4.1 Flashcards
What is a pathogen?
A microorganism that causes disease
How do pathogens thrive?
A host body creates a good habitat in which the microorganism can live.
Pathogens live by taking nutrition from their host, but also cause damage in the process.
What is a host?
The organism in which a pathogen lives in. A host body creates a good habitat in which microorganisms can live.
Pathogens live by taking nutrition from their host, but also cause damage in the process.
What is transmission?
- Passing a pathogen from an infected individual to an uninfected individual
What are the four main pathogens?
- Bacteria
- Viruses
- Fungi
- Protoctista
What are features of Bacteria?
- Prokaryotic cells
- Can reproduce rapidly in just 20 minutes
- Damage cells or release waste products and/or toxins.
- In plants, the bacteria often live in the vascular tissues
What are features of Fungi?
- Fungi often live in the skin of animals, and where its hyphae, which forms a mycelium, grow under the surface of the skin
- The fungus can send out specialized reproductive hyphae, which grow to the surface of the skin to release spores. This causes redness and irritation.
- Fungi often live in the vascular tissue of plants, where they can gain nutrients.
- The hyphae release extracellular enzymes, such as cellulases, to digest the surrounding tissue, which causes decay.
What are features of Viruses?
- Viruses invade cells and take over the genetic machinery and other organelles of the cell. They then cause the cell to manufacture more copies of the virus.
- The host cell eventually bursts, releasing many new viruses which will infect healthy cells.
What are features of Protoctista?
- These animal-like organisms usually cause harm by entering host cells and feeding on the contents as they grow
What are examples of diseases caused by BACTERIA?
- Tuberculosis (Mycobacterium Tuberculosis and M. Bovis)
- Bacterial Meningitis
- Bacterial Ring Rot (potatoes, tomatoes)
What are examples of diseases caused by VIRUSES?
- Human immunodeficiency virus (HIV)
- Influenza
- Tobacco mosaic virus
What are examples of diseases caused by PROTOCTISTA?
- Blight (potatoes and tomatoes)
- Malaria (Plasmodium falciparum)
What are examples of diseases caused by FUNGI?
- Ringworm (cattle)
- Athlete’s Foot
- Black Sigatoka (bananas)
What does the life cycle of a pathogen involve?
- Transmision
- Entering a host’s tissues
- Reproducing
- Leaving the host’s tissues
What is direct transmission?
- Passing a pathogen from host to host, with no intermediary
What are the four methods of Direct Transmission?
- Direct physical Contact
- Faecal-Oral Transmission
- Droplet infection
- Transmission by spores
What are the factors that affect the rate of transmission via Direct Physical contact?
- Washing hands regularly
- Keeping surfaces clean
- Cleaning and disinfecting cuts and abrasions
- Sterilizing surgical instruments
- Using Condoms
What are the factors that affect the rate of transmission via Faecal-oral?
- Using Human sewage to fertilise crops
- Treatment of drinking water
- Washing of food
- Careful preparation and thorough cooking of all food
What are the factors that affect the rate of transmission via Droplet infection?
-Catch in, Bin it, Kill it
- Cover your mouth when coughing and sneezing
What are the factors that affect the rate of transmission via Spores?
- Use of a mask
- Washing skin after contact with soil
What social factors affect transmission?
- Hygiene
- Cultural practices
- Overcrowding
- Poor Ventilation
- Poor previous health
- Poor diet
- Homelessness
What are some diseases caused by direct physcial contact?
- HIV
- Bacterial Meningitis
- Ringworm
- Athletes foot
What are some diseases caused by Faecal-Oral transmission?
- Cholera
- Food Poisoning
What are some diseases caused by Droplet infection?
- Tuberculosis
- Influenza
What are some diseases caused by transmission by spores?
- Anthrax
- Tetanus
What is indirect transmission?
- Passing a pathogen from host to host, via a vector
What is a vector?
An organism that carries a pathogen from one host to another
What are some diseases caused by vectors?
- Malaria
How is Malaria Transmitted?
- A person with malaria contains Plasmodium gametes in their blood
- A female Anopheles mosquito bites and sucks the human’s blood
- Plasmodium develops and migrates to the mosquitos’ salivary glands
- An uninfected person is bitten
- Plasmodium migrates to the liver and blood
How are pathogens transmitted in plants?
Direct transmission:
- Entering the roots from soil
- Airborne transmission of spores
- Pathogens within seeds
Indirect Transmission:
- Result of an insect attack
- Spores or bacteria become attached to a burrowing insect, which attacks an infected plant
What are passive defenses?
