Lecture 7 - Cellular Form and Function Flashcards
What is the Extracellular Matrix?
Specific to Animal Cell - specialized material outside of the cell
What are Lysosomes?
Specific to Animal Cell - degradation of cellular components that are no longer needed
What are the two type of vacoules?
Only in the plant cell - degradation and water storage
What is the cytoplasm?
Contents of the cel outside of the nucleus (includes organelles and cytosol)
What is Cytosol?
Aqueous part of the cytoplasm (does not include membrane bound organelles) - includes ribosomes and cytoskeleton
What is the lumen?
Inside the organelles (except the nucleus)
Why is it called the Fluid Mosaic Model of the Membrane?
Fluid - due to the mobility of lipids and some of the proteins, stuff moves around but is still stable
Mosaic - many different lipids and proteins
Membrane = 1 lipid bilayer = 2 layers/leaflets
What’s the basic structure of a phospholipid?
Hydrophilic Head - group + phosphate + glycerol
Hydrophobic Tail - 2 hydrocarbon chains
What type of molecules is a phospholipid?
Amphipathic - both hydrophilic and hydrophobic parts
Different biochemical/biophysical properties
What type of lipids are present in the membrane?
Phospholipids, Sterols (cholesterol) and Glycolipids (has a sugar group)
Whats the name of a phospholipid with a glycerol group?
Phosphoglycerides
Whats the average length of a hydrocarbon chain?
14-24 carbons + unsaturated/saturated
In an aqueous environment how do phospholipids orient themselves?
Spontaneously self-associate into a bilayer (polar - water, and hydrophobic tail - other hydrophobic tail)
What are artificial sealed phospholipid bilayers called?
Liposomes
How does the bilayer orient its self to become energetically favourable?
Naturally forms a sphere to prevent the tails from facing the aqueous side
What are the three uses of liposomes?
- Study lipid properties
- Membrane protein properties
- Drug delivery into cells
Why are membranes fluid?
A membrane can be deformed without causing damage - laser tweezer pull on it like skin (lipids move around to adapt to mechanical disruption)
What are the three rapid movements of phospholipids?
- Diffuse laterally (deeper into the plane)
- Rotate (spins)
- Flex (wobble side to side)
What phospholipid movement rarely occurs on its own?
Flip flip - movement from one leaflet to other (needs help to happen)
What’s the important of cell membrane fluidity?
It is carefully regulated as it is important for function (membrane proteins depend on it)
What are two things membrane fluidity is affected by?
Temperature and composition (maintain fluidity)
What happens at low temperatures?
The membrane becomes more viscous and less fluid, molecules don’t move, don’t want this to happen!
Composition: Phospholipid Saturation
Increase fluidity - make unsaturated (add cis-double bonds at lower temps to reduce tight packing due to kinks)
Composition: Phospholipid tail length
Increase fluidity: shorter tails (fewer interactions between the lipid tails and makes more space)
Composition: Lipid Composition
Decrease mobility - add cholesterol (stiffen membrane, less permeable to water and only in animal cells)
What is cholesterol’s affect on mobility?
Decreases cell membrane mobility - insert themselves to fill spaces - slow movement (1:1 ratio of cholesterol and phospholipids)
What is structure of sterols?
polar head group + hydrophobic ring top + ONE hydrophobic tail
Animal vs Plant Sterols:
Animals - mainly cholesterol
Plants - plant sterol and some cholesterol
(plasma membrane is less permeable to polar molecules)
What promotes Lipid movement from one leaflet to another?
Scramblase - Enzyme in the ER (phospholipic translocator)
What is the role of scramblase?
Promote flip flop - phospholipids are made in the cytosolic leaflet of ER, this helps balance the two leaflets of the bilayer
What’s the role of Flippases?
Catalyze membrane flips in the golgi, specific phospholipid movement only!
Asymmetry of Bilayer - Glycoproteins and Glycolipids
- formed by adding sugar groups ot the lipids/proteins of the laminal face of golgi
- end up on plasma membrane (inside organelles and non cytosolic face)
- protect membrane from harsh environments
Integral Membrane Proteins
Proteins directly attached to lipid bilayer, extraction methods use detergents — destroy lipid bilayer
What are the 3 types of integral membrane proteins?
Transmembrane, Monolayer and lipid linked
What are peripheral membrane proteins?
They do not insert into the membrane, located on either face of the membrane
What are peripheral membrane protein properties?
Can be bound to other proteins that are transmembrane, bound to lipids, or attached by non covalent interactions (use gentle extraction methods that keep the bilayer intact)
How do covalent interactions differ between the two types?
Integral - covalent
Peripheral - noncovalent
Transmembrane proteins
Amphipathic which hydrophilic (outside) and hydrophobic (inside)
Things to remember about alpha helices and transmembrane domains
1) not all alpha helices pass through the membrane
2) not all transmembrane domains are alpha helices
What are the three types of transmembrane proteins?
1) Single a-helix: single pass, has one hydrophobic domain
2) Multi a-helices: multipass, many hydrophobic domains
3) B-barrel - multipass but not a-helices
How many hydrophobic amino acids are present in a membrane spanning a-helix?
20-30
Which two transmembrane proteins serve as channels?
multiple a-helices and b-barrel (inside is hydrophillic, outside is hydrophobic) - based on amino acid side chains
What is essential for transmembrane protein in terms of function?
Specific orientation - proteins don’t flip-flop so it cant be fixed
Techniques for identifying these structures?
1) X-ray crystallization - determines 3D structure
2) Hydrophobicity plots - segments of 20-30 hydrophobic amino acids that span bilayer
Hydrophobicity plots
(-) –> hydrophillic
(+) –> hydrophobic
0 –> N-terminus
100 –> C-terminus
Calculation depends on the neighbouring amino acids, can identify number of passes
Monolayer Associated Membrane Proteins
Amphipathic - anchored on the cytosolic face
ex. Sar 1 - membrane bending - vesicle bending at the ER
Lipid-linked Membrane Protiens
1) Protein with GPI anchor (made in ER lumen end up on cell surface)
2) Protein with another lipid anchor (cytosolic enzymes add an anchor and directs it to cytosolic face)
Extraction of Membrane Proteins
Also amphipathic (detergents) - formation of micelles and complex (tails connected to tails etc)
Studying the Properties
Use detergents to isolate, then purify, remove detergent, addition of phospholipids —> protein incorporated into an artificial bilayer
Lateral Diffusion of Membrane Proteins
lateral diffusion within leaflet (no flip-flop), FRAP, protein is fuse to Green fluorescent protein.
Fluorescence Recovery after Photobleaching (FRAP)
- Photo bleach an area after labelling
- proteins move quickly –> cover up –> fast diffusion
Rate of Fluorescence recovery
time taken for neighbouring unbleached fluorescent protein to moving into bleached area
