2.2 Cell Membrane Transport Flashcards
What materials does the cell need to take in?
Food (carbohydrates, sugars, proteins), amino acids, lipids, salts, O₂, and H₂O.
Can the cell membrane be an impenetrable boundary?
No, the cell membrane is not impenetrable; it allows necessary materials in and waste or products out.
What materials does the cell need to expel?
Waste (ammonia, salts, CO₂), H₂O, and other products.
What does it mean for the plasma membrane to be differentially permeable?
It selectively allows some materials to pass while preventing others.
Which substances can typically pass through the plasma membrane?
Water, oxygen, and carbon dioxide
Which substances are usually prevented from passing through the plasma membrane?
Proteins and carbohydrates.
What factors determine how a substance may be transported across the plasma membrane?
Size, polarity (polar or nonpolar), and charge.
What law governs passive diffusion in biological systems?
The 2nd Law of Thermodynamics, which states that the universe tends toward disorder (entropy).
How does passive diffusion work?
Substances move from an area of high concentration to an area of low concentration without the use of energy.
What type of molecules can diffuse across a phospholipid bilayer using passive diffusion?
Small, relatively hydrophobic molecules.
What is a requirement for molecules to pass through the membrane via passive diffusion?
They must dissolve in the lipid interior of the membrane.
What are some examples of molecules that use passive diffusion?
- Gases (oxygen, carbon dioxide)
- water molecules (slow due to polarity)
- lipids (steroid hormones)
- lipid-soluble molecules (hydrocarbons, alcohols, some vitamins)
- small noncharged molecules (NH₃).
Why is diffusion important to cells and humans?
Give 5 processes in the body where diffusion in needed
Diffusion is crucial for several processes:
- Cell respiration: Allows the exchange of oxygen and carbon dioxide in cells.
- Alveoli of lungs: Facilitates the transfer of oxygen into the blood and removal of carbon dioxide.
- Capillaries: Enables nutrient and gas exchange between blood and tissues.
- Red blood cells: Helps in the transport of oxygen from the lungs to the tissues and carbon dioxide back to the lungs.
- Medications (time-release capsules): Allows controlled release of drugs into the bloodstream over time.
The diffusion of molecules through protein channels that bypass the hydrophobic interior of the cell membrane.
facilitated diffusion
What is facilitated diffusion?
The diffusion of molecules through protein channels that bypass the hydrophobic interior of the cell membrane.
What type of molecules require facilitated diffusion?
Biological molecules that are unable to dissolve in the hydrophobic interior of the membrane.
Does facilitated diffusion require energy?
No, facilitated diffusion does not require energy.
What types of molecules are transported via facilitated diffusion?
Ions (Na⁺, K⁺, Cl⁻)
Sugars (e.g., glucose)
Amino acids
Small water-soluble molecules
Water (at a faster rate compared to passive diffusion)
They bind specific molecules, undergo a conformational change, and release the molecule on the other side of the membrane.
carrier proteins
Can you give an example of a carrier protein?
Glucose transporters - facilitated diffusion of glucose across cell membranes
Sodium-Potassium Pump - moves sodium ions out of the cell and potassium ions into the cell against their concentration gradients
Do all carrier proteins extend through the membrane?
No, some do not extend through the membrane but bond to molecules, dragging them through the lipid bilayer.
They form open pores in the membrane, allowing free diffusion of molecules.
channel proteins
How do molecules move through channel proteins?
Molecules randomly move through the pores in channel proteins.
What limits the rate of facilitated diffusion?
The number of protein channels or carriers present in the membrane.
Why does facilitated diffusion lead to the net inward transport of glucose in most cells like erythrocytes?
Because extracellular glucose concentrations are higher than inside the cell.
What are the roles of facilitated diffusion of glucose in different cell types? (cells, neurons, small intestine cells, muscle cells)
Cells: Obtain food for cell respiration.
Neurons: Communicate.
Small intestine cells: Transport glucose to the bloodstream.
Muscle cells: Facilitate contraction.
How does water move across the cell membrane? (a water channel)
aquaporins
Protein pores that provide corridors for water molecules to cross the membrane. They allow for fast transport of water and enable massive amounts of diffusion.
aquaporins
The diffusion of water across a differentially permeable membrane.
osmosis
What are aquaporins?
Protein pores that provide corridors for water molecules to cross the membrane. They allow for fast transport of water and enable massive amounts of diffusion.
What is osmosis?
The diffusion of water across a differentially permeable membrane.
What is osmotic pressure?
The pressure that develops in a system due to osmosis.
The pressure that develops in a system due to osmosis.
osmotic pressure
What are the different types of solutions in terms of osmosis?
- Hypertonic: More solute, less water.
- Hypotonic: Less solute, more water.
- Isotonic: Equal solute, equal water.
What happens when an animal cell is immersed in an isotonic solution?
