6 Flashcards
Diffusion across cell membrane
Cell membrane is the boundary between inside & outside…
and it separates cell from its environment
Can it be an impenetrable boundary?
NO!
Why it cannot be an impenetrable boundary?
Because cell needs materials in & products or waste out.
What are the substances inside of the cell membrane?
Food such as
carbohydrates,
sugars,
proteins,
amino acids,
lipids,
salts,
O2,
H2O
What are the substances outside of the cell membrane?
Waste such as
ammonia,
salts,
CO2,
H2O, and
products
Permeability of the Plasma Membrane
Differentially (selectively) Permeable
Allows some materials to pass.
- Water, oxygen, carbon dioxide
Prevents others from passing.
- Proteins, carbohydrates
Permeability of the Plasma Membrane
Factors that determine how a substance may be transported across a plasma membrane:
Size
Polar or Nonpolar
charge
PASSIVE DIFFUSION
2nd Law of Thermodynamics
governs biological systems
– universe tends towards disorder (entropy)
is a measure of disorder or randomness in a system, often interpreted as the tendency for energy to disperse and systems to move toward equilibrium
Entropy
is the movement of molecules across a membrane without the need for energy input, occurring naturally from an area of high concentration to an area of low concentration. This process helps equalize concentrations on both sides of the membrane, allowing substances like oxygen, carbon dioxide, and small uncharged molecules to move freely.
Passive diffusion
PASSIVE DIFFUSION
Only ____, relatively ____ molecules are able to diffuse across a _______ at significant rates by using passive diffusion.
small
hydrophobic
phospholipid bilayer
Passive Diffusion
Molecules have to _______ in lipid interior.
dissolve
Molecules have to dissolve in lipid interior. Molecules such as?
- 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)
Water molecules has slow rate due to?
polarity
Why large polar molecules (e.g glucose) and charged molecules (e.g amino acids and ions) cannot pass through the plasma membrane?
Because the membrane is composed of a lipid bilayer, which is hydrophobic (water-repelling). This structure prevents these molecules from dissolving in or diffusing through the lipid layer. Instead, they often require specific transport proteins or channels to facilitate their movement across the membrane.
Why is diffusion important to cells and humans?
Because it allows essential substances, like oxygen and nutrients, to move into cells while enabling waste products to exit, maintaining cellular function and homeostasis.
Why is diffusion important to cell respiration?
Oxygen diffuses into cells for aerobic respiration, while carbon dioxide, a waste product, diffuses out.
Why is diffusion important to Alveoli of lungs?
Oxygen from inhaled air diffuses into the bloodstream, and carbon dioxide diffuses from the blood into the alveoli to be exhaled.
Why is diffusion important to Capillaries?
Nutrients and oxygen diffuse from the blood into surrounding tissues, while waste products diffuse from tissues into the blood.
Why is diffusion important to Red Blood Cells?
Oxygen binds to hemoglobin for transport, and carbon dioxide diffuses into red blood cells to be carried back to the lungs.
Why is diffusion important to Medications: timerelease capsules?
Drugs diffuse slowly through the capsule membrane, allowing for gradual absorption into the bloodstream over time.
What is Facilitated Diffusion?
Facilitated diffusion is the process by which molecules move across a cell membrane through specific transport proteins, allowing substances that cannot easily pass through the lipid bilayer (such as large polar or charged molecules) to enter or exit the cell. This process still occurs along the concentration gradient and does not require energy.
Facilitated Diffusion
Is a diffusion through protein channels which do not interact with hydrophobic interior.
Facilitated Diffusion
Diffusion through protein channels which do not interact with hydrophobic interior
- For biological mol unable to dissolve in hydrophobic interior.
– No energy needed.
facilitated = _______
with help
open channel = _______
fast transport
Facilitated Diffusion
The passage of materials is aided both by a ________ and by a _________.
concentration gradient
transport protein
Two kinds of Proteins
Carrier Proteins
Channel Proteins
Carrier Proteins
bind specific molecules, undergo conformational change to release molecule
- ex. Glucose transporters
Channel Proteins
- form open pores for free diffusion
- found in gap junctions
Molecules will randomly move through the pores in ________
Channel Proteins
Some _________ do not extend through the membrane.
