Week 7 Part 1: Membrane Structure (Lipids) Flashcards
Section 2: Week 1
What parts of an animal cell are animal cell specific?
Extracellular Matrix, Lysosome
What is the name for the part of an animal cell that is the specialized material outside the cell?
Extracellular Matrix
What happens within the lyososome?
Degredation of cellular components that are no longer needed
In plant cells, what is the function of the cell wall?
Holds cell shape and acts as protection against mechanical stress
What are the two types of vacuoles within plant cells?
A vacuole for degredation (like an animal cell’s lysosome) and a vacuole for storage (small molecules and proteins)
What is the chloroplast?
The site of photosynthesis
What is the cytoplasm? What does it include?
The cytoplasm are the contents of the cell outside the nucleus. This means that this includes all the organelles except the nucleus
What is the name for the aqueous part of the cytoplasm?
Cytosol (this does not include membrane bound organelles, but it does incude things like ribosomes, cytoskeleton, etc.)
What is lumen?
The inside of organelles (usually in between the membranes)
What model for membrane bilayers did Singer and Nicolson propose in 1972?
The Fluid Mosaic Model of the Membrane
When considering the name of the 1972 model of a membrane bilayers, what does “Fluid” and “Mosaic” mean?
Fluid refers to the mobility of the lipids and some of the proteins that the membrane is composed of. Mosaic refers to the many different lipids and many different proteins.
Why are lipids amphipathic?
They have hydrophilic (or polar) heads, and hydrophobic tails
What are the different types of lipids that a membrane is composed of?
Phospholipids, sterols, gycolipids
What is the name for a phospholipid with a glycerol group?
Phosphoglycerides
What does a general phosphoglyceride consist of?
Different groups + phosphate (polar head group), glycerol, hydrocarbon tails (non polar/hydrophobic)
What are the characteristics of a phosphoglyceride’s hydrocarbon tails?
They’re usually 14-24 carbon atoms long and they can be saturated/unsaturated
What is a kink? (In a phosphoglyceride)
It is a tail that is unsaturated and it contains a cis-double bond
Where do membrane bilayers usually form?
In water
In an aqeuous environment, phospholipids ____________ ________-_________ into a bilayer
spontaneously self-associate
In a membrane bilayer, what does each layer interact with?
The polar/hydrophilic head interacts with water. The nonpolar/hydrophobic tails interact with other hydrophobic tails.
What is a liposome?
Artificial lipid bilayer
What are the three uses of liposomes?
- Study lipid proteins
- Membrane protein properties
- Drug delivery into cells (either via the water within the spherical compartment or within the hydrophobic layer)
Because a planar phospholipid bilayer causes hydrophobic tails to be exposed to water, what formation does the phospholipid bilayer adopt? Is this energetically favourable?
The planar phospholipid bilayer curls inward forming a spherical sealed compartment which shields hydrophobic tails from water. This is energetically favourable
True or False: Cell membranes are not fluid
False
Can a membrane be deformed without causing damage?
Yes it can. An example of this is a technique called live cell imaging where laser tweezers are used to manipulate the membrane.
What are the three kinds of movement that phospholipids within each leaflet rapidly do?
- Diffuse laterally
- Rotate
- Flex
Which movement do phospholipids rarely do?
They rarely move from one leaflet to the other (flip-flop) on their own
Describe lateral diffusion
While the phospholipid can move from side to side in one plane (i.e. on an x axis) it can also move deeper within the plane (i.e. on a z axis)
Why is cell membrane fluidity carefully regulated?
It is carefully regulated because it is important for its function
What are examples of the functions of membrane proteins?
Transport, enzyme activity, signaling
What are factors affecting membrane fluidity?
Temperature and composition
What happens to molecules at lower temperatures?
They are more viscous and less fluid – you want to avoid this as it is supposed to be fluid
Describe the effect of cis-double bonds at lower temperatures
Cis-double bonds increase fluidity at lower temperatures
What does shorter phospholipid lengths cause?
Shorter hydrocarbon tails increase fluidity at lower temperatures (lipid tailds interact less)
What does addition of cholesterol cause in animal cell membranes?
It stiffens membrane, makes it less permeable to water
What ratio can cholesterol and phospholipids exist in? What does this mean for the membrane?
1:1 ratio. This means that cholesterol is a big part of the membrane.
What does cholesterol cause in phospholipid tails?
It decreases mobility of phospholipid (stiffens membrane)
Why does having cholesterol in plasma membranes make it less permeable to polar molecules?
It’s because parts of the cholesterol are hydrophobic
What is the function of scramblase
It catalyzes rapid flip-flop of random phospholipids from one leaflet to the other
Why is scramblase needed?
Phospholipids are synthesized in cytosolic leaflet of endoplasmic reticulum and must be moved to the lumen facing leaflet for symmetric growth of both halves of bilayer
Which enzymes in the golgi membrane flip lipids from one leaflet to the other?
Flippases
What do flippases do?
They catalyze the rapid flipflop of specific phospholipids to the cytosolic leaflet. Some can bind cytosolic proteins at the plasma membrane
What is the purpose behind the job of flippases?
Flippases flip lipids so that in the membrane they are the right orientation
True or False: Proteins flip-flop
Mega false
How are glycolipids and glycoproteins formed?
They are formed by adding sugar groups to lipids/proteins on luminal face of Golgi
Which way do glycolipids and glycoproteins face? What is their purpose?
Glycolipids and glycoproteins face the noncytosolic side always. Their purpose is to protect the membrane from hash environments.
