Cells Flashcards
(140 cards)
1
Q
What is the equation for magnification?
A
magnification= image size/actual size
2
Q
What is cell fractionation?
A
In order to obtain the structure and function of the organelles that make up cells, it is necessary to obtain large numbers of isolated organelles. Cell fractionation is the process where cells are broken up into different organelles
3
Q
What must the solution be for cell fractionation? (3 points)
A
1 - Ice cold to reduce enzyme activity
2 - Same water potential as the tissue, preventing bursting/shrinking of organelles
3 - pH buffered so pH does not fluctuate and no proteins/enzymes can be denatured
4
Q
What is the first stage to cell fractionation?
A
Homogenation - cells are broken up by a homogeniser. This breaks the plasma membrane and releases the organelles fromthe cell. The resultant fluid (homogenate), is filtered to remove any complete cells and large pieces of debris
5
Q
What is the second stage to cell fractionation?
A
Ultracentrifugation - process where the fragments in the homogenate are separated in a centrifuge. This spins the tubes of homogenate at very high speed in order to create a centrifugal force
- The tube of filtrate is placed in the centrifuge and is spun at slow speed
- The most dense organelles (nuclei) are forced to the bottom of the tube creating a pellet
- The fluid at the top (supernatant) is removed and is transferred into another tube where it is spunat a faster speed and for a longer time
- The mitochondria are separated next
High speed - ER/golgi
Very high speed - ribosomes
6
Q
What is a light microscope?
A
Light passes through the specimen and is focused by glass lenses
7
Q
What are the advantages and limitations of light microscopes?
A
Advantages:
- Magnification up to x1500
- Resolution 200nm
- Wide range of specimen can be viewed, including living organisms
Limitations:
- Can’t be used for viewing ultrastructure
8
Q
What is an electron microscope?
A
Uses beams of electrons which are focused by magnets
9
Q
What are the two types of electron microscopes?
A
Transmission (TEM) and scanning (SEM)
10
Q
What is the difference in the two electron microscopes?
A
Transmission electron microscopes electron beams pass through very thin section of sample whichis dipped in heavy metals e.g. lead
Scanning electron microscopes electron beams directed on to the surface of the sample (not through)
11
Q
What is the magnification and resolution of both SEMs and TEMs?
A
TEM:
Magnification - x500,000
Resolution - 0.1nm
SEM:
Magnification - x100,000
Resolution - 20nm
12
Q
Describe TEMs
A
Black and white image
2D
13
Q
Describe SEMs
A
Final image is 3D and black and white
14
Q
What are the limitations of electron microscopes?
A
- Whole system must be in a vacuum so living organisms cannot be observed
- Complex staining process
- Specimen must be extremely thin
- May contain artefacts (e.g. dust, staining)
15
Q
What is the equation for working out the size of a specimen using an eyepiece graticule and stage micrometer
A
Number of divisions on stage micrometer x length of one division on stage micrometer/ number of divisions on eyepiece graticule
16
Q
Describe the nucleus in eukaryotes
A
- 10-20 micrometers in size
- Nuclear envelope (double membrane with fluid between) contains nuclear pores to allow the entrance and exit of substances
- Nuclear pores allow passage of large molecules such as mRNA
- Nucleoplasm jelly like material that makes up bulk of the nucleus.
