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IMS > Membranes and lipids > Flashcards

Membranes and lipids Flashcards

1
Q

Which bacteria has one cell membrane

A

Gram positive

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2
Q

What membranes to gram negative bacteria have

A

One inner and one outer

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3
Q

Three lipid types found in membranes

A

Glycerophospholipids
Sphingolipids
Sterols

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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

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5
Q

Structure of sphingolipids

A
  • An acyl chain is attached via an amide linkage.

- Sphingolipids have saturated acyl chains

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6
Q

Structure of sterols

A
  • Have a hydroxyl group and a hydrocarbon tail

- Cholesterol is the most common

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7
Q

What affects Membrane curvature

A

The relative size of the head groupand the hydrophobic tails leads to spontaneous curvature

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8
Q

Can membrane curvature be negative?

A

Negative spontaneous curvature of PE can lead to bilayer-disrupting properties

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9
Q

Why is it known as the fluid mosaic model

A

Bilayer can move and is filled with intrinsic proteins

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10
Q

How can lipids move

A

Rotationally
Laterally
Transversely

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11
Q

Transverse lipid movement

A

Lipids can move across the bilayer by transverse diffusion or protein-mediated transloaction

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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

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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
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14
Q

What are the 3 types of membrane protein

A

Intrinsic membrane protein
Lipid-linked membrane protein
Peripheral membrane proteins

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15
Q

Intrinsic membrane proteins

A

Span the membrane with transmembrane segments

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16
Q

What make up TM segments

A

Amino acids with hydrophobic side chains

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17
Q

Structure of lipid-linked membrane proteins

A

Proteins are covalently bonded to a lipid - the lipid is inserted into the membrane

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18
Q

Structure of peripheral membrane proteins

A

Do not interact with hydrophobic core of the bilayer - Interact with headgroups

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19
Q

What causes Alzheimer’s disease

A

Plaques mainly consisting of the amyloid beta peptide

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20
Q

Where does the amyloid beta peptide come from

A

Derived from the larger amyloid precursor protein

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21
Q

Impact of cholesterol on Alzheimer’s

A

Proteins involved in cholesterol transport are more prevelant in AD patients

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22
Q

Effect of statins

A

Lower cholesterol levels and lower amyloid beta peptide production

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23
Q

Lipid rafts in Alzheimers disease

A

Lipid rafts rich in choletserol encourage production of amyloid beta peptide, leading to worse AD effects

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24
Q

Where are carbohydrates found in the membrane

A

Glycolipids and glycoproteins - always extracellular

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25
Q

Importance of carbohydrates

A

Stabilisation of proteins
Intercellular recognition
Cell signalling

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26
Q

What is the cause of cholera

A

The bacteria Vibrio Cholerae

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27
Q

Treatment of cholera

A

Oral rehydration therapy - a mixture of water, salts and glucose

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28
Q

Features of a pure lipid bilayer

A

Only permeable to water, small hydrophobic molecules and small uncharged molecules

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29
Q

What is the bilayer permeable to

A

Gases
hydrophobic molecules
Small polar molecules (water)

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30
Q

What is the bilayer impermeable to

A

Large polar molecules
amino acids
Charged molecules

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31
Q

2 forms of passive transport

A

simple diffusion

Facilitated diffusion

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32
Q

2 forms of active transport

A

ATP-driven

Ion-driven

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33
Q

Simple diffusion

A

No energy required
Small molecules (gases)
No specificty

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34
Q

Facilitated diffusion

A

No energy required
Uses membrane proteins
Proteins are specific

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35
Q

what is an ionophore

A

ion carrier

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36
Q

How is glucose transported into erythrocytes

A

Facilitated diffusion

IMembrane protein - glucose transporter (GLUT1)

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37
Q

How to water molecules cross the membrane in bulk

A

Aquaporins are water channel proteins

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38
Q

How do active transport mechanisms aquire energy

A

Hydrolysis of ATP

Movement of an ion down its conc gradient

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39
Q

Importance of the sodium/potaassium pump

A

Controls cell volume
Excites nerve and muscle cells
Facilitates movement of amino acids and sugars

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40
Q

Mechanism of the sodium/potassium pump

A

Pumps 3 Na+ out and 2 K+ in
Cell membrane becomes polarised
Requires ATP as ions are being pumped against their concentration gradient

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41
Q

Symport

A

Both molecules move coupled in the same direction

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42
Q

Antiport

A

The molecules move in opposite directions

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43
Q

Features of intestinal epithelial cells

A

line the lumen of the small intestine
Large surface area for absoprtion
Absorb nutrients and transfer them to the blood

