Lecture 1 - Cell membranes (prior to class review) Flashcards
What are the different strategies for studying cell biology?
1) Biochemistry
2) Forward genetics
3) Reverse genetics
4) Imaging
5) Protein structure analysis
(BFRIP or RIP best friends)
What are the different model systems used for cell biology?
1) Yeast
2) C. elegans
3) Mammalian cell culture
4) Xenopus
5) Mouse
The basic structure common to all cells and almost all eukaryotic organelles is what?
lipid bilayer
The lipid bilayer is composed primarily of ______ and more specifically _____.
- Lipids
2. phospholipids (and cholesterol)
What are some of the basic characteristics of the lipid bilayer?
- Asymmetric
- Will form spontaneously and seal spontaneously
- Acts as a barrier to diffusion of charged molecules, most polar molecules and macromolecules
- Animal cells maintain a negative membrane potential
Among other activities, membrane proteins regulate _______ and maintain membrane _________.
- transport
2. potential
Where is phosphotidylinositol found in relation to the plasma membrane?
Found in cytosolic layer of membrane.
The inositol ring is phosphorylated by what?
PI kinases to form PIPs.
PI phosphorylation is important in many ________ _________ pathways.
intracellular signalling
PI cleavage is accomplished by?
phospholipases
What is a phospholipase?
An enzyme that hydrolyzes phospholipids into fatty acids and other lipophilic substances
Polar or charged molecules are __________ and will interact with water.
Hydrophilic
Non-polar molecules are _________ and are repelled by water.
Hydrophobic
Lipids are ______ molecules.
Bi-polar
Glycoproteins and glycolipids are oriented with the ________ groups on the cell _______.
- glycosyl
2. exterior
Charged lipids such as phosphotidylinositol occur in the _______ layer.
inner
Transmembrane domains can be predicted from the ___________ ______.
hydropathy index
What are hydrophobicity scales?
Values that define the relative hydrophobicity of amino acid residues. These scales are often used to predict the transmembrane alpha-helices of membrane proteins.
What are the two different types of membrane proteins?
- Integral membrane proteins
2. Peripheral membrane proteins
What are the basic characteristics of integral membrane proteins?
- Transmembrane (single pass or multi-pass)
- Covalently linked to lipids on the cytosolic side
- GPI anchor on the lumenal (extracellular side)
- Solubilized by membrane disrupting agents.
What are the basic characteristics of peripheral membrane proteins?
Associated with integral membrane proteins by non-covalent interactions
Solubilized by mild detergents, low or high pH, high or low ionic strength
Integral membrane proteins are _______, meaning that they have polar ends and a hydrophobic transmembrane domain.
amphipathic
The transmembrane domain of integral membrane proteins is typically composed of _____ ______ with mainly __________ amino acids or _____ _____.
- Alpha-helices
- hydrophobic
- Beta Barrel
Most molecules are brought into or taken out of cells by specific ________ that recognize only that molecule.
transporters (carriers)
What are the steps for the identification of lac mutants?
- Irradiate cells to make mutants
- Place into full media (contains many sugars) (permissive)
- Replica plate onto media with lactose as only sugar/Carbon source (certain colonies fail to grow)
- Isolate colonies
What E. coli mutants are unable to grow on lactose as sole carbon source?
Lac Z/Y mutants
True or False? Both Lac Z and lac Y are required for utilization of lactose.
True
What experiment was done was done to determine whether the lacZ/Y genes were involved in import or cleavage of the disaccharide lactose?
- Add 14C carbon lactose to growth media
- Wash away media
- Measure radioactivity with cells
What was the observation of the lactose experiment? (Mutant for Y/Z)
Lactose enters wt and lacZ mutant cells but does not enter lac Y mutant cells
Lac Y is required for _______ of lactose into the cell.
transport
It was later shown that _____ enters with lactose.
H+
True or False? Lac Y also affects the uptake of sugars related to lactose.
False
The lac Y protein has 12 predicted transmembrane ______ _______.
Alpha helices
Ion channels and transporters are also important in all cells for maintenance of _________ and establishing ____ and __________ gradients.
- Osmolarity
- Ion
- Electrochemical
Animal cells are ______ charged.
Negatively
The electrochemical gradient for a given ion is equivalent to?
The ion gradient plus the membrane electrical potential.
The sodium-potassium ATPase transports 3 _____ out while bringing in 2 ________.
- sodium
2. potassium
___ leak channels allow ___ to passively leave the cell.
K+ (bis)
In a typical resting cell, ___ is near its electrochemical potential while ___ is far from equilibrium.
- K+
2. Na+
__ channels allow __ to exit the cell - toward its electrochemical eqb, partially offsetting the negative membrane potential.
Cl- (bis)
