Glycoproteins

Why is cell surface uniqueness crucial

Cell surface uniqueness is critical because cells spend their lifespan in contact with other cells, with which they need to communicate. So, molecular structures on a cell are recognising and responding to molecules on adjacent cell surfaces.

What are glycoproteins

Glycoproteins are proteins which are covalently attached to carbohydrates.

How does the composition of glycoproteins vary

Glycoprotein composition is varied, with anywhere from 1% to 90% of the biomolecule mass being carbohydrate.

How is the polypeptide part of a glycoprotein synthesised

Translation (encoded by genes )

How is the carbohydrate component of glycoprotein formed

Enzymatically generated

Name types of glycoproteins

• as components of structural proteins (as part of a matrix ground called “ground substance”)

• in mucous secretions

• immunoglobulins

• interferons

• blood plasma proteins

What part of the membrane are glycoproteins important constituents of

Plasma membrane

How has the location of glycoprotein carbohydrate parts been determined

By electron microscopy

Where are the carbohydrate groups of membrane-based glycoproteins found

Mostly located on the external surfaces

What is the function of carbohydrate groups of membrane-based glycoproteins?

They are heavily involved in intercellular communication.

Name different carbohydrates on membrane surfaces

• glycolipid

• peripheral protein

• oligosaccharide

• integral protein

• hydrophobic α- helix

• phospholipid

• cholesterol

• lipid-linked protein

What diverse areas do the interaction between cell glycoproteins play important roles in

• infection

• prevention of infection

• egg fertilisation

• inflammatory disease

• septic shock

• blood clotting

How are the carbohydrates often linked in O-linked glycoproteins

In the O-linked glycoproteins the carbohydrates are often linked to the polypeptide chains via the -OH of the following amino acid side groups: serine, threonine, or hydroxylsine.

Describe the structure that O-linked polysaccharides are often found in to provide protective functions

O-linked polysaccharides tend to be clustered in heavily glycosylated segments, rather than being spread out along the polypeptide chain.

Describe the charge of the O-linked glycoproteins found in mucus

Mucus contains O-linked glycoproteins with negatively charged sulfate groups. These negatively charged groups repel one another and prevent any form of protein secondary structure from developing.

What are mucins

The protein component of mucus

Function of mucins

Mucins form inter-tangled networks that act as viscoelastic gels which protect and lubricate mucous membranes.

What are antigenic determinants of blood an example of?

Antigenic determinants of blood are examples of information and recognition roles for carbohydrates of glycoproteins.

What does the structure of the carbohydrate on the cell surface glycoprotein determine

The structure of the carbohydrate on the cell surface glycoprotein determines the blood group as O, A, B , or AB.

What does the presence of glycoprotein carbohydrates mean for blood transfers

Blood can only be transferred between people if the carbohydrate in the donor and acceptor are compatible. Otherwise, blood is considered as a foreign substance, leading to agglutination (clumping) of erythrocytes and fatal blood vessel blockage.

What blood types can recognise each other as foreign

The immune system of type A people recognise blood of type B as foreign and vice versa.

Is type O blood recognized as foreign by people with type A, B or AB?

No, as the carbohydrate portion of type O blood is a component of type A, B and AB blood.

Anyone can accept type O blood

What type of blood can AB people accept

AB people can accept A, B, AB, and O blood, AB people are universal acceptors.