Membranes and lipids Flashcards
(126 cards)
1
Q
Which bacteria has one cell membrane
A
Gram positive
2
Q
What membranes to gram negative bacteria have
A
One inner and one outer
3
Q
Three lipid types found in membranes
A
Glycerophospholipids
Sphingolipids
Sterols
4
Q
Structure of glycerophospholipids
A
Chemically diverse due to the combination of 2 fatty acids.
The sn-1 fatty acid is saturated (no double bonds)
The sn-2 fatty acid is polyunsaturated
This results in lipids with varied charges
5
Q
Structure of sphingolipids
A
- An acyl chain is attached via an amide linkage.
- Sphingolipids have saturated acyl chains
6
Q
Structure of sterols
A
- Have a hydroxyl group and a hydrocarbon tail
- Cholesterol is the most common
7
Q
What affects Membrane curvature
A
The relative size of the head groupand the hydrophobic tails leads to spontaneous curvature
8
Q
Can membrane curvature be negative?
A
Negative spontaneous curvature of PE can lead to bilayer-disrupting properties
9
Q
Why is it known as the fluid mosaic model
A
Bilayer can move and is filled with intrinsic proteins
10
Q
How can lipids move
A
Rotationally
Laterally
Transversely
11
Q
Transverse lipid movement
A
Lipids can move across the bilayer by transverse diffusion or protein-mediated transloaction
12
Q
Why is Asymmetry in the bilayer important?
A
As there is a charge difference between the 2 leaflets of the bilayer - symmetry ensures the overall charge remains neutral
13
Q
What are lipid rafts
A
- There are specific domains within a membrane
- These domains are enriched in cholesterol and sphingomyelin
- Proteins are either excluded or included in the raft regions
- Lipids in rafts are in the L0 phase and thus more ordered than the lipids in the bulk
14
Q
What are the 3 types of membrane protein
A
Intrinsic membrane protein
Lipid-linked membrane protein
Peripheral membrane proteins
15
Q
Intrinsic membrane proteins
A
Span the membrane with transmembrane segments
16
Q
What make up TM segments
A
Amino acids with hydrophobic side chains
17
Q
Structure of lipid-linked membrane proteins
A
Proteins are covalently bonded to a lipid - the lipid is inserted into the membrane
18
Q
Structure of peripheral membrane proteins
A
Do not interact with hydrophobic core of the bilayer - Interact with headgroups
19
Q
What causes Alzheimer’s disease
A
Plaques mainly consisting of the amyloid beta peptide
20
Q
Where does the amyloid beta peptide come from
A
Derived from the larger amyloid precursor protein
21
Q
Impact of cholesterol on Alzheimer’s
A
Proteins involved in cholesterol transport are more prevelant in AD patients
22
Q
Effect of statins
A
Lower cholesterol levels and lower amyloid beta peptide production
23
Q
Lipid rafts in Alzheimers disease
A
Lipid rafts rich in choletserol encourage production of amyloid beta peptide, leading to worse AD effects
24
Q
Where are carbohydrates found in the membrane
A
Glycolipids and glycoproteins - always extracellular
25
Importance of carbohydrates
Stabilisation of proteins
Intercellular recognition
Cell signalling
26
What is the cause of cholera
The bacteria Vibrio Cholerae
27
Treatment of cholera
Oral rehydration therapy - a mixture of water, salts and glucose
28
Features of a pure lipid bilayer
Only permeable to water, small hydrophobic molecules and small uncharged molecules
29
What is the bilayer permeable to
Gases
hydrophobic molecules
Small polar molecules (water)
30
What is the bilayer impermeable to
Large polar molecules
amino acids
Charged molecules
31
2 forms of passive transport
simple diffusion
| Facilitated diffusion
32
2 forms of active transport
ATP-driven
| Ion-driven
33
Simple diffusion
No energy required
Small molecules (gases)
No specificty
34
Facilitated diffusion
No energy required
Uses membrane proteins
Proteins are specific
35
what is an ionophore
ion carrier
36
How is glucose transported into erythrocytes
Facilitated diffusion
| IMembrane protein - glucose transporter (GLUT1)
37
How to water molecules cross the membrane in bulk
Aquaporins are water channel proteins
38
How do active transport mechanisms aquire energy
Hydrolysis of ATP
| Movement of an ion down its conc gradient
39
Importance of the sodium/potaassium pump
Controls cell volume
Excites nerve and muscle cells
Facilitates movement of amino acids and sugars
40
Mechanism of the sodium/potassium pump
Pumps 3 Na+ out and 2 K+ in
Cell membrane becomes polarised
