3.2 Cells Flashcards

Question

Compare optical microscropes, TEM and SEM

Answer 1

Optical (light) microscopes -use light to form an image -can be used to observe eukaryotic cells, their nuclei and possibly mitochondria and chloroplasts, but not to observe smaller organelles e.g. ribosomes, endoplasmic reticulum or lysosomes -maximum useful magnification of optical microscopes is about ×1500 Advantages of optical: -cheaper -portable -species is alive -colour images can be produced Disadvantages of optical: -limited resolution and magnification Transmission electron microscopes (TEMs) -TEMs use electromagnets to focus a beam of electrons that are transmitted through the specimen -Denser parts of the specimen absorb more electrons, which makes these denser parts appear darker on the final image produced (produces contrast between different parts of the object being observed) Advantages of TEMs: -give high-resolution images (more detail) -allows the internal structures within cells/organelles to be seen Disadvantages of TEMs: -can only be used with very thin specimens -only dead specimens can be observed -vacuum inside a TEM, so water must be removed from specimen -lengthy treatment required to prepare specimens means that artefacts can be introduced -colour image not produced Scanning electron microscopes (SEMs) -scan a beam of electrons across the specimen -bounces off surface of specimen -the electrons are detected, forming an image Advantages of SEMs: can be used on thick 3D specimens produces 3D images of external structure of specimen Disadvantages of SEMs: -lower resolution images (less detail) than TEMs -cannot be used to observe live specimens (unlike optical microscopes that can be used to observe live specimens) - do not produce a colour image (unlike optical microscopes that produce a colour image)

Answer 2

look like real structures but are actually the results of preserving and staining

Answer 3

Electron microscopes use electrons to form an image increases the resolution of electron microscopes compared to optical microscopes, giving a more detailed image A beam of electrons has a much smaller wavelength than light, so an electron microscope can resolve (distinguish between) two objects that are extremely close together maximum resolution of around 0.0002 µm or 0.2 nm (i.e. around 1000 times greater than that of optical microscopes) can be used to observe small organelles such as ribosomes, the endoplasmic reticulum or lysosomes maximum useful magnification of electron microscopes is about ×1,500,000 There are two types of electron microscopes: Transmission electron microscopes (TEMs) Scanning electron microscopes (SEMs)

Answer 4

Magnification tells you how many times bigger the image produced by the microscope is than the real-life object you are viewing Resolution is the ability to distinguish between objects that are close together (i.e. the ability to see two structures that are very close together as two separate structures)

Answer 5

Many biological structures are too small to be seen by the naked eye Optical microscopes are an invaluable tool for scientists as they allow for tissues, cells and organelles to be seen and studied For example, the movement of chromosomes during mitosis can be observed using a microscope When using an optical microscope always start with the low power objective lens: It is easier to find what you are looking for in the field of view This helps to prevent damage to the lens or coverslip incase the stage has been raised too high A graticule must be used to take measurements of cells: A graticule is a small disc that has an engraved scale. It can be placed into the eyepiece of a microscope to act as a ruler in the field of view As a graticule has no fixed units it must be calibrated for the objective lens that is in use. This is done by using a scale engraved on a microscope slide (a stage micrometer) By using the two scales together the number of micrometers each graticule unit is worth can be worked out After this is known the graticule can be used as a ruler in the field of view Electron microscopes can produce highly detailed images of animal and plant cells The key cellular structures within animal and plant cells are visible within the electron micrographs below Drawing Cells To record the observations seen under the microscope (or from photomicrographs taken) a labelled biological drawing is often made Biological drawings are line pictures which show specific features that have been observed when the specimen was viewed There are a number of rules/conventions that are followed when making a biological drawing The conventions are: The drawing must have a title The magnification under which the observations shown by the drawing are made must be recorded A sharp HB pencil should be used (and a good eraser!) Drawings should be on plain white paper Lines should be clear, single lines (no thick shading)No shading The drawing should take up as much of the space on the page as possible Well-defined structures should be drawn The drawing should be made with proper proportions Label lines should not cross or have arrowheads and should connect directly to the part of the drawing being labelled Label lines should be kept to one side of the drawing (in parallel to the top of the page) and drawn with a ruler

