BIOCHEM LEC Flashcards
What is Carbohydrates?
Providing energy and regulation of blood glucose. 》Carbohydrates are the most abundant type of biomolecules on earth in terms of biomass.
》Their biological role spans from the stabilization of protein structure to their involvement in crucial biological events such as the development, growth or survival of a cell/organism.
》Protein-carbohydrate interactions are involved in intracellular trafficking of proteins, cell adhesion, cell recognition, cell differentiation and the development of the neuronal network.
》They are also involved in pathological events such as inflammation, metastasis and host-pathogen interactions
What are the 6 major functions of Carbohydrates in the Body?
●Sparing the use of proteins for energy
● Breakdown of fatty acids and preventing ketosis
● Biological recognition processes
● Flavor and Sweeteners
● Dietary fiber
Carbohydrates
play the role of a marker, identifier, a site for recognition and attachment during cell-cell recognition.
Carbohydrates
found on the plasma membrane of plants and animals. are usually attached to proteins and lipids to form glycoproteins
Several viruses, bacteria and parasites have exploited the presence of cell surface oligosaccharides using them to enter into the cells.
For example:
- Rhinoviruses attach to ICAM-1 (intercellular adhesion molecule-1)
- Parvoviruses attach to the erythrocyte- specific cell surface P-antigen
- Influenza virus and Plasmodium falciparum (protozoan causing malaria) use glycophorin (the MN blood group system) to enter the erythrocytes
- Herpesvirus type I enter the cells via FGFR (fibroblast growth factor receptor)
- Bacteria adhere to tissues selectively due to their fimbriae ( containing lectins) which bind exclusively to certain surface carbohydrates
Adhesion carbohydrates: Embryonic development.
As the fertilized egg divides, the carbohydrates on resulting embryonic cells change in characteristic ways. For example a trisaccharide LeX appears at the 8 to 16 cell stage when the embryo compacts from a group of loose cells into a smooth ball. LeX trisaccharide plays an important role in compaction.
Glycoproteins surrounding the egg (forming zona pellucida) prevent the polyspermy.
Carbohydrates
means “hydrate of carbon”
- the most abundant organic compounds in the plant world; the storehouses of chemical energy (glucose, starch, glycogen)
- are polyhydroxyaldehydes or polyhydroxyketones, or substances that on hydrolysis, yield these compounds
- components of supportive structures in plants (cellulose), crustacean shells (chitin), and connective tissues in animals (acidic polysaccharides)
- are essential components of nucleic acids (D-ribose and 2-deoxy-D-ribose)
- account for approximately ¾ of the dry weight of plants
- animals do not store much of what they consume. In fact, less than 1% of the body weight of animals is made up of carbohydrates
Monosaccharide
A carbohydrate that cannot be hydrolyzed to a simpler carbohydrate. Monosaccharides have the general formula C_{n} H_{2 n} O_{n} where n varies from 3 to 8.
Aldose
A monosaccharide containing an aldehyde group.
Ketose
A monosaccharide containing a ketone group.
Triose
A monosaccharide with three carbon atoms.
Tetrose
A monosaccharide with four carbon atoms.
Pentose
A monosaccharide with five carbon atoms.
Hexose
A monosaccharide with six carbon atoms.
Heptose
A monosaccharide with seven carbon atoms.
Dissacharide
A carbohydrate formed by the joining of two monosaccharides.
Oligosaccharide
A carbohydrate composed of 3-10 monosaccharide units.
Polysaccharide
A carbohydrate composed of a large number of monosaccharide units linked together.
Homopolysaccharide
A polysaccharide composed of a single type of monosaccharide.
Heteropolysaccharide
A polysaccharide composed of two or more different types of monosaccharides.
Stereoisomers
Molecules with the same chemical formula but different spatial arrangements of their atoms.
Enantiomers
Pairs of non-identical molecules that are non-superimposable mirror images of each other and that have at least 1 chiral carbon or chiral center, making them chiral compounds.
Chiral Center
An atom with 3 or more different attachments; interchanging of 2 of these attachments leads to another stereoisomer.
Fischer Projection
A two-dimensional representation for showing the configuration of tetrahedral stereocenters.
D-Monosaccharide
A monosaccharide where the -OH on its penultimate (next to last) carbon is on the right in a Fischer projection.
L-Monosaccharide
A monosaccharide where the -OH on its penultimate carbon is on the left in a Fischer projection.
Haworth Projection
A planar representation of a cyclic monosaccharide, where the ring is shown as a flat hexagon or pentagon.
Pyranose
A six-membered cyclic hemiacetal ring.
Furanose
A five-membered cyclic hemiacetal ring.
Anomeric Carbon
The new stereocenter created in forming the cyclic structure.
Anomers
Stereoisomers that differ in configuration only at the anomeric carbon.
Alpha Anomer
The anomer where the -OH on the anomeric carbon is on the side of the ring opposite from the terminal -CH2OH.
Beta Anomer
The anomer where the -OH on the anomeric carbon is on the same side of the ring as the terminal -CH2OH.
Chair confrontation
A more accurate representation of a six-membered ring than the Haworth projection, where the ring is depicted in a three-dimensional, chair-like shape.
Reducing Sugars
Monosaccharides that have a free carbonyl group (aldehyde or ketone) are called reducing sugars. These sugars can be oxidized by mild oxidizing agents.
Non-reducing Sugars
Monosaccharides that do not have a free carbonyl group are called non-reducing sugars. They cannot be oxidized by mild oxidizing agents.
Cyclization
Monosaccharides, particularly hexoses, can cyclize to form cyclic structures, such as pyranose or furanose rings.
Biological Functions of Carbohydrates
- Energy Source: Carbohydrates are the primary source of energy for living organisms.
- Regulation of Blood Glucose: Carbohydrates play a crucial role in maintaining stable blood sugar levels.
- Sparing Protein Use: Carbohydrates spare the use of proteins for energy, allowing them to perform their essential structural and functional roles.
- Preventing Ketosis: Carbohydrates help prevent ketosis, a metabolic state characterized by an excess of ketone bodies in the blood.
- Biological Recognition Processes: Carbohydrates are involved in cell-cell recognition, immune responses, and other crucial biological processes.
- Flavor and Sweeteners: Carbohydrates contribute to the taste and sweetness of many foods.
- Dietary Fiber: Carbohydrates, in the form of dietary fiber, promote digestive health and regularity.
Examples of Carbohydrates
- Glucose: Blood sugar or dextrose.
- Fructose: Fruit sugar.
- Galactose: Milk sugar.
- Lactose: Milk sugar: glucose + galactose
- Maltose: Malt sugar: glucose + glucose
- Sucrose: Table sugar: glucose + fructose
Starch
A storage polysaccharide in plants, composed of amylose and amylopectin.
Glycogen
A storage polysaccharide in animals, similar to starch.
Cellulose
A structural polysaccharide found in plant cell walls, providing rigidity and support.
