Biology Chapter 5 Biological macromolecules Small molecules (like water and NaCl) have certain properties that arise from the bonds which hold atoms together in a particular arrangement. Many of the molecules that compose the cells in a living thing are huge and are often termed macromolecules. very large molecules - some proteins for examples contain thousands of covalently bonded carbon atoms 1
There are four categories of biological macromolecules: 1. Carbohydrates * 2. Lipids 3. Proteins* 4. Nucleic Acids* * these three categories are composed of molecules that are formed as polymers Polymers Polymers are long molecules consisting of many similar or identical building blocks linked by covalent bonds. These basic units (or building blocks) are known as monomers. As we will see, the monomers of each of the three different macromolecules are different, but the chemical mechanism to build polymers from these monomers is very similar. 2
Synthesis and breakdown of polymers Each monomer molecule will be connected to an adjacent monomer by a chemical reaction known as dehydration synthesis When a covalent bond forms between the two monomers, each monomer contributes a part of a water molecule the H + (hydrogen ion) OH - (hydroxide group) These reactions are building reactions (anabolic reactions) and require the input of energy. Enzymes are used to help speed up these reactions by lowering the activation energy of the reaction. 3
Polymers may also be broken down into smaller units by a catabolic reaction. This process requires the addition of water and is known as hydrolysis. Split with water The reverse of dehydration synthesis Also requires enzymes to activate 4
Functions: 1. Carbohydrates Quick energy source (fuel) Structural building materials Sugars (monosaccharides) form the basic monomers of polysaccharides. monosaccharides Glucose is the most common (most sugar names end in ose) Glucose is important in the cellular respiration reaction easy to catabolize 5
Glycosidic linkages Covalent bonds formed by dehydration synthesis linking monosaccharides Glucose Fructose Sucrose a disaccharide Other disaccharides: maltose found in beer Lactose found in milk Large polysaccharides Macromolecules of a few hundred to a few thousand monosaccharides. Used for storage may be catabolized by hydrolysis to create monosaccharides for fuel. Used for building materials for cells 6
Polysaccharide examples Starch storage polysaccharide in plants Glucose bank for plants Most animals have enzymes that can hydrolyze starch Glycogen storage polysaccharide in animals Stored in liver and muscle tissue Used when demand for sugar increases; only a day s worth of stored energy Cellulose - the most abundant organic compound on earth Structural polysaccharide found only in plants Found in the cell wall of plant cells Very strong Forms long fibers Most animals do not have enzymes to hydrolyze cellulose Termites and cows use symbiotic microorganisms 7
Chitin structural polysaccharide found in arthropods Insects, crustaceans, arachnids Composes the exoskeleton Also found in some fungi Used to make surgical thread very thin, very strong and decomposes easily. 2. Lipids Do not consist of polymers Grouped together because they are hydrophobic little or no affinity for water Classes of lipids: Fats Phospholipids Steroids 8
Fats Consist of a glycerol and fatty acids Are formed by dehydration synthesis Function - energy storage (2X sugar) - insulation in adipose tissue Saturated fats fatty acid tail does not have double bonds in the hydrocarbon chains This makes them very stable and more difficult to break down Solid at room temperature Most animal fats lard, butter increased risk of CV disease atherosclerosis Unsaturated fats fatty acid tails have double bonds in hydrocarbon chains Most plant oils olive oil Liquid at room temperature 9
Similar to fat but only has two fatty acid tails attached to glycerol and has a phosphate group (PO 4 ) as well. Amphipathic - Phospholipids hydrophobic and hydrophilic properties When placed in water, forms phospholipid bilayer 10
Steroids Cholesterol fond in animal cells Some hormones estrogen, testosterone 3. Proteins Very diverse group with many functions Monomers are amino acids 20 naturally occurring Amino group α carbon Carboxyl group R group (variable) 11
Linked during dehydration synthesis to form peptide bonds. Functions of proteins Enzymes catalysts in reactions Digestive enzymes Structural proteins physical support Collagen Storage proteins stores amino acids Casein milk protein Transport proteins aid in transport in organs or cells Hemoglobin Hormonal proteins coordinates body activities Insulin Receptor proteins cell s response to stimuli Acteylcholine binding sites Contractile proteins contraction for movement Actin and myosin Defense proteins protection against disease antibodies 12
Protein function is determined by shape There are four levels of protein structure Primary structure sequence of amino acids Secondary structure Hydrogen bonding along backbone causes the polypeptide chain to : coil (α helix) fold (ß pleated sheet) 13
Tertiary structure interactions among side (R groups) chains causes additional folding and produces a truly threedimensional molecule Quaternary structure occurs between two or more polypeptide chains 14
Protein are very large 3-D molecules and their shape is crucial to their function. When proteins change their shape they change their function If the shape change is dramatic the protein may become denatured and lose its functionality 4. Nucleic Acids Nucleic acids store and transmit hereditary information Hereditary information Primary structure of a protein is determined by the sequence of amino acids. This sequence of amino acids is ultimately programmed by the units of inheritance called genes Genes consist of molecules of DNA Deoxyribonucleic Acid DNA Ribonucleic Acid - RNA 15
Nucleic acids as polymers Composed of monomers called nucleotides Three components of a nucleotide Nitrogenous base Adenine, cytosine, thymine, guanine, uracil Phosphate Pentose sugar Ribose or deoxyribose The nucleotides are joined by the bonding of the phosphate group from one nucleotide to the pentose sugar from the next Forming the phosphate sugar backbone This also makes these chains directional 3 and 5 ends 16
DNA structure Two complementary strands of nucleotides Formed by the hydrogen bonding of complementary base pairs A T and G C double helix Discovered by Watson and Crick The structure of DNA allows DNA to carry genetic information (in the sequences of the bases) and to self-replicate (make a copy of itself). The strands are directional 3 and 5 ends antiparallel 17
RNA Single stranded Made from DNA template Uracil replaces thymine in RNA (pairs with Adenine) Several types: mrna messenger RNA trna transfer RNA Used to build polypeptides DNA and RNA at work 18