Lipids and Proteins Are Associated in Biological

advertisement
Lipids and Proteins Are Associated
in Biological Membranes
Chapter 8
What is a lipid?
 Lipids: consists of nonpolar groups
- Classified on the basis of common solubility
properties
- insoluble in water
- soluble in organic solvents like chloroform and
acetone
- Amphipathic in nature
What are the two groups of lipids?
 Lipids include:
 Open Chain forms
 fatty acids, triacylglycerols, sphingolipids,
phosphoacylglycerols, and glycolipids,
 lipid-soluble vitamins
 prostaglandins, leukotrienes, and thromboxanes
 Cyclic forms
 cholesterol, steroid hormones, and bile acids
What are Fatty Acids?
 - Carboxyl group at polar end and hydrocarbon chain at
non polar tail
 - Length of fatty acid plays a role in its chemical
character
- Usually contain even numbers of carbons (can contain
odd, depending on how they are biosynthesized)
What are saturated fatty acids?
-
Contain only C-C bonds - saturated
What are unsaturated fatty acids?
 In most unsaturated fatty acids, the cis isomer
predominates; the trans isomer is rare
 FA that contain C=C, are unsaturated
 Unsaturated fatty acids have lower melting points
than their saturated counterparts
What are triacylglycerols?
 Triacylglycerol (triglyceride): an ester of glycerol with three
fatty acids
 natural soaps are prepared by boiling triglycerides (animal
fats or vegetable oils) with NaOH, in a reaction called
saponification (Latin, sapo, soap)
What are soaps?
 Soaps form waterinsoluble salts when
used in water containing
Ca(II), Mg(II), and
Fe(III) ions (hard
water)
 Results in characterisitc
scum left on insides of
bathtubs and sinks
What are phosphoacylglycerols?
 When one alcohol group of glycerol is esterified by a phosphoric
acid rather than by a carboxylic acid, phosphatidic acid
produced
 Phosphoacylglycerols (phosphoglycerides) are the second most
abundant group of naturally occurring lipids
Other important members
 Phosphatidyl ethanolamine (cephalin),
phosphatidyl serine, phosphatidyl choline
(lecithin), phosphatidyl inositol, phosphatidyl
glycerol and diphosphatidyl glycerol
(cardiolipin)
What are Waxes?
 A complex mixture of esters of long-chain carboxylic
acids and long-chain alcohols
 Found as protective coatings for plants and animals
What are Sphingolipids?
 Contain sphingosine, a longchain amino alcohol
sphingosine
 Found in plants and animals
 Abundant in nervous system
 Bares structural similarity to
phospholipids
What are Glycolipids?
 a compound in which a
carbohydrate is bound
to an -OH of the lipid
 many glycolipids are
derived from
ceramides
 Gangliosides are
Glycolipids with
complex carbohydrate
moiety that contains
more than 3 sugars
What are Steroids?
 Steroids: a group of
lipids that have fusedring structure
- of 3 six-membered rings
- and 1 five-membered
ring
Sex Hormones
 Androgens: male sex hormones
 synthesized in the testes
 responsible for the development of male secondary
sex characteristics
 Testosterone
 Estrogens: female sex hormones
 synthesized in the ovaries
 responsible for the development of female secondary
sex characteristics and control of the menstrual cycle
What is Cholesterol?
 Present in biological
membrane
 Does not occur in
prokaryotes
 Precursor of vitamin D3
 Harmful - when present
in excess Atherosclerosis
What is the structure of lipid bilayers?
 The polar surface of the
bilayer contains charged
groups
 The hydrophobic tails
lie in the interior of the
bilayer
How does the composition of bilayer affect
its properties?
 Both inner and outer
layers of bilayer contain
mixtures of lipids
 Compositions on inside
and outside of lipid
bilayer can be different
How does the composition of bilayer affect
its properties?
 In saturated fatty acids,
a linear arrangement of
hydrocarbon chains
leads to close packing of
molecules in bilayer
 Provides rigidity
How does the composition of bilayer affect
its properties? (Unsaturated)
 Kink in hydrocarbon chain
 Causes disorder in packing
against other chains
 This disorder causes greater
fluidity in membranes with
cis-double bonds vs......
saturated FA chains
Biological Membranes
 Plant membranes have a higher percentage of unsaturated
fatty acids than animal membranes
 The presence of cholesterol is characteristic of animal
rather than plant membranes
 Animal membranes are less fluid (more rigid) than plant
membranes
 The membranes of prokaryotes are fluid - contain no
steroids
Temperature Transition in Lipid Bilayer
• With heat, the transition temperature is higher for
more rigid membranes
- it is lower for less rigid membranes
Membrane Proteins
 Functions: transport substances across membranes; act as receptor
sites, and sites of enzyme catalysis
 Peripheral proteins
 bound by electrostatic interactions
 can be removed by raising the ionic strength
Membrane Proteins
 Integral proteins
 bound tightly to the interior of the membrane
 can be removed by treatment with detergents or
ultrasonification
 removal generally denatures them
Fluid Mosaic Model
 Fluid: there is lateral motion of components in the
membrane
 Proteins float in the membrane and can move along its
plane of membrane
 Mosaic: components in the membrane exist side-by-side as
separate entities
 Forms a lipid bilayer with proteins, glycolipids, and
steroids such as cholesterol embedded in it
 no lipid-protein complexes, are formed
Fluid Mosaic Model of Membrane
Structure
How does transport through membranes take
place?
Passive transport
 driven by a
concentration gradient
(from higher to lower)
 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
How does transport through membranes take
place?
 Active transport
 a substance is moved against 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
How do membrane receptors work?
 Membrane receptors
 oligomeric proteins
 binding of a biologically
active substance to a
receptor initiates an
action within the cell
Lipid-Soluble Vitamins
 Vitamins are divided into two classes: lipid-soluble and watersoluble
How are prostaglandins related to lipids?
 Prostaglandins: a family of compounds that
have the 20-carbon skeleton of prostanoic acid
 First detected in seminal fluid…from prostate
 The metabolic precursor is arachidonic acid (20
carbon atoms: 4 double bonds)
How are leukotrienes related to lipids?
 Compounds also derived from arachidonic acid
 Found in white blood cells (leukocytes)
 Consists of 3 conjugated double bonds
 Constriction of smooth muscles, especially in
the lungs



This project is funded by a grant awarded under the President’s Community Based Job Training
Grant as implemented by the U.S. Department of Labor’s Employment and Training
Administration (CB-15-162-06-60). NCC is an equal opportunity employer and does not
discriminate on the following basis:
against any individual in the United States, on the basis of race, color, religion, sex,
national origin, age disability, political affiliation or belief; and
against any beneficiary of programs financially assisted under Title I of the Workforce
Investment Act of 1998 (WIA), on the basis of the beneficiary’s citizenship/status as a lawfully
admitted immigrant authorized to work in the United States, or his or her participation in any
WIA Title I-financially assisted program or activity.
Disclaimer

This workforce solution was funded by a grant awarded
under the President’s Community-Based Job Training
Grants as implemented by the U.S. Department of Labor’s
Employment and Training Administration. The solution was
created by the grantee and does not necessarily reflect the
official position of the U.S. Department of Labor. The
Department of Labor makes no guarantees, warranties, or
assurances of any kind, express or implied, with respect to
such information, including any information on linked sites
and including, but not limited to, accuracy of the
information or its completeness, timeliness, usefulness,
adequacy, continued availability, or ownership. This
solution is copyrighted by the institution that created
it. Internal use by an organization and/or personal use by
an individual for non-commercial purposes is
permissible. All other uses require the prior authorization
of the copyright owner.
Download