These are defenses present before infection, and their role is to prevent entry and the spread of the pathogen.
Passive defenses include physical barriers and chemicals.
How does the Cellulose cell wall act as a physical defence?
This not only acts as a physical barrier but most plant cell walls contain a variety of chemical defenses that can be activated when a pathogen is detected
How does the Lignin thickening of cell walls act as a physical defence?
Lignin is waterproof and almost completely indigestible
How does the waxy cuticle act as a physical defence?
These prevent water from collecting on the cell surfaces.
Since pathogens collect in water and need water to survive, the absence of water is a passive defense
How does Bark act as a physical defence?
Bark contains a variety of chemical defences that work against pathogenic organisms
How does stomatal closure act as a physical defence?
Stomata are the possible entry points for pathogens. The stomatal aperture is controlled by the guard cells.
When pathogenic organisms are detected, the guard cells will close the stomata in that part of the plant.
What is callose?
A large polysaccharide deposit that blocks old phloem sieve tubes
How does Callose act as a physical defence?
Callose is a large polysaccharide that is deposited in the sieve tubes/phloem at the end of a growing season.
It is deposited around the sieve plates and blocks the flow in the sieve tube. This can prevent a pathogen from spreading around the plant.
What is Tylose?
A balloon-like swelling or projection that fills the xylem vessel
How does Tylose formation act as a physical defence?
A Tylose is a balloon-like swelling or projection that fills the xylem vessel.
When a tylose is fully formed, it plugs the vessel meaning the vessel can no longer carry water.
Blocking the xylem vessel prevents the spread of pathogens through the heartwood. The tylose contains a high concentration of chemicals such as terpenes that are toxic to pathogens.
What chemical defences do plants have?
Plant tissues contain a variety of chemicals that have anti-pathogenic properties.
These include terpenoids, phenols, alkaloids, and hydrolytic enzymes.
Many chemicals are produced after infection as producing them requires a lot of energy. However, some are present as passive defenses.
What are active defences?
Active defences are employed in response to the presence of a pathogen; they try to kill the pathogen and prevent its spread.
How do plants know when they’ve been infected?
Specific chemicals in pathogen cell walls can be detected by the plant cells. These chemicals include specific proteins and glycolipids.
The plant responds by fortifying the defences already present.
What happens to Cell walls during active defence?
- Cell walls become thickened and strengthened with additional cellulose
- Callose is deposited between the cell wall and membrane. It blocks cellular penetration, strengthens the cell wall, and blocks the plasmodesmata.
What happens to chemicals during active defence?
- An increase in the production of chemicals
- Oxidative bursts produce highly reactive oxygen molecules capable of damaging the cells of invading organisms.
What is the action of Terpenoids?
- Essential oils that have anti-pathogenic properties. Their scent may also deter pathogens.
What is the action of Phenols?
- Have anti-pathogenic properties. Tannins found in bark kill some insects.
What is the action of Alkaloids?
- Nitrogen-containing alkaloids give plants a bitter taste to inhibit herbivores feeding.
- Some alkaloids inhibit protein synthesis
What is the action of hydrolytic enzymes?
- Found in the spaces between cells
- They include chitnases, gluucanases and lysozomes
What is the action of defensins?
- Small cysteine-rich proteins that have broad anti-microbial activity which can inhibit the plasma membrane in pathogens
What is Necrosis?
- Deliberate cell suicide. A few cells are sacraficed to save the rest of the plant.
- By killing cells surrounding the infection, the plant can limit the pathogens access to water and nutrients.
What is a Canker?
A sunked necrotic lesion in woody tissue. It causes death of the cambium tissue in the bark.
What are primary defences?
Those that prevent pathogens from entering the body. They are non-specific.
What are 5 primary defences?
- The skin
- Blood clotting and skin repair
- Mucous membranes
-Coughing and Sneezing - Inflammation
How does the Skin act as a primary defence?
The outer layer of skin cells are called Keratinocytes.
These cells are produced via mitosis in the epidermis.
They then die, dry out and the cytoplasm is replaced by keratin.
The keratinized layer of dead cells acts as an effective barrier to pathogens.
How does Blood Clotting and Skin Repair act as a primary defence?
Blood clotting involves calcium ions and at least 12 other clotting factors.
These factors are released from platelets and from damaged tissue. These factors activate an enzyme cascade.
- The first stage of skin repair is the deposition of fibrous collagen under the scab.
