Unit 4: Cell Membrane

plasma (cell) membrane

the semipermeable membrane surrounding the cytoplasm of a cell

• defines the boundary of a cell and determines what gets in/out of the cell

• contains integral and peripheral proteins (determine membrane function)

cholesterol

can also help regulate spacing, & stabilize the membrane during high temperature exposure

osmosis

diffusion of water

• movement of water through a selectively permeable membrane

active transport

requires energy, low → high concentration

• Counteracts diffusion

• Uses energy (ATP) and a protein channel to pump proteins from low to high concentration

ATP

• is a molecule our cells use to provide energy.

  • Special type of nucleotide that’s an energy molecule

  • —-: Adenine + ribose sugar + triphosphate = energy released for cell + loss of a phosphate 

  • —-: adenine + ribose sugar + diphosphate = energy absorbed from food + addition of a phosphate 

hypotonic

 the extracellular fluid has a lower concentration of solutes than the fluid inside the cell and water will enter the cell

• The extracellular fluid has a higher concentration of water than the cell

• Water will follow its concentration gradient and enter the cell which could cause it to burst (lyse)

isotonic

extracellular fluid has the same osmolarity of the cell

• If the concentration of solutes in the cells matches the extracellular fluid then there will be no net movement of water

hypertonic

the extracellular fluid contains less water than the cell does with a lower concentration of solutes and water will exit the cell

• The solute is drawing water out of the cell

• May cause a cell to shrivel (crenate)   

concentration gradient

the movement of molecules from where they are more concentrated to where they are less concentrated, which continues on and on until there is an equal number of molecules on either side

exocytosis

process by which bulky molecules are transported (such as polysaccharides)

• In the cell this process involves:

  • The transport vesicle leaves the golgi apparatus

  • Vesicle moves to the plasma membrane

  • Fuses with the plasma membrane

  • Contents the vesicle was carrying are spilled in/become one with the plasma membrane 

endocytosis

the process by which a cell takes in large molecules (opposite of exocytosis) 

• In the cell this process involves:

  • the plasma membrane depressions pinch in to form a material that will close in around the vesicle of a cell

phospholipid bilayer

• Phospholipids made in the smooth ER

• Phospholipids self-assemble into a bilayer

  •   Hydrophobic tails inward

  • Hydrophilic heads outward

• Exposed tails bend until all hydrophobic portions are protected, creating a sphere

• Phospholipids help keep the membrane fluid which is essential for 

          it to work properly in different environments

channel proteins

a protein that allows the transport of specific substances across the cell membrane

• provide a hydrophilic bridge across a hydrophobic core

glycoproteins

proteins that have a carbohydrate groups attached to the polypeptide chain

receptors

has a binding site that allows communication between the environment outside the cell (hormones) and inside the cell

diffusion

• when particles spread out evenly in a space creating an equilibrium (a result of thermal energy from molecules vibrating and randomly moving)

solute

a substance that dissolves in a solvent

solvent

a liquid a solute dissolves in

substance

a mixture of a solute and solvent (transparent)

simple diffusion

diffusion without a helper protein

facilitated diffusion

diffusion using a helper protein

passive transport

does not require energy, high → low concentration

• diffusion

• osmosis

equilibrium

when things are balanced (opposing balances are balanced)

turgid

swollen (hypotonic)

flaccid

drooping from lack of water (isotonic)

aquaporin

integral membrane proteins (reside within the bilayer membranes that surround cells and organelles) that serve as channels in the transfer of water and sometimes in small solutes across the membrane

semipermeable

allowing certain substances to pass through it but not others, especially allowing the passage of a solvent but not of certain solutes

vesicle

bubble-like membrane structures that stores and transports cellular products and digest metabolic wastes within the cell

cytosol

the component (usually containing water typically as a solvent) of the cytoplasm of a cell, within which various organelles and particles are suspended

fluid mosaic

• part of the membrane is a thicker sort of liquid (compared to oil) that holds components that can float around, kinks are produced by some phospholipids

• when the double bond in unsaturated fatty acid tails of the phospholipids prevents them from packing too tight together

• Steroid cholesterol, found in animal membrane cells, has the ability to keep the membrane warm but the “fluid” cooler

• “mosaic” aspect comes from the diverse types of proteins that different types of cells have or the diverse range of jobs that proteins can have

• a “mosaic” is the protein diversity coming together to help complex organisms such as ourselves function.

concentration

the quantity of solute that is dissolved in a certain quantity of solvent in a solution

• concentration solution = has a large mass of solute in a certain quality of solvent

dilution

the process of adding a solvent to a solution to reduce the concentration of the solute

• dilute solution = has a small mass of solute in a certain quantity of solvent

paramecium

• freshwater protist

  • Solution inside has a higher concentration of solutes (hypotonic)

  • Exocytosis (release water so it doesn’t explode, requires energy)

  • Contractile vacuole + radiating canals

cytolysis/lysis

the bursting or rupturing of cell membrane when the cell can no longer contain the excessive inflow of water (or extracellular fluid)

proton pump

a special kind of transporter that pushes hydrogen ions from areas of low concentration to areas with high concentration

• ions moving down release energy and vice versa

bulk transport

exocytosis and endocytosis

plasmolysis

contraction/shrinkage due to water loss (hypertonic)

osmoregulation

the process in which cells and simple organisms maintain fluid and electrolyte balance with their surroundings

soluable

a substance that is able to dissolve in a certain solovent

insoluable

a material that is unable to dissolve in a certain solvent

selectively permeable

 is that only substances can pass through while others struggle to get through the membrane

• Ex. would be essential ions and molecules that need proteins to transport them to allow them to enter or exit the cell

permeable

 it must allow liquids or gasses to pass through it

• more specifically refers to a passage of molecules through a membrane or any other barrier molecules may encounter in a cell

concentration gradient

is the movement of molecules from where they are more concentrated to where they are less concentrated, which continues on and on until there is an equal number of molecules on either side

• when a molecule moves “down” it is referring to the molecules moving to a place with fewer molecules (less concentration) from a place with more concentration

tonic

amount of solute in a solution