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Small organic molecules are the building blocks
of biological macromolecules…
Building blocks
Larger units
Sugars
Polysaccharides
Fatty acids
Fats/lipids/Membranes
Amino acids
Proteins
Nucleotides
Nucleic acids
Adapted from ECB figure 2-15 (Garland Publishing)
Most lipids are in membranes
Plasma membrane
Various organelle membranes
Fatty Acids
(Amphipathic)
Hydrophilic
Carboxylic acid
head group
Hydrophobic
hydrocarbon
tail
1
Fatty acids are distinguished by chain length and double bonds
Stearic acid
18 carbons
Saturated = no double bonds
Oleic Acid
18 carbons
(common in fats)
Unsaturated 1 double bond,
(common in oils)
Most lipids in cells are formed by covalent bonds
between fatty acids and glycerol
ECB Fig. 11-10
Triacyl Glycerol = 3 fatty
acids bonded to glycerol
Ester bond - carboxylic acid and
alcohol
(animal fat, plant oils)
Energy storage
Very Hydrophobic
Phospholipid - 3 parts
Major component of membranes
Polar Head Group = phosphate + polar moiety (Variable)
glycerol
Hydrophobic tails =
fatty acid side
chains
2
Hydrophilic
region
Hydrophobic tail region
Phospholipid
Phospholipid
Bilayer
Lipid bilayer forms sphere in aqueous solution
Forms barrier defining
inside and outside spaces
Cell Membrane-more complex
Contains a variety of lipids, proteins, and carbohydrates
Outer leaflet
Lipids
Lipid bilayer
5 nm
Multiple types of lipids
are found in membranes
Inner
leaflet
Protein
Cytosol (inside)
ECB Fig. 11-4
3
Three Types of Membrane Lipid Molecules
Glycolipids
all amphipathic
Phospholipids
Sterols
serine
(sugar lipid)
(cholesterol)
ECB 11-7
galactocerebroside
phosphatidylserine
Lecture 4
Membranes
Fatty Acids
Phospholipids
Lipid bilayer
Other membrane lipids
Membrane properties
Proteins
Amino Acids
Peptide bond
Protein Structure
Influence of FA saturation on lipid bilayer order
ordered
Saturated straight
hydrocarbon chains
chains
(no double bonds)
bonds)
less ordered
Unsaturated
hydrocarbon chains
(with double bonds)
Less ordered state increases membrane fluidity
4
Membrane Fluidity (viscosity)
Describes the physical state of the membrane
Pure lipid bilayer - two states
Gel state
Liquid state
Hydrophobic tails free to move
Liquid at temperatures
Above the transition temp.
Movement is greatly restricted
(crystalline gel)
Transition
temperature
Crystalline gel at
temperatures below the
transition temp
Living cells require a fluid membrane, but not too fluid:
Membrane fluidity is regulated by the cell
11.2-membrane_fluidity.mov
Membrane fluidity is governed by FA length and
saturation
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
Melting points of 18-carbon Fatty Acids
Fatty Acid
Double bonds
Stearic acid
Oleic acid
α-Linoleic acid
Linolenic acid
0
1
2
3
Melting point (˚C)
70
13
-9
-17
3. Presence of cholesterol - broadens the temperature
over which transition occurs.
Rigid
Planar
Steroid
ring
Polar head
group
Nonpolar
hydrocarbon
tail
ECB 11-16
Mainly in animal cells,
Not in plants
Cholesterol
stiffens lipid
bilayers
Polar head
group
Stiffened
region
Fluid
region
5
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
Lipid Bilayer
Permeability
Small hydrophobic
Molecules
O 2, CO 2, N 2, benzene
Small Uncharged
polar molecules
H2O, glycerol, ethanol
Large, uncharged
Polar molecules
Amino acids, glucose,
nucleotides
IONS
H+, Na+, HCO 3-,
K+, Ca 2+, Cl -, Mg 2+
ECB Fig.12-2
6
Cell membrane
ECB Fig. 11-4
Have discussed lipid bilayer, cholesterol, glycolipid
Now move on to proteins
Small organic molecules are the building blocks
of biological macromolecules…
Building blocks
Larger units
Sugars
Polysaccharides
Fatty acids
Fats/lipids/Membranes
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
Enzymes
Structural proteins
Motor proteins
Signaling proteins
Gene regulatory proteins
Etc.
7
Amino Acids - the building blocks of proteins
20 different amino acids
All amino acids have
the same backbone,
but the “R” group
varies.
See ECB Fig. 2-21
Amino Acid Groups
Based on chemical characteristics of R groups
Polar Amino Acids
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 Charged Amino Acids (5)
Negative charge
Aspartic
Acid (Asp, D)
Glutamic
Acid (Glu, E)
Positive charge
Lysine
(Lys, K)
Arginine
(Arg, R)
Histidine
(His, H)
8
Polar
Uncharged
Amino Acids
(5)
Glutamine
(Gln, Q)
Serine
(Ser, S)
Threonine
(Thr, T)
Asparagine
(Asn, N)
Tyrosine
(Tyr, Y)
Non-polar
amino acids
(10 total)
Alanine
(Ala, A)
Valine
(Val, V)
Leucine
(Leu,
Leu, L)
Isoleucine Methionine
Methionine Phenylalanine Tryptophan
(Trp,
(Ile,
(Met, M)
(Phe,
Trp, W)
Ile, I)
Phe, F)
Non-polar amino acids
(cont’d)
Glycine
(Gly,
Gly, G)
Cysteine
(Cys,
Cys, C)
Proline
(Pro, P)
9
Polymerization of Amino Acids to Proteins
+
Peptide bond
H2O
Condensation rx
Carboxyl
end
Amino
end
Dipeptide
See also ECB figure 5-1
Lecture 4
Membranes
Fatty Acids
Phospholipids
Lipid bilayer
Other membrane lipids
Membrane properties
Proteins
Amino Acids
Peptide bond
Protein Structure
4 Levels of Protein Structure
1˚ structure: the linear sequence of amino acids
N-terminal to C-terminal
2˚ structure: stretches of the polypeptide chain
that fold into α-helix or β-sheet (H-bonding)
3˚ structure: 3-dimensional conformation of a
polypeptide chain
4˚ structure: multiple polypeptide chains interacting
to form a complex
10
1˚ structure = sequence of amino acids
(ECB Fig. 4-2)
Higher levels of organization are determined by protein folding
Tertiary
structure
Secondary
structure
quaternary
structure
Improper protein folding is associated with disease
Prion diseases - scrapie (sheep), mad cow (bovine), chronic wasting
disease (deer, elk), Creutzfeldt-Jacob disease (CJD, humans)
Alzheimers and Huntingtons diseases - aggregated proteins in brain
11
Secondary Structure
α-helix and β-pleated sheet
α helix
H bond
C
O
H
N
R groups are on outside of helix
H bond
between peptide
bonds, 4 a.a. apart
H bond
β pleated sheet
12
Tertiary Structure
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)
Folding into tertiary structure forms domains in
polypeptide
Two different domains
Single domain
Polypeptide made
up of several
domains
Quaternary structure
Multiple polypeptides interact via noncovalent and covalent
(disulfide) bonds
Disulfide bridge
tetramer
dimer
13