B2.1 Membranes and Membrane Transport Flashcards
What is the primary function of pump proteins in animal cells?
Pump proteins transport specific particles into or out of cells, facilitating essential physiological processes.
How do proton pumps contribute to cellular functions?
Proton pumps aid in ATP generation during photosynthesis and cellular respiration through chemiosmosis.
What role does the sodium-potassium pump play in neurons?
The sodium-potassium pump generates membrane potentials necessary for nerve impulse transmission in neurons.
What is the significance of indirect active transport in nutrient absorption?
Indirect active transport enables selective glucose absorption in the small intestine and kidney.
How are different cell types related to pump proteins?
Different cell types utilize specialized pump proteins for their unique functions and physiological roles.
What role does membrane fluidity play in molecule diffusion?
Membrane fluidity enables molecules to diffuse through the membrane towards areas where needed.
How does membrane fluidity affect protein interaction?
It facilitates interaction between proteins, crucial for effective cell signaling.
Define the term plasma membrane.
The plasma membrane, also known as the cell membrane, is a biological structure that surrounds and encloses the contents of a cell, separating it from its external environment. It consists of a lipid bilayer primarily composed of phospholipids, along with proteins and other molecules.
Explain the concept of amphipathic molecules in the context of lipid bilayers.
Amphipathic molecules have both hydrophilic and hydrophobic regions. Phospholipids, which make up lipid bilayers, are amphipathic, with hydrophilic heads and hydrophobic tails.
Explain how hydrophobic and hydrophilic properties of the phospholipid bilayer allow a membrane to maintain its structure.
The hydrophobic tails repel water, forming a hydrophobic interior that prevents the uncontrolled passage of hydrophilic molecules, while the hydrophilic heads interact with the aqueous environment.
Define selectively permeable in the context of the plasma membrane.
Selectively permeable, also known as semipermeable, refers to the property of the plasma membrane that allows it to regulate the passage of certain substances while restricting the movement of others.
Explain why the phospholipids must form a bilayer when introduced into an aqueous environment.
Phospholipids naturally form a bilayer structure when introduced into an aqueous environment due to their amphipathic nature, with hydrophilic heads oriented toward the aqueous surroundings.
Why are lipid bilayers considered effective barriers in biological systems?
Lipid bilayers are effective barriers because their hydrophobic interior prevents the passage of hydrophilic molecules and ions, while hydrophobic molecules can pass through the membrane.
What is simple diffusion?
Simple diffusion is the passive movement of molecules from an area of higher concentration to an area of lower concentration, driven by the concentration gradient.
What types of molecules can undergo simple diffusion across a lipid bilayer, and why?
Small, nonpolar molecules like oxygen and carbon dioxide can undergo simple diffusion due to their size and lack of charge.
List the six main functions of membrane proteins.
- Enzymatic activity
- Receptors
- Trasnport
- Adhesion
- Recognition
- Anchorage
Describe the structure of integral membrane proteins.
Integral membrane proteins are embedded in one or both of the lipid layers of a membrane and interact with the hydrophobic core of the lipid bilayer.
What is the specialized type of membrane protein used to transport water?
Aquaporins.
What happens to cells in isotonic solutions?
There is no net movement of water; cells maintain their shape.
What happens to cells in hypertonic solutions?
Cells lose water and may shrink or crenate.
What happens to cells in hypotonic solutions?
Cells gain water and may swell or burst.
Explain the concept of selectivity in channel proteins.
Channel proteins ensure that only specific molecules can pass through them by having a selective binding site that allows only certain ions or molecules to diffuse.
Provide examples of channel proteins and the types of molecules they transport.
- Sodium channels: transport sodium ions
- Potassium channels: transport potassium ions
- Aquaporins: transport water molecules
What is active transport?
Active transport is the movement of molecules against a concentration gradient, requiring energy, typically from ATP.
What is the sodium-potassium pump?
The sodium-potassium pump is a type of pump protein that transports sodium ions out of the cell and potassium ions into the cell, crucial for maintaining membrane potential.
What are sodium-dependent glucose cotransporters (SGLTs)?
