B- Eukaryotic Cell
3- The Endomembrane System
a) The endoplasmic reticulum ‫ الشبكة اإلندوبالزمية‬manufacturers
membranes and performs many other biosynthetic
functions
b) The Golgi apparatus ‫ جهاز جولـﭽـى‬finishes, sorts, and ships
cell products
c) The Lysosomes ‫ اليسوزومات‬are digestive compartments
d)
The Vacuoles ‫ الفجوات‬have diverse functions in cell
maintenance
A)- The endoplasmic reticulum (ER)
manufacturers membranes and performs many other
biosynthetic functions
•
The ER includes
membranous tubules
•
There are two types of
ER that differ in
structure and function.
1. Smooth ER looks
smooth ‫ ناعمة‬because it
lacks ribosomes.
2. Rough ER looks rough
‫ خشنة‬because ribosomes
(bound ribosomes) are
attached to its outside.
Fig. 7.11, Page 119
• The smooth ER: ‫الشبكة اإلندوبالزمية الناعمة‬
- It is rich in enzymes and plays a role in metabolic
processes.
- Its enzymes synthesize lipids ‫( دهون‬oils, phospholipids,
and steroids) including the sex hormones ‫الهرمونات الجنسية‬.
- Extensive ‫ توجد بكثرة‬in the liver, it helps detoxify ‫إبطال األثر السام‬
drugs ‫ المخدرات‬and poisons ‫السموم‬
• The rough ER: ‫الشبكة اإلندوبالزمية الخشنة‬
- is especially abundant ‫ متوفرة‬in those cells that
secrete proteins as it contains ribosomes.
- These secretory proteins are packaged in transport
vesicles that carry them to their next stage.
B)- Golgi apparatus:
finishes, sorts ‫تـ ُ َجهز‬, packaging and ships ‫ تغلف وتنقل‬cell products
• Many transport vesicles ‫ أوعية ناقلة‬from the ER travel to the
Golgi apparatus for modification ‫ تطوير‬of their contents.
• The Golgi function is manufacturing ‫تصنيع‬, warehousing
‫تغليف‬, sorting ‫( تـ َ ْجهيز‬Packaging), and shipping ‫ نقل‬materials to
outside the cell.
• The Golgi apparatus is especially extensive in cells
specialized for secretion ‫خاليا إفرازية‬.
• The Golgi also manufactures pectin and polysaccharides.
‫وعاء ناقل‬
‫‪Fig. 7.12, Page 120‬‬
C)- Lysosomes
‫ األجسام ال ُمحللة‬are digestive components
• The lysosome is a membrane-bounded sac ‫ كيس‬of enzymes that
digests macromolecules.
Fig. 7.13a, Page 121
Lysozomal enzymes
Lysosomal enzymes work best at pH = 5 (acidic).
The lysosomal enzymes are synthesized by rough ER and then
transferred to ‫ تنقل إلى‬the Golgi then to lysosomes.
Function of Lysozomal enzymes
1) They hydrolyse ‫ يحلل‬proteins, fats, polysaccharides, and nucleic
acids.
2) Can destroy the cell by autodigestion (autophagy) ‫الهضم الذاتى‬.
3) Can fuse with food vacuoles ‫ الفحجوة الغذائية‬to digest food, (when a
food item is brought into the cell by phagocytosis).
4) Can also fuse with another organelle or part of the cytosol. This
process of autophagy called recycling which renews the cell
Fig. 7.14, Page 122
D)- Vacuoles: ‫الفجوات‬
have diverse functions ‫وظائف متنوعة‬in cell maintenance ‫للحفاظ على الخلية‬
•
Vesicles ‫ أوعـية‬and vacuoles ‫ فجوات‬are
membrane-bound sacs ‫ أكياس ذات أغشية‬with varied
functions.
1.
Food vacuoles ‫فجوة غذائية‬, from phagocytosis, fuse with lysosomes.
2.
Contractile vacuoles ‫فجوة منقبضة‬, found in freshwater protists, pump
excess water out of the cell.
3.
Central vacuoles ‫ فجوة مركزية‬are found in many mature plant cells.
‫خلية نباتية‬
‫الفجوة المركذية‬
‫خلية حيوانية‬
‫‪Figs. 7.15 & 166, Page 123‬‬
Other Membranous Organelles
A)- Peroxisomes
contain enzymes that transfer hydrogen from various substrates to
oxygen
Functions of peroxisomes
1- Hydrogen peroxide (H2O2) is a poison,
but the peroxisome has enzyme
that converts H2O2 to water.
2- Some peroxisomes break fatty acids down
to smaller molecules that are transported to
mitochondria for fuel ‫إلنتاج الطاقة‬.
3- They detoxify ‫سمى‬
ُّ ‫ يبطل المفعول ال‬alcohol and
other harmful compounds. Thus, it exists
extensively in the liver
cells
Other Membranous Organelles
B)- Mitochondria:
Thy are the main energy transformers of cells as they
convert energy to fuel ‫ الطاقة‬that cells can use for work.
• Mitochondria are the sites of cellular respiration,
• generating ‫ تـُن ِتج‬ATP from the catabolism ‫ هدم‬of sugars,
fats, and other fuels ‫ مصادر طاقة‬in the presence of oxygen.
• Almost all eukaryotic cells have mitochondria.
• Mitochondria and chloroplasts are mobile and move
around the cell along tracks in the cytoskeleton.
• Mitochondria have a smooth outer membrane and a highly folded
inner membrane forming cristae ‫نتوءات‬.
• The inner membrane encloses the mitochondrial matrix, a fluid-filled
space with DNA, ribosomes, and enzymes.
Fig. 7.17, Page 124