Chromosomes consist of linear DNA and histone proteins
Nucleolus is a small dense spherical region within nucleoplasm which makes mRNA and ribosomes
17
Q
Describe the endoplasmic reticulum
A
Series of lfattened membrane bound sacs called cisternae
- Rough endoplasmic reticulum: (studded woth ribosomes) provide large surface area for protein synthesis. Provide a pathway for the transport of proteins
- Smooth endoplasmic reticulum: No ribosomes, so appears smooth, so its function is to sysnthesise, store and transport lipids and carbohydrates
Cells that manufacture and store large quantities of carbohydrate, proteins and lipids have a very extensive ER e.g. liver cells, epithelial
18
Q
Describe the mitochondria
A
- Spherical or sausage shaped (depending on cross section) with a double membrane that controls the entry or exit of material. Inner membrane highly folded into cristae to provide large surface area for the attachment of enzymes for respiration
- Central part is the matrix. This contains proteins, lipids, ribosomes and mitochondrial DNA
- Provides/sysnthesis of ATP by aerobic respiration which requires oxygen
Metabolically active cells such as muscle and epithelial cells require lots of ATP, and so will contain lots of mitochondria
19
Q
Describe the golgi apparatus
A
Stack of membrane bound flattened sacs called cisternae, with small rounded hollow structures called vesicles
- The golgi receives proteins and lipids from ER and may modify them (add carbohydrates). It also labels them allowing them to be sorted then sent to the correct destination. Once sorted they are transported in a vesicle which are ‘pinched off’ from the ends of the golgi cisternae. Exocytosis may occur when the vesicles transport the material
- Golgi also forms lysosomes
Golgi apparatus is well developed in secretory cells e.g. epithelial cells that line intestines
20
Q
Describe the chloroplast
A
- Found in plant cells and some protocists
- Double membrane
- Carry out photosynthesis to make carbohydrates from carbon dioxide and water
- Inner membrane folded into sacs called thylakoids (stack of thylakoids is a granum) Provides large SA
- Stroma is a fluid filled matrix where the second stage of photosynthesis takes place. Contains required enzymes. Starch granules can also be found here
- Chloroplasts contain DNA and ribosomes so they manufacture some of the proteins needed for photosynthesis
21
Q
Describe the lysosomes
A
- Spherical sacs with single membrane
- Contain powerful digestive enzymes to hydrolyse materials e.g. white blood cell lysosome helps break down microorganisms
22
Q
Describe the vesicles
A
- Membrane bound sacs
- Carry different substances around cells
23
Q
Describe the ribosomes in eukaryotes
A
- Are size 80S in eukaryotes
- No membrane, some in ER and some in cytoplasm
- Have two subunits (one large and one small)
- Site of protein synthesis
24
Q
Describe the vacuoles
A
- Fluid filled sac surrounded by a single membrane called a tonoplast
- Maintains cell stability by pushing cytoplasm against the wall to make cell turgid
25
Describe the cell walls
- In plants
- Made of cellulose (beta glucose)
- Provides strong wall for support and strength in the plant
- In fungi made of chitin
- In bacteria/prokaryotes made of peptidoglycan
26
Describe the cytoskeleton
- Network of protein fibres which provide support and shape to cell
- Made up of microtubules
27
What is division of labour?
Processes in a cell are carried out by individual organelles within the cells working together
E.g. in protein synthesis
28
Describe the process of protein synthesis (i.e. insulin synthesis)
1 - mRNA copy made in nucleus
2 - mRNA leaves nucleus through nuclear pore
3 - mRNA attaches to ribosome on RER - protein synthesised
4 - Proteins are 'pinched off' in vesicles and travel towards Golgi apparatus
5 - Vesicle fuses with golgi apparatus
6 - Golgi processes, labels and modifies protein, ready for release
7 - Packaged proteins are 'pinched off' in vesicles from golgi and travel to membrane
8 - Vesicle fuses with cell surface membrane
9 - Cell surface membrane opens to release proteins outside of cell
Processes 8 and 9 are exocytosis
29
How do cell become specialised?
By switching specific genes off - when unspecialised cells have most/all genes 'switched on' as they have the potential to specialise into all/most cells
30
What 3 ways can a cell become specialised by?
