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A-level Biology > Unit 3.2 - Cells > Flashcards

Unit 3.2 - Cells Flashcards

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1
Q

what are eukaryotic cells?

A

they are larger and have a nucleus bounded by nuclear membranes (nuclear envelope)

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2
Q

what is the function and appearance of the cell-surface (plasma) membrane?

A
  • it regulates the movement of substances into and out of the cell. it has receptor molecules which allow it to respond to chemicals like hormones
  • its the membrane found on the surface of animals cells and inside the wall of other cells. its made up of a phospholipid bilayer and proteins embedded into the double membrane
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3
Q

what is the function and appearance of the nucleus?

A
  • its controls the cells activities by controlling the transcription of DNA
  • nuclear envelope controls what enters and leaves the nucleus
  • nuclear pore allow molecules eg RNA to move between the nucleus and cytoplasm
  • nucleolus is inside the nucleus and synthesises the components of ribosomes and makes ribosomal DNA
  • nucleoplasm is a granular, jelly like substance
  • chromatin are DNA molecules bound with proteins
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4
Q

what is the function and appearance of ribosomes?

A
  • its the site where protein synthesis occurs
  • a very small organelle that either floats in the cytoplasm or is attached to the rough endoplasmic reticulum, its made up of RNA and protein and isn’t surrounded by a membrane
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5
Q

what is the function and appearance of rough endoplasmic reticulum (RER)?

A
  • folds and processes proteins that have been made at the ribosomes
  • a system of membranes enclosing a fluid-filled shape, its attached to the nuclear envelope of the nucleus and the surface is covered with ribosomes
  • provides large surface area for synthesis of proteins and glycoproteins
  • provides pathway for transport of materials especially proteins
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6
Q

what is the function and appearance of smooth endoplasmic reticulum (SER)?

A
  • synthesise, store and processes lipids
  • similar to (RER) but with no ribosomes
  • synthesises, store and transport carbs
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7
Q

what is the function and appearance of the Golgi apparatus?

A
  • it processes and packages new lipids and proteins and also make lysosomes
  • a group of fluid filled membrane bound flattened sacs called cisternae & vesicles are often seen at the edges of the sacs
  • add carbs to proteins to form glycoproteins
  • produce secretory enzymes
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8
Q

what is the function and appearance of the mitochondrion?

A
  • the site of aerobic respiration, where ATP is produced, they’re found in large numbers that are very active and require a lot of energy
  • usually oval shaped and have a double membrane, the inner one is folded to form cristae. inside is the matrix, which contains enzymes involved in respiration
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9
Q

what is the function and appearance of chloroplasts?

A
  • where PHS takes place, some parts pf PHS happen in the grana other in the stroma (thick fluid in the chloroplast)
  • small flattened structure surrounded by a double membrane and has membranes inside called thylakoid membranes. these membranes are stacked up in some parts of the chloroplast to form grana
  • grana are linked together by lamellae, which are thin flat pieces of thylakoid membrane
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10
Q

what is the function and appearance of the cell wall?

A
  • supports cells and presents them from changing shape
  • in plants and algae its mainly made of carbohydrates whilst in fungi its chitin
  • the first layer is the middle lamella which is formed after the cell division, its not rigid and allows cell to grow
  • primary cell wall forms after the ML and contains pectin, glycoproteins and cellulose fibres -> rigid
  • secondary cell wall formed when the cell is mature, strong and contains layers made of cellulose, hemicellulose and lignin
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11
Q

what is the function and appearance of the vacuole?

A
  • helps maintain pressure inside the cell and keeps the cell rigid, which stops it wilting. also involved in the isolation of unwanted chemicals in the cell
  • a membrane bound organelle found in the cytoplasm of plants, contains cell sap which is a weak solution of sugar and salts. the surrounding membrane is the tonoplast
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12
Q

what is the function and appearance of a lysosome?

A
  • hydrolyse material ingested by phagocytic vells eg WBC’s
  • release enzymes to the outside of the cell (exocytosis) in order to destroy material
  • digest worn out organelles so that the useful chemicals made can be re-used
  • break down cells after they have died (autolysis)
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13
Q

what is the function and appearance of a Golgi vesicle?

A
  • stores lipids and proteins made by the Golgi apparatus and transports them out of the cell via the cell surface membrane
  • its a small fluid filled sac in the cytoplasm, surrounded by a membrane and produced by the Golgi apparatus
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14
Q

what are the components of a cell membrane?

