Week 6 Recall Questions Flashcards
What are the key parts of a phospholipid and why is it amphipathic?
What are the hydrophobic and hydrophilic parts?
B/c both philic and phobic.
- bilayer effect caused by hydrophobic effect and clumping AA together and slightly attracted to 1 another.
Heads are philic = outside
- stable
Tails are phobic = inside
- stable
Van der waals interactions between lipids inside dictate physical state (solid or fluid)
What are the key elements of the plasma membrane?
• Selectively permeable, maintains structural integrity of cell.
- barrier between inside cell, cytoplasm and outside environment.
• regulates movement of ions and molecules (into and out of cell. permeability barrier, regulation of transport)
• cell-cell recognition, communication between cells and connecting cells to form tissues and organs (detection of signals, intercellular communication)
Quick cheat sheet:
• detection of signals
• intercellular communication
• Selectively permeable
- regulation of transport
- acts as barrier
- maintains shape
How or why is a plasma membrane selectively permeable?
• the phospholipid bilayer prevents the diffusion of most molecules across the membrane, due to the hydrophobic nature of the tails.
• inside of cytoplasm can have a different concentration of molecules than outside.
= some molecules can cross, others can’t, and some need a “window or door to get through”
• regulates movement of ions and molecules (into and out of cell. permeability barrier, regulation of transport)
- pH
-temperature
What was a key finding of the experiment by Frye and Edidin?
What were the variables for the experiment?
• wondered if membrane was static and solid or dynamic and fluid.
• if static (not moving): then the different dyed would stay in respective parts
• if dynamic (fluid): then dyed proteins would mix.
• provided evidence of idea vicious or Liquid membrane (fluid).
• phospholipids, and proteins move laterally (side to side)
• rarely flip-flop
• 1970
• fused mouse and human cells
• dyed the proteins and membranes and forced them to fuse
• 40 minutes of incubation time for the dyed proteins to mix.
• 70°C
• IV: (x-axis- time measured in minutes)
• DV: (y-axis- amount of mixing. Double stained cells)
• control variables: temperature, experimental control: unmixed cells in same conditions to show cells done spontaneous change colours)
• calculate a rate of mixing, based on this rate, bilayer is about as liquid as olive oil for light machine oil.
• another experiment they looked at different temp affects
- IV: temp
- DV: time
What are the key elements of the fluid mosaic model of membrane?
• the plasma membrane, is a mosaic of components— primarily, phospholipid, cholesterol, and proteins— that move freely and fluently in the plane off the membrane.
• mechanism for the fluidity is that the phospholipids move side to side. (10^7 times per second)
• phospholipids flip-flip rarely (once per month)
- this is an unfavourable condition b/c charged polar head that needs to go through hydrophobic layer.
- ions also don’t cross hydrophobic core
What factors are influencing membrane fluidity?
- Temperature:
- ⬆️ temperature = ⬆️ Kinetic energy = ⬆️ phospholipids laterally movement even more = ⬆️ gaps and leakages of ions and molecules from cytoplasm into cells (or other way around) = ⬆️ fluidity
• Membrane becomes more permeable
- ⬇️temperature = ⬇️ kinetic energy = ⬇️ phospholipids laterally movement = ⬆️ density of packed phospholipids = ⬆️ membrane becomes more viscous (possibly even solid) = ⬇️ fluidity
• Membrane solidifies
• too fluid membrane: molecules that shouldn’t cross the membrane, cross.
• not fluid enough membrane: nothing can cross.
• optimal functioning membranes: all have very similar fluidity and viscosity. (Similar to olive oil).
- important for: transport of molecules, movement of peripheral proteins electron transport chain, no ion leakage in or out.
- Type of phospholipids (fatty acids)
- Cholesterol
How do cells regulate membrane fluidity?
• Organisms can regulate membrane fluidity by changing the degree of fatty acid unsaturation
• Enzymes (desaturases) remove 2 H from saturated fatty acids and introduce double bonds or insert sterols. = changes saturated fatty acid in phospholipid to unsaturated fatty acid
- can activate or deactivate desaturases
• Fig(not in this): as temperatures get higher, amount of desaturases declines.
- as temperature goes low = ⬆️ amount of desaturases enzyme = means cell has more unsaturated fatty acids in membrane. = keeping fluidity similar. Even tho temp went down
- as temp changes, cell can regulate enzyme activity.
