Cells (3.2) Flashcards
1
Q
Describe the process of cell fractionation.
A
- Chop up liver
- Put over ice, add water and a buffer solution
3.blend in a liquidiser - Filter the homogenate formed
- Add to a test tube and spin in a centrifuge
- Remove supernatant (left with the sediment- nuclei)
- Spin at a faster speed each time to separate different organelles in the cell.
2
Q
During cell fractionation, what is the filtered homogenate spun in?
A
A centrifuge
3
Q
What does the process of cell fractionation do?
A
Separate sub cellular components
4
Q
Why is ice, water and a buffer added to the ‘liver?
A
Ice: prevent any enzyme activity
Water: same water potential (isotonic), no osmotic loss/ gain so the cells doesn’t shrink/ expand
Buffer: no ph fluctuation which may alter the structure/ functioning of the enzyme
5
Q
What type of lens does a light microscope use?
A
Convex lens
6
Q
A light microscope can only distinguish between objects if they are at least___ apart?
A
0.2 micrometers
7
Q
An electron microscope can distinguish between objects if they are at least ___ apart?
A
0.1 nm
8
Q
How do you calculate magnification ?
A
Magnification = image size
____________
Actual/ object size
9
Q
What do you multiply by each time?
m mm micrometers nm
—-> ——-> ———->
A
m mm = 10 -3
mm micrometers = 10 -6
Micrometers nm = 10 -9
10
Q
Define resolution
A
How distinct/ how clear the image is
11
Q
The resolving power of an electron microscope is ____ than a light microscope.
A
Higher
12
Q
Resolving Power of a light microscope?
A
0.2 um
13
Q
Resolving power of an electron microscope?
A
0.1 nm
14
Q
What is another word for a slide?
A
Temporary mound
15
Q
What is the field of view when looking through a microscope?
A
What you can see?
16
Q
What two pieces of equipment do you need to calculate cell size?
A
Stage micrometer
Eyepiece gratitude
17
Q
How do an eyepiece gratitude and stage micrometer work together?
A
You match up the stage micrometer with the eyepiece gratitude ‘reading’ to see what units the eyepiece gratitude represents
18
Q
What are the steps involved in measuring a cell?
A
- Calibrate- focus he stage micrometer under low power. This must be done for each magnification
2.work out how many eyepiece divisions equal every stage division e.g. in one eyepiece division there could be 30um - Remove stage micrometer and place your slide containing cells under the microscope and count the number of eyepiece divisions under the microscope.
19
Q
What should you record when drawing a microscope slide/specimen?
A
Magnification
Date of observation
Name of specimen
20
Q
What are the ‘principles’ of electron microscopes?
A
-image contains ‘artefacts’
-in a vacuum
-non-living sample
-complex staining process
-thin sample
21
Q
what are the limitations of an electron microscope?
A
-electron beams may destroy sample
-preparation difficulties lead to resolution problems
22
Q
What is a photomicrograph?
A
The image that is produced of the specimen in a computer from an electron microscope
23
Q
Is a TEM microscope 2D or 3D?
A
2D
24
Q
Is an SEM microscope 2D or 3D?
A
3D
25
How TEM and SEM microscopes operated?
Electrons are fired (which are directed by magnets, because electrons are negatively charged)
26
Nucleus
1.what are the dark patches called?
2.what type of envelope is it surrounded by?
3. What does chromatin consist of?
4. What feature allows large molecules through?
5.contains instructions for making…?
