Carbohydrates

Question 1

Classify carbohydrates.

Answer 1

• monosaccharides
• disaccharides: 2 monosaccharides
• oligosaccharides: 3-10 monosaccharides
• polysaccharides: 11+ monosaccharides

Question 2

Classify monosaccharides.

Answer 2

• according to no. of C atoms (3-7): ​trioses, tetroses, pentoses, hexoses, heptoses
• according to functional group:
  
  • aldoses (aldehyde), ketoses (ketone)
  • reducing, non-reducing sugars
  • polyols (only -OH)

Question 3

How are cyclic monosaccharides formed?

Reaction type?

Consequence?

Answer 3

mutarotation via intramol. nucleophilic addition
→ ​hemiacetal/-ketal formed (alcohol + ald./ket. resp.)

⇒ chiral center at C¹ → 2 anomers are formed, in equilibrium with open chain form

_{here: mutarotation of D-glucose shown}

Question 4

What are epimers?

Most important epimers of glucose?

Answer 4

isomers differing at the position of one -OH

epimers of glucose:

• mannose (at C²)
• galatose (at C⁴)

Question 5

What is an anomer?

Which form is preferred in nature? Why?

Answer 5

epimer w/ different configuration at hemiacetal or hemiketal carbon (anomeric C¹), formed by mutarotation

• α = down
• β = up

→ β preferred bc most stable when in equatorial position

Question 6

Explain the optical activity of sugars.

Naturally occuring form of fructose, glucose?

Answer 6

light rotated either

• dextrorotatory (+), glucose in nature → dextrose
• laevorotatory (-), fructose in nature

Question 7

What is D, L isomerism?

Which form is preferred in nature?

Answer 7

depends on orientation of -OH group on terminal alcohol C (C⁵ in glucose)

• D = dextro = right
• L = leavo = left

→ mostly D sugars in nature

Question 8

What are pyranoses and furanoses?

Answer 8

• pyranoses = 6-membered ring
• furanoses = 5-membered ring

Question 9

List and describe important physiological pentoses.

Answer 9

Question 10

List and describe important physiological hexoses.

Answer 10

Question 11

Which bonds/compounds are formed btw the -OH of the anomeric C of glucose and… ?

Answer 11

O-/N-glycosides

hemiacetal + -OH → acetal link

• ​if 2^nd compound glucose → glucoside
• if 2^nd compound galatose → galactoside

hemiacetal ​+ -NH₂ → N-glycosidic bond

Question 12

What are amino sugars?

List some important N-acetyl derivatives.

Function?

Answer 12

sugar molecule in which a -OH group has been replaced with an -NH₂ group

• D-glucosamine, D-galactosamine, D-mannosamine
• sialic acid

⇒ important components of glycoproteins, glycosphingolipids (blood group antigens), glycosaminogylcans

_{​ex: D-glucosamine}

Question 13

Describe the general structure of sugar phosphate esters.

Examples.

Functions?

Answer 13

sugar + phosphate esterified (pretty obv lol)

• glucose-6-phosphate
• fructose-1t,6-bisphosphate

⇒ important intermediates of glycolysis and other processes of carbohydrate metabolism

Question 14

List important reduced/oxidized monosaccharides.

Function?

Answer 14

reduction:
aldehyde/keto group reduced → prim./sec. alcoholic -OH group

• glucose/fructose → sorbitol (causes diarrhea)

oxidation:

• prim. -OH oxidized: uronic acid
• aldehyde oxidized: aldonic acid
• both terminal groups oxidized: aldaric acid

Question 15

Which common disaccharides are non-/reducing?

Answer 15

• reducing sugars: maltose, lactose + other sugars w/ free glycosidic end
• non-reducing: sucrose

Question 16

Explain the structure of starch.

What is the difference to glycogen?

Answer 16

α-glucosidic chain (glucosan), 2 constituents:

• amylose (20%): nonbranching, α-1-4 linkages
• amylopectin (80%): α-1-4 linkages, α-1-6 linkages at branches

glycogen same structure, but more highly branched

Question 17

Explain the structure of cellulose.

Answer 17

β-D-glucose linked by β-1-4 bonds (cellobiose subunits)

→ insoluble fibers

Question 18

Explain the structure of dextran.

Clinical relevance?

Answer 18

• *α-1,6 linkage**s between glucose +
• *α-1,3 linkages** that form branches

→ used as antithrombotic

Question 19

Which components make up the ground substance for connective tissue?

How do they cushion other structures?

Examples?

Answer 19

proteoglycans = protein + glcusaminoglycan (amino sugars + uronic acids)

large no. of -OH groups/neg. charges → repulsion, keep carbohydrate chains apart

• hyaluronic acid
• heparin

Question 20

What are glycoproteins?

Another name.

Function?

Examples.

Answer 20

also: mucoproteins = protein + oligosaccharide chains

→ important part of cell membranes (e.g. glycocalyx)

• fucose
• N-acetylneuraminic acid (sialic acid)