Lecture 3: The Cell The Cell Theory In 1838, the German botanist Matthias Schleiden concluded that all plants were composed of cells In 1839, Theodor Schwann concluded the same thing for animals In 1855, Rudolf Virchow noted that all cells come from other cells The cell theory states that: all living organisms are made of one or more cells, cells are the basic units of structure and function, and cells come only from pre-existing cells. A cell is the smallest unit that can carry on all of the processes of life

The Cell Types of cells متقدمة بدائية Eukaryotic Prokaryotic Cellulae (Small room) The Organism’s Basic Unit of Structure and Function Types of cells متقدمة بدائية Eukaryotic Prokaryotic All other forms of life Micro-organisms الكائنات الدقيقة

1). Prokaryotic and eukaryotic cells differ in size and complexity Similarities أوجه التشابه All cells are surrounded by a plasma membrane غشاء بلازمى. The semi-fluid substance المادة النصف سائلة within the cell is called “cytosol”, السيتوبلازم containing the cell organelles عِضيات الخلية. All cells contain chromosomes which have genes in the form of DNA. All cells have tiny organelles عضيات صغيرة called “Ribosomes” that make proteins.

1). Prokaryotic and eukaryotic cells differ in size and complexity Differences أوجه الإختلاف A major difference الفرق الأساسى between prokaryotic and eukaryotic cells is the location of chromosomes موضع الصبغيات. In an eukaryotic cell, chromosomes are contained in a true nucleus (النواة ). In a prokaryotic cell, the DNA is concentrated in the nucleoid (شـبه نواة) without a membrane ( بدون غـشاء) separating it from the rest of the cell. In prokaryotic cell, DNA is a single strand (أحادى الشريط) or double strand (ثنائى الشريط) DNA. But in eukaryotic cell, DNA is double strand.

Prokaryotes Bacteria Archaea Types of Prokaryotes - Exist in extreme environments البيئات القاسية (hot and salty) - Exist in most environments They are differing in some other structural, biochemical and physiological characteristics صفات

A)-Prokaryotes Bacteria

شبه نواة الريبوزومات الكبسولة الأسواط غشاء بلازمى الجدار الخلوى الكبسولة الأسواط Fig. 7.4 The prokaryotic cell is much simpler in structure, lacking a nucleus and the other membrane-enclosed organelles of the eukaryotic cell.

Prokaryotic Cell Plasma membrane Cell Wall Capsule Ribosomes Nucleoid Cytoplasm (Cytosol)

B- Eukaryotes An eukaryotic cell has internal membranes, which partition تـُقـَســم the cell into compartments أعضاء وظيفية. These membranes also participate in metabolism as many enzymes are built into membranes. The general structure of a biological membrane is a double layer ثنائى الطبقات of phospholipids and diverse proteins بروتينات متنوعة. Each type of membrane has a unique combination تركيب مـُمـَيـٍز of lipids and proteins for its specific functions. For example, those in the membranes of mitochondria function in cellular respiration.

B- Eukaryotic Cell Plant Cell Animal Cell Eu: True Karyon: Nucleus Plant Cell Animal Cell Compare between Animal and Plant cell? What are the functions of cell organelles ?

الشبكة الإندوبلازمية المادة الوراثية نوية النواة الجدار النووى سوط حركى جسم مركزى ريبوسوم حهاز جولـﭽـى غشاء بلازمى حلمات دقيقة ميتوكوندريا جسم مُحلل الهيكل الخلوى

فجوة مركزية بلاستيدة خضراء الجدار الخلوى ثقوب بينية

عضيــات الخليـــــــــة The Cell Organelles عضيــات الخليـــــــــة

1. The nucleus: Contains the cell’s genetic library المحتوى الـﭽينى The nucleus contains most of the genes in an eukaryotic cell. The nucleus is separated from the cytoplasm by a double membrane غشاء مزدوج called nuclear membrane. The nuclear membrane contains pores ثقوب that allow large macromolecules and particles to pass through. The nuclear membrane الغلاف النووى is maintaining the shape of the nucleus

The nucleus contains “chromatin fiber” الخيوط الكروماتينية which is the DNA associated with proteins. When the cell prepares to divide, the chromatin fibers coil up تلتف to be seen as “chromosomes”. Each eukaryotic species has a characteristic number of chromosomes رقم مُمَيـٍز من الكروموسومات. - A typical human cell has 46 chromosomes, but sex cells (eggs and sperm) have only 23 chromosomes. The nucleus directs protein synthesis by synthesizing messenger RNA (mRNA). The mRNA travels to the cytoplasm and combines with ribosomes to translate its genetic message into the primary structure of a specific protein. Nucleolus is a dark region involved in production of ribosomes.