2b- Cell membrane transport Flashcards
in
Food
- carbohydrates
- sugars,
- proteins
- amino acids
- lipids
- salts
- O2
- H2O
out
Waste
- ammonia
- Salts
- CO2
- H2O products
Permeability of plasma membrane
- Differentially (selectively) permable
Materials allowed to pass
Water, oxygen, carbon dioxide
prevents other from passing
Protein, Carbohydrates
Factors that determine how a substance may be transported across a plasma membrane:
- Size
- Polar or nonpolar
- Charge
- 2nd law of Themodynamics
- governs biological systems
– universe tends towards disorder (entropy)
Passive diffusion
movement from high to low concentration
Passive diffusion
Are the molecules are able to diffuse across a phospholipid bilayer at significant rates by using passive diffusion.
Only small, relatively hydrophobic
Gases
- Oxygen
- carbon dioxide
Water molecules
- rate slow due to polarity
Lipid
Steroid Hormones
lipid soluble molecules
- Hydrocarbons
- alcohols
- some vitamins
small nonecharged molecules
- NH3
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
- no energy needed
Facilitated diffusion
with help
facilitated
fast transportation
Open channel
two kinds of proteins
- Carrier proteins
- Channel proteins
bind specific molecules, undergo conformational change to release molecule
Carrier proteins
example of carrier protein
Glucose transporters
- form open pores for free diffusion
- found in gap junctions
Channel proteins
Molecules will randomly move through the pores in ____ ____
Channel proteins
do not extend through the membrane
Some carrier proteins
Other carrier proteins ____ ___ to move materials across the cell membrane
change shape
How do molecules move through the plasma membrane by facilitated diffusion?
- Channel and Carrier proteins are specific:
- Channel Proteins allow ions, small solutes, and water to pass
- Carrier Proteins move glucose and amino acids
- Facilitated diffusion is rate limited, by the number of
proteins channels/carriers present in the membrane.
- provide corridors allowing water molecules to cross the membrane.
- Allow for fast transpor
- water channels
- protein pores used during osmosis
Aquaporins
is the diffusion of water across a differentially permeable membrane.
Osmosis
is the pressure that develops in a system due to osmosis.
Osmotic pressure
Different concentration
Hypertonic
Hypotonic
Isotonic
more solute, less water
Hypertonic
less solute, more water
Hypotonic
equal solute, equal wate
Isotonic
- animal cell immersed in mild saltsolution
- volume of cell is stable
- no net movement of water
isotonic
a cell in fresh water
- Gains water, swell & can burst
Hypotonic
plant cell in hypotonic
turgid
a cell in salt water
- lose water and die
Hypertonic
plant cells in hypertonic
Plasmolysis = wilt
Water regulation in Paramecium
Contractile vacoule
Examples of Osmosis in Cells and Humans
Cells:
- Removes water produce by cell respiration
Human:
- Large intestine cells transport water to bloodstream
- Kidney cells form urine
regulates the opening/closing of the channel
Member potential (voltage)
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
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
open or close depending on the presence or absence of a physical or chemical stimulus.
Gated channels
Examples of voltage gated channels
- K+ voltage-gated channels
- Na+ voltage gated channels
regulates opening/closing of the channel
Membrane potential
exist as either open or close depending on the membrane voltage. It has only an activation gate.
K+ voltage-gated channels
- opens when the membrane potential depolarizes
- It has activation and
inactivation gates
Na+ voltage gated channels
Cells may need to move molecules against concentration gradient
- costs energy = ATP
Active transport
Importance active transport
- Bring essential molecules
- Rid cell of unwated molecules
- Maintain internal conditions
2 groups of active transport
- Primary active transport
- 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
transport only a single molecule using the facilitated diffusion of glucose.
Uniport
uses active transport to move two molecules in opposite directions.
Antiport
- moving things out.
- Transport of large molecules
Vesicle formation
Substance transported in Exocytosis
- Neurotransmitters
- Hormones
- Digestive enzymes
Exocytosis of Proteins
- Vesicle formation -> Golgi body -> ER
Vesicles form as a way to transport molecules out of a cell
Exocytosis
susbtance transported in exocytosis
Neurotransmitters, hormones and digestive enzymes.
Vesicles form as a way to transport molecules
into a cell.
Endocytosis
Types of endocytosis
- Phagocytosis
- Pinocytosis
- Receptor mediated endocytosis
Large,particulate matter (Bacteria, viruses, and aged or dead cells).
Phagocytosis
Liquids and small particles dissolved in liquid
Pinocytosis
Ligandreceptor complexes trigger infolding of a clathrin pit that forms a vesicle containing ligands
Receptor mediated endocytosis
Substance/Products transported by Receptor mediated endocytosis
- Some Vitamins
- Certain Hormones
- Antibodies
Most common form of
endocytosis
Pinocytosis
pinocytosis is also called
Cell drinking
Examples of pinocytosis
- Intestinal cells
- Kidney cells
- Plant root cells
a form of pinocytosis, provides a mechanism for the selective uptake of specific macromolecules.
Receptor-mediated endocytosis
Example of materials transported by Receptor mediated endocytosis
- Uptake of cholesterol by animal cells
if with receptors in the surface
- Hormones, Cholesterol
are specialized regions of the plasma membrane where specific cell surface receptors are found
Clathrin-coated pits
a membrane associated GTP-binding protein, assists in the budding off of pits from the plasma membrane.
Dynamin
Clathrin occupied space
About 1-2% of the surface area of plasma membranes
What does clathrin formes
forming invaginated pits
___ assembles into a ____ structure that ____ the membrane
- Clathrin
- basketlike
- distorts
located at the periphery of the cell, that fuse with clathrin-coated vesicles which have shed their coats
Endosomes
Important features of early endosomes
- Maintain acidic internal pH as the result of the action of a membrane H+ pump
is the major fate of membrane proteins taken up by receptor-mediated endocytosis
Recycling to the plasma membrane
is a phenomenon where receptor-ligand complexes are removed from the plasma membrane
Receptor-down regulation
are phagosomes fused to lysosomes, contain lysosomal acid hydrolases that digest the ingested material
Phagolysosomes
Does not move chloride ions causing sticky mucus to build up on the out side of the cell
- Mutant CFTR channel
moves chloride ions to the outside of the cell
- Normal CFTR channel
