Membranes (wk 5 and 6) Flashcards
T/F:
Different compartments of the cells all have the same environments of the cytosol
False
They can have different environments than the cytosol
List some organelles that may have two membranes rather than one
Nucleus
Mitochondria
Chloroplast
In organelles that have two membranes, the inter-membrane is topologically equivalent to the ______ of the cell
Exterior
In organelles that have two membranes, the internal aqueous space is topologically equivalent to the _____ of the cell
Cytoplasm
List some functions of lipids
Store energy Insulation from the environment Water repellent Membrane structure Cofactors for enzymes Signalling molecules Pigments Antioxidants
What is the most important function of membranes?
Allows cells to exist and be unique
Allows differentiation of different cell types/organs
T/F:
Unsaturated fatty acids pack in a fairly orderly way because of favourable reactions
False
Saturated fatty acids
T/F:
Unsaturated cis fatty acids have a lower melting point resulting in less thermal energy to disrupt disordered packing of unsaturated fatty acids
True
Why do unsaturated fatty acids pack badly?
Double bonds cause kinks
What’s the benefit of having more saturated fats compared to unsaturated fats in the blood stream?
More thermostable, can survive heat better
How do trans fatty acids form?
Partial dehydrogenation of unsaturated fatty acids
T/F:
Trans fatty acids pack more regularly and show higher melting points than cis forms
True
T/F:
Consuming trans fatty acids decreases risk of cardiovascular disease
False
Increases
T/F:
The properties of the tail group in a lipid determines the surface properties of membranes
False
properties of the head groups will determine the surface properties of the membranes
Describe the net charge of the inner and outer side of the membrane and what this allows
The charges will be different
Allows polarization and depolarization
Allows for synapses
Life without this would not exist
Which lipid is the major constituent of eukaryotic cell membranes?
Phosphatidylcholine
T/F:
Bacterial cells can synthesise phosphatidylcholine
False
Therefore our immune system can recognise bacterial cells and remove them
T/F:
The backbone of sphingolipid is glycerol
False
T/F:
The backbone of sphingolipids is a long-chain amino alcohol sphingosine
True
Which phospholipid constitutes myelin that surrounds nerves?
Sphingomyelin
What confers flexibility to phosphatidylcholine rather than sphingomyelin?
Phosphatidylcholine has two saturated bones (double bonds)
What is the physiological role of sterols in the cell?
Modulate fluidity and permeability
Thicken the plasma membrane
Most bacteria lack sterols
How can you obtain cholesterol?
In food
Synthesize in the liver
When do micelles form?
When in the presence of a solution of amphipatic molecules that have larger heads than tails
T/F:
A vesicle has a single layer
False
Double layer
How does sterol affect membranes?
Planar so makes the membranes rigid
What type of components can the central aqueous cavity of a vesicle contain?
Dissolved molecules
What shape are the individual units of the lipid monolayer
Cylindrical
List some of the roles of membranes
• Define the boundaries of the cell
• Allow import and export
o Selective import of nutrients (e.g., lactose)
o Selective export of waste and toxins (e.g., antibiotics)
• Retain metabolites and ions within the cell
• Sense external signals and transmit information into the cell
• Provide compartmentalization within the cell
o separate energy-producing reactions from energy-consuming ones
o keep proteolytic enzymes away from important cellular proteins
• Produce and transmit nerve signals
• Store energy as a proton gradient
• Support synthesis of ATP
What type of forces stabilise membranes?
Non-covalent forces
Especially the hydrophobic effect
T/F:
Lipid bi layers in cells are symmetric
False
asymmetric
T/F:
Carbohydrates are always intracellular to the membrane
False
always extracellular
Are integrins firmly or weakly attached to the membrane?
Firmly attached
Are proteins firmly or weakly attached to the membrane?
Weakly attached
Can be removed easily
T/F:
Fatty acids can diffuse laterally in membranes
True
T/F:
Glycolipids are mostly found on the inside of membranes
False
mostly on the outside
they are used as secondary markers for our immune response
T/F:
Prokaryotes lack sterols
True
T/F:
Plasma membranes have lots of cholesterol that confer flexibility
False
lots of cholesterol that confer rigidity
Which side of the bilayer is more positively charged?
Outside leaflet
T/F:
Membranes are permeable to polar molecules
False
non-polar
Which part of the membrane does CO2 interact with when it passes easily through
Interacts with the fatty part
What two phases can the membrane be in?
Gel phase= molecules do not move around
Fluid phase= molecules can move around
Which phase are membranes most likely to be found in physiological conditions?
Fluid phase
What mostly determines membrane fluidity?
Fatty acid composition
What types of fatty acids are required for a membrane to maintain their fluidity?
Unsaturated fats
These have lower melting points
Need them to maintain the fluidity
T/F:
Proteins move faster than lipids
False
T/F:
Lateral diffusion of individual lipids is fast
True
T/F:
‘flip flop’ rarely occurs
True
Why are spontaneous flips from one leaflet to another rare (transverse diffusion)
The charged polar head must traverse the hydrophobic tail region of the membrane
Floppases move individual lipids from the ___ to the ____
inside to outside
Flippases move individual lipids from the outside to the inside
outside to the inside
Scramblases move lipids in ____
either direction, towards equilibrium
