Topic 4,5 bio 1020

plasma membrane

plasma membrane

• selectively permeable

• regulates what can pass through

what is the plasma membrane composed of

composition of phospholipids, other lipids such as cholesterol, and associated proteins

• all components are able to move around within the membrane

how are phospholipids amphipathic

• polar heads face the outside of the membrane and interact with water

• non polar fatty acid tails are hydrophobic and turn inwards to form the lipid bilayer

• interactions are hydrophobic, which are weaker than covalent bonds

what way do lipids move

laterally

what way do proteins move

laterally

how do hydrophobic lipid tails move

they wiggle as the C-C bonds rotate

• more heat = more movement

amphipathic

having both a hydrophilic and hydrophobic region

what happens when the membrane fluidity is too slow

permeability changes, proteins embedded in membrane do not work

what happens when the membrane fluidity is too fast

not enough membrane organization to function properly

membrane fluidity is affected by…

• temperature of the membrane

  • cooler temps result in closer packing of lipids, resulting in a solid membrane (bacon fat)

• saturated vs unsaturated hydrophobic tails of phospholipids

  • more kinks in the tails space the fats out, keeping it more fluid than saturated tails

• presence of cholesterol

  • acts as a buffer to fluidity changes in membrane

  • at higher temps, restricts the movement/spacing of phospholipids

  • hinders the close packing of phospholipids, so lower temp of the membrane solidification

integral membrane proteins

first main type of protein suspended in the membrane

they penetrate the hydrophobic interior of the lipid layer

• transmembrane proteins go all the way through

• other proteins only go partially through

• integrins ¾ throgh

peripheral proteins

second main type of protein suspended in the membrane

they are associated with only a single side of the membrane

in eukaryotes, what do membrane proteins usually consist of

• non polar alpha helices (20-30 amino acids in length)

• proteins associated with the plasma membrane are held in place by fibres

  • on the cytoplasm side, held by the cytoskeleton

  • on the extracellular side, held by ECM fibres

how do proteins get to the plasma membrane

stitched into the membrane of RER as soon as they are translated and transported via vesicles in the EM system to the plasma membrane

RER→vesicles→golgi apparatus→vesicles→membrane

functions of membrane proteins 1-3

1. transport - selectively allows substances through

2. enzymatic activity - assists in reactions that occur around the plasma membrane

3. signal transduction - proteins have a binding site that accepts specific chemical substances (such as hormones)

functions of membrane proteins 4-6

4. cell-cell recognition - glycoproteins and glycolipids can be specific in different cell types, serve as ID tags (how blood types work)

5. intercellular joining - hook together to join adjacent cells (tight junctions)

6. attachment to cytoskeleton/ECM - non covalently bonds to microfilaments, which maintains cell shape and stabilizes the position of membrane proteins

what does HIV rely on

the receptor protein CD4 on the immune cells

how does HIV infect the cell

it needs to bind with a protein called CCR5 which is a co-receptor protein

how are people HIV resistant

some individuals have a mutation in the gene that codes for CCR5, resulting in a lack of the CCR5 protein on the plasma membrane of immune cells

which protein is essential for immune response in cells

CD4

aquaporin

channel protein that allows water to pass through the membrane - simple diffusion

what does the selectivity of the membrane depend on

the lipid bilayer being discriminatory, and on specific transport proteins that are in it

simple diffusion

movement from higher to lower concentrations straight through the lipid bilayer

passive transport - no energy

simple diffusion through a channel

movement from higher to lower concentrations through the pore of a membrane channel protein (aquaporin)

passive transport

facilitated diffusion

movement from higher to lower concentrations via a membrane carrier protein (facilitative transporter)…still diffusion (glucose transporter)

active transport

movement from low to high concentrations via a protein transporter. requires energy, which often comes from ATP hydrolysis

(against gradient)

diffusion

the movement of particles of any substance to evenly spread out within a space

• the movement of each individual molecule is random

• the movement of the population of molecules can be directional (high to low concentration)

passive transport

allows substances to pass through channel proteins without the use of energy - it just diffuses

osmosis

the diffusion of water across its concentration gradient

osmosis steps

• the selectively permeable membrane has pores that are too small for sugar but large enough for water

• some water molecules will cluster around the solute, making it unavailable. the leftover water not bound to sugar is the free water concentration

