Lectures 3 and 4: Cell Membranes Flashcards
what are the 4 general functions of the cell membrane?
- it acts as a protective barrier between the intracellular and extracellular environments
- it facilitates transport of substances in and out of the cell
- signal transduction-it may house receptors important for cell signaling and initiation of cellular events
- energy storage-there is a charge difference between the outside and the inside of the cell
what is the fluid mosaic model?
the membrane of the cell is “fluid” meaning it can bend and move
and
the membrane is “mosaic” meaning it is composes of many different macromolecules put together
what are the major parts of the membrane?
- membrane lipids
- membrane proteins
- glycocalyx
(kinda have an idea how to diagram)
what are phospholipids and what are they made up of?
Phospholipids make up the cell, and they are made up of a hydrophilic head and a hydrophobic tail (mainly) but more precisely: phosphate, glycerol, unsaturated fatty acids/saturated fatty acids or both at the same time
(know how to diagram)
what is a hydrophilic head made up of?
-phosphates and glycerol
-holds a negative charge
what are hydrophobic tails made up of?
-fatty acid chains
1. saturated fatty acid chains
(straight tail)
2. unsaturated fatty acids
(kinked tail)
what does cholesterol do in regards to the cell membrane and the phospholipid bilayer?
-is rigid, contributes to the cell membrane structure and fluidity
-is also temperature sensitive
-acts like glue**
explain membrane fluidity (also know how to diagram)
- when temperature rises, so does membrane fluidity,, phospholipids are more spaced out
- Cholesterol acts like glue holding phospholipids together, so when there is more cholesterol fluidity goes down because things are more rigid. When there is less cholesterol, fluidity goes up.
- The more unsaturated fatty acids there are the more fluidity goes up. Unsat. fatty acids need more space for their kinked legs and therefore aren’t as compact. Whereas saturated fatty acids can be more tightly packed, less fluid, and more rigid.
what are the two types of membrane proteins and what do they do?
- integral proteins:
-function as channels and receptors
-embedded in membrane - peripheral proteins
-not embedded
-usually have specialized function
what are the functions of membrane proteins? (be able to diagram)
- transport
- receptor
- cell to cell adhesion
- enzymes
- communication
- attachment to ECM (extracellular matrix)
what are the types of integral proteins? (aka transmembrane proteins)
Look at the photo in notes of both
- channels
-includes aquaporins - receptors:
-selectively bind specific molecules, which initiates a chemical reaction inside of the cell (type of signaling)
what do aquaporins do?
transport H2O
what is the glycocalyx?
- decreases cell dehydration
- antigenic function (aka autoimmune and blood type)
-made up of the glycolipid ad glycoprotein (be able to draw and label)
the cell membrane is _____________ permeable.
selectively
what can move freely across the membrane?
-small
-non-polar
-lipid soluble
substances
examples: O2, CO2, steroid hormone
what are the two ways substances get moved across the cell membrane?
- passive transport
- active transport
explain passive transport and the types you may have
movement across the membrane WITHOUT the use of ATP
- simple diffusion
- facilitated diffusion
- osmosis
what is active transport?
movement across the membrane that DOES require ATP
commonly achieved with protein pumps (ex ATPases)
typically moves substances AGAINST the concentration gradient
what is diffusion?
-the movement of particles from an area of high concentration to an area of lower concentration
aka “moving down or with the concentration gradient”
what are the two main terms used when talking about diffusion?
- solvent: the LIQUID component of a solution
- solute: a dissolved SUBSTANCE in a solution
with no membranes present, which direction will solute diffuse?
from areas of high concentration to low concentration
solutes will become equally distributed over time
what is dynamic equilibrium?
the phenomenon that solutes will become equally distributed over time
what is simple diffusion?
(a form of passive transport)
this is where “selectively permeable” comes into play
there is a cell membrane, but the particles that are able pass through with no help from an outside channel or ATP they just simply pass through
what is facilitated diffusion?
