Transport Through Cell Membrane - humsc.net

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Transport Through Cell Membrane 2

Substance can pass through a cell membrane in three separate ways:

Passive transport:

I. Diffusion (simple , facilitated)

II. Osmosis.

Active transport Vesicular transport

بشكل عام منقدر نحكي عنهactive transport

No energy consuming (ATP)

energy consuming (ATP)

energy consuming (ATP)

Transport of material according to the concentration gradient .

Transport of material against the concentration gradient.

Osmosis:

Diffusion of water (solvent) across semipermeablemembrane( which is

permeable to water and not permeable to solute) from high conc to

low conc.

الفكرة العامة من الخاصية الاسموزية بكون في بمرور الماء عندي جزئين وبينهم غشاء بسمح

وما بسمح بمرور الجزيئات الاخرى زي الجلوكوز والاملاح مثلا .

في )كمثال ع المذاب(هسا وجود الجلوكوزالجزء الثاني من الوعاء بخلي الماء الموجود

, ومشان 1بنفس الجزء اقل من الماء بالجزء

نصل للاتزان يا اما الجلوكوز )المذاب( بتجه

مشان الغشاء( ) بس ما بقدر 1الى 2من

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2الى 1فهون بيجي دور الماء الي تتجه من

osmotic pressure : the pressure needed to stop osmosis.

Water flows from the

solution containing a

low concentration of

solute to the solution

containing a high

concentration of

solute.

The water is forced

through the

membrane by an

osmotic pressure

difference between

the two

compartments.

Water conc.

on this side

is higher.

Water conc.

on this side

is lower.

هون نفس فكرة المثال

السابق

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Aquaporins : Channels allowing the

passage of water(lipid

insoluble)through the osmosis.

It contributes homeostasis by

maintaining blood volume and

water balance.

It has many types that differ from

one cell to another.

The concentration of water in

compartment B higher than compartment

A and according to osmosis the water

should move to compartment A to achieve

the equilibrium.

If we want to stop this movement, we must

applied pressure in compartment A gradually until the water stops

moving across semipermeable membrane.

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The higher the amount of solute, the lower the water concentration.

The more solute, the more gradient

for osmosis of water from

compartment with high water to

compartment with solute, this is mean

more pressure to stop osmosis.

The concentration gradient is directly

proportional to the diffusion.

kinetic energy depend on number

of particles , not by the mass of

the particles.

the large molecule do not have

osmotic effect more than small.

This is because the higher the

particle’s mass, the smaller its

velocity

so, the kinetic energy of small and

large particles is almost similar.

To express the concentration of a solution in

terms of numbers of particles, called the

osmole place of grams.

1 osmole is one gram molecular wight of

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osmotically active solute(substances can be defined as the solutes cannot

pass the given semi-permeable membrane).

The concentration of osmotically active particles is usually expressed in osmoles.

Osmolarity Versus Osmolality

Active Transport

كلهم انشرحوا بالمحاضرة الماضية

Number of milliosmosles in

a liter of solution .

Volume

In a practical we depend

on it

Number of milliosmoles

in a kilogram of solution.

weigh

More stable or accurate.

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Primary active transport

from the example of a

primary active transport

and more popular and

found of all cell the

sodium- potassium

pump.

the sodium-potassium

pump transports

material from that low

concentration to high

concentration.

o has The carrier

enzymatic activity

مشان يحصل على الطاقة اللازمة لعملية النقل. ATPبقدر يحطم ال

Active Transport

Primary active transport(direct consumption of energy)

Secondary active transport(indirect consumption of energy)

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The alpha has 3 site for binding of sodium and 2 for binding of potassium

and has ATP binding site, and phosphorylation binding site.

وم العكس.الخلية قليل وخارج الخلية عالي وتركيز البوتاسي زي ما منعرف انه تركيز الصوديوم داخل

وفي فرق جهد مخلي داخل الخلية سالب بالمقارنة مع خارجها

leak channelsوكمان في عنا قنوات مفتوحة طوال الوقت

ن الصوديوم بكو concentration gradientوم عالي خارج الخلية ف تبعا لل ولانه تركيز الصودي

بده يدخل جوا الخلية .