There is no net movement of water; it flows across the membrane equally in both directions.
Can you give an example of an isotonic solution? (in the body)
Blood cells in blood plasma.
- the concentration of solutes (such as electrolytes and proteins) in the plasma is equal to the concentration of solutes inside the red blood cells.
- If red blood cells are placed in an isotonic solution, they retain their biconcave shape and perform their role in oxygen transport effectively. Conversely, if the solution is hypotonic, water will enter the cells, causing them to swell and potentially burst. If it’s hypertonic, water will leave the cells, causing them to shrink.
What is the effect of an isotonic solution on the cell’s volume?
remains stable.
What happens when a cell is in a hypotonic solution?
In animal and plant cells
Animal cell: The cell gains water, swells, and can burst (lysed) due to excessive water intake.
Plant cell: turgid (normal)
Can you give an example of an organism affected by a hypotonic solution? How does it manage excess water in a hypotonic environment?
- Paramecium
- By using a contractile vacuole, which pumps water out of the cell using ATP.
How do plant cells handle hypotonic solutions?
Plant cells become turgid due to the buildup of water pressure inside the cell.
What happens when a cell is in a hypertonic solution?
In animal and plant cells
The cell loses water and may die due to dehydration.
Animal cells: Shriveled
Plant cells: plasmolyzed; as the vacuole shrinks, the cell membrane may pull away from the rigid cell wall, creating a gap between the cell wall and the membrane; it can result in cell damage or death.
Can you give an example of an organism affected by a hypertonic solution? How do organisms manage water loss in a hypertonic environment?
- Shellfish
- By taking up water or pumping out salt.
How do plant cells respond to hypertonic solutions?
Plant cells undergo plasmolysis, leading to wilting.
How does osmosis contribute to cell function?
It helps regulate water balance and removes excess water, ensuring proper cell function and maintaining homeostasis.
Why is osmosis important for cells? (cells, large intestine cells, kidney cells)
- Cells remove water produced by cell respiration.
- Large intestine cells transport water to the bloodstream.
- Kidney cells form urine.
How do non-lipid soluble substances diffuse through the membrane?
through membrane channels
- facilitated diffusion
- active transport
- endocytosis
What drives the passive diffusion of non-lipid soluble substances?
Their electrochemical gradient.
How do some membrane channels differ in their behavior?
Some are open all the time, while others are gated.
What regulates the opening and closing of gated channels?
The membrane potential (voltage).
What do porins permit the passage of through bacterial outer membranes?
Porin-channel protein in the outer membranes of gram-negative bacteria
Ions and small polar molecules.
What are porins?
permit the passage of ions and small molecules through bacterial outer membranes
- a type of channel protein in the outer membranes of gram-negative bacteria.
A channel that mediate the passage of ions across plasma membranes.
Ion channels
What is the function of ion channels?
They mediate the passage of ions across plasma membranes.
A channel that opens in response in the binding of neurotransmitters or other signaling molecules.
Ligand-gated channels (a type of receptor channel)
What are ligand-gated channels?
Opens in response on the binding of neurotransmitters or other signaling molecules.
A channel that opens in response to changes in electric potential across the plasma membrane.
Voltage-gated channel
What are voltage-gated channels?
A channel that opens in response to changes in electric potential across the plasma membrane.
What determines whether gated channels open or close?
The presence or absence of a physical or chemical stimulus.
What happens when neurotransmitters bind to specific gated channels on a receiving neuron?
channels open
What does the opening of gated channels allow into a nerve cell?
Sodium ions
What is the state of gated channels when neurotransmitters are not present?
closed
What regulates the opening and closing of voltage-gated channels?
membrane potential/membrane voltage
What is a membrane potential/membrane voltage?
regulates the opening and closing of voltage-gated channels
A channel that opens when the membrane potential depolarizes (becomes more positive). It has activation and inactivation gates
Na+ voltage-gated channels
What are Na+ voltage-gated channels?
A channel that opens when the membrane potential depolarizes (becomes more positive). It has activation and inactivation gates
What types of gates do Na+ voltage-gated channels have?
Activation and inactivation gates.
What is required for cells to move molecules against their gradient?
Energy (ATP).
What facilitates the movement of molecules against their gradient?
A protein “pump” that undergoes a shape/conformational change
What type of transport involves a protein pump and energy expenditure?
Active transport
What is an active transport?
A type of transport involves a protein pump and energy expenditure to move molecules against gradient
What essential molecules are brought into cells by active transport? (4)
- Ions
- amino acids
- glucose
- nucleotides
How does active transport help in eliminating unwanted molecules? (Give an example)
By removing substances like sodium from urine in the kidneys.
What does active transport help maintain within a cell?
Internal conditions different from the external environment.
What are examples of ions actively transported against their concentration gradients?
Sodium (Na+) out of the cell and potassium (K+) into the cell.