Answer 6

1) Homogenisation -sample of tissue is placed in a cold, isotonic buffer solution -solution must be: -Ice-cold to reduce the activity of enzymes that break down organelles -Isotonic (same WP as cells being broken up) to prevent water from moving into organelles via osmosis, which would cause them to expand and eventually damage them -Buffered to prevent organelle proteins/enzymes, from becoming denatured -the tissue-containing solution is then homogenised using a homogeniser, which grinds the cells up -homogeniser breaks the plasma membrane of the cells and releases the organelles into a solution called the homogenate 2) Filtration -homogenate is then filtered through a gauze -filters out any large unbroken cell/tissue debris -the organelles are all much smaller than the debris and are not filtered out (they pass through the gauze) -the filtrate is the mixture of organelles remaining 3) Ultracentrifugation -filtrate is placed into a tube, which is placed in a centrifuge to separate materials by spinning -filtrate is first spun at a low speed -causes the largest, heaviest organelles (e.g. the nuclei) to settle at the bottom of the tube, where they form a thick sediment known as a pellet -rest of the organelles stay suspended in the solution above the pellet (solution is known as the supernatant) -supernatant is drained off and placed into another tube, which is spun at a higher speed -Once again, this causes the heavier organelles (e.g. mitochondria) to settle at the bottom of the tube, forming a new pellet and leaving a new supernatant -new supernatant is drained off and placed into another tube, which is spun at an even higher speed -process is repeated at increasing speeds until the desired organelle is separated out -each new pellet formed contains a lighter organelle than the previous pellet -order of mass of these organelles (from heaviest to lightest) is usually: Nuclei Chloroplasts (if carrying out cell fractionation of plant tissue) Mitochondria Lysosomes Endoplasmic reticulum Ribosomes

Answer 7

M = I/A A = I/M I = AM

Answer 8

-DNA replication occurs during interphase -mitosis: eukaryotic cell divides to produce two daughter cells -each has identical copies of DNA produced by the parent cell during DNA replication Also need to know: -behaviour of chromosomes during interphase, prophase, metaphase, anaphase and telophase of mitosis -role of spindle fibres attached to centromeres in the separation of chromatids -division of the cytoplasm (cytokinesis) usually occurs, producing two new cells. -mitosis is a controlled process -uncontrolled cell division can lead to the formation of tumours and of cancers -many cancer treatments are directed at controlling the rate of cell division Binary fission in prokaryotic cells involves: -replication of circular DNA and of plasmids -division of cytoplasm -produces two daughter cells, each with a single copy of the circular DNA and one or more plasmids -as viruses are non-living, they do not undergo cell division -following injection of their nucleic acid, the infected host cell replicates the virus particles

Answer 9

-chemical signals called cyclins trigger the movement from one phase to another -cell increases in mass and size and carries out its normal cellular functions (eg. synthesising proteins and replicating its DNA ready for mitosis) G1 phase -a signal is received telling the cell to divide again -cells make RNA, enzymes and other proteins required for growth S phase -DNA in the nucleus replicates (results in each chromosome consisting of two identical sister chromatids) G2 phase -cell continues to grow -new DNA that has been synthesised is checked -any errors are usually repaired -other preparations for cell division are made -e.g. production of tubulin protein (used to make microtubules for the mitotic spindle)

Answer 10

-cells constantly die, so are replaced -damaged tissues can be repaired by mitosis Asexual reproduction -production of new individuals of a species by a single parent organism -the offspring are genetically identical to the parent Growth of multicellular organisms: -two daughter cells produced are genetically identical to one another (clones) -have the same number of chromosomes as the parent cell -enables unicellular zygotes (as the zygote divides by mitosis) to grow into multicellular organisms

