2.2. Ribosomes: Ribosomes: build the cell’s proteinsbuild the cell’s proteins

مرتبطة

حرة

Ribosomes contain rRNArRNA and protein.A ribosome is composed of two subunits وحدتينوحدتين that

combine تتحدتتحد to carry out protein synthesis تخليق البروتينتخليق البروتين.

Lecture 4: The Lecture 4: The CellCell

Lecture 4: The Lecture 4: The CellCell

In the In the nucleolusnucleolus, ribosomal RNA (, ribosomal RNA (rRNArRNA) is synthesized ) is synthesized and assembled with and assembled with proteinsproteins from the cytoplasm to from the cytoplasm to form form ribosomal subunitsribosomal subunits..

The subunits pass from the nuclear pores to the The subunits pass from the nuclear pores to the cytoplasm where they combine to form cytoplasm where they combine to form ribosomesribosomes..

Cell types that synthesize large quantities of proteins Cell types that synthesize large quantities of proteins (e.g., pancreas) have large numbers of ribosomes(e.g., pancreas) have large numbers of ribosomes..

Types of Ribosomes:-Types of Ribosomes:-

1)1) Free ribosomesFree ribosomes are suspended معلقمعلق in the cytosol and synthesize proteins that function within the cytosol.

2)2) Bound ribosomesBound ribosomes are attached to بـملتصقملتصق the outside of the endoplasmic reticulum.

These synthesize proteins that are either included into membranes or for secretion outside the cell.

2

3- The Endomembrane System3- The Endomembrane System

a)a) The The endoplasmic reticulumendoplasmic reticulum اإلندوبالزمية اإلندوبالزمية الشبكة manufacturers manufacturers الشبكة

membranes and performs many other biosynthetic membranes and performs many other biosynthetic

functionsfunctions

b)b) The The Golgi apparatusGolgi apparatus جولـچـى جولـچـى جهاز finishes, sorts, and ships finishes, sorts, and shipsجهاز

cell productscell products

c)c) The The LysosomesLysosomes اليسوزوماتاليسوزوماتare digestive compartmentsare digestive compartments

d)d) The The VacuolesVacuoles الفجواتالفجواتhave diverse functions in cell have diverse functions in cell

maintenancemaintenance

A)-A)- The endoplasmic reticulum (The endoplasmic reticulum (ERER)) manufacturers membranes and performs manufacturers membranes and performs many other biosynthetic functionsmany other biosynthetic functions

The The ERER includes includes membranous tubulesmembranous tubules

There are two types of There are two types of ERER that differ in that differ in structure and structure and function.function.

1.1. Smooth ERSmooth ER looks looks smoothsmoothناعمةناعمة because it because it lacks ribosomeslacks ribosomes..

2.2. Rough ERRough ER looks rough looks rough because ribosomes because ribosomes خشنةخشنة((bound ribosomesbound ribosomes) are ) are attached to attached to itsits outside. outside.

The smooth ER:The smooth ER: الشبكة اإلندوبالزمية الناعمة - It is rich in enzymes and plays a role in

metabolic processes.

- Its enzymes synthesize lipids دهون (oils, phospholipids, and steroids) including the sex hormones .الهرمونات الجنسيةالهرمونات الجنسية

- Extensive توجد بكثرةتوجد بكثرة in the liver, it helps detoxify إبطال األثر السامإبطال األثر السام

drugs المخدراتالمخدرات and poisons السمومالسموم

The rough ER:The rough ER: الشبكة اإلندوبالزمية الخشنة - is especially abundant متوفرةمتوفرة in 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:B)- Golgi apparatus:

finishes, sorts finishes, sorts تُـج9هزتُـج9هز, packaging and ships , packaging and ships تغلف وتنقلتغلف وتنقل cell productscell products

Many transport vesicles أوعية ناقلةأوعية ناقلة from the ER travel to the Golgi apparatus for modification تطويرتطوير of their contents.

The Golgi function is manufacturing تصنيعتصنيع, warehousing تغليفتغليف, sorting هيزCهيزتَـجCتَـج (PackagingPackaging), and shipping نقل materials to outside the cell.

The Golgi apparatus is especially extensive in cells specialized for secretionspecialized for secretion خاليا إفرازيةخاليا إفرازية.

The Golgi also manufactures pectin and polysaccharides.

وعاء ناقل

C)- LysosomesC)- Lysosomes حللةEحللةاألجسام المEاألجسام الم are digestive are digestive componentscomponents

The lysosomelysosome is a membrane-bounded sac كيسof enzymes that digests macromolecules.

Lysosomal enzymes Lysosomal enzymes work best at work best at pH = 5pH = 5 ( (acidicacidic).).

The The lysosomal enzymeslysosomal enzymes are synthesized by are synthesized by rough rough ERER and then and then transferred to transferred to تنقل إلىتنقل إلى the the GolgiGolgi then to then to lysosomeslysosomes..

Function of Lysozomal enzymesFunction of Lysozomal enzymes

1) They hydrolyse يحللproteins, fats, polysaccharides, and

nucleic acids.

2) Can destroy the cell by autodigestion (autophagy) الهضم الذاتىالهضم الذاتى.

3) Can fuse with food vacuoles الفحجوة الغذائيةالفحجوة الغذائية to 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 recyclingrecycling which renews the

cell

Lysozomal enzymesLysozomal enzymes

D)- Vacuoles: D)- Vacuoles: الفجواتالفجوات

have diverse functions وظائف متنوعةوظائف متنوعةin cell maintenance للحفاظ على الخليةللحفاظ على الخلية

Vesicles أوعـيةأوعـية and vacuoles فجواتفجوات are membrane-bound sacs أكياس ذات أغشيةأكياس ذات أغشية with varied functions.

1.1. Food vacuoles Food vacuoles فجوة غذائيةفجوة غذائية, from phagocytosis, fuse with lysosomes.

2.2. Contractile vacuoles Contractile vacuoles فجوة منقبضةفجوة منقبضة , found in freshwater protists, pump excess water out of the cell.

3.3. Central vacuolesCentral vacuoles فجوة مركزيةفجوة مركزية are found in many mature plant cells.

الفجوة المركذية

خلية نباتية

خلية حيوانية

Other Membranous Organelles

A)- PeroxisomesA)- Peroxisomes

contain enzymes that transfer hydrogen from various contain enzymes that transfer hydrogen from various substrates to oxygensubstrates to oxygen

Functions of peroxisomesFunctions of peroxisomes

1- Hydrogen peroxide (H(H22OO22) 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 الطاقةإلنتاج الطاقة.

3- They detoxify مىRيبطل المفعول الس alcohol and other harmful compounds. Thus, it exists

extensively in the liver cellsliver cells

B)- MitochondriaMitochondria::Thy are the main energy transformers of cells Thy are the main energy transformers of cells

aas they convert energy to fuel الطاقة that cells

can use for work.

MitochondriaMitochondria are the sites of cellular

respiration,

generating جd dجتُـنت of هدمهدم ATPATP from the catabolism تُـنت

sugars, fats, and other fuels طاقةمصادرمصادر in 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.

Other Membranous Organelles

MitochondriaMitochondria have a smooth outer membrane and a highly folded inner membrane forming cristae نتوءاتنتوءات.

The inner membrane encloses the mitochondrial matrixmitochondrial matrix, a fluid-filled space with DNA, ribosomes, and enzymes.