Week 4 Flashcards
In the plane of a single membrane lipid composition is _________.
non-homogeneous
How do plants and microbes adapt to high temperatures?
reducing the content of PUFAs in their phosphoglycerides. This decreases membrane fluidity.
How do plants and microbes adapt to low temperatures?
involves increasing the PUFA content of biological membranes to ensure that they remain fluid.
What does variations in lipid composition reflect?
from membrane to membrane and in a single membrane is asymmetric. This is likely to reflect differences in membrane function.
What are membranes composed of?
Proteins
Lipids
Cells surrounded by a plasma membrane with various organelles such as mitochondrian and surrounding a nucleus and ER.
What are lipids?
are a heterogeneous group of compounds having in
common the fact that they are soluble in organic solvents
and insoluble in water.
What can we divide lipids into?
simple lipids (such as fatty acids) and complex lipids.
What can complex lipids be divided in to?
Complex lipids are subdivided into
neutral lipids and polar lipids.
Within neutral lipids what do we find?
Within the neutral lipids we
find the storage fats and oils typified by the
triacylglycerols, while within the polar lipids we find
various classes of lipid found in membranes.
What is signal transduction?
All about the way in which cells respond to extracellular stimuli.
What are the two glycerolipids?
phosphoglycerides
glycosylglycerides
What is the general structure of a phosphoglyceride?
Glycerol backbone
Two Fatty acids- are esterified to glycerol.
headgroup-phosphate
How many fatty acids does phosphoglyceride contain?
2 fatty acids.
What type of molecules are fatty acids?
amphipathic
What are the properties of the hydrocarbon tail?
HYDROPHOBIC
What are the properties of the carboxyl head
group?
HYDROPHILIC
What does Amphipathic mean?
describes a molecule that has
hydrophobic and hydrophilic regions
Fatty acids can either be what?
either saturated in which case there are
no c = c bonds or unsaturated where there can be
between 1 and 4 c = c bonds in the molecule.
What do fatty acids consist of?
hydrocarbon tail
Carboxyl head group
What does a C=C bond result in?
When there are multiple C=C
bonds the result is a Poly Unsaturated Fatty Acid (PUFA)
What does a C=C bond introduce?
The presence of a c=c double bond introduces a kink
into the hydrocarbon chain.
Why is saturation and unsaturation important?
Saturation / unsaturation becomes important because
when fatty acids are part of membrane
phosphoglycerides this helps to dictate the properties of
the membrane
How do phosphoglycerides arrange themselves?
themselves into a bilayer such that the polar (hydrophillic)
headgroups face outwards into the aqueous solution while the
hydrophobic fatty acyl tails face inwards into the hydrophobic centre
of the bilayer
How do we isolate membrane enriched fractions?
Using differential centrifugation
How do we isolate highly purified membrane fractions?
using
equilibrium density-gradient centrifugation.
Example: purifying mitochondrial membranes
What is the process of purifying mitochondrial membranes?
1) We set up a density gradient using sucrose solution.
2) Take our pellet from previous centrification containing mixed membranes and add it to top of tube.
3) place in centrifuge.
Why is there a density gradient?
Have a density gradient so our mixed membranes in this mixed fraction has its own specific buoyant density. Will migrate through this gradient until they reach the density.
What are the major differences in membrane composition?
There are major differences in the amounts of
proteins, phosphoglycerides, lipids and sterols present
in plasma membrane from different sources and
this must reflect differences in the function of
the plasma membrane in different cells
What does the difference in lipid composition of the outer and inner leaflets reflect?
reflecting the role that individual
lipids play in determining membrane function.
What are the physical properties of biological membranes influenced by?
Temperature
What happens as temperature decreases?
As temperature decreases the
lipid bilayer alters from a fluid to a rigid or gellike crystalline structure. As fluidity is a key
feature of biological membranes maintaining
this state is important in ensuring that
biological membranes continue to function when
exposed to reduced temperatures.
What happens when temperature increases?
In contrast
when temperatures increase membranes
become more fluid.
Why is keeping the lipid bilayer in the fluid state important?
essential for maintaining the activity of
membrane enzymes and ion channels.
lipid composition is ______ _______.
membrane specific
the fluidity of the membrane is determined by ______ and by the ______ _______.
blank 1-temperature
blank 2- lipid composition
there are differences in ____ composition from
one side of the membrane bilayer to the other
lipid
How do sessile organisms adapt to reduced temperature?
Sessile organisms such as microbes and plants
which are not able to escape the detrimental
effects of reduced temperatures on
membrane properties alter lipid composition
in order to maintain membrane fluidity.
How does the kink affect phosphoglycerides?
This kink affects how the
phosphoglycerides pack into the membrane.
What happens as the degree
of unsaturation of the phosphoglyceride increases?
that membrane fluidity increases as the degree
of unsaturation of the phosphoglyceride increases.
How do plants react to reduced temperatures?
in the
winter many plants decrease the ratio of sat to
unsat FAs esterified to membrane
phosphoglycerides
What do plants increase as a adaption to reduced temperature?
Specifically they increase the
insertion of phosphoglycerides containing PUFAs
into biological membranes.
What does the increased presence of sterols and PUFAs help maintain?
maintain
the membrane in the fluid state despite the
decrease in air temperature.
Why is Maintaining membrane fluidity and preventing low temperature-induced rigidification essential?
is essential to keep membranes functioning correctly.
In response to low temperatures plants do what?
plants increase
the proportion of unsaturated fatty acids in their
membrane lipids.
What enzyme is responsible for inserting C=C double bonds into fatty acids?
fatty acid
desaturase
What happens when we knock out the gene encoding this enzyme (the FAD gene)?
we should produce
plants that have less unsaturated fatty acids in
their membrane lipids and therefore should
tolerate high temperatures.