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Cells Flashcards

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1
Q

What is the structure of the nucleus?

A

Nuclear envelope- 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 make ribosomes.

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2
Q

What is the function of the nucleus?

A

Site of DNA replication and transcription (making mRNA)
Contains the genetic code for each cell.

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3
Q

What is the structure of both endoplasmic reticulum’s?

A

Rough and Smooth both have folded membranes called cisternae.
Rough ER have ribosomes on the cisternae.

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4
Q

What is the function of both endoplasmic reticulum’s?

A

RER- protein synthesis.
SER- synthesis and store lipids and carbohydrates.

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5
Q

What is the structure of the Golgi Apparatus and vesicles?

A

Folded membranes making cisternae.
Secretary vesicles pinch off from the cisternae.

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6
Q

What is the function of the Golgi Apparatus and vesicles?

A

Add carbohydrates to proteins to form glycoproteins.
Produce secretory enzymes.
Secrete carbohydrates.
Transport, modify and store lipids.
Form lysosomes.
Finished products are transported to cell surface in Golgi vesicles where they fuse with the membrane and the contents are released.

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7
Q

What is the structure of lysosomes?

A

Bags of digestive enzymes — can contain 50 different enzymes.

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8
Q

What is the function of lysosomes?

A

Hydrolyse phagocytic cells.
Completely break down dead cells (autolysis)
Exocytosis — release enzymes to outside of cell to destroy material
Digest worn out organelles for reuse of materials.

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9
Q

What is the structure of mitochondria?

A

Double membrane.
Inner membrane called the cristae.
Fluid centre called the mitochondrial matrix.
Loop of mitochondria DNA.

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10
Q

What is the function of mitochondria?

A

Site of aerobic respiration.
Site of ATP production.
DNA to code for enzymes needed in respiration.

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11
Q

What is the structure of ribosomes?

A

Small, made up of two sub-units of protein and rRNA.
80s- large ribosome found in eukaryotic cells.
70s- smaller ribosome found in prokaryotic cells, mitochondria and chloroplasts.

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12
Q

What is the function of ribosomes?

A

The site of protein synthesis.

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13
Q

What is the structure of the vacuole?

A

Filled with fluid surrounded by a single membrane called a tonoplast.

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14
Q

What is the function of the vacuole?

A

Make cells turgid and therefore provide support
Temporary store of sugars and amino acids
The pigments may colour petals to attract pollinators.

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15
Q

What is the structure of chloroplasts?

A

Surrounded by a double membrane
Contains thylakoids (folded membranes embedded with pigment)
Fluid filled storma contains enzymes for photosynthesis.
Found in plants.

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16
Q

What is the function of chloroplasts?

A

Site of photosynthesis.

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17
Q

What is the structure of the cell wall?

A

In plant and fungi cells.
Plants- made of microfibrils of the cellulose polymer.
Fungi- made of chitin, a nitrogen-containing polysaccharide.

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18
Q

What is the function of the cell wall?

A

Provides structural strength to the cell.

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19
Q

What is the structure of the plasma membrane?

A

Found in all cells
Phospholipid bilayer — molecules embed within and attached on the outside (proteins, carbohydrates, cholesterol)

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20
Q

What is the function of the plasma membrane?

A

Controls the entrance and exit of molecules.

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21
Q

What are the key differences in prokaryotic cells and eukaryotic cells?

A

The cells are much smaller.
No membrane bound-organelles.
Smaller ribosomes (70s).
No nucleus.
A cell wall made of murein.

May contain:
Plasmids
Flagella
A capsule around the cell.

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22
Q

What is replaced for the nucleus in prokaryotic cells?

A

A single circular DNA molecule free in the cytoplasm which is not protein bound.

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23
Q

What are the sub-cellular structures in a prokaryotic cell?