Carrier proteins
Carrier proteins _______ molecules through the lipid bilayer and release them on the opposite side.
bond and drag
__________ change shape to move materials across the cell membrane.
Other carrier proteins
How do molecules move through the plasma membrane by facilitated diffusion?
Facilitated diffusion allows molecules like glucose and ions to move across the plasma membrane via specific transport proteins. These proteins create a pathway that helps the molecules bypass the lipid bilayer, moving from areas of higher concentration to lower concentration without energy expenditure.
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.
Most cells, including erythrocytes, are exposed to __________ that are higher than those inside the cell, so facilitated diffusion results in the net inward _________.
- extracellular glucose concentrations
- transport of glucose
Most cells, including erythrocytes, are exposed to extracellular glucose concentrations that are higher than those inside the cell, so facilitated diffusion results in the net inward transport of glucose.
- Cells obtain food for cell respiration
- Neurons communicate
- Small intestine cells transport food to bloodstream
- Muscle cells contract
The Special Case of Water
Movement of water across the cell membrane
Aquaporins
- Water Channels
- Protein pores used during Osmosis
- provide corridors allowing water molecules to cross the membrane.
- Allow for fast transport
- water channel proteins, aquaporins, make possible massive amounts of diffusion
What is Osmosis?
– Osmosis is the diffusion of water across a differentially permeable membrane.
– Osmotic pressure is the pressure that develops in a system due to osmosis.
Concentration of water
Direction of osmosis is determined by comparing total solute concentrations.
Hypertonic
more solute, less water
Hypotonic
less solute, more water
Isotonic
equal solute, equal water
What does net movement of water mean?
Net movement of water refers to the overall direction and amount of water that moves across a membrane, influenced by concentration gradients, with water moving from areas of lower solute concentration to areas of higher solute concentration until equilibrium is reached.
Managing water balance
Cell survival depends on balancing water uptake & loss.
Hypotonic Solution (freshwater)
Animal Cell - Lysed
Plant Cell - Turgid (normal)
Isotonic solution (balanced)
Animal Cell - Normal
Plant Cell - Flaccid
Hypertonic solution (saltwater)
Animal Cell - Shriveled
Plant Cell - Plasmolyzed
Managing water balance
- animal cell immersed in mild salt solution.
- example: blood cells in blood plasma
- problem: none
– no net movement of water
» flows across membrane
equally, in both directions
– volume of cell is stable
Isotonic
Managing water balance
– a cell in fresh water
* example: Paramecium
* problem: gains water,
swells & can burst
– water continually enters Paramecium cell
* solution: contractile vacuole
– pumps water out of cell
– ATP
– plant cells
* turgid
Hypotonic
Managing water balance
Hypertonic
– a cell in salt water
* example: shellfish
* problem: lose water & die
* solution: take up water or pump out salt
– plant cells
* plasmolysis = wilt
Why is osmosis important to cells and humans?
- Cells remove water produced by cell respiration.
- Large intestine cells transport water to bloodstream.
- Kidney cells form urine.
Why is osmosis important to cells and humans? (chatgpt answer)
Osmosis is important because it allows cells to remove excess water produced by cellular respiration, enabling large intestine cells to effectively transport water into the bloodstream, and helps kidney cells concentrate waste, forming urine while maintaining the body’s fluid balance.
DIFFUSION OF NON-LIPID SOLUBLE SUBSTANCES
Non-lipid soluble substances diffuse through ________.
membrane channels
DIFFUSION OF NON-LIPID SOLUBLE SUBSTANCES
They passively diffuse _______________ through channels that cross the lipid bilayer; some channels are open all the time whereas others are
_____.
down their electrochemical gradient, gated
DIFFUSION OF NON-LIPID SOLUBLE SUBSTANCES
The ________ regulates the opening/closing of the channel.
membrane potential (voltage)
DIFFUSION OF NON-LIPID SOLUBLE SUBSTANCES
Example of a specific stimulus:
i) Voltage; ______
ii) Ligand; ________
iii) Specific stress; ______
i) VOLTAGE - GATED CHANNEL
ii) LIGAND -GATED CHANNELS
iii) STRESS – ACTIVATED CHANNELS
Porins
permit the free passage of ions and small polar molecules through the outer membranes of bacteria.
