Topic 6 Flashcards by Caley Sloan

What is a virus

Smallest microorganisms
Arrangement of genetic material and protein
Obligate intracellular parasites (can only exist and reproduce in the cells of other organisms

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Structure of viruses

What is the capsid?

Protein coat

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What makes up the capsid

Capsomere

Repeating protein units

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What is the point of repeating units in the capsid

Minimise the amount of genetic material needed to code for coat production

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Some viruses have an envelope in their structure what is the purpose of this and what is it made up of

Lipid derived membrane
Presence makes it easier for the virus to pass from cell to cell
However it makes it vulnerable to substances such as Ethers which dissolve lipids

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Structure of a virus what is contained in the nucleic acid

Viral genetic material can be RNA or DNA and the nucleic acid is sometimes double-stranded and sometimes single

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What is viral DNA used for

Acts as a template for both new viral DNA and for the mRNAs needed to induce synthesis of viral proteins

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Give examples of DNA viruses

Smallpox virus

Adenoviruses (which causes colds etc)

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What are bacteriophages

Viruses that infect bacteria

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What is a viral RNA used for

Synthesis of enzyme called reverse transcriptase which proceeds to make DNA molecules corresponding to the viral genome
This DNA is used as a template for new viral proteins

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Give examples of RNA viruses

Tobacco mosaic virus

Human immunodeficiency virus

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How do viruses attach to their host cells

By antigens which target proteins in the host cell surface membrane

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What two ways can viruses infect a cell

Lysogenic pathway

Lytic pathway

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Describe the life cycle of a retrovirus

Viral RNA translated into DNA by reverse transcriptase in the cytoplasm
Viral DNA enters nucleus where it is inserted into the host cell
Host makes viral genome RNA, mRNA and coat proteins
Virus particles assemble and leave by exocytosis
Viral DNA remains in the nucleus the cell continues to act as a virus factory

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What can viral infections be specific to

Particular tissues

E.G Adenoviruses viruses which cause colds affect the tissues of the respiratory tract

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What is the specificity due to

The presence or absence of cell markers on the surface of host cells
Each type of cell has its own recognition markers and different types of virus can only bind to particular markers

The presence or absence of these markers can affect vulnerability

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What are angiosperm and Gymnosperms

Flowering Plants (vulnerable)
Conifers (not vulnerable)

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Describe the lysogenic pathway

Bacteriophages attacks bacterium

Phage DNA injects viral dna into host cell synthesis of viral enzymes

Viral DNA is incorporated into host cell DNA
Viral DNA is replicated each time the bacterium divides without causing any damage

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Describe the Lytic pathway

Phage DNA inactivates the host DNA and takes over the cell

Phage DNA is replicated

New Phage Particles are assembled as new protein coats are made around phage DNA
the enzyme lysozyme is synthesised or released

Lysis- the bacterial cell bursts due to the action of the lysozyme releasing up to 1000 phages to infect other bacteria

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Are the contents of bacteria hypertonic hypotonic or isotonic?

Hypertonic this results in more water moving in By osmosis

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State the main features in bacteria

Cell-surface membrane 
Cell wall
Circular DNA
 photosynthetic membrane*
Capsule or slime layer*
Flagellum 
Small ribosomes
Glycogen granules, lipid droplets

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What is the purpose of a cell wall in bacteria

Prevents the swelling and bursting
Maintain shape and support
Protection

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Where is the site of respiration in bacterial cells

Bacterial cells have no mitochondria so cell membrane is the site of respiratory enzymes

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Some bacterial cells have a slime capsule, why?

Formed from starch gelatin protein

protects bacteria from phagocytosis by covering cell markers

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flagellum????

