Cells Flashcards

Question

What is a plasmid in some prokaryotic cells?

Answer 1

Small loops of DNA which only carry a few genes.

Answer 2

The capsule is a slimy layer made of protein. This prevents the bacteria from desiccating (drying out) and protects the bacteria against the host’s immune system.

Answer 3

Rotates to enable the bacteria to move.

Answer 4

Optical (light) microscopes Transmission electron microscopes Scanning electron microscopes

Answer 5

How many times larger the image is compared to the object.

Answer 6

The ability to distinguish details of a specimen or sample. The minimum distance between two objects in which they can still be viewed as separate.

Answer 7

A beam of light is condensed to create the image. Poorer resolution due to light having a longer wavelength. Lower magnification. Colour images. Can view living samples.

Answer 8

A beam of electrons is condensed to create the image. Electromagnets are used to condense the beam. Higher resolving power as electrons have a short wavelength. Higher magnification. Black and white images. Sample must be in a vacuum, and therefore non-living.

Answer 9

Extremely thin specimens are stained and placed in a vacuum. An electron gun produces a beam of electrons that pass through the specimen. Some parts absorb the electrons and appear dark. The image produced is 2D and shows detailed images on the internal structure of cells.

Answer 10

The specimens do not need to be thin, but do need to be stained. Instead, the electrons are beamed onto the surface and scattered in different ways depending on the contours of the specimen. This produces only a 3D shape because the beams are reflected and in this type of microscope you are unable to see its internal structures.

Answer 11

Magnification= image size/actual size

Answer 12

Metre to millimetres is x1000 Millimetre to micrometres is x1000 Micrometres to nanometres is x1000

Answer 13

A scale on a glass disc which is inside the optical microscope lens.

Answer 14

Can be used to measure the size of objects you are viewing under the microscope.

Answer 15

It is used to calibrate the eyepiece graticule. It’s a glass slide with a scale on it that you place on the stage. The scale is usually 2mm long and the sub-divisions are 10 micro metres apart.

Answer 16

It’s used to isolate different organelles so they can be studied. This enables individual organelle structures and functions to be studied.

Answer 17

Cells are broken open to release the contents and the organelles are then separated. The cells must be prepared in a cold, isotonic and buffered solution.

Answer 18

Cold- to reduce enzyme activity. When the cell is broken open, enzymes are released which could damage the organelles. Isotonic- the organelles must be the same water potential as the solution to prevent osmosis, as this could cause the organelles to shrivel or burst. Buffered- the solution has a pH buffer to prevent damage to the organelles.

Answer 19

Step 1 is homogenisation where the cells must be broken up. This is done by using a blender. The cells are blended in the cold, isotonic and buffered solution. The solution is then filtered to remove the large cell debris. Step 2 is ultracentrifugation where the filtered solution is spun at a high speed in a centrifuge. This separates organelles according to their density.

Answer 20

This is where the centrifuge spins at high speeds and the centrifugal forces cause pellets of the most dense organelle to form at the bottom of the tube. The speed increases removing the supernatant (liquid) each time and leaving the isolated organelle (pellet) behind. The supernatant is spun again in the centrifuge and the process is repeated. The speed of the centrifuge always depends on how dense the organelle is.

Answer 21

• The cell cycle starts when a cell has be produced by cell division and ends with the cell dividing to produce two identical cells. • Consists of a period of cell growth and DNA replication, called interphase, and a period of cell division called mitosis. • The cell cycle starts with mitosis and then is completed with interphase.

Answer 22

• This is cell growth. • During interphase the cell carries out normal functions, but also prepares to divide. The cells DNA is unravelled and replicated to double its genetic content. • The organelles are also replicated so it has spare ones, and its ATP content is increased. (The ATP provides the energy needed for cell division). • Interphase is subdivided into three separate growth stages. These are called G1, S and G2.

Answer 23

• G1, gap phase 1, is where the cell grows and new organelles and proteins are made. • S, synthesis, is where the cell replicates its DNA, ready to divide by mitosis. • G2, gap phase 2, is where the cell keeps growing and proteins needed for cell division are made.

