Cell Membranes Flashcards
What are the three main components of a phospholipid?
Acyl groups
Phosphate group
Head group
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Name and describe the different charges of phospholipids
Anionic phospholipids have a net negative charge
Zwitterionic have zero charge
What are the three types of phospholipid?
Glycerophospholipids
Sphingolipids
Sterols
What are the key functions of cell membranes?
- Provide a functional barrier
- Provide cells with energy
- Organise and regulate enzyme activities
- Facilitate signal transduction
- Supply substrates for biosynthesis and for signalling molecules
What are the two types of tail of glycerophospholipids?
The sn-1 fatty acid (usually saturated)
The sn-2 fatty acid (usually mono/poly-saturated)
What are the main structural components of a sphingolipid?
Sphingoid base backbone
Head group
N-Acyl chain
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What type of membrane lipid is important in cell to cell adhesion?
Glycosphingolipids
Where are glycosphingolipids exclusively found?
In the outer leaflet of the membrane
What do glycosphingolipids have in place of a head?
Different oligosaccharides
What is the structure of sterols?
Hydroxyl group and hydrocarbon tail
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Where are the following sterols found?
-cholesterol
-ergosterol
-sitosterol and stigmasterol
Cholesterol = animals
Ergosterol = fungi and yeast
Sitosterol and stigmasterol = plants
What factors affect the shape of the lipid?
relative size of head group and hydrophobic tails
What are the three types of lipid movement in membranes and how do they work?
Rotational - when lipids spin around their axis, not changing position but interacting differently
Lateral - neighbouring lipids exchange spaces
Transverse - exchange of lipids between leaflets, sometimes requires ATP
What are membrane rafts?
In eukaryotic plasma membrane there are domains with lots of cholesterol and sphingomyelin making them more rigid
What are the three different classes of membrane proteins?
Integral (intrinsic)
Lipid-linked
Peripheral (extrinsic)
What are the roles of integral membrane proteins?
Transport
Enzymatic activity
Signal transduction
Cell-cell interactions
Attachment to the cytoskeleton or extracellular matrix
What molecule is this?..
- found in nearly all cells
- composed of 12 a helices
- undergoes conformational change causing transport across membrane
GLUT (glucose transporter)
What things can cause integral channel proteins to open?
Ligand binding
electric potential
pH
Temperature
Pressure
Lipids
What is the role of carbohydrates in cell membranes?
Stabilisation of proteins
Cell-cell recognition
What causes Alzheimer’s disease?
Nerves cells in the brain die causing the connections between cells to degenerate
Loss of memory is usually the first presenting symptom
What will you find in the brain of an Alzheimer’s patient during a postmortem?
Full of senile-plaques made of amyloid-beta peptide
What is hereditary spherocytosis?
Loss of cohesion between the plasma membrane and skeleton as a result of defective anchoring
Cell shape changes to spherocytes
What is the most common cause of hereditary spherocytosis?
Anaemias
Deficiencies in ankyrin, spectrin, band 3
What are the main types of lipids in the body?
Triglycerides
Cholesterol
Phospholipids
Steroids
What are the functions of lipids?
Energy storage
Major components of membranes
Signalling molecules
Solubisung fat soluble vitamins
Bio synthetic precursors
Where does cholesterol come from?
From diet or synthesised in the liver
What is the role of lipoproteins?
Transporting lipids in the plasma
Describe the structure of lipoproteins?
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What determines the function of lipoproteins?
Apolipoproteins - Specific protein strands embedded in the surface of lipoproteins
What is the function of the following lipoproteins? INSERT PIC
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What does lipid + apolipoprotein =
Lipoprotein
What are the different classes of apolipoproteins?
ApoA - present in HDL
ApoB - recognises apoB/E receptors, facilitates LDL uptake
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Where is the synthesis of apolipoproteins regulates?
By dietary fat intake
By hormones/drugs in the liver
Describe the structure of LDL
ApoB wraps round the circumference
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Describe the structure of HDL
Why is HDL considered good cholesterol?
ApoB prevents it from being oxidised
What pH is a lysosome?
<5
What are the two types of both passive and active transport of small molecules?
Passive - simple and faciliated diffusion
Active - ATP driven and ion driven
What type of transport is this?
- no metabolic energy required
- small molecules
- no specificity
- rate of diffusion proportional to concentration gradient
Simple diffusion
What type of transport is this?
- occurs down a concentration gradient
- no energy required
- depends on integral membrane proteins
- proteins are specific
- similar kinetics to enzymes
Facilitated diffusion