Quick cheat sheet:
• ⬆️ temp = ⬇️ desaturases (enzyme) activity = ⬇️ unsaturated fatty acids
• ⬇️ temp = ⬆️ desaturases (enzyme) activity = ⬆️ unsaturated fatty acids
• how do regulate? = by changing relative proportion of unsaturated fatty acids through desaturases
What is the role of saturated and unsaturated fats and cholesterol in the phospholipid bilayer?
To regulate the fluidity or viscosity of the membrane.
Fats:
• Saturated fatty acids = straight = ⬆️ packing or stacking of phospholipids more tightly = ⬇️ less space between phospholipids = ⬆️ viscosity of membrane = ⬇️ (less) fluidity
• Unsaturated fatty acids more fluid than saturated ones.
• Kinks from double bonds = ⬆️ spaces between phospholipids = ⬆️ increase freedom of movement = ⬆️ fluidity
— Shorter fatty acids more fluid than longer fatty acids
• more carbon chains ⬆️ fluidity
• not as important as saturation level of fatty acids
Cholesterol:
- Large planar molecule (hydrogen bonds to polar head)
- Regulates fluidity in animal membranes
- At low temp prevents close packing of phospholipids therefore hinders solidification. = retains fluidity
- At high temp restricts lateral movement in membrane therefore decreases disruption = limits extreme fluidity
- Decreases permeability to small ions and small polar molecules
- keeps layers organized
- adding sterols or cholesterol acts as buffer
Where in the membrane are membrane proteins located and what terms are used to describe the location?
Proteins are embedded in or attached to fluid phospholipid bilayer (mosaic part):
•Peripheral proteins
- Proteins associated with outside part of membrane = edge of periphery = peripheral
- include receptor proteins for hormones, matrix of structural proteins that attach to membrane and provide shape, etc.
• Integral proteins
- When span whole membrane = philic & phobic = full integrated = integral
- Include transport proteins (permeases).
What are 4 key functions of proteins?
- Transport (most substances do not diffuse freely)
—windows and doors into or out of cell - Enzymatic activity (e.g. ETC)
—catalyze rxn - Signal transduction (e.g. for hormones)
— receive and transmit signals - Attachment/recognition (e.g. to cytoskeleton (inside), cell to cell (outside))
— provide stability
— recog = attach to “friends” —> important for multicellular organisms
What are the differences between peripheral and integral membrane proteins?
Peripheral proteins:
• Hydrophilic (interact with water based solutions = cytoplasm or outside environment
• loosely bound to side of membrane through lipid or protein attachment (non-covalent).
• peripheral proteins assist transmembrane proteins with their function, e.g. electron transport chains
• non-polar functional group —> associated with hydrophobic core = extend through phospholipid bilayer = little more attached.
• if mostly hydrophilic and only attached to phospholipids = little less attached.
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Integral membrane proteins:
• Span both sides of membrane = transmembrane proteins
• Are amphipathic
— in order to be long & anchored membrane —> transmem pros reflect structure of membrane = amphipathic
• Interact with water based cytoplasm and outside environment
• Pass through hydrophobic core of the lipid bilayer
- have hydrophobic domains (17- 20 nonpolar AA inside membrane) and polar or charged (AA) domains are exposed (outside or inside (cyto) of membrane)
On which side of the membrane would you find carbohydrates/glycoproteins?
The outside.
What is a glycoprotein and a glycolipid?
• Carbohydrates are attached to proteins = glycoprotein
• Carbohydrates are attached to lipids = glycolipids
How is a membrane (or the bilayer) asymmetrical?
- not organized in same way from outside to inside. = outside environment is different from cytoplasm.
- Membrane layers (called leaflet) (outer and inner) have different lipid compositions
— diff fatty acids in upper leaflet & lower - Proteins have a specific orientation
- Outside face: Carbohydrates are attached to lipids (= glycolipids) and proteins (= glycoproteins)
- diff sides of membrane have diff peripheral proteins and diff densities of them. = v
- Outside face: Proteins anchor membrane to fibres of extracellular matrix (ECM)
- Inside face: integral and peripheral Proteins anchor membrane to diff components of cytoskeleton
Why is transport of substances across the membrane necessary?
The exchanges between the membrane is necessary to maintain function.
- What we eat needs to transported to each and every cell of our body so that energy could be made out of it.
- protein, hormone, enzymes needs to be transported to target cells or target organs.
What kind of substances are repelled by the hydrophobic interior of the plasma membrane?