- Stem cells in the epidermis then divide to form new cells which migrate to the edges of the cut and differentiate to form new skin.
New blood vessels grow to supply the new tissues.
How do mucous membranes act as a primary defence?
The epithelial layer of vulnerable areas contains mucus-secreting, goblet cells.
In the airways, the mucus lines the passages and traps any pathogens that may be in the air. They are then moved up and swallowed.
Mucous membranes are also found in the gut, genital areas, anus, ears, and nose.
What is mucous membrane?
Specialized epithelial tissue that is covered by mucus.
How does coughing and sneezing act as a primary defence?
A cough or sneze is a natural reflex in response to irritation in which the sudden expulsion of air will carry the pathogen out.
What is inflammation?
Swelling and redness of tissue caused by infection
How does inflammation act as a primary defence?
- The presence of microorganisms in the tissue is detected by specialized cells called Mast Cells, which release a cell signaling substance called Histamines.
- Histomaines vasodilate capillaries and allow White Blood cells and proteins to drain into the tissue fluid. This leads to an increase in the production of tissue fluid which causes swelling.
- Excess tissue fluid is then drained into the lymphatic system carrying the WBC which can cause them to come into contact with pathogens.
What are two other primary defences?
- Tear fluid contains antibodies and enzymes
- Ear canal is lined by wax, which traps pathogens
What are Secondary Defences?
Defenses used to combat pathogens that have already entered the body.
What are Antigens?
Antigens are Protein or glycoprotein chemical markers on the cell surface of pathogens.
What are Opsonins?
Opsonins are a type of antibody that bind to the antigen on a pathogen and then allow phagocytes to bind and engulf the pathogen.
What is the first line of secondary defence?
Phagocytosis.
Specialized cells in the blood and tissue fluid engulf and digest the pathogens.
What is the process of Phagocytosis?
- Pathogen becomes attached to the surface of a phagocyte
- The cytoplasm/ cell membrane extends to surround the pathogen
- The pathogen is consumed via endocytosis/phagocytosis and is put into a phagosome/ phagocytic vesicle
- The phagosome and lysosome fuse. Hydrolytic enzymes and hydrogen peroxide are injected into the pathogen.
- Pathogen is broken down into amino acids/ fatty acids
- Products are absorbed into the cytoplasm. Unwanted products are removed by exocytosis.
What are the features of neutrophils?
- Most common Phagocyte
- Mulit-lobed nucelus
- Manufactured in the bone marrow and travel in the blood and tissue fluid.
- Are short-lived so are released in large numbers after an infection
- Contain large nuumbers of lysosomes to engluf and destroy pathogens
How are neutrophils specilaised fro their role?
Plasma membrane contains receptors for opsonins, well developed cytoskeleton for phagocytosis, many mitochondria for respiration, many ribosomes to make enzymes, many lysosomes.
What are the features of macrophages?
- Another type of phagocyte
- Manufactured in the bone marrow, move as monocytes, and settle in the body tissues and lymph nodes.
- Engulfs pathogens but does not fully digest them. The antigen from the pathogen is saved and moved to a specilal protein complex on the surface of the macrophage.
- The macrophage becomes an Antigen-presenting cell so that lymphocytes can recognise the antigen quicker to destroy the other pathogens.
What is clonal selection?
The selection of a specific B or T cell that is specific to the antigen.
It is stimulated and coordinated by chemicals called cytokines.
What are antibodies?
Specific proteins released by plasma cells that can attach to pathogenic antigens
What is clonal expansion?
An increase in the number of cells by mitotic cell division
What is the role of T Helper Cells?
- Binds onto foreign Antigen
- Undergoes clonal selection (clones itself)
- Secrets Cytokines called interleukins which stimulate the B cells to develop and phagocytes to undergo phagocytosis
What is the role of T Killer/ Cytotoxic Cells?
- Binds onto foreign Antigen on APC
- Undergoes clonal selection (clones itself)
- Destroys the cell they are bound to (Enzymes or hydrogen peroxide)
What is the role of T Memory Cells?
- Able to live for a long time
- Capable of responding quickly if pathogen re-enters the body
- Provides long-term immunity
What is the role of T Regulator Cells?
- Shuts down the immune response after the pathogen has been removed
- Involved in preventing autoimmunity
What is the role of B Plasma Cells?
- Contain additional protein-making machinery
- Rapidly sythesise lots of specific antibodies and release them by exocytosis
- Dont live for a long time
What is the role of B Memory Cells?
