Carbohydrate structure and properties

Question 1

Carbohydrate structure

Answer 1

Molecules with a 1:2:1 ratio of carbon, hydrogen, oxygen- “hydrated carbon”

Empirical formula (CH2O)n

Good energy storage molecules

• C-H covalent bonds
• Examples: starch, sugars, glucose

Question 2

Combination of two to ten simple sugars =

Answer 2

oligosaccharides

Question 3

carbon atom attached to four different functional groups is called a __________

Answer 3

Chiral carbon

Question 4

same chemical formula, different 2D structures

Answer 4

isomers

Question 5

stereoisomers = cis/trans

Answer 5

isomers, different 3D orientation.

1. epimers = D/L (position of OH around C atom). configuration around one specific carbon atom. eg for glyceraldehyde
2. anomers = cyclic epimers

Question 6

enantiomers

Answer 6

non superimposable mirror images

Question 7

Monosaccharides - defined by number of C they possess

Answer 7

3 = triose = glyceraldehyde
4=tetrose = erythrose
5 = pentose = ribose
6=hexose=glucose
7=heptose= sedoheptose

Question 8

Monosaccharides - defined by chemical groups they possess

Answer 8

aldoses = aldehydes eg D-glucose

ketones = ketose eg D-fructose

Question 9

D & L sugars are _________ of one another

Answer 9

enantiomers (non-superimposable mirror images)

Biologically different

Most naturally occurring sugars are D isomers

For sugars with more than one chiral centre, the D or L designation refers to the asymmetric carbon farthest from the aldehyde or keto group

Question 10

Predominant form of glucose in solution is

Answer 10

not linear but cyclic

Question 11

alpha D glucose

Answer 11

Oh down on C1,2,4

Question 12

beta D glucose

Answer 12

Oh down on C2,4

Question 13

glucose alterations

Answer 13

glucosamine - precursor of cartilage components

glucitol/sorbitol - Sweetener/ Lower calorific value

glucoronic acid - Present in many mucus secretions / detoxification

Question 14

In disaccharides the monosaccharides are joined by a _____________ bond.

Answer 14

O-glycosidic bond

This is formed between two –OH groups from each sugar with the elimination of H2O forming leaving – O -

Depending on carbon molecules linked glycosidic bond links you can have 1-2, 1-4 or 1-6 glycosidic bonds.
Depending on their position can also be a (in maltose and sucrose - U bond) or b (in lactose - S bond).

Question 15

condensation of 2 monosaccharides gives

Answer 15

1 disaccharide with H - O - H bond + 1H2O molecule

Question 16

starch composition

Answer 16

20-30% amylose (a-1,4 Glycosidic bonds)

70-80% amylopectin (a-1,6 Glycosidic bond approx every 30 units) generates branching

Gives S shape bonding –

Both rapidly broken down by amylase

Question 17

Cellulose

Answer 17

b-1,4 linked D-glucose molecules

‘S’ shape type bonding –

Major structural component of green plants, trees etc

• Most abundant organic molecule on earth
• Insoluble

Question 18

Glycogen

Answer 18

Mainly a-1,4 glycosidic bonds.

Approx. every 7-11th glucose a-1,6 glycosidic bond for branching.

Each glycogen granule can contain up to 30,000 glucose residues
In humans the major storage sites are the liver (100g) and skeletal muscle (400g)

Question 19

Glycoproteins are formed by linking oligosaccharides and proteins as a post translational modification, in a process called __________

Answer 19

glycosylation.

sugars are linked to polymers via:
1. Asparagine (N-linked)

2. Threonine or serine (O-linked)

Question 20

What does glycosylation of proteins do?

Answer 20

It affects:

1. proteins function/activity
2. protein folding and processing
3. cell interaction with macro-molecules

Question 21

there are 3 classes of glycoproteins:

Answer 21

3 classes of glycoproteins

1. Simple glycoproteins (mainly protein)
2. Mucins (mainly carbohydrate) components of mucus
3. Proteoglycans (mainly carbohydrate)

Question 22

Some examples of glycoproteins in humans

Answer 22

Structural: Collagen
Lubrication and cell protection: Mucins
Immunogenic: Antibodies, Cell surface receptors
Protein folding: Calnexin, chaperone in the ER
Hormonal: Erythropoietin
Transport: Transferrin
Clotting: Platelet co-factors

Question 23

What are:

Congenital Disorders of Glycosylation (CDGs)

Answer 23

lead to deficiency or lack of enzymes involved in glycosylation of proteins

symptoms:
Developmental delay with multi-organ involvement
Hypotonia
Failure to thrive
Coagulopathy
Seizures

Question 24

Mucins and mucus

Answer 24

Mucus forms a protective layer on epithelial surfaces

1. Airways
   Traps foreign particles and bacteria
2. Digestive tract
   Lubricates
   Protects stomach lining from acidic environment
3. Reproductive
   Cervical mucus prevents infection

Question 25

Mucus is complicated mixture of :

Answer 25

(95%) Water
(1 – 10%) Mucins - mainly Muc 5AC/ Muc 5B in respiratory tract
Salts
Protein
Lipid
Carbohydrate
nucleic acid
secretory IgA

Mucins are a critical component of mucus. Diverse range of mucins: At least 19 different types of mucins in humans

Question 26

Mucin structure

Answer 26

Basic structure of mucin comprises a protein backbone ( 1 horizontal S )

Protein backbone is highly O-glycosylated ( vertical S’s )

O-Glycans hygroscopic (attracts and retain H2O)

D-domain that allows polymerisation with other mucins via disulfide bonds

Polymerisation via of mucin via disulfide bond (SS) allows formation of hydrated gel lattice