Carbohydrates

Question 1

What are carbohydrates attached to proteins called?

Answer 1

Glycoproteins

Question 2

What are carbohydrates attached to lipids called?

Answer 2

Glycolipids

Question 3

Where are glycoproteins/glycolipids located?

Answer 3

On extracellular face of membrane –> form part of extracellular matrix surrounding cells

Question 4

What are glycolipids/glycoproteins important for?

Answer 4

Immune recognition and disguise the cell from foreign bodies

Question 5

What is glycosylation?

Answer 5

When a carbohydrate is attached to a hydroxyl or other functional group of another molecule

It is completed and determined by the Golgi

Question 6

The external side of the protein is covered in carbohydrates. What is the purpose of this?

Answer 6

Used for interaction with the extracellular matrix fibres and binding ligands

Question 7

What are O-linked glycoproteins?

Answer 7

• Contain a carbohydrate attached to a serine or threonine amino acid (sugar attached to hydroxyl group in side chain of serine or threonine residues)
• Often short sugars (2-5)

Question 8

What are N-linked glycoproteins?

Answer 8

• Contain a carbohydrate attached to an asparagine amino acid
• Usually large branched sugars (30-40)

Question 9

What is the condition for N-linked glycoproteins?

Answer 9

Asparagine must be in the consensus sequence Asn-X-Ser/Thr (as long as the X isn’t Pro)

Question 10

How are carbohydrates involved in blood groups?

Answer 10

Blood group antigens (ABO) arise from glycolipids

• Lipid has X group
• X determines type of antigen

1. No extra sugar in O antigen
2. N-acetyl-galactosamine in A antigen
3. Galactose in B antigen