Biochem #8 Flashcards
cell (plasma) membrane
: semipermeable phospholipid bilayer.
o Barrier that only some things can pass through passively while others can’t or have to find a different method of transportation.
o Fat-soluble compounds can cross easily while larger water-soluble compounds must seek alternate entry.
o Regulates what gets in and out, protects the interior of the cell, intracellular and intercellular communication, signal transduction via the receptors on it.
what easily diffuses through the plasma membrane and what has to find alternate entry?
o Fat-soluble compounds can cross easily while larger water-soluble compounds must seek alternate entry.
glycoprotein coat
created when carbohydrates are associated with membrane bound proteins.
o The cell wall of plants, bacteria, and fungi contain higher levels of carbohydrates.
phospholipids
move rapidly in the plane of the membrane via diffusion, spread throughout
lipid rafts
collections of similar lipids with or without associated proteins that serve as attachment points for other biomolecules.
Important for signaling.
flippases
assist in the transition or flip of phospholipids between layers (or just lipids)
o What is on the surface of the cell can be regulated
the surfaces of cells can be ____
regulated, such as what is on them.
cell membrane: steroid and cholesterol provide ___ while waxes provide ____
fluidity
stability
lipids in the cell membrane
o Primarily phospholipids but some free fatty acids. Steroid molecules and cholesterol lend to fluidity of the membrane while waxes are present for membrane stability.
o Fatty Acids and Triacylglycerols
Fatty acids: carboxylic acids that contain a hydrocarbon chain and terminal carboxyl group.
Triacylglycerol (triacylglyceride): storage lipids involved in human metabolic processes.
• Unsaturated fatty acids: healthier, liquid at room temperature, more double bonds, fluidity in the membrane.
o Chylomicrons: used to transport triacylglycerols from the intestine whose fatty acids are used in the membrane.
• Saturated fatty acids: the main components of animal fats and tend to exist as solids at room temperature, unhealthy, decrease membrane fluidity.
o Phospholipids (glycerophospholipid)
When one of the fatty acid chains in triacylglycerol is exchanged for a polar phosphate group head.
Hydrophobic interactions cause phospholipids to assemble into micelles (small monolayer vesicles) or liposomes (bilayered vesicles) due to hydrophobic interactions.
In the cell membrane
Can also serve as second messengers in signal transduction.
triacylglycerol in cell membrane
storage lipids involved in human metabolic processes.
• Unsaturated fatty acids: healthier, liquid at room temperature, more double bonds, fluidity in the membrane.
o Chylomicrons: used to transport triacylglycerols from the intestine whose fatty acids are used in the membrane.
• Saturated fatty acids: the main components of animal fats and tend to exist as solids at room temperature, unhealthy, decrease membrane fluidity.
saturated vs. unsaturated fatty acids in cell membrane
unsaturated: more double bonds, more fluidity
saturated: decrease membrane fluidity
how do you get from triacylglyercol to phospholipid (glycerophospholipid)
When one of the fatty acid chains in triacylglycerol is exchanged for a polar phosphate group head.
sphingolipids and cell membrane
Important for the cell membrane.
Very similar in structure to phospholipids, some just differ in the identity of their hydrophilic regions.
Role (internet): the regulation of cell growth, differentiation, diverse cell functions, and apoptosis.
steroids are derived from ______
cholesterol
how does cholesterol act during high and low temperatures?
Important for membrane fluidity roles: high temp limits movement and holds the membrane together. Low temp prevents formation of crystal structures and increases fluidity.
how do waxes act in the cell membrane?
Extremely hydrophobic and are rarely found in the cell membranes of cells.
• Only in hydrophobic part for stability and rigidity.
Consists of long chain fatty acid and long chain alcohol, very high melting point.
Mainly extracellular function of protection and waterproofing.
integral proteins
associated with the interior of the plasma membrane and can include both transmembrane proteins and embedded proteins
transmembrane proteins
pass completely through the lipid bilayer (transporters, channels, and receptors)
embedded proteins
associated with only the interior or exterior surface of the cell membrane.
membrane-associated proteins (peripheral)
may be bound through electrostatic interactions with the lipid bilayer (lipid rafts or other transmembrane or embedded proteins)
Ex: G proteins
carbohydrates and the cell membrane
o Generally attached to the protein molecules on the extracellular surface of cells.
o Hydrophilic, glycoproteins interact with water to form coat around the cell.
o Can act as signaling and recognition molecules (ABO blood type antigens)
membrane receptors
o Transmembrane proteins that can activate facilitated diffusion and active transport.
o Ex: ligand-gated ion channels.
o Ex: G protein couple receptor signal transduction cascade
o Mainly proteins but can be carbohydrates and lipids in viruses.
what are the types of cell junctions?