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44
Q

Glucose transport in intestinal epithelial cells

A
  • Sodium ions move down their conc gradient through the sodium glucose symport
  • Glucose diffuses across basolateral membrane through GLUT1 into the blood
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45
Q

Basis of oral rehydration therapy

A

uptake of glucose is dependant on Na+ therefore the solution given contains Na+

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46
Q

2 methods of exocytosis

A

Constitutive

Regulates

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47
Q

Constitutive exocytosis

A

Continuous
all cells are secreted
Secreted proteins and plasma membrane proteins

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48
Q

Regulated exocytosis

A

Movement of specialised cells

Dependant on a signal such as calcium

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49
Q

3 methods of endocytosis

A

Phagocytosis
Pinocytosis
Receptor-mediated endocytosis

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50
Q

Phagocytosis

A

Ingestion of large particles by specialised cells

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51
Q

Pinocytosis

A

Uptake of fluid in all cells

52
Q

Receptor-mediated endocytosis

A

selective uptake via clathrin-coated pits and vesicles

53
Q

Why do cells communicate with eachother

A

Regulate development
Control growth and division
Co-ordinate their functions

54
Q

2 ways cells can communicate with eachother

A

Remote signalling

Contact signalling

55
Q

Remote signalling

A

By secreted molecules that signal to cells quite far away

56
Q

Contact signalling (Juxtacrine)

A

By membrane-bound molecules that make physical contact with receptors etc

57
Q

Contact signalling (gap junctions)

A

2 cells form gap junctions that join the cytoplasms so signals can pass directly

58
Q

What are the 4 1st messengers

A

Growth factors
Neurotransmitters
Hormones
Cytokines

59
Q

Types of intercellular signalling

A

Autocrine
Endocrine
Paracrine
Neuronal

60
Q

Paracrine

A

SIgnalling molecule acts on nearby cells

61
Q

Autocrine

A

Cells respond to a signalling molecule secreted by itself

62
Q

Endocrine

A

Signalling molecule is released into the blood where it can circulate the body

63
Q

Neuronal

A

In response to a nerve impulse, neurotransmitters are released

64
Q

What are endocrine hormones

A

Hormones secrted directly into the blood from endocrine glands

65
Q

What are Paracrine hormones

A

Hormones that diffuse through interstitial tissue to target cells

66
Q

What is the difference between hydrophilic hormones and lipid-based hormones

A

Recpetors are located ON the cell membrane for hydrophilic

Recpetors are INSIDE the cell for lipid-based

67
Q

Examples of Hydrophilic hormones

A

Insulin
Glucagon
Adrenaline

68
Q

Examples of lipid-based hormones

A

Oestrogen
Testoterone
Thyroxine
Calcitrol

69
Q

4 Receptor superfamilies

A

Ligand-gated ion channel
G protein-coupled receptor
Receptor tyrosine kinase
Nuclear hormone recpetor

70
Q

Ligand-gated ion channel structure

A

Ligand binding site

4 or 5 heteromeric subunits surrounding a central pore

71
Q

Ligand-gated ion channel

A

Involved in fast synaptic transmission

Ligand binding causes conformational change so ions can flow through

72
Q

Example of Ligand-gated ion channel

A

Nicotinic acetylcholine receptor

  • Increases sodium and potassium permeability
  • causes membrane depolarisation
73
Q

G protein-coupled receptors structure

A

A single polypeptide comprising of 7 membrane-spanning alpha-helical regions

74
Q

G protein-coupled receptor example

A

Angiotensin II recpetor

Cause vasoconstriction and inccreased noradrenaline release

75
Q

Kinase-linked receptor structure

A

Single transmembrane helix with a large extracellular binding domain

76
Q

Roles of kinase-linked recpetors

A

Cell divison
Tissue repair
Apoptosis

77
Q

Kinase-linked receptor example

A

Tyrosine-kinase recpetor is a catalytic receptor which is activated by insulin

78
Q

Nuclear hormone receptor sturcture

A

Seperate ligand and DNA binding domains

79
Q

Nuclear hormone recpetor role

A

Regulate gene transcription

80
Q

Nuclear hormone receptor example

A

Progesterone
oestrogen
glucocorticoids

81
Q

Where are the neurotransmitters held

A

Nerve terminal

82
Q

Life cycle of a neurotransmitter

A 
Synthesis
Storage
Release
Receptor activation
Neurotransmitter activation
83
Q

What is the role of antidepressants

A

To increase monoaminergic transmission within the synaptic cleft

84
Q

Monoamine reuptake inhibitors

A

Treatment for depression

Bind to the pre-synaptic terminal (monoamine transporters) thereby inhibiting reuptake