6. What happens to the chromatin when the cell divides?
7. What does the nucleolus make?
1. Chromatin
2. Nuclear envelope
3. DNA and proteins
4. Nuclear pore
5. Proteins
6. Condenses into visible chromosomes
7. RNA and ribosomes
27
Endoplasmic Reticulum
1. What is the name of the membrane bound sacs?
2. What does the RER have that the smooth ER hasn’t?
3. What is the smooth ER involved in making?
4. What does the RER transport?
1. Cisternae
2. Ribosomes
3. Lipids
4. Proteins made on attached ribosomes
28
Golgi apparatus
1. What does it do to the proteins received from the ER?
2. What does it package proteins into?
1. Modifies the e.g. adds sugar
2. Vesicles that are transported inside the cell or to the outside of the cell
29
Mitochondria
1. What is its function?
2. What is the folded inner membrane called?
3. What is the central part called?
1. The site where ATP is produced during respiration
2. Cristae
3. Matrix
30
Chloroplasts
1. What are they the site of?
2. How is light energy used?
3. What is a stack of thylakoids called?
1. Photosynthesis
2. It is used to drive carbohydrate molecules from CO2
3. Granum
31
Lysosome
1. What type of enzymes do they contain?
2. What is an example of a specialised lysosome?
3. What is the structure?
1. Digestive enzymes
2. Sperm cell
3. Spherical sacs surrounded by a single membrane
32
Ribosome
1. What is their function?
2. What are they bound to?
3. How many subunits does a ribosome consist of?
1. Site of protein synthesis- acts as an assembly line to use mRNA to assemble proteins
2. Rough ER (RER)
3. 2
33
Cell surface membrane
1. What are the 2 proteins involved in?
1. - signalling and communication between cells
2. - antigens for self and foreign recognition
34
Plant organelles
1. What does the cell wall protect against?
2. What do all plant cells have?
1. Invading pathogens
2. Cellulose cell wall
35
vacuoles
1. What does it contain?
2. What is the membrane of the vacuole called? - what does it do?
1. Sap
2. Tonoplast - allows some small molecules through (selectively permeable)
36
What are the level of organisation?
{1. Chemical }
{2. Organelle }
3. Cell
4. Tissue
5. Organ
6. System
37
What is a tissue?
A collection of cells that perform a specific function
38
What is an organ?
A combination of tissues that are coordinated to perform a variety of functions
39
What is an organ system?
Organs that work together as a single unit
40
What are the similarities between prokaryotic and eukaryotic cells?
-cell wall in plant and bacteria cells
-DNA
-ribosomes
-energy released as ATP
41
What are the differences between prokaryotic and eukaryotic cells?
-no nucleus
-60s vs 70s ribosomes
-cellulose vs meurin cell wall
-prokaryotic cells have no membrane bound organelles
42
What is a virus?
An acellular non-living particle
43
What are 3 facts about a virus?
-20-300nm
-contain DNA or RNA as genetic material (can only reproduce in living cells)
-genetic material enclosed in a CASPID which may have attachment proteins (protein coat)
(Some may have a lipid envelope) - these features allow attachment to host cells
44
What are the three stages of celll division?
Interphase
Mitosis
Cytokinesis
45
Why does mitosis happen?
Growth
Differentiation
Repair
46
What does a centromere and 2 chromosomes form?
2 sister chromatids
47
What joins two chromatids?
Centromere
48
What are the four sages of mitosis?
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
49
Describe the 1st stage of mitosis.
1. Prophase- chromosomes become shorter and fatter, each one consisting of a pair of identical chromatids joined at the centromere.
Nucleolus shrinks and disappears.
Nuclear envelope breaks down
50
Describe the 2nd stage of mitosis.
2. Metaphase - chromosomes arrange themselves on the equator of the spindle but not in homologous pairs.
Chromosomes appear attached to the spindle at their centromeres.
51
Describe the 3rd stage of mitosis.
3. Anaphase - centromere split into two, each centromere having its own chromatid.
Spindle fibres contract and pull chromatids apart.
Chromatids now become chromosomes with their centromere leading
52
Describe the 4th stage of mitosis.
4. Telophase - chromosomes reach the opposite poles of the cell at the centrioles.
Nuclear envelope and nucleolus reforms.
Spindle fibres degenerate.
Chromosomes develop into thread like structures of chromatin.
Centrioles replicate.
53
What happens during cytokinesis?
Central cell membrane is pulled in by the cytoskeleton, creating a groove.
The groove deepens and the membranes fuse to from two independent cells.
54
What happens in cytokinesis of a plant cell because they don’t have centrioles?
Vesicles from the Golgi apparatus form membrane structures down the centre of the cell.
These fuse together to form a central cell membrane, dividing the cytoplasm into two.
A new cellulose cell wall forms down the centre
55
What is the name of prokaryotic cell division?
Binary fission
56
What happens during binary fission?
- circular DNA molecules duplicate and attach to the membrane
- plasmids duplicate
- a cell membrane starts to grow between the two DNA molecule and forms a ‘pinch’, dividing the cytoplasm
-the cell wall then forms making two daughter cells with a single copy of the circular DNA and a variable number of plasmids.
57
What are the 4 stages of binary fission?
1. Parent cell
2. Replication of DNA
3. Segregation of DNA
4. Cell splits into two
58
How do viruses replicate?