(a form of passive transport)
when substances are aided by a membrane protein that DOES NOT use ATP
what types of molecules would need to use facilitated diffusion?
look at diagram
larger/charged molecules like Na+
what is osmosis?
look at diagram
(a form of passive transport)
when water can move freely across the cell membrane through special channels called AQUAPORINS via osmosis
“the diffusion of water through a semipermeable membrane”
follows a concentration gradient
what is Na-K-ATPase?
is an important ion pump found in most cells (more later)
what are the key points of transport?
- passive v. active transport:
-passive: diffusion
-simple (diffusion through
membrane) —> small, non polar,
lipid soluble substances
-facilitated (diffusion through
channel or carrier)—>some larger,
polar, H2O soluble substances
-active: requires ATP—> large, polar, H2O soluble substances and when moving AGAINST a gradient - membranes are differentially permeable to solutes, including ions
- this leads to an unequal
distribution of solutes between the
intracellular fluid and the
extracellular fluid
compartmentalization of water
cells create a protective barrier and transport things in and out of the cell.
Water is the main solvent of the body and is separated into multiple compartments
2/3 of your total body water is inside your cells and 1/3 is outside
what percentage of your total body weight is your total body water?
60%
what is osmolarity?
the concentration of solute particles in a solvent
expressed as mOsm/kgq
composition of the solutes is different, but osmolarity as a whole is heavily regulated by the body
what is normal ECF osmolarity?
300 mOsm/kg
what is normal ICF osmolarity?
300 mOsm/kg
osmolarity is based on_______, whereas tonicity is based on__________.
- solute concentration 2. how the osmolarity effects cell volume
**tonicity is not expressed with units
what are the three types of tonicity
- hypotonic
- isotonic
- hypertonic
hypotonicity
when the solutes coming out are less than the solutes coming in,, this causes H2O to move into the cell and the cell will swell
isotonicity
solutes out are equal to the solutes coming in
what is hypertonicity?
when the solutes out are more than the solutes in,, H2O moves out of the cell and the cell shrivels/shrinks
why is it important to understand unequal distributions of solutes?
unequal distribution of solutes means an unequal distribution of charge
many cell sin the body are very electrically and excitable
what is the shorter way to say resting membrane potential?
Em
E=voltage
m=across membrane
what is resting membrane potential?
the difference in voltage measured across a cell membrane AT REST
occurs in all cells due to the unequal distribution of ions and differential permeability to those ions
what is the typical Em for a cell?
depends on cell type but usually -70mv to -90mv
Na+ is more concentrated….
outside the cell
this means it’s gradient has it move in
K+ is more concentrated…
inside the cell
this means it gradient has it move out of the cell
what are the ways the cell gets itself to -70mv,, aka what are the ways ions move in and out of the cells?
(helpful diagram in notes)
- Na-K-ATPase (active transport)
- leaky K+ channels (passive diffusion)
- Leaky Na+ channels
what does Na-K-ATPase do in regards to resting membrane potential?
-moves substances against the concentration gradient
-establishes a net negative charge
(releases 3Na and brings in 2K+)
how many more times of leaky K+ channels are there than leaky Na+ channels?
20x
the permeability of K+ is ________ than the permeability of Na+
wayyyyyyyy greater
how do we measure RMP
using a volt meter
a microelectrode is inserted into the cell membrane and then records the potential over time
know the diagram in notes
each ion has a_____which is calculated using_____
- an equilibrium potential
- the Nerst Equation
what is equilibrium (Nerst) potential?
the membrane potential where the net flow through any open channel is 0
ex. K+ out = K+ in both electrically and chemically
how do you know when to use the Nerst Equation?
when a question asks about ONE ion and does not ask about permeability
**also make sure you simplify the equation before you plug it into the calculator
what is the Goldman-Hodgkin-Katz equation? When do you use it
Takes into account MULTUPLE ions as well as relative Permeability of each,, allows us to estimate resting membrane potential
**also make sure you simplify the equation before you plug it into the calculator
RMP is a _________ NOT a _______________
- steady state 2. equilibrium
why is RMP a steady state and not an equilibrium?
no ion is at it’s equilibrium potential at RMP (look at our calculation bs the typical RMP of -70 mv)
ions are constantly moving in and out of the cell meaning there is always some fluctuation
RMP is s steady state of voltage maintenance not static equilibrium
look at the diagram for RMP maintenance
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