- Able to live for a long time
- Capable of responding quickly if pathogen re-enters the body (differentiates back into B Plasma cells)
- Provides long-term immunity
How do macrophages communicate with other cells?
- Release monokines
- Some attract neutrophils by chemotaxis
- Some stimulate B cells to release antibodies
How do T Cells and Macrophages communicate with other cells?
- Release interleukins
- Stimulate clonal expansion
- Stimulate B and T cells to differentiation
What is interferon?
A distress signal which inhibits virus replication and stimulates T KIller/Cytotoxic cells
What is an autoimmune disease?
A disease in which the body’s immune system attacks healthy cells.
Antibodies start to attack the body’s own antigens - possibly because antigens that are not normally exposed become exposed.
Normally, any B or T cells that are specific to our own antigens are destroyed during the early development of the immune system.
What is the structure of antibodies?
Antibodies are immunoglobin proteins produced by the plasma cells.
They are Y-shaped and have two distinct regions. The variable region has a specific shape to the shape of the antigen. The constant region is the same in all antibodies.
They consist of four polypeptide chains held together by disulfide bridges. There is a light and heavy polypeptide chain with a hinge region in between to allow greater flexibility when holding more than one antigen.
What is an immunogloblin?
An immunoglobulin is a complex protein associated with the immune system. They are found in the blood and are able to bind to antigens.
What are the three main types of antibodies?
- Opsonins
- Agglutinins
- Anti-toxins
What do Opsonins do?
Opsonins are antibodies that make it easier for phagocytes to engulf pathogens.
Some opsonins attach to pathogens and act as binding sites for phagocytes.
Some opsonins attach to antigens involved in binding to host cells. This renders the pathogen useless as it prevents the pathogen from entering a host cell. This is known as neutralization.
What do Agglutinins do?
Agglutinins are antibodies that cause pathogens to stick together.
Because each antibody has two identical binding sites, it is able to form crosslink pathogens.
When many antibodies form crosslinks they clump together (agglutinate) pathogens.
This means that pathogens are impeded from carrying out some functions, such as entering host cells, and the pathogens are readily engulfed by pathogenic cells.
What are Anti-toxins?
Anti-toxins are antibodies that render toxins harmless
Some antibodies bind to molecules that are released by pathogenic cells.
These molecules may be toxic and the action of anti-toxins renders them harmless.
What is the primary immune repsonse?
The initial response is caused by a first infection. It usually takes a while as the body has to work through all the stages of the immune response.
What is the secondary immune response?
A more rapid and vigorous response is caused by subsequent reinfection by the same pathogen. It is much quicker as the memory cells quickly recognize the antigen and begin to churn out large quantities of antibodies.
Why does it take several days for the primary immune response to become effective?
After infection, the pathogen must be detected and attacked by macrophages; antigen presentation occurs to select the correct B and T cells; these cells must reproduce in clonal expansion; then they must differentiate to form plasma cells; the plasma cells must start to produce the antibodies - each step takes time.
What is Vaccination?
A way of stimulating an immune response so that immunity is achieved.
What is active immunity?
Where the immune system is activated and manufactures its own antibodies
What is artificial immunity?
Where immunity is achieved as a result of medical intervention
What is natural immunity?
What is natural immunity?
What is passive immunity?
Immunity achieved when antibodies are passed to the individual through breastfeeding or injection
How do vaccines work?
Deliberate exposure to antigenic material that has been rendered harmless.
The antigenic material is usually injected, but in some cases taken orally. The immune system treats the antigenic material as a real disease.
What different forms can antigenic material be in vaccines?
- Whole, live organisms
These are usually not as harmful, but contain very similar antigens. - A harmless or attenuated (weakened) version of the pathogenic organism
- A dead pathogen
- A preparation of the antigens from a pathogen
- A toxoid, which is a harmless version of a toxin
What is herd vaccination?
Using a vaccine to provide immunity to all or almost all of the population at risk.
Once enough people are immune, the disease can no longer be spread and you achieve ‘herd immunity
What is ring vaccination?
Using a vaccine when a new case of disease is reported and all those in the immediate vicinity of the new case are vaccinated.
Why are new drugs always needed?
- New diseases are always emerging
- There are still many diseases for which there are no effective treatments
- Some antibiotic treatments are becoming less effective
How can medicines be discovered?
- Accidental discovery
- Traditional remedies
- Observation of Wildlife
- Further plant research
- Research into disease-causing mechanisms
- Synthetic Biology
