Week 4 Flashcards
1
Q
In the plane of a single membrane lipid composition is _________.
A
non-homogeneous
2
Q
How do plants and microbes adapt to high temperatures?
A
reducing the content of PUFAs in their phosphoglycerides. This decreases membrane fluidity.
3
Q
How do plants and microbes adapt to low temperatures?
A
involves increasing the PUFA content of biological membranes to ensure that they remain fluid.
4
Q
What does variations in lipid composition reflect?
A
from membrane to membrane and in a single membrane is asymmetric. This is likely to reflect differences in membrane function.
5
Q
What are membranes composed of?
A
Proteins
Lipids
Cells surrounded by a plasma membrane with various organelles such as mitochondrian and surrounding a nucleus and ER.
6
Q
What are lipids?
A
are a heterogeneous group of compounds having in
common the fact that they are soluble in organic solvents
and insoluble in water.
7
Q
What can we divide lipids into?
A
simple lipids (such as fatty acids) and complex lipids.
8
Q
What can complex lipids be divided in to?
A
Complex lipids are subdivided into
neutral lipids and polar lipids.
9
Q
Within neutral lipids what do we find?
A
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.
10
Q
What is signal transduction?
A
All about the way in which cells respond to extracellular stimuli.
11
Q
What are the two glycerolipids?
A
phosphoglycerides
glycosylglycerides
12
Q
What is the general structure of a phosphoglyceride?
A
Glycerol backbone
Two Fatty acids- are esterified to glycerol.
headgroup-phosphate
13
Q
How many fatty acids does phosphoglyceride contain?
A
2 fatty acids.
14
Q
What type of molecules are fatty acids?
A
amphipathic
15
Q
What are the properties of the hydrocarbon tail?
A
HYDROPHOBIC
16
Q
What are the properties of the carboxyl head
group?
A
HYDROPHILIC
17
Q
What does Amphipathic mean?
A
describes a molecule that has
hydrophobic and hydrophilic regions
18
Q
Fatty acids can either be what?
A
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.
19
Q
What do fatty acids consist of?
A
hydrocarbon tail
Carboxyl head group
20
Q
What does a C=C bond result in?
A
When there are multiple C=C
bonds the result is a Poly Unsaturated Fatty Acid (PUFA)
21
Q
What does a C=C bond introduce?
A
The presence of a c=c double bond introduces a kink
into the hydrocarbon chain.
22
Q
Why is saturation and unsaturation important?
A
Saturation / unsaturation becomes important because
when fatty acids are part of membrane
phosphoglycerides this helps to dictate the properties of
the membrane
23
Q
How do phosphoglycerides arrange themselves?
A
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
24
Q
How do we isolate membrane enriched fractions?
A
Using differential centrifugation
25
How do we isolate highly purified membrane fractions?
using
equilibrium density-gradient centrifugation.
Example: purifying mitochondrial membranes
26
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.
27
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.
28
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
29
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.
30
What are the physical properties of biological membranes influenced by?
Temperature
31
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.
32
What happens when temperature increases?
In contrast
when temperatures increase membranes
become more fluid.
33
Why is keeping the lipid bilayer in the fluid state important?
essential for maintaining the activity of
| membrane enzymes and ion channels.
34
lipid composition is ______ _______.
membrane specific
35
the fluidity of the membrane is determined by ______ and by the ______ _______.
blank 1-temperature
| blank 2- lipid composition
36
there are differences in ____ composition from
| one side of the membrane bilayer to the other
lipid
37
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.
38
How does the kink affect phosphoglycerides?
This kink affects how the
| phosphoglycerides pack into the membrane.
39
What happens as the degree
| of unsaturation of the phosphoglyceride increases?
that membrane fluidity increases as the degree
| of unsaturation of the phosphoglyceride increases.
40
How do plants react to reduced temperatures?
in the
winter many plants decrease the ratio of sat to
unsat FAs esterified to membrane
phosphoglycerides
41
What do plants increase as a adaption to reduced temperature?
Specifically they increase the
insertion of phosphoglycerides containing PUFAs
into biological membranes.
42
What does the increased presence of sterols and PUFAs help maintain?
maintain
the membrane in the fluid state despite the
decrease in air temperature.
43
Why is Maintaining membrane fluidity and preventing low temperature-induced rigidification essential?
is essential to keep membranes functioning correctly.
44
In response to low temperatures plants do what?
plants increase
the proportion of unsaturated fatty acids in their
membrane lipids.
45
What enzyme is responsible for inserting C=C double bonds into fatty acids?
fatty acid
| desaturase
46
```
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.
