3/17/2015 1 LIPIDS, MEMBRANE AND CELLULAR TRANSPORT CHAPTER VII LIPID
Feb 06, 2016
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LIPIDS, MEMBRANE AND
CELLULAR TRANSPORT
CHAPTER VII
LIPID
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• Lipid is not a polymer
• But they still high tendency to associate through non
covalent forces
• They characterized by their structure
a-hydrophilic head
b-hydrophobic tail
b
a
LIPID
• Membrane or barrier of cell membrane that
control materials in and out of the cell
• Energy storage (triacylglyceride)
• Cushioning (adipose tissue)
• Transmission(signal transduction)
• Communication between cell (steroid and
hormone)
GENERAL FUNCTION OF
LIPIDS
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• Natural foods (unprocessed foods) contain two main types of fatty acids - saturated and unsaturated
– Saturated fatty acids - which come from animal fats (meat, lard, dairy products) and tropical oils such as coconut and palm oils - raise the levels of LDL cholesterol
– Unsaturated fats - which come from vegetable oils - in general do not increase cholesterol levels, and may reduce them
TRANS FATTY ACIDS
• Trans fatty acids (trans fats) are a third form of fatty
acids
• While trans fats do occur in tiny amounts in some
foods (particularly foods from animals), almost all
the trans fats now in our diets come from an
industrial process that partially hydrogenates (adds
hydrogen to) unsaturated fatty acids
• Trans fats, then, are a form of processed vegetable
oils
TRANS FATTY ACIDS
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Unsaturated Fatty Acids
Saturated Fatty Acids
• Propionic Acid
CH3CH2COOH
• Butyric Acid
CH3(CH2)2COOH
• Valeric Acid
CH3(CH2)3COOH
• Caproic Acid
CH3(CH2)4COOH
• Myristoleic acid
CH3(CH2)3CH=CH(CH2)7COOH
• Palmitoleic acid
CH3(CH2)5CH=CH(CH2)7COOH
• Sapienic acid
CH3(CH2)8CH=CH(CH2)4COOH
• Oleic acid
CH3(CH2)7CH=CH(CH2)7COOH
FATTY ACIDS:
THE COMMON NAMES
The difference between
cis and trans fatty acid’s
structure
Example of
trans fatty
acids:
Burger and fries
What Is Unhealthy About Trans Fats?
• Trans fats increase total cholesterol levels and
LDL cholesterol levels; worse (and in contrast
to saturated fats), they reduce HDL
cholesterol levels
• Trans fats also appear to interfere with the
body's usage of omega-3 fatty acids, which
are important for heart health
TRANS FATTY ACIDS
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1 Fatty Acid + 3 Glycerol = Triacylglycerol
• Remove water (condensation)
• Linked by ester bond
TRIACYLGLYCEROL
• Oil
– Unsaturated fatty acid
– Liquid at room temperature
– Can undergo hydrogenation process
• Fat
– Mainly saturated fatty acid
– Solid/semisolid at room temperature
TRIACYLGLYCEROL
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• Glycerophospholipids or Phosphoglycerides are glycerol
based phospholipids
• They are the main component of biological membranes such
as phospholid bilayer
Structures
• It contains a glycerol core with fatty acids
• They can be the same or different subunits of fatty acids
• Carbon 1 (tail, non-polar) contains a fatty acid,
typically saturated.
• Carbon 2 (tail, non-polar) contains a fatty acid,
typically unsaturated and in the cis conformation, thus
appearing "bent“
• Carbon 3 (head, polar) contains a phosphate group or an
alcohol attached to a phosphate group
GLYCEROPHOSPHOLIPIDS GLYCEROPHOSPHOLIPIDS
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Uses in membranes:
• Each glycerophospholipid molecule consists of a
small polar head group and two long hydrophobic chains
• In the cell membrane, the two layers of phospholipids are
arranged as follows: – The hydrophobic tails point to each other and form a fatty, hydrophobic center
– The ionic head groups are placed at the inner and outer surfaces of the cell
membrane
• This is a stable structure because the ionic hydrophilic head
groups interact with the aqueous media inside and outside
the cell, whereas the hydrophobic tails maximize hydrophobic
interactions with each other and are kept away from the
aqueous environments
GLYCEROPHOSPHOLIPIDS • Sphingolipids are a class of lipids containing a
backbone of sphingoid bases, a set of aliphatic amino alcohols that includes sphingosine
• Play important roles in signal transmission and cell recognition
