Gradients across the Plasma Membrane
‫اي يعني عندنا تدرج بالتركيز او الشحنة‬
Concentration
Selective permeability of the plasma membrane allows certain substances on
either side of the plasma membrane
A concentration is high in ((inside or outside)) of the plasma membrane >>>>
Gradients
Ions and molecules more concentrated in the cytosol or the extracellular
fluid
** (Na+) >>>>> outside the cell
** (k+)>>>>> inside the cell
** (O+) >>> outside the cell……….. Higher con in intercellular fluid
** (CO2+)>>> inside the cell………Higher con in extracellular fluid
Electrical
We talk positively and negatively charged……….. In Two sides of the plasma
membrane
The Difference in electrical charges >>constitutes an electrical gradient (Action
potential)
This charge difference is >>>called (membrane potential)
Both Con and Elect
Help move substances across the plasma membrane
Concentration gradient>>> move ((downhill))>>>more to less cons >> to reach
equilibrium
Electrical gradient >>> move negatively charged area to positively charged
Electrochemical gradient: concentration gradient and the electrical
gradient on movement of a particular ion
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TRANSPORT ACROSS THE PLASMA MEMBRANE
Very essential to the life of a cell
Support>>>>> metabolic reactions
Produced by the cell>>>>> for export
Cellular waste products>>>> must move out of the cell
* Substances move …….across cellular membranes
1-Passive processes
Moves down its concentration
Electrical gradient using only KE
NO Energy
Ex: simple diffusion
2-Active processes
“Uphill” against its concentration or electrical gradient
Used Energy
**Passive processes
Diffusion: is passive processes in which the random mixing of particles in a solution occurs because of the particles’ kinetic energy.
(The dissolved substances, and the solvent, and solutes)>>>>>> Diffusion
High concentration>>>>>>>>low concentration………..downhill
After some time the particles continue to move about randomly due to their kinetic energy
But their concentrations do not change
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The different concentration gradient across the membrane is steepness is the higher
rate of diffusion >>>> faster
The higher the temperature, >>> the rate of diffusion faster
‫ نقول ان الشخص الذي يصيب بالحمى‬::::: ‫مثال للفهم وليس للحفظ كما انتو متعودين يابتاع البصم ياصيدلة‬
‫يزيد في جسمه عمليات االنتشار‬
Mass of the diffusing substance: Smaller molecules diffuse more rapidly than
larger ones
Surface area: is larger>>>>> faster the diffusion rate
Diffusion distance is higher>>>>> the diffusion slower
‫ فرح يصير حركة السوائل من خالل ال‬pores ‫ طردية النو كل ما زاد مساحة ال‬surface area ‫هأل العالقة بحالة‬
‫أسهل‬membrane
‫ فبالتالي بتصير‬membrane ‫ بتزيد لما يزيد سماكة ال‬.. ‫بالحالة التانية رح يكون عكسي ليه ؟ ألنو كيف المسافة بتزيد‬
‫حركة السوائل والجزيئات من خالله أصعب‬
Types of diffusion
1- Simple diffusion
2- facilitated diffusion
3- osmosis
Simple diffusion:
Passive process
Move freely through the lipid bilayer of the plasma membranes of cells without the help
of membrane transport protein
*The molecules move across the lipid bilayer
- Nonpolar(( hydrophobic)): oxygen, carbon dioxide, and nitrogen gases; fatty acids;
steroids
-Small polar molecules((hydrophilic)) : water, urea, alcohols
Function: - Movement of oxygen and carbon dioxide between blood and body cells
- Movement between blood and air within the lungs during breathing
- the route for absorption of some nutrients Down con gradient
- excretion of some wastes by body cells
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Facilitated Diffusion:
- Integral proteins (help)not move>>>> a specific substance across the membrane
- Channel or a carrier
1- CHANNEL-MEDIATED FACILITATED DIFFUSION:
-No any energy
-Down its concentration gradient
-Most membrane are ion channels
-Integral trans membrane>>>>>>allow passage of >> small, inorganic ions , hydrophilic
to penetrate the nonpolar interior of the lipid bilayer
**simple dif is faster than Facilitated dif >>>>>>> surface area
**Diffusion channels is slower than free diffusion >>>surface area
- Facilitated diffusion through channels is a very fast process>> million potassium flow through a
K+ channel in one second!