A
  • has a phospholipid bilayer that also have proteins embedded into the double membrane, the centre is hydrophobic so doesn’t allow water-soluble substances through it and acts like a bilayer
  • glycoproteins
  • glycolipids
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15
Q

what is cholesterol?

A
  • its a type of lipid that helps maintain the shape of animal cells and is important for cells that aren’t supported by other cells
  • the molecules fit between the phospholipids and bind to the hydrophobic tails of the phospholipids causing them to pack more closely together. this restricts the movement making the membrane less fluid and more rigid
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16
Q

what is the fluid mosaic model?

A
  • in 1972, the model was suggested to describe the arrangement of molecules in the membrane. the phospholipid bilayer is fluid as the phospholipids are constantly moving
  • cholesterol is present within the bilayer and proteins are scattered through the bilayer,
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17
Q

what are the proteins molecules in the FMM like?

A
  • proteins include channel and carrier proteins which allow larger molecules and ions to pass through the membrane
  • receptor proteins on the cell surface membrane allow the cell to detect chemicals released from other cells. the chemicals signal the cell to respond in the same way
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18
Q

what is the plasma membrane?

A

mainly made up of lipids and proteins, it controls the movement of substances into and out of the cell

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19
Q

what is the cytoplasm?

A

the cytoplasm of a prokaryotic cell has no membrane bound organelles, it has ribosomes but they’re smaller than those in a eukaryotic cell

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20
Q

what is the flagellum?

A

a long hair-like structure that rotates to make the prokaryotic cell move, not all cells have one some have more than one

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21
Q

how does DNA move in a prokaryotic cell?

A

it floats free in the cytoplasm, its circular DNA, presents as one long coiled up strand its not attached to any histone proteins

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22
Q

what are plasmids?

A
  • they are small loops of DNA that aren’t part of the main circular DNA molecule
  • plasmids contain genes for things like antibiotic resistance, and can be passed between prokaryotes.
  • they aren’t always present in p.cells and some cells have several
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23
Q

what is the cell wall?

A

supports the cell and prevents it from changing shape, its made up of a polymer called murein which is a glycoprotein

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24
Q

what is the capsule?

A
  • its made up of secreted slime and helps to protect bacteria from attack by cells of the immune system
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25
Q

what are viruses?

A
  • they are just nucleic acids surrounded by protein, all viruses invade and reproduce inside the cells of other organisms. these are also known as host cells
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26
Q

what do viruses look like?

A
  • they’re smaller than bacteria and unlike bacteria, they have no plasma membrane, no cytoplasm and no ribosomes
  • they contain a core of genetic material either RNA or DNA, the protein coat around the core is called the capsid
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27
Q

what are attachment proteins?

A

they stick out from the edge of the capsid, these let the virus cling on to the suitable host cell

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28
Q

what is the process of binary fission?

A
  1. the circular dna and plasmids replicate. the main dna loop is only replicated once, but plasmids can be replicated lots
  2. the cell gets bigger and the dna loops move to opposite poles of the cell
  3. the cytoplasm begins to divide and a new cell wall begins 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 plasmids
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29
Q

how do viruses bind to complementary receptor proteins?

A
  • they use their attachment proteins to bind to the complementary receptor proteins on the surface of host cells
  • different viruses have different attachment proteins and therefore require different receptor proteins on host cells. some viruses can only infect one type of cell then
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30
Q

what happens due to viruses not being alive?

A

they don’t undergo cell division, and inject their dna or rna into the host cell, this hijacked cell then uses its own machinery to replicate viral particles

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31
Q

what is magnification?

A

its how much bigger the image is than the specimen

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32
Q

what is resolution?

A

how detailed the image is. its how well a microscope distinguishes between two points that are close together

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33
Q

what is the equation for magnification?

A

magnification = size of image divided by size of real object

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34
Q

what are optical microscopes?

A
  • they use light to form an image
  • they have a minimum resolution of approx. 0.2 micrometres
  • the maximum useful magnification is x1500
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35
Q

what are light microscopes?

A
  • they use electrons to form an image
    1- they have a higher resolution than optical microscopes so give a more detailed image as it has a short wavelength
    -
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36
Q

what are transmission electron microscope TEMs?

