Topic 4 - Lipids, Membranes, and Membrane Transport Flashcards
Lipid
Macromolecule that is nonpolar and insoluble in water (hydrophobic); hydrocarbons that include mostly nonpolar carbon-carbon or carbon-hydrogen bonds
List four functions of lipids
- Energy storage
- Insulation from environment in plants and animals
- Building blocks of many hormones
- Form plasma membrane
What are some examples of lipids?
Fats and oils (aka triglycerides), phospholipids, steroids, waxes, etc.
What are the main components of a fat molecule?
Glycerol and three fatty acids
Saturated fatty acid
Single bonds between neighboring carbons in the hydrocarbon chain - i.e. saturated with hydrogen; compact, solid at room temperature, and inflexible in cold temperature
Ex. butter
Unsaturated fatty acid
Hydrocarbon chain contains a double bond (C=C); fluid, liquid at room temperature, flexible in cold temperature
Ex. vegetable oil
Monounsaturated
One double bond (C=C)
Polyunsaturated
Multiple double bonds
What causes an unsaturated fatty acid to be liquid at room temperature?
Double bonds cause a bend/”kink” that prevents fatty acids from packing tightly, keeping them liquid at room temperature.
Why are fats (triglycerides) important?
Fats are an excellent source of stored energy, may be used for insulation and cushioning
Phospholipids
Plasma membrane constituents that comprise cell’s outermost layer; glycerol backbone linked to a modified phosphate group (polar, hydrophilic head) and 2 fatty acid tails (nonpolar, hydrophobic)
- Tails may be saturated or unsaturated
- Spontaneously form micelles or bilayers in water
Steroids
Chemical messengers; precursors to water-insoluble vitamins (A, K, D, and E) and hormones (testosterone and estradiol)
- Composed of 4 carbon rings
Cholesterol
Sterol found in the plasma membrane of animal cells; located within phospholipid bilayer
Fluid mosaic model
Plasma membrane is a mosaic of components - including phospholipids, cholesterol, proteins and carbohydrates - that gives the membrane a fluid character (i.e. lipids are fluid, mosaic is made of proteins)
Phospholipid bilayer
Barrier that separates the inside of the cell from the outside environment; comprised of phospholipids
Functional membranes must be…
Fluid
What affects the fluidity of the bilayer?
Temperature, size of protein, protein attachment to cytoskeleton, saturation of hydrocarbon tails, and cholesterol
What is the function of cholesterol in the membrane?
Prevents lower temperatures from inhibiting fluidity and higher temperatures from increasing fluidity too much
What are the functions of integral proteins (transmembrane proteins)?
- Transporting/channeling molecules across membrane
- Cell-surface receptors - cell recognition, signal transduction
- Cell-to-cell adhesion; carbohydrate chains attached to some proteins act as labels that identify cell type
- Enzymatic activity
- Attachments to cytoskeleton
What are the functions of peripheral proteins?
- Enzymatic activity
- Attachments to cytoskeleton
- Cell recognitions sites - cell-specific proteins
Integral proteins are found…
Embedded in lipid bilayer
Peripheral proteins are found…
On the periphery of lipid bilayer, attached to either integral proteins or phospholipids
Cell surface markers
Classify cells according to their markers
What are the functions of carbohydrates in the cell membrane?
- Cell recognition (“self” vs. “non-self”)
- Glycoproteins and glycolipids - AKA glycocalyx
- Hydrophilic - attracts H2O to cell’s surface
- Cell-to-cell adhesion
Selective permeability / semipermeability
Plasma membranes allow some substances to pass through but not others
Passive transport
A type of membrane transport that does not require energy (ATP) to move substances across cell
Diffusion
A type of passive transport where substances move down their concentration gradient (high to low)
What are the requirements for simple diffusion?
Substances must be small, nonpolar, and lipid-soluble
Dynamic equilibrium
Lack of concentration gradient (no net movement)
Facilitated diffusion
Process in which integral proteins allow membrane diffusion to be selective
Transport proteins
Integral proteins involved in facilitated diffusion; function as either channels for the material or carriers
Channel proteins
Membrane proteins that allow a substance to pass through its hollow core across a plasma membrane
- Hydrophilic interior allows polar compounds, ions and/or water to pass through, which avoids the nonpolar central layer of the plasma membrane
Aquaporins
Channel proteins that allow water to pass through the membrane at a high rate
Ion channels
Allow ions to pass through membrane; diffusion depends on charge (membrane potential), concentration, open/closed status of gate
- Na+, K+ channels in nerve impulses
- Ca2+ channels in muscle cells
Gated channels
Transport proteins that open a “gate,” allowing a molecule to pass through a membrane
- Stimulus (chemical/electrical signals, temperature, mechanical force) causes gate to open/shut
Carrier proteins
Assist specific molecule to pass through by changing shape
- Binds to a substance, triggering a change in shape and moves bound molecule across membrane
Ex. glucose transporter in RBC
Osmosis
The movement (diffusion) of water across a semipermeable membrane down its concentration gradient
Solutions
Solute: substance dissolved in solvent
Solvent: dissolving agent (water)
Tonicity
Amount of solute in a solution
Hypertonic
Higher solute concentration
Hypotonic
Lower solute concentration
Isotonic
Equal solute concentration
Cells without a cell wall will _____ when placed in a hypotonic solution
Lyse/burst
Cells with a cell wall will _____ when placed in a hypotonic solution
Become turgid (firm)
Cells without a cell will _____ when placed in a hypertonic solution
Shrivel/crenate
Cells with a cell wall will _____ when placed in a hypertonic solution
Plasmolyze (shrivel)
Animal cells do best in a _____ environment
Isotonic
Plant cells do best in a _____ environment
Hypotonic
How is osmotic balance maintained?
- Contractile vacuoles pump water out
- Isosmotic regulation - regulation of solutes in the body
- Turgor prevents plant cells from bursting due to pressure from cell wall
Active transport
Method of transporting material the requires energy (ATP, diffusion gradient or light)
ATP stands for…
Adenosine triphosphate
ATP moves substances _____ their concentration gradient
Against
What carrier proteins are involved in active transport?
- Uniporter: carries one specific ion/molecule
- Symporter: carries two different ions/molecules in same direction
- Antiporter: carries two different ions/molecules in a different direction
Give an example of an active transport pump
Na+-K+ ATPase
Electron flow
Proton pumps: H+ is pumped across membrane using electron flow; H+ gradient is used to make ATP as H+ diffuses
Light-driven
Light drives H+ out of cell, H+ gradient is harvested to make ATP
Coupled transport
Gradient of one molecule is used to transport another molecule; maintained indirectly by ATP
Endocytosis
A type of active transport that moves particles, such as large molecules, parts of cells, and whole cells, into a cell
Phagocytosis
“Cell eating”
Process by which a cell engulfs large particles via invagination
Pinocytosis
“Cell drinking”
Process by which a cell takes in molecules, including water, from extracellular fluid
Receptor-mediated endocytosis
Variation of endocytosis that involves using specific binding proteins in the plasma membrane for specific molecules/particles (e.g. hormones)
Exocytosis
Process of passing bulk material out of a cell
- Vesicles fuse with membrane, releasing contents
