FATTY  ACIDS

Fatty acids consist of a hydrocarbon chain with a carboxylic acid at one end.

• are usually in esterified form as major components of other lipids

• are often complexed in triacylglycerols (TAGs)

• most have an even number of carbon atoms (usually 14 to 24)

• are synthesized by concatenation of C2 units.

• C16 & C18 FAs are the most common FAs in higher plants and animals

• Are either:

—saturated (all C-C bonds are single bonds) or

—unsaturated (with one or more double bonds in the chain)

—monounsaturated (a single double bond)

1.Example of monounsaturated FA: Oleic acid 18:1(9) (the number in unsaturated FA parentheses indicates that the double bond is between carbons 9 & 10)

2. Double bonds are almost all in the cis conformation

—polyunsaturated (more then one double bond)

Polyunsaturated fatty acids contain 2 or more double bonds. They usually occur at every third carbon atom towards the methyl terminus (-CH3 ) of the molecule. Example of polyunsaturated FA: Linoleic acid 18:2(9,12)

• the number of double bonds in FAs varies from 1 to 4 (usually), but in most bacteria it is rarely more than 1

Saturated FAs are highly flexible molecules that can assume a wide range of conformations because there is relatively free rotation about their C-C bonds.

BIOLOGICAL BUFFER SYSTEMS 

Cells and organisms maintain a specific and constant cytosolic pH, keeping biomolecules in their optimal ionic state, usually near pH 7. In multicelled organisms, the pH of the extracellular fluids (blood, for example) is also tightly regulated. Constancy of pH is achieved primarily by biological buffers : mixtures of weak acids and their conjugate bases 

Body fluids and their principal buffers

Body fluids                     Principal buffers

Extracellular fluids        {Biocarbonate buffer Protein buffer } 

Intracellular fluids         {Phosphate buffer, Protein }

Erythrocytes                 {Hemoglobin buffer}

3-D Structure of proteins

Proteins are the main players in the life of a cell. Each protein is a unique sequence of amino acid residues, each of which folds into a unique, stable, three dimentional structure that is biologically functional.

Conformation = spatial arrangement of atoms that depends on rotation of bonds. Can change without breaking covalent bonds.

• Since each residue has a number of possible conformations, and there are many residues in a protein, the number of possible conformations for a protein is enormous.

Native conformation = single, stable shape a protein assumes under physiological conditions.

• In native conformation, rotation around covalent bonds in polypeptide is constrained by a number of factors ( H-bonding, weak interactions, steric interference)
• Biological function of proteins depends completely on its conformation. In biology, shape is everything.
• Proteins can be classified as globular or fibrous.

There are 4 levels of protein structure

• Primary structure
  • linear sequence of amino acids
  • held by covalent forces
  • primary structure determines all oversall shape of folded polypeptides (i.e primary structure determines secondary , tertiary, and quaternary structures)
• Secondary structure
  • regions of regularly repeating conformations of the peptide chain (α helices, β sheets)
  • maintained by H-bonds between amide hydrogens and carbonyl oxygens of peptide backbone.
• Tertiary structure
  • completely folded and compacted polypeptide chain.
  • stabilized by interactions of sidechains of non-neighboring amino acid residues (fibrous proteins lack tertiary structure)
• Quaternary structure
  • association of two or more polypeptide chains into a multisubunit protein.

Glycogen Storage Diseases are genetic enzyme deficiencies associated with excessive glycogen accumulation within cells.

• When an enzyme defect affects mainly glycogen storage in liver, a common symptom is hypoglycemia (low blood glucose), relating to impaired mobilization of glucose for release to the blood during fasting.
• When the defect is in muscle tissue, weakness and difficulty with exercise result from inability to increase glucose entry into Glycolysis during exercise.

Various type of Glycogen storage disease are

BIOLOGICAL ROLES OF LIPID

Lipids have the common property of being relatively insoluble in water and soluble in nonpolar solvents such as ether and chloroform. They are important dietary constituents not only because of their high energy value but also because of the fat-soluble vitamins and the essential fatty acids contained in the fat of natural foods

Nonpolar lipids act as electrical insulators, allowing rapid propagation of depolarization waves along myelinated nerves

Combinations of lipid and protein (lipoproteins) are important cellular constituents, occurring both in the cell membrane and in the mitochondria, and serving also as the means of transporting lipids in the blood.

The Phosphate Buffer System

This system, which acts in the cytoplasm of all cells, consists of H₂PO₄^–  as proton donor and HPO₄ ^2– as proton acceptor :

H₂PO₄^–  = H⁺ + H₂PO₄^–

The phosphate buffer system works exactly like the acetate buffer system, except for the pH range in which it functions. The phosphate buffer system is maximally effective at a pH close to its pKa of 6.86 and thus tends to resist pH changes in the range between 6.4 and 7.4. It is, therefore, effective in providing buffering power in intracellular fluids.