A
  • they use electromagnets to focus a beam of electrons, which are then transmitted through the specimen
    1- denser parts of the specimen absorbs more electrons, which makes them look darker on the image you end with
    2- they give high resolution images
    3- only can be used on thin specimens
    4- living specimens cant be observed
    5- image not in colour
    6- may contain artefacts
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37
Q

what are scanning electron microscopes SEMs?

A
  • they scan a beam of electrons across the specimen. this knocks off electrons from the specimen, which are gathered in a cathode ray tube to form an image
  • the images you end up with show the surface of the specimen & they can be 3D
  • they can only be used on extremely thin specimens
  • give a lower resolution image than TEMs
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38
Q

what is homogenisation?

A
  • it done by vibrating the cells or grinding them in a blender, this breaks up the plasma membrane and releases the organelles into solution
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39
Q

what 3 conditions are needed during homogenisation?

A
  • ice cold to reduce any activity of the enzymes that break down the organelles
  • isotonic so it should have the same concentration of chemicals as the cells being broken down to prevent any damage to the cell by osmosis
  • buffer solution should be added to maintain pH
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40
Q

what is filtration?

A
  • the homogenised solution is then filtered through a gauze to remove any large cell debris or tissue debris from the organelles which are smaller so pass through the gauze
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41
Q

what is ultracentrifugation?

A
  • the cell fragments are poured into a tube. the tube is put into a centrifuge and is spun at a low speed. the heaviest organelles eg nuclei go to the bottom of the tube and form a thick sediment called the pellet. the rest of the organelles stay suspended in the fluid above the sediment - the supernatant
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42
Q

what happens to the supernatant after the first spin?

A
  • the supernatant is drained off, and poured into another tube and spun at a higher speed. the heaviest organelles eg the mitochondria form a pellet at the bottom. the supernatant containing the rest is drained off and spun in the centrifuge at an even higher speed
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43
Q

what is mitosis?

A
  • the cell division where a parent cell divides and produces two genetically identical daughter cells
  • it is needed for the growth of multicellular organisms and for repairing damaged tissues
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44
Q

what is the cell cycle?

A
  • it consists of a period of cell growth and dna replication called interphase, mitosis happens after
  • in G1 the cell grows and new organelles and proteins are made
  • in S (synthesis) the cell replicates its dna ready to divide
  • in G2 cell keeps growing and proteins needed for cell division are made
  • mitosis
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45
Q

what happens in interphase? 1

A
  • the cell carries out normal functions, but also prepares to divide. the cell’s dna is unravelled and replicated to double its genetic content. the organelles are also replicated so it has spares and its ATP content is increased
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46
Q

what happens in prophase? 2

A
  • 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 a spindle. the nuclear envelope breaks down and chromosomes lie free in the cytoplasm
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47
Q

what happens in metaphase? 3

A
  • the chromosomes each with two chromatids line up along the middle of the cell and become attached to the spindle by their centromere
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48
Q

what happens in anaphase? 4

A
  • the centromeres divide, separating each pair of sister chromatids. the sister chromatids contract, pulling chromatids to opposite poles of the spindle, centromere first. this makes the chromatids appear v-shaped
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49
Q

what happens in telophase? 5

A
  • the chromatids reach the opposite poles on the spindle. they uncoil and become long and thin, they are now called chromosomes again. a nuclear envelope forms around each group of chromosomes so there are two nuclei. the cytoplasm divides (cytokinesis) and there are 2 daughter cells that are genetically identical to the original cell and each other. - mitosis is finished and each daughter cell starts interphase to get ready for mitosis again
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50
Q

describe a chromosome?

A
  • they are made up of two strands joined in the middle by a centromere
  • the separate strands are called chromatids
  • there are two strands because each chromosome has already made an identical copy of itself during interphase
  • when mitosis is over, the chromatids end up one strand chromosomes in the daughter cell
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51
Q

what is mitosis and cell cycle controlled by?

A
  • by genes
  • normally, when cells have divided enough times to make enough new cells they stop. but if theres a mutation, in a gene that controls cell division, the cells grow out of control.
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52
Q

what is cancer?

A
  • cancer is a tumour than invades surrounding tissue

- a tumour is formed when cells keep on dividing to make more and more cells which forma tumour

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53
Q

how are some treatments for cancer designed?