1 - Changing the shape of the cell
2 - Changing the number of specific organelles
3 - Changing the plasma membrane
31
Give two examples of specialised cells
- Red blood cells (erythrocytes)
| - Sperm cells
32
Describe and explain how erythrocytes (RBCs) are specialised
1. Biconcave shape - increases surface area
2. No nuclei - more space inside cell for oxygen
3. Presence of haemoglobin - high affinity for oxygen (aids respiration)
33
Describe and explain how sperm cells are specialised
1. Undulipodium (tail) - controls locomotion of cell
2. Lots of mitochondria - site for aerobic respiration, roduces lots of ATP (energy)
3. Streamlined head - more efficient movement
4. Acrosom/acrosomal cap - contains enzymes for hydrolysis of egg membrane
5. Haploid nucleus - half the original number of chromosomes for fertilisation
34
What is a tissue? Give examples
- Collection of cells that are similar to each other and perform a similar function
- E.g. xylem tissue, nervous tissue, ciliated epithelium
35
What is an organ? Give examples
- Collection of tissues that work together to perform a particular function
- E.g. heart, lungs, liver, intestine
36
What is an organ system? Give examples
- Group of organs working together
| - E.g. respiratory system, circulatory system, excretory system, digestive system
37
Describe a squamous epithelium cell
- Flattened cells
- Very thin
- Line the inside of blood vessels and tubes to provide smooth surface for passage of fluids
- Thin walls provide a short diffusion pathway
- E.g. alveoli for oxygen and carbon dixoide
38
Describe ciliated epithelial tissue
- Made up of column shaped cells
- Found on inner surface of tubes e.g. bronchi, trachea, uterus, oviducts
- Goblet cells produce and secrete mucus
- Cilia hairs can waft mucus
NOTE: Nicotine can paralyse cilia and tar can damage them so they can't sweep mucus
39
What is the process of cell division in prokaryotes (bacteria)?
Binary fission
40
Describe the process of binary fission
1 - The circular DNA and plasmid(s) replicate. The main DNA loop is only replicated once, but plasmids can be replicated many times
2 - The cell increases in size and the DNA loops move to opposite poles of the cell
3 - The cytoplasm begins to divide (and new cells 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 plasmids
41
Explain the differences in structure of prokaryotes and eukaryotes
Prokaryotes:
- No distinct nucleus, only an area where DNA is found
- DNA not associated with histone proteins
- Circular DNA
- Presence of plasmids
- No membrane bound organelles
- Ribosomes are smaller (70S)
- Cell wall made of peptidoglycan (murein)
- May have outer capsule
Eukaryotes:
- Distinct nucleus with a nuclear envelope
- DNA is associated with histone proteins
- Linear DNA
- Plasmids not present
- Membrane bound organelles such as golgi apparatus, mitochondria etc.
- Ribosomes are larger (80S)
- Cell wall in plants made of cellulosde, in fungi made of chitin
- No capsule present
42
Describe the structure of viruses (akaryotes)
- Genetic material (DNA or RNA)
- Capsid (protein coat)
- Attachment points
- Do not undergo cell division
- Instead they inject their genetic material into the host cell
NOTE: Viruses are non-living (do not follow MRSGREN processes) and do not contain organelles
43
What are the 6 stages to cell division in eukaryotes?
```
- Interphase
(Mitotic division)
- Prophase
- Metaphase
- Anaphase
- Telophase
```
- Cytokenesis
44
Describe the 3 parts to interphase
Growth 1
- Cell growth
- Increase in organelle number
- Proteins synthesised
- ATP synthesised
Synthesis
- DNA replication via semi-conservative replication
Growth 2
- Cell growth
- Proteins synthesised
- ATP synthesised
45
What is the longest phase of the cell cycle?
Interphase
46
Describe DNA replication during interphase
- Chromosomal DNA is replicated exactly and the two pieces of DNA are held together by the centromere
- If the copies are not done accurately mutations may occur and daughter cells will NOT receive identical genetic material
- Following mitosis the two new cells will contain one of each sister chromatids
47
What is mitosis (nuclear division) important for?
1 - All organisms that need to produce genetically identical daughter cells
2 - Asexual reproduction - single celled organisms divide to produce daughter cells. Multi-celled organisms may also divide asexually
3 - Growth - multi-cellular organisms grow by producing new extra cells that are genetically identical to each other and the parent cell
4 - Repair - damaged cells need to be replicated by new ones that perform the same function so must be identical
5 - Replacement - erythrocytes and skin cells need to be replaced
48
What are the 4 phases of mitosis?
