Carbohydrates

Carbohydrates are an ideal source of energy for the body. This is because they can be converted more readily into glucose, the form of sugar that's transported and used by the body, than proteins or fats can.

Even so, a diet too high in carbohydrates can upset the delicate balance of your body's blood sugar level, resulting in fluctuations in energy and mood which leave you feeling irritated and tired.

It is better to balance your intake of carbohydrates with protein, a little fat and fibre.

- Monosaccharides: simple sugars with multiple OH groups. Based on # of carbons, a monosaccharide is a triose, tetrose, pentose, or hexose. 


- Disaccharide: 2 monosaccharides covalently linked. 


-Oligosaccharides: a few monosaccharides covalently linked. Polysaccharides:polymer consisting of chains of monosaccharide or disaccharide units.

- A monosaccharide can be a aldose (having an aldehyde group at one end) or a ketose (having a keto group, usually at C2)

- Pentoses and hexoses can form rings as ketone or aldehyde reacts with OH group.

- Special type of bond called glycosidic bond joins two carbohydrate molecules: (R-OH + HO-R' ---> R-O-R' + H₂O)

- Condensation (dehydration synthesis) reactions join together smaller sugar molecules to form larger, more complex sugar molecules by forming a glycosidic bond between the smaller sugar molecules resulting in the release of one water molecule per glycosidic bond formed as a product.

- Hydrolysis reactions split complex sugar molecules by adding a water molecule to each glycosidic bond, causing the bond to break and form hydroxyl groups on both product molecules.

- alpha linkage is shaped like "A" or "V", beta linkage is shaped like " / " or " \ "

- Common disaccharides include: maltose [glucose + glucose with a(1→4) glycosidic bond],lactose [galactose + glucose with B(1→4) bond], sucrose [glucose + fructose with a(1→2) bond]

- Plants store glucose in polymer form as amylose or amylopectin, collectively called starch. Glucose storage in polymer form minimizes osmotic effects.

- Amylose is a glucose polymer with a(1→4) linkages. It adopts a helical structure.

- The end of a polysaccharide with an anomeric C1 not involved in a glycosidic bond is called thereducing end.

- Amylopectin is a glucose polymer with mainly a(1→4) linkages, but also has branches formed by a(1→6) linkages. Branches produce a compact structure and provide multiple chain ends at which enzymatic cleavage can occur.

- Glycogen, the glucose storage polymer in animals, is similar to amylopectin, but it has morea(1→6) branches. The highly branched structure allows the rapid release of glucose. The ability to rapidly mobilize glucose is more important in animals than in plants (ex. during strenuous physical activity).

- Cellulose, the material in plant cell walls, consists of long linear chains of glucose with B(1→4) linkages. In cellulose, every other glucose is flipped over due to beta linkages. This promotes intra-chain and inter-chain H-bonds and Van der Waals interactions that cause cellulose chains to be straight and rigid, and pack with a crystalline arrangement in bundles called microfibrils.

- Multisubunit Cellulose Synthase complexes in the plasma membrane produce very strong microfibrils consisting of 36 parallel, interacting cellulose chains. Cellulose gives strength and rigidity to plant cell walls, making them able to withstand high hydrostatic pressure gradients and prevent osmotic swelling.

- Oligosaccharides are sugars that are often covalently attached to proteins or membrane lipids. May be linear or branched chains.

- Lectins are glycoproteins (proteins that contain oligosaccharide chains covalently bonded to polypeptide side chains) that recognize and bind to specific oligosaccharides.

- Selectins are proteins in the plasma membrane with lectin-like domains that protrude on the outer surface of mammalian cells. They are involved in cell-cell recognition and binding.