A
  • to control the rate of cell division in tumour cells by disrupting the cell cycle. this kills the tumour cells.
  • they don’t distinguish between tumour cells and normal cells so they kill normal body cells that are dividing. tumour cells divide faster than normal cells so treatments are more likely to kill tumour cells
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54
Q

what is the G1 cell cycle target treatment?

A
  • chemical drugs (chemotherapy) prevent the synthesis of enzymes needed for dna replication. if they aren’t produced the cell is unable to enter the synthesis phase (S) which disrupts the cell cycle forcing the cell to kill itself
55
Q

what is the S cell cycle target treatment?

A
  • radiation and some drugs damage dna. at several points in the cell cycle the dna in the cell is checked for damage. if severe damage is detected, the cell will kill itself preventing further tumour growth
56
Q

what is diffusion?

A
  • the net movement of particles from a area of high concentration to a area of low concentration
  • its a passive process so doesn’t require energy
  • particles can diffuse across membranes as long as they can move freely through the membrane
57
Q

how will molecules dissolve?

A
  • both ways, but the net movement will be to the area of lower conc. this continues until particles are evenly distributed through liquid or gas
  • particles diffuse down a conc gradient, which is the path from a high conc to a low conc
58
Q

why can o2 and co2 diffuse easily?

A
  • they are small, so they can pass through spaces between phospholipids. they are also non polar which makes them soluble in lipids so they can diffuse in the hydrophobic bilayer
59
Q

what is simple diffusion?

A

when molecules diffuse directly through a cell membrane

60
Q

what types of molecules diffuse slowly through a membrane?

A
  • large ones eg amino acids or glucose as they are too big to pass through the phospholipid bilayer
  • charged particles eg ions as they’re water soluble and the centre of the bilayer is hydrophobic
61
Q

what is facilitated diffusion?

A
  • to speed things up… large or charged particles diffuse through carrier proteins or channel proteins in the membrane instead
  • it moves down a conc gradient and is a passive process
62
Q

what do channel proteins do?

A
  • they form pores in the membrane for charged particles to diffuse through
  • different channel proteins facilitate different charged particles
63
Q

what does simple diffusion depend on?

A
  • the higher the conc gradient the faster the rate. as diffusion takes place, the difference in conc gradient between the two sides of the membrane decreases until it reaches equilibrium this means that diffusion slows over time
  • the thinner the exchange surface the faster the rate
  • the larger the surface area the faster the rate
64
Q

what does facilitated diffusion depend on?

A
  • the higher conc gradient, the faster the rate. as equilibrium is reached, the rate of facilitated diffusion levels off
  • number of carrier/channel proteins - once all proteins are in use, facilitated diffusion cant happen. the greater the number of proteins the faster the rate
65
Q

what is osmosis?

A
  • the diffusion of water molecules across a partially permeable membrane from an area of higher water potential to an area of lower water potential
66
Q

what is water potential?

A
  • the potential of water molecules to diffuse out of or into a solution. pure water has the highest water potential
  • if two solutions have the same water potential they are isotonic
67
Q

what does osmosis depend on?

A
  • the higher the potential the faster the rate. as osmosis takes place, the difference in water potential on either sides of the membrane decreases so the rate levels off
  • the thinner the exchange surface the faster the rate
  • the larger the surface are the faster the rate
68
Q

what is active transport?

A
  • uses energy to move molecules and ions across membranes, it moves solutes from a low conc to a high conc and requires energy
  • carrier proteins are used also and the process is similar to facilitated diffusion
69
Q

what energy does active transport use?

A
  • ATP, its produced by respiration

- it undergoes a hydrolysis reaction splitting into ADP and Pi, this releases energy so that solutes can be transported

70
Q

what are co-transporters?

A
  • they are a type of carrier protein
  • they bind to two molecules at a time
  • the conc gradient of one of the molecules is used to move the other molecule against its own conc gradient
71
Q

what does active transport depend on?

A
  • the faster individual proteins work the faster the rate
  • the more proteins there are the faster the rate
  • the rate of respiration in the cell and the availability if ATP. if respiration is inhibited, active transport cant take place
72
Q

where is glucose absorbed?

A
  • in the final part of the small intestine the ileum, the concentration is too low for glucose to diffuse out into the blood. so glucose is absorbed from the lumen (middle) of the ileum by co-transport.
73
Q

what are antigens?