- Prophase
- Metaphase
- Anaphase
- Telophase
49
Explain what happens in prophase
- Chromosomes shorten and thicken into supercoils
- Each chromosome consists of a pair of sister chromatids
- Nuclear envelope breaks down and disappears
- Centriole divides into two
- Daughter centriole moves to opposite ends of the cell to form a spindle
50
Explain what happens in metaphase
Metaphase (Middle)
- Chromosomes line up down the middle of the cell
- Each chromosome is attached to a different spindle fibre by its centromere
51
Explain what happens in anaphase
Anaphase (Apart)
- The replicas of each chromosome are pulled apart from each other towards opposites poles of the cell
- Identical sister chromatids are pulled to different poles by the shortening of the spindle fibres
52
Explain what happens in telophase
Telophase (Two)
- Two new nuclei are formed
- Spindle breaks down and disappears
- Chromosomes uncoil and cannot be seen in light microscope anymore
53
Explain what happens in cytokenesis
- This is when the cell divides
- Occurs between telophase and interphase
- Each new daughter cell is identical to the parent cell and to each other
- In animal cells microtubules form a 'draw string' just inside the membrane which then fuses as it is pinched in
- In plant cells microtubules direct vesicles to the middle of the cell to form a cell plate, which forms a new cell wall. New cell surface membrane is made on either side to enclose the two cells
54
How does cancer occur?
A mutation in a gene that controls cell division, the cells can grow out of control which can lead to the formation of tumours. A tumour becomes cancerous if it changes from benign (contained and not spreading to other parts of the body) to malignant ( opposite of benign)
55
Drugs used to treat cancer usually disrupt the cell cycle by:
- Preventing DNA from replicating. Radiation and some drugs drugs damage DNA. If severe damage to DNA is detected the cell will kill itself (apoptosis)
- Inhibiting the metaphase stage if mitosis by interfering with spindle formation
- Preventing the synthesis of enzymes needed for DNA replication in growth 1
56
How is it possible to detect cancer cells in terms of looking at the cell cycle?
The mitotic phase of the cell cycle is longer than the whole of interphase
57
Where are plasma membranes found?
Around cells and some organelles
58
Describe the structure of plasma membranes
- Partially permeable
- Made up of phospholipids in a bilayer
- Composed of proteins and phospholipid bilayer
- Under an electron microscope you can see the bilayer as two dark bands (the distance across the membrane is about 7nm)
59
What type of model is used to describe plasma membranes?
Fluid mosaic model
60
Why are plasma membranes described as a fluid mosaic model?
Fluid - Phospholipids and proteins move around each other
Mosaic - Arrangement of proteins within the phospholipid bilayer
(Model - a diagrammatical representation of the structure)
61
What are all the components of plasma membranes?
- Phospholipids
- Cholesterol
- Glycolipids
- Intrinsic/extrinsic proteins
- Glycoproteins
62
Describe the structure and function of phospholipids in plasma membranes
- Make up most of the membrane. Arranged in a bilayer
- Hydrophobic tails face inwards, hydrophilic heads face outwards
- Act as a barrier to water soluble, polar molecules
- Allows lipid soluble, small, non-polar substances to diffuse through
63
Describe the structure and function of cholesterol in plasma membranes
- Found in eukaryotic cells for stability and fluidity
| - Binds to the hydrophobic tails of the phospholipids, causing them to pack more closely together
64
Describe the structure and function of glycolipids in plasma membranes
- Phospholipids with carbohydrate attached
| - Used in cell signalling and recognition
65
Describe the structure and function of proteins in plasma membranes
Intrinsic - span the entire membrane
- Channel or carrier proteins that allow the transport of hydrophilic and large molecules (like glucose) through the phospholipid bilayer
Extrinsic - span half of the membrane
- Cell signalling
- Cell recognition
- Enzymes e.g. in mitochondria cristae for respirstion
66
Describe the structure and function of glycoproteins in plasma membranes
- Proteins with carbohydrate attached
- Receptors for signalling molecules e.g. hormones, drugs
- Cell signalling and recognition e.g. cell surface antigens
- Binding cells together to basement membrane, making tissues, cell adhesion
67
What is the role of membranes WITHIN cells?
- Separate cell components from cytoplasm - COMPARTMENTALISATION
- Holding the components of metabolic pathways in place e.g. mitochondria
- Control what enters and leaves the organelle/cell
- Site of attachment for enzymes and ribosomes
68
What is the role of membranes at SURFACE of cells?
- Separate cell contents from the outside environment
- Cell signalling and recognition
- Regulate transport of materials into or out of cells
- Create/maintain concentration gradients
69
Describe the process of cell signalling?
