BIOLOGICAL MACROMOLECULES 

BIOLOGICAL MACROMOLECULES 


Biological Macromolecules are polymers built from monomers

  1. All living things are made up of four classes of large biological molecules

    1. Carbohydrates

    2. Lipids

    3. Proteins

    4. nucleic acids

  2. Within cells, small organic molecules are joined together to form larger molecules

    1. Macromolecules are large molecules composed of thousands of covalently connected atoms

    2. Molecular structure and function are inseparable


A polymer is a long molecule consisting of many similar building blocks 

  1. These small building-block molecules are called monomers

    1. An immense variety of polymers can be built from a small set of monomers

    2. Three of the four classes of life’s organic molecules are polymers

      1. Polysaccharides are built from monosaccharides

      2. Nucleic Acids (DNA and RNA) are built from nucleotides (A, T/U, C, and G)

      3. Proteins are built from amino acids (A, R, N, D, C, E, Q, G, H, I, L, K, M, F, P, S, T, W, Y, and V)

  2. Polymers are formed by dehydration synthesis

    1. A dehydration synthesis occurs when two monomers bond together through the loss of a water molecule

    2. Enzymes are macromolecules that speed up the dehydration process

  3. Polymers are disassembled to monomers by hydrolysis

    1. Hydrolysis is essentially the reverse of the dehydration reaction


Carbohydrates

  • Carbohydrates include sugars and the polymers of sugars

  • The simplest carbohydrates are monosaccharides, or single sugars

  • Carbohydrate macromolecules are polysaccharides, polymers composed of many sugar building blocks called monosaccharides

  1. Monosaccharides

    1. have molecular formulas that are usually multiples of CH2O

    2. Numbering of monosaccharide carbons (from functional group)

    3. Glucose (C6H12O6) is the most common monosaccharide

    4. Monosaccharides are classified by 

      1. The location of the carbonyl group (as aldose or ketose)

      2. The number of carbons in the carbon skeleton

      3. Spatial arrangement of carbons

        1. Though often drawn as linear skeletons, in aqueous solutions many sugars form rings

    5. Monosaccharides serve as a major fuel for cells and as raw material for building molecules

  2. Disaccharides

    1. A disaccharide is formed when a dehydration reaction joins two monosaccharides 

    2. This covalent bond is called a glycosidic linkage

  3. Polysaccharides

    1. Polymers of sugars

    2. The structure and function of a polysaccharide are determined by its sugar monomers and the positions of glycosidic linkages

    3. Roles of polysaccharides 

      1. Energy storage roles 

        1. Starch – amylose (unbranched and amylopectin)





  1. Storage polysaccharide of plants

  2. consists entirely of glucose monomers

  3. Plants store surplus starch as granules within chloroplasts and other plastids 

  • Glycogen (more branched than amylopectin)

    1. Glycogen is a storage polysaccharide in animals

    2. Humans and other vertebrates store glycogen mainly in liver and muscle cells

  • Structural roles

    1. Cellulose

      1. The polysaccharide cellulose is a major component of the tough wall of plant cells

      2. Like starch, cellulose is a polymer of glucose, but the glycosidic linkages differ

      3. The difference is based on two ring forms for glucose: alpha (a) and beta (b)

      4. Structure function relationships

  1. Polymers with a glucose are helical

  2. Polymers with b glucose are straight





  1. In straight structures, cellulose, H atoms on one strand can bond with OH groups on other strands

  2. Parallel cellulose molecules held together this way are grouped into microfibrils, which form strong building materials for plants

  3. Enzymes that digest starch by hydrolyzing a linkages can’t hydrolyze b linkages in cellulose

  4. Cellulose in human food passes through the digestive tract as insoluble fiber

  5. Some microbes use enzymes to digest cellulose

  6. Many herbivores, from cows to termites, have symbiotic relationships with these microbes

  • Chitin

    1. Chitin, another structural polysaccharide, is found in the exoskeleton of arthropods

    2. Chitin also provides structural support for the cell walls of many fungi

    3. Used to make “dissolving stitches”

Lipids

  • Share one important trait: mix poorly with water

  • Are not true polymeric macromolecules

  • Some polar parts, but generally hydrocarbons (non-polar)

  • We will focus on Fats, Phospholipids and Steroids


  1. Fats 

    1. Fats are constructed from two types of smaller molecules: glycerol and fatty acids

      1. Fatty acids

        1. Think about the name fatty acid (Hydrocarbon + Carboxyllic acid)

        2. A fatty acid consists of a carboxyl group attached to a long carbon skeleton

      2. Glycerol

        1. three-carbon alcohol with a hydroxyl group attached to each carbon

      3. Three fatty acids are joined to glycerol by an ester linkage, creating a triacylglycerol, or triglyceride

      4. Fatty acids vary in 

        1. length (number of carbons) 

