MEMBRANE TRANSPORT

Dr. Vijay Marakala, MBBS, MD.

Assistant professor BIOCHEMISTRY SIMS & RC

MEMBRANE TRANSPORT• Cell membrane is the boundary between inside &

outside…

IN foodcarbohydratessugars, proteinsamino acidslipidssalts, O2, H2O

OUT wasteammoniasaltsCO2

H2O products

IN

OUT

Can it be an impenetrable boundary? NO!

MEMBRANE TRANSPORT• Biological membrane are semipermeable

Channel proteins

Carrier proteins

Lipid bilayer interstices

Passive transport Active

transport

PASSIVE TRANSPORT• Transport of solute molecules from high concentration to low

concentration across membrane• It is a down hill transport and requires no energy

Simple diffusion

Facilitated diffusion

2 types

SIMPLE DIFFUSION• Move from HIGH to LOW concentration

– “passive transport”– no energy needed

Diffusion

Through the channel protein and lipid bilayer

interstices.E.g., Transport of O2, CO2, N2, ethanol and

urea

SIMPLE DIFFUSION

Passive transport protein

Lower concentration

Higher concentration of

Protein channel

FACILITATED DIFFUSION

E.g., Transport of glucose and most amino acids

Through carrier protein

conformational change

ACTIVE TRANSPORT• Molecule moves against a concentration gradient.• Needs an external energy (ATP)

Primary active transport• Energy is derived directly from hydrolysis of

ATP

Secondary active transport• ATP provides the energy for transport

indirectly

Two types

PRIMARY ACTIVE TRANSPORT

Sodium-Potassium pump

High Na+

Low Na+

Low K+

High K+

SECONDARY ACTIVE TRANSPORT• ATP provides the energy for transport indirectly.• Uses an energy of an electrochemical gradient or membrane

potential produced originally by primary active transport process by using ATP

Co-transport or Symport

Both the substances move across in same direction

Sodium- glucose cotransport

Counter transport or antiport

Each substance moves in opposite direction

Sodium-calcium counter transport

VOLTAGE GATED CHANNELS

Voltage gated channels are opened by membrane depolarization

Membrane potential change (voltage difference) switches the ion channel to open

Voltage gated sodium channels

Voltage gated potassium channels

IONOPHORE

TRANSPORT OF MACROMOLECULES

ENDOCYTOSISPinocytosis

(cellular drinking)

Phagocytosis (cellular eating)

EXOCYTOSIS

Exocytic vesicles

Vesicle forming

ENDOCYTOSIS

Vesicle

Fluid outside cell

Protein

Cytoplasm

EXOCYTOSIS

AQUAPORINS• Water moves rapidly into & out of cells

– evidence that there were water channels

1991 | 2003

Peter AgreJohn Hopkins

Roderick MacKinnonRockefeller