- Process that leads to communication and coordination between cells, so that they can work together to trigger a response
- Allows cells to be recognised as self and so prevent cells from being destroyed by immune cells
- A receptor in the cells plasma membrane picks up the cells and brings about actions within the cell
E.g. hormone receptors
Structure: protein receptors found on target cells. Have a specific shape complementary only to a specific hormone
Function: bind to the hormone to allow the cell to respond in a particular way
E.g. Insulin receptor. Insulin is released when there is increased blood sugar. Insulin receptors on liver and muscle cells bond the insulin and the cells respond by taking up more glucose to reduce the blood glucose levels
70
How is the plasma membrane affected by temperature?
As temperature increases:
25-45 degrees - increase in temperature increases kinetic energy, molecules can diffuse across membrane more quickly (increases permeability)
50-60 degrees - increase in temperature denatures proteins making membrane more leaky. Lipids melt and become more fluid, so ions/molecules can diffuse more quickly (more permeable)
60-70 degrees - increase in temperature membrane is displaced and breaks down. Ions/molecules diffuse in first few movements of experiment and reach equilibrium quickly
NOTE: When temperature reaches 0 or less, permeability increases as the water freezes, expands and creates gaps/hole in the membrane
71
Define diffusion
Movement of substances from an area of high concentration to an area of low concentration down a concentration gradient, across the partially permeable membrane via the phospholipid bilayer
72
Describe diffusion
- There is a concentration gradient
- Molecules have kinetic energy
- No ATP required (passive process)
- No specific proteins are required
73
What type of molecules can diffuse through the bilayer?
- Lipid soluble e.g. steroid hormones
- Small e.g. CO2, O2
- Small and polar e.g. H2O
74
What are the 4 factors affecting the rate of diffusion?
1 - Temperature
2 - Concentration gradient
3 - Thickness of exchange surface
4 - The surface area
75
How does temperature affect the rate of diffusion?
- After 0 degrees, as temperature increases so does rate of diffusion until another factor becomes the limiting factor
76
How does concentration gradient affect the rate of diffusion?
The greater the concentration gradient, the greater the diffusion rate until another factor becomes limiting
77
How does surface area affect the diffusion rate?
As surface area increases, so does rate of diffusion until another factor becomes limiting
78
How does exchange surface thickness affect the diffusion rate?
As the exchange surface thickens, the rate of diffusion becomes lower
79
Define facilitated diffusion
Movement of substances from an area of high concentration to an area of low concentration, down a concentration gradient, across the membrane via carrier/channel proteins
80
Describe facilitated diffusion
- There is a concentration gradient
- Molecules have kinetic energy
- No ATP/energy is required - passive process
- Channel/carrier proteins are present
81
How are channel proteins used in facilitated diffusion?
- Act as pores in the membrane, some only allow specific ions through e.g. Na ions (due to specific shape).
- They can be gated so they only open/close in specific circumstances
82
How are carrier proteins used in facilitated diffusion?
- Only allow specific large molecules to pass through
- When the molecule, e.g. glucose, binds it changes shape and transfers the molecule to the other side of the membrane
NOTE: Different membranes can have different proteins in their bilayer and so can control the enrty and exit of different substances into and out of the cell
83
What 2 factors affect the rate of facilitated diffusion?
1 - Concentration gradient
| 2 - Number of carrier/channel proteins
84
How does concentration gradient affect the rate of facilitated diffusion?
As concentration gradient increases, so does facilitated diffusion rate
85
How does number of channel/carrier proteins affect the facilitated diffusion rate?
More proteins, faster rate of facilitated diffusion
86
Define osmosis
Movement of water from an area of high water potential to an area of low water potential, down a water potential gradient, across the phospholipid bilayer or via aquaporins
87
What is water potential?
A measure of the ability of water molecules to move freely in solution
88
Describe osmosis
- A water potential gradient is required
- Can occur through aquaporins or water can diffuse through the body layer because it is small and polar
- Pure water is 0KPa, adding solutes to water makes the water potential lower
- Water potential is measured in kilopascals (KPa)
89
What is a hypertonic solution?
Have a lower water potential (higher solute concentration)
90
What is an isotonic solution?
Have the same water potential
91
What is a hypotonic solution?
