CELL 201: Lecture 7 - Transport across membranes

What are the THREE MECHANISMS involved in moving solutes across membranes?

1. Simple Diffusion

2. Facilitated transport

3. active transport

Which of the 3 mechanisms require input of E?

Active transport

****What things can cross the membrane via Simple Diffusion? (3 categories)

Gases, Non-polar molecules or small polar molecules

eg. oxygen + red blood cells + lungs

***What are some small polar molecules that can pass via Simple Diffusion?

Water, glycerol  or Ethanol

Fill in the blank: Diffusion creates a _____ _____ (concentration is the same everywhere), Thus, diffusion is always the movement towards _______.

Creates a RANDOM SOLUTION (via random movement)

Thus = always moving towards EQUILIBRIUM

****If the rate of simple diffusion is graphed against [ ] gradient, What type of line would you get and WHY?

LINEAR

• RATE of diffusion = proportional to the concentration gradient

• Higher the difference in concentrations = the faster the rate of diffusion

****Define Osmosis

the movement of water across a SEMIPERMEABLE membrane

• solutes cannot move

• water will move in the direction of higher solute concentration

Compare Hypertonic vs. Isotonic vs. Hypotonic and the result of the cell

Hypertonic = solution high in solutes = cell SHRIVEL

Isotonic = Equal = no change

Hypotonic = Solution low in solutes = cell LYSE

What is Facilitated diffusion. Compare it to Simple diffusion. Does it require energy?

Protein mediated movement down the concentration gradient

• No E required, Exergonic

Just like simple diffusion except need a TRANSPORT PROTEIN to assist in the movement of substances TOO LARGE or POLAR across membrane

****If the rate of Facilitated diffusion is graphed against [ ] gradient, What type of line would you get and WHY?

HYPERBOLIC

• Saturation kinetics

  • transport proteins can become saturated as concentrations rise

***What are the 2 TYPES of TRANSPORT PROTEINS associated with facilitated diffusion?

1. Channel

2. Carrier

What is the main difference between Channel + Carrier transport proteins?

Channel = FREE FLOW of substances

CARRIER = SPECIFIC number of solutes transported

Are Channels or carrier proteins FASTER at moving solutes?

Channels bc free flow

****What are the 3 TYPES OF CHANNELs (facilitated diffusion)

1. Porins

2. Aquaporins

3. Ion channels

TRUE or FALSE: Ion channels are NOT selective

FALSE

• Highly selective (most allow passage on just one type of Ion)

****What 2 things are the selectivity of ION channels based on?

1. Amino acid side chain lining the hydrophilic channel

2. Size

***What are the 3 types of GATED ion channels?

1. Ligand gated

2. Voltage gated

3. Mechanosensitive gated (respond to mechanical forces acting on membrane)

What are some Functions of ION channels

• Cellular communication

• Muscle

• Electrical signaling

• Maintaining homeostasis

****What protein structures are ION channels made of?

multiple ALPHA-HELICES (multipass)

****What is CFTR + what role does it play?

Chloride Ion Channel = needed for maintaining salt balance in cells + airways within the lungs

• mutation in channel gene = cystic fibrosis

***What are Porins?

Transmembrane Proteins that allow rapid passage of various solutes (type of CHANNEL)

How do Porins DIFFER from ION CHANNELS?

they are LARGER + LESS SPECIFIC

****WHERE are Porins located (3 places)

Outer membrane of bacteria

Mitochondria

Chloroplast

****What protein structures are PORINS made of?

BETA-BARRELS

*****Between ION channels + PORINS which can be seen of a Hydropathy analysis + which cannot + WHY?

ION channels = can

• Hydrophobic aa = grouped together to form hydrophobic passes of the alpha-helix = PEAKS

Porins = CANNOT

• due to trans nature of polypep + shape of Beta barrel, Hydrophobic + phillic aa = ALTERNATE = average remains the same = NO PEAKS to indicate hydrophobicity

Finish the sentence: CARRIER PROTEINS alternate between ____ CONFORMATIONAL states

TWO conformational states

HOW are carrier proteins similar to ENZYMES

1. Specificity = specific solute binding site

2. Kinetics = Can be saturated

Fill in the Blank: Carrier protein for glucose in RBC = is ____ to a few monosacch. and is _____ for ONLY their D-Isomer

SPECIFIC to a few monosacch. and is STEREOSPECIFIC for only the D-isomer

****Can competitive inhibition occur with carrier proteins like with enzymes?

Yes

****WHEN does competitive inhibition of Carrier proteins occur?

in the presence of molecule or ions that are structurally related to the correct substrate

• eg. glucose carrier may be receptive of galactose, or mannose

****What are the 2 TYPES of Carrier Proteins (based on # of types of solute it transports)

1. Uniport

2. Coupled transport

***What is an example of a UNIPORT?

Glucose transporters

***How many different types of glucose transporters do we have?

14

• tissue specific

How many transmembrane segments do glucose transporters have?

12

****HOW does GLUT TRANSPORT WORK? How does the rate of transport reflect the concentration gradient?

****How do we make diffusion of Glucose more efficient into the cell. HOW DO WE OVERCOME THE CONCETRATION GRADIENT to get more glucose into the cell?

Phosphorylation of Glucose —> G6P

****What enzymes Catalyzes the Phosphorylation of Glucose?

Hexokinase using ATP

****HOW does the Phosphorylation of glucose allow for more glucose to diffuse into the cell than the [ ] gradient would allow?

