Download Chapter Eight Lipids and Proteins Are Associated in Biological

Chapter Eight
Lipids and Proteins Are
Associated in
Biological Membranes
What is a Lipid
• Lipids: a ___________________________ class of naturally occurring
organic compounds classified together on the basis of common
solubility properties
• insoluble in water, but soluble in aprotic organic solvents including
______________________________________
• _______________________________ in nature
• Lipids include:
• Open Chain forms
• fatty acids, triacylglycerols, sphingolipids, phosphoacylglycerols,
glycolipids,
• lipid-soluble vitamins
• prostaglandins, leukotrienes, and thromboxanes
• Cyclic forms
• cholesterol, steroid hormones, and bile acids
Fatty Acids
• Fatty acid: an unbranched-chain carboxylic acid, most commonly of
__________ carbons, derived from hydrolysis of animal fats, vegetable
oils, or phosphodiacylglycerols of biological membranes
• In the shorthand notation for fatty acids
• the number of carbons and the number of double bonds in
the chain are shown by two numbers, separated by a colon
Fatty Acids (Cont’d)
Length of fatty acid plays a role in its
_____________________
• Usually contain _________numbers of carbons (can
contain ___________, depending on how they are
biosynthesized)
• FA that contain C=C, are ____________________:
If contain only C-C bonds, they are
_______________________
Fatty Acids (Cont’d)
• In most unsaturated fatty acids, the ______________ isomer
predominates; the ______________ isomer is rare
• Unsaturated fatty acids have ____________ melting points than
their saturated counterparts; the greater the degree of unsaturation,
the _______________ the melting point
Triacylglycerols
• Triacylglycerol (triglyceride): an ester of
______________ with three
__________________________
• natural soaps are prepared by boiling triglycerides
(animal fats or vegetable oils) with NaOH, in a reaction
called _______________ (Latin, sapo, soap)
Soaps
• Soaps form water-insoluble salts
when used in water containing
Ca(II), Mg(II), and Fe(III) ions
(____________________)
• Reactions with acids/bases as
catalysts
• Salts formed by
______________________
Phosphoacylglycerols (Phospholipids)
• When one alcohol group of glycerol is esterified by a phosphoric acid rather
than by a carboxylic acid, _________________________________ acid
produced
• __________________ (phosphoglycerides) are the second most abundant
group of naturally occurring lipids, and are found in plant and animal
____________________________
_________________________
• A complex mixture of ___________________ of longchain carboxylic acids and alcohols
• Found as protective coatings for plants and animals
Sphingolipids
• Contain
_________________, a longchain amino alcohol
• Found in plants and animals
• Abundant in
______________ system
• Structurally similar to
_______________________
Glycolipids
• Glycolipid: a compound in
which a _____________ is
bound to an -OH of the lipid
• In most cases, sugar is either
glucose or galactose
• many glycolipids are derived
from ceramides
• Glycolipids with complex
carbohydrate moiety that
contains more than 3 sugars are
known as
______________________
(Fig. 8.8, p. 207)
Steroids
• Steroids: a group
of lipids that have a
fused-ring structure
of three
_______________
rings, and one
_______________
ring.
Sex Hormones
• _____________________________: male sex hormones
• synthesized in the ____________________
• responsible for the development of male secondary sex
characteristics
• Testosterone
• _____________________________: female sex hormones
• synthesized in the ____________________
• responsible for the development of female secondary
sex characteristics and control of the menstrual cycle
(refer to Figure 8.9, p. 207)
Cholesterol
• The steroid of most interest in our discussion of
____________________________ is cholesterol
Biological Membranes
• Every cell has a cell membrane (plasma membrane)
• ___________________ cells also have membrane-enclosed
organelles (nuclei, mitochondria…etc.)
