Where are sphingolipids mainly present?
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In the plasma membrane.
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Where are sphingolipids mainly present?
In the plasma membrane.
What is the function of tight junctions in epithelial cells?
They connect cells near the apical surface to prevent movement of proteins from the basolateral membrane to the apical membrane.
What are the two groups of active transport based on the source of energy?
Primary active transport and secondary active transport.
What are the important roles of the sodium-potassium pump?
Maintaining cell membrane potential, transporting nutrients, regulating cell volume, and signal transduction.
What conditions may the presence of acanthocytes indicate?
Liver disease and several inherited neurological disorders, such as neuroacanthocytosis.
What are the main components of biological membranes?
Phospholipids and proteins.
What are peripheral proteins?
Proteins that are either attached to integral membrane proteins or associated with the polar region of the lipid bilayer due to electrostatic interactions.
Which phospholipids are most abundant in biological membranes?
Glycerophospholipids, especially phosphatidyl-cholines and phosphatidyl-ethanolamines.
What changes occur in the lipid composition of acanthocytes?
Increased levels of cholesterol and sphingomyelin, and decreased levels of phosphatidylcholine.
What is the function of the Na+/K+ ATPase?
It pumps 3 sodium ions out and 2 potassium ions in, leading to membrane polarization.
What determines the ratio of proteins to lipids in a membrane?
The function of the particular membrane.
What do glucose transporters (GLUT) do?
Facilitate the diffusion of glucose from extracellular space to the cells.
What drives secondary active transport?
Chemical gradients established by the action of ATPases.
What characterizes simple diffusion?
Random movement of gases or small uncharged molecules, continuing until equilibrium is reached.
What is the asymmetric distribution of lipids in the plasma membrane?
Outer layer contains phosphatidyl cholines, sphingomyelins, and some glycolipids; inner layer contains phosphatidyl ethanolamines and phosphatidyl serines.
What are the two types of endocytosis?
Non-specific endocytosis and specific (receptor-mediated) endocytosis.
What are the functions of membrane proteins?
Transport of ions and molecules, and some act as enzymes.
What types of proteins can be classified as transmembrane proteins?
Single-passing or multi-passing proteins, including membrane receptors.
What is the transitional temperature in membrane fluidity?
The temperature when the membrane transitions from gel to liquid state.
What produces the secretory vesicles involved in exocytosis?
The Golgi apparatus.
How does membrane fluidity affect membrane-bound receptors?
It influences their activity.
What is the distribution of membrane proteins in polarized cells?
It is not even; proteins in apical and basal/lateral membranes can diffuse in their own domains.
What is the main role of transepithelial transport?
Involved in the absorption of nutrients from the gastrointestinal tract, like glucose or amino acids.
What are erythrocytes called when their membrane is altered?
Acanthocytes.
What are integral (transmembrane) proteins?
Proteins embedded in the whole bilayer that interact strongly with hydrophobic fatty acid chains.
What type of channel is the nicotinic acetylcholine receptor?
A Na+ channel that is permeable for sodium ions after binding of acetylcholine.
What is the role of ATP binding cassette transporters?
They bind and hydrolyze ATP and are involved in multidrug resistance of tumor cells.
What is the role of ATP-binding cassette transporters?
They transfer a variety of endogenous substances across membranes and extrude exogenous substances like drugs and toxins.
How does water pass through biological membranes?
Via water-selective facilitated diffusion through aquaporins (AQPs).
What is endocytosis?
Transport of substances from extracellular space into the cells, especially large polar molecules that cannot pass through the plasma membrane.
What are the key characteristics of facilitated diffusion?
Specific, saturable, and inhibitable.
How are ionophores classified?
Into mobile carriers and channel forming.
What is the function of ion channels in facilitated diffusion?
They allow controlled entry of ions into the cell.
What happens to fatty acids at low temperatures?
They are tightly arranged, creating an ordered system (gel-crystalline state).
What is exocytosis?
Transport of compounds to the plasma membrane or through the plasma membrane out of the cells.
How does Ca2+ affect membrane fluidity?
It lowers fluidity by interacting with negatively charged phospholipid head groups.
What are the three steps involved in the mechanism of exocytosis?
Vesicle trafficking, docking, and fusion with the plasma membrane.
What occurs during vesicle fusion?
Fusion of vesicles with membrane lipids, incorporating proteins or lipids into the membrane or releasing proteins or peptides to the extracellular matrix.
What does the γ-glutamyl transferase system catalyze?
The attachment of extracellular amino acids to glutamic acid of intracellular glutathione.
What is active transport?
A type of transport that requires energy and moves substances against the concentration gradient, from low to high concentration.
What are the three domains of transmembrane proteins?
Hydrophilic cytosolic domain, hydrophobic membrane-spanning domain, and hydrophilic extracellular domain.
What factors influence the opening of mechanically dependent channels?
Stretch, pressure, vibration, and displacement.
What are the three groups of Ca2+ ATPase based on localization?
Plasma membrane Ca2+-ATPase (PMCA), sarco-/endoplasmic reticulum Ca2+-ATPase (SERCA), and secretory pathway Ca2+-ATPase (SPCA).
What is the mechanism of glucose transport by glucose transporters?
Glucose uniport.
What is the function of the Na+/Ca2+ exchanger?
It removes calcium from cells in exchange for sodium ions.
How many sodium ions are exchanged for one calcium ion in the Na+/Ca2+ exchanger?
Three sodium ions for one calcium ion.
