Comprehensive Biochemistry: Metabolic Regulation, Carbohydrates, and Ethanol Metabolism

Vocabulary flashcards covering key metabolic concepts, hormonal regulation, carbohydrate structures and enzymes, glycogen dynamics, pentose phosphate pathway, and ethanol metabolism.

Insulin

The major anabolic hormone of the body secreted by pancreatic beta cells that promotes fuel storage by stimulating glycogen synthesis, fatty acid synthesis, and amino acid uptake into tissues.

Glucagon

A $29$ -amino-acid peptide hormone secreted by pancreatic alpha cells that acts as a signal for fuel mobilization, promoting gluconeogenesis, glycogen degradation, and fatty acid release.

Normal Blood Glucose Range

The physiologically maintained blood glucose concentration kept between $80\,mg/dL$ and $100\,mg/dL$ by counter-regulatory hormones.

GLUT2

A high-capacity, low-affinity glucose transporter present on pancreatic beta cells and liver hepatocytes that senses blood glucose concentrations and allows entry of glucose to trigger insulin release.

GLUT4

The insulin-sensitive glucose transporter located primarily in skeletal muscle and adipose tissue that translocates to the plasma membrane in response to insulin signaling.

GLUT5

A member of the SLC facilitative transporter family that acts specifically as a fructose transporter across intestinal epithelial cell membranes.

Alpha-Amylase

An endoglucosidase present in salivary and pancreatic secretions that hydrolyzes internal $\alpha\text{-1,4}$ glycosidic bonds in starch to generate random chain-length alpha-dextrins.

Glucoamylase

A membrane-spanning exoglucosidase located in the brush border that sequentially cleaves external $\alpha\text{-1,4}$ glycosidic bonds from the non-reducing end of starch chains to release single glucose residues.

Sucrase-Isomaltase Complex

An intestinal brush border enzyme complex accounting for $100\%$ of the intestine's ability to hydrolyze sucrose and capable of cleaving $\alpha\text{-1,6}$ glycosidic linkages in isomaltose.

Amylose

A plant starch consisting of glucose residues linked in a linear polymer exclusively by $\alpha\text{-1,4}$ glycosidic bonds.

Amylopectin

A branched plant starch polymer composed of glucose residues joined by $\alpha\text{-1,4}$ glycosidic bonds with $\alpha\text{-1,6}$ branch points.

Glycogenin

A core protein located at the center of a glycogen molecule that acts as the primer upon which glucose chains are synthesized.

Branching Enzyme (4,6-Transferase)

An enzyme in glycogen synthesis that cleaves a segment of an $\alpha\text{-1,4}$ linked glucose chain and transfers it to create an $\alpha\text{-1,6}$ branch point.

Glycogen Phosphorylase

An enzyme that degrades glycogen by using inorganic phosphate to cleave $\alpha\text{-1,4}$ glycosidic bonds, generating glucose 1-phosphate.

Aldolase B

The rate-limiting enzyme in hepatic fructose metabolism that cleaves fructose 1-phosphate into dihydroxyacetone phosphate (DHAP) and glyceraldehyde.

Polyol Pathway

A metabolic pathway in which glucose is reduced to sorbitol and oxidized to fructose; sorbitol accumulation in the lens increases osmotic pressure, contributing to diabetic glaucoma.

Glucose 6-Phosphate Dehydrogenase

The rate-limiting enzyme of the oxidative phase of the pentose phosphate pathway that oxidizes glucose 6-phosphate to generate NADPH.

Pentose Phosphate Pathway

A metabolic pathway branching from glucose 6-phosphate that yields two moles of NADPH per mole of glucose 6-phosphate for cellular detoxification and produces ribose 5-phosphate for nucleotide synthesis.

Alcohol Dehydrogenase (ADH1)

A cytosolic enzyme that oxidizes ethanol into toxic acetaldehyde while generating a mole of NADH.

Acetaldehyde Dehydrogenase (ALDH)

A mitochondrial enzyme that converts toxic acetaldehyde into non-toxic acetate while generating a mole of NADH.

Disulfiram

An aldehyde dehydrogenase (ALDH) inhibitor used to treat alcoholism that causes accumulation of toxic acetaldehyde, resulting in severe nausea and vomiting upon ethanol ingestion.

Microsomal Ethanol Oxidizing System (MEOS)

A cytochrome P450-mediated pathway (primarily CYP2E1) that utilizes NADPH and oxygen to metabolize ethanol to acetaldehyde during chronic or high ethanol exposure.