• since the sugar is too large to cross the membrane by diffusion, it is termed a non penetrating solution

what is the free water concentration

the left over water not bound to sugar - this is what diffuses

osmolarity

(osmotic concentration) of a solution is the number of osmoles of all solutes per liter of solution (Osm/L)

• the concentration of solutes per liter of solution

tonicity

the ability of the surrounding solution to cause a gain or loss of water within the cell

depends on the solute concentration that cannot cross the membrane relative to what is inside the cell

isotonic

iso=same, no net movement of free water across the plasma membrane

• our cells in our body are isotonic, as with sea water and marine invertebrate cells

hypertonic

hyper=more, concentration solutes is greater outside the cell

• cell loses water, shrivels and dies

hypotonic

hypo=less, concentration of solutes is greater inside the cell

• water enters the cell, and the cell will swell and burst (lyse)

osmoregulation

only for some animal cells

controls solute and water concentration within their cells

• paramecium(unicellular eukaryotes) live in freshwater, which is hypotonic to the cell

what do cell walls do

keeps plants (and fungi and bacteria) cells rigid

prevents a plant cell from exploding in hypotonic solutions

water is taken up, the central vacuole swells, exerting pressure on the cell wall

• turgor pressure results in a turgid cell

what happens when a plant cell becomes isotonic

the plant goes flaccid (wilted) due to reduced turgor

plasmolysis

when a plant cell loses water causing the plasma membrane to pull away from the cell wall, usually due to a hypertonic environment.

some substances need a carrier or channel to help them pass through the plasma membrane like…

ions, hydrophilic molecules, larges sugars, etc

the proteins involved are still selective → only certain kinds of molecules can be transported by certain kinds of proteins

• sugar proteins carry sugars through

what kind of proteins carry our facilitated diffusion

transmembrane

channel proteins

simple diffusion via a channel

• provides corridors or pores which specific substances can pass through while diffusing down the concentration gradient

  • ion channels

  • aquaporins

carrier proteins

first binds to the substance

then the protein changes shape, allowing the molecule to pass through

• glucose transporter

active transport uses energy to move solutes

moves solutes against their concentration gradient

• low to high concentration

• requires ATP due to thermodynamics

active transport uses what kind of proteins

only carrier proteins

what does active transport enable the cell to do

to regulate and maintain internal concentrations of select substances (sodium ions)

sodium potassium pump

protein pump that exchanges Na+ for K+ ions

• pumps out Na+ and in K+

• dominant pump in animals

membrane potential

membranes with a voltage

• ranges from -50 to -200mV

• negative means inside the cell is more negative relative to outside

chemical force

the ion’s concentration gradient

• higher concentration of an uncharged molecule on one side of the membrane is a store of energy due to entropy (thermodynamics)

electric force

effect of the membrane potential on the ion’s movement

electrical gradient

the combination of the store of energy due to entropy (chemical force) and the difference in charge across the membrane

active transport uses what kind of proteins

use energy of ATP hydrolysis to move H+ across the membrane against its concentration gradient

• an electronegative pump dominant in plants, fungi and bacteria

the stored energy can be used to bring in sucrose against its concentration gradient

sucrose H+ co transporter

allows H+ down its electrochemical gradient to re enter the cell at the same time as sucrose transport.

• called co transport or coupled transport

plasma osmolarity

is the tendency of blood plasma to attract water based on various floating substances

• NaCl

• Glucose

• Urea

• other ionic compounds

blood plasma

needs to restore a balance to equilibrium when stuff enters the blood, usually by pulling water to or from the red blood cells

tonicity relates to the

solution

osmolarity relates to the

effect of the membrane potential on the ion’s movement

chemical force

the ion’s concentration gradient

• higher concentration of an uncharged molecule on one side of the membrane is a store of energy due to entropy (thermodynamics)

electric force

effect of the membrane potential on the ion’s movement

electrical gradient

the combination of the store of energy due to entropy (chemical force) and the difference in charge across the membrane

anabolic pathways

consume energy to build (dehydration) complex molecules from simpler compounds

• ex amino acid synthesis

sucrose H+ co transporter

allows H+ down its electrochemical gradient to re enter the cell at the same time as sucrose transport.

