Download Fatty acid

Lipids & Biological Membranes
Biological
membranes
that
define
the
boundaries of cells are composed largely of lipid
molecules, which form a permeability barrier
allowing only certain molecules to enter the cell.
Lipids are one of the four important classes of
biomolecules that have a variety of structural
and functional roles.
Harini Chandra
Master Layout (Part 1)
1
This animation consists of 4 parts:
Part 1 – Fatty acids
Part 2 – Membrane lipids
Part 3 – Proteins in membrane structures
Part 4 – Properties of cell membranes
b
w
2
w
3
2
a
Fatty acid –
general structure
w-3 double
bond
3
Degree of
unsaturation
Chain length
4
5
Source: Biochemistry by Lubert Stryer, 5th & 6th edition (ebook)
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1
2
Definitions of the components:
Part 1 – Fatty acids
1. Fatty acid: Fatty acids, more simply known as fats, are the key components of
lipids that play an important role in signal transduction pathways and as structural
elements of membranes. They are long hydrophobic chains of different lengths that
possess a carboxylate group at one end. Most naturally occuring fatty acids have an
even number of carbon atoms with varying degrees of unsaturation.
2. Degree of unsaturation: The number of double bonds present in a fatty acid
chain defines its degree of unsaturation.
3
4
5
3. Chain length: The total number of carbon atoms present in a fatty acid chain is its
chain length.
4. w-carbon: Fatty acids are numbered starting from their carboxyl group with the
second and third carbon atoms being known as the a and b carbons. The carbon
atom that is furthest away from the carboxylate group, at the distal end of the chain
is known as the w carbon.
1
Part 1, Step 1:
Fatty acids – general structure
w
b
w
2
3
Degree of
unsaturation
w-3 double
bond
Chain length
Carboxylate
group (C1)
3
Saturated fatty acid
Short chain length &
increased unsaturation
enhance fluidity &
decrease MP of fatty
acids.
Action
As
shown in
animatio
n.
5
1
a
w-carbon
4
2
Description of the action
(Please redraw all figures.)
First show the figure on the left appearing
with its labels from the right end to the left
in parts as depicted in the animation.
Next, show the figure on the right with the
labels appearing after the figure.
Unsaturated fatty acid
Audio Narration
Fatty acids are long hydrophobic chains of carbon atoms
having different lengths and a carboxylate group at one end.
Fatty acids that do not contain any double bonds are said to be
saturated while those possessing one or more double bonds in
their structure are unsaturated. Most naturally occuring fatty
acids have an even number of carbon atoms with varying
degrees of unsaturation. The carboxylate group is numbered as
one and the last carbon atom that is furthest away from the
carboxylate group is known as the omega carbon.
Source: Biochemistry by Lubert Stryer, 6th edition (ebook)
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2
Part 1, Step 2:
Palmitic acid (C16, saturated)
12
14
16
13
15
3
9
4
7
2
1
3
5
Oleic acid (C18, monounsaturated)
2
Double bonds referred to by cis/trans- ∆4
number at which the double bond is
15 located in superscript.
17
6
5
13
16
12
10
9
8
7
Action Description of the action
As
shown
in
animati
on.
1
3
18:1 indicative of 18 carbon
atoms with 1 double bond.
11
14
5
6
8
10
11
18
4
Systematic name is derived by
replacing the final ‘e’ of the parent
hydrocarbon with ‘oic’/’oate’. For eg.
C16 fatty acid is hexadecanoate
(parent hydrocarbon is hexadecane).
Fatty acids - nomenclature
(Please redraw all figures.)
First show the figure on top followed by
the green callour located above it. Next
show the figure below followed by the
two text boxes and then the violet callout
shown.
Systematic name: cis-∆9-octadecenoate
Audio Narration
The fatty acid names are derived from their corresponding parent
hydrocarbons by replacing the ‘e’ at the end with ‘oic’ or ‘oate’. A
saturated fatty acid with 16 carbon atoms, for instance, is known
as hexadecanoate. If there is one double bond, then it become
deceneoate with the position of the double bond being indicated
as a superscript after a delta symbol. For instance, a 18 carbon
fatty acid with one double bond is known as ocatadecenoate while
with two double bonds, it is known as octadecadienoate.
