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Cells Flashcards

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1
Q

Nucleus structure?

A

•nuclear envelope - plasma membrane on outside, double membrane
•nuclear pores
•nucleoplasm - granular, jelly-like material
•chromosomes - protein-bound, linear DNA
•nucleolus - smaller sphere inside which is the site of rRNA production and makes ribosomes

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2
Q

Nucleus function?

A

•site of DNA replication and transcription (making mRNA)
•contains the genetic code for each cell

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3
Q

Smooth and Rough Endoplasmic Reticulum structure?

A

•rough AND smooth both have cisternae (folded membranes)
•RER have ribosomes on the cisternae

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4
Q

Smooth and Rough Endoplasmic Reticulum function?

A

•RER - protein synthesis happens here
•SER - synthesis + storage of lipids and carbohydrates

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5
Q

Golgi apparatus + vesicles structure?

A

• cisternae
• secretary vesicles pinch off the cisternae

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6
Q

Golgi apparatus + vesicles function?

A

• add carbohydrates to proteins to form glycoproteins
• produce secretory enzymes
• secrete carbohydrates
• transport, modify and store lipids
• form lysosomes
• molecules are “labelled” with their destination, e.g by adding a receptor
• finished products are transported to cell surface in golgi vesicles where they fuse with the membrane + the contents are released

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7
Q

Lysosomes structure?

A

• sacs of digestive enzymes

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8
Q

Lysosomes function?

A

• hydrolyse phagocytic cells
• autolysis - completely break down dead cells
• exocytosis - release enzymes to outside of cell to destroy material
• digest worn out organelles for reuse of materials

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9
Q

Mitochondria structure?

A
  • double membrane
  • inner membrane = cristae
  • mitochondrial matrix - fluid centre
  • loop of mitochondria DNA
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10
Q

Mitochondria function?

A
  • site of aerobic respiration
  • site of ATP production
  • the mitochondria DNA codes for enzymes needed in respiration
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11
Q

Ribosomes structure?

A
  • small
  • made up of 2 sub-units of protein and rRNA
  • 80s - large ribosome, found in eukaryotic cells (25nm)
  • 70s - smaller ribosome, found in prokaryotic cells, mitochondria and chloroplasts
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12
Q

Ribosomes function?

A
  • site of protein synthesis
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13
Q

Vacuole structure?

A
  • filled with fluid surrounded by a tonoplast (a single membrane)
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14
Q

Vacuole function?

A
  • make cell turgid + therefore provides support
  • temporary store of amino acids and sugars
  • pigments may colour petals to attract pollinators
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15
Q

Chloroplasts structure?

A
  • surrounded by a double membrane
  • has grana (granum singular) which contains 100s of disc like structures called thylakoids (folded membranes with added pigment)
  • fluid-filled stoma which contains enzymes for photosynthesis
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16
Q

Chloroplast function?

A
  • site of photosynthesis
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17
Q

Cell wall structure?

A
  • plants - made of microfibrils of the cellulose polymer
  • fungi - made of chitin (nitrogen-containing polysaccharide)
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18
Q

Cell wall function?

A
  • provide structural strength to the cell
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19
Q

Plasma membrane structure?

A
  • found in ALL cells
  • phospholipid bilayer in which molecules embed within + attach on the outside (inc. proteins, carbohydrates, and cholesterol)
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20
Q

Plasma membrane function?

A

controls the entrance and exit of molecules

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21
Q

list 5 key differences between prokaryotic and eukaryotic cells

A
  • prokaryotic cells much smaller
  • prokaryotic cells have no membrane-bound organelles
  • prokaryotic cells have smaller ribosomes
  • prokaryotic cells have no nucleus
  • prokaryotic cell’s cell wall is made from murein, rather than cellulose (plants) or chitin (fungi)
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22
Q

list 3 organelles that only some prokaryotic cells may contain

A
  • plasmids
  • a capsule around the cell
  • flagella
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23
Q

which organelles cannot be found in a prokaryote? why?

A

prokaryotes do not contain membrane-bound organelles so they do not contain mitochondria, chloroplasts, endoplasmic reticulum, golgi apparatus, nucleus or any lysosomes

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24
Q

what are ribosomes made of?

