Bulk transport

BULK TRANSPORT:    cells have also developed mechanism to transport across the membrane, larger molecules cannot pass through the membrane , generally like secretory molecules like protein, hormones .  This transportation  is done by the formation of  carrier vesicles.

ENDOCYTOSIS:  molecules are transported insides the cells by a process called endocytosis.

It is of two type :

1.Pinocytosis: intake of fluid ion through the vesicles, is called pinocytosis and its also called cell drinking.

2.Phagocytosis: intake of food , cell eating , for eg: macrophages, white blood cells , and amoeba etc.

EXOCYTOSIS:  molecules are transported outside the cells by a process called exocytosis. Exocytosis perform secretion , excretion, and ephagy.

Active transport

                       Active transport:

§ Cell has the continuously translocation of K+ ions , into the cell by active transport mechanism at the expense of metabolic energy.

§ Most of the inorganic substances or ions , uncharged particles like, amino acids , and carbohydrates are actively transported across the membrane.

§ Cell always intake the essential nutrients from the outside , many cells equilibrium of diffusion can be adjusted by coupling energy yielding reaction, so the cells are able to translocates solute or metabolite against the concentration gradient.

For eg: movement of Na+  and K+ ions pump.

§ATP DRIVEN ACTIVE TRANSPORT:

§ Na+ and k+ pump : In all cell membrane having a high content of k+ ion at the inner side and high Na+ ions at the outer side of cells, so here these are pumped against their concentration gradient. 

§ Here integral membrane protein is Na+ and k+ ATPase.

§ Na + and k+ ATPase exist in hetero tetramer  form . Its having  two subunits, α ‌and β and it also  exist in dimer form. On Hydrolysis  of ATP, gives ADP+ iP and protein changes its conformation transport 3 Na+ ions outside and 2K+ ions at the inside the cell membrane , against their concentration gradient these are pumped  at the opposite direction , so its required energy.

§ When the hydrolysis of ATP is not done then the transport of molecules is not done so its also called the coupling mechanism.

LOW DRIVEN ATP ACTIVE TRANSPORT: The molecules are transported across the membrane via coupled with the ions[ Na+ and H+ ions] 

Ø For eg: glucose is diffused by simple diffusion or via facilitated mechanism but in intestine and kidney glucose is absorbed against the concentration gradient  by an active transport system .

Ø  glucose molecules is release into the cell against concentration gradient  by the protein conformation change , after  release the glucose , protein pick up the Na+ ion  and pump them out side the cells to balance the ions concentration.

Ø Glucose is also transported into the blood stream by  diffusion.

facilitate transport

FACILIATED TRANSPORT: 

It is a type of transport in which:

the uncharge molecules are passed from the cell membrane with the help of  carrier molecules, that’s means for a specific substance a specific carrier molecules are found. 

Ø These carrier proteins are pick up the molecules and  these protein changes their conformation according to the substance  and release the substance inside the cell.

Ø If the carrier is saturarted with solute molecule, the rate of solute transport is maximum.

MECHANISM OF PASSIVE TRANSPORT

Mechanism of passive transport: passive transport can continue to occurs if the absorbed solute is immobilised . Cations have tendency to move from electropositive to electronegative side while anions have tendency to move from electronegative to electropositive side.

There are two mode of active transport  :

i.Lipid matrix permeability: - lipid soluble substances can pass from the semi permeable membrane according to their solubility and concentration gradient

ii. Hydrophilic membrane channel: - these are the channels which are formed by tunnel proteins, channels makes the membrane semipermeability so water can pass outside and inside according their osmotic gradient , co2and o2 also can diffuse from through these channels as per their conc. Gradient .

TYPES OF TRANSPORT MECHANISM

Transport mechanisms are described as four types:

1)Passive transport

2)Faciliated transport

3)Active transport

4)Bulk transport

PASSIVE  TRANSPORT OR DIFFUSSION:

§Simple diffusion :-

                                molecules are passing through membrane on their concentration gradient from higher to lower concentration due to their own kinetic energy.

§It does not require any metabolic energy.

§[solution = solute particle in less amount + solvent in higher amount],   when the solute particles arranged uniformly then solution is called homogenous solution.

§For eg : cells are having higher amount of  k+ ions instead of environment , so cells draw k+ ions from environment.

§Membrane of kidney cells , epithelial cells, red blood cells and muscles cells are impermeable to substance unless their transport is facilitated .All membranes are permeable for o2 , co2 , and water .

Diffusion down concentration gradient: 

Simple diffusion :In a concentration solution , a substance separated by its dilution , so the solute molecule move from higher to lower concentration until equilibrium is reached , it a physical phenomenon and its does not depends on cellular energy.

  Empirical term of diffusion can be explained by the first law of fick:             

                         dm/dt= - DA [dc/dx]

                                                       dm/dt= flow of matter in per moles

                                                      dc/dx = concentration gradient

                                                     D = diffusion gradient. [cm2 s-1]

Diffusion down the electrical gradient:                                        In a solution the solutes are dissociates into ions and having charge. Cell are also having charge particles inside and outside the media, cell membrane maintain their potential difference, this difference is measured by MICROELECTRODE.  Its range from 50mV to 100mV.  The ions which involved to form potential gradient are k+ and Na+ ions .

                              Each individual substance will diffuse independently of others as per gradient of its own concentration, diffusion pressure, or partial pressure.

OSMOSIS:  Diffusion of water from semi permeable membrane that occurs under the influence or osmotically active solution.

                     ^= RTc               c= molar concentration

                                                R= constant

                                                 T= temperature

                                                ^= osmotic pressure