85
Q

Gasotransmitters

A

Gaseous molecules made in the body

  • Nitric oxide
  • Carbon monixide
  • Hydrogen sulphide
86
Q

How are gasotransmitters made

A

Synthesized by enzymes and they pass readily across plasma membranes

87
Q

What is signal transduction

A

intracellular signalling - converts an extracellular signal into a response

88
Q

Hierachy - signal transduction

A

Specific order that components of the pathway are arranged in

89
Q

What is the Hierachy order

A 
1st messenger
receptor
G-protein
Effector enzyme
2nd messenger
Protein kinase
Target protein
Cellular response
90
Q

Amplification

A

More molecules are activated to create a bigger response

91
Q

Specificity

A

Transduction pathways are highly specific, different messengers and receptors stimulate different responses

92
Q

Complexity

A

Signal transduction pathways are highly complex

93
Q

Features of a transduction pathway

A

Hierachy
Amplification
Specificity
Complexity

94
Q

What are G proteins

A

Guanine nucleotide binding proteins

95
Q

What are the 2 groups of G-proteins

A
  • Receptor-associated G proteins

- Small GTPases

96
Q

How are G-proteins switched on

A

Ligand binding to a receptor

97
Q

What are the 3 different alpha subunits of G-proteins

A

Gi
Gs
Gq

98
Q

Gs

A

Binds to and activates adenyl cyclase which catalyses the formation of cAMP

99
Q

Gi

A

Binds to adenyl cyclase but INHIBITS it so cAMP levels are reduced

100
Q

Gq

A

Binds to and stimulates Phospholipase C, produces more IP3

101
Q

Cholera and G proteins

A

Inactivates GTPase activity on Gs so adenyl cyclase is over-stimulated and cAMP accumulates

102
Q

Pertussis toxin and G proteins

A

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
Q

What are second messengers

A

Short-acting intracellular molecules that are released as a result of recpetor activation

104
Q

5 common secondary messengers

A 
cAMP
cGMP
DAG
IP3
intracellular calcium
105
Q

how is cAMP made

A

formed from ATP, catalysed by adenylate cyclase

106
Q

How is cGMP formed

A

Formed from GTP, catalysed by guanylate cyclase

107
Q

What is the role of adenylate cyclase

A

Stimulate production of cyclic AMP

108
Q

What is the role of guanylate cyclase

A

Stimulate production of cyclic GMP

109
Q

What is the role of phosphodiesterases

A

Reduce the level of cyclic nucleotides to stop over-stimulation of pathways

110
Q

How are IP3, DAG and intracellular calcium made

A

Gq pathway, GTP bound Gq stimulates phospholipase C which produces the secondary messengers

111
Q

What are protein kinases

A

Enzymes that facilitate transfer of a phosphate group from ATP to a specific amino acid residue

112
Q

What is protein phosphorylation

A

A mechanism by which an amino acid binds to a phosphate group - can be activating or inhibiting

113
Q

Which residues can be phosphorylated

A

Serine
Threonine
Tyrosine

114
Q

Why can it only bind to 3 amino acids?

A

They have side chains containing a hydroxyl group

115
Q

What are phosphotases

A

Enzymes that remove phosphate groups from amino acids to oppose the effect of kinases

116
Q

What are kinase cascades

A

The cascade of reactions resluting from the effect of a kinase

117
Q

Kinases and cancer

A

In all tumours, changes to kinase expression levels and activity can contribute to cancer development

118
Q

Treatment of cancer - kinases

A

Kinase inhibitors are being used to target kinase pathways as a way of inhibiting tumour growth

119
Q

What are lipoproteins

A

The carriers for lipids which are otherwise insoluble in the blood

120
Q

Structure of lipoproteins

A

Ball surrounnded by Phospholipid layer with intrinsic cholesterol molecules. Contain a Apoliprotein and a centre of Triacylglycerol and cholesterol esters

121
Q

4 classes of lipoprotein

A

ApoA
ApoB
ApoC
ApoE

122
Q

Function of Apolipoproteins

A
  • Regulate key enzymes in lipoprotein metabolism

- Are ligands for interaction with lipoprotein receptors

123
Q

Role of lipoproteins in cholesterol transport

A

Transport molecules of choletserol so they can form components of cell membranes

124
Q

The role of cholesterol in atherosclerosis

A

When cholesterol is deposited in blood vessel walls

125
Q

Statins as treatment for lowering cholesterol – how they work

A

Prevent cholesterol synthesis in the liver

- Inhibiting HMG-CoA reductase reduces mevalonate and hence synthesis of cholesterol

126
Q

The concept of statin pleiotropism

A

Statins are capable of producing more than one benefit

  • Improve endothelial dysfunction
  • Antioxidant properities
  • Stabilise atherosclerotic plaques

IMS (4 decks)

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