Lecture 2b: Cell Membrane Transport Flashcards
Factors that determine how a substance may be transported across a plasma membrane:
(1) Size
(2) Polarity
(3) Charge
Why is diffusion important to cells and humans?
- Cell respiration
- Alveoli of lungs
- Capillaries
- Red Blood Cells
- Medications: time release capsules
Diffusion through protein channels which do not interact with hydrophobic interior
Facilitated Diffusion
Molecules able to undergo passive diffusion
- Gases (oxygen, carbon dioxide)
- Water molecules (rate slow due to polarity)
- Lipids (steroid hormones)
- Lipid soluble molecules (hydrocarbons, alcohols, some vitamins)
*Small noncharged molecules (NH3)
Molecules undergoing facilitated diffusion
- Ions (Na+, K+, Cl-)
- Sugars (Glucose)
- Amino Acids
- Small water soluble molecules
- Water (faster rate)
provide corridors allowing water molecules to cross the membrane in massive amounts
Aquaporins
The diffusion of water across a differentially
permeable membrane
Osmosis
The pressure that develops in a system due to osmosis
Osmotic Pressure
more solute, less water
Hypertonic
less solute, more water
Hypotonic
equal solute, equal water
Isotonic
What happens to an animal cell when placed in freshwater?
Undergoes lysis
What happens to an animal cell when placed in saltwater?
Becomes shriveled
What happens to a plant cell when placed in freshwater?
Turgid (normal)
What happens to a plant cell when placed in saltwater?
Plasmolyzed
What happens to a plant cell when placed in balanced solution?
Flaccid
Organelle that pumps water out of the cell; found in Paramecium
Contractile vacuole
permit the free passage of ions and small polar molecules through the outer membranes of bacteria.
Porins
mediate the passage of ions across plasma membranes
Ion Channels
Open in response to the binding of neurotransmitters or other signaling molecules
Ligand-gated Channels
Open in response to changes in electric potential across the plasma membrane
Voltage-Gated Channels
Importance of Active Transport
- Bring in essential molecules: ions, amino acids, glucose, nucleotides
- Rid cell of unwanted molecules
- Maintain internal conditions different from the environment
- Regulate the volume of cells
- Control cellular pH
- Re-establish concentration gradients to run facilitated diffusion.
Classifications of Active Transport
(1) Primary Active Transport
(2) Secondary Active Transport
ATP is directly used to move substances across the membrane against its concentration gradient
Primary Active Transport
involves two channels: the first actively transports a substance out of the cell using ATP, and the second allows that substance to move back into the cell passively, using the energy released to transport another substance against its concentration gradient.
Secondary Active Transport
Two substances are transported in the same direction across a plasma membrane
Symporter
Two substances are transported across the membrane in opposite directions across the plasma membrane
Antiporter
Can transport only
a single molecule
using facilitated
diffusion
Uniport
Substances transported using vesicle formation:
(1) Neurotransmitters
(2) Hormones
(3) Digestive Enzymes
Vesicles form as a way to transport molecules
into a cell
Endocytosis
Vesicles form as a way to transport molecules out of a cell
Exocytosis
Transports large, particulate matter (Bacteria, viruses, and aged or dead cells)
Phagocytosis
Transport of liquids
and small particles dissolved in liquid
Pinocytosis
Ligand receptor complexes trigger infolding of a clathrin pit that forms a vesicle containing ligands such as (LDLs); some vitamins, certain hormones, and antibodies.
Receptor Mediated Endocytosis
Are vesicles with tubular extensions, located at the periphery of the cell, that fuse with clathrin-coated vesicles which have shed their coats.
Endosomes
are phagosomes fused to lysosomes, contain lysosomal acid hydrolases that digest the ingested material
Phagolysosomes