-have gated >>>changing shape in one way to open the pore and in another way to close it and
some gated randomly
- regulated by chemical or electrical changes
- ion channels >>>>different permeability to various ions
2- CARRIER-MEDIATED FACILITATED DIFFUSION
- Used to move >> down concentration gradient across
-carrier one side released on the other side after the carrier undergoes a change shape >higher co
-Carrier both sides carrier on the cytosolic side and move out to the extracellular fluid > rapidly
bind to the carrier extracellular side, move into cytosol
- Number of carrier available maximum were crossing membrane (transport maximum)
-Saturated
- Move by carrier mediated facilitated diffusion include (glucose, fructose, galactose, and some vitamins)
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‫ يجب علينا ان تحدث مثال مهم وهو عن الغلوكوز في االنتشار والذي يشكل قناة لنقلها‬carrier ‫وعندما نتحدث عن‬
‫بمساعدة االنسولين‬
Carrier very selective certain molecule but no other ((con grad…)
Glucose is Duct in the membrane >>> into the membrane By virtue of insulin bounded
receptor >>>phosphorylation receptor>>>intracellular Pass way with result traffic and ducting
‫ مساعد للغلوكوز ومن هذه الكالم يمثل تماما ً كما يصيب الشخص(( بداء السكري نوع‬insulin ‫**هذه الصورة فقط للتعبير ان ال‬
‫ ليحرر ال غلوكوز‬insulin ‫اول )) يستعمل ال‬
The selective permeability ………. achieve homeostasis
Fun insulin WITH GLU:
1 - Promotes the insertion of many copies of glucose transporters into the plasma membranes of
certain cells
2- Elevate the transport maximum for facilitated diffusion of glucose into cells
** Glucose transporters available>>> pick up glucose from the blood more rapidly
** produce or utilize insulin >>> diabetes mellitus ‫انتاج او استخدام االنسولين‬: ‫داء السكري‬
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
Osmosis:
Type of Diffusion in which there is net movement of a solvent through a selectively
permeable from an area of high concentration of water to lower concentration of
water
And water moves through a selectively permeable membrane from an area of lower
solute concentration to an area of higher solute concentration
Water can pass through plasma membrane in 2 ways:
- Through the lipid bilayer via simple diffusion
- Through aquaporins, integral membrane proteins
A membrane is permeable to water but is not permeable to certain solutes
U-shaped tube
figure ‫هنا نشرح معلومات عن ال‬Can’t pass through poured into the right arm>>> water concentration is higher on the left and lower on the right >>> so that the
water is moving down its concentration gradient
The same time into the left arm from right >> result…. left arm
decreases> right arm increases
‫تعتقد ان انتقال الماء سيستمر حتى عدم بقاءه ال هذه ليس صحيحا وانما االنتقال التاني يبين‬
‫االنتقال انه وجود ضغط على جانبي الغشاء وهنا نعرف ذلك الضغط ويسمى‬
Hydrostatic pressure: forces water molecules to move back into the
left arm
>>>>> Equilibrium ……. due to the hydrostatic pressure
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‫ولمزيد من التعقيد في التجارب يمارس ضغط اخر هو اقوى فعالية وباستخدام مكبس يجعل المحلول يرجع كما‬
‫قبل بداية العملية ليس تماما بل تقريبا‬
Osmotic pressure: is proportional to the concentration of the solute particles
that cannot cross the membrane
In our experiment stop movement ……
Tonicity: is a measure of the solution’s ability to change the volume of the
certain cell
 Isotonic: A solution that has the same concentration both extracellular fluid and
cytosol normal
 Hypotonic solution: a solution that has a lower concentration of solutes than
the cytosol inside the RBCs hemolysis
 hypertonic solution: has a higher concentration of solutes than does the
cytosol causing shrinkage the cell called crenation
Active Processes:
Active Transport
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