Flashcards in Carbohydrates 1 Deck (39):
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?
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?
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)
Why is glucose stored in polymers?
What do the many non-reducing ends of amylopectin and glycogen allow them to do?
Allows them to be readily synthesised and degraded to and from monomers respectively. Thus speeds up the formation or degradation.
Polymers form hydrated gels and are not really in solution. What does this mean?
This means they are osmotically inactive. If free glucose were in the cells then [Glc]inside >>[Glc]outside. Either the glucose would move out of the cell down the concentration gradient, or, the cell would use huge amounts of energy keeping it in the cell.
What are glycoproteins?
Proteins that have carbohydrates covalently attached
Most extracellular eukaryotic proteins have associated carbohydrate molecules.
What may carbohydrate attached to proteins do?
Increases the protein solubility.
Influence protein folding and conformation
Protect it from degradation
Act as communication between cells.
What are glycosaminoglycan (GAGs)?
GAGs (mucopolysaccharides) are unbranched polymers made from repeating units of hexuronic acid and an amino-sugar which alternate through the chains. GAGs are found in mucus and also in synovial fluid around the joints.
What are proteoglycans?
Proteoglycans are macromolecules found on the surface of cells or in between cells in the extracellular matrix. Therefore the form part of many connective tissues in the body.
How are proteoglycans formed?
They are formed from GAGs covalently attaching to proteins
Where are glycoproteins found?
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)
What are mucopolysaccharidoses?
Group of genetic disorders caused b the absence or malfunction of enzymes that are required for the breakdown of glycosaminoglycans.
What happens if glycosaminoglycans build up in the connective tissue, blood or other body cells?
Build up of glycosaminoglycans damages cellular architecture and function. This 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 inflamed and become severely damaged.
What are 4 examples of mucopolysaccharidoses?
What is the prognosis of Hurler syndrome?
Development stops at around 4 and death at around 10 years old.
What are the symptoms of Hurler syndrome?
Clouding and degradation of the cornea.
Arterial wall thickening.
Dementia caused by a build of CSF and enlarged ventricular spaces.