Answer 11

Mitosis: - nuclear division by which two genetically identical daughter cells are produced - Also genetically identical to parent cell - Due to same number of chromosomes in nucleus Prophase: - Chromosomes condense and now visible when stained - Two centrosomes move towards opposite poles - Spindle fibres begin to emerge from them - Nuclear membrane breaks down into small vesicles Metaphase: - Centrosomes reach opposite poles - Chromosomes line up at the equator - Spindle fibres continue to emerge and attach to the centromere - Each sister chromatid is attached to a spindle fibre originating from opposite poles Anaphase: - Sister chromatids separate at the centromere - Centromere divides into two - Chromosomes are now pulled to poles by spindle fibres - Spindle fibres begin to shorten Telophase: - Chromosomes arrive at opposite poles and start to decondense - Nuclear membrane begins to reform around each set of chromosomes - Spindle fibres break down Cytokinesis: - Cytoplasm divides - Two genetically identical cells are produced

Answer 12

Prophase Chromosomes are visible The nuclear envelope is breaking down Metaphase Chromosomes are lined up along the middle of the cell Anaphase Chromosomes are moving away from the middle of the cell, towards opposite poles Telophase Chromosomes have arrived at opposite poles of the cell Chromosomes begin to decondense The nuclear envelope is reforming Cytokinesis Animal cells: a cleavage furrow forms and separates the daughter cells Plant cells: a cell plate forms at the site of the metaphase plate and expands towards the cell wall of the parent cell, separating the daughter cells

Answer 13

-arise due to uncontrolled mitosis -Cancerous cells divide repeatedly and uncontrollably, forming a tumour (an irregular mass of cells) -start when changes occur in the genes that control cell division -a change in any gene is known as a mutation -if the mutated gene is one that causes cancer it is referred to as an oncogene -Mutations are common events and don’t lead to cancer most of the time -Most mutations either result in early cell death or result in the cell being destroyed by the body’s immune system -As most cells can be easily replaced, these events usually have no harmful effect on the body -mutations that result in the generation of cancerous cells do not result in early cell death or in the cell being destroyed by the body’s immune system -means that the harmful mutation occurring in the original cell can be passed on to all that cell’s descendants -Carcinogens are any agents that may cause cancer (eg. UV light, tar in tobacco smoke and X-rays) -Some tumours (such as warts) do not spread from their original site – these are known as benign tumours and do not cause cancer -Some tumours spread through the body, invading and destroying other tissues – these are known as malignant tumours and cause cancer -Malignant tumours interfere with the normal functioning of the organ / tissue in which they have started to grow (eg. they may block the intestines, lungs or blood vessels -Malignant tumour cells can break off the tumour and travel through the blood and / or lymphatic system to form secondary growths in other parts of the body -spreading of cancers in this way is known as metastasis, and it is very dangerous as it can be very difficult to detect, locate and remove secondary cancers

Answer 14

-no nucleus, chromosomes, membrane-bound organelles or spindle fibres -have a single, circular DNA molecule and plasmids (smaller, circular DNA molecules that are also replicated and inherited) The process of binary fission: -different from mitosis as there is no nuclear envelope to breakdown and no spindle fibres present -the single, circular DNA molecule undergoes DNA replication -any plasmids present undergo DNA replication -parent cell divides into two daughter cells -each contain a single copy of the circular DNA molecule and a variable number of plasmids -daughter cells die if they don’t receive the single circular DNA molecule or at least one copy of a plasmid

Answer 15

-net movementof a substance from a region of higher concentration to a region of its lower concentration (down a concentration gradient) -due to random motion of its molecules or ions (caused by the natural kinetic energy of the molecules or ions) -only small, non-polar molecules can diffuse across bilayer -large, polar molecules require a channel or carrier protein

Answer 16

-large surface area of exchange surface = high rate of simple diffusion -larger difference in concentration on either side of the surface = higher concentration gradient = higher rate of simple diffusion -as diffusion occurs, concentration gradient decreases until an equilibrium is reached -thinner exchange surface = higher rate of simple diffusion -due to shorter diffusion pathway

Answer 17

-the higher the concentration gradient, the faster the rate of diffusion -up to a point, depending on the number of channel and carrier proteins available -once all the carrier proteins and channel proteins are in use (*saturated*), the rate of diffusion of a particular molecule can no longer increase -therefore, more channel and carrier proteins available = faster rate of diffusion Other factors: -surface area -water potential gradient