Source: Biochemistry by Lubert Stryer, 6th edition (ebook)
Master Layout (Part 2)
1
This animation consists of 4 parts:
Part 1 – Fatty acids
Part 2 – Membrane lipids
Part 3 – Proteins in membrane structures
Part 4 – Properties of cell membranes
2
Cholesterol
Fatty acid
Sugar unit
3
Glycolipids
4
Fatty
acid
Fatty
acid
G
L
Y
C
E
R
O
L
5
Phosphate
Phospholipids
Source: Biochemistry by Lubert Stryer, 6th edition (ebook)
Alcohol
1
2
3
4
5
Definitions of the components:
Part 2 – Membrane lipids
1. Lipids: These are water insoluble biomolecules that readily dissolve in organic
solvents like chloroform and have a wide range of biological functions. They are
important components of membranes, serve as fuel reserves and signalling molecules.
Three important membrane lipids include phospholipids, glycolipids and cholesterol.
2. Phospholipid: Phospholipids are composed of four components – fatty acids, a
platform to which the fatty acid is attached, phosphate residue and an alcohol attached to
the phosphate. The platform to which the fatty acids are linked is commonly glycerol but
in some cases, a more complex alcohol known as sphingosine may also be present.
Phospholipids containing glycerol are known as phosphoglycerides, with two OH groups
of glycerol being esterified with the carboxylate groups of fatty acids. The fatty acid
chains form the hydrophobic tail while the remaining components constitute the
hydrophilic head group.
3. Glycolipid: Lipids that have a sugar component in them are known as glycolipids.
They are made up of a sphingosine backbone with the amino group acylated by a fatty
acid and one or more sugar residues attached to the primary hydroxyl group. The
simplest glycolipid is known as cerebroside which contains either glucose or galactose as
its sugar residue.
4. Cholesterol: Cholesterol is a steroid molecule whose structure is significantly different
from that of phospholipids and glycolipids. Cholesterol is found in varying quantities in
animal membranes but is not present in prokaryotes. It is composed of a hydrocarbon
chain linked to one end and a hydroxyl group at the other end.
Part
2,
Step
1:
1
Membrane lipids - phospholipids
G
L
Y
C
E
R
O
L
Fatty
acid
2
Fatty
acid
Phosphatidate
(Diacylglycerol 3-phosphate)
Glycerol
backbone
Phosphate
group
Shorthand depiction
Hydrophobic tail
Action
As shown in
animation.
5
Alcohol
Fatty acids
3
4
Phosphate
Polar head
group
Ester
linkage
Description of the action
Audio Narration
(Please redraw all figures.)
Phospholipids are composed of four components – fatty acids, a
First show the coloured block diagram structures on left top.
platform to which the fatty acid is attached, phosphate residue
First the blue rectangle must appear followed by the two ovals and an alcohol attached to the phosphate. The platform to which
and then the green rectangle and finally the violet
the fatty acids are linked may be glycerol or sphingosine.
parallelogram. Next, the structure on bottom right must appear. Phospholipids containing glycerol are known as
First the central region must appear marked ‘glycerol
phosphoglycerides, with two OH groups of glycerol being
backbone’. Next, the groups on the left marked ‘fatty acids’
esterified with the carboxylate groups of fatty acids. The simplest
must appear followed by the pink group on the right. The green
phospholipid, phosphatidate, is made up of only the phosphate
box must then highlight the region as indicated with the
corresponding label. The figure on bottom left must then appear group and fatty acids attached to the glycerol backbone.
with the labels.
Source: Biochemistry by Lubert Stryer, 6th edition (ebook)
Part
2,
Step
2:
1
Common phosphoglycerides
Glycerol
backbone
2
Fatty acids
3
4
Phosphatidyl ethanolamine
Phosphatidyl serine
Phosphatidyl choline
Phosphatidyl inositol
Diphosphatidyl glycerol
(cardiolipin)
Action Description of the action
As shown
in
animation
.
5
Audio Narration
The important phophoglycerides found in membranes
(Please redraw all figures.)
