Biological Membranes Flashcards
(51 cards)
1
Q
Fluid Mosaic Model
A
accounts for presence of lipids, proteins, and carbohydrates in a dynamic semisolid plasma membrane surrounding cells
2
Q
Phospholipids
A
move rapidly in the plane of the membrane through simple diffusion
3
Q
Lipid Rafts
A
- collections of similar lipids with or without associated proteins that serve as attachment points for other biomolecules
- travel slowly within the plane of the membrane
4
Q
Flipases
A
enzymes that assist in the flipping/movement of lipids between the membrane layers
5
Q
What are the different components of a membrane?
A
- lipids (fatty acids, triacylglycerols, glycerophospholipids, sphingolipids, cholesterol, steroids)
- Proteins
- Carbohydrates
6
Q
Lipids
A
- most plentiful in the cells membrane
- most are phospholipids and few are free fatty acids
7
Q
Triacylglycerols
A
- storage lipids involved in metabolic processes
- contain 3 fatty acid chains esterified to a glycerol backbone
8
Q
Unsaturated Fatty Acids
A
- “healthier”
- one or more double bonds
- exist in liquid form at room temperature
9
Q
Saturated Fatty Acids
A
- main component of animal fat
- exist as solids at room temperature
- “less healthy”
- decrease membrane fluidity
10
Q
Glycerophospholipids
A
- replace one fatty acid with a phosphate group which is often linked to other hydrophobic groups
- used for membrane synthesis
- can produce a hydrophilic surface layer of lipoproteins like VLDL
11
Q
Sphingolipids
A
- contain a hydrophilic region and two fatty acid derived hydrophobic tails
- classes: ceramide, spingomyelins, cerebrosides, gangliosides
12
Q
Cholesterol
A
- regulates membrane fluidity
- necessary for synthesis of steroids
- contains hydrophilic and hydrophobic region
- increases fluidity at low temperatures and decreases fluidity at high temperatures
13
Q
What are the functions of proteins in a cell membrane?
A
- transporters
- cell adhesion molecules
- enzymes
14
Q
Transmembrane Proteins
A
- have one or more hydrophobic domains
- function as receptors or channels
15
Q
Embedded Proteins
A
- either part of a catalytic complex or involved in cellular communication
- usually linked to nearby enzymes
16
Q
Peripheral Proteins
A
involved in signaling or are recognition molecules on the extracellular surface
17
Q
Carbohydrates
A
- usually attached to proteins on extracellular surface
- generally hydrophilic and can form protective glycoprotein coat
- function in signaling and recognition
18
Q
Cell Adhesion Molecules
A
- typically compose cell-cell junctions
- proteins that allow cells to recognize each other and contribute to cell differentiation and development
19
Q
Gap Junctions
A
- allow direct cell-cell communication
- found in small bunches
- made up of connexons which are formed by alignment and interaction of pores composed of 6 molecules of connexin
- permit movement of water and some solutes (ions) directly between cells
- essentially like a tunnel that connects two cells
20
Q
Tight Junctions
A
- not used in intercellular transport
- form a water tight seal and prevent paracellular transport of water and solutes
- found in epithelial cells
- function as physical link between cells
- limit permeability enough to create a transepithelial voltage difference
21
Q
Desmosomes
A
- anchor cytoskeletons of adjacent cells together via interactions between transmembrane proteins associated with intermediate filaments
- ions and water can flow between cell gaps
22
Q
Where do tight junctions occur in the human body?
A
- bladder
- intestines
- kidney
23
Q
Where do desmosomes occur in the human body?
A
- skin
- intestines
24
Q
Where do gap junctions occur in the human body?
A
cells/tissue that spread action potential or cells that use electrical coupling
- cardiac muscle
- neurons
25
Passive Transport
- spontaneous processes that don't require energy (- delta G)
- includes: diffusion, facilitated diffusion, osmosis
- primary thermodynamic motivator is an increase in entropy (delta S)
26
Simple Diffusion
involves movement of small, nonpolar, lipid-soluble molecules down their concentration gradient
27
Osmosis
- movement of water through aquaporins from an area of low solute concentration to a high solute concentration
- referred to when a specific solute is impermeable
28
What is the osmolarity of red blood cells?
300 mOsm / L
29
Hypotonic
- internal solute concentration > external solute concentration
- leads to swelling of cell
30
Hypertonic
- internal solute concentration < external solute concentration
- leads to cell shriveling
31
Isotonic
solutions inside and outside of cell are equimolar
32
Osmotic Pressure
- colligative property [physical property of solutions that depends on the concentration of dissolved particles and not their chemical identity]
- the pressure applied to a pure solvent to prevent osmosis and is used to express the concentration of the solution
33
Facilitated Diffusion
- uses transport proteins to move impermeable solutes across the cell membrane
- transports large, polar, charged molecules across the membrane
34
Active Transport
- non-spontaneous processes that require energy (+ delta G)
- results in net movement of solute against its concentration gradient
- includes: primary active, secondary active
35
Primary Active Transport
- uses ATP directly or use of transmembrane ATPase
| - Ex. Sodium/Potassium pump
36
Secondary Active Transport
- no direct coupling to ATP hydrolysis
- uses an electrochemical gradient – generated by active transport – as an energy source to move molecules against their gradient, and thus does not directly require a chemical source of energy such as ATP
- can transfer molecules in a symport or antiport direction
37
Endocytosis
- cell membrane invaginates and engulfs material to bring into cell
- initiated by substance binding to specific receptors then carried out by vesicle-coating proteins (ex. clathrin)
- includes: pinocytosis, phagocytosis
38
Pinocytosis
endocytosis of fluids and dissolved particles
39
Phagocytosis
endocytosis of large solids like bacteria
40
Exocytosis
- secretory vesicles fuse with membrane and release material into extracellular fluid
- important in neurotransmitter release and intercellular signaling
41
Membrane Potential
different in electrical potential across cell membranes
42
Leak Channels
allow ions to passively diffuse down their concentration gradient through the cell
43
What type of leak channel occurs most in neurons?
K+ leak channels
44
Sodium/Potassium Pump
- primary active transport
- pumps 3 Na+ out of the cell and 2 K+ into the cell
- maintains low concentration of sodium ions and high concentration of potassium ions intracellularly
45
Nernst Equation
used to determine the membrane potential from the intra- and extracellular concentrations of various ions
46
Goldman-Hodgkin-Katz Voltage Equation
flows from the Nernst Equation but takes into account the relative contribution of each major ion to the membrane potential
47
How do Mitochondria produce ATP?
oxidative phosphorylation
48
Outer Mitochondrial Membrane
- highly permeable to ions and small proteins because has many large pores
- small intermembrane space between outer and inner membranes
49
Inner Mitochondrial Membrane
- more restricted permeability
- membrane lacks cholesterol
- contains cristae (infoldings of the membrane) which increases surface area for integral proteins associated with the ETC and ATP synthesis
- encloses the mitochondrial matrix
- contains a high level of cardiolipin
50
What important process occurs in the mitochondrial matrix?
Citric Acid Cycle
51
Does a pH gradient exist between the cytoplasm and intermembrane space in the mitochondria?
No -- this is because the outer membrane has such a high permeability to biomolecules
