Glycobiology - Glycoproteins

This set of vocabulary flashcards covers carbohydrate metabolism, glycosidic linkages, various types of mucopolysaccharides, the role of the glycocalyx in mammalian and bacterial cells, and the mechanisms of N-linked and O-linked glycosylation including clinical markers for diabetes.

Saccharides

Derived from the Latin word 'Saccharum' for sugar, these are carbohydrate units ranging from simple monomers (monosaccharides) to complex polymers (polysaccharides).

Glycosidic linkages

Bonds formed between the $-OH$ groups of sugar rings via condensation reactions; the most common are $(1-4)$ and $(1-6)$, while $(1-5)$ is not possible due to steric hindrance.

Polysaccharides

Molecules consisting of multiple monosaccharide subunits that can be branched or unbranched, and categorized as homo or heteropolymers.

Hyaluronic Acid

An anionic, non-sulphated glycosaminoglycan (GAG) distributed across connective, epithelial, and neural tissues; it is also involved in wound healing.

Chondroitin Sulphate

A sulphated glycosaminoglycan (GAG) composed of alternating N-acetylgalactosamine and glucuronic acid, typically found as part of a proteoglycan.

Heparin

A sulphated glycosaminoglycan (GAG) composed of alternating N-acetylgalactosamine and glucuronic acid, clinically exploited for its anti-thrombotic potency.

Keratan Sulphate

A linear polysaccharide repeating unit consisting of $\beta$-galactose (Gal) and N-acetyl-$\beta$-glucosamine (GlcNAc), typically sulphated at the 6-position.

Dermatan Sulphate

A glycosaminoglycan carbohydrate composed of linear polymers of disaccharide units containing iduronic acid (IdoA) and N-acetyl galactosamine (GalNAc).

Hydration shell

A large volume of water surrounding glycosaminoglycan chains formed via hydrogen bonding, creating hydrated gels that provide cushioning and lubrication to joints.

Microheterogeneity

A phenomenon in proteins where carbohydrate modifications add nuance to function, creating a spectrum of activities or properties despite the same amino acid sequence.

Glycocalyx (Capillary)

A negatively charged layer that modifies capillary permeability, supports laminar blood flow, and functions as a 'mechanotransduction' unit for endothelial cells.

Bacterial Glycocalyx

A complex microbial layer consisting of a capsule and a slime layer that contributes to virulence, adherence to substratum, and protection from dehydration or biocides.

Glycoprotein

Proteins that have undergone post-translational modification by carbohydrate units, where the carbohydrate component is determined by enzyme access and carbohydrate availability.

N-Linked Glycosylation

Covalent binding of a sugar (typically N-acetyl-glucosamine) to the amide residue of Asparagine in the sequence $\text{ASN-X-SER}$ or $\text{ASN-X-THR}$ (where X is not Proline), occurring in the Endoplasmic Reticulum.

O-Linked Glycosylation

Binding of carbohydrates through the hydroxyl- group on Serine or Threonine amino acids; this process is the origin of the ABO blood groupings.

HbA1c

A glycated form of haemoglobin used to monitor long-term blood glucose control because red blood cells survive for approximately $120\text{ days}$.

Fructosamine

An advanced glycation end-product (AGE) formed when fructose or glucose covalently modifies serum proteins, primarily albumin; it monitors blood glucose control over a $1-2\text{ week}$ period.