- viruses are non-living so they attach to their host cell with attachment proteins on their surface.
- they then inject their nuclei acid into the host cell
- the genetic information on injected viral nucleic acid provides ‘instructions’ for the host cell to start producing viral components e.g. enzymes and nucleic acid.
59
Describe the 6 stages of virus replication.
1. Virus enters cell.
2. Substances in the cell begin to strip off the virus’s outer coat of protein.
3. The nucleic acid in the centre of the virus is released.
4. The nucleic acid gets into the cell’s chemical manufacturing system.
5. The cell ‘ignores’ its own chemical needs and switches to make new viruses.
6. The cell is sometimes destroyed in the process. Many of the viruses are released to infect other cells.
60
Where is the genetic material stored in a virus?
Capsid
61
What feature of a virus allows them to attach to host cells?
Attachment proteins (glycoprotein spikes)
62
What are the three stages of the cell cycle?
Interphase
Mitosis
Cytokinesis
63
What happens during cytokinesis ?
Cell splits into 2
64
What does the interphase of a cell look like under a microscope?
Dormant
65
What are the three stages of interphase?
G1 - growth stage one
S- synthesis
G2 - growth stage 2
66
What is the DNA content in the cell during G1 of interphase?
20
67
What is the DNA content of the cell during the S stage of interphase?
40
68
What is the DNA content of the cell during the G2 stage of interphase?
40
69
What happens in the G1 stage of interphase?
- cell makes preparations to ensure the cell is ready to go into the ‘S’ phase
-e.g. duplicating organelles, growing in size, making proteins that will be needed in the ‘S’ phase
70
What happens in the ‘S’ phase of interphase?
- DNA synthesis (the cell replicates the more important sequences of DNA first. Bits of DNA that are only required in some types of cell are replicated last.)
- at the end of ‘S’ phase all the chromosomes will be replicated.
71
What happens in the G2 phase of interphase?
-prepares the cell of mitosis
-cytoskeleton breaks down and protein microtubule components reassemble into spindle fibres.
72
What is the G0 phase in interphase?
-cells exit the cycle. They may differentiate, die or enter senescence where they no longer divide.
73
What do ‘proof reading’ enzymes do between each stage of interphase?
Check the chromosomes for a mistake. The cell will ‘kill itself’ if harmful mutations are present.
74
What effects cell division?
The availability of nutrients.
75
What are homologous chromosomes?
A pair of similar chromosomes that are a different sex
76
What causes cancer and tumours?
Uncontrolled cell division
77
What do cancer drugs do?
Prevent the cell cycle (stop division). However treatment will kill healthy cells.
78
What is a benign tumour?
A tumour that stays in the same place it originated from. This means they can be treated by targeted radiotherapy or surgery.
79
What is a malignant tumour?
A tumour that can travel round the body. This means they are harder to treat.
80
What are the 6 elements of a fluid mosaic model of a phospholipid bi-layer?
Embedded protein
Intrinsic protein (protein channel)
Phospholipid
Cholesterol
Glycolipid
Glycoprotein
81
What substances cannot pass through a cell- surface molecule? What is the exception and why?
Polar molecules (hydrophilic substances).
Water- is is a very small molecule
82
What are the functions of a cell surface membrane?
Barrier - between internal contents of the cell and external environment. Between contents of an organelle and cytoplasm
Location for chemical reactions
Cell signalling (the ability of a cell to receive, process, and transmit signals with its environment and with itself)
83
What substances **can** pass through a cell surface membrane?
Hydrophobic substances
84
What is an embedded protein molecule in the fluid mosaic model and what are their roles?
A protein that is on the surface or partially embedded in a cell surface membrane.
Gives the membrane support.
85
What is the role of cholesterol in the fluid mosaic model?
- adds strength
- reduces lateral movement
- prevents water leaking (because it is hydrophobic)
- pulls together fatty acid tails
86
What is the role of glycolipids in the fluid mosaic model?
- cell surface receptors e.g antigens
-helps cells attach to each other to form tissues
- maintain stability of the membrane
87
What is the role of glycoproteins in the fluid mosaic model?
- receptors for: - neurotransmitters at nerve synapses. Peptide hormones,
- drugs bind to cell receptors
- help attach to one and other, forming tissues.
88
Define the term diffusion.
The net movement of particles from a high concentration to a low concentration.
89
What does **active diffusion** require?
Energy in the form of ATP
90
What is passive diffusion?
