Microbiology Lecture Exam 4

Viruses

Small, acellular, composed of nucleic acids and proteins, obligate intracellular parasites

Obligate intracellular parasites

Require a host cell to replicate, don’t perform any metabolic functions outside of cells

Capsid

Protein coat composed of capsomeres

Envelope

Derived from host membrane and may contain spikes

Virion

Complete, fully developed, infectious viral particle

Attachment

Viral proteins bind to host cell receptors

Entry

Crossing cell’s plasma membrane via receptor mediated fusion or endocytosis

Receptor mediated fusion

Performed by envelope viruses only —viral envelope fuses with cell’s plasma membrane and capsid and nucleic acids are released into cell’s cytoplasm

Receptor mediated endocytosis

Performed by enveloped and non-enveloped viruses — host cell’s plasma membrane folds over virus — whole virus enters the cell

Host range

Spectrum of cells a virus can infect determined by interaction between viral proteins and receptors on host cell

Uncoating

Capsid and nucleic acids are separated by host lysosomal enzymes or acidification —> nucleic acids travel to replication site

Biosynthesis

DNA/RNA replication, mRNA transcription, protein translation

DNA Virus Replication

DNA replication via host cell DNA polymerase in nucleus —> DNA transcribed in mRNA via host cell RNA polymerase in nucleus —> viral mRNA translated into viral proteins in ribosomes

RNA Virus Replication

viral RNA is replicated via RNA-Dependent RNA Polymerase in cytoplasm—> translated into proteins (can be + or - sense)

+sense

Function as mRNA and can be translated immediately in ribosomes

-sense

Doesn’t function as mRNA —> must be replicated into + sense mRNA via RNA-dependent RNA polymerase in the cytoplasm —> + sense mRNA is then translated into viral proteins in the ribosomes

Retrovirus

RNA viruses that integrate into host cell genome

Retrovirus Replication

RNA is converted to DNA via reverse transcriptase in the cytoplasm —> viral DNA integrates into host cell chromosome —> provirus

Maturation

Assembly of virions — viral nucleic acids put inside capsids

Release

Enveloped — budding

Non-enveloped — rupture

Budding

Capsid pushes through plasma membrane —> part of plasma membrane sticks to capsid —> becomes envelope

Rupture

Viruses repute plasm membrane and non enveloped viruses are released from host cell —> results in cell death

Antiviral drugs

Inhibit any of the steps of infection

Acyclovir and Valacyclovir

Inhibit Herpes virus by inhibiting nucleic acid synthesis using nucleic acid analog

Nucleic acid analog

Look Luke nucleic acids

Infererons

Boost immune response

Herpes Simplex Virus (HSV-1, HSV-2)

Enveloped DNA Virus example

Rabies Virus

Enveloped RNA virus example

HIV

Retrovirus example

HSV-1

Oral herpes, latent in trigeminal ganglia, active in oral mucosa

HSV-2

Genital here pets, latent in sacral ganglia, active in genital mucosa

Rabies

Transmitted via animal bites

Symptoms: hydrophobia, muscle spasms, paralysis

Furious Rabies

Hydrophobia, excessive salivation, aggression, viral encephalitis — death in 5-7 days

Paralytic rabies

Muscle paralysis, viral encephalitis, coma — death in 11 days

Oncogene

Gene with ability to convert normal cell —> cancer cell

Caused by mutagens, viruses, or inherited

HPV 16 and 18

Linked to cervical cancer

HPV 6 and 11

Cause genital warts

Bacteriophages

Viruses that infect bacteria

Lytic cycle

Result in cell death

Lysogenic cycle

Viral DNA integrates → cell lives

Lambada

Example of bacteriophage with Lysogenic cycle

1. Attachment

Bacteriophage tail fibers attach to receptors on bacteria

2. Penetration

Lysosome is released to degrade bacterial cell wall → sheath contracts and corer plunges through cell wall

3. Biosynthesis

Bacteriophage DNA is copied → transcribed into mRNA → translated into bacteriophage proteins

4. Maturation

Bacteriophage parts are assembled

5. Release

Lysozyme breaks up bacterial cell wall → lyses → bacteriophages are released

Prions

Infectious proteins that can infect animals and humans and are resistant to heat, radiation, and enzymes causing TSE

TSE

Transmissible spongiform encephalitis

PrPC

Cellular form found in tissues of healthy people/animals — sensitive to denaturing agents

PrPSC

Scrapie protein, harmful form, resistant to denaturing agents

Prions disease

Cause PrPC → PrPSC

Kuru

Example of Prion disease that is transmitted via cannibalism of the brain resulting in trembling, depression/uncontrollable laughter, loss of ability to walk, swallow, and sleep

Immune System

Functions to prevent or limit infection

Antigen

Anything that elicits an immune response

Innate immunity

Rapid, nonspecific, no memory

Adaptive immunity

Slow, specific, memory

First line of defense

Physical, chemical, microbiological

Physical

Skin, mucus, tears, vaginal secretions, reflexes, and hairs of nose and ears

Chemical

Lysozyme and acids

Microbiological

Normal flora

Second line of defense

Phagocytes, inflammation, fever, antimicrobial substances

Red blood cells

Oxygen transport

White blood cells

Immunity

Platelets

Clotting

Hematopoiesis

Process of forming new blood cells in bone marrow from hematopoietic stem cells

Granulocytes

Contains visible granules

Neutrophils

40-70%, bacterial and fungal infections, phagocytosis

Eosinophil

1-5%, parasitic infections and allergies

basophils

<1%, parasitic infections and allergies

Agranulocytes

No visible granules

Lymphocytes

25-40%, viral infections

Monocytes

2-6%, viral infections and antigen presentation

Mast cells

Parasites and allergies in tissues

Dendritic cells

Antigen presentation in tissues

T cells

Cellular immunity

B cells

Humoral immunity

Lymphatic system

Collect, circulate, and filter fluid before it returns to blood

Lymph

Water, antibodies, lymphocytes

Primary lymphoid tissue

Bone marrow and thymus

Secondary lymphoid tissue

Lymph nodes, spleen, MALT (mucous associated lymphoid tissue: tonsils, appendix, Peyer’s patches)

Cytokines

Cell communication between immune cells

Chemokines

Attract WBCs through chemotaxis

Interleukins (IL)

WBC communication

Interferons (IFN)

Viral replication/tumor formation inhibition

Tumor necrosis factors (TNF)

Inflammation

Phagocytosis recognition

Toll-like receptor (TLR) on phagocyte binds to pathogen associated molecular pattern (PAMP) on microbe

Inflammation

Confine, destroy and remove damaging agent → repair tissue

Fever

Triggered by IL-1 and TNF alpha

Classical Pathway

Antibody → MAC

MAC

Membrane attack complex

Alternative pathway

C3b binding → MAC

Lectin Pathway

Mannose binding lectin binds to mannose → MAC

Opsonization

Coating antigen with molecules that enhance phagocytosis — c3b

interferons

Cytokines released by damaged cells

C3 → C3 Convertase → c3a + c3b

All compliment pathways involve

Iron binding proteins

Bind to iron to make it less available to pathogens

Ex. Hemoglobin

Cellular immunity

T cell response

Humoral immunity

Antibody response

B cells

Hematopoietic stem cells in bone marrow → immature B cell → mature in bone marrow

T cells

Hematopoietic stem cells in bone marrow → immature T cell → mature in thymus