Infection and Response Topic 3

• Pathogens are microorganisms that enter the body and cause disease.
• They cause communicable diseases.

Bacteria:

• Very small cells (about 1/100th the size of your body cells), which can reproduce inside your body. They can make you feel ill by producing toxins that damage your cells and tissues. 

Viruses:

• Not cells, they're tiny, about 1/100th the size of a bacterium. 
• They can reproduce quickly inside your body. 
• They live inside your cells and replicate themselves using the cell's machinery to produce many copies of themselves.
• The cell will usually then burst, releasing all the new viruses. 
• This cell damage is what makes you feel ill.

Protists:

• they're all eukaryotes, most are singe-celled. 
• some protists are parasites - parasites live on or inside other organisms and can cause them damage. They are often transferred to the organism by a vector, which doesn't get the disease itself. 
• Fungi: 
• some are single-celled
• others have a body which is made up of hyphae (thread like structures). These hyphae can grow and penetrate human skin and the surface of plants, causing diseases. The hyphae can produce spores, which can be spread to other plants and animals. 
• Pathogens can be spread in different ways: 
• Through the water, by drinking or bathing in dirty water.
• Through the air, can be carried in air and then breathed in. 
• By direct contact, by touching contaminated surfaces, including the skin.

Measles: spread by droplets from an infected person's sneeze or cough. Symptons: red skin rash, signs of a fever. Measles can be very serious, even fatal, if there are complications - can sometimes lead to pneumonia or a brain infection. Most people are vaccinated against measle when they're young. 

HIV: virus spread by sexual contact or by exchanging bodily fluid such as blood. HIV initially causes flu-like symptons for a few weeks. During this time, HIV can be controlled with antiretroviral drugs which stop the virus replicating in the body. The virus attacks the immune cells. 

TMV: (Tobacco Mosaic Virus) virus that effects many species of plants e.g tomatoes. Causes mosaic pattern on the leaves of the plants and parts of the leaves become discoloured. This means tha the plant can't carry out photosynthesis as well, so the virus affects growth. 

Rose Black Spot: fungus that causes purple or black spots to develop on the leaves of rose plants. The leaves then turn yellow and drop off. This means that les photosynthesis can happen, so the plant doesn't grow very well. Spreads through environment in water or by the wind. can be treated by using fungicides and ********* infected leaves off the plant and destroying the leaves so that the won't spread to other rose plants (BURN BABY BURN!!!)

Malaria: mosquito's are vectors, pick up malarial protist when they feed on infected animal. Infects animal every time it feeds on an animal by inserting protist into animals blood vessels. Malaria causes repeating episodes of fever, can be fatal. People can be protected from mosquitos using insecticides and mosquito nets. 

Salmonella: type of bacteria that causes food poisoning. Symptons: fever, stomach cramps, vomiting and diarrhoea. Symptons caused by toxins that the bacteria produce. Can be infected by eating food that's been contaminated with Salmonella bacteria. 

Gonorrhoea: STD, passed on be sexual contact, caused by bacteria, symptons: pain when urinating, thick yellow or green discharge from penis or vagina. Was originally treated with antibiotic (penicillin) but strains of bacteria became resistant now. People can be treated with antibiotics to prevent the spread and should use barrier methods of contraception such as condoms. 

spread of disease can be reduced or prevented by: 

• being hygienic - using simple hygiene measures.
• Destroying vectors - to prevent the disease from getting passed on. Vectors that are insects can be killed using insecticides or by destroying their habitat so that they can no longer breed. 
• Isolating infected individuals 
• Vaccination - means people can't develop infection and then pass it on to someone else. 

• Skin acts as a barrier to pathogens. Also secretes antimicrobial substances that kill pathogens. Hair and mucus in your nose trap particles that could contain pathogens. Trachea and bronchi secrete mucus to trap pathogens. Trachea and bronci lined with cilia (hair-like structures) which waft the mucus up to the back of the throat where it can be swallowed. Stomach produces Hydrochloric acid that kills pathogens. 
• white blood cells travel in bloodstream. they have 3 lines of attack:
•  
• 1) engulf foreign cells and digest them. This is called phagocytisis. 
• 2) producing antibodies: every invading pathogen has unique antigens on surface. When a w.b.c comes across a foreign antigen, they will start producing proteins called antibodies - they are specific to that type of antigen. Antibodies are then produced rapidly and carried around the body to find all similar bacteria or viruses. Person is naturally immune next time this pathogen comes into body as antibodies will be rapidly produced. 
• 3) producing antitoxins which counteract toxins produced by the invading bacteria. 

Vaccinations involve injecting small amounts of dead or inactive pathogens, These have antigens which cause your body to produce antibodies to attack them. Pathogen is harmless. 

But if live pathogens of the same type appear later, the w.b.c's can rapidly mass-produce antibodies to kill off the pathogen. 

MRSA= vaccination against measles mumps and rubella. 

PROS: helped control lots of communicable diseases that were once common in UK. Epidemics or even pandemics can be prevented if large % of the population is vaccinated. 

CONS: vaccines dont always work, you can sometimes have a bad reaction to a vaccine but bad reactions are rare.