A
  • they are molecules (usually proteins) that can generate an immune system response. they are usually found on the surface of cells and
    identify;
  • pathogens, abnormal body cells, toxins and cells from other individuals of the same species
74
Q

what is a phagocyte?

A
  • its a type of a white blood cell that carries out phagocytosis. they’re found in the blood and in tissues and are the first cells to respond to an immune system trigger inside the body
75
Q

describe phagocytosis?

A

1- the phagocyte is attracted to the pathogen by chemical products of the pathogen so move towards it
2- the phagocyte has many receptors on its surface membrane which attaches to chemicals on the surface of the pathogen
3- lysosomes within the phagocyte migrate towards the phagosome formed by engulfing the bacteria
4- lysosomes release their lysozymes into the phagosome, where they hydrolyse the bacteria
5- the hydrolysis products of the bacteria are absorbed by the phagocyte

76
Q

what is a T-cell?

A
  • its another type of white blood cell, it has receptor proteins on its surface that bind to the complementary antigens presented to it by phagocytes, this activates the T-cell.
77
Q

what are the different types of T-cells?

A
  • helper T-cells (T H cells) release chemical signals that activate and stimulate phagocytes. they also activate B-cells, which secrete antibodies
  • cytotoxic T-cells (T c cells) kill abnormal and foreign cells
78
Q

what are B-cells?

A
  • they are another type of white blood cell. they’re covered with antibodies - are 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
79
Q

what are plasma cells?

A
  • produce the antibodies needed to destroy the pathogen

FOUND IN PRIMARY RESPONSE

80
Q

how does an antibody lead to the destruction of the antigen?

A
  • they cause agglutination of the bacterial cells, as each antibody has two binding sites. clumps of bacterial cells are formed, making it easier for the phagocytes to locate them.
  • they then serve as markers that stimulate phagocytes to engulf the bacterial cells to which they’re attached
81
Q

describe the structure of a antibody?

A
  • they have 4 polypeptide chains.
  • the chains of one pair are long called heavy chains, while the chains of the other pair are shorter and are called light chains.
  • the binding site is different on different antibodies and the variable region, the rest of the antibody is the constant region which binds to receptors on cells such as B-cells.
82
Q

what is the primary immune response?

A

1- when an antigen enters the body for the first time it activates the immune system
2- the primary response is slow as they aren’t many B-cells that can make the antibody needed to bind to it
3- eventually the body will produce enough of the right antibody to overcome the infection. meanwhile the infected person will show symptoms
4- after being exposed to an antigen, both T-cells and B-cells produce memory cells. these cells remain in the body for a long time, memory T-cells remember the specific antigen and memory B-cells record the specific antibody needed to bind to the antigen
5- this person is now immune

83
Q

what is the secondary immune response?

A

1- if the same pathogen enters the body again, the immune system will produce a quicker, stronger immune response
2- 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 divide into the correct type of T-cells to kill the cell carrying the antigen
3- the secondary response often gets rid of the pathogen before symptoms show

84
Q

what are vaccines?

A
  • they contain antigens which may be free or attached to a dead or attenuated pathogen. they cause your body to produce memory cells against a particular pathogen without the pathogen causing disease. this means you become immune without getting symptoms
85
Q

how can vaccines be taken?

A
  • either orally or injected
  • the disadvantage of taking it orally is that it could be broken down by enzymes in the gut or the molecules of the vaccine may be too large to be absorbed into the blood
86
Q

what is herd immunity?

A
  • vaccines protect individuals who have them as they reduce the occurrence of of the disease, those not vaccinated are also less likely to catch the disease as there are fewer people to catch it from -> herd immunity
87
Q

what is antigenic variation?

A
  • where some pathogens can change their surface antigens
  • this means that when you’re 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 again and carry out a primary response
  • this makes it difficult to develop vaccines against some pathogens
88
Q

how does antigenic variation affect the production of influenza vaccines?

A
  • the flu vaccine changes every year, as the antigens on the surface of the influenza virus changes regularly, forming new strains
  • memory strains produced from the vaccination with one strain of flu wont recognise other strains with different antigens, the strains are immunologic-ally distinct
89
Q

what happens every year with the influenza vaccine?

A
  • new vaccines are developed and one is chosen that is most effective against the recently circulating influenza virus. governments and health authorities then implement a programme of vaccination using the most suitable vaccine
90
Q

what is active immunity?

