Exam 2 Flashcards
What are a couple of tools cells use for movement?
Shape change
Flagella
What are the functions of the membrane?
Define boundaries
Selective barriers
Cell signaling
What is meant by “dynamic” when we talk about the membrane
It has complex patterns of internal movement and organelles move within it.
What are the major lipid bilayer components
Amphipatic lipids
Proteins
Carbohydrates
How much of membrane does each component make up?
Phospholipids - 50 to 90% Sterols - 2-25% Glycolipids - less than 5% Proteins -20 to 80% Carbohydrates - none. They are outside membrane.
What are the four polar heads of major lipids? Which one is charged?
Phosphatidylethanolamine
Phosphatidyl serine - charged
Phosphatidyl choline
Sphingomyelin - a sphingosine derivative
Is there an example to the exception to the lipid bilayer?
Lipid mono layers are seen in archea, extremophiles. Made up of bipolar molecules with a fatty acid in the middle. Laid next to each other vertically with polar side on each end.
What force drives the shape of the lipid bilayer?
Hydrophobic forces
Van der waals forces
What lipid is only found in eukaryotes?
Sterols
What is the function of lipids and carbs in the lipid bilayer?
Help protect plasma membrane
Cell to cell signaling
How can one change the fluidity of a membrane?
Change fatty acid length
Change fatty acid saturation/desaturation
How is a membranes fluidity helpful?
Allows cells to fit surroundings
Prevents membrane from becoming leaky
How can we chemically control a membranes fluidity
Fatty acyl desaturated help lipids become desaturated. Fatty acid reductases help fatty ticks become more saturated.
What are phospholipids made of
Glycerol, two fatty acids with a polar head
Are both fatty acids saturated in a phospholipid?
No. One is saturated. The other is unsaturated.
What phospholipid is important in signaling
Phosphatidyl inositol
Why do hydrophobic forces roll lipid into ball
More energetically favorable
How do we use synthetic vesicles
We use these liposomes for drug delivery. Sometimes used in aerosols. Liposomes are then endocytosed.
What is the structure of a sterol?
Four rigid rings, single polar hydroxyl group, short nonpolar hydrocarbon chain
What is the function of a sterol
Controls membrane fluidity. Cholesterol. Stick in between phospholipids in bilayer
What is attached to lipid in glycolipids
Sugars
What kind of fluid is the lipid bilayer
Two dimensional
What can change fluidity of lipid bilayer?
Temperature
Chemical composition
If something is fluid at a low temperature, is it saturated or desaturated?
It is less saturated
How does organism adjust to temperature change?
Change fluidity of membrane
Control total cholesterol
How does one change fluidity of membrane?
Use desaturated to desaturated the membranes in order to get more fluidity
Which bacteria I’ll be the most fluid at low temps
Those with shorter tails
What happens to fluidity if cholesterol increases?
It decreases
What kind of bond exists phospholipid and cholesterol on lipid membrane
Hydrogen bond
What technique is used to measure membrane fluidity
Fluorescence recovery after photo bleaching
three steps of FRAP
- Label membrane with fluorophore
- Bleach label with laser in small area of cell. Destroy label, not membrane,
- Monitor recovery of signal. This will show how quickly diffusion happens.
Why are lipid bilayers asymmetrical?
Leaflets are different, have different chemical compositions
Why are lipid bilayers asymmetrical
So cell knows which way is up and down
How is membrane generated and maintained
1-new membrane made in ER
2-proteins inserted in lipid bilayer with specific orientation
3-glycolipids and glycoproteins are made/modified in Golgi apparatus
What are flip passes in ER
Transfer p-lipid from Cytosolic side to external side of bilayer
How is new membrane sent out of ER
Vesicles
What happens if a protein is inserted backwards
It may not work
In Golgi, what do sugars never face?
The cytosol
Four purposes of proteins
Transporters
Anchors
Receptors
Enzymes
Two types of membrane proteins
Peripheral
Integral
Peripheral protein
Loosely associated
Noncovalent interaction with integral protein or lipid
Integral protein
Transmembrane domain containing protein - usually has one or more hydrophobic or amphipatic alpha helix or beta barrels
Lipid linked protein
What is orientation of alpha helix? How many subunits doe it have?
Vertical
One
Multi pass
More than one subunit threading through PM, and will have both hydrophobic and hydrophilic parts. Side chains are hydrophobic. Are often transporters.
Beta barrels
Form huge holes in membrane. Are always open. Undergo no conformation change.
Porins
Beta barrels. Found outside mitochondria and chloroplasts. Static. No large scale conformation change.
Lipid linked protein
Post translational modifications Palmitoylation Prenylation Protein is anchored to bilayer even though amino acids do interact Lipid linkages allow for fast diffusion
Palmitoylation
Covalent attachment of fatty acid
Prenylation
Addition of hydrophobic molecule to protein or chemical compound
How does one study integral membrane proteins
Add detergent to solubilize protein (SDS, triton, etc.)