A passive process in which the motion of particles is random and in constant rotation . The particles bounce off each other in the vessel they are contained in. No energy from ATP is required (it only requires the kinetic energy or the particles).
91
What is Fick’s Law?
Diffusion is proportional to the difference in concentration between two regions (concentration gradient).
92
What factors effect diffusion?
Temperature
Concentration gradient
Surface area
Moving
Thickness of diffusion pathway
Size of molecule
93
What molecules **can** go through membranes?
Small and lipid based molecules
94
What molecules **cannot** go through membranes without facilitated diffusion?
Non lipid soluble and polar molecules
95
What two types of proteins are involved In facilitated diffusion?
Protein channels
Carrier proteins
96
What is a protein channel?
An intrinsic protein that forms pores in the membrane. They are hydrophilic channels which may only let one type of molecule through.
97
What is a carrier protein?
A molecule that fits in the membrane. The protein changes shape to pass the molecule through.
98
What are the two types of active transport?
Direct active transport
Co-transport
99
In **direct active transport** the molecules move from a ____ concentration to a _______ concentration. Therefore the particles move _______ the concentration gradient.
1. Low
2. High
3. Against
100
What does direct active transport require?
Metabolic energy which is provided by ATP
101
Describe the process of direct active transport.
1. A molecule attaches to the receptor site on the carrier protein
2. A molecule of ATP then binds to the carrier protein
3. The ATP undergoes hydrolysis producing phosphate and a molecule of ADP
4. The phosphate binds to the protein and causes it to change shape
5. This shape change causes the carrier protein to transport the molecule to the other side of the membrane where it is released
6. The phosphate now leaves the carrier protein causing it to return to its original shape. The ADP and phosphate will later reform ATP during respiration.
102
The carrier proteins in active transport are ____.
Specific
103
When does bulk transport take place?
When something is too big to fit through the carrier protein e.g enzymes, hormones, whole cells
104
What is endocytosis?
Bulk transport into cells
105
What is exocytosis?
Bulk transport out of cells.
106
What happens in endocytosis?
The cell membrane **invaginates** forming **vesicles**. These are then moved into the cytoplasm for further processing.
107
What happen in exocytosis?
The cell membrane **invaginates** forming **vesicles**. These are then moved into the cytoplasm for further processing.
108
What happens in exocytosis?
The vesicles formed by the Golgi apparatus are released outside the cell.
109
Energy in the form of ______ is required for the movement of vesicles.
ATP
110
Define osmosis.
The movement of water molecules from a region of high water potential to a region of low water potential through a partially permeable membrane.
111
Does osmosis require metabolic energy?
No, it is a passive process.
112
What can represent water potential?
Psi
113
What is water potential measured in?
Kilopascals (kPa)
114
What is water potential?
A measure of pressure (water molecules colliding with the partially permeable membrane).
115
What is pure water’s water potential?
0 kPa
116
What decreases water potential?
More dissolved solutes in the water?
117
What are animal cells surrounded by to keep osmosis a equilibrium?
Blood plasma
118
What happens if an animal cell is placed in pure water?
Water molecules move into the cell by osmosis meaning the hydrostatic pressure in the cell increases causing the cell membrane to rupture and the cell to burst.
119
What happens to an animal cell is it is placed in a solution with a lower water potential?
Water will move out the cell by osmosis causing the cell to shrink.
120
What happens if a plant cell is placed in pure water?
Water moves into the cell by osmosis causing the hydrostatic pressure inside the cell to increase. The protoplast (in between cell wall and vacuole) pushes outwards against the cell wall. The cellulose cell wall is strong and doesn’t burst, instead it becomes firm (turgid).
121
What happens to a plant cell when it is placed in a solution with a negative water potential?
Water leaves the cell by osmosis, protoplast pulls away from cell wall (plasmolysis).
122
What is an isotonic solution?
An isotonic solution contains the same amount of solutes and therefore has the same water potential as the cell suspended in the solution.
123
What is a hyp**o**tonic solution?
A hypotonic solution contains more solutes and therefore has a higher water potential than the cell suspended in the solution.
124
What is a hyp**er**tonic solution?
A hypertonic solution has less solutes and therefore has a higher water potential than a cell suspended in the solution.
125
How can a cell become **turgid**?
Water enters the ell by osmosis, the vacuole swells and pushes against the cell wall.
126
How can a cell become **flaccid**?
Water leaves the cell by osmosis meaning the cell shrinks/shrivels.
