Macromolecules

• Are large molecules composed of smaller molecules

• Are complex in their structure

• Most macromolecules are polymers, built from monomers

• Four classes of life’s organic molecules are polymers

  • Carbohydrates

  • Proteins

  • Nucleic acids

  • Lipids

• A polymer

  • A long molecule consisting of many similar building blocks called monomers

  • Specific monomers make up each macromolecule

    • E.g. amino acids are the monomers for proteins

The Synthesis and Breakdown of Polymers

• Monomers form larger molecules by condensation reaction called dehydration synthesis

• Polymers and disassemble by hydrolysis

  • Addition of water molecules

• Although organisms share the same limited number of monomer types, each organism is unique based on the arrangement of monomers into polymers

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

Carbohydrates

• Serve as fuel and building material

• Include both sugars and polymers

  • Starch, cellulose, etc.

Sugars

• Monosaccharides

  • Are the simplest sugars

  • Can be used for fuel

  • Can be converted into other organic molecules

  • Can be combined into polymers

  • Can be linear

  • Can form rings

• Disaccharides

  • Consist of two monosaccharides

  • Are joined by a glycosidic linkage

• Polysaccharides

  • Are polymers of sugars

  • Serve many roles in organism

• Storage Polysaccharides

  • Starch

    • Is a polymer consisting entirely of glucose monomers

    • Is the major storage form of glucose in plants

  • Glycogen

    • Consists of glucose monomers

    • Is the major storage form of glucose in animals

  • Cellulose

    • Is a polymer of glucose

    • Has different glycosidic linkages than starch

    • Difficult to digest

      • Cows have microbes in their stomach to facilitate this process

  • Chitin

    • Is found in the exoskeleton of arthropods

    • Can be used as surgical thread

Lipids

• Are the one class of large biological monomers that do not consist of polymers

• Share the common trait of being hydrophobic

Fats

• Constructed from two types of smaller molecules

  • A single glycerol and usually three fatty acids

• Vary in length and number and location of double bonds they contain

• Saturated fatty acids

  • Have the maximum number of hydrogen atoms possible

  • Have no double bonds

• Unsaturated fatty acids

  • Have one or more double bonds

• Phospholipids

  • Have only two fatty acids

  • Have a phosphate group instead of third fatty acid

  • Structure

    • Consists of a hydrophobic “head” and hydrophobic “tails”

    • Results in a bilayer arrangement founds in cell membranes

      

Steroids

• Lipids characterized by a carbon skeleton consisting of four fused rings

• Cholesterol

  • Found in cell membranes

  • Is a precursor for some hormones

Proteins

• Proteins have many structures, resulting in a wide range of functions

• Proteins do most of the work in cells and acts as enzymes

• Proteins are made of monomers called amino acids

• Enzyme

  • Type of protein that acts as a catalyst, speeding up chemical reactions

• Polypeptides

  • Polymers of amino acids

  • A protein consists of one or more polypeptides

• Amino acids

  • Are organic molecules possessing both carboxyl and amino groups

  • Differ in their properties due to differing side chains, called R groups

  • Linked by peptide bonds

Protein Conformation and Function

• A protein’s specific conformation (shape) determines how it functions

Four Levels of Protein Structure

• Primary structure

  • Unique sequence of amino acids in a polypeptide

• Secondary structure

  • Folding or coiling of the polypeptide into a repeating configuration

  • Includes the a helix and β pleated sheet

• Tertiary Structure

  • Overall three-dimensional shape of a polypeptide

  • Results from interactions between amino acids and R groups

• Quaternary structure

  • The overall protein structure that results from the aggregation of two or more polypeptide subunits

Sickle Cell Disease

• Results from a single amino acid substitution in the protein hemoglobin

What determines Protein Conformation

• Protein conformation depends on the physical and chemical conditions of the protein’s environment

  • Temperature, pH, etc.

• Denaturation is when a protein unravels and loses its native conformation

The Protein Folding Problem

• Most proteins

  • Probably go through several intermediate states on their way to a stable conformation

  • Denaturated proteins no longer work in their unfolded conditions

  • Proteins may be denaturated by extreme changes in pH or temperature

• Chaperonins

  • Protein molecules that assist in the proper folding of other proteins

• X-ray crystallography

  • Used to determine a protein’s three-dimensional structure

Nucleic Acids

• Store and transmit hereditary information

• Genes

  • Are the units of inheritance

  • Program the amino acid sequence of polypeptides

  • Are made of nucleotide sequences of DNA

• DNA

  • Deoxyribonucleic acid

  • Stores information for the synthesis of specific proteins

  • Found in the nucleus of the cell

  • Functions

    • Directs RNA synthesis

      • Transcription

    • Directs protein synthesis through RNA

      • Translation

• Structure

  • Nucleic acids exist as polymers called polynucleotides

  • Each polynucleotide

    • Consists of monomers called nucleotides

    • Sugar + phosphate + nitrogen base

  • Nucleotide monomers

    • Made up of nucleosides (sugar + base) and a phosphate group

  • Nucleotide polymers

    • Are made up of nucleotides linked by the -OH on the 3’ carbon of one nucleotide and the phosphate on the 5’ carbon of the next

  • Gene

    • The sequence of bases along a nucleotide polymer

  • DNA double helix

    • Have two polynucleotides that spiral around an imaginary axis

    • Form a double helix

    • Consists of two antiparallel nucleotide strands

  • A, T, C, G

    • The nitrogenous bases in DNA

    • Form hydrogen bonds in a complementary fashion

      • A with T only

      • C with G only

DNA and Proteins as Tape Measures of Evolution

• Molecular comparisons

  • Help biologists sort out the evolutionary connections among species