What are the structural and chemical reasons why bile salts don’t form typical micelles?

Although bile salts possess a polar head group, the hydrocarbon tail usually contains polar hydroxyl groups. Therefore the rigid ring system gives a tightly packed, almost solid, nonpolar phase rather than a liquid one. However, like cholesterol, bile salts can form mixed micelles with phospholipids.

Can cholesterol form micelles and bilayers?

Cholesterol does not form micelles because it is not sufficiently amphiphilic (even though it does have an OH group) and its flat, rigid, fused-ring structure gives a solid rather than a liquid hydrocarbon phase at physiological temperatures. Such fluidity is required for micelle formation. However, cholesterol can form mixed micelles with amphiphilic lipids, and it enters monolayers as well where it constitutes ∼25% of the mass of the lipid bilayer in the plasma membranes of mammalian cells.

What is the chemical basis of this reactivity? β-D-Glucose

Question

β-D-Glucose is the most prevalent monosaccharide in the bloodstream. It can react with many differentcompounds. What is the chemical basis of this reactivity?


Answer
Glucose is an aldehyde and hence is a reducing compound. The aldehyde group is reactive and can be reduced to form an alcohol, can be oxidized to form a carboxylic acid, or can react with many other compounds to form a glucosyl adduct with them.

What is the difference between a sugar and a carbohydrate?

Sugar is a term that is sometimes used incorrectly to refer to carbohydrates in general, because many carbohydrates have a sweet taste. But not all carbohydrates are sugars, e.g., starch. However, in common usage sugar usually refers specifically to sucrose, or perhaps to a few other simple carbohydrates such as fructose and glucose.

Is it strictly correct to call proline an amino acid?

No. The side chain of proline bends around and is covalently linked to the backbone nitrogen atom replacing one of the hydrogen atoms. Thus it is actually an imino acid.

Why is water such an important molecule in living systems?

The strength and specificity of interactions between biological molecules depend on the medium in which they reside. The major biological solvent is water, although fat deposits readily dissolve hydrophobic molecules such as some pesticides and various drugs. Because of the large electronegativity of oxygen relative to hydrogen, the oxygen atom attracts electrons from the two hydrogen atoms, making them more negative and leaving the hydrogen atoms with a net positive charge. Thus, water molecules are highly polarized, and they associate with one another through hydrogen bonds. The angle between the two O—H bonds in water is not 180Degree; hence the molecule is bent, and hydrogen bonds form in which each water molecule interacts with several neighbors in a three-dimensional network. Without these interactions, water with a molecular weight of 18 would be a gas at normal atmospheric temperatures and pressures, like dinitrogen of molecular weight 28.

What is inside a living cell?

The inside of a cell is crowded with molecules, and these are in continuous vigorous motion that is driven by thermal energy. In prokaryotic cells the cytoplasm is the only compartment; in most eukaryotic cells it is still the largest single compartment. The cytoplasm (also called the cytosol) is so crowded with small and large molecules that it is significantly more viscous than a typical aqueous solution encountered in laboratory experiments.
As molecules in random motion collide, they diffuse throughout the cell; large molecules diffuse more slowly than
small ones. It is the diffusion and collisions between molecules that enable biochemical reactions to occur.

What is the nature of the interactions between biomolecules?

Interactions between biomolecules depend on the forming and breaking of chemical bonds.
The covalent bond is the strongest chemical bond. It links individual atoms within a molecule and involves sharing of a pair of electrons between adjacent atoms. Its formation requires considerable energy, and its breakage releases this energy. The formation and breakage of covalent bonds are not readily reversible processes.
Noncovalent bonds are weaker and are often readily reversible. The four major ones differ in their length,strength, specificity, and response to water. Although noncovalent interactions are weaker than covalent bonds .

What types of molecules are the foundations of life?

There are four major classes of biomolecules that are synthesized by living systems: nucleic acids, proteins, lipids, and polysaccharides (carbohydrates). They are all polymers of simple building blocks sugar, phosphate, and a nitrogenous base for the nucleic acids; amino acids for proteins; glycerol and fatty acids for lipids; and simple sugars (monosaccharides) for polysaccharides. These can be combined in some specialized biomolecules such as carbohydrate and protein in glycoproteins; lipid and protein in lipoproteins; and carbohydrate and lipid in glycolipids.

All biomolecules are remarkably similar throughout the evolutionary or phylogenetic tree. Since living systems primarily exist within an aqueous environment, the unique structures and properties of biomolecules are determined by their reactions within this environment. The reactions between small molecules that take place in living systems depend on higher-order interactions between the larger biomolecules that modify the aqueous environment.