A

2 sub-units of protein and rRNA

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25
Q

compare the ribosomes in a prokaryote vs in a eukaryote

A
  • prokaryotes contain 70s ribosomes whereas eukaryotes contain 80s ribosomes
  • 70s ribosomes are smaller and a found in prokaryotic cells, mitochondria and in chloroplasts
  • 80s ribosomes are larger ribosomes found in eukaryotic cells and they usually measure around 25nm in length
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26
Q

compare the nucleus in a eukaryotic cell vs in a prokaryotic cell

A
  • prokaryotic cells don’t contain a nucleus instead contain a single circular DNA molecule free in cytoplasm which is not protein bound
  • nucleus in eukaryotic cell made of a nuclear envelope (a double membrane), nuclear pores. nucleoplasm ( a granular, jelly-like material, chromosomes (which are protein-bound, linear DNA), + a nucleolus (a smaller sphere which is the site of rRNA production and makes ribosomes.
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27
Q

compare the cell wall in a prokaryotic cell vs in a eukaryotic cell

A
  • prokaryotic cell wall made of murein (a glycoprotein)
  • eukaryotic cell wall is made up of microfibrils of the cellulose polymer (plants) or chitin (a nitrogen-containing polysaccharide, fungi)
  • all prokaryotic cells contain a cell wall whereas only plants or fungi eukaryotic cells do
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28
Q

what are plasmids? what are their function?

A

small loops of DNA which only carry a few genes

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29
Q

what is a (slime) capsule? what is its function?

A
  • thick slimy layer made of protein
  • prevents bacteria from desiccating (drying out)
  • protects the bacteria against host’s immune system by covering antigens on outside of cell
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30
Q

what are flagella? what is their function?

A

tail-like structure that rotates to enable the bacteria to move

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31
Q

what is cell fractionation used for? why is it useful?

A
  • used to isolate different organelles so they can be studied
  • enables individual organelle structures and functions to be studied
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32
Q

describe the process of cell fractionation

A

1) homogenisation: cell must be homogenised (broken open) using a blender. The cells are blended in a cold, isotonic + buffered solution. The solution is then filtered to remove large cell debris

2) ultracentrifugation: filtered solution is spun at different speeds in a centrifuge. organelles separate according to their density. this is done by differential centrifugation

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33
Q

describe the process of differential centrifugation

A
  • centrifuge spins and the centrifugal forces cause the pellets of the most dense organelles to form at the bottom
  • the centrifuge is first spun at a low speed and the process is repeated at increasingly faster speeds
  • each time the supernatant (liquid) is removed leaving behind a pellet of organelles
  • the supernatant is then put back and spun at a faster speed to remove the next pellet of organelles
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34
Q

during cell fractionation, why must the cell be prepared in a cold solution?

A

reduces enzyme activity
when the cell breaks open, enzymes are released which could damage the organelles

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35
Q

during cell fractionation, why must the cell be prepared in an isotonic solution?

A

to prevent osmosis as water moving in/out could cause the organelles to burst/shrivel

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36
Q

during cell fractionation, why must the cell be prepared in a buffered solution?

A

prevent damage to organelles

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37
Q

what is the order of the organelle pellets produced?

A
  • nuclei
  • chloroplasts (if plant)
  • mitochondria
  • lysosomes
  • endoplasmic reticulum
  • ribosomes
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38
Q

what are the 3 types of microscopes?

A
  • light microscope
  • transmission electron microscope
  • scanning electron microscope
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39
Q

what is magnification?

A

how many times larger an image is compared to an object

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40
Q

what is resolution?

A

the minimum distance between 2 objects in which they can still be viewed as separate

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41
Q

what are the resolutions of light and electron microscopes determined by?

A

the wavelength of light determines light microscope resolution, whilst the wavelength of the beam of electrons determines electron microscope resolution

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42
Q

how does a light microscope work?

A

a beam of light is condensed to create the image

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43
Q

disadvantages of a light microscope

A
  • poorer resolution due to light having a longer wavelength
  • lower magnification
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44
Q

why are small organelles in a cell not visible using a light microscope?

A

they have a poor resolution due to the long wavelength of light

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45
Q

advantages of a light microscope

A
  • colour images
  • living samples can be examined
  • can be used by almost anyone
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46
Q

how does an electron microscope work (TEM and SEM)?

