Carbohydrates

Question 1

What are carbohydrates?

Answer 1

Carbon-based molecules rich in OH groups, written as (CH2O)n for many

Question 2

What are monosaccharides?

Answer 2

Simple sugars/monomers that make up polysaccharides, fuel

Aldehydes or ketones with 2 or more OH groups, smallest are composed of 3C

Question 3

What are polysaccharides?

Answer 3

Complex carbs of polymers of covalently linked monosaccharides.

Question 4

The variety and multiplicity of linkages forming polysaccharides allows carbs to

Answer 4

provide cells with a vast assay of 3D structures that can be used for a variety of purposes

Question 5

How to determine D and L config for monosaccharides?

Answer 5

Look at the asymmetrical C furthest from the aldehyde or ketone.
D = OH on right

Question 6

What are epimers?

Answer 6

Sugars that differ in config at only one asymmetric centre and are disasteroisomers

Question 7

How do the predominant form of common sugars (cyclic) form their ring?

Answer 7

Aldehyde reacts with an alcohol to form hemiacetal

Question 8

What additional asymmetric centre is created when a cyclic hemiacetal is formed?

Answer 8

Anomer (another diasteroisomer)

Question 9

Where is the OH group for alpha and beta respectively?

Answer 9

Below the plane (alpha), above the plan (beta)

Question 10

Pyranose rings adopt two classes of conformations:

Answer 10

chair and boat

Question 11

Monosaccharides commonly react with

Answer 11

alcohols, amines, and phosphates

Question 12

What is a glycosidic bond?

Answer 12

Formed between the anomeric C atom of glucose and O-atom of an alcohol = O-glycosidic bond, product is glycoside

Question 13

When are glycosidic bonds predominant?

Answer 13

When carbs are linked together to form long polymers and when they are attached to proteins

Question 14

What are oligosaccharides?

Answer 14

Built by a linkage of 2 or more monosaccharides by O-glycosidic bonds

Question 15

Why are there many different glycosidic linkages possible?

Answer 15

Because monosaccharides have multiple OH groups = many possibilities

Question 16

How are oligosaccharides synthesized?

Answer 16

Through the action of specific enzymes, glycotransferases, which catalyze the formation of glycosidic bonds

Question 17

What are the common disaccharides?

Answer 17

Sucrose (alpha-D-glucopyranosyl-(1->2)-beta-D-fructofuranose)
Lactose (beta-D-galactopyranosyl-(1->4)-alpha-D-glucopyranose)
Maltose (alpha-D-glucopyranosyl-(1->4)-alpha-D-glucopyranose)

Question 18

What are glycoproteins?

Answer 18

A carb group covalently attached to a protein

Question 19

What are the 3 classes of glycoproteins?

Answer 19

1. Glycoproteins
2. Proteoglycans
3. Mucins/Mucoproteins

Question 20

What are the 1st class of glycoproteins?

Answer 20

Protein constituent is the largest component by weight, component of cell membranes (part in processes i.e cell adhesion and binding of sperm to egg)

Question 21

What are proteoglycans?

Answer 21

Protein component is conjugated to a particular part of polysaccharide called glycosaminoglycan, carbs are much larger % of weight, function as structural components and lubricants

Question 22

What are mucins/mucoproteins?

Answer 22

Predominantly carb, key component of mucus = lubricant, N-Acetylgalactoamine is usually caeb bound to protein

Question 23

In all classes of glycoproteins, sugar are attached to either?

Answer 23

Amide N atom in side chain of Asn or to hydroxyl O atom in side chain of Ser or Thr
This process is called glycosylation

Question 24

Carb structures are recognition sites for a special class of proteins called?

Answer 24

glycan-binding proteins, which bind specific carb structures on neighbouring cell surfaces

Question 25

What are lectins?

Answer 25

A class of glycan-binding proteins, partners for lectin binding are often the carb part of glycoproteins, function: facilitate cell-to-cell contact
- Lectins and carbs are linked by a number of weak noncovalent interactions that ensure specificity yet permit unlinking as needed