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Flashcards in Carbohydrates Deck (12):

What is glucose?

A monosaccharide which forms the building block for the polysaccharides.


What is the structure of a glucose?

The glucose monomers can exist in a linear form and so can be drawn out as a straight line of 6 carbons. Carbon 1 (1') is shown at the top. However, the chain form is really a C-shape due to the 3-D angles of chemical bonds. This brings the OH of 5' near to the oxygen of 1'.


What happens to the linear and ring forms in solution?

They are interchangeable and exist in an equilibrium. This equilibrium is heavily skewed to the ring form; for every one in a linear form, there are 4000 of the ring form. The ring form is a perspective view of the molecule with 2' and 3' coming towards you. If you look closely at the ring form diagrams you can see that a glucose molecule can take on two slightly different structures. If the OH group of Carbon 1 is below the ring then it is an alpha-glucose. If the OH group of Carbon 1 is above the ring then it is a beta-glucose.


Hoe are glucose monomers linked?

Enzyme catalysed reactions. These enzymes cause a a condensation reaction between the OH groups of Carbon 1 and Carbon 4 and so lead to the removal of a water molecule. The bond formed to link the glucoses is called a glycosidic bond.


What are monomers of alpha-glucose linked by?

Alpha-1,4-glycosidic bond.


What bod links beta-glucoses together?

Beta-1,4-glycosidic bond.


How is starch formed?

The excess glucose made during photosynthesis can be built up to form starch in plant cells for energy storage. Starch is made from thousands of alpha-glucose monomers; there are two forms of starch.


What is amylose?

Many glucose monomers joined by alpha-1,4-glycosidic bonds. This forms a long, linear molecule with no side branches. Because if the bond angles, amylose is actually twisted and forms a long branched helix.


What is amylopectin?

Long chains of alpha-1,4- linked glucoses but it also has side branches every 25-30 units. These branches are linked to the main chains by alpha-1,6-glycosidic bonds which are formed between carbon 1 and carbon 6.


What is glycogen made up from?

From thousands of alpha-glucose monomers and is made in animal cells for energy storage. Glycogen is similar in structure to amylopectin with glucose monomers in long chains of alpha-1,4 linked glucoses with an alpha-1,6 side branches. The branches are every 10-12 units and so there is higher degree of branching in glycogen than in amylopectin. Glucose units are removed from the ends of the chain when required. So, since there are more ends in glycogen, glucose can be released quicker from glycogen molecules than from amylopectin molecules.


Why do organisms build storage polysaccharides?

A high concentration of glucose tends to draw water into a cell by osmosis, leading to problems for the cell. The huge starch and glycogen molecules are insoluble; they do not affect osmosis and so osmotic problems are avoided.


What is cellulose?

Is the structural carbohydrate providing support and rigidity in plant cell walls; it is made from thousands of beta-glucose monomers joined by beta-1,4-glycosidic bonds. Every alternate glucose unit is inverted producing a rigid straight chain with no branches. Because of the inverted glucose units, hydrogen bonds form between cellulose chains. Groups of about 49 cellulose chains are aligned and cross-linked to form fibrils. Many fibrils, arranged in layers produce in cell walls.