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Lipids. Hydrophobic molecules Carbons bound to hydrogens are not polar Most often found as fatty-acid Carboxyl group at one end Carbon/hydrogen chain Chain may be saturated or unsaturated
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Lipids • Hydrophobic molecules • Carbons bound to hydrogens are not polar • Most often found as fatty-acid • Carboxyl group at one end • Carbon/hydrogen chain • Chain may be saturated or unsaturated • Saturated means that each carbon (except the carboxyl carbon) is bound to the maximum number of hydrogen atoms
Fats • Used primarily as a long term method of energy storage • Animal fats tend to contain saturated lipids • Plant fats contain unsaturated fat • Saturated fats are linear molecules and thus able to pack in more tightly and are solid at room temp • Unsaturated fats have angles and do not pack in tightly. They are liquid at room temp. • Fats that are liquid at room temp are called oils
Fig. 5-12 Structural formula of a saturated fat molecule Stearic acid, a saturated fatty acid (a) Saturated fat Structural formula of an unsaturated fat molecule Oleic acid, an unsaturated fatty acid cis double bond causes bending (b) Unsaturated fat
Structure of fats • Three fatty acid chains bound to a glycerol backbone • Also called triaclyglycerol • Formed by dehydration reaction • Fatty acids are bound to glycerol by ester linkage
Phospholipids • Major component of cell membranes • Contain hydrophilic domain that contains phosphate (and other hydrophilic structure) • Contains hydrophobic domain of lipid chains
Amphipathic Molecules • Contain both hydrophobic and hydrophilic domains • Tend to aggregate with hydrophobic domains turned together and hydrophilic domais turned outward • Can for bilayers or micelle structures • Bilayers are essential for membrane structure
Fig. 5-14 Hydrophilic head WATER Hydrophobic tail WATER
Hormones • Derived from cholesterol molecules • Used as global regulators in biology • Send signals to distant cells to affect behavior • Are complicated ring structures • Are essential for homeostasis
Lipids Summary • Non-polar molecules that are hydrophobic • Typically found as fatty acids • Contain carboxyl group at end of a hydrocarbon chain • Can be saturated or unsaturated • Are used for long-term energy storage • Phospholipids are amphipathic molecules that are essential for membrane structure • Are the basis for hormone structure
Protein Functions • Most versatile of the macromolecules • Structural: collagen, keratin, silk, tubulin • Storage: casein, ovalbumin • Transport: hemoglobin • Hormones: insulin • Receptor: ASGPR • Contractile: actin • Defensive: antibodies • Enzymatic:lysozyme and many others
Monomeric subunit of polypeptides Have amino group and carboxyl group 20 natural amino acids Each has different R group Differences in R group makes amino acids react differently Amino acids
Functional Groups of Amino Acids • Based on the chemical properties of the R side group • Nonpolar (hydrophobic):glycine, alanine, valine, leucine, isoleucine, methionine, phenylalanine, tryptophan and proline • Polar (hydrophilic): serine, threonine, cysteine, tyrosine, asparagine and glutamine • Electrically charged: • Acidic: aspartic acid, glutamic acid • Basic: lysine, arginine and histidines
Synthesis of Polypeptides • Polypeptide is synthesized by dehydration reaction • Chain grows from amino terminus to carboxy terminus • Chain has a repetitive backbone with variable side groups • R groups frequently interact with others
Fig. 5-18 Peptide bond (a) Side chains Peptide bond Backbone Amino end (N-terminus) Carboxyl end (C-terminus) (b)
Four Levels of Protein Structure • Biological activity of protein is determined by these levels • Primary structure is the sequence of amino acids in a polypeptide (Usually read N-C) • Secondary structures are localized folds or helices that form within a region of a polypeptide • Tertiary structures are larger folding events that are stabilized by interactions between R groups • Quaternary structure is the interaction of multiple polypeptides within one active proteins
Primary Structure • Sequence of amino acids within a single polypeptide • Are often similar among proteins of similar function • Usually written from amino terminus to carboxy terminus • Can also provide some insight into additional structures by the position of particular groups of amino acids
Secondary Structure • Localized within regions of polypeptide • Stabilized by hydrogen bonding • a helix-stabilized by frequent polar groups • Right handed helices • b-pleated sheets are formed by consecutive polar groups on two regions of polypeptide
Tertiary Structure • Large folding events that are stabilized by interactions between amino acids • Hydrophobic interactions • Nonpolar regions generally internalize in structure • Disulfide bridge • Very stable bond formed between two distant cysteine residues • Ionic interactions • Strong bond between oppositely charged side groups -Hydrogen bonds form between polar groups
Quaternary Structure • Only seen in compound proteins • Interactions are maintained between polypeptide chains by bonds similar to tertiary structure • Function is often unique to quaternary structure • Individual components are unable to accomplish task alone
Protein Conformation • The 3D structure in which the protein is biologically active is called the active conformation • Denatured protein has lost its active conformation • Shape of a protein is consistent under identical conditions • Proteins will attempt to find the lowest energy form under conditions • Conditions that affect conformation • Solvent (polar versus non-polar),pH, temperature and chemical agents (2-mercaptoethanol)
Protein summary • Very important biological macromolecules that perform a wide array of functions • Polymers of amino acids • 20 natural amino acids that have distinct R side groups • The side groups determines the shape and function of a polypeptide • There are four levels of structural organization of proteins