Membrane structure

Phospholipid structure

contains 2 fatty acid tails linked to a glycerol, a phosphate group and a compound such as choline

Tails of phospholipids

hydrophobic and non-polar

repelled by water

face interior of membrane

Heads of phospholipids

hydrophilic and polar

outside of cell

Formation of bilayer

forms spontaneously

non-polar fatty acids collect together

polar heads face water

Effect of temperature on bilayer

if temperatures are too low, lipid molecules become too tightly packed forming a semisolid gel

more unsaturated fatty acids=lower temperature

Sterols

act as membrane stabilizers

restrain movement of lipid molecules in membrane at high temperatures

ex. cholesterol

Fluid Mosaic Model

The idea that a biological membrane consists of a fluid phospholipid layer, in which proteins are embedded and float freely

Plasma Membrane

Outer cell membrane

Selective transport channel

a specific compound passing through a hydrophilic channel

protein can shape shift to allow molecules to move from in and out of the cell

Enzyme proteins

accelerate reactions in cells

Cell surface receptor protein

 Signalling molecule binds to receptor site on extracellular surface. This causes a reaction to occur inside the cell

Cell surface identity marker

carbohydrates attached proteins (glycoproteins) act like an ID card/fingerprint, allowing cells to recognize each other and interact appropriately.

Cell adhesion proteins

Proteins adhere together, allowing cells to stick together to form tissues.

Attachment to cytoskeleton proteins

Proteins attach to microtubules/microfilaments, anchoring and stabilizing the membrane’s shape and structure. 

Passive cell transport

the movement of a substance across a membrane without expending energy

driven by diffusion

Simple diffusion

the ability of substances to move across a membrane unassissted

Facilitated diffusion

facilitated transport of ions and polar molecules through a membrane via protein complexes

continues until equilibrium is reached

Channel proteins

form hydrophilic channels that water and certain ions can pass through

controlled by gates

Carrier proteins

binds to a specific solute and transports across bilayer

driven by diffusion

selective

osmosis

passive diffusion of H2O across a membrane

diffuses from low to high solute concentration

hypotonic solution

solution surrounding cell has a lower solute concentration than inside the cell

water enters the cell and swells cell

hypertonic

solution surrounding cell has a higher solute concentration than inside the cell

water moves from inside to outside of cell

cell shrinks

isotonic solution

concentration in and out of the cell is equal

no net osmosis

Active transport

the movement of substances across membranes against their concentration gradient using pumps

uses energy

Primary active transport

move positively charged ions across membrane

Secondary active transport

uses concentration gradient of ion, established by primary transport as it’s energy source

Symport transport

solute moves through membrane channel in same direction as driving ion

Antiport transport

driving ion moves through membrane channel in one direction, providing energy for active transport molecule in opposite direction

metabolism

the sum of all chemical reactions in a cell or organism

kinetic energy

the energy of motion

potential energy

the stored energy that an object possess as a result of its position relative to other objects or to its internal structure

First law of Thermodynamics

energy can be transferred or transformed but it cannot be created or destroyed

Second law of thermodynamics

every time energy is converted to another form, some of the energy becomes unusable and increases the entropy of the universe

entropy

a measurement of disorder in a system

mole

standard quantity: 6.02×10²³

activation energy

minimum amount of energy needed to start a reaction

transition state

a temporary condition during a reaction where bonds in reactants are breaking and bonds in products are forming

catabolic pathway

a pathway in which energy is released and complex molecules are broken down to simple molecules

anabolic pathway

a pathway in which energy is supplied to build complex molecules from simple molecules