Biology Chapter on Lipids and Carbohydrates

Bioprocess Fundamentals - CENV 2200

• Course instructor: Dr. Ali Al Jibouri, P.Eng.
• Office: SW01-1580
• Email: [email protected]

The Molecules of Life

• Organic molecules are the most important large molecules found in living things.
• These include carbohydrates, proteins, nucleic acids, and lipids.

Macromolecules

• Macromolecules are large molecules composed of thousands of covalently connected atoms.
• Most macromolecules are polymers.
• Polymers are long molecules consisting of many similar building blocks (monomers).

Polymers

• Monomers form larger molecules through condensation reactions called dehydration reactions.
• One molecule loses hydrogen, the other loses OH.
• Polymers are disassembled to monomers by hydrolysis.
• Hydrolysis is the reverse of dehydration reaction.

Polymers (continued)

• Each cell has thousands of different kinds of macromolecules.
• Macromolecules vary among cells of an organism, vary more within a species, and vary even more between species.
• An immense variety of polymers can be built from a small set of monomers.

Carbohydrates

• Carbohydrates include sugars and the polymers of sugars.
• Simple carbohydrates are monosaccharides.
• Monosaccharides are single sugars.
• Carbohydrate macromolecules are polysaccharides.
• Polysaccharides are polymers composed of many sugar building blocks.

Monosaccharides

• Monosaccharides have molecular formulas that are usually multiples of CH2O.
• Glucose is the most common monosaccharide.
• Monosaccharides are classified by the location of the carbonyl group and by the number of carbons in the carbon skeleton.
• Monosaccharides serve as a major fuel for cells and as raw material for building molecules.
• In aqueous solutions, monosaccharides form rings, the most stable form.

Disaccharides

• Disaccharides are formed when a dehydration reaction joins two monosaccharides.
• The covalent bond formed is called a glycosidic bond.
• Examples include: Lactose (glucose and galactose), Maltose (glucose and glucose), Sucrose (glucose and fructose).

Polysaccharides

• Polysaccharides, the polymers of sugars, have storage and structural roles.
• The structure and function of a polysaccharide are determined by its sugar monomers and the positions of the glycosidic linkages.

Storage Polysaccharides

• Starch is a storage polysaccharide of plants, consisting entirely of glucose monomers.
• Two types of starch are amylose and amylopectin.
• Plants store surplus starch as granules within chloroplasts and other plastids.
• Glycogen is a storage polysaccharide in animals.
• Humans and other vertebrates store glycogen in liver and muscle cells.

Structural Polysaccharides

• Cellulose is a major component of the tough wall of plant cells.
• Cellulose is a polymer of glucose, but the glycosidic linkages differ.
• The difference is based on two ring forms for glucose: alpha (a) and beta (β).
• Polymers with a-glucose are helical, while polymers with β-glucose are straight.
• In straight structures H atoms on one strand can bond with OH groups on other strands.
• Parallel cellulose molecules are grouped into microfibrils, strong building material for plants.
• Chitin is another structural polysaccharide found in the exoskeleton of arthropods and cell walls of many fungi.

Lipids

• Lipids are the only class of large biological molecules that do not form polymers.
• The unifying feature of lipids is having little or no affinity for water.
• Lipids are hydrophobic because they consist mostly of hydrocarbons which form nonpolar covalent bonds.
• The most biologically important lipids are fats, phospholipids, and steroids.

Fats

• Fats are constructed from glycerol and fatty acids.
• Glycerol is a three-carbon alcohol with a hydroxyl group attached to each carbon.
• A fatty acid consists of a carboxyl group attached to a long carbon skeleton.
• In a fat, three fatty acids are joined to glycerol by an ester linkage, creating a triacylglycerol, or triglyceride.
• Fatty acids vary in length (number of carbons) and in the number and locations of double bonds.
• Saturated fatty acids have the maximum number of hydrogen atoms possible and no double bonds.
• Unsaturated fatty acids have one or more double bonds.
• The major function of fats is energy storage.

Phospholipids

• In a phospholipid, two fatty acids and a phosphate group are attached to glycerol.
• The two fatty acid tails are hydrophobic, but the phosphate group and its attachments form a hydrophilic head.
• When phospholipids are added to water, they self-assemble into a bilayer.
• The structure of phospholipids results in a bilayer arrangement found in cell membranes.
• Phospholipids are the major component of all cell membranes.

Steroids

• Steroids are lipids characterized by a carbon skeleton consisting of four fused rings.
• Cholesterol, an important steroid, is a component in animal cell membranes.

Proteins

• Proteins account for more than 50% of the dry mass of most cells.
• Protein functions include structural support, storage, transport, cellular communications, movement, and defense against foreign substances.
• Proteins consist of a backbone of an amino group (-NH2) and a carboxyl group (-C(=O)OH).
• Twenty different amino acids are involved in the structure of a variety of proteins which have various functions.

Polypeptides

• Polypeptides are polymers of amino acids.
• A protein is a biologically functional molecule composed of one or more polypeptides.
• Amino acids are linked by peptide bonds.

Amino Acid Monomers

• An amino acid is an organic molecule with both an amino group and a carboxyl group.
• Amino acids differ in their properties due to differing side chains (R groups).
• Proteins are constructed from the same set of 20 amino acids, linked in unbranched polymers.

Protein Structure and Function

• A functional protein consists of one or more polypeptides twisted, folded, and coiled into a unique shape.
• The sequence of amino acids determines a protein's three-dimensional conformation.
• A protein's conformation determines its function.
• Ribbon models and space-filling models can depict a protein's conformation.

Protein Structure - Primary

• The amino acid sequence in a protein.
• Determined by inherited genetic information

Protein Structure - Secondary

• Coils and folds found in most proteins
• Result from hydrogen bonds between repeating constituents of polypeptide backbone.
• Include a-helix and ẞ pleated sheet.

Protein Structure - Tertiary

• Overall shape of a polypeptide, resulting from interactions between side chains (R groups) of various amino acids.
• Includes hydrogen bonds, ionic bonds, hydrophobic interactions, and disulfide linkages.

Protein Structure - Quaternary

• Results when a protein consists of multiple polypeptide chains.

Protein Folding

• It is hard to predict a protein's conformation from its primary structure.
• Most proteins probably go through several states on their way to a stable conformation.
• Chaperonins are protein molecules that assist the proper folding of other proteins.

Protein Denaturation

• Denaturation is loss of conformation which occurs in protein structure due to physical or chemical conditions (pH, salt concentration, temperature).
• Denatured proteins are biologically inactive.

Nucleic Acids

• Nucleic acids are polymers called polynucleotides.
• Each polynucleotide is made of monomers called nucleotides.
• Each nucleotide consists of a nitrogenous base, a pentose sugar, and a phosphate group.
• DNA provides directions for its own replication.
• DNA directs synthesis of messenger RNA (mRNA) in which mRNA controls protein synthesis.
• Protein synthesis occurs in ribosomes.

DNA double helix

• A DNA molecule has two polynucleotides spiralling around an imaginary axis, forming a double helix.
• In the DNA double helix, the two backbones run in opposite 5' to 3' directions, antiparallel.
• One DNA molecule includes many genes.
• The nitrogenous bases in DNA form hydrogen bonds in a complementary fashion. A always with T, and G always with C