SGLTs are membrane proteins that facilitate the absorption of glucose in the small intestine by using the sodium gradient established by the sodium-potassium pump. Glucose “hitches a ride” with the sodium ion and, using the energy from the sodium ion travelling with its concentration gradient, is able to traverse across the glucose concentration gradient.
What is endocytosis?
Endocytosis is the process by which cells internalize substances by engulfing them in a membrane-bound vesicle.
What is exocytosis?
Exocytosis is the process by which cells expel substances by vesicles fusing with the plasma membrane.
What role do cell-adhesion molecules (CAMs) play?
CAMs are proteins that facilitate the adhesion of cells to each other and to the extracellular matrix, essential for tissue formation.
How does the fluidity of the lipid bilayer impact its function in biological membranes?
Fluidity allows for the movement of proteins and lipids within the membrane, which is vital for processes such as cell signaling and transport.
What is the role of cholesterol in membranes?
Cholesterol acts as a modulator of membrane fluidity, stabilizing membranes at higher temperatures and preventing stiffening at lower temperatures.
How do organisms adapt their membrane lipids to extreme environments?
Organisms may increase unsaturated fatty acids in their membranes to maintain fluidity in cold environments or increase saturated fatty acids in hot environments for stability.
What is simple diffusion?
The passive movement of molecules from an area of higher concentration to an area of lower concentration, driven by the concentration gradient.
How does simple diffusion differ from facilitated diffusion?
Simple diffusion does not involve the assistance of membrane proteins.
What types of molecules can undergo simple diffusion across a lipid bilayer?
Small, nonpolar molecules like oxygen, carbon dioxide, and lipids.
What factors can affect the rate of simple diffusion?
- Surface area
- Membrane thickness
- Membrane permeability
What are the six main functions of membrane proteins?
- Transport
- Receptor
- Anchor
- Cell Adhesion
- Identification (Identity Marker)
- Enzymatic Activity
Describe the structure of integral membrane proteins.
Integral proteins have hydrophobic regions that interact with the hydrophobic tails of phospholipids in the lipid bilayer.
What examples of integral membrane proteins exist?
- Ion channels
- G protein-coupled receptors (GPCRs)
- Transporters and pumps
Why can peripheral proteins be easily removed from the membrane?
Peripheral proteins are loosely associated with the membrane and can be easily detached without disrupting the lipid bilayer.
What happens to cells in an isotonic solution?
Cells maintain their normal shape and volume because there is no net movement of water.
What happens to cells in a hypertonic solution?
Water flows out of the cells, causing them to shrink or undergo crenation.
What happens to cells in a hypotonic solution?
Water moves into the cells, causing them to swell and potentially burst (lyse).
How do channel proteins ensure selectivity?
Channel proteins allow specific molecules to pass based on size, shape, charge, and chemical properties.
What are examples of channel proteins and what do they transport?
- Aquaporins: Transport water molecules
- Ion channels: Transport ions like sodium (Na+), potassium (K+), calcium (Ca2+), and chloride (Cl-)
- Gap junction proteins (connexins): Facilitate the passage of small molecules and ions between adjacent cells.
What is active transport?
A cellular process that moves molecules or ions against their concentration gradient, requiring energy input, usually in the form of ATP.
What are examples of pump proteins?
- Sodium-Potassium Pump (Na+/K+ Pump)
- Proton Pump (H+-ATPase)
What role does the sodium-potassium pump (Na+/K+ pump) play in neurons?
It maintains the resting membrane potential by actively pumping sodium ions out of the cell and potassium ions into the cell.
What is the fluid mosaic model of the cell membrane?
- Lipid Bilayer
- Fluidity
- Mosaic of Proteins (Integral and Peripheral)
- Protein Diversity
- Membrane Asymmetry
- Dynamic Nature
- Selective Permeability
- Recognition and Signaling
How does the fluidity of the lipid bilayer impact its function?
It influences the mobility of membrane proteins, the permeability of the membrane to various molecules, and the ability to adapt to changes in temperature.
What is the relationship between fatty acid saturation and lipid bilayer fluidity?
- Unsaturated fatty acids increase fluidity
- Saturated fatty acids decrease fluidity
How does cholesterol affect membrane fluidity?
Cholesterol reduces fluidity at higher temperatures and prevents stiffening at lower temperatures.
