Carbohydrate Metabolism

Flashcards covering key vocabulary and concepts from the carbohydrate metabolism lecture notes.

Carbohydrate

A macronutrient made up of carbon, hydrogen, and oxygen, serving as a primary energy source for the body.

Monosaccharides

The simplest form of carbohydrates; single sugar molecules such as glucose and fructose.

Disaccharides

Carbohydrates composed of two monosaccharides joined by a glycosidic bond; examples include sucrose and lactose.

Polysaccharides

Complex carbohydrates consisting of long chains of monosaccharide units; examples include starch, glycogen, and cellulose.

Glycosidic bond

A type of covalent bond that connects monosaccharides to form disaccharides and polysaccharides.

Alpha-amylase

An enzyme that hydrolyzes alpha bonds in carbohydrates, primarily starches.

Glycogen

A highly branched polysaccharide that serves as energy storage in animals, primarily found in the liver and muscle.

Glycemic index (GI)

A measure of how quickly carbohydrates in food raise blood glucose levels compared to reference food.

Insulin

A hormone that facilitates the uptake of glucose into cells, helping to regulate blood sugar levels.

Glut Transporters

Proteins that facilitate the transport of glucose across cell membranes; different types include GLUT1, GLUT2, GLUT4, etc.

Glycolysis

The metabolic pathway that converts glucose into pyruvate, producing ATP and NADH as energy outputs.

Glycogenesis

The process of converting glucose to glycogen for storage in the liver and muscle.

Glycogenolysis

The metabolic process of breaking down glycogen into glucose for energy.

TCA cycle

A series of enzyme-catalyzed chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA.

NADH

A coenzyme that carries electrons during cellular respiration, playing a key role in producing ATP.

Gluconeogenesis

The synthesis of glucose from non-carbohydrate sources, primarily occurring in the liver.

Absorption of Monosaccharides

The process by which monosaccharides are taken up into the cells of the intestine and transported into the bloodstream.

SGLT1

Sodium-glucose cotransporter 1, responsible for the active transport of glucose and galactose into intestinal cells.

Fructose

A monosaccharide that is absorbed differently than glucose, primarily via GLUT5 transport.

Allosteric regulation

The regulation of an enzyme's activity through the binding of molecules at sites other than the active site.

Covalent regulation

The regulation of enzyme activity through the addition or removal of chemical groups, such as phosphate.

Carbohydrate

A macronutrient made up of carbon, hydrogen, and oxygen, serving as a primary energy source for the body.

Monosaccharides

The simplest form of carbohydrates; single sugar molecules such as glucose and fructose.

Disaccharides

Carbohydrates composed of two monosaccharides joined by a glycosidic bond; examples include sucrose and lactose.

Polysaccharides

Complex carbohydrates consisting of long chains of monosaccharide units; examples include starch, glycogen, and cellulose.

Glycosidic bond

A type of covalent bond that connects monosaccharides to form disaccharides and polysaccharides.

Alpha-amylase

An enzyme that hydrolyzes alpha bonds in carbohydrates, primarily starches, active in the mouth (salivary) and small intestine (pancreatic).

Glycogen

A highly branched polysaccharide that serves as energy storage in animals, primarily found in the liver and muscle.

Glycemic index (GI)

A measure of how quickly carbohydrates in food raise blood glucose levels compared to a reference food.

Insulin

A hormone released during high blood glucose that facilitates the uptake of glucose into cells and promotes glucose storage, helping to regulate blood sugar levels.

Glut Transporters

Proteins that facilitate the transport of glucose across cell membranes, enabling cells to take up glucose for energy or storage.

Glycolysis

The metabolic pathway that converts glucose into pyruvate, producing ATP and NADH as energy outputs, occurring in the cytosol during fed states or energy demand.

Glycogenesis

The process of converting glucose to glycogen for storage in the liver and muscle, primarily occurring during the fed state.

Glycogenolysis

The metabolic process of breaking down glycogen into glucose for energy, occurring in the liver and muscle during fasting states or high energy demand.