47
Plants and microbes adapt to ____ ______ by
______ the content of PUFAs in their membrane
lipids. This ______ membrane fluidity.
high temperatures
reducing
decreases
48
In contrast, adapting to ____ _______ involves
______ the PUFA content of biological membranes
to ensure that they remain fluid.
low temperature
| increasing
49
What are amino acids?
the building blocks of proteins. The formation of a peptide bond allows amino acids to combine into peptides.
50
What does the addition of more amino acids result in?
```
formation of a polypeptide.
The polypeptide coils and
folds to make the
characteristic “shape” or
structure of the protein.
```
51
What are the three different types of membrane protein?
Integral
Peripheral
Lipid anchored
52
What is an integral membrane protein?
span membrane itself
53
What is a peripheral membrane protein?
Associated with membrane as interact/bind to integral proteins.
54
What is a lipid anchored membrane protein?
Has lipid modification- FA allows itself to anchor into the membrane
55
What is glycophorin A and what is it made up of?
Integral membrane proteins
| glycophorin A is made up of 2 monomers and therefore is present as a dimer in the membrane.
56
what does each monomer in glycophorin A contain?
contains 3 distinct segments known as domains.
1) Extracellular domain
2) Membrane spanning domain.
3) Cytosolic domain
57
What are the extracellular and cytosolic domains
| largely composed of?
hydrophilic amino acids
58
What is the membrane spanning the domain largely composed of?
the membrane spanning domain is largely composed of hydrophobic amino acids
59
What is the role of the biological membrane?
cell-to-cell recognition/communication
• semi-permeable barrier
• platform for linked reactions
• compartmentalisation
60
Explain the role of cell-to-cell recognition/communication.
Receptors on plasma membrane and recognise extracellular cellular signals.
61
Explain the role of semi-permeable barrier.
Allows inside of the cell to be different in terms of fluid concentration.
62
Explain the role platform for linked reactions
Form a surface in which for example you can have enzymes that work together in a series of biochemical reactions that can be located on the same surface. positive interactions caused by diffusion whereas on a platform the reactions will be much more efficient.
63
Explain the role of compartmentalisation
Reactions can be localised to these environments with specific organelles.
64
Outline protein mobility in membranes.
Some of the proteins in the membrane are relatively free to diffuse across the surface of the plasma membrane while others tend to remain in the same location.
65
How can we demonstrate protein mobility in the membrane?
We can demonstrate this experimentally by
using the technique of fluorescence
recovery after photobleaching (FRAP)
66
Outline the process of FRAP.
You have the membrane protein. Fluorescent reagent - add label to protein and attach label to cell surface proteins. Visible as surface of cell is tagged.
Shine a laser at restricted part of the cell. some of the area is bleached.
67
What can be concluded from the experiment- FRAP?
At the end of the experiment, fluorescence from the laser treated region is 50% of the value it was at the start of the experiment. The recovery from 0 – 50% is due to proteins from other (un-lasered) parts of the plasma membrane moving into the bleached region. This shows that some proteins are free to diffuse in the PM while others are not (because the fluorescence does not recover to 100%).
68
Proteins are made from _______.
chains of amino acids (polypeptides)
69
Proteins are made up
| of
different domains.
70
Some proteins are ______ in the plane of
the membrane while
others are ____.
MOBILE
| FIXED
71
What is signal transduction?
The study of the cellular events responsible for
coupling an extracellular stimulus to its
characteristic intracellular response.
72
What are some examples signal transduction?
Phototropism
Cancer
Bitter taste
73
Why is phototropism related to signal transduction?
detection of the sunlight in the plant. Bending towards light therefore signal is light and transduction signal is bending.
74
Why is bitter taste related to signal transduction?
Bitterness is signal has been detected by taste buds and leads to a response.
75
Why is cancer related to signal transduction?
when signalling pathways dont work consequences can be severe.
76
what is signal transduction pathways a collection of?
is a collection of
components that work together to relay the
stimulus from its point of perception to the
location inside the cell where it can initiate its
characteristic response.
77
What is another way to describe a signal
| transduction pathway?
The process of coupling an extracellular stimulus
to its characteristic intracellular response is
achieved through the operation of a signal
transduction pathway.
78
What is the operation of the simple signalling pathway?
operation of a SP is all about the perception of the signal- series of events that occur after this ultimately leads to a typical response.
79
What are the domains of the protein that makes up the cell surface receptor?
