Question

1. (a) Use diagrams to show the shape and structural difference between a membrane lipid molecule and a detergent molecule? (b) How would the structure of a membrane lipid molecule have to change to make it a detergent? (

Answer 1

please find the answer their is some technical problem so digram is not post ,so i give only explaination

Detergent

Detergents are amphipathic molecules, consisting of a polar head group and a hydrophobic chain (or tail), and exhibit unique properties in aqueous solutions in which they spontaneously form (generally) spherical micellar structures. Membrane proteins are frequently soluble in micelles formed by amphiphillic detergents. Detergents solubilize membrane proteins by creating a mimic of the natural lipid bilayer environment normally inhabited by the protein

Detergents are classified according to their structure and fall into four major categories

• Ionic detergents contain a head group with a net charge that can be either cationic oranionic They also contain a hydrophobic hydrocarbon chain or steroidal backbone. The critical micelle concentration (cmc) of an ionic detergent is determined by the combined effect of the head group repulsive forces and the hydrophobic interactions of the tails. Ionic detergents, such as sodium dodecyl sulfate (SDS), are extremely effective in the solubilization of membrane proteins but are almost always denaturing to some extent.
• Nonionic detergents Contain uncharged hydrophilic head groups of either polyoxyethylene or glycosidic groups . Nonionic detergents are generally considered to be mild and relatively non-denaturing, as they break lipid–lipid interactions and lipid–protein interactions rather than protein–protein interactions. This allows many membrane proteins to be solubilized in nonionic detergents without affecting the protein's structural features, such that it can be isolated in its biologically active form..
• Other alkylglucosides, such as n-dodecyl-β-d-maltoside (DDM), are increasingly used in membrane protein solubilization as many proteins can be readily solubilized in a functional state in DDM but with retention of functional properties

·   Zwitterionic detergents combine the properties of ionic and nonionic detergents and are in general more deactivating than nonionic detergents. They have, however, found uses in structural studies of membrane proteins

Mechanism at molecular level

The cmc can be defined as the minimum concentration of detergent for individual detergent molecules to cluster and form micelles, such that there is a sudden change in surface tension and other physical properties. Above the cmc the detergent monomer concentration is also independent of the total detergent concentration. The cmc varies with conditions, including pH, ionic strength, temperature as well as the presence of protein, lipid and other detergent molecules . The cmc decreases with the length of the alkyl chain of the detergent and increases on the introduction of double bonds and branch points

At low temperatures, detergents remain mainly in a crystalline insoluble form that is in equilibrium with small amounts of solubilized monomers. As the temperature is increased, more monomer dissolves until the cmc is reached; this is known as the critical micellar temperature (cmt). The temperature at which the crystalline form, monomer and micelles exist in equilibrium is known as the Kraft Point. In most cases, this will be equal to the cmt.

LIPID

Fats, oils, waxes, and sterols are collectively known as lipids. Like the carbohydrates, the true fats contain only carbon, hydrogen, and oxygen. The molecules of such a lipid are made up of a glycerol molecule with three fatty acid molecules attached to it.

Fats make up the largest category of lipids, and also go by the terms triacylglycerols, triglycerides, and glycerolipids.

There are several types of fats.

• Saturated fat- Saturated fat is a lipid that exists as a solid substance when it is at room temperature. Milk, cheese, meat, and other animal foods contain saturated fat.
• Unsaturated fat-An unsaturated fat is a fat or fatty acid in which there is at least one double bond within the fatty acid chain. A fatty acid chain is monounsaturated if it contains one double bond, and polyunsaturated if it contains more than one double bond.

Mechanism at Molecular level

The structure of the lipid bilayer explains its function as a barrier. Lipids are fats, like oil, that are insoluble in water because of its long hydrophobic tails. The hydrophobic interactions among several phospholipids and glycolipids, a certain structure called lipid bilayer or bimolecular sheet is favored. Phospholipids and glycolipids have both hydrophilic and hydrophobic moieties (amphiphilic or amphipathic). Thus, when several phospholipids or glycolipids come together in an aqueous solution, the hydrophobic tails interact with each other to form a hydrophobic center, while the hydrophilic heads interact with each other by forming a hydrophilic coating on each side of the bilayer point radically towards the polar solvent.

This lipid bilayer formation is spontaneous since the hydrophobic interactions are energetically favorable to the structure. The lipid bilayer is a noncovalent assembly. The proteins and lipid molecules are held together by noncovalent interactions such as Van der Waals forces (which holds the hydrophobic tails together) and hydrogen bonding (which binds the hydrophilic heads with water), which help to stabilize the lipid bilayer structure.

Proteins are embedded in the biological lipid bilayer membrane. The mass ratio of the lipid molecules and the proteins that are embedded in them ranges from 1:4 to 4:1.

Two types of proteins exist in the lipid bilayer: integral and peripheral membrane proteins. Integral membrane proteins traverse the lipid bilayer. That is, they interact extensively with the hydrophobic region (hydrocarbon region) of the lipid bilayer. Integral membrane proteins interact by nonpolar interactions. Peripheral membrane proteins are usually attached to surfaces of integral proteins; therefore, they are on both faces of lipid bilayer. Peripheral membrane proteins interact with the hydrophilic polar head groups of the lipid molecule. Peripheral proteins bind through electrostatic and hydrogen bonds with the head group of the lipid. They usually bind to integral proteins on the cytoplasmic or extracellular side. However, they can also be covalently attached to the bilayer by a hydrophobic chain

How would the structure of a membrane lipid molecule have to change to make it a detergent?

A micelle is an aggregate or supramolecular assembly of surfactant molecules dispersed in a liquid colloid. A typical micelle in aqueous solution forms an aggregate with the hydrophilic "head" regions in contact with surrounding solvent, sequestering the hydrophobic single-tail regions in the micelle centre. This phase is caused by the packing behavior of single-tail lipids in a bilayer

The existence of “colloidal ions” to explain the good electrolytic conductivity of sodium palmitate solutions. These highly mobile, spontaneously formed clusters came to be called micelles, which help in formation of detergent .