TCA cycle (Krebs Cycle)

A series of enzyme-catalyzed chemical reactions occurring in the mitochondrial matrix, used by aerobic organisms to generate energy through the oxidation of acetyl-CoA, producing CO\text{2}, ATP/GTP, NADH, and FADH\text{2}.

NADH

A coenzyme that carries electrons during cellular respiration, playing a key role in producing ATP through oxidative phosphorylation.

Gluconeogenesis

The synthesis of glucose from non-carbohydrate sources (e.g., lactate, amino acids, glycerol), primarily occurring in the liver during the fasting state.

Absorption of Monosaccharides

The process by which monosaccharides are taken up into the cells of the intestine and transported into the bloodstream, involving active and facilitated transport mechanisms.

SGLT1

Sodium-glucose cotransporter 1, responsible for the active transport of glucose and galactose into intestinal cells against a concentration gradient.

Fructose

A monosaccharide that is absorbed primarily via GLUT5 transport, differing from glucose and galactose absorption.

Allosteric regulation

The regulation of an enzyme's activity through the binding of molecules at sites other than the active site, providing rapid responses to metabolic changes.

Covalent regulation

The regulation of enzyme activity through the addition or removal of chemical groups, such as phosphate, often mediated by hormones.

Beginning of Carbohydrate Digestion

The digestion of carbohydrates begins in the mouth with the action of salivary alpha-amylase.

Completion of Carbohydrate Digestion

Carbohydrate digestion is completed in the small intestine by pancreatic alpha-amylase and brush border enzymes (e.g., lactase, sucrase, maltase).

End Products of Carbohydrate Digestion

The final products of carbohydrate digestion are monosaccharides: glucose, fructose, and galactose.

Main Pathways for ATP Formation

ATP is primarily formed during cellular respiration through glycolysis, the TCA cycle, and oxidative phosphorylation.

Role of ATP

ATP serves as the primary energy currency for various essential cellular processes, including muscle contraction, active transport, and the synthesis of macromolecules.

Importance of Dehydrogenases

Dehydrogenases are important in biological oxidation because they catalyze the removal of hydrogen atoms and electrons from substrates, transferring them to coenzymes (NAD\text{+}{} , FAD) for ATP synthesis.

Starch

A complex polysaccharide used as the primary energy storage form in plants.

Cellulose

A complex polysaccharide forming the structural component of plant cell walls, largely indigestible by humans.

Monosaccharide Configurations

Monosaccharides can exist in configurations such as D- and L-forms, alpha and beta anomers (upon cyclization), and cyclic pyranose or furanose rings.

Stereospecificity of Digestive Enzymes

Digestive enzymes exhibit stereospecificity, meaning they specifically recognize and act upon the three-dimensional structure of natural D-sugars and particular glycosidic bond configurations.

GLUT1 Transporter

A glucose transporter responsible for basal glucose uptake, found in red blood cells, brain, and fetal tissues.

GLUT2 Transporter

A high-capacity, low-affinity glucose transporter found in the liver, pancreatic beta cells, kidney, and intestine, involved in glucose flux out of cells.

GLUT3 Transporter

A high-affinity glucose transporter primarily expressed in neurons for glucose uptake.

GLUT4 Transporter

An insulin-sensitive glucose transporter found in muscle and adipose tissue, increasing glucose uptake into these cells in response to insulin.

Glucagon

A hormone released during low blood glucose (fasting state) that stimulates glycogenolysis and gluconeogenesis in the liver to raise blood glucose levels.

Glycemic Load (GL)

A measure that quantifies the impact of carbohydrate quality (GI) and quantity in a standard food serving on blood glucose levels.

Hormonal Control of Carbohydrate Metabolism

Regulation of carbohydrate metabolism by hormones like insulin (promotes storage, fed state) and glucagon (promotes glucose production, fasting state) to maintain blood glucose homeostasis.

Directional Shifts in Metabolism

Regulatory mechanisms that ensure metabolic pathways proceed in a specific direction, often through irreversible steps catalyzed by key enzymes, preventing futile cycles.