127
Microvilli on epithelial cells can only be seen by a/an __________ microscope.
Electron
128
What do villi and microvilli increase on an epithelial cell and why?
Surface area
Increased rate of diffusion
129
Name three components of a villus.
Lacteal
Blood capillary
Epithelium cells
130
What does the lacteal in a villus do?
Absorb fatty acids and glycerol
131
What do blood capillaries in a villus do?
Absorb glucose and amino acids
132
Name three properties of villli and their benefits.
- rich network of blood vessels - blood can carry away absorbed molecules maintaining a diffusion gradient.
- villi contain muscles - they contract and mix products of digestion meaning there is always glucose rich rood next to epithelial cells of villi.
- villi can move - maintains a diffusion gradient
133
Why is some glucose taken up by active transport rather than diffusion?
Diffusion can only make both sides off the epithelium equal so not all the available glucose is absorbed so some glucose is taken up by active transport so all glucose can be taken up by the blood.
134
Describe the process of uptake by **co-transport**.
**Indirect active transport:**
Sodium leaves the cell and potassium enters the cell via the sodium-potassium pump. This happens through a carrier protein in the ratio of 2:3 (S:P). This means that there is now a low concentration of sodium in the epithelial cell.
**Co-transport:**
Due to a low concentration in the cell, sodium diffuses into the cell. When it does this brings a glucose (or amino acid) molecule into the epithelial cell by a symport (channel protein).
**Facilitated diffusion:**
The glucose molecule leaves the epithelial cell by facilitated diffusion (channel protein) with the concentration gradient.
135
Co transport requires…?
ATP
136
Define phagocytosis.
The process in which white blood cells engulf and subsequently digest pathogenic organisms.
137
Phagocytes are able to **ingest** and subsequently **digest** a pathogen through ____________ reactions.
Hydrolysis
138
what are the two main types of phagocyte?
Macrophages and neutrophils
139
What do pathogens release when they infect the body?
Chemoattractants
140
Describe the process of chemotaxis.
Chemoattractants cause phagocytes to migrate towards the pathogen along a concentration gradient.
141
Why can a phagocyte bind to the surface of a pathogen?
The cell surface membrane of the phagocyte has several **protein receptors** that are able to **bind** to the complimentary **antigens** present on the surface of the pathogen.
142
Describe how a phagocyte **engulfs** a pathogen.
The phagocyte’s cell membrane extends outwards around the site of attachment and surrounds the material, **engulfing** it.
143
What happens once the phagocyte has engulfed the pathogen?
The pathogen is enclosed in a vesicle called a **phagosome**. The phagosome moves towards the interior and fuses with a **lysosome**.
This fusion releases ***lysosomal enzymes*** onto the ingested pathogen. The enzymes digest the pathogen by hydrolysis- breaking down larger, insoluble molecules into smaller, soluble ones.
144
What happens once lysosomal enzymes have digested the pathogen?
The soluble products of digestion are absorbed into the cytoplasm of the phagocyte.
145
How can bacteria be destroyed by phagocytosis?
They can be destroyed by hydrolysis of their cell walls
146
What cells are involved in the humoural response?
B- cells and T- cells
147
Describe the role of plasma cells in the humoural response.
They secrete soluble antibodies that are the correct shape to bind to the foreign antigen.
They can make approximately 2000 antibodies a second.
148
Plasma cells are responsible for the _________ defence of the body against infection.
Immediate
149
Describe the role of memory cells in the humoural response.
They remain in the body, circulating in the blood and tissue fluid for a long time (decades).
If they encounter the same antigen at a later date they can rapidly divide into more plasma and memory cells at a faster rate, this means they are responsible for the secondary immune response.
150
Memory cells are responsible for the ___________ immune response.
Secondary
151
Describe how the B cell is **activated**, causing it to divide rapidly in the humoural response.
The antibody on the specific b cell binds to the antigen to form a antigen-antibody complex.
This binding causes the antigen to enter the specific b cells by **endocytosis**.
The antigen is the presented on the cell surface membrane of the b cell (it is processed).
Helper T cells then bind to the processed antigens.
This activates the b cell, causing it to divide rapidly by mitosis.
152
The humoural response is a __________ immune response.
Specific
153
Outline the humoural response.
- When a foreign antigen enters the body or tissue fluid, there will be one B cell with a receptors that/antibody that is complimentary to that of the antigen.
