Lecture 10: Carbohydrates and proteins

Question 1

How are carbohydrates attached to proteins (2)?

Answer 1

• O-linked glycosylation
• N-linked Glycosylation

Question 2

O-linked glycosylation

Answer 2

• the carbohydrate chain is attached to the hydroxyl group of a serine (Ser) or threonine (Thr) residue in the protein.

Question 3

Glycosylation

Answer 3

where carbohydrate molecules are covalently attached to specific amino acid residues on proteins

Question 4

N-Linked Glycosylation

Answer 4

• the carbohydrate chain is attached to the side chain of an asparagine (Asn) residue in the protein, specifically to the amide group of the asparagine side chain.

Question 5

How are carbohydrates attached to proteins during glycosylation?

Answer 5

The glycosidic bond forms between the anomeric carbon of the carbohydrate and the oxygen/nitrogen of the side chain and the enzyme glycosyltransferase does this

Question 6

Which features of carbohydrate chemistry make carbohydrates information rich molecules (4)?

Answer 6

1. Variation in number and type of monosaccharide
2. Many types of linkages (a-1,4 and b-1,4 and a-1,6)
3. Type of linkage to protein
4. Increases the amount/complexity of chemical information on the protein surface-> change function)

Question 7

Classes of Glycoproteins: glycoprotein (2)

composition+ linkages

Answer 7

• protein>carbohydrate (by weight)
• N- or O-linked glycosylation

Question 8

Proteoglycans (3)

composition+ 2 functions+attached to

Answer 8

• carbohydrate>protein
• protective biological lubricants (slimy in throat and gut)
• lubricants and structural components in connective tissue, adhesion of cells to extracellular matrix
• Proteins attach to glycoaminoglycans (muccopolysaccharide)

Question 9

Mucin (3)

composition+ linkages+2 functions

Answer 9

• Carbohydrate>protein
• extensive O-linked
• form a physical barrier, which protects epithelial cells from stress-induced damage
• Acts as a lubricant in saliva

Question 10

The Hormone Erthropoietin (EPO)

Answer 10

• a glycoprotein hormone, naturally produced by the peritubular cells of the kidney, that stimulates red blood cell production
• 3 N-linked glycosylation, 1 O-linked glycosylation site (enhances stability)
• 40% carbohydrate

Question 11

glycoaminoglycans (muccopolysaccharide)

Answer 11

Proteoglycans have long chains of sugar molecules called glycosaminoglycans (GAGs), which have a high affinity for water molecules due to their highly negatively charged sulfate and carboxyl groups. This property allows proteoglycans to trap water molecules, creating a gel-like structure within the ECM.

Question 12

Aggrecan

Answer 12

• a proteoglycan
• This molecule is important in the proper functioning of articular cartilage because it provides a hydrated gel structure (via its interaction with hyaluronan and link protein) that endows the cartilage with load-bearing properties

Question 13

Mucins are —- components of mucus

Answer 13

• glycoprotein

Question 14

mucus vs mucin

Answer 14

Mucus: Mucus is a gel-like substance produced by mucous membranes throughout the body, including the respiratory, digestive, and reproductive tracts. It serves several important functions, such as lubricating and protecting the epithelial surfaces, trapping and clearing foreign particles, and providing a barrier against pathogens. Mucus is primarily composed of water, mucins, electrolytes, and various other proteins and lipids.

Mucin: Mucins are large glycoproteins that are the main structural component of mucus. They are heavily glycosylated, meaning they have numerous carbohydrate (sugar) chains attached to the protein backbone. These carbohydrate chains give mucins their gel-like properties and contribute to the viscosity and adhesive characteristics of mucus. Mucins are produced and secreted by specialized cells called goblet cells, as well as other epithelial cells, and they play a critical role in the formation and function of mucus.

In summary, mucus is the gel-like substance that lines various mucous membranes in the body, while mucins are the specific glycoproteins that make up the bulk of mucus and confer its unique properties.

Question 15

Lectins

Answer 15

• proteins that non-covalently bind specific carbohydrates
• Lectins are on one cell surface while glycoprotein on another. Theres partners then come together for an interaction

Question 16

Selectins (3)

type+what it does

Answer 16

• Type of lectin
• Help immune system cells bind to sites of injury for the inflammatory response
• Immune cells have selectins and wonds/cuts express glycoprotein. As white blood cell circulate the selectin the the surface helps binds to the glycoprotein of the cut/wound

Question 17

Hemmagglutinin

Answer 17

Hemagglutinin (HA) binds to the monosaccharide sialic acid which is present on the surface of its target host cells. The cell membrane then engulfs the virus through endocytosis and forms endosome. The cell then attempts to begin digesting the contents of the endosome by acidifying its interior and transforming it into a lysosome. When the pH within the endosome drops to 6.0, the HA molecule becomes partially unfold, and releasing a very hydrophobic portion of its peptide chain that was previously hidden within the protein.