composition of cells Flashcards
volumes of plasma
3 liters
volume extracellular fluid (ECF) ___ L
about 13 liters plus another 5 for the ‘third space’)
volume intracellular fluid (ICF) ____ L
27 liters
__% of all the chemical particles in the __ liters of body fluids are water molecules.
99%
45L
Of the remaining 1%, about 5 out of every 6 are simple
inorganic ions, principally Na+, K+, and Cl-. All of the rest – all carbohydrates, proteins, nucleic acids, lipids, and so forth – constitute a very small fraction of the total.
the fluids in the various body compartments _________;
do not have the same composition
the ion content of cells, for example, is vastly different from that of blood plasma.
The boundary between the intra- and extracellular fluids is
plasma membrane
extracellular fluid (ECF) comprises
plasma (~3 liters – plasma is whole blood without the cells), lymph, and interstitial fluid, all of which have nearly identical inorganic ion and water compositions.
ECF we will mean the
interstitial fluid.
Intracellular fluid (ICF) comprises
mitochondrial, vesicular, nuclear, and other subcompartments.
ICF
Na+
14
ICF K+
145
ICF
Cl-
5
ICF
A-n
126
ICF
H2O
~55,000
ECF
Na+
140
ECF K+
5
ECF
Cl-
145
ECF
A-n
~0
ECF H2O
~55,000
membrane permeability
Na+
- (no)
membrane permeability
K+
+ (yes)
membrane permeability
Cl-
+ (yes)
membrane permeability
A-n
- (no)
membrane permeability
H2O
+ (yes)
A note on the word permeable: _____ are permeable (or impermeable) to solute,
while a _____ is permeant (or impermeant) or permeating (or nonpermeating)
membranes
solute
Membranes are mostly _____, which are_______ to water and charged substance
lipid molecules
impermeable
Lipids are also ‘strong’, in an _______. they can keep opposite _______.
electric sense.
electric charges separated, without collapsing
he cytoplasm of nearly all cells is electrically ______, compared to the ECF, because:
negative
because cells contain a few more negative than positive ions.
membrane potential, is caused by:
The excess anions create an electrical potential difference between the inside and the outside of the cell
Membrane potential governs some:
vital cell processes, is wholly dependent on the integrity of the plasma membrane
The ability of the membrane to withstand the imposed electric force (which has a whopping strength of about 100,000 volts/cm) is due to its_______
lipid composition.
Many charged and polar molecules can cross membranes. Through:
- channels
2. transporters
channels are ______ for particular ions
selective
Sodium channels will pass ___________.
Na+ ions, but not K+, or Cl-, or other ions
voltage gated channels depend on _____
The gate open when the membrane is _____
electric field across the membrane or membrane potential.
the gates open when the membrane is depolarized
depolarized means
cell is less negative inside
aquaporins
channel that has no gate,
pumping means work, energy can come from
- directly from metabolism: primary active transport
2. other sources: secondary
active transport
pump molecules across a membrane to concentrate them on one side against their energy gradient.
primary active transport example
Na+ pump, which extrudes Na+ from the cell and requires ATP
secondary active transport,
use the energy released when Na+ ions leak into cells, and the energy released is captured and used to pump another ion across the membrane.
Transporters work ______ than channels, usually not exceeding _____
thousands of times slower
usually not exceeding several hundred transport cycles per second.
by mutating only a few amino acid residues, a transporter of chloride and hydrogen ions, which pumps only about a hundred ions per second, can be turned into a _______
chloride-selective ion channel that allows the passage of tens of thousands of ions per second.
From a functional standpoint, there are two kinds of proteins that mediate the transmembrane movements of charged substances:
channels and transporters.
Understand the routes by which a given substance can traverse a membrane.
- diffusion
- passive transport: channels
- active transport: transporters
Diffusion:
This is primarily for water, which crosses membranes through special channels called aquaporins.
Water always diffuses down its concentration gradient – there is no active transport for water.
Passive transport: Channels
- Charged and polar substances can cross membranes through these
- passive pores/tunnels through the membrane
- selective for specific ions/substances
- Some are gated, and substances can only pass when the gate is open
Active transport: Transporters
• substances cross membranes by binding to proteins and being escorted across
• big molecules, like glucose
• selective
• needed to pump molecules across a membrane, concentrating them on one side
against their energy gradient
– requires ATP
dentify physical forces that can determine the gating properties of ion channels.
- Electric field (membrane potential) across the membrane
- Mechanical stimulation (stretching of the membrane)
- Binding of a particular chemical
- Temperature
in secondary active transport, the transporter uses
the energy released when Na+ ions leak
into cells: the energy released is captured and used to pump another ion across the membrane
Ultimately, secondary active transport also depends on
metabolism.
