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

Structuralformula of asaturated fatmolecule

Stearic acid, asaturated fattyacid

(a) Saturated fat

Structural formulaof an unsaturatedfat molecule

Oleic acid, anunsaturatedfatty acid

(b) Unsaturated fat

cis doublebond causesbending

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

Hydrophilichead

Hydrophobictail WATER

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

Amino acids

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

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

Peptidebond

Fig. 5-18

Amino end(N-terminus)

Peptidebond

Side chains

Backbone

Carboxyl end(C-terminus)

(a)

(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

helix-stabilized by frequent polar groups Right handed helices

-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 Structure Revisited

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