A
  • this is the type of immunity you get when your immune system makes it own antibodies after being stimulated
    1- natural = when you become immune after catching a disease
    2- artificial = when you become immune after you’ve been given a vaccination containing a harmless dose of antigen
91
Q

what is passive immunity?

A
  • this is the type of immunity you get from being given antibodies made by a different organism, your immune system doesn’t produce its own
    1- natural = when a baby becomes immune due to the antibodies it receives from its mother via breast milk and placenta
    2- artificial = when you become immune after being injected with antibodies from someone else
92
Q

what are the differences between passive and active immunity?

A
  • active requires exposure to antigen, passive doesn’t
  • active takes a while for protection to develop, passive is immediate
  • memory cells are produced in active, not in passive
  • protection is long term in active as antibody is made in response to complementary antigen being present in body, in passive protection is short term as antibodies given are broken down
93
Q

what are the problems with vaccines?

A
  • they are all tested on animals before being tested on humans
  • risk of side effects
  • religious reasons
  • if there was a epidemic with 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 get it
94
Q

what are monoclonal antibodies?

A
  • antibodies that are produced from a single group of genetically identical B-cells. they are specific as their binding sites have a unique tertiary structure that only one particular antigen will fit into
95
Q

how are monoclonal antibodies used in cancer cells?

A
  • cancer cells have antigens called tumour markers that are not found on normal body cells
    1 - MA can be made that will bond to the tumour markers
    2 - you can also attach anti-cancer drugs to the antibodies
    3 - when the antibodies come into contact with the cancer they will bind to the tumour markers
    4 - this means the drug will only accumulate in the body where there are cancer cells
    5 - the side-effects of an antibody-based drug are lower than other drugs as they accumulate near specific cells
96
Q

how do pregnancy tests work?

A
  • they detect the hormone human chorionic gonadotropin (hCG) found in urine
    1 - the application area contains antibodies for hCG bound to a coloured bead (blue)
    2 - when urine is applied to the application area any hCG will bind to the antibody on the beads, forming an antigen-antibody complex
    3 - urine moves up the stick to the test strip, carrying any beads with it
    4 - the test strip contains antibodies to hCG that are immobilised
    5 - if there is hCG present the test strip turns blue as the immobilised antibody binds to any 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 it wont go blue
97
Q

what is the ELISA test?

A
  • the enzyme-linked immunosorbent assay allows you to see if a patient has any antibodies to a certain antigen or any antigens to a certain antibody
  • there are different types: the direct ELISA uses a single antibody thats complementary to the antigen you are testing for. the indirect ELISA uses two different antibodies
98
Q

what are the problems with vaccines?

A
  • they are all tested on animals before being tested on humans
  • risk of side effects
  • religious reasons
  • if there was a epidemic with 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 get it
99
Q

how does the ELISA test work?

A

1 - HIV antigen is bound to the bottom of a well in a well plate
2 - a sample of the patients blood plasma which might contain several antibodies, it added to the well. if there are any HIV-specific antibodies these will bind tp the HIV antigens stuck to the bottom of the well. the well is then washed out to remove any unbound antibodies
3 - a secondary antibody, that has a specific antibody attached to it is added to the well. this antibody will bind to the HIV-specific antibody. the well is washed out again to remove any unbound secondary antigen. if there is no primary antibody in the sample all the secondary is washed away
4 - a solution is added to the well which contains a substrate, which is able to react with the enzy,e attached to the secondary antibody and produce a coloured product. if the solution changes colour, it indicates the patient has HIV-specific antigens and is infected

100
Q

what is HIV and AIDS?

A
  • HIV (human immunodeficiency virus) affects the immune system and eventually leads to acquired immune deficiency syndrome (AIDS) which is a condtion where the immune system deteriorates and fails.
  • people with HIV develop AIDS when the T-helper cell numbers in their body reach a low level
101
Q

what is the structure of HIV?

A
  • a core that contains the genetic material (RNA) and some proteins (including the enzyme reverse transcriptase, which is needed for viral replication)
  • a outer coating of protein called a capsid
  • an extra layer called an envelope. this is made up of membrane stolen from the cell membrane of a proteins host cell
  • sticking out from the envelope are lots of copies of an attachment protein that helps HIV attach to the host helper T-cell
102
Q

how does HIV replicates?

