chapter 7 membrane structure and function Flashcards
What is the most abundant lipid in the plasma membrane?
Phospholipids
Phospholipids are amphipathic molecules containing hydrophilic and hydrophobic regions.
What does the fluid mosaic model state about cellular membranes?
Membrane is a fluid structure with a ‘mosaic’ of various proteins embedded in it.
How do phospholipids move within the plasma membrane?
They drift laterally within the bilayer.
What happens to membranes as temperature cools?
They switch from a fluid state to a solid state.
What role does cholesterol play in the animal cell membrane?
Reduces membrane fluidity.
What is the significance of membrane fluidity?
Fluidity affects permeability and movement of proteins.
What type of proteins determine most of the membrane’s specific functions?
Proteins.
What defines transmembrane proteins?
Integral proteins that span the membrane.
What is the role of membrane carbohydrates in cell recognition?
They recognize each other by binding to surface molecules containing carbs.
What are glycolipids and glycoproteins?
Glycolipids are carbohydrates bonded to lipids, and glycoproteins are carbohydrates bonded to proteins.
What determines the asymmetrical distribution of proteins, lipids, and carbohydrates in membranes?
The endoplasmic reticulum (ER) and Golgi apparatus.
What is selective permeability in the context of plasma membranes?
Regulation of molecular traffic in and out of the cell.
Which molecules can pass through the lipid bilayer rapidly?
Hydrophobic (nonpolar) molecules.
What are transport proteins?
Proteins that allow passage of hydrophilic substances across the membrane.
What are aquaporins?
Channel proteins that facilitate the passage of water.
What is passive transport?
Diffusion of a substance across a membrane with no energy investment.
What is dynamic equilibrium in diffusion?
As many molecules cross in one direction as do in the other.
What is tonicity?
Ability of a surrounding solution to cause a cell to gain or lose water.
Define hypotonic, hypertonic, and isotonic solutions.
Hypotonic: less solute outside; Hypertonic: more solute outside; Isotonic: equal solute concentration.
What is osmoregulation?
Control of water balance and solute concentration.
What is facilitated diffusion?
Passive transport aided by proteins.
What is active transport?
Movement of substances against their concentration gradient requiring energy.
How does the sodium-potassium pump function?
It moves sodium out and potassium in against their gradients, generating membrane potential.
What is an electrogenic pump?
A transport protein that generates voltage across the membrane.
What are cations and anions?
Cations are positively charged ions; anions are negatively charged ions.
What is cotransport?
Coupled transport by a membrane protein where active transport of one solute drives the transport of others.
What are the three types of endocytosis?
- Phagocytosis
- Pinocytosis
- Receptor-mediated endocytosis
What is the cell membrane?
A double layer of lipids and proteins that surrounds a cell.
What are the main functions of the cell membrane?
- Separates cytoplasm from external environment
- Controls movement of substances in and out of cells and organelles
- Involved in cell adhesion, ion conductivity, and cell signaling.
What is the phospholipid bilayer?
A thin polar membrane made of two layers of phospholipid molecules held together by hydrophobic interactions.
What role does the phospholipid bilayer play?
Acts as a barrier that keeps ions and large molecules in designated areas and selectively allows some small molecules to pass.
What factors influence cell membrane fluidity?
- Temperature
- Presence of cholesterol
- Phospholipid length
- Phospholipid saturation.
How does temperature affect membrane fluidity?
Increased temperature leads to increased fluidity.
What is the melting temperature (Tm) of a membrane?
The temperature at which the membrane transitions from a gel-like state to a fluid-like state.
What is the role of cholesterol in membrane fluidity?
At high temperatures, it helps hold the membrane together; at low temperatures, it disrupts interactions, preventing freezing.
What are the four major phospholipids in mammalian cell membranes?
- Phosphatidylcholine (PC)
- Phosphatidylethanolamine (PE)
- Phosphatidylserine (PS)
- Shingomyelin.
How does phospholipid length affect fluidity?
Increased length leads to increased strength of interaction and decreased fluidity.
What is the difference between saturated and unsaturated phospholipid tails?
Saturated tails have no double bonds and are straight; unsaturated tails have double bonds and are kinked.
What are membrane proteins?
Proteins that interact with or are part of biological membranes.
What are the major functions of membrane proteins?
- Transport
- Enzymatic activity
- Signal transduction
- Cell-cell recognition
- Inter-cellular joining
- Attachment to cytoskeleton and extracellular matrix.
How are membrane proteins classified?
- Integral (membrane penetrating)
- Peripheral (attached via non-covalent bonds)
- Lipid-anchored (attached through covalent bonds).
What are integral proteins?
Proteins that are permanently attached to the biological membrane.
What are transporters?
Membrane proteins involved in the movement of ions, small molecules, and macromolecules across the membrane.
What are receptors in the context of membrane proteins?
Proteins that bind to external molecules and perform signal transduction.
What are lipid-anchored proteins?
Proteins located on the surface of the cell membrane that are covalently attached to lipids.
What are peripheral proteins?
Proteins that interact with the surface of cell membranes and can attach/detach based on factors like pH and temperature.
What are membrane carbohydrates?
Carbohydrate chains that may consist of 2-60 units and can be linked to proteins (glycoproteins) or lipids (glycolipids).
What are the major roles of membrane carbohydrates?
- Cell adhesion
- Cell recognition.
Additionally, they serve a structural role.
What are the types of cellular transport?
- Passive
- Active.
Includes diffusion, osmosis, active transport, and bulk transport.
What is diffusion?
The net passive movement of molecules from regions of higher to lower concentration.
What is facilitated diffusion?
The process where substances cross the plasma membrane with the help of proteins.
What is osmosis?
The movement of water from a region of higher concentration to one of lower concentration.
What is active transport?
The movement of substances against their concentration gradient, requiring energy.
What is the Na+/K+ pump?
A transmembrane protein pump that transports sodium and potassium ions across the cell membrane in a 3:2 ratio.
What is endocytosis?
The cellular process of bringing large molecules into the cell by surrounding them with the cell membrane.
What are the types of endocytosis?
- Pinocytosis (cell drinking)
- Phagocytosis (cell eating)
- Receptor-mediated endocytosis.
What is exocytosis?
The process of transporting molecules from inside the cell to the outside.
What are the pathways of exocytosis?
- Constitutive secretory pathway
- Regulated secretory pathway
- Lysosome secretory pathway.