How does active transport regulate the volume of cells?
By controlling osmotic potential.
What cellular aspect does active transport help control?
Cellular pH.
How does active transport contribute to facilitated diffusion?
By re-establishing concentration gradients.
Give examples of pumps involved in active transport.
Sodium-potassium pump and proton pumps.
How many potassium ions (K+) are moved into the cell by the pump?
2 potassium ions (K⁺)
How many sodium ions (Na+) are moved out the cell by the pump?
3 sodium ions (Na⁺)
How does ATP drive the sodium-potassium pump?
By splitting ATP and adding/removing a phosphate group
What type of gradient does the sodium-potassium pump help establish?
Electrochemical gradient
What happens to the protein in the pump after ATP is hydrolyzed?
It undergoes a conformational change
What are the two types of active transport?
- Primary active transport
- secondary active transport
What is directly used in primary active transport?
Cellular energy (ATP)
In primary active transport, substances move from an area of ___ concentration to ___ concentration.
Low concentration to high concentration
Does secondary active transport directly use ATP for the molecule of interest?
No, ATP is not directly coupled to the molecule of interest.
What is created in secondary active transport to move the molecule of interest?
An electrochemical gradient.
How is the molecule of interest transported in secondary active transport? What happens to the other molecule in secondary active transport?
- It is transported down the electrochemical gradient.
- It is moved up its concentration gradient.
What role does ATP play in secondary active transport?
ATP is used indirectly to generate the electrochemical gradient.
What is an example (in the body) of active transport driven by an ion gradient?
The Na⁺ gradient in epithelial cells lining the intestine.
In a symporter, how are two substances transported across the membrane?
In the same direction.
How does the first substance move in a secondary active transport? How does the second substance move in a symporter?
- Passively down its concentration gradient.
- Against its concentration gradient, using energy from ATP.
In an antiporter, how are two substances transported across the membrane?
In opposite directions.
How many molecules does a uniport transport?
a single molecule
What type of transport is involved in a uniport?
Facilitated diffusion (passive transport).
What is an example of a molecule transported by a uniport?
Glucose
What type of molecules are transported via vesicle formation? What does vesicle formation help to keep contained?
- Large molecules
- Macromolecules
Does vesicle formation require energy?
Yes
What process involves vesicles transporting molecules out of a cell?
Exocytosis
Name three substances commonly transported via exocytosis.
- Neurotransmitters
- hormones
- digestive enzymes.
What does endocytosis involve?
Vesicles forming to transport molecules into a cell.
What type of matter is transported via phagocytosis?
Large, particulate matter such as bacteria, viruses, and aged or dead cells.
What is pinocytosis?
- The uptake of liquids and small particles dissolved in liquid.
- Dissolved molecules in a vesicle.
What triggers the formation of a vesicle in receptor-mediated endocytosis?
Ligand-receptor complexes.
What is the role of clathrin in receptor-mediated endocytosis?
It helps form the vesicle by infolding at the pit.
Name some substances that can be internalized through receptor-mediated endocytosis.
LDLs (low-density lipoproteins), some vitamins, certain hormones, and antibodies.
What is the most common form of endocytosis? And it is referred as?
Pinocytosis “Cell drinking”
How does the cell form a pinocytic vesicle?
By forming an invagination that pinches off to create the vesicle.
In which types of cells is pinocytosis commonly observed?
- Intestinal cells
- kidney cells
- plant root cells.
What is a key feature of receptor-mediated endocytosis?
clathrin-coated vesicle
Receptor-mediated endocytosis is a form of __,
Pinocytosis
What role does dynamin play in receptor-mediated endocytosis?
Dynamin assists in the budding off of pits from the plasma membrane.
What percentage of the plasma membrane surface area is occupied by clathrin-coated pits?
About 1-2%.
Vesicles with tubular extensions located at the periphery of the cell. Fuse with clathrin-coated vesicles that have shed their coats.
endosomes
What are endosomes?
Vesicles with tubular extensions located at the periphery of the cell. Fuse with clathrin-coated vesicles that have shed their coats
What is an important feature of early endosomes?
They maintain an acidic internal pH.
What causes the acidic internal pH of early endosomes?
The action of a membrane H⁺ pump.
What is the major fate of membrane proteins taken up by receptor-mediated endocytosis?
Recycling to the plasma membrane.
Where are ligands and membrane proteins destined for degradation transported from early endosomes?
To late endosomes, which are located near the nucleus.
The removal of receptor-ligand complexes from the plasma membrane, terminating the cell’s response to growth factor stimulation.
receptor down-regulation
What is receptor down-regulation?
The removal of receptor-ligand complexes from the plasma membrane, terminating the cell’s response to growth factor stimulation.
Phagosomes fused to lysosomes.
Phagolysosomes
What is the function of lysosomal acid hydrolases in phagolysosomes?
They digest the ingested material.
