Biomolecules and Enzymes

• Structural proteins are the proteins that are generally fibrous and stringy. They are the most abundant class of proteins in nature. Their main function is to provide mechanical support. Examples of structural proteins can be keratin, collagen, fibrin and elastin.
  
• Albumin is a type of transport protein which help to transport the materials in the cells and form channels in the plasma membrane.
  

There are 20 amino acids found inside our body. The name of these 20 common amino acids is as follows: alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, and valine. They get combined in an unlimited number of configurations to construct all the required proteins with which our body is built.

Bacterial cell walls are composed of peptidoglycan (murein), not cellulose. Cellulose is found in plant cell walls.

Cellulose is a polysaccharide consisting of linear chain of numerous linked D-glucose units whereas proteins are formed of number of amino acids linked together by peptide linkage.

Prions are proteinaceous infectious agents that cause spongiform encephalopathies, such as Creutzfeldt-Jakob disease and bovine spongiform encephalopathy. Potato spindle tuber disease is caused by a viroid, which is a naked RNA molecule. Red rust of tea and white rust of crucifers are caused by algal and fungal pathogens, respectively.

Carbohydrates are the primary fuel used in cellular metabolism. Excess carbohydrates are stored as glycogen and fats. The fats are a very concentrated source of energy. One gram of fat provides 8.8 kcal of energy as against 4.2 kcal provided by one gram of carbohydrate.

Fats are energy dense, providing approximately 9 kcal/g (often cited as 9.3 kcal/g), whereas carbohydrates and proteins provide approximately 4 kcal/g.

In reductive amination, alpha-ketoglutaric acid reacts with ammonia and NADPH to form glutamate. Note: The option 'Glumate' is a typo for 'Glutamate'.

Nitrogen is essential for producing proteins (amino acids contain nitrogen) and nucleic acids (DNA/RNA nitrogenous bases). While carbon and oxygen are also crucial, nitrogen is specifically required for these macromolecules. Water is a solvent, not a building block.

Actin and myosin are muscle proteins, while rhodopsin is a photoreceptor protein. 

Enzymes are biocatalyst. These are proteinaceous substances that are capable of catalysing chemical reactions of biological systems without themselves undergoing any change. The term enzymes were first used by Kuhne in 1877.

The activity of an enzyme can be affected by a change in the conditions which can alter the tertiary structure of the protein. These include temperature, pH, change in substrate concentration or binding of specific chemicals that regulate its activity. Enzymes generally function in a narrow range of temperature and pH. Each enzyme shows its highest activity at a particular temperature and pH called the optimum temperature and optimum pH. Activity declines both below and above the optimum value. Low temperature preserves the enzyme in a temporarily inactive state whereas high temperature destroys enzymatic activity because proteins are denatured by heat. At boiling temperature all proteins including enzymes are denatured.

All proteins are not enzymes. Proteins are most versatile biochemicals fulfilling a diverse set of structural and functional roles. For example, haemoglobin, keratin, albumin, etc., are all proteins but are not enzymes. Similarly, all enzymes are not proteins. In fact, most of the enzymes, are proteinaceous in nature. But ribozymes are not proteins in nature, they are catalytic RNAs.

Enzymes are the specialized proteins which are capable of catalyzing reactions in the living cells.