Carbohydrates 1 Flashcards
Carbohydrates are highly oxidizable. What does this mean?
The sugar and starch molecules have ‘high energy’ H atom associated electron. Thus they are a major energy source. Carbohydrate catabolism is the major metabolic process for most organisms.
What is the function of carbohydrates?
To store potential energy. Stored as starch in plants and glycogen in animals.
Where do carbohydrates exhibit structural and protective functions?
In plant cell walls and in the extracellular matrices of animal cells.
How do carbohydrates contribute to cell - cell communication?
Via ABO blood groups
Monosaccharides: What are the 3 important hexoses in human biochemistry?
Glucose (Glc)
Galactose (Gal)
Fructose (Fru)
How are disaccharides formed?
Formed from monomers that are linked by glycosidic bonds. Covalent bond formed when the hydroxyl group of one monosaccharide reacts with anomeric carbon of another monosaccharide.
What’s an anomeric carbon?
It is the carbon numbered one in a glucose residue. It stabilises the structure of glucose and is the only residue that can be oxidised.
What are the 3 important disaccharides in human biochemistry?
Maltose
Lactose
Sucrose
What is maltose and where is it found?
It is the break down product of starch. Maltose can be found in beer and in many baby foods.
Why can maltose be classed as a reducing sugar?
Maltose can be oxidised as the anomeric carbon one is available for oxidation.
How is lactose formed?
Formed from a glycosidic bond between galactose and glucose.
Why can lactose be classed as a reducing sugar?
Anomeric carbon on the glucose is available for oxidation.
What is sucrose and how is it made?
Sucrose (common table sugar) makes up approx. 25% of dietary carbohydrate and is only made by plants.
Why is sucrose a non-reducing sugar?
It doesn’t have a free anomeric carbon so there is no oxidation site.
What are polysaccharides?
Polymers of medium to high molecular weight.
How are polysaccharides distinguished from each other?
In the identity of their recurring monomer units.
The length of their chains.
The types of bonds linking monosaccharide units.
The amount of branching they exhibit.
What is a homopolysaccharide?
A single monomeric species.
What is a heteropolysaccharide?
Have two or more monomer species
What does starch contain?
It contains two type of glucose polymer: amylose and amylopectin
What is amylose?
Makes up 20-25% of starch.
D-glucose residues in (a1-4) linkage.
Can have thousands of glucose residues.
What is amylopectin?
Makes up 75-80% of starch.
Similar structure as amylose but branched.
Glycosidic (a1-4) bonds join glucose in the chains but branches are (a1-6) and occur every 24-30 residues.
How is starch arranged?
Has many non-reducing ends and very few reducing ends.
Amylose and amylopectin are believed to form alpha helices.
Why is glycogen more extensively branched than starch?
Polymer of glucose linked sub-units with (a1-6) branches every 8 to 12 units. This makes glycogen more extensively branched than starch.
Where is 90% of glycogen found?
Liver (acts to replenish blood glucose when fasting) Skeletal muscle (catabolism produces ATP for contraction)
