A polymer is a large molecule consisting of many identical or similar subunits (monomers) strung together.

Polymers are often created by linking monomers together by condensation reactions (i.e. a dehydration process). A condensation reaction makes a larger molecule out of two smaller molecules by extracting water. If a large molecule is broken down into two smaller molecules the process is called hydrolysis.

Glucose + Glucose à Maltose + Water

The above reaction is a condensation reaction. The reverse reaction (shown below) is a hydrolysis reaction.

Maltose + Water à Glucose + Glucose

If many monosaccharides are joined together by glycosidic linkages we get polysaccharides.

Plants produce starch, animals produce glycogen as storage polysaccharides.

The most abundant organic compound is a structural polysaccharide produced by plants called cellulose. Cellulose may be an isomer of starch. It differs in that the hydroxyl and hydrogen groups on carbon #1 have their orientations reversed. In starch, the hydroxyl is oriented downward in the figure and the hydrogen upward (this is the alpha configuration). In cellulose, the hydroxyl is oriented upward and the hydrogen downward (the beta configuration). Cellulose is indigestible by animals, but starch is regularly part of animal’s diets.

LIPIDS

Lipids are hydrophobic, they includes fats, phospholipids and steroids.

Fats are composed of glycerol and fatty acids. Fatty acids are made of a long chain of carbons (usually 16-18) terminating in a carboxyl group.

There are three positions in glycerol where fatty acids may bind by condensation reactions (ester linkages between hydroxyl and carboxyl groups).

If any fatty acids have C=C then it is an unsaturated fat, and is liquid at room temperature. Otherwise it is saturated and solid at room temperature.

Fats are used as energy storage molecules in animals because for the same weight they can store twice as much energy than carbohydrates or proteins.

Phospholipids have 2 fatty acids bound to glycerol. On the third position on glycerol it is bound to a phosphate group that itself may bind to different small polar groups. Therefore the phospholipids are part polar and part nonpolar. They are said to be amphipathic.

Steroids are small lipids that are found in cell membranes and may function as hormones. Cholesterol is an example of a steroid that plays a significant role in our cell membranes.

Polypeptide chains are sequences of amino acids bound together by peptide bonds. There are 20 different amino acids that are used in biological proteins. All amino acids have the following general structure.

A protein consists of one or more polypeptide chains twisted, wound and folded upon themselves to form a macromolecule with a definite 3-dimensional shape or confirmation. The proteins shape is influential to its function. Sometimes the folding of proteins is assisted by other proteins called chaperones that prevent the developing protein from folding incorrectly.

We describe the confirmation of a protein at different levels.

The primary structure is the unique sequence of amino acids along its length. The primary structure is established by the peptide bonding of amino acids. If amino acids were randomly bonded together there would be a very low probability that a functional protein would arise. Instead the primary structure of a protein is established by translating the message contained in an organism’s genetic blueprint.

The secondary structure forms due to hydrogen bond formation between functional groups that repeat at regular intervals along the polypeptide backbone. Examples are alpha helices and beta pleated sheets.

The tertiary structure represents irregular contortions of the protein formed due to bonding between the unique side chains of the various amino acids. The bonds may be due to weak interactions (hydrogen bonds or hydrophobic interactions) or strong covalent disulphide bridges between cysteine amino acids.

Quaternary structure emerges from bonding between 2 or more polypeptide chains.

NUCLEIC ACIDS

There are two types of nucleic acids: deoxyribonucleic acids (DNA ) and ribonucleic acids (RNA ). DNA is the genetic blueprint that is transmitted from one generation to another.

Nucleic acids are polymers of monomers called nucleotides. A nucleotide is composed of a nitrogenous base, 5 carbon sugar and phosphate group. In RNA the sugar is ribose, in DNA it is deoxyribose. The bases are pyrimidines or purines.

Remember: CUT PY

Cytosine, Uracil and Thymine are pyrimidines. The others are purines.