First show the blue and green parts of the are derived from phosphatidate by esterification of the
structure with their labels. Next, the red phosphate group with the hydroxyl group of various
groups must appear sequentially one after
alcohols. The most commonly observed
another with their corresponding names
appearing below as shown in animation. phosphoglycerides include phosphatidyl serine, choline,
ethanolamine, inositol and diphosphatidyl glycerol, also
(The red groups are layered one over
another – watch in slide show mode only) known as cardiolipin.
Source: Biochemistry by Lubert Stryer, 6th edition (ebook)
Part
2,
Step
3:
1
Phospholipids - sphingomyelin
2
Sphingosine
Fatty acid
3
Choline
Sphingomyelin
4
Action
As shown
in
animation.
5
Description of the action
(Please redraw all figures.)
First show the figure on top with its
label followed by the figure below
with its labels as shown.
Audio Narration
Sphingosine is another amino alcohol backbone that serves
as a platform for attachment of fatty acids and alcohols.
Sphingomyelin, derived from sphingosine , consists of a
fatty acid linked to the amino group via an amide bond and a
choline moiety attached to the primary hydroxyl group via a
phosphate group.
Source: Biochemistry by Lubert Stryer, 6th edition (ebook)
Part
2,
Step
4:
1
Membrane lipids - glycolipids
Fatty acid
2
SPHINGOSINE
Sugar
residue(s)
3
4
5
Cerebroside
Action
Description of the action
As shown
in
animation
.
(Please redraw all figures.)
First show the box diagrams shown on top
left. The green rectangle must appear first
follwed by the blue parallelogram and then
the brown oval. Next show the structure
below in which the blue region must appear
first followed by the green region and finally
the pink labeled box.
Audio Narration
Lipids that have a sugar component in them are
known as glycolipids. They are made up of a
sphingosine backbone with the amino group acylated
by a fatty acid and one or more sugar residues
attached to the primary hydroxyl group. The simplest
glycolipid is known as cerebroside which contains
either glucose or galactose as its sugar residue.
Source: Biochemistry by Lubert Stryer, 6th edition (ebook)
Part
2,
Step
5:
1
Membrane lipids - cholesterol
2
Alkyl side chain
3
4
Polar head group
Action
As shown
in
animation.
5
D
C
A
B
Steroid nucleus
Description of the action
(Please redraw all figures.)
Show the appearance of the structure
above. First ring A must appear followed
by ring B, then ring C and then ring D. All
the other groups attached at the various
positions must appear after all four rings
have appeared.
Audio Narration
Another group of structural membrane lipids is the sterols,
found in most eukaryotic cells. The steroid nucleus consists of
four fused rings that are oriented in a planar manner.
Cholesterol is an amphipathic molecule with a polar hydroxyl
head group and a non-polar steroid nucleus and hydrocarbon
side chain. In addition to having a structural role in
membranes, sterols are precursors for several products such
as steroid hormones and bile acids.
Source: Biochemistry by Lubert Stryer, 6th edition (ebook)
Part
2,
Step
6:
1
Micellar
arrangement
Membrane formation by phosphoglycerides
Polar head group
Hydrophobic tail
2
Hydrogen
bonding,
electrostatic
attraction
Hydrophobic,
Van der Waals
interactions
3
Random orientation
Bilayer arrangement
4
Action
As shown
in
animation.
5
Description of the action
(Please redraw all figures.)
First show the green structures oriented
randomly. Next they must be surrounded by
water (blue clouds). When this happens, the
green structures must reorient themselves in
the two arrangements shown on the right
after the arrows. The arrows and green
ovals with the text must then appear.
Audio Narration
The amphipathic nature of the phosphoglyceride molecules consisting
of a polar head group and a hydrophobic tail enables them to
rearrange themselves in an aqueous environment. When they come
in contact with aqueous surroundings, they can either reorient to form
a micellar structure or a bilayer arrangement. In these arrangements,
the polar head groups are in contact with water by means of hydrogen
bonding while the hydrophobic tails interact with each other through
hydrophobic and Van der Waals interactions. The lipid bilayer
arrangement is more favoured for phospholipids and glycolipids.