Extracellular domain
Transmembrane domain
Intracellular domain
80
What is the transmembrane domain?
rich in non-polar hydrophobic amino acids. Some receptor proteins
criss-cross the membrane many times (A), whereas
others (B) only function by forming dimers (2
receptors pairing up for ligand binding and activation).
81
Outline a property of a receptor?
• Highly specific for the ligand they bind
This is why when you bite into a lemon the taste you
experience is bitter rather than, for example, sweet.
Examples of ligands include, insulin, acetylcholine, plant
hormones such as auxins, yeast mating factors or the
nutrients that bacteria are attracted to.
82
Ligand–receptor binding is
reversible
83
Ligand-receptor complexes have defined
half lives
84
What happens when there is an absence of continued supply of ligand?
the receptor will become deactivated because of the lack of ligand.
85
How do we also define receptors?
We also define
| receptors in terms of their affinity for their ligands.
86
What does a high affinity receptor do?
will bind its ligand when the
| ligand is present at very low concentrations.
87
What does a low affinity receptor do?
a low affinity receptor will only become activated when
| there are high concentrations of ligand present.
88
What does ligand binding induce?
induces a conformational
| change (an alteration in the three dimensional “shape”) in the receptor
89
Why is the change in shape of the receptor important?
This change in “shape” is very
important because it allows the receptor to interact
with other proteins. It is the interaction with other
proteins further down the signal transduction pathway
that is responsible for relaying the signal into the cell.
90
Activated receptors _______ other proteins.
recruit
91
Why do Activated receptors recruit other proteins?
This is
required to relay the signal into the cell. Precisely what
proteins are recruited dictates the nature of the response
92
Signal transduction pathways are composed of _________.
multiple components.
93
Receptors are _______ that have ______ sites for their ______.
proteins
binding
ligands
94
Binding is
specific and reversible.
95
Activated receptors
| recruit other proteins, which serve to
relay the
| signal further into the cell.
96
What is cytosol?
is the intracellular fluid
97
What are Intracellular second messengers?
• simple molecules that amplify the signal
• the concentration of the second messenger
increases in the cytosol after cell stimulation
• the concentration of the second messenger
decreases when the stimulus is removed
98
What does an increase in the concentration of the intracellular second messenger activate?
activates target
proteins with the result that the signal is
relayed further in the cell
99
What are the three intracellular second messengers?
-Calcium ions – Ca2+
free ion not bound to anything else.
-Cyclic guanosine monophosphate(cGMP)
-Cyclic adenosine monophosphate(cAMP)
100
What happens when proteins interact with each other?
leads to a change in conformation.
Allows them to interact with new proteins become active/inactive and alter their location in the cell. therefore the signal is relayed into the cell.
101
What is Protein Modification
| Example: Protein phosphorylation?
Transfer of a phosphate from ATP to an
amino acid on a target protein catalysed by
an enzyme called a protein kinase.
Phosphorylation results in a change in the
conformation of the substrate protein. If
the substrate is an enzyme then protein
phosphorylation could activate the enzyme
and serve to relay the signal further down
the signal transduction pathway.
102
What is the role of Protein kinases(PKs)?
phosphorylate
their substrates
-catalyses reaction and transfer of gamma terminal phosphate from ATP onto an acceptor AA on its target protein.
103
What is the role of Phosphoprotein
| phosphatases (PPs)?
dephosphorylate
their substrates
remove substrate
104
What do PKs and PPs function as?
molecular switches activating or deactivating their substrate proteins.
105
When happens when the Second messenger activated protein kinases are activated?
when the concentration of an
intracellular second messenger is increased in the
cytosol following cell stimulation.
106
Protein kinase A (PKA) is activated by
cAMP
107
• Calcium dependent protein kinase (CDPK) is
| activated by
Ca2+
108
• Protein kinase C (PKC) is activated by
Ca2+ and
| a lipid called diacylglycerol (DAG)
109
Ligand binding causes
receptor dimerization.
110
receptor dimerization results in what?
results in the formation of a complex of proteins around the receptor resulting in signal relay through protein-protein
interactions until a series of protein kinases (Raf, MEK and MAP) work together to carry the signal into the nucleus.
111
There are __ different types of membrane protein.
3
112
Protein mobility in membranes is studied using
FRAP
113
The basic elements in intracellular signalling pathways are,
receptors, intracellular second messengers and intracellular signalling proteins.
114
Protein kinases phosphorylate their substrates frequently leading to
changes in shape and activity of their targets.
115
Lipid layer that forms foundation of cells membrane is.....
Bilayer formed by phospholipids