A

a beam of electrons is condensed using electromagnets to create the image

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47
Q

advantages of an electron microscope

A
  • higher resolution
  • higher magnification
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48
Q

disadvantages of an electron microscope

A
  • images produced are black and white
  • non-living samples only
  • must be in a vacuum
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49
Q

how do TEMs work? what kind of image is produced?

A
  • extremely thin specimens stained + placed in vacuum
  • electron gun produces beam of electrons that pass through specimen
  • some parts absorb the electrons more + appear darker
  • 2D detailed image produced, shows internal structure of cells
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50
Q

how do SEMs work? what kind of image is produced?

A
  • electrons are beamed onto the surface and the electrons are scattered in different ways, depending on the contours
  • a 3D image is produced
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51
Q

advantages of using a TEM rather than a SEM

A

-better resolution than the SEM which only has a resolution of 2nm and the TEM has a resolution of 0.2nm
- can see internal structures rather than just the surface

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52
Q

advantages of using SEM rather than a TEM

A
  • specimens do not need to be thin as the electrons are not transmitting through
  • 3D image produced
  • cost less
  • require less preparation
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53
Q

why must a vacuum be used when viewing a specimen with an electron microscope?

A

electrons are absorbed or deflected by molecules in the air, and this prevents them from reaching the specimen

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54
Q

why must specimens be stained?

A

makes organelles more visible + improves contrast so can distinguish between different types of cells and different organelles

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55
Q

how to get from a large unit to a smaller unit (e.g metres to millimetres)

A

multiply (usually by 1000, unless converting m to cm which is x100 or cm to mm which x10)

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56
Q

how to convert from a small unit to a larger unit (e.g millimetres to metres)

A

divide
(usually by 1000, unless converting cm to m which is divide by 100 or mm to cm which is divide by 10)

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57
Q

what is an eyepiece graticule? what is it used for?

A

a scale on a glass disc inside of a light microscope
can be used to measure the size of the object you are viewing under the microscope

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58
Q

what is a stage micrometer? what is it used for?

A

glass slide with a scale on it which you place on the stage
used to calibrate the eyepiece graticule

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59
Q

how long is a typical scale on a stage micrometer?

A

2mm

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60
Q

how long are the subdivisions on a typical stage micrometer?

A

10um

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61
Q

how is an eyepiece graticule calibrated?

A

1) line up the stage micrometer and eyepiece graticule whilst looking through the eyepiece
2) count how many divisions on the eyepiece graticule fit into one division on the micrometer
3) each division on the stage micrometer is 10um, so this can be used to calculate what 1 division on the eyepiece graticule is at that magnification:

10um / (how many divisions fit into 1 division of stage micrometer)

4) count how many divisions long the object is and multiply by answer from step 3

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62
Q

how do eukaryotic cells divide?

A

mitosis or meiosis

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63
Q

how do prokaryotic cells replicate?

A

binary fission

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64
Q

why don’t viruses undergo cell division?

A

they are non-living

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65
Q

how do viruses replicate?

A

inside the host cells they invade by injecting their nucleic acid into the cell to replicate the virus particles

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66
Q

what are the 3 key phases of the cell cycle?

A
  • interphase (G1, S, G2)
  • nuclear division (mitosis/meiosis)
  • cytokinesis
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67
Q

what happens during the interphase stage of the cell cycle?

A

organelles double, cell grows and DNA replicates

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68
Q

what happens during the nuclear division stage of the cell cycle?

A
  • can either be mitosis (2 identical diploid cells created) or meiosis (4 genetically different haploid cells created)
  • mitosis creates cells with identical DNA for growth + repair, whereas meiosis creates gametes
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69
Q

what happens during the cytokinesis stage of the cell cycle?

A

division of the cytoplasm to create new cells

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70
Q

what happens in the G1 stage of the cell cycle?

A
  • mRNAs and proteins synthesised
  • cell grows larger + some organelles are copied
  • cellular checks made to ensure DNA is in a good enough condition to be replicated - if DNA damaged then cell division is terminated at this stage
71
Q

what happens in the S stage of the cell cycle?

A
  • DNA is replicated
  • generates sister chromatids, (identical pairs of chromosomes)
  • sister chromatids are attached to each other by a centromere
72
Q

what happens in the G2 stage of the cell cycle?

