Small organic molecules are the building blocks of biological macromolecules…

Building blocks Larger units

Fatty acids Fats/lipids/Membranes

Sugars Polysaccharides

Amino acids Proteins

Nucleotides Nucleic acids

Adapted from ECB figure 2-15 (Garland Publishing)

Most lipids are in membranes Plasma membrane

Various organelle membranes

Hydrophilic Carboxylic acid

head group

(Amphipathic)

Fatty Acids

Hydrophobic hydrocarbon

tail

Fatty acids are distinguished by chain length and double bonds

Stearic acid

18 carbonsSaturated = no double

bonds(common in fats)

Unsaturated 1 double bond,

Oleic Acid18 carbons

(common in oils)

Triacyl Glycerol = 3 fatty acids bonded to glycerolEster bond - carboxylic acid and alcohol

(animal fat, plant oils)Energy storage

Most lipids in cells are formed by covalent bonds

between fatty acids and glycerol

Very Hydrophobic

ECB Fig. 11-10

Phospholipid - 3 partsMajor component of membranes

Hydrophobic tails = fatty acid side chains

glycerol

Polar Head Group = phosphate + polar moiety (Variable)

Phospholipid

Hyd

rop

hob

ic t

ail r

eg

ionH

yd

rop

hili

c re

gio

nPhospholipid

Bilayer

Lipid bilayer forms sphere in aqueous solution

Forms barrier defining inside and outside spaces

LipidsLipids

Lipid bilayerLipid bilayer5 nm5 nm

ProteinProtein

Cell Membrane-more complex

Contains a variety of lipids, proteins, and carbohydrates

Cytosol (inside)

Outer leaflet

Innerleaflet

Multiple types of lipidsare found in membranes

ECB Fig. 11-4

Three Types of Membrane Lipid Moleculesall amphipathic

phosphatidylserinegalactocerebrosi

de

PhospholipidsSterols

(cholesterol)

Glycolipids (sugar lipid)

serine

ECB 11-7

MembranesFatty Acids

Phospholipids

Lipid bilayer

ProteinsAmino Acids

Peptide bond

Protein Structure

Other membrane lipids

Membrane properties

Lecture 4

Influence of FA saturation on lipid bilayer order

Saturated straightSaturated straighthydrocarbon chainshydrocarbon chains(no double bonds)(no double bonds)

ordered

Unsaturated Unsaturated hydrocarbon chains hydrocarbon chains (with double bonds) (with double bonds)

less ordered

Less ordered state increases membrane fluidity

Describes the physical state of the membrane

Pure lipid bilayer - two states

Liquid stateHydrophobic tails free to move

Gel stateMovement is greatly

restricted (crystalline gel)

Transition Transition temperaturetemperature

Liquid at temperaturesAbove the transition temp.

Crystalline gel at temperatures below the

transition temp

Membrane Fluidity (viscosity)

Living cells require a fluid membrane, but not too fluid:Membrane fluidity is regulated by the cell

11.2-membrane_fluidity.mov

1. Fatty acid length - shorter the FA, the lower the transition temperature (melting point), favors liquid state

2. Fatty acid saturation - the more saturated, the higher the transition temperature, favors gel state

3. Presence of cholesterol - broadens the temperature over which transition occurs.

Melting points of 18-carbon Fatty Acids

Fatty Acid Double bonds Melting point (˚C)

Stearic acid 0 70Oleic acid 1 13-Linoleic acid 2 -9Linolenic acid 3 -17

Membrane fluidity is governed by FA length and saturation

Polar headPolar headgroupgroup

Nonpolar Nonpolar hydro-hydro-carboncarbon

tailtail

RigidRigidPlanarPlanarSteroidSteroid

ringring

FluidFluidregionregion

StiffenedStiffenedregionregion

Polar headPolar headgroupgroup

Cholesterol stiffens lipid

bilayers

Mainly in animal cells, Not in plants

ECB 11-16

Lipid composition varies in inner and outer leaflet

Glycolipids in outer leaflet

Phospholipids

1. Spin (fast)

2. Lateral movement (less fast)

3. Flip-flop Almost never

IONSH+, Na+, HCO3

-, K+, Ca2+, Cl-, Mg2+

Large, unchargedPolar molecules

Amino acids, glucose, nucleotides

Small Uncharged polar molecules

H2O, glycerol, ethanol

Small hydrophobicMolecules

O2, CO2, N2, benzene

Lipid Bilayer Permeability

ECB Fig.12-2

Have discussed lipid bilayer, cholesterol, glycolipidNow move on to proteins

Cell membrane

ECB Fig. 11-4

Small organic molecules are the building blocks of biological macromolecules…

Building blocks Larger units

Fatty acids Fats/lipids/Membranes

Sugars Polysaccharides

Amino acids Proteins

Nucleotides Nucleic acids

Adapted from ECB figure 2-15 (Garland Publishing)