Source: Biochemistry by Lubert Stryer, 6th edition (ebook)
Master Layout (Part 3)
1
This animation consists of 4 parts:
Part 1 – Fatty acids
Part 2 – Membrane lipids
Part 3 – Proteins in membrane structures
Part 4 – Properties of cell membranes
Glycoprotein
2
Outside
Glycolipid
Integral protein
3
Lipid
bilayer
Phospholipids
4
Sterol
Inside
Peripheral
protein
5
Source: Biochemistry by A.L.Lehninger, 4th edition (ebook)
1
2
Definitions of the components:
Part 3 – Proteins in membrane structures
1. Lipid bilayer: The flat membrane sheets that form a barrier around cells consisting of
two layers of lipid molecules is known as the lipid bilayer. The hydrophobic tail regions
are sequestered within the bilayer, away from the aqueous environment while the polar
heads face outward and interact with the surrounding molecules. The bilayer is also
embedded with proteins that perform specific functions for the cell.
2. Integral proteins: Those proteins that span the membrane and are embedded within
the lipid bilayer are known as integral proteins. They interact extensively with the
hydrophobic chains of lipids and cannot be easily dissociated from the membrane.
3
4
5
3. Peripheral proteins: Peripheral membrane proteins, however, are only bound to the
membrane surfaces by means of electrostatic and hydrogen bond interactions with the
polar head groups of the lipids. They can be easily dissociated from the membrane with
mild agents such as salts, acids or alkali since they are not embedded within it.
4. Glycoprotein: Carbohydrate groups are often covalently attached to proteins to form
glycoproteins. The sugar residues are typically attached to the amide nitrogen atom of the
aspargine side chain or to the oxygen atom of the serine or threonine side chain. These
glycoproteins are components of cell membranes and have a variety of functions in cell
adhesion processes.
Part
3,
Step
1:
1
Integral proteins - Bacteriorhodopsin
Amino acid sequence of membrane protein
AQITGRPEWIWLALGTALMGLGTLYFLVKGM
GVSDPDAKKFYAITTLVPAIAFTMYLSMLLGY
2
GLTMVPFGGEQNPIYWARYADWLFTTPLLLL
D LALLVDADQ G TI LALVGAD GIM IGTGLV GAL
T K VYS YR F V W WAI S TAAM LYI LYV LF F G F T S K
3
AESMRPEVASTFKVLRNVTVVLWSAYVVVW
LIGSEGAGIVPLNIETLLFMVLDVSAKVGFGL
I LLR S RAI F G EAEAPE PSAD GAAAT S
Membrane spanning a-helices
4
Charged residues
Action Description of the action
As shown (Please redraw all figures.)
in
First show the figure on the left. The red
animation. box must then appear which must be
5
Residues of the 7 membrane-spanning helices
(largely non-polar)
zoomed into to show the figure on the right
with the highlighted regions as depicted
along with all the labels and the key shown
below.
Audio Narration
Bacteriorhodopsin is an archaeal integral membrane protein that
plays a role in energy transduction, using light energy for the
transport of protons from inside to outside the cell. It is made of seven
membrane-spanning alpha helices that are oriented perpendicular to
the plane of the membrane. Determination of the amino acid
sequence of this protein revealed that most of the residues within the
membrane are non-polar, thereby allowing favorable interactions with
the lipid hydrocarbon chains. Very few charged residues were found
in the structure.
Source: Biochemistry by Lubert Stryer, 6th edition (ebook)
Part 3, Step 2:
1
Integral proteins – Porins
---
Hydrogen bonded b-strands
2
3
Amino acid sequence of porin from
Rhodopseudomonas blastica
Hydrogen
bonds
Hydrophobic
residues (on
surface of
structure)
Hydrophilic
residues
(buried inside)
4
5
Action Description of the action
Audio Narration
Porins are another class of integral membrane proteins that form channels
As shown in (Please redraw all figures.)
animation. First show the structure on top with its label. within the membrane. They are composed entirely of b-strands with
essentially no alpha helices in their structure. These beta strands are
Then show the dotted arrows and the figure
hydrogen bonded to each other to form a beta sheet which folds to form a
on right top. The brown circles must appear
and pass through the blue cylinder. This must hollow cylindrical structure. The folding occurs such that the polar amino
acid residues line the inside of the cylinder, thereby making it hydrophilic.
happen continuously throughout this
This allows the channel to be filled with water and also allows passage of
animation. Simultaneously, the green box
must appear and this region must be zoomed small ions and charged molecules. The non-polar residues facing outside
into and the figure below must be shown with interact hydrophobically with the lipid chains of the membrane.
its labels and the key on the left.
