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5/23/12
Macromolecules pt 2
Lipids
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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 hydrogens
Fats
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Used primarily as a long term method of energy storage
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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
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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
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
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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
Hormones
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Derived from cholesterol molecules
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Are complicated ring structures
Used as global regulators in biology
– Send signals to distant cells to affect behavior
Are essential for homeostasis
Lipids Summary
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Non-polar molecules that are hydrophobic
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Can be saturated or unsaturated
Typically found as fatty acids
– Contain carboxyl group at end of a hydrocarbon chain
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
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Most versatile of the macromolecules
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Structural: collagen, keratin, silk, tubulin
Storage: casein, ovalbumin
Transport: hemoglobin
Hormones: insulin
Receptor: ASGPR
Contractile: actin
Defensive: antibodies
Enzymatic:lysozyme and many others
Amino acids
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Monomeric subunit of polypeptides
Have amino group and carboxyl group
20 natural amino acids
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Each has different R group
Differences in R group makes amino acids react differently
Functional Groups of Amino Acids
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Based on the chemical properties of the R side group
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Nonpolar (hydrophobic):glycine, alanine, valine, leucine, isoleucine, methionine, phenylalanine,
tryptophan and proline
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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
Four Levels of Protein Structure
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Biological activity of protein is determined by these levels
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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
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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
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Localized within regions of polypeptide
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-pleated sheets are formed by consecutive polar groups on two regions of polypeptide
Stabilized by hydrogen bonding
 helix-stabilized by frequent polar groups
– Right handed helices
Tertiary Structure
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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
Quaternary Structure
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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
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The 3D structure in which the protein is biologically active is called the active conformation
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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
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Solvent (polar versus non-polar),pH, temperature and chemical agents (2-mercaptoethanol)
Protein summary
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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
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The side groups determines the shape and function of a polypeptide
There are four levels of structural organization of proteins