A

Plasma membrane
DNA (nuceloid)
Capsule
Cell wall
Mesosome
Ribosomes
Cytoplasm
Bacterial flagellum

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24
Q

What does the cell wall contain in a prokaryotic cell?

A

Murein, which is a glycoprotein.

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25
Q

What is a plasmid in some prokaryotic cells?

A

Small loops of DNA which only carry a few genes.

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26
Q

What is a capsule and its function in a prokaryotic cell?

A

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

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27
Q

What is the function of the flagellum in some prokaryotic cells?

A

Rotates to enable the bacteria to move.

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28
Q

What are the three different types of microscopes?

A

Optical (light) microscopes
Transmission electron microscopes
Scanning electron microscopes

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29
Q

Define magnification

A

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

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30
Q

Define resolution

A

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

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31
Q

What are the characteristics of an optical microscope?

A

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

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32
Q

What are the characteristics of the electron microscopes?

A

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

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33
Q

How does a Transmission Electron Microscope work?

A

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

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34
Q

How does the Scanning Electron Microscope work?

A

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

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35
Q

What is the formula for magnification?

A

Magnification= image size/actual size

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36
Q

What are the conversions for metres to millimetres, millimetres to micrometres and micrometres to nanometres?

A

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

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37
Q

What is the eyepiece graticule?

A

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

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38
Q

What is the function of the eyepiece graticule?

A

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

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39
Q

What is a stage micrometer?

A

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

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40
Q

What is cell fractionation?

A

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

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41
Q

How does cell fractionation work?

A

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

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42
Q

Why must the cell be cold, isotonic and buffered before it can go through its cell fractionation process?

A

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

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43
Q

What are the two steps in cell fractionation and describe how they occur?

A

Step 1 is homogenisation where the cells must be broken up. This is done by using a blender. The cells are blended in the cold, isotonic and buffered solution.
The solution is then filtered to remove the large cell debris.

Step 2 is ultracentrifugation where the filtered solution is spun at a high speed in a centrifuge. This separates organelles according to their density.

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44
Q

What is differential centrifugation?

A

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

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45
Q

What is the cell cycle?

A

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

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46
Q

What is interphase?

A

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

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47
Q

Explain each growth stage of interphase.

A

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

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48
Q

Explain mitosis.

A

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

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49
Q

What are the 4 division stages of mitosis?

A

• Prophase
• Metaphase
• Anaphase
• Telophase

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50
Q

Explain ‘prophase’ in the stages of mitosis.

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 the spindle.
• The nuclear envelope (the membrane around the nucleus) breaks down and chromosomes lie free in the cytoplasm.

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51
Q

Explain ‘metaphase’ in the stages of mitosis.

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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52
Q

Explain ‘anaphase’ in the stages of mitosis.

A

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

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53
Q

Explain ‘telophase’ in the stages of mitosis.

A

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

Mitosis is finished and each daughter cell starts the interphase part of the cell cycle to get ready for the next round of mitosis

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54
Q

How long does each stage of mitosis take?

A

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

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55
Q

What is cancer?

A

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

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56
Q

How is a tumour formed?

A

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

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57
Q

How are tumours reduced?

A

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

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58
Q

How are prokaryotic cells replicated?

A

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

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59
Q

Wha is the process of binary fission?

A
  1. The circular DNA and plasmid(s) replicate. The main DNA loop is only replicated once, but plasmids can be replicated loads of times.
  2. The cell gets bigger and the DNA loops move to opposite ‘poles’ (ends) of the cell.
  3. The cytoplasm begins to divide (and new cell walls begin to form).
  4. The cytoplasm divides and two daughter cells are produced. Each daughter cell has one copy of the circular DNA, but can have a variable number of copies of the plasmid(s).
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60
Q

What are viruses and its function?

A

• Viruses are acellular— they’re not cells.
• Viruses are nuclei acids surrounded by protein— they’re not alive.

• All viruses invade and reproduce inside the cells of other organisms. These cells are known as host cells.