A

1 - a protein on the HIV combines to a protein called CD4 on the cell-membrane of the host helper T-cell
2 - the capsid is released into the cell, where it uncoats and releases genetic material (RNA) into the cell’s cytoplasm
3 - inside the cell, reverse transcriptase is used to make a complementary strand of a DNA from the viral RNA template
4 - from this, double stranded- DNA is made and inserted into the human DNA
5 - host cell enzymes are used to make viral proteins from the viral DNA found within the human DNA
6 - the viral particles are assembled into new viruses, which bud from the cell and go on to infect other cells

103
Q

describe the symptoms of AIDS?

A
  • initial symptoms include minor infections of mucus membranes and recurring respiratory infections
  • as it progresses the number of immune system cells decreases and people become more susceptible to more serious infections eg chronic diarrhoea and sexual bacterial infections
  • late stages, patients have a very low number of immune system cells and can develop serious infections eg toxoplasmosis of the brain and candidiasis of the respiratory system
104
Q

what are antibiotics?

A
  • they kill bacteria by interfering with their metabolic reactions, by targeting the bacterial enzymes and ribosomes.
  • bacterial enzymes and ribosomes are different to human ones
105
Q

what are antiviral drugs?

A

viruses don’t have their own enzymes and ribosomes, they use the one’s in the host cells, so because humans viruses use human enzymes and ribosomes to replicate antibiotics cant inhibit them as they don’t target human processes.
- antiviral drugs are designed to target the few virus-specific enzymes that exist

106
Q

what is the best way to control HIV infections?

A
  • by reducing the spread. it spread via unprotected sex, bodily fluids and a HIV-positive mother to her fetus. not all babies from HIV-positive mothers are born infected and taking antiviral drugs during pregnancy can reduce the chance of the baby being HIV-positive
107
Q

what is a tissue?

A

a collection of similar cells that perform a specific function is a tissue

108
Q

what is a organ?

A

its a combination of tissues that are specialised/ coordinated to perform a variety of functions, more often they have only one main function

109
Q

what is an organ system?

A

organs work together as a single unit to form an organ system. these systems may work together to perform particular functions more efficiently.

110
Q

what is a prokaryotic cells?

A

they are smaller and have no nucleus or nuclear envelope

111
Q

what are the differences between prokaryotic and eukaryotic cells?

A
  • prokaryotic dna isn’t associated with proteins, but eukaryotic is (histones)
  • prokaryotic have no membrane-bound organelles, eukaryotic cells do
  • prokaryotic cell wall made of murein, eukaryotic is mostly cellulose
  • prokaryotic ribosomes are smaller and eukaryotic are bigger
112
Q

what are glycolipids?

A
  • they are made up of a carbohydrate covalently bonded with a lipid. its function in the membrane is to
    1. act as recognition sites,
    2. help maintain the stability of the membrane
    3. helps cells to attach to one another and so form tissues
113
Q

what are glycoproteins?

A
  • they are carbohydrate chains attached to many extrinsic proteins the outer surface of the cell membrane. their function is to act as
    1. recognition sites
    2. help cells to attach to one another to form tissues,
    3. allows cells to recognise one another
    4. they also act as cell-surface receptors for hormones and neurotransmitters.
114
Q

describe osmosis in a plant cell?

A
  1. when the water potential outside the cell is higher (more positive) water enters the cell, it swells and becomes turgid
  2. when the water potential is lower outside the cell (more negative), water leaves the cell, its shrinks and becomes plasmolysed
115
Q

describe the differences between active transport and facilitated diffusion?

A
  1. both use carrier proteins
  2. FD occurs down a concentration gradient and AT occurs against a concentration gradient
  3. FD doesn’t require metabolic energy, but AT does it needs ATP
116
Q

describe a non specific defence mechanism?

A

the response is immediate and the same for all pathogens and involves physical barriers eg skin and phagocytosis

117
Q

describe a specific defence mechanism?

A

the response is slower and specific to each pathogen and involves cell-mediated responses eg T-lymphocytes and humoral responses B-lymphocytes

118
Q

how can T-lymphocytes distinguish between invader cells and normal cells?

A
  • phagocytes that have hydrolysed a pathogen present the pathogens antigens on their own membrane
  • body cells invaded by a virus present some of the viral antigens on their own membranes
  • transplanted cells from other people have different antigens on their surface
  • cancer cells are different from normal cells and present antigens on their own membrane
119
Q

what are antigen-presenting cells?