Plants produce a variety of chemicals to defend themselves against pests and pathogens. Some of these chemicals can be used as drugs to treat human diseases or relieve symptons. 

A lot of our current medicines were discovered  by studying plants used in traditional cures.

Some drugs were exctracted from microorganisms. 

 These days, drugs are made on a large scale in the pharmaceutical industry - they're synthesised by chemists in labs. 

However, the process still might start with a chemical extracted from a plant.

Stage 1) preclinical testing- tested on human cells and tissues. however drugs that affect whole or multiple body systems can't be tested. Then it's tested on live animals to test whether the drug works, if it produces the effect you're looking for, to find out it's toxicity and find the best dosage (concentration, how often should be given). in britain drug as to be tested on 2 different live animals. 

stage 2) clinical trial:  tested on healthy volunteers first, to make sure that it doesn't have any harmful side effects when the body is working normally. At the start of the trail, very low dose given and is gradually increased.

Then tested on people suffering from the illness. optimum dose is found (dose that is most effective with few side effects)patients put randomly into 2 groups - one given new drug and other placebo so that doctor can see the actual difference the drug makes and allows for for placebo effect to be dismissed. Clinical trails are blind, sometimes double- blind so that doctors monitorin results and analysing results aren't subconsciously influenced by their knowledge. 

results aren't published until been through peer review. this prevents false claims. 

Antibodies are produced by B-lymphocytes. Monoclonal antibodies produced from lots of clones of a single w.b.c. This means that all of them are idenical and will only target one specific protein antigen. 

lymphocytes dont divide very easily, tumour cells do however - they can be grown easily. 

You can fuse a mouse B-lymphocyte with a tumour cell to create a cell called a hybridoma. 

Mouse injected with chosen antigen before. 

Hybridoma cells can be cloned to get lots of idenical cells. These cells all produce the same antibodies (monoclonal) which are collected and purified. 

You can make them bind to anything you want, useful because you can get them to bind or target a specific cell or chemical in body. 

the bit of the stick you wee on has some antibodies to the hormone HCG (found in urine of pregnant women), with blue beads attached. The test ***** (bit of stick that turns blue if you're pregnant) has more antibodies to the hormone stuck onto it (so they can't move)

if you're pregnant: hormone binds to the antibodies on the blue beads, urine moves up the stick, carrying the hormone and the beads. beads and hormone bind to the antibodies of the *****. so the blue beads get stuck on the *****, turning it blue. 

if you're not pregnant: urine still moves up the stick carrying the blue beads but there's nothing to stick the blue beads onto the test *****, so it doesn't go blue. 

can be used to treat diseases: different cells in body have different antigens on their cell surface. so you can make m. antibodies that will bind to specific cells in your body. Cancer cells have antigens on their cell membranes that aren't found on normal body cells. They're called tumour markers. In the lab, you can make m.antibodies that will bind to these tumour markers and an anti-cancer drug can be attached to these antibodies. This might be a radioactive substance, a toxic drug or a chemical which stops cancer cells growing and dividing. Given to the patient through a drip. Antibodies target specific cells because they only bind to the tumour markers and the drug kills the cancer cells but doesn't kill any normal body cells near the tumour. This means that the side effects of an antibody-based drug are lower than for standard radio or chemotherapy. This is an advantage. They can also be used to bind to hormones and other chemicals in blood to measure their levels, test blood samples in labs for certain pathogens, locate specific molecules on a cell or in a tissue. (antibodies bound to a flourescent dye so that molecules can be detected using this dye)However these antibodies do cause more side effects than were originally expected, such as fever, vomiting and low blood pressure. because of this they're not as widely used as treatments as scientists had originally thought they might be. 

Plants need mineral ions from the soil or they suffer deficiency symptons if there aren't enough. Nitrates are needed to make proteins and therefore for growth. lack causes stunted growth. Magnesium ions needed for making chlorophyll, which is needed for photosynthesis.  lack causes chlorisis and have yellow leaves. 

Plants can be infected by viral, bacterial and fungal pathogens, they can also be infested and damaged by insects. common signs a plant has a disease are: stunted growth, spots on leaves, patches of decay, abnormal growths e.g lumps, malformed stems or leaves, discolouration.

diseases can be identified by looking up the signs in a gardening manual or on a gardening website, taking the infected plant to a laboratory where scientists can identify the pathogen, using testing kits that identify the pathogen using monoclonal antibodies. 

physical defences: most plant leaves and stems have a waxy cuticle which provides a barrier to stop pathogens entering. plant cells surrounded  by cell wallks made from cellulose which form a physical barrier against pathogens that make it past the waxy cuticle. some plants have layers of dead cells, these act as a barrier to stop pathogens entering e.g outer part of bark on trees.

chemical defences: some can produce antibacterial chemicals which kill bactera. other plants produce poisons which can deter herbivores.

mechanical defences: some plants have adapted to have thorns or hairs which stop animals from touching and eating them. others have leaves that droop or curl when someting touches them, they can prevent themselves from being eaten by knocking insects off them and moving away from things. some can cleverly mimic other organisms - this tricks other organisms into not eating them.