Ion channels
mediate the passage of ions across plasma membranes.
Ligand-gated
channels open in response to the binding of neurotransmitters or other signaling molecules.
Voltage-gated
channels open in response to changes in electric potential across the plasma membrane.
Gated Channels
Open or close depending on the ________ or _______ of a physical or chemical stimulus.
presence
absence
Gated Channels
Ex. neurotransmitters bind to specific gated channels on the receiving neuron, so these channels will ________
open
Gated Channels
This allows ________ into a nerve cell.
sodium ions
Gated Channels
When the ________ are not present, the channels are closed.
neurotransmitters
VOLTAGE – GATED CHANNELS
Membrane potential
regulates opening/closing of the channel.
VOLTAGE – GATED CHANNELS
a) K+ voltage-gated channels
exist as either open or close depending on the membrane voltage. It has only an activation gate.
VOLTAGE – GATED CHANNELS
b) Na+ voltage gated channels
opens when the membrane potential depolarizes (i.e. becomes more positive).
- It has activation and inactivation gates.
What is the Model of the operation of a G protein-linked receptor?
The model of a G protein-linked receptor describes how a ligand binds to the receptor, causing a conformational change that activates an associated G protein. This activated G protein then exchanges GDP for GTP, dissociates into its subunits, and interacts with target proteins in the cell, ultimately leading to a specific cellular response.
Active Transport
Cells may need to move molecules _______ concentration gradient.
against
Active Transport
Cells may need to move molecules against concentration gradient.
– shape change transports solute from one side of membrane to other
– protein “pump”
– “costs” energy = ATP
Facilatated DIffusion = ________
Active Transport = __________
Th Bouncer
The Doorman
The Importance of Active Transport
- Bring in essential molecules: ions, amino acids, glucose, nucleotides
- Rid cell of unwanted molecules (Ex. sodium from urine in kidneys)
- Maintain internal conditions different from the environment
- Regulate the volume of cells by controlling osmotic potential
- Control cellular pH
- Re-establish concentration gradients to run facilitated diffusion. (Ex. Sodium- Potassium pump and Proton pumps)
Sodium-Potassium Pump Action summary
- 3 Sodium ions move out of the cell and then 2 Potassium ions move into the cell.
- Driven by the splitting of ATP to provide energy and conformational change to proteins by adding and then taking away a phosphate group.
- Used to establish an electrochemical gradient across neuron cell membranes.
Active transport can be classed into 2 groups
- PRIMARY ACTIVE TRANSPORT
- SECONDARY ACTIVE TRANSPORT
(a) PRIMARY ACTIVE TRANSPORT
Cellular energy (i.e. ATP) is directly used to move substances across the membrane against its concentration gradient (i.e. from an area of low concentration to an area of high concentration)
(b) SECONDARY ACTIVE TRANSPORT
Secondary active transport uses the energy from the concentration gradient of one molecule to move another molecule against its gradient, either in the same direction (symport) or in opposite directions (antiport).
Active Transport Driven by ATP Hydrolysis
____________, a process in which energy is provided by another coupled reaction, is used to drive the uphill transport of molecules in the energetically _____________.
Active transport
unfavorable direction
Active Transport Driven by ATP Hydrolysis
___________ responsible for
maintaining gradients of ions
across the plasma membrane,
provide important examples of
active transport driven directly by
ATP hydrolysis
Ion pumps
Active Transport Driven by Ion Gradients
Some molecules are transported against their concentration gradients using energy derived not from ATP hydrolysis, but from the _________________ in the energetically favorable direction.
coupled transport of a second molecule
Active Transport Driven by Ion Gradients
The ___________ lining the intestine provide a good example of active transport drive by the Na+ gradient.
epithelial cells
SECONDARY ACTIVE TRANSPORT – 1. SYMPORTER
- Two substances are transported in the same direction across a plasma membrane.
- One of the substance moves passively down its concentration gradient while the second substance uses ATP to move against its concentration gradient across the plasma membrane.
