Carbohydrate structure and function

Question 1

Characteristics of carbohydrates?

Answer 1

Highly oxidizable

Function to store potential energy

Have structural and protective functions

Contribute to cell-cell communication

Question 2

Describe how carbs are highly oxidizable?

Answer 2

Sugar and starch molecules have “high energy” H atom-associated electrons

Thus they are a major energy source

Carbohydrate catabolism is the major metabolic process for most organisms

Question 3

Describe how carbs function to store potential energy?

Answer 3

Starch in plants

Glycogen in animals

Question 4

Describe how carbs have structural and protective functions ?

Answer 4

In plant cell walls

Extra cellular matrices of animal cells

Question 5

Describe how carbs contribute to cell-cell communication?

Answer 5

ABO blood groups

Question 6

What are the 3 important monosaccharides in human biochemistry? (hexoses -6C sugar)

Answer 6

glucose
galactose
fructose

Question 7

How are disaccharides formed?

Answer 7

Formed from monomers that are linked by glycosidic bonds

Covalent bond formed when hydroxyl group of one monosaccharide reacts with anomeric carbon of another monosaccharide

Question 8

What’s an anomeric carbon?

Answer 8

Different anomers are mirror images of each other (left- and right-handed forms)

It is carbon #1 on the glucose residue

It stabilises the structure of glucose

Is the only residue that can be oxidised

Question 9

What are the three important dissacharides in biochem?

Answer 9

Maltose
lactose
sucrose

Question 10

Characteristics of maltose?

Answer 10

Don’t have much directly from the diet

It is a break-down product of starch

It is in beer (from the starch of the barley)

Found in many baby foods as a “natural” sweetener

Anomeric C-1 is available for oxidation, so maltose can be oxidised (termed a reducing sugar)

Question 11

Characteristics of Lactose?

Answer 11

Main sugar in milk

It is formed from a glycosidic bond between galactose and glucose

Anomeric carbon on the glucose is available for oxidation so it is termed a reducing sugar

Question 12

Characteristics of Sucrose?

Answer 12

Common (table) sugar

Only made by plants

Approx. 25% of dietary carbohydrate

Sweetener in most processed food

Does not have a free anomeric C-1 so there is no oxidation site, hence sucrose is termed a non-reducing sugar

Question 13

Characteristics of amylose?

Answer 13

D-glucose residues in (α1→4) linkage (straight chained)

Can have thousands of glucose residues

Question 14

What are homopolysaccharides and heteropolysaccharides?

Answer 14

Homopolysaccharides
Single monomeric species
Heteropolysaccharides
Have two or more monomer species

Question 14

Characteristics of glycogen?

Answer 14

Animal cells use a similar strategy as plants to store glucose

Polymer of glucose (α1→4) linked sub-units with (α1→6) branches every 8 to 12 residues

This makes glycogen more extensively branched than starch

Question 15

Characteristics of Starch?

Answer 15

Contains two types of glucose polymer:
Amylose (20-25% of starch)
and
Amylopectin (75-80% of starch)

Question 15

Characteristics of amylopectin?

Answer 15

Similar structure as amylose but branched

Glycosidic (α1→4) bonds join glucose in the chains but branches are (α1→6) and occur every 24 – 30 residues

Question 16

Where is glycogen stored?

Answer 16

90% is in:
Liver (acts to replenish blood glucose when fasting
Skeletal muscle (catabolism produces ATP for contraction

Question 17

Glycogen structure?

Answer 17

highly branched
enzyme in middle

Question 18

Why store glucose in polymers?

Answer 18

Compactness

Amylopectin and glycogen have many non-reducing ends
This allows them to be readily synthesised and degraded to and from monomers respectively
Thus speeds up the formation or degradation

The polymers form hydrated gels and are not really “in solution”
This means they are osmotically inactive
If free glucose were in the cells then [Glc]inside > > [Glc]outside
Either Glc would move out of the cell down the concentration gradient
Or, the cell would use huge amounts of energy keeping it in the cell

Question 19

What are glycoproteins?

Answer 19

Proteins that have carbohydrates covalently attached
Most extracellular eukaryotic proteins have associated carbohydrate molecules
Carbohydrate content varies between 1-80% by mass

Question 20

What effect might carbohydrates attached to proteins have ?

Answer 20

Increases the proteins solubility
Influence protein folding and conformation
Protect it from degradation
Act as communication between cells

Question 21

What are Glycosaminoglycans (GAGs) ?

Answer 21

A protein
In the ‘olden days’ they were called mucopolysaccharides
Hints at their function – in mucus and also synovial fluid around the joints
Un-branched polymers made from repeating units of hexuronic acid and an amino-sugar, which alternate through the chains

Question 22

What are proteoglycans?

Answer 22

A protein
Carbohydrate > > protein
Formed from GAGs covalently attaching to proteins
They are macromolecules found on the surface of cells or in between cells in the extracellular matrix
Therefore form part of many connective tissues in the body

Question 23

What are glycoproteins?

Answer 23

Protein > > carbohydrate
Very similar to proteoglycans
Usually found on the outer plasma membrane and extra cellular matrix, but also in the blood and within cells in the secretory system (Golgi complex, secretory granules)
Some cytoplasmic and nuclear proteins are also glycoproteins

Question 24

What are Mucopolysaccharidoses?

Answer 24

Group of genetic disorders caused by the absence or malfunction of enzymes that are required for the breakdown of glycosaminoglycans

Question 25

How do the genetic disorders caused by Mucopolysaccharidoses come about?

Answer 25

Over time the glycosoaminoglycans build up in connective tissue, blood and other cells of the body
This build up damages cellular architecture and function

Question 26

What are the negative physical effects and syndromes of Mucopolysaccharidoses?

Answer 26

Can cause severe dementia, problems with the heart and any other endothelial structure as the glycosaminoglycans build up between the endothelial cells

Also, bones tend to be stunted and joints will be inflammed and become severely damaged

Hurler, Scheie, Hunter, Sanfilippo syndromes are all examples of mucopolysaccharidoses

Question 27

Describe characteristics of Hurler syndrome?

Answer 27

Severe developmental defects:
Stop developing at around 4 years
Death at around 10 years old

Clouding and degradation of the cornea

Arterial wall thickening

Dementia caused by, amongst other things:
Build up of CSF (Cerebral sinal fluid)
Enlarged ventricular spaces