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61
Q

What is the general structure of virus?

A

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

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62
Q

What is the process of viral replication?

A
  1. Virus uses their attachment proteins and attaches to host cell receptor proteins.
  2. Genetic material is released into the host cell.
  3. Genetic material and proteins are replicated by host cell ‘machinery’.
  4. Viral components assemble.
  5. Replicated viruses are released from host cell.
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63
Q

What is the basic structure of all cell membranes?

A

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

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64
Q

What are cell-surface membranes?

A

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

65
Q

Why was the fluid mosaic model used as a term to describe the arrangement of molecules in the membrane?

A

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

66
Q

What type of proteins are present in the bilayer?

A

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

67
Q

What are the two membrane components?

A

• Phospholipids
• Cholesterol

68
Q

What is the role of phospholipids as a membrane component?

A

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

69
Q

What is the role of cholesterol as a membrane component?

A

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

70
Q

What is diffusion?

A

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

71
Q

What is the concentration gradient in diffusion?

A

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

72
Q

What is simple diffusion?

A

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

73
Q

What are the 3 factors affecting the rate of diffusion?

A

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

74
Q

How does the concentration gradient affect the rate of diffusion?

A

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

75
Q

How does the thickness of the exchange surface affect the rate of diffusion?

A

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

76
Q

How does the surface area affect the rate of diffusion?

A

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

77
Q

What is facilitated diffusion?

A

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

78
Q

What are carrier proteins?

A

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

79
Q

How do carrier proteins work?

A

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

80
Q

What are channel proteins?

A

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

81
Q

What are the factors affecting the rate of facilitated diffusion?

A

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

82
Q

How does the concentration gradient affect the rate of facilitated diffusion?

A

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

83
Q

How does the number of channel or carrier proteins affect the rate of facilitated diffusion?

A

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

84
Q

How can we calculate the rate of diffusion?

A

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

85
Q

What are the adaptations in specialised cells which affects the rate of diffusion?

A

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

86
Q

Define osmosis.

A

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

87
Q

What is water potential?

A

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

88
Q

What is the water potential of pure water? And how is the amount of water potential able to be changed?

A

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

89
Q

What happens when solutions are called isotonic?

A

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

90
Q

What occurs when a cell is placed in a solution that has a higher water potential?

A

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

91
Q

What occurs when a cell is placed in a solution that has a lower water potential?

A

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

92
Q

What are the 3 net movements of water in osmosis?

A

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

93
Q

What are the 3 factors affecting the rate of osmosis?

A

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

94
Q

How does the water potential gradient affect the rate of osmosis?

A

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

95
Q

How does the thickness of the exchange surface affect the rate of osmosis?

A

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

96
Q

How does the surface area of the exchange surface affect the rate of osmosis?

A

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

97
Q

What is active transport?

A

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

98
Q

How do carrier proteins work in active transport?

A

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

99
Q

What are the two main differences between active transport and facilitated diffusion?

A

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

100
Q

What are co-transporters?

A

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

101
Q

What is the process of glucose being absorbed into the bloodstream in the final part of the small intestine (ileum)?

A
  1. Sodium ions are actively transported out of the epithelial cells in the ileum, into the blood, by the sodium-potassium pump.
    This creates a concentration gradient — there’s now a higher concentration of sodium ions in the lumen of the ileum than inside the cell.
  2. This causes sodium ions to diffuse from the lumen of the ileum into the epithelial cell, down their concentration gradient. They do this via the sodium-glucose co-transporter proteins.
    The co-transporter carries glucose into the cell with the sodium. As a result the concentration of glucose inside the cell increases.
  3. Glucose diffuses out of the cell, into the blood, down its concentration gradient through a protein channel, by facilitated diffusion.
102
Q

What are the factors affecting the rate of active transport?

A

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

103
Q

How does the speed of individual carrier proteins affect the rate of active transport?