Answer 18

Facilitated diffusion: -large polar molecules (e.g. glucose/amino acids) and ions (e.g. Na+ or Cl-) cannot diffuse through phospholipid bilayer -require channel proteins or carrier proteins (facilitated diffusion) -both are highly specific (only allow one type of molecule/ion to pass through) Channel proteins: -water-filled pores with fixed shape -allow charged substances (e.g. ions) to diffuse through cell membrane -diffusion of these ions does not occur freely -most channel proteins are ‘gated’, so that part of the channel protein on the inside surface of the membrane can move to open/close the pore -allows channel protein to control the exchange of ions Carrier proteins -carrier proteins can switch between two shapes -causes binding site of the carrier protein to be open to one side of the membrane first -can then open to the other side of the membrane when the carrier protein switches shape -concentration of molecules on each side of the membrane affects direction of movement across the membrane -can work down a concentration gradient (facilitated diffusion), but typically works against it (active transport)

Answer 19

In a solution of lower water potential: -in both plant/animal cells, water leaves cell by osmosis through the partially permeable cell surface membrane -volume decreases in both plant/animal cells -animal cells shrink/shrivel up (crenation) -in plants cell, the protoplast shrinks and pulls away from cell wall -plant cell is plasmolysed In a solution of higher water potential -in both plant/animal cells, water enters cell by osmosis through the partially permeable cell surface membrane -volume increases in both plant/animal cells -in animal cells, there is no cell wall to withstand increased pressure created -cell membrane is eventually stretched too far so cell bursts (cytolysis) -in plant cells, cell wall withstands increased pressure created -pressure increases until cell is rigid and turgid -no more water can enter -plant wilts

Answer 20

-movement of molecules/ions through a cell membrane from a region of lower concentration to a region of higher concentration using energy from ATP hydrolysis -requires carrier proteins (specific for a particular molecule or ion) -energy is required to make the carrier protein change shape -allows it to transport substances across cell membrane -provided by hydrolysis of ATP produced during respiration important in: -reabsorption of useful molecules/ions into blood after filtration into the kidney tubules -absorption of some products of digestion from the digestive tract -loading sugar from leaves into the phloem tissue for transport around the plant after photosynthesis -loading inorganic ions from the soil into root hairs

Answer 21

-movement of two substances across a cell membrane via a carrier protein -combination of facilitated diffusion and active transport -e.g. co-transporter protein can be found on cell surface membrane of epithelial cells lining the ileum -involved in the absorption of glucose -Na+ ions and glucose molecules are transported into the epithelial cells via facilitated diffusion -can only continue if a concentration gradient is maintained -active transport of Na+ ions out of cell into blood helps to maintain this gradient -glucose molecules exit the epithelial cell and enter the blood via facilitated diffusion

Answer 22

Epithelial cells are cells that line the surfaces of organs. Some epithelial cells have cilia which are hair-like structures on their surface. -Ciliated epithelial cells’ main role is to move substances in one direction -structures move together to waft substances -E.g. in the airways, ciliated epithelial cells help move mucus (that traps unwanted inhaled substances) up towards the throat. -This is then swallowed and doesn’t reach the lungs thus, protecting the lungs

Answer 23

Intracellular = inside cell Extracellular = outside cell

Answer 24

Intrinsic proteins: -span both bilayers of the plasma membrane -act as channels or carrier proteins to transport water-soluble molecules. Extrinsic proteins: -found on the surface of the plasma membrane -usually function as enzymes and catalyse chemical reactions inside the cell.

Answer 25

-entry of pathogens prevented by a variety of physical and chemical defences -skin -mucous membranes -tears (contains lysozymes, which destroys bacteria) -saliva Non-specific response -phagocytosis -inflammation (swelling and heating) of the region invaded by the pathogen Specific response: -recognising ‘foreign’ cells and targeting any pathogenic cells -cell-mediated and humoral response

Answer 26

-white blood cells known as phagocytes have surface proteins that act as receptors -bind to the antigen (protein on the surface of pathogen) -enables pathogens to be engulfed and digested -antigens that were found on the pathogen can then be presented on the surface of the phagocyte (now an antigen-presenting cell) -APCs are used to recruit other cells of the immune system, leading to a specific immune response

