and active acetate is oxidized by citric acid cycle to CO2.

Which molecules are gluconeogenic substrates?

Pyruvate, oxaloacetate, alanine, and lactate