Answer 24

• Mitosis is a form of cell division that occurs during the cell cycle. • In mitosis a parent cell divides to produce two genetically identical daughter cells. • Mitosis is needed for the growth of multicellular organisms and for preparing damaged tissues. • It is a continuous process and is described as a series of division stages.

Answer 25

• Prophase • Metaphase • Anaphase • Telophase

Answer 26

• The chromosomes condense, getting shorter and fatter. • Tiny bundles of protein called centrioles start moving to opposite ends of the cell, forming a network of protein fibres across it called the spindle. • The nuclear envelope (the membrane around the nucleus) breaks down and chromosomes lie free in the cytoplasm.

Answer 27

• The chromosomes (each with two chromatids) line up along the middle of the cell and become attached to the spindle by their centromere.

Answer 28

• The centromeres divide, separating each pair of sister chromatids. • The spindles contract, pulling chromatids to opposite ends of the spindle, centromere first. • This makes the chromatids appear v-shaped.

Answer 29

• The chromatids reach the opposite poles on the spindle. They uncoil and become long and thin again. They’re now called chromosomes again. • A nuclear envelope forms around each group of chromosomes, so there are now two nuclei. • Division of the cytoplasm (cytokinesis, which starts in anaphase) finishes in telophase. • There are now two daughter cells that are genetically identical to the original cell and to each other. Mitosis is finished and each daughter cell starts the interphase part of the cell cycle to get ready for the next round of mitosis

Answer 30

• The time taken for each stage of mitosis varies depending on the cell type and environmental conditions. • To find how long it takes you have to find the amount of cells in the wanted stage and divide it by how many cells in total. You then times it by how long the cell cycle takes in minutes.

Answer 31

• Cancer is a tumor that invades surrounding tissue. • There are two types of cancers; benign and malignant.

Answer 32

• When there is a mutation in the gene that controls cell division the cell can grow out of control. The cells keep on dividing to make more and more cells, which form a tumour.

Answer 33

• Cancer treatments are able to kill tumour cells. The treatments are able to control the rate of cell division in tumour cells by disrupting the cell cycle. • Unfortunately, the treatments aren’t able to distinguish tumour cells from normal cells, so they also kill normal body cells that are dividing.

Answer 34

• Prokaryotic cells replicate by a process called binary fission. In this process, the cell replicates its genetic material, before physically splitting into two daughter cells.

Answer 35

1. The circular DNA and plasmid(s) replicate. The main DNA loop is only replicated once, but plasmids can be replicated loads of times. 2. The cell gets bigger and the DNA loops move to opposite ‘poles’ (ends) of the cell. 3. The cytoplasm begins to divide (and new cell walls begin to form). 4. The cytoplasm divides and two daughter cells are produced. Each daughter cell has one copy of the circular DNA, but can have a variable number of copies of the plasmid(s).

Answer 36

• Viruses are acellular— they’re not cells. • Viruses are nuclei acids surrounded by protein— they’re not alive. • All viruses invade and reproduce inside the cells of other organisms. These cells are known as host cells.

Answer 37

• They have a protein coat called a capsid with attachment proteins sticking out of it. • In the centre is a core of genetic material— either DNA or RNA.

Answer 38

1. Virus uses their attachment proteins and attaches to host cell receptor proteins. 2. Genetic material is released into the host cell. 3. Genetic material and proteins are replicated by host cell ‘machinery’. 4. Viral components assemble. 5. Replicated viruses are released from host cell.

Answer 39

• They’re composed of lipids (mainly phospholipids), proteins and carbohydrates, • It’s said that the arrangement of molecules in the membrane is a fluid mosaic model.

Answer 40

• They are a barrier between the cell and its environment, controlling which substances enter and leave the cell. • They’re partially permeable— they let some molecules through but not others. • Substances are able to move across the cell-surface membrane by diffusion, osmosis or active transport. • The cell-surface membrane is sometimes called the plasma membrane.

Answer 41

• Fluid- the bilayer is fluid because the phospholipids are constantly moving. • Mosaic- proteins are scattered through the bilayer, like tiles in a mosaic.