A
  • cell undergoes additional growth
  • organelles are copied
  • components of microtubules (which will move chromosomes during mitosis) are synthesised
  • G2 ends when mitosis begins
73
Q

what is a centromere?

A

a specialised sequence of DNA that links the sister chromatids

74
Q

what are the 4 stages of mitosis?

A
  • prophase
  • metaphase
  • anaphase
  • telophase
75
Q

what happens during prophase?

A
  • chromosomes condense + become visible
  • in animals, the centrioles separate + move to opposite poles of cell
  • nucleolus disappears
76
Q

what happens during metaphase?

A
  • chromosomes align along the equator of the cell
  • the spindle fibres released from the poles now attach to the centromere + chromatids
77
Q

what happens during anaphase?

A
  • spindle fibres retract + pull the centromere + chromatids they are bound to to opposite poles
  • causes centromere to divide in 2
  • requires energy in form of ATP
78
Q

what happens during telophase?

A
  • chromosomes become longer and thinner again
  • spindle fibres disintegrate and nucleus starts to reform
  • final stage in the cell cycle (cytokinesis) takes place : cytoplasm splits in two to create 2 new genetically identical cells
79
Q

what is mitotic index?

A

the proportion of cells which are undergoing mitosis

80
Q

what is the formula for mitotic index?

A

(number of cells in mitosis/total number of cells) x100

81
Q

how do you know if a cell is undergoing mitosis?

A

chromosomes are visible

82
Q

what is the fluid mosaic model?

A

the mixture and movement of the phospholipids, proteins, glycoproteins and glycolipids the membrane is made of

83
Q

describe the fluid mosaic model of membranes

A
  • fluid: has a phospholipid bilayer in which individual phospholipids can move = membrane has flexible shape
  • mosaic: proteins, glycoproteins and glycolipids are embedded on both the inside and outside of the membrane
84
Q

list 4 components of a plasma membrane

A
  • phospholipid bilayer
  • cholesterol
  • proteins
  • partially permeable membrane
85
Q

describe the phospholipid bilayer of a plasma membrane

A
  • phospholipids align as a bilayer due to the hydrophilic heads being attracted to the water and the hydrophobic tails being repelled by the water
86
Q

describe the cholesterol in a plasma membrane

A
  • is present in some membranes
  • will restrict the lateral (sideways) movement of other molecules in the membrane
  • useful as it makes the membrane less fluid (more rigid) at high temperatures and prevents water + dissolved ions leaking out of the cells which in turn prevents dehydration/bursting of cell
87
Q

what are the 2 types of proteins embedded across a cell surface membrane? what’s the difference in structure?

A
  • peripheral protein (do not extend completely across the membrane)
  • integral ( span across from one side of the bilayer to the other)
88
Q

what is the function of a peripheral protein?

A
  • provide mechanical support
  • connect to proteins/lipid to make glycoproteins which in turn are used as receptors (for example) for cell recognition
89
Q

what are integral proteins?

A

protein carriers or channel proteins involved in the transport of molecules across the membrane

90
Q

how do protein channels carry out their function?

A

they form tubes that fill with water to enable water-soluble ions to diffuse

91
Q

how do carrier proteins carry out their function?

A

they bind with larger molecules, e.g. glucose or amino acids, and change shape to release the molecule to the other side of the membrane (transport them to the other side of the membrane)

92
Q

what molecules can pass through the semi-permeable membrane of a plasma membrane?

A
  • lipid-soluble substances (e.g. some hormones)
  • very small molecules (e.g. CO2, O2, H2O)
93
Q

what molecules cannot pass through the semi-permeable membrane of a plasma membrane?

A
  • water-soluble (polar) substances (e.g. sodium ions)
  • large molecules (e.g. glucose)
94
Q

define simple diffusion

A

net movement of molecules from an area of higher concentration to an area of lower concentration (until equilibrium is reached)

95
Q

is simple diffusion an active or passive process?

A

passive (does not require ATP)

96
Q

what are the properties of molecules that are able to diffuse across the plasma membrane by simple diffusion?

A

lipid-soluble and small

97
Q

how does facilitated diffusion differ from simple diffusion?