Requires ATP as ions are being pumped against their concentration gradient
41
Symport
Both molecules move coupled in the same direction
42
Antiport
The molecules move in opposite directions
43
Features of intestinal epithelial cells
line the lumen of the small intestine
Large surface area for absoprtion
Absorb nutrients and transfer them to the blood
44
Glucose transport in intestinal epithelial cells
- Sodium ions move down their conc gradient through the sodium glucose symport
- Glucose diffuses across basolateral membrane through GLUT1 into the blood
45
Basis of oral rehydration therapy
uptake of glucose is dependant on Na+ therefore the solution given contains Na+
46
2 methods of exocytosis
Constitutive
| Regulates
47
Constitutive exocytosis
Continuous
all cells are secreted
Secreted proteins and plasma membrane proteins
48
Regulated exocytosis
Movement of specialised cells
| Dependant on a signal such as calcium
49
3 methods of endocytosis
Phagocytosis
Pinocytosis
Receptor-mediated endocytosis
50
Phagocytosis
Ingestion of large particles by specialised cells
51
Pinocytosis
Uptake of fluid in all cells
52
Receptor-mediated endocytosis
selective uptake via clathrin-coated pits and vesicles
53
Why do cells communicate with eachother
Regulate development
Control growth and division
Co-ordinate their functions
54
2 ways cells can communicate with eachother
Remote signalling
| Contact signalling
55
Remote signalling
By secreted molecules that signal to cells quite far away
56
Contact signalling (Juxtacrine)
By membrane-bound molecules that make physical contact with receptors etc
57
Contact signalling (gap junctions)
2 cells form gap junctions that join the cytoplasms so signals can pass directly
58
What are the 4 1st messengers
Growth factors
Neurotransmitters
Hormones
Cytokines
59
Types of intercellular signalling
Autocrine
Endocrine
Paracrine
Neuronal
60
Paracrine
SIgnalling molecule acts on nearby cells
61
Autocrine
Cells respond to a signalling molecule secreted by itself
62
Endocrine
Signalling molecule is released into the blood where it can circulate the body
63
Neuronal
In response to a nerve impulse, neurotransmitters are released
64
What are endocrine hormones
Hormones secrted directly into the blood from endocrine glands
65
What are Paracrine hormones
Hormones that diffuse through interstitial tissue to target cells
66
What is the difference between hydrophilic hormones and lipid-based hormones
Recpetors are located ON the cell membrane for hydrophilic
| Recpetors are INSIDE the cell for lipid-based
67
Examples of Hydrophilic hormones
Insulin
Glucagon
Adrenaline
68
Examples of lipid-based hormones
Oestrogen
Testoterone
Thyroxine
Calcitrol
69
4 Receptor superfamilies
Ligand-gated ion channel
G protein-coupled receptor
Receptor tyrosine kinase
Nuclear hormone recpetor
70
Ligand-gated ion channel structure
Ligand binding site
| 4 or 5 heteromeric subunits surrounding a central pore
71
Ligand-gated ion channel
Involved in fast synaptic transmission
| Ligand binding causes conformational change so ions can flow through
72
Example of Ligand-gated ion channel
Nicotinic acetylcholine receptor
- Increases sodium and potassium permeability
- causes membrane depolarisation
73
G protein-coupled receptors structure
A single polypeptide comprising of 7 membrane-spanning alpha-helical regions
74
G protein-coupled receptor example
Angiotensin II recpetor
| Cause vasoconstriction and inccreased noradrenaline release
75
Kinase-linked receptor structure
Single transmembrane helix with a large extracellular binding domain
76
Roles of kinase-linked recpetors
Cell divison
Tissue repair
Apoptosis
77
Kinase-linked receptor example
Tyrosine-kinase recpetor is a catalytic receptor which is activated by insulin
78
Nuclear hormone receptor sturcture
Seperate ligand and DNA binding domains
79
Nuclear hormone recpetor role
Regulate gene transcription
80
Nuclear hormone receptor example
Progesterone
oestrogen
glucocorticoids
81
Where are the neurotransmitters held
Nerve terminal
82
Life cycle of a neurotransmitter
```
Synthesis
Storage
Release
Receptor activation
Neurotransmitter activation
```
83
What is the role of antidepressants
To increase monoaminergic transmission within the synaptic cleft
84
Monoamine reuptake inhibitors
Treatment for depression
| Bind to the pre-synaptic terminal (monoamine transporters) thereby inhibiting reuptake
85
Gasotransmitters