- The antibody on that specific B cell therefore binds to the antigen to form an antigen-antibody complex.
- This binding causes the antigen to enter the specific B cell by endocytosis.
- The antigen is then presented on the cell surface membrane of the B cell (it is processed).
- Helper T cells then bind to the processed antigens.
- This activates the B cell, causing it to divide rapidly by mitosis.
- The result is genetically identical clones of B cells
- The clone of B cells then differentiate into one of 2 cell types.
- The majority become plasma cells; these secret soluble antibodies that are the correct shape to bind to the foreign antigen.
- Although they only live for a few days, each can make approximately 2000 antibodies a second. They are responsible for the immediate defence of the body against infection.
- Other B cell differentiate into memory B cells. These remain in the body, circulating in the blood and tissue fluid for a long time (decades).
- If they encounter the same antigen later the can rapidly divide into more plasma and memory cells at a faster rate. This is a secondary immune response.
154
Phagocytosis is non-_________ and does not give you _____________.
Specific
Immunity
155
What is another word for a phagocyte?
Macrophage
156
B lymphocytes are the type of white blood cel that make ___________ antibodies.
Specific
157
An antibody is a _______ molecule.
Protein
158
what is another word for an antibody?
Immunoglobulin
159
How many polypeptide chains are antibodies made up of?
4
160
How are the polypeptide chains in a pan antibody joined together?
By disulphide bonds
161
What shape does an antibody have?
Y
162
Why is the stem of the Y (antibody) called the constant region?
In all antibodies it has the same amino acid sequence, therefore the same structure.
163
Why are the ends of the arms of the ‘Y’ in an antibody Called the variable region?
They differ from one antibody to the next by having different amino acid sequences, therefore different structures .
164
What happens at the antigen-binding sites on an antigen?
Antigens bind to form a highly specific antigen-antibody complex. The antigen-binding site is complementary to the antigen.
165
Antibodies do not ___________ antigens directly, but ____________ them for destruction.
Destroy
Prepare
166
What do antibodies cause pathogenic cells to do?
Clump (agglutination)
167
Why is agglutination important?
It makes it much easier for the phagocytes to locate the pathogenic cells as they are less spread out in the body.
168
What do antibodies then do after agglutination?
Stimulate the phagocytes to engulf the pathogen in which they are attached to.
169
T cells can only respond to cells that are…….
Presenting the antigen
170
How can T cells distinguish invader cells from normal cells? e.g in transplanted cells and cancer cells
- phagocytes that have engulfed and hydrolysed a pathogen present some of a pathogen’s antigens on their own cell crusade membrane.
- transplanted cells from individuals of the same species have different antigens on the cell surface membranes.
- cancer cells are different from normal body cells and present antigens on their cell surface membranes.
171
What are antigen presenting cells?
Cells that display foreign antigens on their surface.
172
What response is it where T cells respond to antigens that are presented on a body cell?
Cell mediated response
173
What is the primary concept in the cell mediated response?
The receptors on each T cell respond to a single specific antigen?
174
Describe how T-lymphocytes respond to infection using the cell mediated response.
1. Pathogens invade the body cells or are taken in by phagocytosis.
2. The phagocyte paces antigens from the pathogen onto its cell surface membrane (antigen presenting cell).
3. Receptors on a specific helper T cell fit exactly onto these antigens.
4. This attachment activates the T cel to divide rapidly by mitosis and form a clone of genetically identical cells.
175
What do clones T cells from the cell mediated response differentiate into?
- **memory cells** - they enable a rapid response to future infections by the same pathogen.
- **stimulate phagocytes** to engulf pathogens by phagocytosis.
- **stimulate B cells to divide** and secrete their antibody,
- **activate cytotoxic T cells**
176
How do cytotoxic T cell destroy a cell?
Identify abnormal or virally infected cells ——> attach to cell and release **perforin** ——> perforin destroys cell by forming holes in cell membrane.
177
List 2 similarities between B and T cells.
- produced by stem cells in the bone marrow
- both provide a specific immune response
178
List 3 differences between B and T cells.
- B cells mature in the bone marrow whereas T cells mature in the thymus gland
- B cells are associated with humoral immunity (immunity involving antibiotics that are present in body fluids or ‘humour’ such as blood plasma, whereas T cells are associated with cell-mediated immunity (immunity involving body cells).
179
What type of white blood cells ingests and destroys pathogens?
Phagocyte
180
What attracts phagocytes to a pathogen?