A
  • in facilitated diffusion, proteins are used to transport molecules
  • ions and polar molecules which cannot simply diffuse can be transported across membranes by facilitated diffusion using protein channels and carrier proteins
  • this is still selective as the channel proteins only open in the presence of specific ions when they bind to the protein
98
Q

define osmosis

A

net movement of water from an area of high water potential to an area of lower water potential across a partially permeable membrane

99
Q

what is water potential? what is it measured in? what is the symbol for water potential?

A
  • the pressure created by water molecules
  • measured in kPa
  • symbol is Ψ
100
Q

what is the water potential of pure water?

A

0

101
Q

what happens to the water potential of pure water as more solutes are dissolved?

A

the water potential will become more negative

102
Q

what is an isotonic solution (in terms of water potential)?

A

water potential is the same in the solution and the cell within the solution

103
Q

what is a hypotonic solution (in terms of water potential)?

A

water potential of a solution is more positive that in the cell, causing water to move into the cell (cell may swell/burst)

104
Q

what is a hypertonic solution (in terms of water potential)?

A

water potential of a solution is more negative that the cell, causing water to move out of the cell (cell may shrink/shrivel)

105
Q

what happens if you place an animal cell in a hypotonic solution? how does this differ from a plant cell?

A
  • a lot of water will move into the animal cell by osmosis
  • due to the lack of a cell wall the pressure will cause the cell to burst
  • plant cells do not burst because of the strengthened cell wall + instead become turgid
106
Q

what happens if you place an animal cell in a hypertonic solution? what about a plant cell?

A

both animal and plant cells will shrivel if placed in a hypertonic solution due to large volumes of water leaving the cell by osmosis

107
Q

define active transport

A

movement of molecules + ions from an area of lower concentration to an area of higher concentration (Against a concentration gradient) using ATP + carrier proteins

108
Q

what makes active transport selective?

A

only certain molecules which are complementary in shape to the protein can bind to the carrier proteins to be pumped

109
Q

how are ATP + carrier proteins used in active transport?

A
  • ATP will bind to the protein on the inside of the membrane + is then hydrolysed into ADP + Pi, causing a small amount of energy to be released
  • energy is used to change the shape of the protein which causes it to open towards the inside of the membrane and therefore the molecule is released to the other side of the membrane
  • the Pi (inorganic phosphate) molecule is then released from the protein so the protein reverts back to its original shape
  • process can now continue to happen as long as there is a supply of ATP available
110
Q

why are active transport and co-transport required in the ileum (small intestine)?

A

to absorb glucose from the lumen to the gut there must be a higher concentration of glucose in the lumen compared to the epithelial cell (for facilitated diffusion) however there is usually more glucose in the epithelial cell so active transport and cotransport are required

111
Q

describe the cotransport of glucose and sodium ions in the ileum (small intestine)

A

1) sodium ions are actively transported out of the epithelial cell into the blood (reduces the sodium ion concentration in the epithelial cell)
2) sodium ions can then diffuse from the ileum down their concentration gradient into the epithelial cell
3) the proteins the sodium ions diffuse through is a cotransporter protein (2 different molecules attach before either of them are transported to the other side), so either glucose or amino acids also attach and are transported into the epithelial cell against their concentration gradient
4) glucose then moves by facilitated diffusion from epithelial cell to blood

112
Q

how is the concentration gradient of glucose maintained during the cotransport of glucose and sodium ions in the ileum (small intestine)?

A

the concentration of glucose in the blood is lower than in the epithelial cells because the blood flows and is carried away

113
Q

why are microvilli useful in the cotransport of glucose and sodium ions in the ileum (small intestine)?

A

increase surface area for cotransporter proteins so sodium ions can diffuse through

114
Q

are phagocytes specific or non-specific? how?

A

non-specific - any non-self cell (e.g. a pathogen) that is detected will trigger the same response to destroy it

115
Q

what is a phagocyte?