• Molecular basis of membrane structure is in ____________
component(s):
• polar head groups are in contact with the _____________
environment
• nonpolar tails are buried within the _____________
• the major force driving the formation of lipid bilayers is
_______________________________ interaction
• the arrangement of hydrocarbon tails in the interior can be
______________ (if rich in saturated fatty acids) or
__________________ (if rich in unsaturated fatty acids)
Lipid Bilayers
• The ___________
_____________ of
the bilayer contains
charged groups
• The ____________
_________ lie in the
interior of the bilayer
Biological Membranes
• Plant membranes have a higher percentage of
___________ fatty acids than animal membranes
• The presence of cholesterol is characteristic of
___________ rather than _________ membranes
• __________________ membranes are less fluid
(more rigid) than plant membranes
• The membranes of _________________, which
contain no appreciable amounts of steroids, are the
most fluid
Membrane Layers
• Both inner and outer layers
of bilayer contain
____________ of lipids
• Compositions on inside
and outside of lipid bilayer
can be different
• This distinguishes the layers
Effect of Double Bonds on the
Conformations of Fatty Acids
• ___________ in
hydrocarbon chain
• Causes
_________________ in
packing against other
chains
• This disorder causes
__________________ in
membranes with cisdouble bonds vs
saturated FA chains
Cholesterol reduces Fluidity
• Presence of cholesterol
reduces fluidity by
stabilizing
_______________
_______________
_______________
of hydrocarbon tails of
FA
• Due to
________________
interactions
Temperature Transition in Lipid Bilayer
• With heat, membranes become more disordered;
the transition temperature is _____________ for
more rigid membranes; it is ______________ for
less rigid membranes
• _______________ of the lipid chains increases
dramatically (Biochemical Connections p. 212)
Membrane Proteins
• Functions: transport substances across membranes; act as receptor sites, and
sites of enzyme catalysis
• ______________________________________ proteins
• bound by electrostatic interactions
• can be removed by raising the ionic strength
• ______________________________________ proteins
• bound tightly to the interior of the membrane
• can be removed by treatment with detergents or ultrasonification
• removal generally denatures them
Membrane Proteins
• 1, 2, and 4 are integral proteins
• 3 is a peripheral protein
Proteins Can be Anchored to Membranes
• N-myristoyl- and
S-palmitoyl
____________
motifs
• ____________
can be via
N-terminal gly
• ____________
linkage with Cys
Fluid Mosaic Model
• Fluid: _________________ of components in the
membrane;
• proteins, for example, “float” in the membrane and can
__________________________________
• Mosaic: components in the membrane exist
________________ as
_____________________________
• the structure is a lipid bilayer with proteins, glycolipids,
and steroids such as cholesterol embedded in it
• no complexes, as for example, lipid-protein complexes,
are formed
Fluid Mosaic Model of Membrane
Structure
Membrane Function: Membrane Transport
Passive transport
• driven by a ______________________________
• simple diffusion: a molecule or ion moves through an
opening
• facilitated diffusion: a molecule or ion is carried across a
membrane by a carrier/channel protein
• Active transport
• a substance is moved ___________________ a
concentration gradient
• primary active transport: transport is linked to the
hydrolysis of ATP or other high-energy molecule; for
example, the Na+/K+ ion pump (Figure 8.24)
• secondary active transport: driven by H+ gradient
Facilitated Transport
• Passive diffusion of species (uncharged) across membrane,
depends on ________________ & presence of carrier
protein
Primary Active transport
• Movement of molecules against a gradient directly
linked to hydrolysis of high-energy yielding molecule
(e.g. _________)
Membrane Receptors
Membrane
receptors
• generally
____________
_ proteins
• binding of a
biologically
active substance
to a receptor
initiates an
action within
the cell
Lipid-Soluble Vitamins
2 classes of vitamins: _____________________________
Vitamin A
• Vitamin A (retinol) occurs only in ______________________
• Extensively unsaturated hydrocarbon (-carotene)
• Vitamin A is found in the plant world in the form of a
provitamin in a group of pigments called ______________
• enzyme-catalyzed cleavage of -carotene followed by reduction
gives two molecules of vitamin A
Vitamin A
• The best understood role of vitamin A is its participation in
the visual cycle in rod cells
• the active molecule is ________ (vitamin A aldehyde)
• retinal forms an imine with an -NH2 group of the
protein opsin to form the visual pigment called
__________________________________
• the primary chemical event of vision in rod cells is
absorption of light by rhodopsin followed by
____________________________________ of the
11-cis double bond to the 11-trans double bond
• (Biochemical Connections, p. 225)
Vitamin D
A group of
structurally related
compounds that are
involved in the
regulation of
________________
and
________________
metabolism
• the most abundant
form
in the circulatory
system is
______________
Vitamin E
The most active vitamin E is _______________________
• Vitamin E is an _____________________; traps HOO• and
ROO• radicals formed as a result of oxidation by O2 of
unsaturated hydrocarbon chains in membrane phospholipids
Vitamin K
• Vitamin K has an
important role in
the
_____________
process
• Long unsaturated
hydrocarbon side
chain consists of
repeating
____________
units
Prostaglandins
• Prostaglandins: a family of compounds that have the
_________________________________ of prostanoic acid
• First detected in seminal fluid…from __________________
• The metabolic precursor is ______________________ acid (20
carbon atoms: 4 double bonds)
• Production of prostaglandins from arachidonic acid occurs in
several steps.
Arachodonic Acid and Some
Prostoglandins
Leukotrienes
• Compounds also derived from arachidonic acid
• Found in _____________________________
• Consists of 3 _________________ double bonds
• An important property is constriction of _________
________________, especially in the lungs
Leukotrienes (Cont’d)