Chemoattractants
181
Which response involved T-lymphocytes?
Cell mediated
182
which response involves B- lymphocytes?
Humoural
183
What is the 1st line of defence preventing entry of pathogens into the humans body?
The skin
184
In the foetus lymphocytes are constantly ……….. with other cells.
Colliding
185
Which type of white blood cell is involved in immunity?
Lymphocytes
186
This type of defence mechanism is slow and is a response to a particular pathogen.
Specific
187
How many different types of enzymes exist in the body?
10 million
188
Since there are so many different types of lymphocytes there are only ________ numbers of each type but large numbers are needed to destroy pathogens. After a pathogen is detected large numbers of lymphocytes are built up to destroy it. This is why after you have been exposed to a pathogen there is a time _______ before your body brigs it under control.
Small
Delay
189
What is an example of a non specific defence mechanism?
Phagocytosis
190
In phagocytosis the pathogen is recognised as foreign. The pathogen is attached to the phagocyte by antibody and surface receptors. The pathogen is ___________ by phagocyte and endocytosis (invagination of plasma cell membrane to form a phagosome - a membrane bound vesicle containing the pathogen). Lysosomes (containing lysins and hydrolytic __________)fuse to the phagosome. A pathogen is ________ and harmless products are removed or used by a phagocyte. Phagocytes also display antigenic components on external surface plasma cell _____________ (antigen presentation) to start immune response.
Engulfed
Enzymes
Digested
Membrane
191
What is an antigen?
A substance recognised as foreign, a protein on the cell-surface membrane, stimulating an immune response e.g pathogens, cells from transplanted organs.
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What does an antibody do?
Identifies foreign objects
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What is it called when an antigen and antibody bind together by the lock and key method?
Antigen-antibody complex
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Immunity from T lymphocytes is cell merited so only responds to ________ attached to the surface of body cells.
Antigens
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Body cells invaded by a virus present the viral antigens on its own cell ___________, phagocytes that have engulfed a pathogen also present the pathogen’s antibodies on its own cell surface, and ___________ - __________ cells present antigens on their cell surface membranes.
Surface
Antigen presenting
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A cell that presents antigens of other cells on its own surface are known as _______ cells.
Cancer
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A cell that presents antigens of other cells on its own surface are known as _______ cells.
Cancer
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T _____ cells have receptors that dit onto the specific antigen.
Helper
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What is the role of T helper cells?
They have receptors that fit onto the specific antigen. This process is the signal for other T cells to divide by mitosis and produce man clones. These cloned T cells become memory cells which circulate in the blood and body fluids.
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What do memory cells allow?
Rapid response against the same pathogen in the future.
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How do T cells kill infected cells?
It uses a protein that makes holes in their cell-surface membranes. This makes the cell freely permeable to all substances and so die.
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Where are B cells made?
In the bone marrow
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What is the flow diagram that shows the role of B cells in humoural immunity?
Antigen complementary to a B cell enters the blood -> B cell divides by mitosis -> clones differentiate it into plasma cells and memory cells. Plasma cell -> primary immune response -> do not produce antibodies -> if encounters antigen it divides into more plasma and memory cells. Memory cell -> secondary immune response -> long term immunity -> response is rapid with great intensity.
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What immune response do plasma cells have?
Primary
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What response immune do memory cells have?
Secondary
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What is the difference between a primary and secondary response?
Primary = does not produce antibodies, slower
Secondary = long term immunity and rapid
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What type of virus is HIV?
Retrovirus
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What does HIV stand for?
The human immunodeficiency virus
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How does HIV infect cells (briefly)?
It uses genetic material to Instruct the host cell’s biochemical mechanisms to produce the new components required to make HIV.
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Describe how HIV infects a helper T cell.
A protein on the HIV readily binds to a protein called **CD4**.
The protein capsid fuses with the cell-surface membrane.
The RNA and enzymes of the HIV enter the helper T cell.
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What enzyme in HIV converts the virus’s RNA into DNA?
Reverse transcriptase
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What does the HIV DNA do once in the nucleus of the helper T cell?
Creates messenger RNA (mRNA) using the cell’s enzymes. This mRNA contains the instructions for making the new viral proteins and the RNA to go into the new HIV.
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How does an infected helper T cell make a new HIV particle?
The mRNA passes out the nucleolus through the nuclear pore and uses the cell’s protein synthesis mechanisms to make new HIV particles.