• Sphingolipidoses, or disorders of sphingolipid metabolism, have particular impact on neural tissue
• A sphingolipid with an R group consisting of a hydrogen atom only is a ceramide
• Other common R groups include phosphocholine, yielding a sphingomyelin, and various sugar monomers or dimers, yielding cerebrosides and globosides, respectively
• Cerebrosides and globosides are collectively known as glycosphingolipids
SPHINGOLIPIDS
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SPHINGOLIPIDS
• Simple Sphingolipids
– Ceramides
• Complex Sphingolipids:
– Sphingomyelins
– Glycosphingolipids
• Cerebrosides
• Sulfatides
• Gangliosides
• Inositol
SPHINGOLIPIDS
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• Sphingoid bases are the fundamental building
blocks of all sphingolipids
• The main mammalian sphingoid bases are
dihydrosphingosine and sphingosine, while
dihydrosphingosine and phytosphingosine are
the principle sphingoid bases in yeast
• Sphingosine, dihydrosphingosine, and
phytosphingosine may be phosphorylated
SPHINGOLIPIDS
FUNCTIONS:
• Protect the cell surface against harmful
environmental factors by forming a
mechanically stable and chemically
resistant outer leaflet of the plasma
membrane lipid bilayer
• Cell recognition and signalling
SPHINGOLIPIDS
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STEROID
4 fused-rings…..3 CYCLOHEXANE, 1 CYCLOPENTANE
FUNCTIONS:
Steroid hormones
Produce sex difference or support reproduction androgens, estrogens, and progestagens
Corticosteroids include glucocorticoids and mineralocorticoids
Glucocorticoids:
Regulate many aspects of metabolism and immune function, whereas mineralocorticoids
help maintain blood volume and control renal excretion of electrolytes
Most medical 'steroid' drugs are corticosteroids
Anabolic steroids:
A class of steroids that interact with androgen receptors to increase muscle and bone
synthesis
There are natural and synthetic anabolic steroids
In popular language, the word "steroids" usually refers to anabolic steroids
Cholesterol, which modulates the fluidity of cell membranes and is the principal
constituent of the plaques implicated in atherosclerosis
STEROIDS
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MEMBRANE STRUCTURE • Integral proteins
– Span lipid bilayer
– Transmembrane proteins
– Hydrophobic regions consist of one or more stretches of nonpolar amino acids
– Often coiled into alpha helices
MEMBRANE STRUCTURE
EXTRACELLULAR
SIDE N-terminus
C-terminus CYTOPLASMIC
SIDE a Helix
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MEMBRANE STRUCTURE
Enzymes Signal
Receptor ATP
Transport Enzymatic activity Signal transduction
Glyco- protein
Cell-cell recognition Intercellular joining Attachment to the
cytoskeleton and extra-
cellular matrix (ECM)
MEMBRANE STRUCTURE
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THE ROLE OF MEMBRANE CARBOHYDRATES
IN CELL-CELL RECOGNITION
• Cells recognize each other by binding to surface
molecules, often carbohydrates, on the plasma
membrane
• Carbohydrates covalently bonded to lipids (glycolipids) or more often to proteins (glycoproteins)
• Much variability of extracellular carbohydrates among species, individuals, cell types in an individual
Plasma membrane:
Cytoplasmic face
Extracellular face Transmembrane
glycoprotein
Plasma membrane:
Secreted
protein
Vesicle
Golgi
apparatus
Glycolipid
Secretory
protein
Transmembrane
glycoproteins
ER
Synthesis and Sidedness of Membranes:
• Membranes distinct inside and outside faces
• Plasma membrane is added to by vesicles from ER & Golgi
• Secreted and integral membrane proteins, lipids and associated carbohydrates transported to membrane by these vesicles
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TRANSPORT ACROSS CELLULAR MEMBRANES
• To exchange materials with surroundings in part to take in nutrients and give off waste
• Exchange(or transport) regulated: selective permeability
• Structure Dictates Membrane Permeability: – Hydrophobic (nonpolar) molecules cross membrane
rapidly – e.g., hydrocarbons, oxygen, CO2 can dissolve in the lipid bilayer and pass
through the membrane rapidly
– Polar molecules cross slowly – e.g. sugars, charged proteins, water
HOW DO HYDROPHILIC SUBSTANCES CROSS
MEMBRANES?