Proteins serve many functions in cells

Transport proteins - move molecules across membranes EnzymesStructural proteinsMotor proteins Signaling proteinsGene regulatory proteinsEtc.

20 different amino acids

All amino acids have the same backbone, but the “R” group varies.

Amino Acids - the building blocks of proteins

See ECB Fig. 2-21

Based on chemical characteristics of R groups

1. Polar and negative charge (aspartic acid and glutamic acid)

2. Polar and positive charge (arginine, lysine, histidine)

3. Polar and uncharged (asparagine, glutamine, serine, threonine, tyrosine)

4. Nonpolar (alanine, glycine, valine, leucine, isoleucine, proline, phenylalanine, methionine, tryptophan, cysteine)

Polar Amino Acids

Amino Acid Groups

AsparticAcid (Asp, D)

GlutamicAcid (Glu, E)

Negative charge

Positive charge

Lysine(Lys, K)

Arginine(Arg, R)

Histidine(His, H)

Polar Charged Amino Acids (5)

Serine(Ser, S)

Threonine(Thr, T)

Glutamine(Gln, Q)

Asparagine(Asn, N)

Tyrosine(Tyr, Y)

Polar Uncharged

Amino Acids (5)

TryptophanTryptophan(Trp, W)(Trp, W)

PhenylalaninePhenylalanine(Phe, F)(Phe, F)

MethionineMethionine(Met, M)(Met, M)

IsoleucineIsoleucine(Ile, I)(Ile, I)

LeucineLeucine(Leu, L)(Leu, L)

ValineValine(Val, V)(Val, V)

AlanineAlanine(Ala, A)(Ala, A)

(10 total)

Non-polar amino acids

GlycineGlycine(Gly, G)(Gly, G)

CysteineCysteine(Cys, C)(Cys, C)

ProlineProline(Pro, P)(Pro, P)

Non-polar amino acids (cont’d)

+

H2OPeptide bond

See also ECB figure 5-1

Condensation rx

Polymerization of Amino Acids to Proteins

Dipeptide

Aminoend

Carboxylend

MembranesFatty Acids

Phospholipids

Lipid bilayer

ProteinsAmino Acids

Peptide bond

Protein Structure

Other membrane lipids

Membrane properties

Lecture 4

1˚ structure: the linear sequence of amino acidsN-terminal to C-terminal

2˚ structure: stretches of the polypeptide chain that fold into -helix or -sheet (H-bonding)

3˚ structure: 3-dimensional conformation of a polypeptide chain

4˚ structure: multiple polypeptide chains interacting to form a complex

4 Levels of Protein Structure

(ECB Fig. 4-2)

1˚ structure = sequence of amino acids

TertiaryTertiarystructurestructure

quaternaryquaternarystructurestructure

SecondarySecondarystructurestructure

Higher levels of organization are determined by protein folding

Improper protein folding is associated with disease

Alzheimers and Huntingtons diseases - aggregated proteins in brain

Prion diseases - scrapie (sheep), mad cow (bovine), chronic wasting disease (deer, elk), Creutzfeldt-Jacob disease (CJD, humans)

-helix and -pleated sheet

Secondary Structure

helix

H bondbetween peptidebonds, 4 a.a. apart

C

O

HN

H bond

R groups are on outside of helix

pleated sheetH bond

3-D conformation of a single polypeptide chain

Driven by many types of bonds (H-bonds, hydrophobic interactions, van der Waals, etc.)

Disulfide bond formation (between cysteine residues)

Tertiary Structure

Folding into tertiary structure forms domains in polypeptide

Polypeptide made up of several domains

Single domain

Two different domains

Quaternary structure

Multiple polypeptides interact via noncovalent and covalent (disulfide) bonds

dimertetramer

Disulfide bridge