The flagellum moves the bacterium by rapid rotations

Describe genetic material found in bacteria cell

Single length of circular DNA lying free in the cytoplasm

What makes up a bacterial cell wall

Consist of a layer of peptidoglycan

Describe the structure of peptidoglycan

Many parallel polysaccharide chains with short peptide cross linkages Net like structure

What are the two types of cell walls

Gram-positive bacteria | Gram-negative bacteria

What colour are gram-positive bacteria compared to gram-negative

+ve = purple -ve= red

State the key differences between the two types of cell walls

+ve Thicker layer of peptidoglycan Contains teichoic acid -ve Thinner layer of peptidoglycan No teichoic acid

Explain the colour differences

The crystal violet binds to the teichoic acid and resists decolourising, leaving the purple/blue colour In negative, no teichoic acid to bind to so crystal violet decolourises and is replaced by red safranine, so cells appear red

What other features can be used to classify bacteria

Shape | Respiratory requirements

What 4 categorical shapes are there

Spherical (cocci) Rod shape (bacci) Twisted. (Spirilla) Comma shape (vibrios)

What's is meant by: Obligate aerobes

Need oxygen

What's is meant by: Facultative anaerobes

Use oxygen if it is available but can manage without

What's is meant by: Obligate anaerobes

Can only respire in the absence of oxygen

2 ways infectious diseases be transmitted?

Transmitted from person to person by invading microorganisms Natural flora getting out of control and becoming pathogenic

What ways can bacteria reproduce

``` asexual reproduction (binary fission) Sexual reproduction ```

Give 3 ways in which genetic material form one bacterium can be taken in and used as part of the DNA of another bacterium

Transformation Transduction Conjugation

Explain transformation

Short piece of DNA is released by a donor and taken up by a recipient where it replaces a similar piece of DNA

Explain transduction

DNA transferred by a bacteriophage

Explain conjugation

Genetic material transferred by direct contact | Sex pilus, cytoplasmic bridge DNA. Transferred

Typically where does bacteria grow

In localised areas, unless they get into the blood stream

What two types of toxins are there

Endotoxins Exotoxins

What are exotoxins, what are they likely to cause?

Lipopolysaccharides- part of the outer layer of gram negative Rarely fatal, tend to cause symptoms such as fever, vomiting or diarrhoea E.g. Salmonella E.coli

What are exotoxins, what damage do they cause? Example?

Soluble proteins produced/releases as bacteria metabolise and reproduce Can damage cell membranes (Cell breakdown, internal bleeding) Poison cells E.g meningitis

Give 6 ways a pathogen can invade the body

``` Fomites Vectors Direct contact Inhalation Ingestion Inoculation ```

Explain how pathogens can enter by vectors (example?)

Living organism transmits infection from one host to another E.g malaria, yellow fever

Explain and give an example of how pathogens can invade the body by fomites

Fomites are inanimate objects that carry pathogens from one host to another E.g. Hospital towels/bedding Staphylococcus infections

How can pathogens be spread by direct contact (examples)

Spreading skin diseases Sexual diseases E.g impetigo and herpes

How can pathogens be spread by inhalation

Cough/sneeze droplets expelled carrying pathogens, water evaporates pathogens remain in air Examples influenza and TB

Describe how ingestion can cause pathogens to invade body | Examples

Gut diseases Transmitted by contaminated food or drink E.g. Salmonella, hepatitis a

Explain inoculation | Examples

Pathogens enter body through breaks in the skin Through injury, contaminated medical instrument or shared needles HIV, tetanus, hepatitis B

How is skin a barrier to infection

Natural flora- out compete Impenetrable layer (toughened with keratin) Sebum-> chemicals inhibit growth of microorganisms Surfaces of tubes/ducts vulnerable so mucus containing lysozyme effective protection

What is lysozyme

Enzyme which destroys microbial cell walls Effective against gram positive Present in tears and mucus

What else is present on the epithelial surface

Phagocytic WBCs engulf and digest pathogens

What are the four non-specific response to infection

Fever Inflammation Lysozymes Phagocytosis

What are the two main groups of white blood cells

Granulocytes | Agranulocytes

Define phagocyte

General term used describe white blood cells which engulf and digest pathogens

What are the two main types of phagocytes

Neutrophils (Mostly granulocytes) Macrophages (Agranulocytes)

What is pus

Accumulation of dead cells, mainly neutrophils but also macrophages which produce antibodies