Carbohydrates Flashcards
State the general formula of monosaccharides
(CH2O)n for monosaccs, Cx(H2O)y for carbohydrates in general
Three ways of classifying carbohydrates
1) Number of C atoms
2) Location of carbonyl group
3) Spatial arrangement
Two types of sugars according to location of carbonyl group
Ketose- ketone sugar with keto group(C=O/carbonyl grp nested within carbon skeleton)
Aldose- aldehyde sugar group with aldo group (carbonyl at beginning of carbon skeleton)
Differentiate between alpha and beta glucose
Alpha glucose has the OH group attached to C1 lying below the plane
Beta glucose has OH group attached to C1 lying above the plane.
Describe the characteristics and properties of monosaccharides, namely glucose
Monosaccharides are made up of a carbonyl group, multiple hydroxyl groups.
1) Soluble in water due to hydroxyl groups on exterior than can interact with water
2) Reducing sugars due to free carbonyl group that gives reducing ability
3) Pentose/hexose can exist as rings which are stable building blocks for larger molcs
4) Exhibit alpha beta isomerism, same chem formula gives rise to structurally diff molcs,
5) Increasing diversity of monosaccs which can become building blocks for diff molcs
Name the bond formed between 2 monosaccharides
Glycosidic bond C-O-C
Show how a glycosidic bond is formed between 2 monosaccharides
A covalent bond formed between two monosaccharides by condensation that involves loss of one water molecule
Describe how to carry our test for:
1) Reducing sugar
2) Non-reducing sugar
Add 2cm3 Benedict’s solution to 2cm3 test solution, place test tube in boiling water bath for
3min and observe colour change.
If no colour change, boil with hydrochloric acid for sugar to undergo acid hydrolysis, then
repeat.
Starch (Structure and its functions)
Starch is a storage polymer in plants, used to store surplus glucose which is used as a respiratory substrate for synthesis of energy in the form of adenosine triphosphate made up of amylose and amylopectin.
Both are made up of alpha glucose and are helical in structure. Amylose is unbranched, linked by alpha(1,4) glycosidic bonds, while amylopectin is branched and has (1,4) bonds within chains, (1,6) bonds at
branchpoints (every 20-30 glucose units).
Starch is 80% amylopectin, 20% amylose.
Glycogen (Structure and its functions)
Glycogen has a structure similar to amylopectin, except it is more extensively branched (every 12 bp) so that there are more ends for enzymes to work on at the same time, increasing rate of enzymatic action when it is broken down. Increase energy generation per unit time
- Many glucose residues
- Large energy store that can be hydrolysed ultimately to numerous monosaccs when req
- Helices: compact, pack many glucose subunits per unit volume.
- Projection of OH into core of formation, relatively fewer OH grps available for HH bonding with water, will not affect water potential of cell when in large amts
Cellulose (Structure and its functions)
Cellulose is a structural polysaccharide in plants. It is made up of beta glucose. It is a linear
Polymer with beta (1,4) glycosidic bonds, each alternate glucose unit is inverted 180 degrees
With respect to each other. Parallel to each other This forms straight chains which can pack closely and form hydrogen
Bonds with adjacent chains to form microfibrils. Criss-crossing of microfibrils creates a meshwork
With high tensile strength, which creates a bundling effect. Most OH groups are involved in
Intermolecular hydrogen bonding so they do not interact with water, not soluble.
Enzymes for digestion are Not commonly available in nature
Porous structure due to gaps between microfibrils, making it freely permeable to water
and solutes. Allows free movement of substances in and out of cells
Strong and rigid structure as meshwork distributes stress in all directions, protects
From physical damage/bursting from osmotic stress
Why is cellulose synthesised outside of the cell?
Macromolecule, too large, might damage organelle, cannot pass through cell membrane
Rosette structure of cellulose synthase allows for molecules to align next to each other for
intermolecular hydrogen bonding giving rise to microfibrils
Significance of monosaccharide molecular structure
1) Small in size
- many OH groups to form H-H with H2O
- readily soluble –> easy transport
2) Linear form
- free carbonyl group
- reducing ability
3) Pentoses and hexoses exist as rings –> stable building blocks
4) Rings exhibit alpha-beta isomerism so same chemical formula gives rise to structurally different molecules, increasing diversity of saccharides that can be formed.
