The Structure and Function of Macromolecules
- 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