Structure and Function of Macromolecules

 
Organic molecules that weigh more than 100,000 Dalton's are referred to as macromolecules.
 
These macromolecules are constructed of smaller units called polymers. These polymers are subdivided into their basic units called monomers.
 
Polymers account for the molecular uniqueness of organisms. Twenty amino acids are responsible for all forms of life. These amino acids form every conceivable protein known to man.
 
Making and breaking of polymers:
 
Dehydration synthesis: is an anabolic process by which two molecules are chemically bonded through the use of enzymes and a loss of water.
glucose + glucose + enzyme = maltose + water + enzyme.
 
Hydrolysis: is a catabolic process by which the bond between monomers are broken by the enzyme and the addition of water.
 
sucrose + water + enzyme = glucose + fructose + enzyme.
 
Carbohydrates: include sugars and their polymers. They include monosaccharides disaccharides, and polysaccharides. The monosaccharide is a monomer, the disaccharide is a polymer,and the polysaccharides are macromolecules.
 
Monosaccharides: The basic formula (CH2O)
Examples: triose sugars, 3 carbons, glyceraldehyde and dihydroxyacetone; pentose sugars. 5 carbons. ribose, deoxyribose, and ribulose; hexose sugars, 6 carbons, glucose, galactose, and fructose.
 

 
 
Disaccharides: These are double sugars with the formula C12H22O11. Notice that one molecule of water is missing from the formula. The covalent bond holding the two monomers together is called a 1-4 or 1-2 glycoside linkage. Examples: sucrose = glucose + fructose. maltose = glucose + glucose, and lactose = glucose + galactose.
 
 

 
Polysaccharides: The basic formula is ( C6H10O5)n . These are macromolecules capable of acting as structural or storage molecules.
 
Storage Polysaccharides: Starch is a plant storage polysaccharide that is composed entirely of glucose joined by @1-4 glycoside linkages. amylose is the simplest form of starch. amylopectin is more complex and is branched. Glycogen is an animal starch stored in the liver and muscles of vertebrates. It is more highly branched than amylopectin.
 
Structural Polysaccharides: Cellulose and chitin are examples of structural polysaccharides.
Cellulose is the most abundant organic compound on earth. It is made of glucose, like starch, but they differ in the type of 1-4 linkage. Instead of an @ linkage as in starch cellulose contains a B 1-4 linkage.
This causes the polysaccharide to take on a step arrangement and not a linear one like in starch.
Enzymes find it difficult to brake the B 1-4 linkage.
 
Lipids: A group of polymers that have one characteristic in common, they do not mix with water. They are hydrophobic. Some important groups are fats, phospholipids, and steroids.
 
Fats: are large molecules composed of 2 types of monomers, glycerol ( an alcohol containing 3 carbons) and 3 fatty acid molecules. The bond connecting the glycerol and fatty acids in the fat molecule is called an ester bond. There are two types of fatty acids: saturated and unsaturated. The saturated fatty acids do not contain any double bonds between the carbons, while the unsaturated fatty acids contain one or more double bonds between the carbons. These double bonds cut down on the number of hydrogen atoms that can be attached to the carbon in the molecule. This causes the molecule to bend or kink at each of the double bond sites.
 

 
Characteristics of Fats:
 
Saturated
Unsaturated

1. solid at room temperature

1. liquid at room temperature

2. found mostly in animals

2. found mostly in plants

3. no double bonds between carbons

3. double bonds found between carbons

 

 
Function of fats: acts as insulation in higher vertebrates, serves as an energy storage source 1g.=9 Kcal of energy, and shock absorber for internal organs.
 
Phospholipids: structurally related to fats but contain 2 fatty acids and one molecule of phosphate. These molecules are found making up the plasma membrane of cells. They exhibit a polar and non polar quality. The phosphate group is hydrophilic while the fatty acid area is hydrophobic.
 
Steroids: Lipids characterized by a carbon skeleton of 4 fused rings. Cholesterol is an important steroid found in all animal tissue. Plants do not contain cholesterol. Cholesterol functions in many ways: it is a precursor from which many of the bodies steroids are constructed from. It also adds strength to the plasma membrane in animal cells.
 
Proteins: macromolecules that make up 50% of the dry weight of most cells.
 
 

Types of proteins:

 
1. Structural functions in support, examples: elastin, collagen, and keratin
2. Storage food source, examples: ovalbumin and casein
3. Transport moves other substances, examples: hemoglobin and cell membrane proteins
4. Hormonal coordinates bodily activities, example insulin,
5. Contractile movement, examples: actin and myosin
6. Antibodies defense, examples: Ig.E, IgA, and Ig.G
7. Enzymes aid in chemical reactions, examples: amylase and proteases
 
Amino Acids: Most amino acids consist of an asymmetrical carbon bonded to an, amino group, hydrogen, an R group,and a carboxyl group.
 

 
There are 20 different amino acids. Each amino acid has an optical isomer. The left amino acid is the functional one. The D- amino acid only rarely function. Proteins are formed by bonding amino acids together. The bond formed is called a peptide bond.
 
Protein conformation: refers to the three dimensional shape of a protein molecule. This shape is important to its function. If the conformation is changed, even slightly , then the function of the protein changes.
 
Levels of Protein structure:
 
1. Primary: refers to the unique sequence of amino acids in the protein. All proteins have a special sequence of amino acids, this sequence is derived from the cell's DNA.
 
2. Secondary : the coiling or bending of the polypeptide into sheets is referred to the proteins secondary structure. alpha helix or a beta pleated sheet are the basic forms of this level. They can exist separately or jointly in a protein.
 
3. Tertiary: The folding back of a molecule upon itself and held together by disulfide bridges and hydrogen bonds. This adds to the proteins stability.
 
4. Quaternary: Complex structure formed by the interaction of 2 or more polypeptide chains.
 
Nucleic Acids: DNA and RNA.
 
Nucleotides: monomers that come together to form a nucleic acid. They contain either a ribose or deoxyribose sugar ( ribose has one more oxygen in its molecule),
 
 
 

Deoxyribose Sugar

  

phosphate, and a nitrogenous base (purine = guanine or adenine, pyrimidine = cytosine, thymine , or uracil). Pyrimidines are constructed of a single ring while purines are characterized by a double ring. The nucleotides are joined together by phosphodiester bonds.

 
Base pairing rule. A-T, A-U, C-G. DNA has a double helix shape, while most RNA is single stranded.