Biomolecules: Carbohydrates in the Body

Vocabulary practice flashcards covering carbohydrate structure, enzymatic digestion, intestinal transport, glucose homeostasis, diabetes mellitus, and associated oral complications.

Biomolecules

Large polymers built from smaller monomers that serve as the building blocks of life and comprise four major classes across all living organisms.

Carbohydrates

Essential biomolecules composed of carbon, hydrogen, and oxygen that provide the primary source of cellular energy and supply $45\text{--}65\%$ of daily caloric intake.

Aldoses

Monosaccharides containing an aldehyde carbonyl group ($\text{-CHO}$), with glucose serving as a primary example.

Ketoses

Monosaccharides containing a ketone carbonyl group ($\text{C=O}$), with fructose serving as a primary example.

Anomers

Isomeric cyclic forms ($\alpha$ and $\beta$) of a monosaccharide that differ in the spatial orientation of the hydroxyl group ($\text{-OH}$) attached to the carbonyl carbon.

Glycosidic Bond

A covalent linkage formed when the carbonyl carbon of one monosaccharide reacts with a hydroxyl group of another sugar molecule.

Maltose

A dietary disaccharide formed by the condensation of two glucose molecules.

Lactose

A dietary disaccharide formed by the condensation of one galactose molecule and one glucose molecule.

Sucrose

A dietary disaccharide formed by the condensation of one glucose molecule and one fructose molecule.

Cellulose

An unbranched structural plant polysaccharide composed of $\beta\text{-glucose}$ monomers joined exclusively by $1\text{-}4$ glycosidic linkages.

Glycogen

A branched animal storage polysaccharide composed of $\alpha\text{-glucose}$ monomers linked by $1\text{-}4$ linear bonds and $1\text{-}6$ branch points.

Salivary Amylase

An enzyme secreted by serous acini of the parotid and submandibular salivary glands with an optimal pH of approximately $6.7$ that cleaves $\alpha\text{-1,4}$ linkages in dietary polysaccharides.

Chyme

The semi-fluid acidic mass of partially digested food mixed with gastric secretions produced in the stomach, where salivary amylase becomes denatured.

Pancreatic Amylase

An enzyme secreted by pancreatic acinar cells into the duodenum via the pancreatic duct that hydrolyses $\alpha\text{-1,4}$ glycosidic bonds at an optimal pH of $6.7\text{--}7.0$.

Brush Border Enzymes

Digestive enzymes embedded in the apical microvilli of small intestinal enterocytes (duodenum and jejunum) responsible for the final breakdown of disaccharides and oligosaccharides into absorbable monosaccharides.

Sucrase-Isomaltase Complex

A brush border enzyme complex consisting of sucrase, which hydrolyses sucrose into glucose and fructose, and isomaltase, which hydrolyses $\alpha\text{-1,6}$ branch linkages.

Maltase-Glucoamylase

A dual-action brush border protein where maltase cleaves maltose into two glucose units and glucoamylase cleaves glucose sequentially from the ends of glucose chains.

SGLT1 (Sodium–Glucose Linked Transporter 1)

An apical transport protein that mediates secondary active transport of glucose and galactose into intestinal enterocytes coupled with $\text{Na}^+$ down its electrochemical gradient.

$\text{Na}^+/\text{K}^+$ ATPase Pump

A primary active transporter on the basolateral membrane of enterocytes that hydrolyses $\text{ATP}$ to pump $\text{Na}^+$ out, maintaining the sodium gradient required by SGLT1.

GLUT2

A bidirectional basolateral transporter protein that facilitates the passive exit of glucose, galactose, and fructose down their concentration gradients into the bloodstream.

GLUT5

An apical membrane transporter on small intestinal epithelial cells that facilitates the energy-independent uptake of fructose into enterocytes down its concentration gradient.

Mineralocorticoids (in Carbohydrate Absorption)

Hormones that regulate intestinal sodium transport, thereby supporting the sodium-dependent secondary active uptake of glucose and galactose via SGLT1.

Insulin

An endocrine hormone secreted by $\beta\text{-cells}$ in the pancreatic islets of Langerhans that lowers blood glucose by stimulating cellular glucose uptake in muscle and adipose tissue and promoting glycogen storage.

Glucagon

An endocrine hormone secreted by $\alpha\text{-cells}$ in the pancreatic islets of Langerhans that elevates blood glucose by stimulating hepatic glycogenolysis and gluconeogenesis.

Glucose Homeostasis

The physiological maintenance of circulating blood glucose around a target concentration of approximately $90\,\text{mg}/100\,\text{ml}$ through antagonistic feedback between insulin and glucagon.

Fasting Plasma Glucose (WHO Threshold)

The healthy upper threshold for fasting blood sugar defined by the World Health Organization, which is below $6.1\,\text{mmol/L}$.

Oral Glucose Tolerance Test (OGTT Threshold)

A diagnostic carbohydrate challenge where normal plasma glucose levels measured $2\,\text{hours}$ following a $75\,\text{g}$ glucose load must remain below $7.8\,\text{mmol/L}$.

Type 1 Diabetes Mellitus

A metabolic disorder caused by absolute insulin deficiency resulting from autoimmune destruction of pancreatic $\beta\text{-cells}$.

Type 2 Diabetes Mellitus

A metabolic disorder characterised by peripheral cellular insulin resistance paired with progressive inadequacy of insulin secretion.

Xerostomia

The subjective feeling of dry mouth resulting from reduced salivary secretion, representing a major oral manifestation of diabetes mellitus.

Oral Candidiasis

An opportunistic fungal infection (thrush) affecting oral mucosa that occurs with increased incidence in individuals with poorly controlled diabetes.