Have a higher water potential (lower solute concentration)
92
What are the effects of a hypotonic solution on animal and plant cells?
Animal cells:
- Water moves into cell, animal cell bursts (haemolysed)
Plant cells:
- Cell wall prevents bursting when turgid - membrane pushes against cell wall
93
What are the effects of a hypertonic solution on animal and plant cells?
Animal cells:
- cell shrinks and becomes wrinkled (crenated)
Plant cells:
- Plant cell membrane pulls away from cell wall (plasmolysed)
94
Using the scale factor, how is it possible to make up any concentration of solution? Do this for 15cm cubed of 0.4M sucrose concentration
1 - Start with a solution of a known concentration, e.g. 1M
2 - Find the scale factor by dividing the concentration of this solution by the concentration of the solution you want to make 1M / 0.4M = 2.5
3 - This means that the solution you want to make is 2.5x weaker than the one that you have. To make the solution 2.5x weaker, use 2.5x less of it, i.e. 15 / 2.5 = 6. Transfer this to clean test tube (if doing practically)
4 - Top the test tube up to the amount you need with distilled water. In this case, 15-6=9 so there would need to be 9cm cubed added to this solution
95
Define active transport
The movement of large, water soluble or charged substances across the membrane via carrier proteins. A concentration gradient is not required, active transport will occur down a concentration gradient or against a concentration gradient. It does require ATP (therefore oxygen must be present for aerobic respiration)
96
Describe active transport
- Molecules may move against a concentration gradient
- Molecules have kinetic energy
- ATP is required
- Carrier proteins are required - change shape to move substances
97
How do carrier proteins work when transporting substances across the membrane?
- Act as pumps
- Their shape is specific and compliments the shape of the molecule they carry
- Carry larger or charged molecules through the membrane as they cannot diffuse through the lipid bilayer
98
What molecules can be actively transported through carrier proteins?
- Non-lipid soluble
- Large e.g. glucose
- Large and water soluble
99
How is one way flow ensured in active transport?
ATP changes the shape of the carrier proteins in active transport and hence on one side of the membrane the shape of the proteins will compliment the specific molecule to be transported. Once energy has been used by the proteins carrier it changes shape and releases the specific molecule
100
Describe the 3 stages to co-transport
1 - Sodium ions are actively transported out the cell into blood and potassium ions enter the cell (sodium-potassium pump). This creates a concentration gradient
2 - Sodium and glucose ions enter the cell via sodium-glucose co-transporter proteins (facilitated diffusion). This results in the concentration of glucose inside the cell to increase
3 - Glucose diffuses out of the cell into the blood, down its concentration gradient through a channel protein by facilitated diffusion
101
Describe the process of endocytosis
- Bulk transport of substances into the cell
- Membrane engulfs the material
- Membrane fuses together
- Vesicle formed
- ATP required
102
Describe the process of exocytosis
- Bulk movement of substances out of the cell
- Vesicle fuses with the membrane
- Substances moved out of cell
- ATP required
103
Give some examples of bulk transport
- Hormones
| - White blood cells
104
What is a pathogen?
Disease causing microorganism
105
Define what an antigen is
- Foreign molecules (usually proteins) that can generate an immune response when detected by the body (only foreign if not usually found in the body)
106
What do antigens allow the immune system to respond to?
- Pathogens
- Abnormal body cells e.g. cancerous or pathogen infected cells have abnormal antigens on their surface
- Toxins
- Cells from other individuals e.g. organ transplant, blood transfusion
107
What are the two types of defence mechanisms?
- Specific
| - Non-specific
108
Describe non-specific defence mechanisms
Response is immediate and the same for all pathogens
109
Describe specific defence mechanisms
Response is slower and specific to each pathogen
110
What two non-specific defences are there?