.وكمان الصوديوم موجب وداخل الخلية سالب فبكون تجاذب وكمان بصير بده يدخل جوا الخلية

set pointداخل الخلية ويطلع عن ال يرتفعالاسباب كلها ممكن تركيز الصوديوم هاي نمشا

صير لو صار يتجمع جوا الخلية ب veosmotically actiوهييك مينفعععش والصوديوم من المواد ال

ازن.ى التويسحب معه مي داخل الخلية فبتموت الخلية.ينهااار اسود فهون بيجي دور المضخة لتحافظ عل

One of the most important functions of the Na+/K+ pump is to

control the cell volume (maintain homeostasis of the cell

volume), Without function of this pump, most cells of the body

would swell until they burst.

To prevent accumulation over the sodium inside the cell which is

osmotically active substance.

In each cycle the cell loses one positivecharge.

Na /k pump also called electrogenic pump.

Electrogenic Nature of the Na -K Pump. The fact that the Na+-

K+ pump moves three Na+ ions to the exterior for every two K+

ions that are moved to the interior means that a net of one

positive charge is moved from the interior of the cell to the

exterior of the cell for each cycle of the pump. This action creates

positivity outside the cell but results in a deficit of positive ions

inside the cell; that is, it causes negativity on the inside.

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Therefore, the Na+-K+ pump is said to be electrogenic because

it creates an electrical potential across the cell membrane.

طبعا ما بتشتغل المضخة الا لما يزيد البوتاسيوم عن الحد الطبيعي

شوفوها ع السلايد اوضح

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Another important primary active transport mechanism is the

calcium pump. Calcium ions are normally maintained at an

extremely low concentration in the intracellular cytosol of virtually

all cells in the body, at a concentration about 10,000 times less

than that in the extracellular fluid.

This level of maintenance is achieved mainly by two primary active

transport calcium pumps. One, which is in the cell membrane,

pumps calcium to the outside of the cell. The other pumps

calcium ions into one or more of the intracellular vesicular

organelles of the cell, such as the mitochondria in all cells.

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Its action is important in the process of HCL(حمض في المعدة)

secretion

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Secondary Active Transport

This type depended

on Primary active

transport (sodium-

potassium pump).

t

When sodium ions are transported out of cells by primary active

transport, a large concentration gradient of sodium ions across the cell

membrane usually develops, with a high concentration outside the cell

and a low concentration inside.

This create certain gradient require other carrier coupling the sodium

transport to another substance .

The cell contains more than one carrier and more than one pump, and one

side of the cell contains the sodium and potassium pump running on it to

create low intracellular sodium concentration , and according to

concentration gradient the sodium should move to inside the cell.

But, there is a specific carrier protein responsible for this type that has a

place to transport sodium and a place to move another substance in the

same direction or opposite.

The ATP consumption in sodium potassium pump to create the gradient

for sodium.

رك والمادة الثانية بتتح concentration gradientفالصوديوم بدخل للخلية تبعا لل

against concentration gradient

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Frequently the lateral and basal border almost have the same transport

basolateral them(protein , channels and carrier ) and called characteristic

has different characteristic alhe lument ,border

cotransport The active of sodium potassium pump result in low concentration of sodium

inside the cell this cause move sodium from lumen to inside the cell.

But sodium does not move alone because the carrier does not move until

another substance is bound to it (glucose amino acid) both move in the same

direction from lumen to inside the cell. .

The second step does not happen unless the first step takes place which

should consuming energy.

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Counter-transport

cotransportنفس خوات ال بس المادة الثانية الي بتربط مع carrier بتتحرك باتجاه معاكس يعني

الصوديوم بدخل والكالسيوم بطلع

Vesicular transport

We use vesicular transport for large materials (larger than materials

which move via protein carrier or ion channel).

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** the vesicle is surrounded by membrane.