• impermeable to large, polar, and/or charged molecules (hydrophilic) + water
- Can’t pass through membrane’s hydrophobic core
- Require membrane proteins for transport
• permeable to small, non-polar molecules
- e.g. O2 and CO2 (gases), small hydrocarbons (hydrophobic)
- Diffuse through the bilayer between the lipids
What kind of molecules move by simple diffusion versus facilitated diffusion (Fig. 4.13)?
Simple Diffusion:
Gases- CO2, N2, O,
Small uncharged polar molecules- Ethanol
Water and Urea
Facilitated Diffusion:
Water and Urea
Large uncharged polar molecules- Glucose
Ions- K^+, mg^2+, Ca^2+, Cl^-, HCO3^-, HPO4^2-.
Charged polar molecules- amino acids, ATP, glucose-6-phosphate
How do you tell/measure the difference between simple and facilitated diffusion (Fig 4.15)?
Passive Simple Diffusion: The tendency of molecules to move down a concentration gradient,
- Move from high conc. to low conc.
- direction and speed are not random
- Releases energy = system becomes less organized
- if Two or more different solutes = move independently from each other
- overall concentration of solutes doesn’t matter, only concentration difference of a specific solute or molecule.
- passive transport can’t establish [] gradient = only dissipate one
- rate is dependent on the concentration gradient and reaches equilibrium
Facilitated diffusion: Diffusion of substances aided by membrane transport proteins (= act like doors) (“accelerated diffusion”)
- Movement AGAINST conc. gradient
- Proteins used to move molecules across membrane
- Rate dependent more on amount of transport proteins than on concentration gradient, (e.g. saturation: all proteins are being used)
- more transport proteins = faster rate
- no energy required as along as have transport proteins or the “door is open
- rate is dependent on concentration gradient AND the number of proteins, maximum rate can be reached before equilibrium,
If a cell reaches diffusion equilibrium do the molecules crossing the membrane still move?
• At equilibrium, movement of molecules does not stop.
• At equilibrium, there is equal movement of materials in both directions
What is the definition of osmosis?
Osmosis: Diffusion of water across a selectively permeable membrane
- simulation osmosis
- high [] to low []
— high [] of solutes has low [] of moving/available H2O molecules. = To lower [] area of solutes or higher [] of H2O - rate is dependent on the gradient (of H2O vs solutes), reaches equilibrium.
- Water can cross membrane, BUT solutes (polar ions) cannot = [] of solutes/ions of each side of membrane can be diff = diff results in measurable force/potential.
- Can be measured as a force/osmotic potential
What are the two ways water moves across the plasma membrane?
- Osmosis which is passive diffusion
- Aquaporin which is active transport.
For osmosis to take place, what must the selectively permeable membrane allow to cross versus what must the membrane hold back?
Selectively permeable to water and impermeable to the solute.
And concentration of the solute must be different on the two sides of the membrane.
What is meant by hyper-, hypo- and isotonic?
What happens to a cell in a hyper- or hypotonic environment (relative to cytoplasm)?
- Hyper-, hypo-, and isotonic relate to solute concentrations relative to the cell
hypertonic: more free H2O molecules outside cell and more solutes inside cell than outside.
• net movement of water- into cell
• cell is- increasing
• solution is- hypotonic
• hyper = “more or lots”
hypotonic: more free H2O molecules inside cell and less solutes inside than outside.
• net movement of water- out of cell
• cell is- shrinking. Loses volume.
• solution is- hypertonic
• hypo = “ less or low”
isotonic: amount of free water on both sides of membrane is the equal and there is no net movement of H2O molecules
• net movement of water- balanced
• cell is- stays the same
• Iso = “ equal or the same”
What are the differences between a channel protein and a carrier protein? Give examples.
Channel proteins:
- Form open hydrophilic channels that allow specific molecules to pass, e.g. ion channels, aquaporins.
- molecules can move in both directions of the protein = movement determined by [] gradient.
- Can be gated, e.g. K+ voltage gated channel: gate opens in response to a voltage change across the membrane
- open channel still selective for molecular properties like polarity, charge, hydrophobic/philic, size,
Ex: aquaporin allows polar water through but hydrogen protons that are smaller but charged can’t go through b/c in the protein channel there are some positive charges that repeal hydrogen protons.
Carrier proteins
• Change shape when specific molecules bind to carry them across membrane
- b/c of binding = carrier proteins highly specific
• Direction of transport follows concentration gradient
• High specificity e.g. Glucose transporter