SECONDARY ACTIVE TRANSPORT– 2.ANTIPORTER
- Two substances are transported across the membrane in opposite directions across the plasma membrane.
- One of the substance moves passively down its concentration gradient while the second substance uses ATP to move against its concentration gradient across the plasma membrane.
Uniport
A uniport can transport only a single molecule using the facilitated diffusion of glucose.
Antiport
An antiport uses active transport to move two molecules in opposite
directions.
Cotransport
Symport and Antiport
Vesicle Formation
– moving things out.
– Transport of large molecules
– Requires energy
– Keeps the macromolecule contained
– Exocytosis - Vesicles form as a way to transport molecules out of a cell.
SUBSTANCES TRANSPORTED: Neurotransmitters, hormones
and digestive enzymes.
What is Exocytosis of proteins?
Exocytosis of proteins is a process where cells transport proteins out of the cell by enclosing them in vesicles that fuse with the plasma membrane, releasing their contents into the extracellular space. This mechanism is essential for processes like hormone secretion, neurotransmitter release, and the export of enzymes.
Endocytosis
Vesicles form as a way to transport molecules into a cell.
Phagocytosis
Large,particulate matter (Bacteria, viruses, and aged or dead cells).
Pinocytosis
Liquids and small particles dissolved in liquid.
Receptor Mediated Endocytosis
Receptor-mediated endocytosis is a specific process where ligand-receptor complexes on the cell surface trigger the inward folding of the membrane, forming a clathrin-coated pit. This pit then buds off to create a vesicle that contains the bound ligands, such as low-density lipoproteins (LDLs), vitamins, certain hormones, and antibodies.
Pinocytosis - Most common form of endocytosis
- Cell forms an invagination
- Materials dissolve in water to be brought into cell
- Called “Cell Drinking”
- Ex. Intestinal cells, Kidney cells, Plant root cells
- Movement of very specific molecules into the cell with the use of vesicles coated with the protein clathrin.
- Coated pits are specific locations coated with clathrin and receptors. When specific molecules (ligands) bind to the receptors, then this stimulates the molecules to be engulfed into a coated vesicle.
- Ex. Uptake of cholesterol (LDL) by animal cells
Some ____________ have receptors on their surface to
recognize & take in hormones, cholesterol, etc.
integral proteins
Receptor-Mediated Endocytosis
Receptor-mediated endocytosis, a form of pinocytosis, ___________
provides a mechanism for the selective uptake of specific macromolecules.
Receptor-Mediated Endocytosis
____________ are specialized regions of the plasma membrane where specific cell surface receptors are found.
Clathrin-coated pits
Receptor-Mediated Endocytosis
__________, a membraneassociated GTP-binding protein, assists in the budding off of pits from the plasma membrane.
Dynamin
Receptor-Mediated Endocytosis
Clathrin assembles into a basketlike structure that
distorts the membrane, forming ________.
invaginated pits
Receptor-Mediated Endocytosis
Clathrin coated pits occupy about _________ of the surface area of plasma membranes.
1-2%
Protein Trafficking in Endocytosis
Endosomes
are vesicles with tubular extensions, located at the periphery of the cell, that fuse with clathrin-coated vesicles which have shed their coats.
Protein Trafficking in Endocytosis
An important feature of early endosomes is that they maintain an?
acidic internal pH as the result of the action of a membrane H+
pump.
Protein Trafficking in Endocytosis
Recycling to the plasma membrane is the major fate of membrane proteins taken up by ________.
recepto rmediated endocytosis
Protein Trafficking in Endocytosis
Ligands and membrane proteins destined for __________ are transported from early endosomes to late endosomes, which are located near the ______.
degradation in lysosomes
nucleus
Protein Trafficking in Endocytosis
________ is a phenomenon where receptor ligand complexes are removed from the plasma membrane, thereby terminating the response of the cell to growth factor stimulation.
Receptor down-regulation
Protein Trafficking in Endocytosis
________, which are phagosomes fused to lysosomes, contain lysosomal acid hydrolases that digest the ingested material.
Phagolysosomes
Protein Trafficking in Endocytosis
The ________ by phagocytosis plays distinct roles in different kinds of cells.
ingestion of large particles