- Primary lines of defence
| - Phagocytosis
111
Describe and explain the 6 types of primary lines of defence
1 - The skin - the outer layer of the epidermis consists of dead keratinised cells - keratinocytes which act as a physical barrier to pathogens
2 - Commensal flora - harmless bacteria which live on the skin surface and compete with pathogenic bacteria (also in gut to help break food down)
3 - Mucous membranes - found in gut, genital areas, anus, ears, nose and respiratory passages. An epithelial layer of the cells containing mucus producing goblet cells. The sticky mucus lines the passages and traps pathogens
4 - Eyes - produce tears, contain antibodies and lysosomes
5 - Ears - produce wax which traps pathogens and lysozymes
6 - Vagina - secretions contain lactic acid which breaks down foreign bodies
112
Describe the process of phagocytosis
Neutrophiles:
- Short lived, tend to die after engulfing pathogen
- Multilobed nucleus
- Number rise as a result of infection
Macrophages:
- Long lived, survive after engulfing bacteria
- Settle in lymph nodes, spleen and kidney
- Important in the specific immune response
Mode of action of phagocytes:
- Host tissue invaded by pathogens
- Damaged cells release histamines which attracts phagocytes
- Phagocyte engulfs the pathogen by phagocytosis
113
What are the two types of specific responses?
- Cell-mediated response (T lymphocytes)
| - Humeral response (B lymphocytes)
114
Name all of the T cells
- Memory T cells
- Killer T cells
- Helper T cells
115
Name all of the B cells
- Plasma B cells
| - Memory B cells
116
Where are T cells found?
Thymus
117
Describe how T cells function
- Type of white blood cell
- Have receptor proteins on the surface that bind to complementary antigens presented to it by phagocytes. This activates the T cell
118
Describe and explain the different types of T cells and how they respond
Helper T cells - release chemical signals that activate and stimulate phagocytes. Activates B cells which secrete antibodies
Cytotoxic T cells (killer) - kills abnormal and foreign cells
119
Where are B cells found?
Bone marrow
120
Describe and explain the different types of B cells and their responses
Plasma B cells - secrete antibodies usually into blood. These cells survive only for a few days, but each can make around 2000 antibodies per second. The production of antibodies and memory cells is known as the primary immune response
Memory B cells - responsible for the secondary immune response. Live considerably longer than plasma B cells, often for decades. These cells do not produce antibodies directly, but circulate in the blood and tissue fluid. When they encounter the same antigen again they divide rapidly and differentiate into plasma B cells and more memory cells. This provides long term immunity. The secondary immune response results in increased quantity of antibodies secreted at a much faster rate than the primary response
121
Describe the processes when a pathogen enters the immune system
Non-specific responses:
1. Phagocytosis - pathogen engulfed by macrophages and antigens presented on plasma membrane
Specific:
Cell Mediated response
2. Clonal selection - specific T cells with complementary receptors selected
3. Clonal expansion - specific T cells cloned by mitosis
4. Differentiation - cytotoxic T cells kill infected cells and secrete toxins, helper T cells release interleukin and stimulate B cells and release cytokines (these stimulate B cells to develop)
Antibody Mediated response
2. Clonal selection - specific B cells with complementary receptors selected
3. Clonal expansion - specific B cell cloned by mitosis
4. Differentiation - plasma B cells secrete antibodies specific to pathogens antigen, memory B cells remain in blood and provide faster response (immunological memory)
122
Describe antibodies
- Large proteins molecules that can recognise and neutralise antigens
- Produced by B lymphocytes
- Made up of 4 polypeptide chains, 2 heavy and 2 light
- Each has a specific binding site complementary to a specific antigen
- They bind to antigens on the surface of the pathogen to form antigen-antibody complexes
- Each binding site consists of a sequence of amino acids that form a specific 3D shape that bonds directly to a specific antigen
- The rest is a constant region that is the same for all antibodies
123
How are antibodies able to combat pathogens?
1. Agglutination - forming antigen-antibody complexes the pathogens are held together in large clumps. This makes it easier for macrophages and neutrophiles to engulf the immobilised pathogens
2. Neutralisation - Antigens which are toxins are rendered harmless if they are blocked by being bound to an antibody
3. They act as markers that stimulate phagocytes to engulf the bacterial cells to which they are attached
124
What are monoclonal antibodies?
Antibodies produced from a single group of genetically identical plasma B cells
125
What can monoclonal antibodies by used for?
