Chapter 4 - Guyton Flashcards
Higher concentration in extracellular fluid.
sodium, calcium, chloride, bicarbonate, glucose
Higher concentration in intracellular fluid.
potassium, magnesium, phosphates, sulfate, amino acids, fats, proteins
Protein components of the lipid bilayer.
contains large amounts, no fluid, transport proteins, channel proteins, carrier proteins, all are highly selective
Simple Diffusion
kinetic movement of ions/molecules occurs through a membrane or opening or intermolecular spaces without interaction of carrier proteins
What are the two pathways through which simple diffusion can occur?
1) interstices of the lipid bilayer if lipid soluble; 2) watery channels that penetrate through large transport proteins
Explain facilitated diffusion.
requires carrier proteins to pass the molecule by binding chemically and shuttling through the membrane
What factors determine the rate of diffusion?
amount of substance available, velocity of kinetic motion (temperature?), number and sizes of openings in membrane
Which substances have a high lipid solubility (and thus diffuse directly through the membrane)?
oxygen, nitrogen, carbon dioxide, and alcohol
The rate of diffusion for lipid-soluble substances is directly related to amount of ______ _______.
lipid solubility (oxygen moves through as if the membrane isn’t even there…)
Which type of proteins form the “pores” in the cell membrane?
integral proteins
Which factors determine the selectivity of pores?
diameter and electrical charge
Although it is not lipid-soluble, water readily passes through the cell membrane. How?
aquaporins allow rapid passage of water through the membrane, narrow pores to permit water molecules to pass through in a single file
Name some factors that affect selectivity of selectively permeable protein channels.
diameter, shape, electrical charges, chemical bonds
Describe potassium channels.
have a tetrameric structure (4 identical subunits) around a center pore, pore loops at top for a selective filter, carbonyl oxygens are at the loop and dehydrate potassium allowing them to pass
Describe a sodium channel.
only 0.3-0.5 nm in diameter, lined with negatively charged amino acids which dehydrate sodium
Gated protein channels are an extension of which membrane protein.
transport protein
Explain the two types of gated protein channels.
voltage-gated - conformation of gate responds to electrical potential on inside of the cell, basic mechanism for action potentials; chemical (ligand) gated - opened by binding of a chemical substance which causes a conformational change in protein to open or close the gate
Example of a ligand-gated channel.
acetylcholine channel for nerve signals
Do channels ever partially open?
no, gates are “all or none” and open and close very rapidly (milliseconds)
Explain the patch-clamp method for recording ion current flow through single channels.
micropipette is put against outside of cell membrane and suction applied to create seal, micropipette is then inserted into a solution to allow concentrations inside and outside cell to be altered, the purpose is to determine the transport characteristics of single channel and its gating properties
In facilitated diffusion, the rate of diffusion approaches a maximum called:
Vmax
Define facilitated diffusion.
carrier-mediated diffusion because substance transported diffuses through membrane using a specific carrier protein to help
What sets the max rate of facilitated diffusion?
the rate can never be greater than the rate at which the carrier protein can undergo conformational changes back and forth
The most important substances that cross the membrane by facilitated diffusion.
glucose and most amino acids
Nernst Potential
effects of membrane electrical potential on diffusion of ions, electrical charges of ions causes them to move even if no concentration difference exists, important for transmission of nerve impulses
Net movement of water by a concentration difference is called:
osmosis
Osmotic Pressure
the exact amount of pressure to stop osmosis
What factor determines osmotic pressure of solution?
concentration of the solution in terms of number of particles (osmolality)
Osmole
1 gram molecular weight of osmotically active solute
Relation of osmolality to osmotic pressure.
the actual osmotic pressure of body fluids is about 0.93 times the calculated value
What is the distinguishing characteristic of active transport?
cell membrane moves molecules against the concentration gradient
Substances transported through active transport:
sodium, potassium, calcium, iron, hydrogen, chloride, sugars, most amino acids
Primary active transport
energy is derived from breakdown of ATP, depends on carrier protein, ex. sodium-potassium pump
Sodium-Potassium Pump
sodium out and potassium in, responsible for maintaining differences across cell membrane and establishing a negative electrical voltage inside the cell
Describe the carrier protein of the sodium-potassium pump.
complex of 2 globular proteins (alpha and beta), alpha subunit has 3 receptor sites for binding sodium on inside, 2 receptor sites for potassium on outside, inside portion near sodium binding site has ATPase activity
What factors control the direction of enzyme reaction in the sodium-potassium pump?
concentrations of ATP, ADP, and phosphate, electrochemical gradients of sodium and potassium
How does the sodium-potassium pump control cell volume?
large numbers of proteins inside the cell attract positive ions, molecules cause osmosis, the pump prevents this by pumping out 3 sodium ions for every 2 potassium ions pumped inside (water follows ions)
Why is there a low concentration of calcium in the intracellular cytosol?
2 calcium pumps, one in the cell membrane to pump calcium out of cell and one to pump calcium into organelles within the cell
What two places in the body is primary active transport of hydrogen ions important?
parietal cells in gastric glands of the stomach, distal tubules of cortical collecting ducts of kidneys (into urine to eliminate it)
Name the two types of secondary active transport.
co-transport and counter-transport
And what is secondary active transport anyway?
energy is derived secondarily from energy that has been stored in the form of ionic concentration differences of secondary molecule between the two sides of the membrane, depends on carrier protein
What occurs during co-transport?
carrier protein is the attachment point for ion and substance to be co-transported, when they are attached the energy gradient of sodium allows the substance to be transported together into the cell
Substances that are co-transported along with sodium?
glucose and amino acids
Where does sodium co-transport of glucose and amino acids occur?
through epithelial cells of intestines and renal tubules
Where does sodium counter-transport of calcium and hydrogen occur?
calcium - all cell membranes (sodium in and calcium out); hydrogen - proximal tubules (sodium in and hydrogen out)
Where in to body does active transport through cellular sheets occur?
epithelium of intestines, renal tubules, exocrine glands, gallbladder, choroid plexus of brain (basic movement through sheet is active transport on one side of cell and then either simple or facilitated diffusion on opposite side of cell)