Answer 27

Non-specific Bone marrow Remove dead cells and invasive microorganisms

Answer 28

Lymphocytes are another type of white blood cell They play an important part in the specific immune response They are smaller than phagocytes They have a large nucleus that fills most of the cell They are produced in the bone marrow before birth There are two types of lymphocytes (with different modes of action). The two types of lymphocytes are: T-lymphocytes (T cells) B-lymphocytes (B cells) T-lymphocytes and the cellular immune response Immature T-lymphocytes leave the bone marrow to mature in the thymus Mature T-lymphocytes have specific cell surface receptors called T cell receptors These receptors have a similar structure to antibodies and are each specific to one antigen The maturation of T-lymphocytes – some become helper T cells and others become killer T cells T-lymphocytes are activated when they encounter (and bind to) their specific antigen that is being presented by one of the host’s cells (host cells being the human’s own cells) This antigen-presenting host cell might be a macrophage or a body cell that has been invaded by a pathogen and is displaying the antigen on its cell surface membrane These activated T-lymphocytes (those that have receptors specific to the antigen) divide by mitosis to increase in number (similar to the clonal selection and clonal expansion of B-lymphocytes) These T-lymphocytes differentiate into two main types of T cell: helper T cells cytotoxic T cells(also known as killer T cells)

Answer 29

The Role of Helper T cells Activated T-lymphocytes (those that have receptors specific to an antigen) divide by mitosis to increase in number (similar to the clonal selection and clonal expansion of B-lymphocytes) These T-lymphocytes differentiate into two main types of T cell: helper T cells cytotoxic (killer) T cells Helper T cells assist other white blood cells in the immune response They release cytokines (hormone-like signals) which stimulate: The maturation of B-lymphocytes into antibody-secreting plasma cells The production of memory B cells The activation of cytotoxic T cells, which destroy virus infected cells and tumour cells An increased rate of phagocytosis

Answer 30

B-lymphocytes and the humoral immune response B-lymphocytes (B cells) remain in the bone marrow until they are mature and then spread through the body, concentrating in lymph nodes and the spleen Millions of types of B-lymphocyte cells are produced within us because as they mature the genes coding for antibodies are changed to code for different antibodies Once mature, each type of B-lymphocyte cell can make one type of antibody molecule At this stage, the antibody molecules do not leave the B-lymphocyte cell but remain in the cell surface membrane Part of each antibody molecule forms a glycoprotein receptor that can combine specifically with one type of antigen If that antigen enters the body, B-lymphocyte cells with the correct cell surface receptors will be able to recognise it and bind to it (clonal selection) These specific B-lymphocytes divide repeatedly by mitosis (clonal expansion) and differentiate into two main types of cell: Plasma cells Memory cells These two cell types each have a specific function Primary immune response When an antigen enters the body for the first time, the small numbers of B-lymphocytes with receptors complementary to that antigen are stimulated to divide by mitosis This is known as clonal selection As these clones divide repeatedly by mitosis (the clonal expansion stage) the result is large numbers of identical B-lymphocytes being produced over a few weeks Some of these B-lymphocytes become plasma cells that secrete lots of antibody molecules (specific to the antigen) into the blood, lymph or linings of the lungs and the gut These plasma cells are short-lived (their numbers drop off after several weeks) but the antibodies they have secreted stay in the blood for a longer time The other B-lymphocytes become memory cells that remain circulating in the blood for a long time This response to a newly encountered pathogen is relatively slow

Answer 31

Structure: -quaternary globular glycoproteins called immunoglobulins -represented as Y-shaped, with two ‘heavy’ (long) polypeptide chains bonded by disulfide bonds to two ‘light’ (short) polypeptide chains -each polypeptide chain has a constant region and variable region -constant region determines the mechanism used to destroy antigens -amino acid sequence in the variable regions of the antibodies (the tips of the "Y") are different for each antibody -variable region = where the antibody attaches to antigen to form antigen-antibody complex -at the end of the variable region is a site called the antigen-binding site -antigen-binding sites vary greatly giving the antibody its specificity for binding to antigens -if pathogen or virus presents multiple antigens, different antibodies need to be produced -the ‘hinge’ region (where the disulfide bonds join the heavy chains) gives flexibility to the antibody molecule -allows the antigen-binding site to be placed at different angles when binding to antigens