• called co transport or coupled transport

energy

the capacity to cause change

kinetic energy

the energy associated with moving things

metabolism

the orderly interaction between molecules

• the sum of all the chemical energy that occurs within a living cell/tissue/organism

• uses or stores energy to do internal functions

metabolic pathway

use energy of ATP hydrolysis to move H+ across the membrane against its concentration gradient

• an electronegative pump dominant in plants, fungi and bacteria

the stored energy can be used to bring in sucrose against its concentration gradient

catabolic pathways

release energy by breaking down (hydrolysis) complex molecules into simpler compounds

• ex cellular respiration→ sugar and other molecules broken down to CO2 and water in the presence of oxygen

anabolic pathways

consume energy to build (dehydration) complex molecules from simpler compounds

• ex amino acid synthesis

advantages of multi step pathways

• multiple points to control how fast the reactions occur

• ability to divert pathway intermediates to other pathways to do other things

• changes to metabolism through evolution

free energy (G)

the amount of energy in the ‘system’

in a chemical reaction, the system changes

• free energy changes (delta G)

• the reactants have an initial free energy state (Gi)

• the products have a final free energy state (Gf)

• delta G = Gf-Gi

when the reactants have more free energy than the products:

delta G of the reaction is less than zero

• it took less energy to break the bonds in the reactants compared to the energy released when the bonds form the products

exergonic

energy releasing

• happens spontaneously

• doesn’t mean instantaneous

when the reactants have less free energy than the products:

potential energy that can be released during a chemical reaction

thermal energy

is kinetic energy associated with the movement of atoms/molecules

• generates heat

potential energy

energy that is not kinetic

• based on molecule’s location and structure

• due to arrangement of electrons around a bond between atoms

chemical energy

potential energy that can be released during a chemical reaction

1st law of thermodynamics

energy cannot be created nor destroyed

• energy can only be converted or transformed

• recall: mitochondria, chloroplasts convert energy

2nd law of thermodynamics

entropy (disorder) increases in isolated systems

• increase in entropy can cause a process to proceed spontaneously (no energy required)

• “energy transfer/transformation increase the entropy of the universe”

• energy transfers aren’t 100% efficient - some energy lost as heat

• need continuous input of energy to keep order in the system

catalyst

enzymes that speed up reactions

most enzymes are proteins

substrate

the reactant molecule

how do you lower the activation energy

enzymes burn the reactant molecules in such a way that they put stress on specific bonds of the reactant lowering the Ea, making those bonds easier to break.

do enzymes change the overall delta G of the reaction

no they speed up the rate of a specific reaction without being consumed themselves.

catalysis

a catalyst selectively speeds up a chemical reaction without being consumed

when an enzyme binds to the substrate, it becomes …

an enzyme substrate complex

endergonic

energy consuming

• doesn’t happen spontaneously (on its own)

• requires energy input to make it happen

all cells do 3 kinds of work

1. chemical work - pushing endergonic reactions (synthesis of polymers)

2. transport work - protein pumps

3. mechanical work - movement (beating cilia, contracting muscle cells)

enzymes are selective

they hold 2 substrates together, they initiate the transition state of the substrates through movement of the protein, provides micro environment in the active site for the reaction to occur, some amino acid groups participate in the reactions by binding the substrate and then releasing it.

more substrate equals

faster reaction (to a limit tho)

when is the enzyme saturated

when all available active sites in the reaction are full.

enzyme shape dictates

function- if it loses its shape it gets denatured (unfolded) and no longer works

increased temperature can ____ a reaction

speed up. until it denatured

normal binding

a substrate can bind normally to an active site of an enzyme- drugs and toxins work by inhibiting enzymes.

competitive inhibition

a competitive inhibitor molecule resembles the substrate and binds to the active site. means the actual substrate can’t bind. rate of reaction is slowed. ex-substrate inhibition

non competitive inhibition

the inhibitor molecule binds elsewhere on the enzyme changing the enzyme shape. active site cannot bind with the substrate ex-feedback inhibition

allosteric regulation

occurs in enzymes that work in complexes (have quaternary structure) where each subunit has an active site. changes shape between active and inactive states due to activators and inhibitors

allosteric activation

a regulatory molecule (not the substrate) binds to a regulatory site which stabilizes the active site

allosteric inactivation

a regulatory molecule (not the substrate) binds to a regulatory site which stabilizes the inactive site

cooperativity

when a substrate binds one unit, which stabilizes the active state on the other units