Chapter 3 - Cellular Level Flashcards
(60 cards)
Define cell and list the 3 major components
Cell: living structural and functional unit enclosed by a membrane divided into 3 main parts:
- Plasma membrane: separates the cells internal membrane from the external environment
- Cytoplasm: consists of cytosol (ICF) and organelles
- Nucleus: a large organelles that contains chromosomes (single DNA molecule) with thousands of genes
What is the fluid-mosaic model?
The molecular arrangement of the plasma membrane resembles a continually moving sea of fluid lipids that contain a mosaic of different proteins
What are the 4 functions of the plasma membrane?
1) Acts as a barrier separating inside or outside of cell
2) Controls the flow of substances into and out of cell
3) Helps identify the cell to other cells (eg immune cells)
4) Participates in intercellular signalling
Describe the basic structure of the lipid bilayer
2 back-to-back layers made up of 3 types of lipid molecules: Phospholipids, cholesterol, and glycolipids
How do phospholipids orient themselves in the lipid bilayer?
They are amphipathic
Hydrophilic heads face outward and hydrophobic fatty acid tails in each half of the bilayer point toward one another forming a nonpolar hydrophobic region
Integral vs. peripheral proteins
Integral: extend into or through the lipid bilayer (most are transmembrane)
Peripheral: not as firmly embedded - attached to the polar heads of phospholipids or integral proteins
Define glycoprotein and glycocalyx
glycoprotein: integral proteins with C groups that protrude into the ECF
Carbohydrate portions form an extensive sugary glyccalyx that enables cells to recognize one another
What are the functions of membrane proteins? (ion, carrier, receptor, enzyme, linker, cell-identity)
Ion channels (integral): forms pore that specific ions can flow through
Carriers (integral): transports specific substances across membrane by undergoing a change in shape
Receptors (integral): Recognizes specific ligand (molecule that binds to receptors) and alters cell’s function in some way
Enzymes (integral & peripheral): catalyze specific chemical reactions
Linkers (integral & peripheral): Anchor filaments inside and outside membrane, providing stability and shape for cell
Cell-identity markers (glycoprotein): distinguishes you cells from anyone else’s and recognize and respond to potentially dangerous foreign cells
Describe membrane permeability
Highly permeable to non-polar molecules
Moderately permeable to small, polar uncharged molecules
Impermeable to ions and large, uncharged polar molecules
The more hydrophobic or lipid-soluble, the greater permeability
Concentration vs. Electrical gradient (membrane potential)?
Concentration: difference in the concentration of a chemical from one place to another
Electrical: inner surface of the plasma membrane is more negatively charged & the outer surface is more positively charged. This difference in electrical charge is called an electrical gradient. Since it is across a membrane it is termed the membrane potential.
What’s the electrochemical gradient?
The combined influence of the concentration gradient and electrical gradient is the electrochemical gradient.
A substance will move downhill from where it’s more concentrated to where it’s less concentrated to reach equilibrium. A positively charged substance will move towards a negatively charged substance and vice versa.
Passive vs. active transport across a membrane?
Passive: substance moves down its gradient using only its own kinetic energy (energy of motion)
Active: cellular energy is used to drive the substance ‘uphill’ against its gradient (ATP or using vesicles)
WHat is diffusion?
A passive process in which random mixing of particles occurs in a solution because of the particles’ kinetic energy.
Both solutes and solvents undergo diffusion. Solute molecules will diffuse towards an area of low concentration and eventually they become evenly distributed and reach equilibrium
5 Factors that influence the diffusion rate of substances across a membrane
Steepness of concentration gradient: greater steepness, faster diffusion
Temperature: higher temp, faster diffusion
Mass of the diffusing substance: the larger the mass the slower the diffusion
Surface area: larger SA, faster diffusion rate
Diffusion distance: greater distance, slower diffusion
What is simple diffusion? Which molecules use this process?
Passive process. Substances move freely through the lipid bilayer without the help of membrane transport proteins.
Non-polar, hydrophobic molecules (O, CO2, N gases, steriods, fatty acids, fat soluble vitamins, small uncharged polar molecules like water and urea) pass via simple diffusion
What is facilitated diffusion?
An integral membrane protein (either channel or carrier) assists a specific substance across a membrane. Usually solutes that are too polar or highly charged
What’s channel-mediated facilitated diffusion?
A solute moves down its concentration gradient across the lipid bilayer through a membrane channel (likely an ion channel)… passage of small inorganic molecules too hydrophilic to penetrate the nonpolar interior of the lipid bilayer
What’s a gated channel?
When a part of the channel acts as a gate or a plug, changing shape in one way to open to pore and another to close
What’s carrier-mediated facilitated diffusion?
A carrier moves a solute down its concentration gradient across the plasma membrane. Solute binds to specific carrier on one side of membrane and is released on other side. The rate of carrier mediated diffusion is determined by the steepness of the concentration gradient across the membrane.
What is the transport maximum?
Once all carriers are occupied the transport maximum is reached, exhibiting saturation (like a sponge)
Define osmosis. What are the two ways water molecules pass through the membrane
Type of diffusion in which there is net movement of a solvent through a selectively permeable membrane; only occurs when membrane is permeable to water but not certain solutes
- By moving between neighbouring phospholipid molecules in the lipid bilayer via simple diffusion
- By moving through aquaporins, integral membrane proteins that function as water channels
Discuss the principles of osmosis using a U-shaped tube
Water is poured into the left and a solute solution is poured into the right
Water moves into the right tube (down its concentration gradient)
The membrane prevents diffusion of the solute so the volume increases in the right leading to hydrostatic pressure
Hydrostatic and osmotic pressure forces the water back into the left until equilibrium is reached
Hydrostatic vs. osmotic pressure
Hydrostatic: pressure from the increased volume forces water back from where it came
Osmotic: pressure exerted from the impermeable solute (the higher the solute concentration, the higher the pressure)
What is Tonicity?
As water moves by osmosis, their volume increases or decreases
Tonicity is a measure of the solution’s ability to change the volume of cells by altering their water content.