Answer 32

-memory cells form the basis of immunological memory -cells can last for many years Primary immune response -after clonal selection and expansion, plasma cells secrete lots of antibody molecules for the antigen into the blood, lymph or linings of the lungs and the gut -these cells are short-lived -but the antibodies they have secreted stay in the blood for a longer time -memory cells remain circulating in the blood for a long time -slow response Secondary immune response -same antigen is found in the body a second time -memory cells recognise the antigen -divide very quickly and differentiate into plasma cells (produces antibodies) and more memory cells -quicker response -ensures infection can be destroyed and removed before the pathogen population increases too much and symptoms develop

Answer 33

-macromolecules which are markers that allow cell-to-cell recognition -found on cell surface membranes, bacterial cell walls, or the surfaces of viruses -some glycolipids and glycoproteins on the outer surface of cell surface membranes act as antigens -can be either self antigens or non-self antigens -self antigens do not stimulate an immune response -non-self antigens stimulate an immune response

Answer 34

• pathogens • cells from other organisms of the same species • abnormal body cells • toxins

Answer 35

-pathogen’s DNA can mutate frequently -mutation in the gene which codes for the antigen will change the shape of antigen -memory cells in blood will have a memory of old antigen shape -no longer complementary -cannot recognise pathogen, so any previous immunity to this pathogen is no longer effective -host gets infected and suffers from the disease again

Answer 36

-Phagocyte = macrophage (type of WBC) found in blood and tissues that carries out phagocytosis -non-specific response -any non-self cell that is detected will trigger the same response every time Stages: -pathogens/abnormal cells release chemicals -phagocytes attracted to chemicals so move towards pathogen -surface of phagocytes has receptor binding sites, allowing it to bind to complementary antigen on pathogen -phagocyte changes shape to engulf pathogen -pathogen is contained with a phagosome vesicle -lysosome from the phagocyte fuses with membrane of phagosome -forms phagolysosome -releases lysozymes into phagosome to digest pathogen -pathogen is hydrolysed

Answer 37

-made when you are foetus -foetuses sre unlikely to be exposed to any other cells than self cells -lymphocytes complementary to the antigens on self-cells will die/production is suppressed -prevents lymphocytes from attacking own cells -remaining lymphocytes are complementary to pathogenic and non-self cells -same process occurs after birth in bone marrow -new lymphocytes made in bone marrow are complementary in shape to antigens on self-cells will be destroyed -if this process goes wrong —> symptoms of autoimmune disease **all lymphocytes are made in the bone marrow but t cells mature in the thymus**

Answer 38

T Cells (T lymphocytes) can be...T helper cells: -Stimulate B cell maturation-Promote phagocytosis -secrete cytokines, which activate or control the activities of other lymphocytes. -Most helper T cells die out once a pathogen has been cleared from the body, but a few remain as memory cells. -These memory cells are ready to produce large numbers of antigen-specific helper T cells like themselves if they are exposed to the same antigen in the future. T killer cells: -Identify and kill infected host cells-Especially important during viral infections

Answer 39

Key point 1: -in the non-specific defence system, macrophages engulf and digest pathogens in phagocytosis -they process antigens from the surface of the pathogen -forms antigen-presenting cells (APC). Key point 2: -receptors on some of the T helper cells fit the antigens -these T helper cells become activated and produce interleukins -this stimulate more T cells to divide rapidly by mitosis -form clones of identical activated T helper cells that carry the right antigen to bind to a particular pathogen Key point 3: The cloned T cells may: -develop into T memory cells, which give a rapid response if this pathogen invades the body again produce interleukins that stimulate phagocytosis produce interleukins that stimulate B cells to divide -stimulate the development of a clone of T killer cells that are specific for the presented antigen and then destroy infected cells.

Answer 40

-Once activated, a cytotoxic T cell divides rapidly -releases a protein called perforin that forms pores in the membrane of the infected cell -any substance can enter and exit -causes the cell to burst, destroying both the cell and the viruses inside it. -After an infection has been brought under control, most cytotoxic T cells die off. -However, a few remain as memory cells.