Transport proteins
– Some create hydrophilic channels across membranes for
polar molecules or ions to pass through
– Example: Aquaporin : water channel protein
Carrier proteins – binds solutes & change the shape of carrier
– help to facilitate passage across membrane
– highly specific for transported solutes
– Examples: glucose transporter is a carrier protein for glucose only
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Molecules of dye Membrane (cross section)
WATER
Net diffusion Net diffusion Equilibrium
Diffusion of one solute
PASSIVE TRANSPORT: DIFFUSION
• Substances diffuse down their concentration gradient from high to low
• Substances reach dynamic equilibrium
• No work (no added energy) required
Net diffusion Net diffusion Equilibrium
Diffusion of two solutes
Net diffusion Net diffusion Equilibrium
PASSIVE TRANSPORT: DIFFUSION
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EFFECTS OF OSMOSIS ON WATER BALANCE
• Osmosis
– diffusion of water across a selectively permeable membrane
• Diffuses across a membrane from the region of lower solute (such as an ion) concentration to the region of higher solute concentration
• The direction of osmosis is determined only by a difference in total solute concentration
Lower
concentration
of solute (sugar)
Higher
concentration
of sugar
Same concentration
of sugar
Selectively
permeable mem-
brane: sugar mole-
cules cannot pass
through pores, but
water molecules can
H2O
Osmosis
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WATER BALANCE OF CELLS WITHOUT WALLS
Tonicity
ability of a solution to cause a cell to gain or lose water
Isotonic solution
solute concentration is equal inside and outside the cell -->
no net water movement cell remains same size
Hypertonic solution
external solute concentration is greater than that inside the
cell-->cell loses water
Hypotonic solution
external solute concentration is less than that inside the cell--> cell
gains water
WATER BALANCE OF CELLS WITH
WALLS VS NO WALLS
• Cell walls help maintain water balance
• Plant cell in hypotonic solution swells -->turgid (firm)
• Plant cell and its surroundings isotonic--> no net water movement; the cell becomes flaccid (limp), and the plant may wilt
• In hypertonic environment, plant cells lose water--> membrane pulls away from the wall: plasmolysis
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EXTRACELLULAR
FLUID
Channel protein Solute
CYTOPLASM
Facilitated diffusion transport proteins speed movement of molecules
across the plasma membrane
PASSIVE TRANSPORT AIDED BY PROTEINS
CHANNEL PROTEIN
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Carrier protein Solute
PASSIVE TRANSPORT AIDED BY PROTEINS
CARRIER PROTEIN
Cytoplasmic Na+ bonds to
the sodium-potassium pump
CYTOPLASM Na+
[Na+] low
[K+] high
Na+
Na+
EXTRACELLULAR
FLUID
[Na+] high
[K+] low
Na+
Na+
Na+
ATP
ADP
P
Na+ binding stimulates
phosphorylation by ATP.
Na+ Na+
Na+
Phosphorylation causes
the protein to change its
conformation, expelling Na+
to the outside.
P
Extracellular K+ binds
to the protein, triggering
release of the phosphate
group.
P P
Loss of the phosphate
restores the protein’s
original conformation.
K+ is released and Na+
sites are receptive again;
the cycle repeats.
ACTIVE TRANSPORT
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Diffusion Facilitated diffusion
Passive transport
ATP
Active transport
H+
ATP
CYTOPLASM
EXTRACELLULAR
FLUID
Proton pump
H+
H+
H+
H+
H+
+
+
+
+
+
–
–
–
–
–
ELECTROGENIC PUMPS
• A transport protein that generates a voltage across a membrane--> opposite charges across membrane (membrane potential)
• Example: In animals, Na-K pump
• In plant fungi and bacteria, proton pump Requires ATP (active transport)
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H+
ATP
Proton pump
Sucrose-H+
cotransporter
Diffusion
of H+
Sucrose
H+
H+
H+
H+
H+ H+
+
+
+
+
+
+
–
–
–
–
–
–
COTRANSPORT
• Coupled Transport by a Membrane Protein • When active transport of one solute indirectly drives transport
of another
• Plants commonly use the proton gradient generated by proton pumps to drive transport of nutrients into the cell
HOW DO LARGE MOLECULES MOVE IN AND OUT OF CELLS?
• Small molecules and water enter or leave the cell through the lipid bilayer or by transport proteins
• Large molecules, such as polysaccharides and proteins, cross the membrane via vesicles
Plasma membrane:
Cytoplasmic face
Extracellular face Transmembrane
glycoprotein
Plasma membrane:
Secreted
protein
Vesicle
Golgi
apparatus
Glycolipid
Secretory
protein
Transmembrane
glycoproteins
ER
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• Exocytosis – Transport vesicles with cargo migrate to the membrane, fuse
with it, and are release contents
– Example:
– Many secretory cells use exocytosis to export their products
– Pancreatic cells (beta-cells) secrete insulin
• Endocytosis
– Cell takes in macromolecules by forming vesicles at the
plasma membrane
– Reversal of exocytosis, involving different proteins
HOW DO LARGE MOLECULES MOVE IN AND OUT OF CELLS?
• Three types of endocytosis:
– Phagocytosis (“cellular eating”): • Cell engulfs particle in a vacuole
– Pinocytosis (“cellular drinking”): • Cell creates vesicle around fluid
– Receptor-mediated endocytosis: • Binding of ligands to receptors triggers vesicle
formation
ENDOCYTOSIS
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Receptor
RECEPTOR-MEDIATED ENDOCYTOSIS
Ligand
Coated
pit
Coated
vesicle
Coat protein
Coat
protein
Plasma
membrane 0.25 µm
A coated pit
and a coated
vesicle formed
during
receptor-
mediated
endocytosis
(TEMs).
ENDOCYTOSIS