Biomolecules A: Carbohydrates in the Body

Vocabulary flashcards covering carbohydrate classification, structural biochemistry, gastrointestinal enzymatic digestion, intestinal transport mechanisms, and endocrine glucose regulation with clinical oral relevance.

Carbohydrates

Essential biomolecules composed of Carbon (C), Hydrogen (H), and Oxygen (O) that serve as the main source of energy for cells and provide 45–65% of daily caloric intake.

Aldoses

Monosaccharides containing an aldehyde carbonyl group $(-\text{CH}=\text{O})$, such as glucose.

Ketoses

Monosaccharides containing a ketone carbonyl group $(>\text{C}=\text{O})$, such as fructose.

Anomers ((\alpha) and (\beta) forms)

Isomeric forms of monosaccharides in ring structures defined by the spatial orientation of the hydroxyl group ($-\text{OH}$) attached to the carbonyl carbon.

Disaccharides

Carbohydrates formed when two monosaccharides link together via glycosidic bonds formed between the carbonyl carbon of one sugar and a hydroxyl group of another.

Maltose

A disaccharide composed of two glucose molecules joined together.

Lactose

A disaccharide composed of one galactose molecule and one glucose molecule.

Sucrose

A disaccharide composed of one glucose molecule and one fructose molecule.

Oligosaccharides

Short carbohydrate chains containing two to ten sugar molecules, such as raffinose and stachyose.

Polysaccharides

Long carbohydrate polymers made of ten or more sugar molecules linked together, such as starch, glycogen, and cellulose.

Amylose

An unbranched plant starch polymer composed of $\alpha$-glucose monomers linked exclusively by 1-4 glycosidic bonds, forming a helical shape.

Amylopectin

A branched plant starch polymer composed of $\alpha$-glucose monomers containing both 1-4 and 1-6 glycosidic bonds.

Glycogen

A branched animal storage polysaccharide made of $\alpha$-glucose units containing 1-4 and 1-6 glycosidic bonds.

Cellulose

An unbranched structural plant polysaccharide made of $\beta$-glucose monomers connected by 1-4 glycosidic bonds.

Salivary Amylase

An enzyme secreted by serous acini of the parotid and submandibular salivary glands that operates at an optimal pH of approximately $6.7$ to hydrolyse $\alpha$-1,4 linkages in dietary polysaccharides.

Chyme

The semi-fluid mass of partly digested food mixed with gastric secretions formed in the stomach, where gastric acid denatures salivary amylase.

Pancreatic Amylase

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

Brush Border Enzymes

Enzymes embedded in the apical membrane microvilli of enterocytes in the duodenum and jejunum responsible for the final hydrolytic breakdown of disaccharides and oligosaccharides into absorbable monosaccharides.

Isomaltase

A component enzyme of the sucrase-isomaltase complex in the brush border that specifically hydrolyses $\alpha(1,6)$ branch linkages that amylases cannot cleave.

Glucoamylase

A brush border enzyme component of the maltase-glucoamylase protein that releases terminal glucose units from the ends of glucose chains.

SGLT1 (Sodium–Glucose Linked Transporter 1)

A symporter on the apical membrane of intestinal epithelial cells that imports glucose and galactose against their concentration gradient using secondary active transport driven by the $\text{Na}^+$ gradient.

GLUT5

A transport protein located on the apical membrane of intestinal epithelial cells that mediates the uptake of fructose via facilitated diffusion.

GLUT2

A carrier protein located on the basolateral border of intestinal epithelial cells that transports glucose, galactose, and fructose into the bloodstream via facilitated diffusion down their concentration gradients.

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

An ATP-dependent basolateral transporter that exports $\text{Na}^+$ out of epithelial cells to maintain the electrochemical sodium gradient required for secondary active transport via SGLT1.

Caloric Yield of Glucose

The amount of metabolic energy supplied per gram of glucose, which is approximately $3.75\,\text{kcal}$.

Insulin

A hypoglycaemic hormone secreted by $\beta$-cells in the pancreatic islets of Langerhans that stimulates cellular glucose uptake into muscle and fat and promotes glycogen synthesis in the liver.

Glucagon

A hyperglycaemic hormone secreted by $\alpha$-cells in the pancreatic islets of Langerhans that stimulates hepatic glycogenolysis and gluconeogenesis to release glucose into the bloodstream.

Glucose Homeostasis Set Point

The physiological baseline concentration at which blood glucose is balanced, maintained at approximately $90\,\text{mg}/100\,\text{mL}$.

Fasting Plasma Glucose (Normal WHO Threshold)

The normal clinical diagnostic threshold for fasting plasma glucose, which is below $6.1\,\text{mmol/L}$.

Oral Glucose Tolerance Test (OGTT)

A clinical diagnostic test measuring plasma glucose 2 hours after ingestion of a $75\,\text{g}$ oral glucose load; normal levels are below $7.8\,\text{mmol/L}$.

Type 1 Diabetes Mellitus

A metabolic disease characterized by an absolute insulin deficiency resulting from the autoimmune destruction of pancreatic beta cells.

Type 2 Diabetes Mellitus

A metabolic disease characterized by peripheral insulin resistance paired with progressively inadequate compensatory insulin secretion.

Xerostomia

Subjective sensation of dry mouth caused by reduced salivary flow, which is a frequent oral complication seen in diabetic patients.

Oral Candidiasis (Thrush)

A fungal infection presenting as white plaques on the oral mucosa and tongue, commonly seen as an oral complication in individuals with poorly controlled diabetes.