Campbell Biology: Concepts & Connections, Chapter 3 -  Carbohydrates, Lipids, Proteins, and Nucleic Acids. 

Distinguish between Inorganic and organic compounds 

• Organic compounds are based on carbon and are found in living things.
• There are a number of exceptions including hydrogen carbonate (HCO3-), carbon dioxide (CO2 ), and Carbon monoxide (CO).
• Inorganic compounds are by default are all the molecules other than those in the category.

Carbohydrates 

• Carbohydrates are a family of organic molecules made up of carbon, hydrogen, and oxygen atoms. Some are small, simple molecules, while others form long polymers.
• Carbohydrates have the general formula (CH2O)x.
• Simple carbohydrates are generally called sugars. The most common arrangements found in sugars are:
• Pentose, a five-sided sugar,
• e.g. ribose and deoxyribose.
• Hexose, a six-sided sugar. 
• Carbohydrates are important as both energy storage molecules and as the structural elements in cells and tissues.
• The structure of carbohydrates is closely related to their functional properties.
• Sugars (mono-, di-, and trisaccharides) play a central role in energy storage.

Monosaccharides

• Monosaccharides are used as a primary energy source for fueling cellular metabolism.
• Monosaccharides are single-sugar molecules. They include:
• glucose (grape sugar and blood sugar).
• fructose (honey and fruit juices).
• Monosaccharides generally contain between three and seven carbon atoms in their carbon chains.
• The 6C hexose sugars occur

Glucose 

• Hexose sugar (six carbons) is most commonly found in this ring structure
• Product of photosynthesis and substrate molecule for respiration
• Glucose is also found in a polymer form of starch, glycogen, and cellulose.
• All bonds are covalent.

Ribose

• Pentose (5 carbon sugar).
• Ribose is part of one of the important organic molecules in photosynthesis, ribulose bisphosphate. (RUBP)
• Found in RNA
• A modified version of ribose, deoxyribose is found in DNA
• Both Ribose and Glucose will attract water molecules (hydrogen bonding ) when in solution.

Disaccharides 

• Disaccharides are double-sugar molecules joined with a glycosidic bond.
• They are used as energy sources and as building blocks for larger molecules.
• Disaccharides provide a convenient way to transport glucose.
• The type of disaccharide formed depends on the monomers (single units)involved and whether they are in their α- or β- form.

Sucrose

• Components: α-glucose + β-fructose
• Source: A simple sugar found in the plant sap.
• 
  
• Maltose
• Components: α-glucose + α-glucose
• Source: Maltose is a product of starch hydrolysis and is found in germinating grains.

Carbohydrate Isomers 

1. Compounds with the same chemical formula can have different arrangements of atoms.
2. These molecules are called isomers.
3. Structural isomers have the atoms linked in a different sequence from one another.
4. Despite the relatively small differences,  structural isomerism can have important consequences for the polymers that result.

For example:

• α glucose polymers form starch.
• β glucose polymers form cellulose.
• These molecules have very different

Polysaccharides - Cellulose 

• Cellulose is a glucose polymer. It is an
• important structural material found in plants.
• It is made up of many unbranched chains of β-glucose molecules
• held together by 1, 4 glycosidic links.
• Parallel chains are cross-linked by hydrogen bonds to form bundles called microfibrils.
• Cellulose microfibrils are very strong.

Polysaccharides - Starch 

• Starch is a polymer of glucose, made up of long chains of α-glucose molecules.
• Starch contains a mixture of:
• 25-30% amylose: long unbranched chains of many hundreds of glucose linked by 1-4 glycosidic bonds.
• 70-75% amylopectin: branched chains with 1-6 glycosidic bonds every 23-30 glucose units.
• Starch is an energy storage molecule in plants.

Polysaccharides - Glycogen

• Glycogen is chemically similar to amylopectin but is more extensively branched.
• It is composed of α-glucose molecules, but there are more than 1,6 glycosidic links mixed with the 1,4 glycosidic links.
• Glycogen is the energy storage compound in animal tissues and in many fungi.

Modified Saccharides 

• Chitin is a tough modified polysaccharide made up of chains of β-glucose molecules.
• Structurally, it is almost the same as cellulose except that the -OH group at carbon atom 2 is replaced by a nitrogen-containing group (NH.CO.CH3).
• Chitin forms bundles of long parallel chains.

Lipids 

• Organic molecules that contain C, H, and O are connected by nonpolar covalent bonds.

• These are therefore not attracted to H2O molecules which are polar. (Hydrophobic)

• Fat is a large lipid made from glycerol and fatty acids.

• Glycerol is an alcohol with three C each with a -OH group.

  • A fatty acid is a long chain of about 15C atoms attached to a carboxyl group.

  • The C-atoms are bonded to H-atoms by nonpolar covalent bonds which makes the tail of a fatty acid to be hydrophobic. (disliking H2O).

  • Fats are used to storing energy.  They store about twice as much energy as carbs.

• Fatty acids join glycerol molecules by dehydration synthesis reactions.

• Fats are also called triglycerides as they are made up of three fatty acids and a glycerol molecule.

• Double bonds cause kinks in fatty acids C-chains.  They prevent the bonding of a C-skeleton to the maximum number of H-atoms.  These fats are said to be unsaturated.

• Fatty acids with the maximum number of H-atoms are said to be saturated.

• Corn oil, vegetable oil are unsaturated. (Liquid at room temp.)

• Most plant fats are unsaturated while most animal fats are saturated.

• Saturated fats might contribute to cardiovascular disease-causing atherosclerosis. (Hardening of the walls of blood vessels.)

Phospholipids

• Phospholipids are structurally similar to fats the only thing is that they have two fatty acids instead of three.

• Waxes have only one fatty acid linked to alcohol.

• Waxes are more hydrophobic than fats which makes them great at protecting surfaces of fruits, vegetables, and insects.

• Steroids are lipids that form 4 rings.  All steroids have 3 6-C rings attached to a 5-C ring.

• Cholesterol is part of cell membranes in animal cells.  They also use it as the starting point for making other steroids, including sex hormones (testosterone and estrogen).