Chapter Eight Lipids and Proteins Are Associated in Biological Membranes

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Chapter EightLipids and Proteins Are Associated
in Biological Membranes
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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

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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

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Fatty Acids (Contd)

• 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 CC, are ____________________
• If contain only C-C bonds, they are
  _______________________

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Fatty Acids (Contd)

• 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

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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)

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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 ______________________

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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
  ____________________________

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_________________________

• A complex mixture of ___________________ of
  long-chain carboxylic acids and alcohols
• Found as protective coatings for plants and
  animals

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Sphingolipids

• Contain _________________, a long-chain amino
  alcohol
• Found in plants and animals
• Abundant in ______________ system
• Structurally similar to ________________________

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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)

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Steroids

• Steroids a group of lipids that have a
  fused-ring structure of three _______________
  rings, and one _______________ ring.

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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)

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Cholesterol

• The steroid of most interest in our discussion of
  ____________________________ is cholesterol

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Biological Membranes

• Every cell has a cell membrane (plasma membrane)
• ___________________ cells also have
  membrane-enclosed organelles (nuclei,
  mitochondriaetc.)
• 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)

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Lipid Bilayers

• The ___________ _____________ of the bilayer
  contains charged groups
• The ____________ _________ lie in the interior of
  the bilayer

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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

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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

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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 cis-double bonds vs saturated FA
  chains

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Cholesterol reduces Fluidity

• Presence of cholesterol reduces fluidity by
  stabilizing _______________ _______________
  _______________ of hydrocarbon tails of FA
• Due to ________________ interactions

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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)

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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

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Membrane Proteins

• 1, 2, and 4 are integral proteins
• 3 is a peripheral protein

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Proteins Can be Anchored to Membranes

• N-myristoyl- and S-palmitoyl ____________ motifs
• ____________ can be via N-terminal gly
• ____________ linkage with Cys

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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

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Fluid Mosaic Model of Membrane Structure
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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

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Facilitated Transport

• Passive diffusion of species (uncharged) across
  membrane, depends on ________________ presence
  of carrier protein

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Primary Active transport

• Movement of molecules against a gradient directly
  linked to hydrolysis of high-energy yielding
  molecule (e.g. _________)

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Membrane Receptors

• Membrane receptors
• generally _____________ proteins
• binding of a biologically active substance to a
  receptor initiates an action within the cell

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Lipid-Soluble Vitamins

• 2 classes of vitamins ___________________________
  _______________

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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

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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)

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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 ______________

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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

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Vitamin K

• Vitamin K has an important role in the
  _____________ process
• Long unsaturated hydrocarbon side chain consists
  of repeating ____________ units

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Prostaglandins

• Prostaglandins a family of compounds that have
  the _________________________________ of
  prostanoic acid
• First detected in seminal fluidfrom
  __________________
• The metabolic precursor is ______________________
  acid (20 carbon atoms 4 double bonds)
• Production of prostaglandins from arachidonic
  acid occurs in several steps.

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Arachodonic Acid and Some Prostoglandins
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Leukotrienes

• Compounds also derived from arachidonic acid
• Found in _____________________________
• Consists of 3 _________________ double bonds
• An important property is constriction of
  _________ ________________, especially in the
  lungs

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Leukotrienes (Contd)