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CHAPTER
5
MEMBRANE
STUCTURE
THE STRUCTURE
AND FUNCTION
AND FUNCTION
OF MACROMOLECULES
Section A: Membrane Structure (Introduction)
This barrier ‫حاجز‬, 8 nm thick, controls entrance ‫دخول‬
into and exit ‫خروج‬out of the cell.
The plasma membrane is selectively permeable ‫ُمن ِفذ‬
‫اختياريا‬, allowing some substances to pass ‫ تمر‬more
easily than others.
Plasma membrane is composed of two layers of
Phospholipids and different types of proteins
Types of membrane proteins ‫أنواع البروتينات في غشاء الخلية‬
•
There are two types ‫ نوعان‬of membrane proteins.
1.
Peripheral proteins ‫البروتين الطرفي‬
They are not embedded in the lipid bilayer ‫ليست مخترقة لطبقة الدهون‬.
2.
Integral proteins ‫ البروتين المندمج‬penetrate ‫ تخترق‬the hydrophobic part of
the lipid bilayer.
Integral
proteins
Peripheral
proteins
Peripheral
proteins
Fig. 8.7, Page 143
‫‪• The proteins in the plasma membrane may provide a variety of major‬‬
‫‪cell functions.‬‬
‫الربط بين الخاليا‬
‫النقل‬
‫التعارف بين الخاليا‬
‫يعمل كإنزيم‬
‫نقل اإلشارات‬
‫الربط مع هيكل‬
‫الخاليا وخارجها‬
‫‪Fig. 8.9, Page 144‬‬
How can materials enter or exit via
plasma membrane?
1- Passive transport ‫االنتقال السلبى‬
It means diffusion ‫ االنتشار‬across ‫ خالل‬plasma membrane
• Diffusion: ‫االنتشار‬
Is the tendency ‫ استعداد‬of molecules to spread out ‫ لالنتشار‬in the available space.
‫صبغة‬
Fig. 8.10a, Page 145
• Passive transport: ‫اإلنتقال السلبى‬
Diffusion of substance ‫ انتشار مادة‬from where it is more
concentrated to where it is less concentrated ‫من التركيز االعلي لألقل‬,
down its concentration gradient ‫مـُنحدر التركيز‬.
It requires no energy ‫ال يحتاج لطاقة‬
Fig. 8.10b, Page 145
CD Unit 2, Chapter 8.
Osmosis ‫ األسموزية‬: is the passive transport of water
• The solution with the higher concentration of solutes is
hypertonic.
• The solution with the lower concentration of solutes is
hypotonic.
• Solutions with equal solute concentrations are isotonic.
Osmosis:
Is a passive transport in which water
diffuses from the hypotonic solution
the hypertonic solution until the
solutions become isotonic.
Fig. 8.11, page 146
to
Passive transport of water (Osmosis)
• Hypertonic solution: ‫عالى التركيز‬
contains high concentration of solute ‫ ُمذاب‬molecules.
• Hypotonic solution: ‫منخفض التركيز‬
contains low concentration of solute molecules.
• Isotonic solution: ‫متعادل‬
contains equal concentrations of solute molecules
Biological
Membrane
H2O
Hypertonic
Hypotonic
2. Facilitated diffusion
Definition ‫ تعريف‬of facilitated diffusion
•
The passive movement of molecules from high concentration to low
concentration via a transport proteins ‫( البروتينات الناقلة‬gated channels ‫قنوات‬
‫) ُمبَوبة‬.