A

a macrophage (type of white blood cell) that carries out phagocytosis

116
Q

describe the process of phagocytosis

A

1) chemicals/debris released by pathogens/abnormal cells attract phagocytes + they will move towards the cells
2) phagocytes attach to chemicals/antigens via receptors
3) phagocytes change shape to move around + engulf pathogen
4) once engulfed pathogen is contained within a phagosome vesicle
5) a lysosome within the phagocytes will fuse with the phagosome and release its contents
6) the lysozyme enzyme is released into the phagosome
7) pathogen is destroyed
8) the soluble products are absorbed + used by the phagocyte

117
Q

state the equation for the rate of diffusion (Fick’s Law)

A

rate = (surface area x difference in concentration)/length of diffusion path

118
Q

how does surface area affect rate of diffusion?

A

larger surface area = faster rate of diffusion

119
Q

how does difference in concentration affect rate of diffusion?

A

larger difference in concentration = faster rate of diffusion

120
Q

how does the length of diffusion path affect rate of diffusion?

A

longer diffusion path = slower rate of diffusion

121
Q

define endocytosis

A
  • the movement of a substance into cell by a vesicle
  • vesicle = form of packaging used by cells
122
Q

define exocytosis

A

the movement of a substance out
of the cell by a vesicle

123
Q

what are lymphocytes?

A

white blood cells involved in the specific immune response

124
Q

where are lymphocytes made?

A

bone marrow

125
Q

where do T cells mature?

A

thymus

126
Q

what kind of lymphocyte is involved in cell-mediated response?

A

T lymphocyte

127
Q

why is cell-mediated response considered specific?

A

T cells respond to specific antigens on the surface of cells

128
Q

what is an antigen-presenting cell?

A

any cell that present a non-self antigen on their surface

129
Q

list 4 examples of antigen-presenting cells

A
  • infected body cells will present the viral antigens on their surface
  • a macrophage which has engulfed + destroyed a pathogen will present the antigens on their surface
  • cells of a transported organ will have differently shaped antigens on their surface compared to self-cell antigens
  • cancer cells will have abnormal shaped self-cell antigens
130
Q

why are T-cell responses called “cell-mediated responses”?

A

T cells only respond to antigens which are present on cells (APC) and not antigens detached from cells within body fluids e.g. the blood

131
Q

describe the process of cell-mediated response

A

1) once a pathogen has been engulfed + destroyed by a phagocyte, the antigens are positioned on the cell surface - it is now an antigen-presenting cell (APC)
2) helper T cells have receptors on their surfaces which can attach to the antigens on APCs
3) once attached, this stimulates the helper T cells to divide by mitosis, producing large numbers of clones
4) cloned helper T-cells differentiate into different cells

132
Q

what kind of cell might a cloned helper T cell differentiate into?

A
  • some remain as helper T cells + activate B lymphocytes
  • some stimulate macrophages to perform more phagocytosis
  • some become memory cells for that specific antigen
  • some become cytotoxic T cells (killer T cells)
133
Q

what do cytotoxic T cells do?

A

destroy abnormal or infected cells

134
Q

how do cytotoxic cells carry out their function?

A
  • they release perforin (a protein) which embeds in the cell surface membrane and makes a pore so that any substances can enter/leave the cell which causes cell death
135
Q

when are cytotoxic T cells most likely to be produced? why?

A

when there is a viral infection, as viruses infect body cells

136
Q

where do B cells mature?

A

bone marrow

137
Q

does humoral response involve B cells or T cells? what else does it involve?

A

B cells
antibodies

138
Q

describe the process of humoral response

A

1) antigens in blood collide with complementary antibody on B cell
2) B cell takes in antigen by endocytosis + then presents it on cell surface membrane
3) when B cell collides with helper T cell receptor, activates B cell to go through clonal selection
4) B cells undergo mitosis to make large numbers of cells - differentiate into memory/plasma cells
5) plasma cells make antibodies
6) B memory cells can divide rapidly into plasma cells when reinfected with same pathogen to make large numbers of antibodies rapidly

139
Q

describe plasma cells and how they carry out their function in humoral immunity

A
  • involved in the primary immune response
  • secrete antibodies directly into body fluids
  • only survive for a few days but produce 2000 antibodies per second
  • response is slow and person will get ill before pathogen destroyed
140
Q

describe memory cells and how they carry out their function in humoral immunity

A
  • involved in the secondary immune response
  • circulate in the blood and tissue fluid
  • remain in body fluids for decades
  • when they encounter the antigen from the primary response they divide rapidly
  • response is rapid and person will not get ill.
141
Q

describe how active immunity works

A
  • during primary response to a pathogen (natural) or to a vaccination (artificial), antibody concentration in blood takes 1-2 weeks to increase.
  • If body invaded by same pathogen again or by pathogen that person was vaccinated against then, during the secondary response, the antibody concentration in blood takes much shorter period of time to increase + is higher than after vaccination or first infection
142
Q

what kind of protein are antibodies?