Answer 42

• Glycoproteins- where proteins have a carbohydrate attached. • Glycolipids- lipids which have carbohydrates attached.

Answer 43

• Phospholipids • Cholesterol

Answer 44

• Phospholipid molecules form a barrier to dissolved (water-soluble) substances. • Phospholipids have a ‘head’ and a ‘tail’— the ‘head’ is hydrophilic and the ‘tail’ is hydrophobic. The molecules automatically arrange themselves into a bilayer. • The centre of the bilayer is hydrophobic so the mebrane doesn’t allow water-soluble substances like ions and polar molecules to diffuse through it. • Small, non-polar molecules can diffuse through the membrane.

Answer 45

• Cholesterol gives the membrane stability. • Present in all cell membranes. • Cholesterol fits between the phospholipids. • Cholesterol binds to the tails of the phospholipids, causing them to pack more closely together. This restricts the movement of the phospholipids, making the membrane less fluid and more rigid. • Cholesterol helps to maintain the shape of animal cells which don’t have a cell wall. • Cholesterol also has hydrophobic regions, so it is able to create a further barrier to polar substances moving through the membrane.

Answer 46

• Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration. • Molecules will diffuse both ways, but the net movement will be to the area of lower concentration. This continues until particles are evenly distributed throughout the liquid or gas. • Diffusion is a passive process — no energy is needed for it to happen.

Answer 47

• The concentration gradient is the path from an area of higher concentration to an area of lower concentration. • Particles diffuse down a concentration gradient.

Answer 48

• This is when molecules diffuse directly through a cell membrane. • Particles can diffuse across cell membranes, as long as they can move freely through the membrane.

Answer 49

• The concentration gradient. • The thickness of the exchange surface. • The surface area.

Answer 50

• The higher it is, the faster the rate of diffusion. • As diffusion takes place, the difference in concentration between the two sides of the membrane decreases until it reaches an equilibrium. This means that diffusion slows down over time.

Answer 51

• The thinner the exchange surface, the faster the rate of diffusion. • This is because the thinner it is then the shorter the distance the particles have to travel.

Answer 52

• The larger the surface area of the cell-surface membrane, the faster the rate of diffusion.

Answer 53

• Where large or charged particles diffuse through carrier proteins or channel proteins in the cell membrane. • Facilitated diffusion moves particles down a concentration gradient, from a higher to a lower concentration. • It is also a passive process. • There are two types of protein involved — carrier proteins and channel proteins.

Answer 54

• They move large molecules across the membrane, down their concentration gradient. • Different carrier proteins facilitate the diffusion of different molecules.

Answer 55

• First, a large molecule attaches to a carrier protein in the membrane. • Then, the protein changes shape according to that molecule. • This releases the molecule on the opposite side of the membrane.

Answer 56

• Channel proteins form pores in the membrane for charged particles to diffuse through their conc. gradient. • Different channel proteins facilitate diffusion of different charged particles.

Answer 57

• The concentration gradient. • The number of channel or carrier proteins.

Answer 58

• The higher the concentration gradient, the faster the rate of facilitated diffusion. • As equilibrium is reached, the rate of facilitated diffusion will level off.

Answer 59

• Once all the proteins in a membrane are in use, facilitated diffusion can’t happen any faster, even if you increase the concentration gradient. • Therefore the larger the number of channel or carrier proteins in the cell membrane, the faster the rate of facilitated diffusion.

Answer 60

• First, we need to find the target of the curve on the graph and using the tangent we find its gradient. • The gradient will be the rate of diffusion.

Answer 61

• Some specialised cells have microvilli, which are projections formed by the cell-surface membrane folding upon itself. • Microvilli give the cell a larger surface area and this can result in more particles being exchanged in the same amount of time, increasing the rate of diffusion.

Answer 62

• Osmosis is the diffusion of water molecules across a partially permeable membrane, from an area of higher water potential to an area of lower water potential.

Answer 63

• The potential (likelihood) of water molecules to diffuse out of or into a solution. • Water molecules are small and can diffuse easily through the cell membrane, but large solute molecules can’t.