G6P = cannot bind to carrier protein any more to be transported out + G6P =/= glucose

• thus the net [glucose] always = ZERO inside the cell

****What are the 2 TYPES of Coupled transporters (Carrier Protein of Facilitated diffusion)

1. Symport

2. Antiport

What is an example of an Antiport carrier?

RBC Anion exchange protein

• reciprocal exchange of Cl- + HCO3- only

***In what ratio does the Anion Exchange protein exchange ions in?

STRICT 1:1 ratio

****How is this strict 1:1 ratio achieved?

Reorientation require the binding of the opposite ion

• exchange will strop if either anion is absent

*****What exchange Mechanism does the Anion exchange (antiport) use?

Ping pong

• Both ion (players) must be present

• Binding = conformational change + flip to other side

****ACTIVE TRANSPORT is Protein mediated movement ____ the gradient

UP/AGAINST/ away from equilibrium

• Requires E aka.

*****Where does ACTIVE transport get its energy?

Couples an Endergonic transport to an EXERGONIC PROCESS

****Which EXERGONIC process is normally used to power Active transport?

ATP HYDROLYSIS

****What 3 IMPORTANT FUNCTIONS does ACTIVE transport perform?

1. Uptake of essential nutrients

2. Removal of Waste

3. Maintenance of NONEQUILIBRIUM CONCENTRATIONS

• Maintain gradient needed for simple diffusion + facilitated diffusion

*****HOW does Active transport differ from both types of diffusion in terms of DIRECTION of TRANSPORT?

Active transport = UNIDIRECTIONAL

• diffusion: Direction = determined by concentration

****What are the 2TYPES of active transport + how are they divided (what criteria)?

1. Direct

2. Indirect

divided based on SOURCE OF E + whether or not the 2 solutes are transporter at the same TIME

***Compare Direct Vs. Indirect transport. What is the Difference?

Direct = use ATP or Exergonic rxn to power transport (a) ATP hydrolysis

Indirect = NOTE POWERED BY ATP hydrolysis. Uses the Gradient of another solute to power transport. Gradient = norm set up by direct transport (b)

****What solutes are involved in INDIRECT Active transport for EUKARYOTES vs. Plant, fungi + bacteria?

Eukaryotes = Na+

Plant, fungi, bacteria = H+ (protons)

***Are indirect transporters ANITPORT or SYMPORTERS?

can be BOTH

**********What are the 4 TYPES of transport ATPases that DIRECT active transport depends on?

1. p - Type (phosphorylation)

2. V-type (Vacuolar')

3. F-Type (ATP synthase)

4. ABC-type (ATP Binding Cassette)

******What is an EXAMPLE of the P-types?

Na+/K+ ATPase

• regulated by PHOSPHORYLATION of ATP

****What Are the STEPS of Na+/K+ pump? (6) How many of each ion go where (in or Out)

• 3 Na+ out

• 2 K+ in

****What does the phosphorylation of ATP on the NA/K pump?

KINASE

***In which LOCATIONS are F + V type ATPases normally found?

• Bacteria

• Mitochondria

• Chloroplasts

Are V types + F types similar in structure?

yes

*****What are the 2 COMPONENTS that make up F type ATPases?

1. Transmembrane pore

2. Peripheral membrane component

****Which of the 2 components correspond to F0 and which correspond to F1?

Transmembrane pore = F0

Peripheral membrane component = F1

****Which of the 2 Components of F-type contains the ATP BINDING SITE?

F1: Peripheral membrane component

****What is the main function of F-type ATPase?

Pump PROTONS = build H+ Gradient

****True or false: The F-Type ATPase can also function in reverse?

True

******Differ the events related to the Forward + Reverse functions of the F-type ATPase.

Forward = Using ATP hydrolysis (direct synthesis) to generate a PROTON GRADIENT

Reverse = using PROTON GRADIENT to make ATP

****What is the more accurate term to describe the REVERSE function of ATPases?

ATP SYNTHASE

• ADP + Pi = ATP

What important principle does F-type ATPase illustrate?

Not only can ATP be used as an E source to generate gradients, but the gradients generated can be used a s an energy source the SYNTH ATP

****How do ABC transporters/ATPases work?

Move substrates in + out of Cells via ATP hydrolysis

****How do ABC transporters differ from F or V-Type?

F + V type are purely used in relation to PROTON gradients

ABC = used for all types of solutes (eg. drugs, sugar, ions etc.)

*****Which of the 4 DIRECT Active transporters are MEDICALLY IMPORTANT? Why?

ABC transporters

• Some pump antibiotics or drugs Out of cells = Cell RESISTANT to the drug

*****How are some HUMAN TUMORS resistant to drugs?

High concentration of ABC transporters called MDR

• pumps drugs out of cell = resistant to drugs

What does MDR stand for?

Multi-Drug Resistant Transport proteins

• eg. cancer

*****What is Bacteriorhodopsin? Which organism is it located in? + What does it do? What new field is it being researched in?

Small integral membrane protein inside ARCHAEA that uses PHOTONS to drive the active transport of PROTONS creating a gradient to POWER ATP SYNTHASE instead of a proton pump

• researched in the fired of biomolecular electronics (can generate charge gradient)

****How does Bacteriorhodopsin work? What molecule is in it that allows the transport of protons?

RETINAL

• when light hits retinal = conformational change = allow protons to flow through + create gradient to power ATP synthase