Produced in a lab and used for treating illness and medical diagnosis. The antibodies can have drugs attached e.g. anti-cancer drugs. This means the drug will only accumulate in the body where there are cancer cells , so the side effects are less
126
Describe the 4 parts to pregnancy testing
1 - hCG produced in urine released onto stick of pregnancy test
2 - hCG-antibody complexes and spare antibodies with dye bound travel up stick to test region
3 - hCG-antibody complexes attach to immobilised antibody in stick - shows blue line
4 - Spare antibodies with dye bound travel to control region and attach to immobilised antibodies - shows blue line
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What does ELISA testing stand for?
Enzyme-linked immunosorbent assay
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What are the two types of ELISA tests?
Direct and indirect ELISA
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What is the point of ELISA testing?
- Allows you to see if a patient has any antibodies to a certain antigen or any antigens to a certain antibody
- Can be used in medical diagnosis to test for pathogenic infections
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Describe the process of direct ELISA
Uses ONE antibody that is complementary to antigen
1 - Collect antigen from patient
2 - Add antibody with enzyme attached
3 - If antigen present antibody bonds
4 - Wash to remove and unbound antibodies
5 - Add substrate complementary to enzyme
6 - Coloured product formed if positive test
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Describe the process of indirect ELISA
Uses TWO different antibodies]
1 - Antibody bound to bottom of well
2 - Sample of patients blood plasma added. Any antibodies specific to antigen will bind
3 - Wash to remove any unbound antibodies
4 - A second antibody is added that has enzyme attached. This will bind to the first antibody
5 - Wash to remove any second antibodies that are unbound
6 - Substrate added and any colour change will indicate a positive test
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What is active immunity?
Immune system produces its own antibodies after being stimulated by an antigen
1. Natural - results from individual becoming infected with a disease under normal circumstances. The body produces its own antibodies
2. Artificial - involves inducing an immune response e.g. vaccination
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What is passive immunity?
Introduction of antibodies into individuals from an outside source. Immune system does not produce any antibodies of its own
1. Natural - antibodies from mother passed through placenta or breast milk
2. Artificial - injected with antibodies e.g. tetanus
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What are the differences between active and passive immunity?
Active:
- Requires exposure to antigen
- Immunity response is not instant
- Memory cells are produced
- Long term protections
Passive:
- Does not require exposure to antigen
- Immediate protection
- Memory cells not produced
- Short term protection as antibodies get broken down
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What is a vaccination
- Deliberate exposure to harmless antigenic material to active the immune response
- Produces antibodies and memory B cells which provide immunity
- Reduce the recurrence of the disease
- Those not vaccinated are also less likely to catch the disease (herd immunity)
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Even with successful immunity why can it still be difficult to eradicate a disease?
- Vaccinations fails to induce immunity in certain individuals
- Pathogen may mutate so its antigens change (antigenic variation) - vaccine no longer effective
- There mat be many varieties of a particular pathogen so it would be impossible to develop a vaccine that is effective against them all
- Individuals may have objections to vaccinations from religious, ethical or medical reasons
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What are the ethics of using vaccines?
- Vaccines are tested on animals
- Testing on humans can be risky. Who should take part in the trails?
- Vaccines have side effects that may cause long term harm
- To be fully effective the whole population should be vaccinated. Should vaccination be compulsory?
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What does HIV stand for?
Human immunodeficiency virus
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What is HIV?
- Virus that affects the human immune system
- Eventually leads to acquired immune deficiency syndrome (AIDS)
- AIDS is a condition where the immune system deteriorates and eventually fails (makes people more vunerable to other infections such as pneumonia
- HIV infects and eventually kills helper T cells, which act as the host cells for the virus Without the helper T cells the immune system is unable to respond effectively
- People develop AIDS when the helper T cell numbers reach a critically low level
- During initial period of infection, HIV replicates rapidly and the infected person may develop flu-like symptoms
- After this period replication drops to a lower level - the latency period. During this time the person will not have any symptoms (this can be 10 years)
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Describe the process of HIV replication
Takes place in the helper T cells of the host
1 - The attachment protein attaches to a receptor molecule on the cell membrane of the host helper T cell
2 - The capsid is released into the cell, where it uncoats and releases the genetic material (RNA) into the the cell's cytoplasm
3 - Inside the cell, reverse transcriptase is used to make a complementary strand of 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 proteins are assembled into the new viruses, which bud from the cell and go on to infect other cells