Answer 64

• Pure water has a water potential of zero. • Adding solutes to pure water for example lowers its water potential — so the water potential of any solution is always negative. • The more negative the water potential, the stronger the concentration of solutes in the solution.

Answer 65

• They have the same water potential as each other. • When cells are isotonic they won’t lose or gain any water —there’s no net movement of water molecules be cause there’s no difference in water potential between the cell and the surrounding solution.

Answer 66

• It will swell as water moves into it by osmosis. • When that solution now has a higher water potential compared with the inside of the cell it is called hypotonic.

Answer 67

• It may shrink as water moves out of it by osmosis. When that solution now has a lower water potential than the cell they are called hypertonic.

Answer 68

• No net movement of water- where the cell is in an isotonic solution. • Net movement of water out of the cell- where the cell is in a hypertonic solution. • Net movement of water into the cell- where the cell is in a hypotonic solution.

Answer 69

• The water potential gradient. • The thickness of the exchange surface. • The surface area of the exchange surface.

Answer 70

• The higher the water potential gradient, the faster the rate of osmosis. • As osmosis takes place, the difference in water potential on either side of the membrane decreases, so the rate of osmosis levels off over time.

Answer 71

• The thinner the exchange surface, the faster the rate of osmosis.

Answer 72

• The larger the surface area, the faster the rate of osmosis.

Answer 73

• Active transport uses energy to move molecules and ions across plasma membranes, usually against a concentration gradient. • Carrier proteins and co-transporters are involved in active transport.

Answer 74

• A molecule attaches to the carrier protein, the protein changes shape and this moves the molecule across the membrane, releasing it on the other side. • ATP is a common source of energy used in active transport. It undergoes a hydrolysis reaction, splitting into ADP and Pi (inorganic phosphate). • This releases energy so that the solutes can be transported through the carrier proteins.

Answer 75

• Active transport usually moves solutes from a low concentration to a high concentration — in facilitated diffusion, they always move from a high to a low concentration. • Active transport requires energy whereas diffusion does not.

Answer 76

• They are a type of carrier protein. They bind two molecules at a time. • The concentration gradient of one of the molecules is used to move te other molecule against its own concentration gradient.

Answer 77

1. Sodium ions are actively transported out of the epithelial cells in the ileum, into the blood, by the sodium-potassium pump. This creates a concentration gradient — there’s now a higher concentration of sodium ions in the lumen of the ileum than inside the cell. 2. This causes sodium ions to diffuse from the lumen of the ileum into the epithelial cell, down their concentration gradient. They do this via the sodium-glucose co-transporter proteins. The co-transporter carries glucose into the cell with the sodium. As a result the concentration of glucose inside the cell increases. 3. Glucose diffuses out of the cell, into the blood, down its concentration gradient through a protein channel, by facilitated diffusion.

Answer 78

• The speed of individual carrier proteins. • The number of carrier proteins present. • The rate of respiration in the cell and the availability of ATP.

Answer 79

• The faster they work, the faster the rate of active transport.

Answer 80

• The more proteins there are, the faster the rate of active transport.

Answer 81

• If respiration is inhibited (hindered), active transport can’t take place.

Answer 82

Antigens are molecules (usually proteins) that can generate an immune response wane detected by the body. They are usually found on the surface of cells. Antigens which aren’t normally found in the body are referred to as foreign antigens— these are the antigens that the immune system usually responds to.

Answer 83

Pathogens. Abnormal body cells. Toxins. Cells from other individuals of the same species.

Answer 84

• These are organisms that cause disease. • All pathogens have antigens on their surface —these are identified as foreign by immune system cells, which then respond to destroy the pathogen.

Answer 85

• Cancerous or pathogen-infected cells have abnormal antigens on their surface, which trigger an immune response.

Answer 86

• Toxins are poisons. They are also molecules and not cells. • Some toxins are produced by bacteria. The immune system can respond to toxins, as well as the pathogens that release them.