Gaseous molecules made in the body
- Nitric oxide
- Carbon monixide
- Hydrogen sulphide
86
How are gasotransmitters made
Synthesized by enzymes and they pass readily across plasma membranes
87
What is signal transduction
intracellular signalling - converts an extracellular signal into a response
88
Hierachy - signal transduction
Specific order that components of the pathway are arranged in
89
What is the Hierachy order
```
1st messenger
receptor
G-protein
Effector enzyme
2nd messenger
Protein kinase
Target protein
Cellular response
```
90
Amplification
More molecules are activated to create a bigger response
91
Specificity
Transduction pathways are highly specific, different messengers and receptors stimulate different responses
92
Complexity
Signal transduction pathways are highly complex
93
Features of a transduction pathway
Hierachy
Amplification
Specificity
Complexity
94
What are G proteins
Guanine nucleotide binding proteins
95
What are the 2 groups of G-proteins
- Receptor-associated G proteins
| - Small GTPases
96
How are G-proteins switched on
Ligand binding to a receptor
97
What are the 3 different alpha subunits of G-proteins
Gi
Gs
Gq
98
Gs
Binds to and activates adenyl cyclase which catalyses the formation of cAMP
99
Gi
Binds to adenyl cyclase but INHIBITS it so cAMP levels are reduced
100
Gq
Binds to and stimulates Phospholipase C, produces more IP3
101
Cholera and G proteins
Inactivates GTPase activity on Gs so adenyl cyclase is over-stimulated and cAMP accumulates
102
Pertussis toxin and G proteins
The toxin prevents GDP/GTP exchange by the Gi subunit. The Gi is locked in the off position so unable to inhibt adenyl cyclase - cAMP accumulation
103
What are second messengers
Short-acting intracellular molecules that are released as a result of recpetor activation
104
5 common secondary messengers
```
cAMP
cGMP
DAG
IP3
intracellular calcium
```
105
how is cAMP made
formed from ATP, catalysed by adenylate cyclase
106
How is cGMP formed
Formed from GTP, catalysed by guanylate cyclase
107
What is the role of adenylate cyclase
Stimulate production of cyclic AMP
108
What is the role of guanylate cyclase
Stimulate production of cyclic GMP
109
What is the role of phosphodiesterases
Reduce the level of cyclic nucleotides to stop over-stimulation of pathways
110
How are IP3, DAG and intracellular calcium made
Gq pathway, GTP bound Gq stimulates phospholipase C which produces the secondary messengers
111
What are protein kinases
Enzymes that facilitate transfer of a phosphate group from ATP to a specific amino acid residue
112
What is protein phosphorylation
A mechanism by which an amino acid binds to a phosphate group - can be activating or inhibiting
113
Which residues can be phosphorylated
Serine
Threonine
Tyrosine
114
Why can it only bind to 3 amino acids?
They have side chains containing a hydroxyl group
115
What are phosphotases
Enzymes that remove phosphate groups from amino acids to oppose the effect of kinases
116
What are kinase cascades
The cascade of reactions resluting from the effect of a kinase
117
Kinases and cancer
In all tumours, changes to kinase expression levels and activity can contribute to cancer development
118
Treatment of cancer - kinases
Kinase inhibitors are being used to target kinase pathways as a way of inhibiting tumour growth
119
What are lipoproteins
The carriers for lipids which are otherwise insoluble in the blood
120
Structure of lipoproteins
Ball surrounnded by Phospholipid layer with intrinsic cholesterol molecules. Contain a Apoliprotein and a centre of Triacylglycerol and cholesterol esters
121
4 classes of lipoprotein
ApoA
ApoB
ApoC
ApoE
122
Function of Apolipoproteins
- Regulate key enzymes in lipoprotein metabolism
| - Are ligands for interaction with lipoprotein receptors
123
Role of lipoproteins in cholesterol transport
Transport molecules of choletserol so they can form components of cell membranes
124
The role of cholesterol in atherosclerosis
When cholesterol is deposited in blood vessel walls
125
Statins as treatment for lowering cholesterol – how they work
Prevent cholesterol synthesis in the liver
| - Inhibiting HMG-CoA reductase reduces mevalonate and hence synthesis of cholesterol
126
The concept of statin pleiotropism
Statins are capable of producing more than one benefit
- Improve endothelial dysfunction
- Antioxidant properities
- Stabilise atherosclerotic plaques