What group does cholesterol belong to?
Cholesterol belongs to the group of lipids known as ‘steroids.’
Where is cholesterol located in the plasma membrane?
Cholesterol is interspersed within the lipid bilayer of the plasma membrane.
What are the functions of glycolipids found in the plasma membrane?
- Cell Recognition
- Cell Adhesion
- Membrane Stability
- Cell Signaling
- Lubrication
- Immune Response
What are the functions of glycoproteins found in the plasma membrane?
- Cell-to-Cell Recognition
- Receptors
- Cell Adhesion
- Protection
- Modulation of Protein Function
- Blood Group Determination
What is the structure of cholesterol?
Cholesterol has a steroid ring structure and is amphipathic.
How does cholesterol affect membrane fluidity?
Cholesterol modulates membrane fluidity by reducing it at higher temperatures and increasing it at lower temperatures.
What impact does cholesterol have on the movement of phospholipids?
Cholesterol restricts the movement of phospholipids, thus reducing membrane permeability.
What are the chemical properties of the membrane affected by cholesterol?
The properties affected are:
* Permeability
* Solubility
* Melting Temperature
* Fluidity
* Thickness
What is pinocytosis?
Pinocytosis, also known as ‘cell drinking,’ is a form of endocytosis where cells engulf small dissolved molecules and extracellular fluid droplets.
What is phagocytosis?
Phagocytosis is the process of engulfing and internalizing larger solid particles, such as bacteria and debris.
How does exocytosis occur?
During exocytosis, vesicles fuse with the plasma membrane to expel cellular contents.
What role does membrane fluidity play in endocytosis?
Membrane fluidity allows the plasma membrane to change shape and curvature for vesicle formation.
What are gated ion channels?
Gated ion channels are membrane proteins that control the flow of ions across the neuronal membrane in response to signals.
What is ion selectivity in gated ion channels?
Ion selectivity is the ability of gated ion channels to allow specific ions to pass through while excluding others.
Give an example of a neurotransmitter-gated ion channel.
Nicotinic acetylcholine receptors (nAChRs) are an example.
What is the function of the sodium-potassium pump?
The sodium-potassium pump actively transports sodium ions out and potassium ions into the cell.
How do voltage-gated sodium channels contribute to action potentials?
They open in response to depolarization, allowing sodium influx and causing rapid depolarization.
What is the role of voltage-gated potassium channels during action potentials?
They open during repolarization, allowing potassium efflux and contributing to membrane repolarization and potential hyperpolarization.
What is the importance of the sodium-potassium pump in neurons?
It maintains the resting membrane potential by establishing ion concentration gradients.
What are sodium-dependent glucose cotransporters (SGLTs)?
SGLTs are membrane proteins that transport glucose across cell membranes, found in the small intestine and nephron.
Explain indirect active transport as exemplified by SGLTs.
It uses energy from ion gradients to transport other molecules against their concentration gradients.
Why are SGLTs important for glucose absorption?
They facilitate the absorption of glucose from the digestive tract into enterocytes.
What is the role of SGLTs in glucose reabsorption in the nephron?
They reabsorb glucose from glomerular filtrate, conserving energy and maintaining blood glucose levels.
What is cell adhesion?
Cell adhesion is the process by which individual cells bind together to form tissues.
Define cell-adhesion molecules (CAMs).
CAMs are proteins on the cell surface that mediate cell-cell adhesion.
What is the significance of cell adhesion in multicellular organisms?
It is essential for tissue development, wound healing, and organ functioning.
How do you calculate percent change?
(Wf - Wi)/Wi x 100
Describe the steps of endocytosis.
- Inward folding of the membrane.
- Membrane fusion, with solutes inside the bilayer.
- Vesicle formation pinched off of cell membrane.
- Cytoplasmic movement - vesicles detach and move into the cytoplasm.
- The membrane becomes smaller.
Describe the steps of exocytosis.
- Vesicles transport to the cell membrane.
- Vesicles attach to the membrane.
- Fusion and release contents to extracellular space.
- Membrane gets bigger.
Examples of exocytosis:
- Neurotransmitters are released for communication between neurons.
- Hormone secretion (insulin and glucagon)
- Water removal by the contractile vacuole.