What does membrane fluidity refer to?
The viscosity of the lipid bilayer affecting the movement of lipids in the membrane.
What role do integral proteins play in cells?
They are involved in signal transduction, structural stability, and cell-cell or cell-extracellular matrix interactions.
Where are sodium/glucose and sodium/amino acid cotransporters mainly expressed?
In the plasma membrane of intestinal epithelial cells.
What is an example of a ligand-dependent ion channel?
Neuronal glutamate receptors that are permeable for calcium.
How do cis double bonds affect membrane fluidity?
They create kinks that prevent tight packing, increasing fluidity.
What is one effect of higher membrane fluidity?
Higher membrane permeability for water and other hydrophilic substances.
How do membrane proteins move within the membrane?
Through lateral diffusion and rotational diffusion.
What does transepithelial transport depend on?
The asymmetric distribution of transporters in the apical and basolateral membranes of epithelial cells.
How much ATP does γ-glutamyl transferase consume per transported amino acid?
3 molecules of ATP.
What is the shape of acanthocytes?
Spherical cells with irregularly spaced, long spiny thorn-like projections.
What is abetalipoproteinemia?
An inherited disorder associated with pathologically low blood cholesterol levels.
What characterizes the transmembrane domains of integral proteins?
They are predominantly alpha helices composed mainly of hydrophobic amino acids like valine, leucine, isoleucine, and tyrosine.
What are the main lipid components of biological membranes?
Phospholipids, glycolipids, and cholesterol.
What is passive transport?
Movement of substances that does not require energy and occurs down the concentration gradient.
What role does cholesterol play in membranes?
It makes the membrane less permeable and is most abundant in plasma membranes and myelin sheath.
Why is facilitated diffusion necessary?
Because the rate of simple diffusion for some substances is not high enough to meet physiological demands.
What is the role of the Na+/H+ exchanger?
It maintains sodium balance and regulates volume and pH, especially in the kidney.
What drives the sodium-dependent symport of glucose and amino acids?
The sodium gradient established by Na+/K+ ATPase.
What are gap junctions?
Specialized intercellular connections between neighboring cells that allow small molecules to pass directly through.
What is phagocytosis?
A specific form of endocytosis involving the internalization of solid particles, such as bacteria, by phagocytes.
What effect does unsaturation have on membrane fluidity?
Increased fluidity.
What is the role of Ca2+ in regulated exocytosis?
It acts as an external signal associated with an increase in intracellular Ca2+, triggering the release of hormones or neurotransmitters.
What is one intoxicating effect of ethanol related to membrane fluidity?
Modification of membrane fluidity, altering the functioning of membrane receptors and ion channels.
What is transepithelial transport?
Transport of substances or ions through epithelial cells.
What is produced when amino acids are transported into the cell via the γ-glutamyl transferase system?
γ-glutamyl amino acid, which is then hydrolyzed to amino acid and 5-oxoproline.
Where is the H+/K+ ATPase located and what does it do?
It is present on the apical membrane of parietal cells in the gastric mucosa and pumps 1 potassium ion in exchange for 1 proton out.
What are the prominent representatives of transporters responsible for multidrug resistance?
P-glycoproteins and Multidrug Resistance Protein (MRP).
What are the two types of passive transport?
Simple diffusion and facilitated diffusion.
What is cardiolipin and where is it found?
Cardiolipin is almost exclusively present in the inner mitochondrial membrane.
How do peripheral proteins interact with biological membranes?
They interact temporarily and can dissociate after performing their function in the cytoplasm.
What causes the formation of the lipid bilayer?
Hydrophobic interactions of hydrocarbon chains of fatty acids.
What characterizes non-specific endocytosis?
Random invagination of transported particles by the plasma membrane, producing an endocytosis vesicle.
What is required for specific endocytosis?
Binding of the transported substance to a specific receptor, leading to the formation of a clathrin-coated vesicle.
What happens to vesicles after phagocytosis?
They fuse with lysosomes to break down the content, which is then returned to the cytoplasm.
What is the effect of cholesterol on membrane fluidity?
It decreases fluidity.
What does constitutive exocytosis involve?
Release of components to the extracellular matrix or delivery of newly synthesized membrane proteins and lipids.
What is the role of the γ-glutamyl transferase system?
It is important for the uptake of amino acids by tissues such as the liver, kidney, heart, and brain.
What is the role of aquaporins in the cell membrane?
Regulate the flow of water and control water distribution across the membrane.
What are ionophores?
Organic substances that disturb the concentration gradient of ions and facilitate their transport across membranes.
What types of transport proteins are involved in facilitated diffusion?
Channel proteins, gated channel proteins, and carrier proteins.
What factors influence membrane fluidity?
Temperature and lipid composition of the membrane.
How are ion channels classified?
According to their gating mechanisms: voltage dependent and ligand dependent.
How does the length of the hydrocarbon chain affect fluidity?
Shorter chains increase fluidity.
What are the two mechanisms of exocytosis in multicellular organisms?
Ca2+ triggered (regulated) and non Ca2+ triggered (constitutive).
What processes are controlled by membrane fluidity?
Phagocytosis, cell growth, and death.
What is vesicle docking?
The attachment of a vesicle to the plasma membrane.
Where is the γ-glutamyl transferase system localized?
In the plasma membrane.
Why is γ-glutamyl transferase considered an important diagnostic marker?
It is used in medicine, particularly for diagnosing alcoholic liver disease.