Transport Across Membranes

Front 1

Functions of Membranal Proteins

Back 1

transport
linking the membrane to the cytoskeleton
signalling molecules

Front 2

Glucose Transport Efficiency

Back 2

1/10,000th less efficient than water

Front 3

Chlorine Transport Efficiency

Back 3

1/1,000,000th less efficient than water

Front 4

Membrane Transport Mechanism

Back 4

1. diffusion
2. facilitated diffusion
3. primary active transport
4. secondary active transport

Front 5

Diffusion Flux

Back 5

proportional to the concentration gradient and the permeability

Front 6

Facilitated Diffusion

Back 6

- protein carriers or pores - passive, down a gradient
- across cell membranes only
- saturates
- competition
- maximum rate of transport: Tm

Front 7

Membrane Transport Proteins - I

Back 7

molecules: ions, sugars, amino acids, nucleotides, cell metabolites
specificity: very specific - large variety and diversity

Front 8

Two Classes of Transport Proteins I

Back 8

1. carrier proteins: bind and undergo conformational change - 100-1000 molecules/second
2. channel proteins: form aqueous pores in the bilayer - specific solutes - weak interaction but faster (10.000x)

Front 9

Cystinuria

Back 9

- inherited recessive autosomal defect - membrane protein that transports cysteine and dibasic from luminal fluid of proximal tubule
- kidney stones rich in cysteine often - can't dissolve in pH of urine - surgery required
- defective genes: SLC3A1 SLC7A9

Front 10

Membrane Transport Proteins - II

Back 10

multipass transmembrane proteins: transverses the membranes multiple times - enables specific hydrophilic solutes to cross without coming into contact with hydrophobic interior

Front 11

Two Classes of Transport Proteins II

Back 11

1. transmembrane channels: hydrophilic pores - regulate the flow by open and closing
2. transmembrane carrier proteins: permeases - larger molecules eg. glucose and amino acids. change conformation

Front 12

Ionophores

Back 12

- hydrophobic molecules - dissolve in lipid bilayer
- increase permeability to specific inorganic ions
- synthesized by microorganisms
- shield the charge, allowing crossing
- only passive

Front 13

Examples of Mobile Ion Carriers

Back 13

1. Valinomycin: cyclic peptide, K+ down gradient
2. FCCP: leaky to H+
3. A23187: divalent cations: Mg, Ca signalling pathways

Front 14

Examples of Channel Formers

Back 14

Gramicidin A: permeable to monovalent cations: H+, K+, Na+ down gradients

Front 15

Uses

Back 15

1. Lab research
2. Antibiotics
3. Growth enhances in cattle feed

Front 16

Determinants of Kinetics of Carriers

Back 16

1. rate at which is can flip conformational change
2. binding constant
3. Km = concentration of solute when transport rate is half maximal
4. competitive, non competitive inhibitors

Front 17

Carrier Proteins and Active Transport Mechanisms

Back 17

1. coupled carrier
2. ATP- driven pump
3. Light-driven pump

Front 18

Carrier Protein by Ion Gradient

Back 18

1. uniporter: single solute - determined by Vmax and Km
eg: passive glucose reabsorption kidney/gut - GLUTI-4

2. symporter/cotransporter: second solute in same direction.
eg: sodium glucose in kidney/gut utilizing sodium for glucose uptake - SGLT1-4

3. antiporter/exchanger: second solute in opposite direction
eg. sodium proton - utilizes sodium for deacidification - NHE1-4

Front 19

Advantages of Coupled Carriers

Back 19

- harvest energy from electrochemical gradient of other
- binding is cooperative

Front 20

Coupled Carriers Regulating pH

Back 20

1. Na+/H+ antiporter: reducing acidity
2. Na+ driven Cl-/HCO3- exchanger: sodium bicarbonate in, hydrochloric acid out
3. Na+ independent Cl-/HCO3 exchanger: HCO3- out down gradient, Cl- in. Efflux rises with raised pH

Front 21

Apical

Back 21

active transport of nutrients into the cell

Front 22

Basal

Back 22

passively down electrochemical gradient

Front 23

Carrier Proteins and Active Transport

Back 23

1. P type ATPases: ATP driven cation transporters that are reversibly phosphorylated by ATP as part of transport mechanism

2. V type ATPases: H+ pumps responsible for acidifying contents of intracellular compartments. eg: lysosomes

3. F type ATPases: central role in energy transducing reactions in mitchondria in mammalian cells - convert potential energy of H+ electrochemical gradient into chemical bond energy - ATP synthesis

4. ATP binding casette pumps: transport small molecules across membranes as well as phospholipids and lipophilic drugs. transport involves ATP binding and hydrolysis - largest family

Front 24

P Type ATPases

Back 24

- present in both prokaryotes and eukaryotes
- form an aspartyl phosphate intermediate
- divided into four major groups
1. Na+/K+ and gastic H+/K+ ATPases
2. Ca2+
3. H+ - proton pumps - plants fungi lower eukaryotes
4. bacterial - except Mg2+ or salmonella

Front 25

Na+/K+ ATPase

Back 25

- discovered in 1957
- high intracellular K+
- low intracellular Na+

Front 26

Na+/K+ ATPase Role

Back 26

1. maintaining pH
2. maintaining volume
3. nerve impulse propagation