A

quaternary structure
4 polypeptide chains

143
Q

define agglutination

A
  • antibodies are flexible + can bind to multiple antigens which causes the clumping together of cells or particles which assists phagocytosis as it makes it easier for phagocytes to locate + destroy the pathogens
144
Q

what is passive immunity?

A
  • antibodies introduced to body (e.g. by injection)
  • pathogen doesn’t enter body so plasma cells and memory cells are not made
  • no long term immunity
145
Q

list 2 examples of passive immunity

A
  • antibodies passed to s fetus through a placenta
  • antibodies passed through breast milk to a baby
146
Q

what is active immunity?

A

immunity created by your own immune system following exposure to the pathogen or its antigen

147
Q

what is natural active immunity?

A

the creation of own antibodies and memory cells following an infection

148
Q

what is artificial active immunity?

A

the creation of antibodies and memory cells following the introduction of a weakened version of the pathogens via a vaccination

149
Q

describe how vaccination works

A

1) small amounts of weakened or dead pathogens/antigens introduced into body
2) activates B cells to go through clonal selection
3) B cells undergo mitosis to make large numbers of cells - these differentiate into plasma cells or memory B cells
4) plasma cells make antibodies
5) B memory cells divide rapidly into plasma cells when reinfected with same pathogen to make large numbers of antibodies rapidly - this means person will not feel symptoms when naturally exposed to the pathogen

150
Q

what is herd immunity? how does it work?

A
  • if enough of the population is vaccinated the pathogen cannot easily spread amongst the population
  • this provides protection for those who are not vaccinated, e.g. those who are too young, already ill, or those with a compromised immune system
151
Q

why does antigen variability occur?

A

a pathogen’s DNA can mutate frequently

152
Q

when does antigen variability occur?

A
  • if a mutation occurs in the gene which codes for the antigen then the shape of the antigen will change
153
Q

why must new vaccines be produced?

A
  • any previous immunity to a pathogen (either naturally through prior infection or artificially through vaccination) will no longer be effective, as all the memory cells in the blood will have a memory of the old antigen shape
154
Q

how do lymphocytes distinguish between self and non-self cells?

A

have unique 3D tertiary structures

155
Q

what happens if a non-self cell is detected?

A

a response will be triggered to destroy the cell

156
Q

how do lymphocytes recognise cells?

A
  • lymphocytes made when fetus and in the womb it is unlikely to be exposed to anything other than self cells
  • the lymphocytes complementary to the antigens on self cells will die/production will be suppressed which prevents lymphocytes from attacking own cells
  • the only remaining lymphocytes are complementary t pathogenic and nonself cells
  • the same process occurs after birth in the bone marrow - any new lymphocytes made in the bone marrow which are complementary in shape to antigens on self cells will be destroyed
157
Q

what causes the symptoms of autoimmune diseases?

A

sometimes lymphocytes that attack self-cells are produced instead of destroyed and so they attack the person’s own immune system leaving them more susceptible to infections and cancer

158
Q

what are antigens?

A
  • molecules that generate an immune response by lymphocyte cells when detected in the body
  • they are usually proteins and are located on the surface of cells
159
Q

why is it difficult to use medication to treat a virus?

A

viruses are non-living, meaning they have to replicate inside of cells - this makes it difficult destroy them without harming host cells

160
Q

why don’t antibiotics work on viruses

A

viruses have different mechanisms to replicate than bacteria, as well as no cell wall. antibiotics often work by interfering with the mechanisms of replication in a bacterial cell, e.g protein synthesis

161
Q

describe 4 components of the structure of HIV

A
  • core = genetic material (RNA) and the enzyme reverse transcriptase, which are needed for viral replication
  • capsid = outer protein coat
  • envelope - extra outer layer made out of membrane taken from the host’s cell membrane
  • protein attachments - on the exterior of the envelope to enable the virus to attach to the host’s helper T cells
162
Q

describe the process of the replication of HIV in helper T cells

A

1) HIV is transported around in the blood until it attaches to a CD4 protein on the helper T cells
2) the HIV protein capsule then fuses with the helper T cell membrane, enabling the RNA and the enzymes (reverse transcriptase) from HIV to enter
3) the HIV enzyme reverse transcriptase copies the viral RNA into a DNA copy and moves to the helper Tcell nucleus
4) here, mRNA is transcribed, and the helper T-cell starts to create viral proteins to make new virus particles

163
Q

when is a person considered HIV positive?