The materials which transport at this way even:

Go out of the cell (secretory product , certain hormone ,waste

product) so it’s a material which the cell secretes it out and

called exocytosis .

برضه و snare-tاسمه هسا هاي الحويصلة الي بدها الخلية تفرزها لبرا في على جدارها بروتين

ار فبصير بينهم تفاعل او اندماج خاص بعدين جد snare-vعلى جدار الخلية في بروتين اسمه

الحويصلة بتكسر وبتخرج محتويات الحويصلة خارج الخلية.

وهاذ الاشي بادي الى زيادة مساحة جدار الخلية .

endocytosisGet in the cell so it called

رة غشاء الخلية بحاوط المواد الي رح تدخل الخلية زي ما موضح بالصو endocytosisب

فوق وبأدي الى نقص مساحة السطح الخارجي للخلية.

These two processes are maintain homeostasis in which the rate of

materials that get the cell and release from it are in balance which

result balance in the surface of the cell.

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.

Exocytosis process is divided to two parts :

1. Constitutive secretion : when the secretory product not storage or

processing (minimal processing or no processing) and get out

2. Regulated secretion (non Constitutive secretion) : the secretion

has been processed and storaged before releasing out side of the

cell (like insulin) .

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We said before that endocytosis getting large material (nutrition or

pathogens in immune cells) from out side to in side or from extracellular fluid

to intracellular fluid and we divide endocytosis to:

1) Pinocytosis (cell drinking): happen when the water move inside the

cell when the cell intake materials

2) Phagocytosis :which is characteristics to certain cells (like immune

cells) .

3) Ligand mediated (receptor mediated) : this type is the most specific

type and has a receptors in the inner side so there is interaction

between the proteins of the cell and the materials .

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Receptor-Mediated Endocytosis In contrast to pinocytosis and

phagocytosis, most cells have the capacity to specifically take up

molecules that are important for cellular function or structure.

In receptor-mediated endocytosis, certain molecules in the

extracellular fluid bind to specific proteins on the outer surface of

the plasma membrane. These proteins are called receptors, and

each one recognizes one ligand with high affinity In one form of

receptor-mediated endocytosis, the receptor undergoes a

conformational change when it binds a ligand. Endocytosis involves

a number of accessory proteins, including adaptin, clathrin

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Transcytosis

Endocytosis across one membrane of the

cell is followed by exocytosis across the

opposite membrane this type called

transcytosis.

The cell is like a pathway …

Transport across epithelia

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To describe the picture above this is intestine in the left side is a lumen of

the intestine which lined by epithelial tissue and in the right side the blood

vessel which transport the materials.

The tight junction is work as a barrier to prevent some substances to move

from lumen to the blood vessel

The epithelial cell has many borders: the border at the side of lumen is

called lumenar membrane and the side which adjacent to another cell is

called lateral membrane also the side which facing the blood is called

basal membrane.

As a function of transport the basal and the lateral membrane are similar

in characters.

There are two ways to transport materials through epithelia:

1. Transcellular pathway: the materials is transported from the lumen

membrane via the epithelial cell and cross the basal membrane to

reach the blood vessel

2. .Paracellular pathway : the materials (epically water) is transported

via the space between the cells .

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This mechanism for the transport of sodium ions through the epithelial

sheet of the intestines, gallbladder, and renal tubules. This figure shows

that the epithelial cells are connected together tightly at the luminal pole

by means of junctions.

The brush border on the luminal surfaces of the cells is permeable to both

sodium ions and water.

Therefore, sodium and water diffuse readily from the lumen into the

interior of the cell.

Then, at the basal and lateral membranes of the cells, sodium ions are

actively transported into the extracellular fluid of the surrounding

connective tissue and blood vessels.

This action creates a high sodium ion concentration gradient across these

membranes, which in turn causes osmosis of water.

Thus, active transport of sodium ions at the basolateral sides of the epithelial

cells results in the transport not only of sodium ions but also of water.

Transport Through Cell Membrane - humsc.net

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