Answer 87

• When you receive cells from another person, such as an organ transplant or blood transfusion, those cells will have some antigens that are different to your own (unlesss the donor is genetically identical to you). • The foreign antigens trigger an immune response. This response leads to the rejection of the transplanted organs if drugs aren’t taken to suppress the recipients immune system. • For blood transfusions, the most important antigens are the ABO blood group antigens — if the blood donated contains A or B antigens that aren’t recognised by the recipients immune system, they will generate an immune response.

Answer 88

A type of white blood cell that carries out phagocytosis (engulfment of pathogens). They're found in the blood and in tissues and are the first cells to respond to an immune system trigger inside the body.

Answer 89

A phagocyte recognises the foreign antigens on a pathogen. The cytoplasm of the phagocyte moves round the pathogen, engulfing it. The pathogen is now contained in a phagocytic vacuole (bubble) in the cytoplasm of the phagocyte. A lysosome fuses with the phagocytic vacuole. the lysozymes break down the pathogen. The phagocyte then presents the pathogen's antigens- it sticks the antigens on its surface to activate other immune system cells.

Answer 90

Also known as t-lymphocytes. It is another type of white blood cell. It has receptor proteins on its surface that bind to complimentary antigens presented to it by phagocytes which activate the t-cells.

Answer 91

Helper T-cells and cytotoxic T-cells.

Answer 92

Helper T-cells; release chemical signals that activate and stimulate phagocytes. They also activate B-cells. Cytotoxic T-cells; kill abnormal and foreign cells.

Answer 93

Also known as B-lymphocytes, another type of a white blood cell. They're covered in antibodies- proteins that bind antigens to form an antigen-antibody complex. Each B-cell has a different shaped antibody on its membrane, so different ones bind to different shaped antigens.

Answer 94

When the antibody on the surface of a B-cell meets a complementary shaped antigen, it binds to it. This, together with substances released from the helper T-cells, activates the B-cell. This process is called clonal selection. The activated B-cell divides into plasma cells.

Answer 95

Identical to the B-cell (clones). They secrete a lot of antibodies specific to the antigen. These antibodies are called monoclonal antibodies. They bind to the antigens on the surface of a pathogen to form lots of antigen-antibody complexes.

Answer 96

Similar to a 'Y' shape. Where there is a light chain, shortest length and a heavy chain, the longest length. At the tip of each chain on both sides of the 'Y', there are variable regions, whilst their bodies are constant regions. A disulfide bridge connects both sides of the 'Y' together.

Answer 97

An antibody has two binding sites, so it can bind to two pathogens at the same time. This allows for pathogens to be clumped together; agglutination.

Answer 98

cellular- the t-cells and other immune system cells that they interact with, e.g phagocytes, form the cellular response. humoral- b-cells, clonal selection and the production of monoclonal antibodies form the humoral response.

Answer 99

When an antigen enters the body for the first time it activates the immune system. The primary response is slow because there aren't many B-cells that can make the antibody needed to bind to it. Eventually the body will produce enough of the right antibody to overcome the infection. At this stage, symptoms will begin to show. After being exposed to the antigen, both T- and B-cells produce memory cells. These memory cells remain in the body for a long time. The person is now immune- their immune system has the ability to respond quickly to a second infection.

Answer 100

They remember the specific antigen and will recognise it a second time round.

Answer 101

they record the specific antibodies needed to bind to the antigen.

Answer 102

Where if the same pathogen enters the body again, the immune system will produce a quicker, stronger immune response. Clonal selection happens faster. Memory B-cells are activated and divide into plasma cells that produce the right antibody to the antigen. Memory T-cells are activated and divided into the correct type of T-cells to kill the cell carrying the antigen. The secondary response often gets rid of the pathogen before you begin to show any symptoms.

Answer 103

While our b-cells are busy dividing to build up their numbers to deal with a pathogen, you suffer from the disease. Vaccinations can help avoid this. Vaccines can protect individuals against disease, and because they reduce the occurrence of the disease, those not vaccinated are also less likely to catch the disease. This is called herd immunity.

Answer 104

vaccines often contain antigens that cause your body to produce memory cells against a particular pathogen, without the pathogen causing disease. this means you can become immune without getting any symptoms. antigens in vaccines may be free or attached to a dead or attenuated (weakened) pathogen.