Answer 41

-surface antigens of an invading pathogen are taken up by a B-cell -B cell processes the antigens and presents them on its surface -helper T cells attach to the processed antigens on the B cell thereby activating the B cell -B cell is now activated to divide by mitosis to give a clone of plasma cells -the cloned plasma cells produce and secrete the specific antibody that fits the antigen on the pathogen’s surface exactly -the antibody attaches to antigens on the pathogen and destroys them -some B cells develop into memory cells that can respond to future infections by the same pathogen by rapid division and developing into plasma cells that produce antibodies (known as secondary immune response)

Answer 42

Humoral immunity: -B lymphocytes -produced and mature in bone marrow -involves production of antibodies -pathogens identified via antigens floating in blood -pathogens killed by antibodies -once stimulated, cells divide into either plasma cells or memory cells Cell mediated immunity: -T lymphocytes -produced in bone marrow, but mature in thymus gland -does not involve production of antibodies -pathogens are identified via antigens on the surface of infected cells -pathogens killed by specialised killer T cells -once stimulated, cells divide into different types of specialist T cells

Answer 43

Antibody: -quaternary structure globular protein (4 polypeptide chains) -has a variable region that binds to the antigen (known as antigen-binding site) and the constant region -has a heavy chain and light chain Antigen: protein on the surface of a pathogen that **stimulates an immune response** Antigen-Presenting Cell: -any cell that presents a non-self antigen on their surface E.g. infected body cells, macrophage that has engulfed and destroyed a pathogen, cells of a transplanted organs, cancer cells

Answer 44

-antibodies are flexible so can bind to multiple antigens to clump them together known as agglutination -antigen-antibody complex can be formed -makes it easier for phagocyte to locate and destroy pathogens

Answer 45

Passive: -antibodies are introduced to the body -pathogen doesn’t enter body so plasma cells and memory cells are not made -no long-term immunity -e.g. antibodies passed to foetus through placenta or breastmilk to a baby Active: -immunity created by own immune system following exposure to pathogen or its antigen -natural: following infection and creation of body’s own antibodies and memory cells -artificial: following introduction of weakened version of pathogen or antigens via a vaccine

Answer 46

-small amounts of weakened/dead pathogen, or antigens are introduced to body -exposure to antigens activates B cell to go through clonal expansion and differentiation (clonal selection) -B cells undergo mitosis to make large number of cells -these differentiate into plasma cells or memory cells -plasma cells make antibodies -B memory cells can collide with antigen and divide rapidly into plasma cells when reinfected, so large number of antibodies made quickly Herd immunity: -if enough of the population are vaccinated, the pathogen cannot spread easily amongst the population -protects those who are not vaccinated

Answer 47

Core = RNA and reverse transcriptase enzyme, which are needed for viral replication Capsid = outer protein wall Envelope = extra outer layer, made out of membrane taken from the host cell’s membrane Attachment proteins = on the exterior of the envelope to enable the virus to attach to the host’s helper T cell

Answer 48

-HIV is transported around in the blood until it attaches to a CD4 protein on the helper T cells -HIV protein capsule fuses with helper T cell membrane -enables RNA and enzymes to enter -reverse transcriptase copies viral RNA into a DNA copy and moves to the helper T cell nucleus (hence called a retrovirus) -here, mRNA is transcribed -helper T cell starts to make viral proteins -new viral particles are made -new HIV proteins and RNA move to the surface of the cell and assemble -they bud, forming new HIV particles as they burst out of the host cell, killing it in the process

Answer 49

AIDS is when the replicating viruses in the helper T cells completely weaken the immune system

Answer 50

They do not have a cell wall that can be attacked

Answer 51

-cell-mediated = specific -T cells **only** respond to antigens which are presented on cells (APC), -no response to antigens detached from cells and within body fluids (e.g. blood) Stages: 1) once phagocyte has engulfed pathogen, the antigens are positioned on the cell surface (hence it is an APC) 2) helper T cells have receptors on their surface, which can bind to **complementary** antigens on APC 3) when attached, activates helper T cells to divide by mitosis, making large numbers of clones 4) cloned helper T cells can: -differentiate into memory cells (enables rapid response to future infections by same pathogen) -stimulate phagocytes (i.e. macrophages) to engulf pathogens by phagocytosis -remain as helper T cells and stimulate B cells to divide and secrete their antibody (humoral response) -become/activate cytotoxic T cells (killer T cells)

