Three Laws of Thermodynamics and Metabolism related

1. The Conservation of Energy. The amount of energy in the universe is constant. Energy cannot be created or destroyed but may be converted from one form to another. 

The First Law applies to metabolism in the sense that energy is not free. For example, if the body needs to do a certain amount of work - let's say 5 kJ - the body needs to consume 5 kJ of chemical energy in the form of food to do the 5 kJ of work required. Any energy that is released by an exergonic reaction is absorbed by the surroundings. Conversely, any energy that is stored by an endergonic reaction causes a commensurate decrease in energy of the surroundings.

2. The Law of Entropy. The entropy in an isolated system increases with any changes that occur. All spontaneous events act to increase total entropy.

The Second Law of Thermodynamics is primarily concerned with whether or not a given process is possible. The Second Law states that no natural process can occur unless it is accompanied by an increase in the entropy of the universe.Stated differently, an isolated system will always tend to disorder. Living organisms are often mistakenly believed to defy the Second Law because they are able to increase their level of organization. To correct this misinterpretation, only must simply refer to the definition of systems and boundaries. A living organism is an open system, able to exchange both matter and energy with its environment. Take, for example, the assembly of a virus molecule from its subunits, which clearly involves an increase of order. If the virus is considered an isolated system, this process would be in defiance of the Second Law. However, a virus molecule interacts directly with its environment. The assembly of a virus molecule results in an increase of entropy in the system as a whole due to the liberation of water of solvation from the components and the resulting increase in rotational and translational entropy of the solvent.

3. Absolute Zero. Absolute zero is the temperature (-273°C) at which all thermal kinetic energy ceases. Nothing can be colder than absolute zero. 

Metabolism is unable to proceed at extremely low temperatures close to absolute zero because of the fact that all molecular motion ceases, making chemical reaction unable to occur. Also, enzymes are unable to function at extremely high and extremely low temperatures. 

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.