CHAPTER 18 2- Viruses Page 328

1- Viruses are much smaller than bacteria 2- Viruse is about 20nm in diameter 3- Viruses are not cells 4- A virus is a genome enclosed in a protective coat Fig. 18.1, Page 329

Virus is a genome enclosed in a protective coat Genome (DNA) Protein coat (capsid) Fig. 18.2a & b, Page 330

Viral Capsid and Envelope A- Capsid A protein shell that encloses the viral genome. It is rode-shaped, helical, polyhedral or more complex. Capsomeres: Are the protein units that form capsid. Capsomeres (proteins) Capsid Membranous envelop (viral envelope) Sometimes further rapped يُغَلف in a membranous envelope (Viral envelope), ex. Influenza virus. Page 329, 330

Some viruses have viral envelopes, membranes cloaking their capsids. These envelopes are derived from the membrane of the host cell. They also have some viral proteins and glycoproteins. Fig. 18.2c, Page 330

Viral Genome: (Hereditary material المادة الوراثية) Viral genomes may consist of double-stranded DNA, single-stranded DNA, double-stranded RNA, or single-stranded RNA, depending on the specific type of virus. The viral genome is usually organized as a single linear or circular molecule of nucleic acid. The smallest viruses have only four genes, while the largest have several hundred. Page 328

Key Characters Viruses - DNA enclosed in a protein coat (membranous envelop) - Can be crystallised - Each type of virus infects a limited range of host cells (host range) - They lack enzymes for metabolism - Have no ribosomes for making their own proteins - Reproduced only within a living host cell (obligate parasitism). Most viruses of eukaryotes attack specific tissues. Eg. Human cold viruses infect only the cells lining the upper respiratory tract, and The AIDS virus binds only to certain white blood cells.

Virus-Reproduction within a living host cell Living Cell obligate parasitism تطفل إجبارى 1-Inter the cell and releases DNA 2- Replication using host nucleotides and enzymes Viral RNA 3- Production of new capsids proteins using host cell resources. 4- The new viral DNA and proteins assemble to form new viruses Capsid Proteins Page 331 (Fig. 18.3)

A viral infection begins when the genome of the virus enters the host cell. Once inside, the viral genome commandeers its host, reprogramming the cell to copy viral nucleic acid and manufacture proteins from the viral genome. The nucleic acid molecules and capsomeres then self-assemble into viral particles and exit the cell. Fig. 18.3, Page 331

Bacteria infecting Viruses Viruses that infect bacteria, called bacteriophages or phages. It has a 20-sided capsid-head that encloses their DNA and protein tail piece that attaches the phage to the host and injects the phage DNA inside. Phages reproduce by Lytic (تحـللية ) Cycle and/or Lysogenic (تحـللية غير) cycle. Fig. 18.2d Page 330

1)- lytic cycle (التحـللية الدورة) , Bacteriophages (on E. coli) Phages reproductive cycles within bacteria: Bacteria Virus 1)- lytic cycle (التحـللية الدورة) , the phage reproductive cycle results in the death of the host. In the last stage, the bacterium lyses (breaks open) and releases the phages produced within the cell to infect others. Virulent phages reproduce only by a lytic cycle.

Phage T4 (virulent viruses) فيروس مميت Fig. 18.4, Page 332

2)- lysogenic cycle (التحـللية الدورة غير) The phage genome replicates without destroying the host cell. Temperate phages, like phage lambda (ג), may use both lytic and lysogenic cycles. Within the host, the virus’ circular DNA engages in either the lytic or lysogenic cycle. During a lytic cycle, the viral gene immediately turn the host cell into a virus-producing factory, and the cell soon lyses and releases its viral products. Temperate virus فـيــروس غير مميت

2)- Lysogenic cycle (التحـللية الدورة غير) Fig. 18.5, Page 333

(التحـللية الدورة غير) Phage T4 Phage lambda (ג) Only 1 tail fibre Many tail fibre (virulent viruses) Temperate virus فيروس مميت فيروس غير مميت lytic cycle (التحـللية الدورة) Lysogenic cycle (التحـللية الدورة غير) & lytic cycle (التحـللية الدورة) CD: Chapter 18

B- Eukaryotic Cell

Internal membranes أغشية داخلية compartmentalize تحدد أعضاء وظيفية the functions of a eukaryotic cell 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. Page 114

B- Eukaryotic Cell Plant Cell Animal Cell Eu: True Karyon: Nucleus Plant Cell Animal Cell What are the functions of cell organelles ? Compare between Animal and Plant cell? Page 114 - 115

المادة الوراثية الشبكة الإندوبلازمية نوية النواة الجدار النووى سوط حركى جسم مركزى ريبوسوم حهاز جولـﭽـى غشاء بلازمى حلمات دقيقة ميتوكوندريا جسم مُحلل الهيكل الخلوى Fig. 7.7, Page 114

فجوة مركزية بلاستيدة خضراء ثقوب بينية الجدار الخلوى ثقوب بينية Fig. 7.8, Page 115