Source: Biochemistry by Lubert Stryer, 6th edition (ebook)
Part
3,
Step
3:
1
Peripheral proteins
Acid/alkali added –
change in pH
Dissociation
Integral proteins
2
Peripheral membrane proteins
3
Dissociation
4
Action
Description of the action
As shown in (Please redraw all figures.)
animation. First show the figure in the middle with the
5
yellow and blue shapes labeled a-e. Next
show the blue cloud appearing on the blue
shapes with the corresponding label. The blue
shapes, d & e, must then dissociate from the
figure as shown.
Audio Narration
Peripheral membrane proteins are attached to either
the outside or inside surface of the membrane via
electrostatic and hydrogen bond interactions with
either the lipid heads of the membrane or with other
integral proteins. These polar interactions can be
easily disrupted by addition of acids or alkali which
modify the pH or by addition of salts.
Source: Biochemistry by A.L.Lehninger, 4th edition (ebook)
Part
3,
Step
4:
1
Prediction of transmembrane helices – Hydropathy index
Each amino acid is associated
with a free energy change for
its transfer from a hydrophobic
to aqueous environment.
Threshold value for
helix detection
~ 20 amino
acid residues
3
4
~ 30 Ao
Free energy calculations are made for
transfer of every 20 amino acid residues
(i.e. 1-20, 2-21, 3-22 etc.) from
hydrophobic to aqueous environment.
This is plotted as a hydropathy plot.
Action Description of the action
As
shown in
animatio
n.
5
(Please redraw all figures.)
First show the long chain like structure
shown in the centre with the labels.
Next show the dialogue box on the
right top followed by the dialogue box
at the bottom. Once this is shown, the
graph on the right must appear with
the arrow mark and text box.
Hydropathy index, kJ/mol
2
First amino acid residue in window
Audio Narration
It is possible to predict transmembrane helix regions of a protein by calculating the free
energy changes associated with the transfer of residues from a hydrophobic to aqueous
environment. The width of a membrane is typically around 30Ao, which can fit
approximately 20 amino acid residues. Therefore the free energy change for
hypothetical alpha helices formed every 20 residues, from residue1 to 20, 2 to 21, 3 to
22 and so on are calculated until the end of the sequence is reached. These free energy
changes are plotted against the first amino acid residue of every 20-residue window ito
obtain a hydropathy plot. A peak above 84 kJ/mol is indicative of a likely membrane
spanning helix. This, however does not detect membrane spanning b sheets.
Source: Biochemistry by Lubert Stryer, 6th edition (ebook)
Master Layout (Part 4)
Bleach
Fluorescence Recovery After Photobleaching (FRAP)
2
Recovery
Bleach
Fluorescence intensity
1
This animation consists of 4 parts:
Part 1 – Fatty acids
Part 2 – Membrane lipids
Part 3 – Proteins in membrane structures
Part 4 – Properties of cell membranes
Recovery
Time
3
Lateral diffusion
Very fast
1 mm/s
4
Transverse diffusion
(flip-flop)
Very slow
t1/2 in
days
5
Source: Biochemistry by A.L.Lehninger, 4th edition (ebook)
1
2
3
4
5
Definitions of the components:
Part 4 – Properties of cell membranes
1. Fluorescence Recovery After Photobleaching (FRAP) : This is a technique by which
a cell surface component is first labelled by means of a fluorescent molecule and a small
region of the cell surface is viewed by means of fluorescence microscopy. The fluorescent
molecules in the region being viewed are destroyed by a laser pulse, a process known as
bleaching. Once this occurs, the time required for fluorescence to reappear in this region
is plotted against the fluorescence intensity. This helps in understanding the movement of
molecules across the cell surface.
