BCH 4033- ch.11 carbs and glycoproteins

exam 3 content

what are carbohydrates?

aldoses or ketoses rich in hydroxyl groups + their derivatives

what are the simplest carbs?

monosacchardes

3-7 Cs long

what can pentoses and hexoses close into?

five-membered furanose rings or six-membered pyranose rings

what are pyranose rings?

rings made from heoxes

adopt a chair conformation

• rapid equilibrium with linear forms in aq. solutions

what are furanose rings?

rings made from pentoses

adopt an envelope conformation

• rapid equilibrium with linear forms in aq. solutions

what happens to sugars undergoing cyclization?

an additional asymmetric center is formed

alpha and beta anomer forms that differ in position of hydroxyl group on anomeric carbon

what happens to anomers in monosaccharides?

they rapidly interchange via the linear form

what is D-glucose?

the most common sugar in living organisms

the human “blood sugar”

a reducing sugar

what structure does D-glucose form?

forms a 6-membered ring with all bulky groups in the equatorial positions

makes it most common sugar in living organisms

what is D-glucose capable of?

nonenzymatically reacting with hemoglobin to form glycated hemoglobin

• glycated hemoglobin = important biomarker for diabetes

courtesy of it being a reducing sugar

how do sugars use glycosidic linkages?

to join to alcohols and amines to form the anomeric C atom

ex.) N-glycosidic linkages connect sugars to purines and pyrimidines in nucleotides, RNA, DNA

how are sugars linked to one another in disaccharides and polysaccharides?

by O-glycosidic linkages

what are the common disaccharides?

sucrose, lactose, maltose

what does sucrose (table sugar) consist of?

alpha glucose and beta fructose joined by a glycosidic linkage between their anomeric Cs

what does lactose (in milk) consist of?

galactose joined to glucose by a beta-1,4 linkage

what does maltose (from starch) consist of?

2 glucoses joined by an alpha-1,4 linkage

what is starch?

a storage homopolymer of glucose in plants

glycogen serves similar role in animals

what is the structure of glucose units in starch and glycogen?

alpha-1,4 linkages with alpha-1,6 branches

what does cellulose consist of?

glucose units joined by beta-1,4 linkages

• give long straight chains that form fibrils with thigh tensile strength

cellulose = major structural polymer of plant cell walls

what is chitin?

the major structural polymer of fungal cell walls and the exoskeletons and shells of arthropods

a homopolymer composed of beta-1,4 linkages

• monomeric unit is GlcNAc (not glucose)

what are carbohydrates in relation to proteins?

commonly conjugated proteins

protein component is predominant in glycoproteins

what are most secreted proteins?

glycoproteins that are prominent on the external surface of the plasma membrane

ex.) signal molecule erythropoietin

what are glycosaminoglycans?

polymers of repeating disaccharides with a derivative of glucosamine or galacosamine and a high density of carboxylate or sulfate groups

what are proteoglycans?

proteins bearing covalently linked glyosaminoglycans

found in the extracellular matrices of animals

key part of cartilage

what are mucoproteins?

proteins that serve as lubricants and are predominantly carbs by weight

what is the protein component of mucoproteins?

the component heavily O-glycosylated with N-aceylgalactosamine joining the oligosaccharide to the protein

what are glycosyltransferases?

enzymes that link the oligosaccharide units on proteins in the lumen of the endoplasmic reticulum

extra sugars = attached in golgi complex to form diverse patterns?

what are lectins used for?

recognizing carbohydrates on cell surfaces

direct proteins to their proper cellular locations and help in protein folding

what is the importance of lectins in animals?

interplay with sugar targets guides cell-cell contact and vital entry