Lectures 3 & 4 Questions Flashcards
Name the 3 body fluid compartments, differential b/t the 3.
- EXTRAcellular fluid (ECF) outside the cells &
- INTRAcellular fluid (ICF) within the cells
- dividing wall b/t ECF & ICF is the cell membrane
- the extracellular fluid SUBDIVIDES further into PLASMA, the fluid portion of the blood, & INTERstitial fluid, which surrounds most cells of the body
give the ionic concentration of intracellular fluid, interstitial fluid (note that this is
usually called extracellular fluid in this course)
extracellular:
K+ 5mM Na+ 145mM Cl- 108mM Ca2+ 1mM ~290 mOsM
intracellular:
K+ 150mM Na+ 15mM Cl- 5mM Ca2+ 0.0001mM ~290 mOsM
list and explain the functions of the cell membrane
- Physical barrier
- separates intracellular fluid from extracellular fluid - Gateway for exchange
- controls movement of solutes: allows some to cross, prevents others from crossing (semipermeable) - Communication
- home to receptors that detect physical & chemical stimuli & starts cascade of response to stimuli - Cell Structure
- some membrane proteins hold cytoskeleton proteins to give cell structure
- may also form specialized junctions
what’s a cell wall?
a rigid layer of polysaccharides lying outside the plasma membrane of the cells of plants, fungi, and bacteria. ?
state the difference between the butter sandwich and fluid mosaic models of
membrane structure
early model of the cell membrane structure was a “Butter sandwich”
- a clear layer of lipids sandwiched b/t 2 dark layers of proteins
- NOT accurate as it implies that it is homogenous
present day model of the cell membrane structure is “Fluid mosaic”
- proteins are afloat on a sea of lipid
draw a typical cell membrane, including phospholipids, glycolipids, glycoproteins,
integral proteins, peripheral proteins, lipid anchored proteins, cytoskeleton and
extracellular matrix
page 63 or slide 8
what is a lipid raft
sphingolipids tend to aggregate together (with themselves rather than with the phospholipids) = lipid rafts
why is it the lipid raft an important structure?
- rafts have a high density of cholesterol (as cholesterol prefers to associate with sphingolipids over phospholipids)
- some proteins associate ONLY with lipid rafts, leading to areas of SPECIALIZATION on cell membrane for ex, some G-protein coupled receptors (that are only associated with lipid rafts)
how many amino acids span the membrane in a membrane spanning domain?
approximately 20-25 hydrophobic amino acids to span the cell membrane ???
what kind of amino acids are they (acidic, basic, hydrophobic, hydrophilic)?
hydrophobic (non-polar) ??
- (this allows those amino acids to create strong noncovalent interactions with the lipid tails of the membrane phospholipids, holding them tightly in place)
What are the ways a molecule gets from one side of a cell membrane to the other?
- diffusion/osmosis
- protein mediated transport
- transport thru channel proteins
- transport via carrier proteins which include:
- facilitated diffusion
- primary active transport
- secondary active transport - vesicular transport
what are the factors that influence diffusion?
- Fast over short distances, slow over long distances
- time taken to get from A to B is a “distance squared” relationship: if distance doubles from 1 to 2, time increases from 1 to 4 (=2 squared) - Rate of diffusion is:
- faster at high temp
- faster for small molecules
- slower across a membrane
what are the factors that influence diffusion across a cell membrane?
1) Permeability (of solute) across cell membrane
- size
- lipid solubility: polar or non-polar or VERY non-polar
2) Concentration gradient
3) Surface area
4) Temp
5) Composition of membrane
- simple lipid bilayer vs membrane with many proteins & extracellular matrix
- types of phospholipids & sphingolipids
- presence of cholesterol
define selective permeability
cell membranes are selectively permeable, which means that some molecules can cross them but others cannot
is a cell membrane selective permeable?
yes - cell membranes are selectively permeable, which means that some molecules can cross them but others cannot
what kinds of molecules can diffuse across a cell membrane ? what kinds cannot?
can:
- hydrophobic, non-polar molecules, such as:
- O2, CO2,
- lipids
- steroids
- fat soluble molecules
- small uncharged polar molecules, such as:
- urea
- H20 ????
cannot:
- large uncharged polar molecules, such as:
- glucose, proteins, amino acids
- charged molecules, such as:
- ions
define osmosis
is the diffusion of water
define concentration gradient in terms of water
water can have a concentration gradient
water will “diffuse down its concentration gradient”
- pure water has the “highest concentration of water”
- solutes lower the concentration of water
movement of water can cause pressure
in a U-tube system with a selectively permeable membrane, identify which solution is
hyperosmolar, and which way water or solutes will move.
slides 40-42 or fig. 4.2 on page 124
- 2 compartments are separated by a membrane that is permeable to water but not glucose. Solution B is more concentrated than solution A
- Water moves by osmosis into the more concentrated solution. Osmosis stops when concentrations are equal.
- Compartment A is pure water, & compartment B is a glucose solution. Osmotic pressure is the pressure that must be applied to oppose osmosis.
define hypertonic
a solution that causes net movement of water out of a cell (cell shrink)
a cell is placed in a solution of 150 mM NaCl. What happens?
What about 150 mM glucose?
What about 150 mM maltose (a dimer of glucose)?
150 mM urea?
? all hyposmotic - non-pen so it would be hypertonic? - non-pen so it would be hypertonic? - non-pen so it would be hypertonic? - pen so it would be hypotonic?
what’s the difference between a channel and a carrier protein?
channel proteins create water-filled passageways that directly link the intracellular & extracellular compartments
carrier proteins, also just called transporters, bind to the substrates that they carry but NEVER form a direct connection b/t the intracellular fluid & extracellular fluid
carriers are open to one side of the membrane or the other, but not to both at once the way channel proteins are
differentiate between facilitated diffusion, primary active transport and secondary
active transport. Give an example of each. ATP is directly used in which processes.