2. Lateral diffusion: The process by which membrane components move laterally from
one region to another in the same plane. This is a quick process and takes place in a
matter of microseconds. Proteins exhibit varying degrees of lateral mobility, with some
being as mobile as lipids and others being almost immobile.
3. Transverse diffusion (flip-flop): This is a process by which molecules in the
membrane transition from one surface of the membrane to the other. The time required
for transverse diffusion is significantly more than that for lateral diffusion and can be
measured by electron spin resonance techniques. This process is made quicker by the
enzyme ‘flippase’.
4. Fluid Mosaic Model: The overall organization and properties of biological membranes
were proposed by Jonathan Singer and Garth Nicolson in 1972 as the Fluid Mosaic
Model. They proposed that membranes are two-dimensional solutions of oriented lipids
and globular proteins, with the lipids serving as a “solvent” for integral membrane proteins
and functioning as a permeability barrier. They also hypothesized that membrane proteins
undergo lateral diffusion freely but not transverse diffusion.
Part
4,
Step
1:
1
Lateral diffusion of membrane components - FRAP
Fluorescence intensity
Bleach
Laser
2
Bleaching
Recovery
Cell surface components labelled
with fluorescent molecule
Action
As shown
in
animation.
5
Time
Region being viewed through
microscope
3
4
Recovery
Description of the action
(Please redraw all figures.)
First show the blue figure with the green spots on it and the
corresponding labels. Followed by the red box and its label. Next, show
the ‘laser’ and its light falling on the green spot at the bottom. Once this
happens, the green spot must change color to grey and the label
‘bleaching’ must appear. Then the laser must be removed and the grey
spot should move down and disappear and simultaneously the green spot
on top must move into the red box as shown in animation. When
bleaching occurs, the downward slope of the graph must be shown and
when the green spot on top enters the red box, the upward curve must be
shown to appear.
Source: Biochemistry by Lubert Stryer, 6th edition (ebook)
Audio Narration
Lateral diffusion of membrane components can be proved
using fluorescence recovery after photobleaching
technique. A cell surface component is first labelled by
means of a fluorescent molecule and a small region of the
cell surface is viewed by means of fluorescence
microscopy. The fluorescent molecules in the region being
viewed are destroyed by a laser pulse, a process known as
bleaching. Fluorescence however reappears in the region
after a certain time that is dependent on the diffusion
coefficient of the molecules.
Part 4, Step 2:
1
Lateral diffusion Vs Transverse diffusion
Lateral diffusion
Very fast
2
3
4
5
1 mm/s
Flippase
Transverse diffusion
(flip-flop)
Very slow
t1/2 in
days
Action Description of the action
Very fast
t1/2 in
seconds
Audio Narration
The Fluid Mosaic model explains the lateral
As shown in (Please redraw all figures.)
animation. First show the green figures on top with the title ‘lateral diffusion’. The diffusion of membrane components but not the
transverse diffusion. Lateral diffusion is a rapid
blue shape must move as indicated by the arrow and reach the
position indicated on the right. This must occur quickly. Next show the process taking place in the range of microseconds.
However, transverse diffusion, also known as the
figure on left bottom with the title ‘transverse diffusion’. The blue
‘flip flop’ reaction takes place very slowly over a
shape alone must flip very slowly in the direction indicated by the
period of several hours. This reaction is facilitated
arrow to reach the position shown on the right. Next, the brown oval
must appear with its label. When this happens, the flipping must take by the enzyme flippase, which carries out transverse
place quickly in the same way as the previous diagram.
diffusion in the time range of few seconds.
Source: Biochemistry by Lubert Stryer, 6th edition (ebook)
Part
4,
Step
3:
1
Factors determining membrane fluidity
3
4
Fluid-like
Solid-like
2
Presence of
cholesterol
– greater
cholesterol,
higher Tm
Tm
Temperature
Action Description of the action
As shown in (Please redraw all figures.)
animation. The graph must appear gradually. As the
graph is appearing in the centre, the text
around it must appear sequentially as
shown.