A

when they are infected with HIV

164
Q

when does HIV develop into AIDs? why is this harmful?

A
  • when the replicating viruses in the helper T cells interfere with their normal functioning of the immune system
  • with the helper T cells being destroyed by the virus, the host is unable to produce an adequate immune response to other pathogens and is left vulnerable to infections and cancer
  • eventually the destruction of the immune system will lead to the patient’s death (not the HIV/AIDS itself)
165
Q

what is a monoclonal antibody?

A

a single type of antibody that can be isolated and cloned

166
Q

what is an antibody?

A

a protein which has a binding site complementary in shape to certain antigens

167
Q

list 4 uses of monoclonal antibodies

A
  • medical diagnosis
  • targeted medication
  • pregnancy testing
  • transplant surgery
168
Q

describe direct MAB therapy

A
  • some cancer can be treated using MABs, which are designed with a binding site complementary to the antigens on outside of cancer cells
  • antibodies given to cancer patient + attach to cancer cells
  • as antibodies are bound to cancer antigens, this prevents chemicals from binding to cancer cells which enable uncontrolled cell division
  • therefore MABS prevent the cancer cells from growing and as they as designed to only attach to cancer cells, they do not cause harm to normal cells
169
Q

describe indirect MAB therapy. why is this a better option for treating cancer than traditional chemotherapy and radiotherapy?

A
  • MABS complementary in shape to cancer cells antigens with cytotoxic drugs attached are delivered directly to cancer cells
  • reduces the harmful side effects that traditional chemotherapy and radiotherapy cause
170
Q

what test can be used to diagnose medical conditions through the use of MABs? how does this work?

A

ELISA test
- MABs used to detect amount of certain substances in blood by binding to them
- used to detect range of diseases inc influenza, chlamydia + prostate cancer

171
Q

describe how MABS can be used in pregnancy testing

A
  • MABS + colour particles are attached to the test strip of home
    pregnancy testing kits
  • pregnant women produce high levels of hCG in urine
  • hCG attaches to the antibodies and as the hCG-antibody-colour complex moves along the
    testing strip they become trapped to form a coloured line
172
Q

describe the process of the ELISA test

A

1) virus proteins (antigens) are added to wells of a 96-well plate
2) the antigens bind to the plastic, coating the bottom of the wells
3) the primary antibody is added to the well- these are from the patient’s serum sample
4) excess antibody is washed away, leaving only antibodies bound to the antigens behind. this wash removes excess antibodies that are unbound and prevents non-specific binding.
5) a secondary antibody which is complementary to the first is added to the wells. the secondary antibody also has an enzyme attached
6) excess secondary antibody is washed away, removing any inbound antibodies and leaving only secondary antibodies bound to the first antibodies
7) substrate is added to the wells
8) secondary antibody containing an enzyme will cause a colour change when exposed to the substrate. a colour change indicates a positive reaction
9) presence of colour indicates presence of antibodies in test sample, meaning the patient will have been exposed to the antigen
- the intensity of the colour indicates the quantity of antibodies present

173
Q

what are some ethical issues of MABs? what are some of the counter-arguments?

A
  • requires mice to produce MABs (spleen gets removed and mice die)
  • guidelines in place to minimise suffering of mice
  • successful in treating cancers
  • caused deaths in MS sufferers
  • informed consent required before treatment
  • drug trials may harm healthy human volunteers
174
Q

what are centrioles responsible for? why is this important for mitosis?

A
  • responsible for creating spindle fibres
  • spindle fibres released from both poles to create spindle apparatus
  • spindle apparatus will attach the centromere and chromatids on the chromosome during mitosis

A-Level Biology (6 decks)

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