MBS Lecture 3 Flashcards
What does the plasma membrane act as?
A barrier, nutrients must get in, products and wastes must get out
What does permeability determine?
It determines what moves in and out of a cell
Types of permeability?
Lets nothing in or out is impermeable
Lets anything pass is freely permeable
Restricts movement is selectively permeable
What is the permeability of plasma
membrane?
Selectively permeable
Allows some materials to move freely – Restricts other materials
What does selective permeability restrict?
Size, Electrical charge, Molecular shape and Lipid solubility
What are the types of transport through
plasma membrane?
Active (requiring energy and ATP)
Passive (no energy required)
Define the types of transport through the
plasma membrane
Transport through a plasma membrane can be Active (requiring energy and ATP) – Passive (no energy required)
Diffusion (passive)
Carrier-mediated transport (passive or active)
Vesicular transport (active)
What are the factors affecting diffusion?
Distance the particle has to move
Molecule size, Smaller is faster
Temperature, More heat, faster motion
Gradient size, The difference between high and low
concentrations
Electrical forces, Opposites attract, like charges repel
What are the types of diffusion across the
plasma membranes?
It can be simple or channeled
What are the materials that diffuse through the plasma membrane by simple diffusion?
Materials that diffuse through plasma membrane by simple diffusion: – lipid-soluble compounds(alcohols, fatty acids,
and steroids)
- dissolved gases (oxygen and carbon dioxide)
What are the materials that diffuse through the
plasma membrane by transmembrane
proteins (channels)?
Materials that pass through transmembrane proteins
(channels):
- are water–soluble compounds and are ions
What does channel mediated diffusion depend
on?
Passage depends on: size , charge and interaction with the channel
What is diffusion?
The net movement of a substance from an area of higher concentration to an area of lower concentration
What is concentration gradient?
The difference between the high and low concentrations.
Diffusion tends to eliminate that gradient.
What is electrical gradient?
The difference in electrical charges between two
compartments is called an electrical gradient. The interior of the plasma membrane has a net negative charge relative to the exterior surface, due in part to the high concentration of proteins in the cell. This negative charge tends to pull positive ions into the cell, while opposing the entry of negative ions.
What do concentration and electrical gradient reach?
Equilibrium
What is osmosis?
A Special Case of Diffusion – Osmosis is the diffusion of water across the cell membrane
What is diffusion-osmosis?
More solute molecules, lower concentration of water molecules
Membrane must be freely permeable to water, selectively permeable to solutes
Water molecules diffuse across membrane toward solution with more solutes
Volume increases on the side with more solutes
What is osmotic pressure?
Is the force of a concentration gradient of water
Equals the force (hydrostatic pressure) needed to block osmosis
Define Tonicity
The osmotic effect of a solute on a cell:
Two fluids may have equal osmolarity, but different tonicity
Hypertonicity
Hypertonic (hyper- = above)
Has more solutes and gains water by osmosis
Hypotonicity
Hypotonic (hypo- = below)
Has less solutes and loses water through osmosis
Isotonic
A solution that does not cause osmotic flow of water in or
out of a cell
What does a cell do in a hypotonic solution?
Gains water
Ruptures(hemolysis of red blood cells)
What does a cell do in a hypertonic solution?
Loses water - Shrinks (crenation of red blood cells)
What is carrier mediated transport?
Carrier-mediated transport of ions and organic substrates
Facilitated diffusion
Active transport
Characteristics of carrier mediated transport
Specificity: – one transport protein, one set of substrates
Saturation limits: – rate depends on transport proteins, not substrate
Regulation: – cofactors such as hormones
Explain cotransport
Two substances move in the same direction at the same time
Explain countertransport
One substance moves in while another moves out
What is facilitated diffusion?
Passive, Carrier proteins transport molecules too large to fit through channel proteins (glucose, amino acids):
- molecule binds to receptor site on carrier protein
- protein changes shape, molecules pass through
- receptor site is specific to certain molecules
What is active transport?
Active transport proteins:
- move substrates against concentration gradient
- require energy, such as ATP
- ion pumps move ions (Na+ , K+ , Ca2+ , Mg2+ )
- exchange pump countertransports two ions at the
same time
Sodium-potassium exchange pump
- active transport, carrier mediated:
» sodium ions (Na+) out, potassium ions (K+) in
» 1 ATP moves 3 Na+ and 2 K+
Secondary active transport
- Na+ concentration gradient drives glucose transport
- ATP energy pumps Na+ back out
Endocytosis
(endo- = inside) is active transport using ATP:
- receptor mediated
- Pinocytosis “cell drinking”-extracellular fluid
- Phagocytosis“cell eating”-solid objects