Purify
Slowly add back
Phospholipids–>liposome–>study
SDS
Strong a ionic detergents
Why difficult to study integral protein
Nonpolar
Highly insoluble, hard to purify, hard to study
Book method to study integral proteins
- Integral membrane protein in sample
- Add detergent micelles and monomers
- Solubilize membrane proteins
- Add lipid-detergent micelles
- Purify protein
- Add phospholipids to remove detergent
- Protein incorporated into phospholipid vesicle
Oleate
Fatty acid with one kink
Stearate
Saturated fatty acid
What are cell solutions for having a weak lipid bilayer?
Cell cortex
Glycocalyx
Cell walls
Tight junctions
Cell cortex
Inside plasma membrane
A network of mesh like proteins
Spectrin, actin linked to transmembrane anchor proteins (reinforce)
Glycocalyx
Carb layer On outside of PM Protective layer in animal cells Like a loose cell wall Importsnt for cell cell attachment
Where do we find cell walls
Fungi, plants, bacteria
How do neutrophils slow down in veins
Lectins recognize their carb layers, bind to them, and slow them down so they can exit veins
What would happen if there were no tight junctions
Proteins would end up on any side of the cell
Why is fluid mosaic model flawed
Cells in tissues have domains on plasma membranes. Protein movement is restricted to specific sides of cells
What does cell polarity mean
They have a top, bottom,left, right, front and back
How is protein movement restricted (3)
Cell cortex
Extracellular matrix
Proteins on adjacent cells
Apical vs basolateral
Apical faces lumen. Basolateral is bottom
How so do we track protein movement
Fluorescence
What are micro domains
Lipid rafts
What are lipid rafts
SDS resistant Aggregates of p lipids Cholesterol rich End up in pellets if you centrifuge cell contents Involved in signaling
What can cross bilayer freely
Small, nonpolar molecules
Steroid hormones
Small noncharged polar molecules
What can’t cross protein membrane freely
Large polar molecules
Anything larger than glucose
Anything with a net charge
Any macromolecule
Transporter
Carrier protein Very specific Precise binding sites Transport one or few at a time Does active or passive transport
Uniport
One type of solute, with conformational change
Channel protein
Not necessarily specific
Transports many molecules at a time
Usually for ions
What is diffusion
Moving from an area of high concentration to an area of low concentration of solute
What are the two types of transport across cells
Passive
Active
What is passive transport
Gradient dependent. No energy used.
What is active transport
Energy dependent. Goes against gradient often.
Types of passive transport (3)
Simple diffusion
Channel mediated
Transporter mediated
Three types of active transport
Use ATP
Use light
Coupled transporter
Two types of coupled transporters
Symport
Antiport
What are the types of ATP driven pumps 4
P-type
ABC transporter
V-type proton pump
F-type ATP synthase
P-type pumps 3
For ions
Multi pass
Phosphorylate themselves during pumping cycle
ABC transporter
Organic molecules (amino acids, sugars) Small molecules
v-type proton pump
Turbine like, made from different subunits, transfer H+ into organelles (lysosomes, vesicles, vacuoles) (acidity interior)
F-type ATP synthase
Use proton gradient across membrane t o drive synthesis of ATP and phosphate. Bacteria, PM, mito, chloroplasts.
Types of ABC transporters
Bacterial
Eukaryotic
How do abc transporters for bacteria work
Both import and export
How do abc transporters for eukaryotes work
Mostly export
- cytosol to extracellular space
- cytosol to membrane bound intracellular compartment
- mito to cytosol
What are the forces affecting transport
Concentration gradient
Membrane potential
What potential does plasma membrane have
Negative
Uniporter
Carrier protein that transports a single solute from one side of the membrane to the other
Occluded
Closed on both sides
Electrochemical gradient for animals-key players
Na+K+ATPase channels -3Na+ out -2K+ in K+ leak channels -voltage gated -an electrical force exerted by an excess of negative charges attracting K+ into the cell balances tendency of K+ to leak down its concentration gradient
What are the concentrations of sodium and potassium outside and inside the animal cell?
Sodium -outside-150 mM -inside- 10 mM Potassium -outside- 10 mM -inside- 150 mM
What is glucose/sodium coupled transport
Binding of glucose and sodium ion is cooperative
Most likely to happen extracellularly because of sodium concentration
Occluded only when bound
Transporter opens randomly in and out
If sodium dissociates, glucose cooperatively dissociates
How does glucose travel through intestinal epithelial cell
Apical membrane has coupled glucose/Na+ transporter bringing glucose into cell against concentration gradient
Low glucose concentration outside both sides of cell. High inside.