Facilitated Diffusion: is defined as moving a molecule across the cell membrane via a carrier protein, & the transport does not require energy other than the concentration gradient
- does NOT require ATP, or other solutes
- AKA passive transport
- this process along cannot accumulate solute against a concentration gradient
EX: glucose transporter: GLUT protein
Primary Active Transport:
- uses ATP
- establishes gradients
- sometimes called pumps
- Na+/K+/ATPase is the most widely known ex, but there are others:
- Ca2+ ATPase
- H+ ATPase
- H+/K+ ATPase
Secondary Active Transport:
- does NOT directly utilize ATP as a source of energy
- instead, uses the concentration gradient of one molecule/ion to move another against its gradient (acts as energy source)
- Na+- glucose secondary active transporter is a good ex: SGLT-protein
explain how glucose moves across gut epithelia into the blood.
- Na+/K+ ATPase - establishes & maintains a Na+ gradient. Primary active transport
- Using the Na+ gradient, glucose is transported into the cell via the Na+ glucose co-transporter. Secondary active transport
- Glucose is transported across the basal membrane by the GLUT transporter. Facilitated diffusion
- & then moves the glucose into the bloodstream & then circulated around your body for general use
what would happen if the Na+/K+ ATPase was blocked with the poison oubain?
The removal of Na+ from the cell is essential if glucose is to continue to be absorbed from the lumen. The potential energy to run the SGLT symporter comes from the sodium concentration gradient, which depends on low intracellular concentrations of Na+.
If the basolateral Na+-K+-ATPase is poisoned with oubain, Na+ that enters the cell cannot be pumped out. The Na+ concentration inside the cell gradually increases until it is equal to that in the lumen. With out a sodium gradient, there is no energy source to run the SGLT symporter, & the absorption of glucose across the epithelium stops.
Assume that a hypothetical cell X can only takes up glucose by facilitated diffusion
(passive and does not move molecules against concentration gradients). How can this
cell accumulate glucose at a concentration higher than found in the extracellular
fluid?
s
differentiate between Phagocytosis, Endocytosis, Exocytosis
phagocytosis: the process by which a cell engulfs a particle into a vesicle by using the cytoskeleton to push the membrane around the particle
endocytosis: by which large molecules or particles move into cells
exocytosis: process in which intracellular vesicles fuse with the cell membrane & release their contents into the extracellular fluid
Discuss the use of liposomes for drug delivery
- some drugs may have low “bioavailability” due to poor solubility
- some drugs may be toxic at useful doses, & must be TARGETED TO A SPECIFIC CELL TYPE
- liposomal drug delivery is an emerging technology that may help address these issues
What is osmotic equilibrium?
water is essentially the only molecule that moves freely b/t cells & the extracellular fluid
- b/c of this free movement of water, the extracellular & intracellular compartments reach a state of OSMOTIC EQUILIBRIUM, in which the fluid concentrations are equal on the 2 sides of the cell membrane
What is chemical disequilibrium? Give some examples of specific solutes
that exist in a state of chemical disequilibrium in our body. (Fig. 5.1d)
although the overall concentrations of the ECF & intracellular fluid (ICF) are equal, some solutes are more concentrated in one of the two body compartments than in the other - this means the body is in a state of CHEMICAL DISEQUILIBRIUM
- fig. 5.2d shows the uneven distribution of major solutes among the body fluid compartments
- for ex: sodium, chloride, & bicarbonate (HCO3-) ions are more concentrated in extracellular fluid than in intracellular fluid
- potassium ions are more concentrated in the extracellular fluid than in the cytosol, although many cells store Ca2+ inside organelles such as the endoplasmic reticulum & mitochondria
How does chemical disequilibrium in the body give rise to electrical disequilibrium? What is the result of electrical disequilibrium?
The concentration differences of chemical disequilibrium are a hallmark of a living organism, as only the continual input of energy keeps the body in this state. If solutes leak across the cell membranes dividing the intracellular & extracellular compartments, energy is required to return them to the compartments they left.
Ex: K+ ions that leak out of the cell & Na+ ions that leak into the cell are returned to their original compartments by an energy-utilizing enzyme known as the Na+-K+-ATPase, or the sodium-potassium pump. When cells die & cannot use energy, they obey the 2nd law of thermodynamics & return to a state of randomness that is marked by loss of chemical disequilibrium.
The body as a whole is electrically neutral, but a few extra negative ions are found in the intracellular fluid, while their matching positive ions are located in the extracellular fluid. As a result, the inside of cells is slightly negative relative to the extracellular fluid. This ionic imbalance results in a state of electrical disequilibrium
What is the physiological significance of the “70-kg man”? What is his total
body water volume?
people ask how much water is in the human body but b/c 1 individual differs from the next, there is no single answer
- however, in human physiology we often speak of standard values for physiological functions based on the “the 70-kg man”
- these standard values are derived from data published in the mid-twentieth century by the International Commission on Radiological Protection (ICRP)
- the ICRP was setting guidelines for permissible radiation exposure, & they selected a young (age 20-30) white European male who weighed 70 kilograms (kg) or 154 pounds as their “reference man,” or “standard man”
*The 70-kg Reference Man has 60% of his total body weight, or 42 kg (92.4 lb), in the form of water. Each kilogram of water has a volume of 1 liter, so his TOTAL BODY WATER is 42 liters. This is equivalent of 21 two-liter soft drink bottles!