Answer 105

it could be broken down by enzymes in the gut or the molecules of the vaccine may be too large to be absorbed in the blood.

Answer 106

antigens on the surface of a pathogen activate the primary response and when youre infected a second time with the same pathogen, with those same antigens on the surface, they activate the secondary response and you dont become ill. though some pathogens are able to change their surface antigens. this antigen variability is called antigenic variation. different antigens are formed due to changes in the genes of a pathogen.

Answer 107

when infected for a second time, the memory cells produced from the first infection will not recognise the different antigens. so the immune system has to start from scratch and carry out a primary response against these new antigens. this primary response takes time to get rid of the infection, which is why we get ill again.

Answer 108

the influenza vaccine hcnages every year. this is because the antigens on the surface of the influenza virus changes regularly, forming new strains of the virus. memory cells produced from vaccinations with one strain of the flu will not recognise other strains with different antigens. the strains are immunologically distinct. every year there are different strains of the influenza virus circulating in the population, so a different vaccine has to be made. new vaccines are developed and one is chosen every year that is most effective against the recently circulating influenza viruses. governments and health authorities would then implement a programme of vaccination using the most suitable vaccine.

Answer 109

active immunity. passive immunity.

Answer 110

this is the type of immunity you get when your immune systems makes it own antibodies after being stimulated by an antigen.

Answer 111

natural- this is when you become immune after catching a disease. artificial- this is when you become immune after you've been given a vaccination containing a harmless dose of antigen.

Answer 112

this is the type of immunity you get from being given antibodies made by a different organism- your immune system doesn't produce any antibodies of its own.

Answer 113

natural- this is when a baby becomes immune due to the antibodies it receives from its mother, through the placenta and in breast milk. artificial- this is when you become immune after being injected with antibodies from someone else. e.g antibodies against a disease from blood donations.

Answer 114

active- requires exposure to antigen. passive- doesn't require exposure to antigen. active- takes a while for protection to develop. passive- protection is immediate. active- memory cells are produced. passive- memory cells aren't produced. active- protection is long-term because the antibody is produced in response to complementary antigen being present in the body. passive- protection is short-term because the antibodies given are broken down.

Answer 115

they are antibodies produced from a single group of genetically identical b-cells (plasma cells). this means that they're all identical in structure.

Answer 116

antibodies are very specific because their binding sites have a unique tertiary structure that only one particular antigen will fit into (one with a complementary shape). monoclonal antibodies will bind to anything you want and they will only bind to/target specific substances or cells.

Answer 117

cancer cells have antigens called tumour markers that are not found on normal body cells. monoclonal antibodies can be made that will bind to the tumour markers. its possible to also attach anti-cancer drugs to the antibodies. when the antibodies come into contact with the cancer cells, they will bind to the tumour markers. this means the drug will only (accumulate) weaken in the body where there are cancer cells. so the side-effects of an antibody-based drug are lower than other drugs because they accumulate near specific cells.

Answer 118

pregnancy tests detect the hormone hCG that's found in the urine of pregnant women. the application area of a pregnancy test contains antibodies for hCG bound to a coloured bead. when urine is applied to the application area any hCG will bind to the antibody on the beads, forming an antigen-antibody complex. the urine moves up the stick to the test strip, carrying any beads with it. the test strip contains antibodies to hCG that are stuck in place (immobilised). if there is hCG present the test strip will turn blue because the immobilised antibody binds to the hCG - concentrating the hCG-antibody complex with the blue beads attached. if no hCG is present, the beads will pass through the test area without binding to anything, and so it won't go blue.

Answer 119

ELISA- an enzyme-linked immunosorbent assay. this allows you to see if a patient has any antibodies to a certain antigen or an antigen to a certain antibody. it can be used to test for pathogenic infections, for allergies and for just about anything you can make an antibody for.

Answer 120

an antibody is used which has an enzyme attached to it. this enzyme can react with a substrate to produce a coloured product. this causes the solution in the reaction vessel to change colour. if there is a colour change, it demonstrates that the antigen or antibody of interest is present in the sample being tested. in some types of ELISA , the quantity of this antigen/antibody can be worked out from the intensity of the colour change.