5
Length of fatty
acyl chain –
longer chain,
higher Tm
Degree of
unsaturation –
Saturated fatty
acids increase
Tm
Audio Narration
The fluidity of any biological membrane is dependent on the properties of the
fatty acid chains present in it. Transition of the membrane from a rigid state to
a fluid state occurs abruptly as the temperature is increased and crosses the
melting temperature, Tm. This melting temperature is a function of the length
of fatty acyl chains present and their degree of unsaturation. Increase in
length of fatty acyl chain increases the Tm while increase in the degree of
unsaturation decreases the Tm. In other words, greater number of double
bonds disrupts the packing order achieved by saturated fatty acids thereby
decreasing the Tm. In animals, the cholesterol content is another regulator of
fluidity. Greater the amount of the bulky steroid, higher is the Tm.
Source: Biochemistry by Lubert Stryer, 6th edition (ebook)
1
2
Interactivity option 1:Step No: 1
Membrane lipids are useful for designing lipid vesicles known as liposomes, which consist of
small aqueous compartments surrounded by a lipid bilayer. These liposomes are increasingly
being used as drug delivery systems in hydrophobic environments. Shown below is an
example for formation of a glycine-containing liposome. Click on the green phospholipid layer
to view liposome formation and then answer the question below.
Glycine in water
Sonication
3
4
Phospholipid
(Click here)
Interacativity Type
5
Gel filtration
Click to view
experiment & then
choose the correct
answer.
Options
(Please redraw all figures.)
User must click on the green
layer at the bottom of the first
figure to view the animation
after which the question with
4 options must appear and
user must be allowed to
choose any 1 option.
Results
When the user clicks on the green layer, the animation must be
shown. The green layer shown at the bottom must gradually form
green circles as shown in the middle panel and must surround a few
red dots. Once this happens, the arrow saying ‘gel filtration’ must be
shown and the red dots must disappear leaving only the green
circles enclosing the red circles. The user must then answer the
question shown in the next slide. Correct answer is C. If user gets it
right, ‘correct answer’ must be displayed otherwise ‘wrong answer’
must be displayed.
1
Interactivity option 1:Step No: 1
What property of membrane lipids allows them to form such liposome vesicles?
2
A) Their low melting temperature
B) The presence of cholesterol
3
C) Their self-sealing nature
D) The presence of glycerol in the phospholipids
4
Interacativity Type
5
Click to view
experiment & then
choose the correct
answer.
Options
(Please redraw all figures.)
User must click on the green
layer at the bottom of the first
figure to view the animation
after which the question with
4 options must appear and
user must be allowed to
choose any 1 option.
Results
When the user clicks on the green layer, the animation must be
shown. The green layer shown at the bottom must gradually form
green circles as shown in the middle panel and must surround a few
red dots. Once this happens, the arrow saying ‘gel filtration’ must be
shown and the red dots must disappear leaving only the green
circles enclosing the red circles. The user must then answer the
question shown in the next slide. Correct answer is C. If user gets it
right, ‘correct answer’ must be displayed otherwise ‘wrong answer’
must be displayed.
1
Questionnaire
1. How many double bonds would be present in a fatty acid having the systematic name
“all-cis-∆9, ∆12, ∆15-Octadecatrienoate”?
2
Answers: a) 1 b) 2 c) 3 d) 4
2. Which of the following is a saturated fatty acid with 18 carbon atoms?
3
Answers: a) cis- ∆9-Octadecenoate b) Octadecanoate
d) Tetradecanoate
c) Eicosanoate
3. Which of the following components is not present in Phosphatidyl inositol?
Answers: a) Sphingosine b) Glycerol c) Phosphate d) Inositol
4
4. If the degree of unsaturation of fatty acyl chains increases, what happens to the Tm?
Answers: a) Tm increases b) Tm remains same c) Tm decreases d) None of the above
5. The threshold value of hydropathy index for detection of alpha helices is?
Answers: a) -22 kJ/mol b) +22 kJ/mol c) +67 kJ/mol d) +84 kJ/mol
5
Links for further reading
Books:
Biochemistry by Stryer et al., 6th edition
Biochemistry by A.L.Lehninger et al., 4th edition
Biochemistry by Voet & Voet, 3rd edition
Research papers:
Singer, S. J. & Nicolson, G. L. The Fluid Mosaic Model of the Structure of Cell Membranes.
Science 1972, 175 (4023), 720-731.