Answer 52

-stands for enzyme-linked immunosorbent assay -can be used to see if a patient has any antibodies to a certain antigen (or any antigens to a certain antibody) -e.g. they can be used to test for infections by pathogens or for allergies In an ELISA test: -An enzyme is attached to antibodies -When this enzyme reacts with a certain substrate, a coloured product is formed, causing the solution in the reaction vessel to change colour -If a colour change occurs, this shows that the antigen or antibody of interest is present in the sample being tested (e.g. blood plasma) There are different types of ELISA test: -Direct ELISA tests use a single antibody that is complementary to the antigen being tested for -Indirect ELISA tests use two different antibodies (known as primary and secondary antibodies)

Answer 53

-first, HIV antigens bind to the bottom of the reaction well -blood plasma sample is then taken from the patient and added to well -any HIV-specific (primary) antibodies present in the blood plasma now bind to the HIV antigens -any other antibodies that are present in the blood plasma are washed out -secondary antibody with an enzyme attached to it is added to the reaction well -these secondary antibodies bind to the primary antibodies -the well is washed out again to remove any unbound secondary antibodies -helps avoid false-positive test results -solution with substrate for enzyme attached to the secondary antibody is added -if any secondary antibodies present, a coloured product is formed, causing the solution in the well to change colour -indicates that the patient has HIV-specific antibodies in their blood (and therefore they are infected with HIV)

Answer 54

-prostate cancer is a cancer of the prostate gland -the blood plasma of a patient can be tested for the presence of prostate-specific antigens (PSAs) -high PSA concentration of blood plasma suggests that patient has prostate cancer -so further diagnostic tests will be carried out -antibodies to PSA are bound to the bottom of the reaction vessel (instead of antigens, as in the HIV example)

Answer 55

1. Helper T cell/TH cell binds to the antigen (on the antigen-presenting cell/phagocyte); 2. This helper T/TH cell stimulates a specific B cell; 3. B cell clones OR B cell divides by mitosis; 4. (Forms) plasma cells that release antibodies;

Answer 56

Joins DNA fragments together by facilitating the formation of a phosphodiester bond between two DNA monomers at a time

Answer 57

Catalyses integration of viral DNA into host genome

Answer 58

-larger than neutrophils -after being produced in the bone marrow, macrophages travel in the blood as monocytes -they become macrophages when they settle into organs including the lungs, liver, spleen, kidney and lymph nodes -although they still carry out phagocytosis in a similar way to neutrophils, they do not destroy pathogens completely -they cut the pathogens up so that they can display the antigens of the pathogens on their surface (through a structure called the major histocompatibility complex) -now they’re APCs -the displayed antigens can then be recognised by lymphocytes

Answer 59

-contain digestive enzymes called lysozymes, which digest unwanted material present in cells -phagocytic vacuole formed around a pathogen once it has been engulfed by a neutrophil is called a phagosome -a lysosome fuses with the membrane of the phagosome (to form a phagolysosome) -releases lysozymes (digestive enzymes) to digest the pathogen -after killing and digesting the pathogens, the neutrophils die -pus is a sign of dead neutrophils

Answer 60

-travel throughout the body and often leave the blood by squeezing through capillary walls -short-lived cells that are released in large numbers during an infection -chemicals are released by pathogens or by the body cells under attack (e.g. histamine) -these attract neutrophils to the site where the pathogens are located (**chemotaxis**) -neutrophils move towards pathogens -they may be covered in antibodies, which are another trigger to stimulate neutrophils to attack the pathogens -neutrophils have receptor proteins on their surfaces that recognise antibody molecules and attach to them -once attached to a pathogen, the cell surface membrane of a neutrophil stretches -allows pathogen to be engulfed and trapped within a phagocytic vacuole -part of the process is known as endocytosis

Answer 61

Neutrophils Macrophages

3.2 Cells Flashcards

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