A

cells that display foreign antigens on their surface are called antigen-presenting cells

120
Q

what is cell-mediated immunity?

A

where T-lymphocytes will only respond to antigens that are presented on a body cell. the receptors here on T-cells respond to a single antigen

121
Q

describe the stages in the response of T-lymphocytes to infection by a pathogen?

A
  1. pathogens invade body cells or are taken in by phagocytes
  2. the phagocyte places antigens from the pathogen on its cell membrane
  3. receptors on a specific helper T-cell fit exactly onto these antigens
  4. this attachment activates the T-cell to divide by mitosis and form a clone of genetically identical cells.
122
Q

what do the cloned T cells in the response of T-lymphocytes do?

A
  1. develop into memory cells that enable a rapid response to future infections
  2. stimulate phaocytes to engulf pathogens in phagoctyosis
  3. stimulate B cells to divide and secrete their antibody
  4. activate cytotoxic T cells
123
Q

what are memory cells?

A

they are responsible for the secondary immune response. they circulate in the blood and tissue fluid ans when they encounter the same antigen again the divide to form plasma cells and more memory cells.

124
Q

describe humoral immunity?

A
  1. the surface antigens of an invading pathogen are taken up by a B cell
  2. the B cell processes the antigens and presents them on its surface
  3. Helper T cells attach to the processed antigens on the B cell which activates the B cell
  4. the B cell is now activated to divide by mitosis to give a clone of plasma cells in clonal selection
  5. the cloned plasma cells produce and secrete the specific antibody that fits the antigen on the pathogen’s surface
  6. the antibody attaches to the antigens and destroys them
  7. some B cells develop into memory cells. (secondary immune response)
125
Q

why may vaccinations not eliminate disease?

A
  1. people may have defective immune systems
  2. individuals may develop the disease immediately after vaccination but before their immunity levels are high enough therefore they infect other people
  3. pathogen may mutate frequently so its antigens change suddenly
126
Q

Describe active transport?

A
  1. the carrier proteins bind to the molecule to be transported on one side of it
  2. the molecule binds to receptor site on protein
  3. on inside of cell, ATP binds to the protein which causes it to split into ADP and Pi. so the protein changes shape and opens to opposite side of membrane
  4. molecule then released on other side of membrane
  5. Pi molecule released from protein which causes protein to revert to original shape.
    - the phosphate recombines with ADP to form ATP during respiration.
127
Q

Describe co-transport?

A
  1. sodium ions are actively transported out of epithelial cells, by sodium potassium pump into blood. this takes place in one type of carrier molecule found in cell membrane of epithelial cells
  2. this maintains a higher concentration of sodium ions in lumen of intestine than inside epithelial cell
  3. sodium then diffuses into epithelial cell down concentration gradient through different type of carrier protein.
  4. as the sodium diffuses in through second carrier protein, they carry either amino acids or glucose molecules into cell with them
  5. the glucose/amino acids pass into blood plasma by facilitated diffusion using another type of carrier
128
Q

why is co-transport an indirect form of active transport?

A

sodium ions moves down their conc gradient and glucose moves against its conc gradient. its the sodium ion concentration rather than ATP directly, that powers movement of glucose and amino acid into cells

129
Q

what are channel proteins?

A
  • these proteins form water-filled hydrophillic channels across membrane. they allow water-specific ions to pass through. the channels are selective, each opening in the presence of specific ion
130
Q

what are carrier proteins?

A
  • when a molecule eg glucose is specific to the protein present, it binds with the protein. causes it to change shape in a way where the molecule is released to the inside of the membrane. no energy needed.
131
Q

what are the ethical issues surrounding monoclonal antibodies?

A
  • involves use of mice
  • some deaths have happened from using these
  • conduct of drug trials
132
Q

what are features of a successful vaccination programme?

A
  • suitable quantity must be available
  • few side effects
  • means of administrating the vaccine properly
  • must be possible to vaccinate the majority to produce herd immunity
  • means of storing, producing and transporting the vaccine available
133
Q

how does ampicillin work?

A
  • they inhibit certain enzymes required for the synthesis and assembly of the peptide-cross linkages in bacterial cell walls. this weakens the walls, making them unable to withstand pressure. as water enters naturally by osmosis, the cell bursts and the bacterium dies

A-level Biology (8 decks)

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