Flashcards · Biology
Culturing Microorganisms and Developing Medicines
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What does aseptic mean?
Free from contamination by unwanted microorganisms.
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What does an autoclave do?
Uses steam under pressure, at about 121 °C, to make equipment and medium sterile.
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Why use an autoclave and not boiling?
It reaches a higher temperature, which kills bacterial spores too.
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What is agar?
A jelly made from seaweed, which sets to give a solid medium.
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What does a culture medium contain?
Carbohydrates, proteins or amino acids, minerals and vitamins.
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How is an inoculating loop sterilised?
By heating it in a Bunsen flame until it is red hot.
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Why is the loop cooled before use?
A hot loop would kill the microorganisms being transferred.
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Why is the neck of the bottle flamed?
The flame makes air move outwards, which stops microorganisms falling in.
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Why is the lid taped but not sealed fully?
To let oxygen in, so that anaerobic pathogens do not grow.
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Why are dishes stored upside down?
So that condensation drips onto the lid, not the agar.
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Why is 25 °C used in schools?
Most human pathogens grow best at 37 °C, so there is less risk at 25 °C.
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At what temperature are cultures incubated in industry?
About 37 °C, for faster growth.
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How are used dishes disposed of?
They are autoclaved, with the lid still on.
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Give two reasons for aseptic technique.
To stop contamination of the culture, and to protect people from pathogens.
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How often can bacteria divide?
As often as every 20 minutes in good conditions.
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Common mistake about the lid?
Sealing the dish completely. Tape is used in short strips, so that air can get in.
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What is a zone of inhibition?
A clear area round a disc where bacteria did not grow.
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What does a larger zone show?
The substance is more effective at stopping bacteria growing.
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Why is a control disc of sterile water used?
To show that the zone is due to the test substance, and not the disc or water.
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What is a lawn of bacteria?
A continuous layer of bacteria spread over the whole agar.
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How are the discs placed on the agar?
Using sterile forceps, well spaced out.
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How long are the dishes incubated for?
24 to 48 hours, at 25 °C in school.
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How is the diameter measured safely?
With a ruler, through the base of the dish, without opening it.
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What is the formula for cross-sectional area?
\(\pi r^2\).
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How do you find the radius?
Divide the diameter by 2.
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What happens to the area if the diameter doubles?
The area becomes four times as large.
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Name two variables that must be controlled.
Any two from: type of bacteria, volume of culture, disc size, concentration, temperature, time.
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Why repeat the experiment?
To calculate a mean, and to find anomalies, so that the results are more reliable.
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Why are antiseptics not taken as medicines?
They can damage human cells as well as microorganisms.
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Which safe precaution applies to a taped dish?
It stays closed and is not opened after incubation.
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Why is area a better measure than diameter?
It shows how much of the culture was affected, and exaggerates differences between zones.
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Common mistake in calculating the area?
Using the diameter in place of the radius.
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What are the main stages in developing a medicine?
Discovery, development, preclinical testing and clinical testing.
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What is preclinical testing?
Testing on cells, tissues and animals, before testing on humans.
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Why are animals used in testing?
They show effects on a whole body, such as side effects, that cells cannot show.
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What is tested in phase 1?
Safety, in a small number of healthy volunteers.
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What is tested in phase 2?
Whether it works, and the best dose, in a small group of patients.
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What is tested in phase 3?
Effectiveness compared with a placebo or standard treatment, in a large group of patients.
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What is a placebo?
A dummy treatment that looks the same but contains no active drug.
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What is the placebo effect?
Patients feel better because they believe they are being treated.
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What is a double-blind trial?
A trial in which neither the patient nor the doctor knows who receives the drug.
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Why are patients allocated at random?
So that the groups are alike, and the result is fair.
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How long does it take to develop a medicine?
About 10 to 15 years.
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Why is testing so expensive?
Many chemicals fail at each stage, and trials involve thousands of people.
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Name a medicine found in a plant.
Aspirin, from willow, or digitalis, from foxglove.
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Why are new antibiotics needed?
Bacteria evolve resistance to existing antibiotics.
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What did the thalidomide disaster show?
The need for thorough testing, including on pregnant animals.
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Common mistake about a placebo?
Thinking it is a drug. It contains no active ingredient.
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What is a monoclonal antibody?
An antibody made by a clone of identical cells, which fits one antigen.
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Why can't a lymphocyte be grown in the laboratory?
It does not divide outside the body.
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Why are tumour cells used?
They divide rapidly and for a long time.
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What is a hybridoma cell?
A cell formed by fusing a lymphocyte with a tumour cell.
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What can a hybridoma cell do?
Make the desired antibody, and divide.
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Which animal is used to make the lymphocytes?
Usually a mouse.
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Why is the mouse injected with an antigen?
So that its lymphocytes make the antibody against that antigen.
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What is done with the hybridoma cells?
They are tested, the right ones are selected, and they are grown in large amounts.
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Why are all of the antibodies identical?
They come from a clone, so they have the same genes.
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What does mono mean?
One.
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What is the final stage?
The antibodies are collected from the liquid, and purified.
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What can be attached to a monoclonal antibody?
A dye, a radioactive label or a drug.
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Who first made monoclonal antibodies?
Köhler and Milstein, in 1975.
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Why are mouse antibodies altered for human use?
Otherwise the human immune system may react against them.
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Which parent cell gives the hybridoma its ability to divide?
The tumour cell.
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Common mistake about hybridomas?
Saying that the tumour cell makes the antibody. It is the lymphocyte that does.
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Which hormone does a pregnancy test detect?
hCG.
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Where is hCG made?
By the placenta, after the embryo implants.
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What does the test line show?
That hCG is present, so the woman is pregnant.
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What does the control line show?
That the test has worked.
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What do two lines on a pregnancy test mean?
The woman is pregnant.
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What does one line, at the control position, mean?
She is not pregnant.
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How are monoclonal antibodies used to find a blood clot?
A radioactive antibody binds to fibrin in the clot, and a scanner detects it.
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How are they used to find cancer cells?
Labelled antibodies bind to tumour markers on the cancer cells.
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What is a tumour marker?
An antigen on cancer cells that is not found on healthy cells.
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How do monoclonal antibodies treat cancer?
They carry a drug, toxin or radioactive substance to the cancer cells.
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Why are they better than chemotherapy?
They target cancer cells, so healthy cells are not harmed as much.
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Name a side effect of chemotherapy.
Hair loss, sickness or tiredness.
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Name a disadvantage of monoclonal antibodies.
They are expensive, or can cause side effects.
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What is Herceptin used for?
Breast cancer cells with large amounts of the HER2 protein.
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What is the advantage of having a label on an antibody?
It shows where the antibody has bound.
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Common mistake about the control line?
Thinking that it shows pregnancy. It only shows that the test worked.