A

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

104
Q

How does the number of carrier proteins present affect the rate of active transport?

A

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

105
Q

How does the rate of respiration in the cell and availability of ATP affect the rate of active transport?

A

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

106
Q

What are antigens?

A

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

107
Q

What 4 things do antigens allow the immune system to identify?

A

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

108
Q

What are pathogens?

A

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

109
Q

What are abnormal body cells?

A

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

110
Q

What are toxins?

A

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

111
Q

What are cells from other individuals of the same species?

A

• When you receive cells from another person, such as an organ transplant or blood transfusion, those cells will have some antigens that are different to your own (unlesss the donor is genetically identical to you).
• The foreign antigens trigger an immune response. This response leads to the rejection of the transplanted organs if drugs aren’t taken to suppress the recipients immune system.

• For blood transfusions, the most important antigens are the ABO blood group antigens — if the blood donated contains A or B antigens that aren’t recognised by the recipients immune system, they will generate an immune response.

112
Q

What is a phagocyte?

A

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

113
Q

How does phagocytosis work?

A

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

114
Q

what are t-cells?

A

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

115
Q

What are the two types of T- cells?

A

Helper T-cells and cytotoxic T-cells.

116
Q

What is the function of helper T-cells and cytotoxic T-cells?

A

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

117
Q

What are B-cells?

A

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

118
Q

How do B-cells work?

A

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

119
Q

What are plasma cells?

A

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

120
Q

What is the structure of an antibody?

A

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

121
Q

What is agglutination?

A

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

122
Q

what are the two ways the immune response can be split in?

A

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

123
Q

what is the primary immune response?

A

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

124
Q

What are memory T-cells?

A

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

125
Q

What are memory B-cells?

A

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

126
Q

What is the secondary immune response?

A

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

127
Q

Why do we use vaccines?

A

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

128
Q

How do vaccines help protect people against disease?

A

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

129
Q

what is the disadvantage of taking a vaccine orally?

A

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

130
Q

what is antigenic variation?

A

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

131
Q

how is antigenic variation able to help some pathogens to evade the immune system?

A

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

132
Q

how does antigenic variation affect the production of vaccines to help prevent people from catching influenza?

A

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

133
Q

what are the two types of immunity?

A

active immunity.
passive immunity.

134
Q

what is active immunity?

A

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

135
Q

what are the 2 types of active immunity?

A

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

136
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 any antibodies of its own.

137
Q

what are the 2 types of passive immunity?

A

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

138
Q

what are the contrasting characteristics of active and passive immunity?

A

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

139
Q

what are monoclonal antibodies?

A

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

140
Q

why do we use monoclonal antibodies?

A

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

141
Q

how can monoclonal antibodies target drugs to a particular cell type, e.g cancer cells?

A

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

142
Q

how do monoclonal antibodies target a particular substance for medical diagnosis, e.g pregnancy testing?

A

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

143
Q

what is an ELISA?

A

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

144
Q

how are antibodies used in an ELISA test?

A

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

145
Q

what are the 2 types of ELISA we need to know about?

A

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

146
Q

how is an ELISA test used in a HIV test?

A

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

147
Q

why are the washing steps in the ELISA test important?

A

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

148
Q

what are the ethical issues surrounding vaccines? (4)

A

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

149
Q

what are the ethical issues surrounding monoclonal antibody therapy? (1)

A

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

150
Q

what is HIV?

A

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

151
Q

what are AIDS?

A

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

152
Q

what is the structure of HIV?

A

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

153
Q

how does HIV replicate inside its host’s helper T-cells?

A

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

154
Q

how does HIV cause the symptoms of AIDS?

A

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

155
Q

what are the initial symptoms of AIDS?

A

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

156
Q

what happens as AIDS progresses?

A

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

157
Q

what happens during the late stages of AIDS?

A

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

158
Q

why are antibiotics ineffective against viruses?

A

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

Biology AQA (8 decks)

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