Answer 121

indirect ELISA- uses two different antibodies. direct ELISA- uses a single antibody that is complementary to the antigen you're testing for.

Answer 122

an indirect ELISA test is used to see if a patient possesses antibodies to the HIV virus. the HIV antigen is bound to the bottom of a well in a well plate. a sample of the patient's blood plasma, which might contain several antibodies, is added to the well. if there are any HIV-specific antibodies, these will bind to the HIV antigen stuck to the bottom of the well. the well is then washed out to remove any unbound antibodies. a secondary antibody, that has a specific enzyme attached to it, is added to the well. this secondary antibody can bind to the HIV-specific antibody (the primary antibody). the well is washed out again to remove any unbound secondary antibody. if there is no primary antibody in the sample, all of the secondary antibodies will be washed away. a solution is added to the well. this solution contains a substrate, which is able to react with the enzyme attached to the secondary antibody and produce a coloured product. if the solution changes colour, it indicates that the patient has HIV-specific antibodies in their blood and is infected with HIV.

Answer 123

to make sure unbound antibodies aren't left in the well which could affect the results.

Answer 124

-all vaccines are tested on animals before being tested on humans; some people disagree with animal testing. also, animal based substances may be used to produce a vaccine, which some people disagree with. -testing vaccines on humans can be tricky where volunteers may put themselves at unnecessary risk of contracting the disease because they think they're fully protected. -some people don't want to take the vaccine due to the risk of side effects, but they are still protected because of herd immunity; other people think this is unfair. -if there was an epidemic of a new disease there would be a rush to receive a vaccine and difficult decisions would have to be made about who would be the first to receive it.

Answer 125

animals are used to produce the cells from which the monoclonal antibodies are produced. some people disagree with the use of animals in this way.

Answer 126

HIV (Human Immunodeficiency Virus) is a virus that affects the immune system. it eventually leads to acquired immune deficiency syndrome (AIDS). HIV infects and eventually kills helper T-cells, which act as the host cells for the virus. without enough helper T-cells, the immune system is unable to mount an effective response to infections because other immune system cells don't behave how they should. when the helper T-cell numbers in the body are critically low, HIV develops into AIDS.

Answer 127

a condition where the immune system deteriorates and eventually fails. this makes someone with AIDS more vulnerable to other infections.

Answer 128

HIV has a core that contains the genetic material (RNA) and some proteins (including the enzyme reverse transcriptase, which is needed for virus replication). there is an outer coating of protein called a capsid. there is an extra outer layer called an envelope. this is made of membrane stolen from the cell membrane of a previous host cell. sticking out of the envelope are loads of copies of an attachment protein that help HIV attach to the host helper T-cell.

Answer 129

the attachment protein attaches to a receptor molecule on the cell membrane of the host helper T-cell. the capsid is released into the cell, where it uncoats and releases the genetic material (RNA) into the cell's cytoplasm. inside the cell, reverse transcriptase is used to make a complementary strand of DNA from the viral RNA template. from this, double-stranded DNA is made and inserted into the human DNA. host cell enzymes are used to make viral proteins from the viral DNA found within the human DNA. the viral proteins are assembled into new viruses, which bud from the cell and go on to infect other cells.

Answer 130

when the symptoms of HIV of their failing immune system start to appear or their helper T-cell count drops to a certain level.

Answer 131

minor infections of mucous membranes (inside the nose, ears and genitals), and recurring respiratory infections.

Answer 132

the number of immune system cells decreases further. patients become susceptible to more serious infections including chronic diarrhoea, severe bacterial infections and tuberculosis.

Answer 133

patients have a very low number of immune system cells and can develop a range of serious infections. these serious infections are what kills AIDS patients and not HIV itself.

Answer 134

viruses don't have their own enzymes and ribosomes which antibiotics target when going against bacteria. viruses use the enzymes and ribsomes of the host cell. human viruses use human enzymes and ribosomes to replicate, and so antibiotics can't inhibit them because they don't target human processes.

Cells Flashcards

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