        2. number and locations of double bonds

          1. Saturated fatty acids 

            1. have the maximum number of hydrogen atoms possible and no double bonds (They are saturated with hydrogens)

            2. solids at room temperature

            3. animal fats (except for fish)

          2. Unsaturated fatty acids 

            1. have one or more double bonds

            2. liquids at room temperature

            3. plant and fish fats

    2. Functions in biology

      1. The major function of fats is energy storage

  2. Phospholipids

    1. Two fatty acids and a phosphate group are attached to glycerol 

      1. Hydrophobic tail: The two fatty acids

      2. hydrophilic head: the phosphate group and its attachments

    2. Formation into bilayers

      1. When phospholipids are added to water, they self-assemble into a bilayer, with the hydrophobic tails pointing toward the interior

      2. The structure of phospholipids results in a bilayer arrangement found in cell membranes

      3. Phospholipids are the major component of all cell membranes

  3. Steroids

    1. Steroids are lipids characterized by a carbon skeleton consisting of four fused rings

    2. Cholesterol

      1. component in animal cell membranes

      2. synthesized in the liver

      3. essential in animals, but high levels in the blood may contribute to cardiovascular disease

      4. Precursor from which other steroids are formed (estradiol, testosterone)

    3. Very important biological molecules that signal gene expression


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

  • Polypeptides are polymers built from the same set of 20 amino acids

  • A protein consists of one or more polypeptides

  • Amino acids are organic molecules with carboxyl and amino groups

  • Amino acids differ in their properties due to differing side chains, called R groups


  1. Proteins have several roles in the cell

    1. Enzymes

      1. Enzymes are a type of protein that acts as a catalyst to speed up chemical reactions

      2. Enzymes can perform their functions repeatedly, functioning as workhorses that carry out the processes of life


  1. Amino Acid Polymers

    1. Amino acids are the building blocks

      1. All have a common chemical structure with differing radical (“R”) groups

      2. R-groups give specific chemical properties

        1. Non-polar – equal distribution of electrons

        2. Polar – Unequal distribution of electrons

        3. Charged – Acidic or Basic

    2. Amino acids are linked by peptide bonds

    3. A polypeptide is a polymer of amino acids

    4. Polypeptides range in length from a few to more than a thousand monomers 

    5. Each polypeptide has a unique linear sequence of amino acids

    6. A functional protein consists of one or more polypeptides twisted, folded, and coiled into a unique shape


  1. Structure Function Relationships

    1. The sequence of amino acids determines a protein’s three-dimensional structure

    2. A protein’s structure determines its function – 4 levels of structure

      1. The primary structure of a protein is its unique sequence of amino acids

      2. Secondary structure, found in most proteins, consists of coils and folds in the polypeptide chain

      3. Tertiary structure is determined by interactions among various side chains (R groups)

      4. Quaternary structure results when a protein consists of multiple polypeptide chains

    3. Primary structure

      1. Primary structure, the sequence of amino acids in a protein, is like the order of letters in a long word 

      2. Primary structure is determined by inherited genetic information

    4. Secondary Structure

      1. The coils and folds of secondary structure result from hydrogen bonds between repeating constituents of the polypeptide backbone

      2. Typical secondary structures are: 

        1. a coil called an a helix 

        2. and a folded structure called a b pleated sheet

    5. Tertiary Structure

      1. Tertiary structure is determined by interactions between R groups, rather than interactions between backbone constituents

      2. These interactions between R groups include: 

        1. hydrogen bonds

        2. ionic bonds

        3. hydrophobic interactions

        4. van der Waals interactions

      3. Strong covalent bonds called disulfide bridges may reinforce the protein’s structure

    6. Quaternary Structure

      1. Quaternary structure results when two or more polypeptide chains form one macromolecule

      2. Collagen is a fibrous protein consisting of three polypeptides coiled like a rope


  1. Other Factors Play a Role in Protein Structure 

    1. In addition to primary structure, physical and chemical conditions can affect structure

    2. Alterations in pH, salt concentration, temperature, or other environmental factors can cause a protein to unravel

    3. This loss of a protein’s native structure is called denaturation

    4. A denatured protein is biologically inactive


  1. Protein Folding in a Cell

    1. It is hard to predict a protein’s structure from its primary structure

    2. Most proteins probably go through several states on their way to a stable structure

    3. Chaperonins are protein molecules that assist the proper folding of other proteins


  1. Protein Structures

    1. Scientists use X-ray crystallography to determine a protein’s structure

    2. Another method is nuclear magnetic resonance (NMR) spectroscopy, which does not require protein crystallization

    3. Bioinformatics uses computer programs to predict protein structure from amino acid sequences