On basal membrane, passive Uniporter of glucose
What helps set up electrochemical gradient in plant and bacteria
V-type pump
-ATP to ADP
H+ out
Hydrogen/nutrient symport
Electrochemical differences between animals and plant cells on cell membrane and cytosol?
Cyrosol
Animal cell: H+ATPase into lysosome
Plant cell: H+ATPase into vacuole
Cell membrane
Animal cell: Na+K+ATPase, Na+ driven glucose symport
Plant cell: H+ATPase, H+ driven transport
How is osmoregulation a role of active transport?
Creates osmosis- movement of h2o across membrane
-h2o flows from [low solute] to [high solute]
Hypotonic solution
Low solute
What are the mechanics of secretions
Ions out into lumen of duct, and water follows
How is aquaporin lined?
One face of pore is lined with hydrophilic amino acids
Gram positive bacteria
Bacteria with single membrane
Gram negative bacteria
Bacteria with double membrane
Keep mucus runny
There are Cl- channels on membranes as well as water pores. Cl leaves through channels, Na leaves, and water follows.
Cystic fibrosis mechanics
Cl channels are blocked so ions can’t leave cell, and water can’t follow. Buildup outside of junk and microbes because there is no mucus to wash it away.
Cholera mechanics
Cholera toxin binds with adenylate Cyclase
Stimulates cAMP production
Camp binds with Cl channels and allows Cl- ions out. Water follows and causes dehydration.
Treatment of dehydration
Imbibe glucose, sodium and potassium so that water will follow it into tissues
What is facilitated diffusion
Uses proteins, is gradient driven
How do ABC transporters cause chemotherapy drug resistance in tumors
P-glycoprotein normally involved in excretion of toxins from cells. Overexpressed at baseline in chemotherapy-resistant tumors. Is upregulates after disease progression following chemotherapy in malignancies like leukemia and cancer.
PH in mito
Inside matrix 8
Intermembrane space 7
What is potential in mito matrix
Negative
What is potential in intermembrane space
There is no potential, just like in cytosol, because the outer membrane is porous and protons enter and leave at will
Where is ETC located
Inner mito membrane
How do protons travel though ETC
Exit through active transport
Proton motive force
Force through electrochemical gradient that drives protons back into mito matrix via thermogenins
Thermogenins
Uncoupling protein. Generates heat.
Uncoupling
Bypassing ATP synthase
How do ion channels select
On size and charge of atom
What is K+ bacterial channel made up of?
Vestibule, selectivity filter and pore helices
How does potassium travel through channel
k+ ions go into vestibule attached to h2o.ed into selectivity filter by pore helices. Carbonyl oxygens along wall of filter bind transiently to dehydrated K+ ions.
What is dipole of alpha helix
N terminal more positive
c terminal more negative
How do ion channels open or close
Conformation changes through stimuli
Four different ways ions are gated
Voltage gated Ligand gated (extracellular) Ligand gated (intracellular) Mechanically gated
How are auditory hair cells gated
Mechanically. Sound waves cause stereocilia to tilt, opening channel and allowing ions from fluid in. Cilia are connected to each other by filaments which stretch when sound waves come through, tilting them.
Five key players in nerve signaling
Sodium electrochemical gradient at PM Calcium gradient Neurotransmitter receptors Voltage gated ion channels Synaptic vesicles at termini
What is membrane potential due to potassium and sodium pump?
-80/-90 mV
Where are neurotransmitter receptors
On dendrites and cell body
Teo types of voltage gated ion channels on neuron
Sodium ion channels that line dendrites/body/axon
Calcium ion channels at termini
What do synaptic vesicles at termini carry
Neurotransmitters
What are neurotransmitters
Small, organic molecules
What are the three states of voltage gated sodium ion channels? When do they happen?
Closed. Membrane is polarized at rest.
Open, membrane depolarized by stimulus
Deactivated, as membrane repolarizes after stimulus
How do sodium ion channels work
Two transmembrane alpha helices surround pore. Separated by sequences that form selectivity filter.
Four addnl alpha helices make up voltage sensor.
S4 helices have Arline, positive. An inactivation gate that is part of flexible loop connecting third and fourth domain acts as plug that obstruct us pore in channels inactivated state. Membrane refractory period.
Key steps in neuro transmission 3
- Neurotransmitter binds to ligand gated ion channel and causes some depolarization
- Adjacent voltage gated sodium ion channels open, causing more depolarization, which leads to action potential or nerve impulse.
- Voltage gated calcium ion channels ole
Patch current recording
Records current flowing through individual channels
In small patch of membrane covering mouth of micro pipette
Tight seal bet. Pipette and membrane.
Current can enter or leave pipette only by passion through ion channel. Either attached or detached from membrane.