Cells can form cohesive layer of intracellular junctions that are useful for communication between cell and cell and cell and extracellular matrix.
cell adhesion molecules (allow the cell-cell junctions to occur) gap junctions tight junctions desmosomes hemidesmosomes
cell adhesion molecules
proteins that allow cells to recognize each other and contribute to proper cell differentiation and development. Makeup cell cell junctions.
gap junctions
Junctions (connexons): allow for direct cell-cell communication and are often found in small bunches together.
Made up of connexin: make the pores of gap junctions. One connexon is composed of 6 monomers of connexin.
Permit movement of water and some solutes directly between cells.
Random locations around the cell.
tight junctions
prevent solutes from leaking into the space between cells via a paracellular route.
Found in epithelial cells and function as a physical link between the cells as they form a single layer of tissue.
Continuous band around the cell
Can lead to transepithelial voltage difference.
desmosomes
bind adjacent cells by anchoring to their cytoskeletons.
Formed by interactions between transmembrane proteins associated with intermediate filaments inside adjacent cells.
Found in interface between two layers of epithelial tissue.
Hemidesmosomes: attach epithelial cells to underlying structures, especially the basement membrane.
hemidesmosomes
attach epithelial cells to underlying structures, especially the basement membrane.
Transport of ____ molecules occurs rapidly through the cell membrane via diffusion, while ____ require more specialized transport processes.
small nonpolar
ions and larger molecules
passive transport
spontaneous processes that do not require energy (ΔG<0), use concentration gradient to supply energy.
Thermodynamic motivator is increase in entropy
simple diffusion, osmosis, facilitated diffusion
simple diffusion
substrates move down their concentration gradient directly across the membrane.
There is potential energy in the chemical gradient
Only particles that are freely permeable to the membrane are able to undergo simple diffusion.
osmosis
specific kind of simple diffusion that concerns water; water will move from a region of lower solute concentration to one of higher solute concentration.
Higher water concentration to lower water concentration.
Hypotonic: when the concentration of solutes inside the cell is higher than the surrounding solution, the solution is hypotonic. Water moves into the cell.
Hypertonic: the solution is more concentrated than the cell, water will move out of the cell.
Isotonic: when the solutions inside and outside are equimolar.
• Still movement, just no net movement.
Osmotic pressure is one driving force behind this. It is a colligative property: a physical property of solutions that is dependent on the concentration of dissolved particles but not on the chemical identity of those dissolved particles.
• Ex: two compartment container and one has more concentrated solution. Only water can pass thru the semipermeable membrane. Water will flow from low solute concentration to high solute concentration only until the hydrostatic pressure in the higher concentrated section counterbalances the tendency of water to flow across the membrane.
• “sucking pressure” (against cell membrane in cells). Water will move to the compartment with the highest osmotic pressure.
hypotonic solution
when the concentration of solutes inside the cell is higher than the surrounding solution, the solution is hypotonic. Water moves into the cell.
hypertonic solution
the solution is more concentrated than the cell, water will move out of the cell.
water moves toward _____
higher concentration of solutes
define an isotonic situation and is there any movement of water?
when the solutions inside and outside are equimolar.
• Still movement of water, just no net movement.
osmotic pressure
It is a colligative property: a physical property of solutions that is dependent on the concentration of dissolved particles but not on the chemical identity of those dissolved particles.
• Ex: two compartment container and one has more concentrated solution. Only water can pass thru the semipermeable membrane. Water will flow from low solute concentration to high solute concentration only until the hydrostatic pressure in the higher concentrated section counterbalances the tendency of water to flow across the membrane.
• “sucking pressure” (against cell membrane in cells). Water will move to the compartment with the highest osmotic pressure.
facilitated diffusion
: simple diffusion for molecules that are impermeable to the membrane (large, polar, charged) because the energy barrier is too high for them to cross freely.
Requires integral membrane proteins to serve as transporters or channels for these substrates.
Ex: Carriers: only open to one side of the cell membrane at any given point
• Substrate walks in, rotate and conformational change of the transporter, and then walks out the other side
• Occluded state: the carrier is not open to either side of the phospholipid bilayer.
Channels: may be in an open or closed conformation and act like a tunnel for the particles to diffuse through.
active transport
net movement of a solute against its concentration gradient.
o Always requires energy but the source of the energy can vary.
o Primary active transport: uses ATP or another energy molecule to directly power the transport of molecules across a membrane.
Ex: transmembrane ATPase
Ex: maintains membrane potential in neurons
o Secondary active transport (coupled transport): harnesses the energy of one particle going down its concentration gradient to drive a different particle up its concentration gradient.
Symport: both molecules flow in the same direction across the membrane
Antiport: the molecules flow in opposite directions across the membrane
Used in the kidneys
endocytosis
IN
occurs when the cell membrane invaginates and engulfs material to bring it into the cell.
o Pinocytosis: endocytosis of fluids and dissolved particles.
o Phagocytosis: ingestion of large solids such as bacteria
o Vesicle-coating proteins: initiate and carry out invagination
Ex: clathrin
o Receptors are embedded in the plasma membrane.
