Chapter Fourteen Viruses Cancer and Immunology Viruses Viruses

Chapter Fourteen Viruses, Cancer, and Immunology

Viruses • • • Viruses are pathogens of bacteria, plants, and animals Can be deadly (e. g. , Ebola, HIV) Can be merely annoying (e. g. , Rhinovirus) Viruses are small particles composed of nucleic acid and protein Entire particle is known as a virion Capsid- surround the center of the virion Nucleocapsid- combination of the nucleic acid and the capsid Membrane envelope- surrounds the nucleocapsid Protein spikes- help viruses attach themselves to the host cell

Architecture of a Virus

Virus Life Cycle

How Does a Virus Infect a Cell • A Virus must attach to the host cell before it can penetrate • A common method of attachment involves the binding of one of the spike proteins on envelope of the virus to a specific receptor on the host cell An example is HIV attachment

Life cycle of a Retrovirus LTR: long terminal repeat

The Immune System • The immune system allows for the distinction between self from nonself • This allows cells and molecules responsible for immunity to recognize and destroy pathogens • The immune system can also go awry in distinguishing self from nonself. This results in an autoimmune disease, in which the immune system attacks the body’s own tissues • Allergies are also another type of improper functioning of the immune system

Innate Immunity (Cont’d) • There are several parts to innate immunity: physical barriers, cells of the immune system (dendritic cells, macrophage, and natural killer (NK) cells) • Dendritic cells and macrophages are members of a class of cells called antigen-presenting cells (APCs) • Major histocompatibility complex (MHC) : antigen presenting proteins on APCs. • Another important cell type in the innate immunity system is the natural killer (NK) cells, which is a type of leukocyte

natural killer (NK) cell • Derived from a type of stem cell called a lymphoid stem cell. • Kill off cells that have been infected by viruses or that are cancerous. • They release cytokines that call up other cells, such as macrophage, another innate immunity cell type. • NK cells help decide whether the acquired immunity system needs to be activated. • They are simulated by interferon, antiviral glycoprotein to fight cancer.

Acquired Immunity • Acquired immnunity is dependent on two other types of lymphocytes : T cells and B cells. • T cell: thymus, cellular aspect • B cell : bone marrow, molecular aspect. • Helper T cells release chemicals called cytokines that stimulate other members of the immune system, e. g. killer T cells and B cells • T cells differentiate, and become specialized for one of several possible functions.

How Helper T Cells Aid in the Development of B Cells

Antibodies • Antibodies are Y-shaped molecules consisting of two identical heavy chains and two identical light chains held together by disulfide bonds • Antibodies are glycoproteins

Antibody role on pathogen removing

Cancer • Cancer is the leading cause of death in human beings • It is characterized by cells that grow and divide out of control, often spreading to other tissues and causing them to become cancerous

Cancer (Cont’d) • All life-threatening cancers have at least six characteristics in common 1) Cancer cells continue to grow and divide in situations in which normal cells do not 2) Cancer cells continue to grow even when the neighboring cells send out “stop-growth” signals 3) Cancer cell manage to keep going and avoid a “self-destruct” signal that usually occurs when DNA damage has occurred 4) They can co-opt the body’s vascular system, causing the growth of new blood vessels to supply the cancerous cells with nutrients 5) They are essentially immortal 6) Cancer cells have the ability to break loose, travel to other parts of the body and create new tumors which make them lethal, this is called metastasis

What Causes Cancer? • Changes in DNA cause changes to specific proteins that are responsible for controlling the cell cycle • Most mutations of DNA affect two types of genes: 1) Tumor suppressor, a gene that makes a protein that restricts the cell’s ability to divide 2) An oncogene is one whose protein product stimulates growth and cell division. Mutations of an oncogene cause it to be permanently active