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what do new HIV particles do to the cell surface membrane of an infected helper T cell?
They break away from the helper T cell with a piece of its cell surface membrane surrounding them which forms their lipid envelope.
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What is a person with the HIV virus called?
HIV positive.
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How does HIV cause the symptoms of AIDS?
HIV causes AIDS by killing or interfering with normal functioning helper T cells. Without a sufficient number of helper T cells, the immune system cannot stimulate B cells to produce antibodies or the cytotoxic T cells that kill cells infected by pathogens.
Memory cells may also be destroyed. As a result the body is unable to produce an adequate immune response and becomes susceptible to other infections and cancers.
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What causes death of a person with AIDS?
Secondary diseases
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What does the ELISA test stand for?
Enzyme linked immunoabsorbant assay
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What does an ELISA test do?
Uses antibodies to detect the presence and quantity of a protein in a sample.
220
Describe how you would carry out an ELISA test.
1. Apply the sample to a surface e.g. a slide to which the antigens in the sample will attach.
2. Wash the surface to remove unattached antigens.
3. Add the antibody that us specific to the antigen you are trying to detect and leave them to bind.
4. Wash the surface to remove excess antibody
5. Add a second antibody that binds with the 1at antibody. This antibody has an enzyme attached to it
6.add the colourless substrate of the enzyme . The enzyme acts on the substrate to change it into a coloured product
7. The amount of antigen Present is relative to the intensity of the colour that develops
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When is the ELISA test useful?
In drug and allergen tests.
222
What is passive immunity?
The introduction of antibodies into individuals from an **outside source**.
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What is active immunity?
Stimulating the production of antibodies by the individual’s **own immune system**.
224
What are the two branches of active immunity?
Natural active immunity
Artificial active immunity
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What is natural active immunity?
- an individual is infected with a disease under normal circumstances. The body produces its antibodies and may do so for many years.
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What is artificial active immunity?
- vaccination. The introduction of an immune response in an individual, without them suffering the symptoms of the disease.
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What type of immunity is vaccination an example of?
Artificial active immunity
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What is vaccination?
The introduction of the appropriate disease antigens into the body (by injection or orally) which stimulates an immune response against a particular disease.
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What does a vaccine contain?
One or more types of an antigen from the pathogen.
230
Describe the immune response that antigens in a vaccine cause.
The response is slight because only a small amount of antigen has been introduced but memory cells are still produced.
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What do memory cells do?
They remain in the blood and allow a greater, more immediate response to a future infection with the pathogen. The result is that there is a rapid production of antibodies and the new infection is rapidly overcome before it can cause any harm and with few if any symptoms.
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What are the features of a successful vaccination programme?
- economically available in sufficient quantities
- few side effects
- means of producing, storing and transporting the vaccine
- means of administering the vaccine properly
- produces herd immunity
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What is herd immunity?
When a large proportion of the population has been vaccinated to make it difficult for a pathogen to spread within that population. If the vast majority of the he population are immune, it is highly improbable that a susceptible individual will come into contact with an infected person.
234
why is herd immunity important?
It is never possible to vaccinate everyone in a population e.g babies or those with compromised immune systems.
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Why may vaccination not **eliminate** disease?
- vaccination fails to induce immunity in certain individuals.
- individuals may develop the disease immediately after the vaccination but before their immunity levels are high enough to prevent it.
- antigenic variability, the pathogen may mutate frequently.
- there may be many varieties of a particular pathogen.
- certain pathogens ‘hide’ from the body’s immune system, either by concealing themselves inside cells or by living in places that are out of reach such as the intestines.
- individuals may have objections to vaccination.
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What is antigenic variation?
The pathogen may mutate frequently so that its antigens change suddenly. This means that vaccines suddenly become ineffective because the new antigens on the pathogen are no longer recognised by the immune system.
237
What questions the ethics behind vaccination? (Examples)
- involves use of animals
- side -effect
- unknown heath risks
- expensive vaccination programmes when a disease is almost eradicated
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What is a monoclonal antibody?
Antibodies of a single type that are isolated and cloned.
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What is a tumour marker?
Antigens that only cancer calls have.
240
What role can monoclonal antibodies have on cancer cells?
They can be made to target tumour markers
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What role do monoclonal antibodies have on transplant surgery?
They can be used to block T cells that will case rejection of a transplanted organ.
242
Antibody forming cell + myeloma———->
Hybridoma
243
In monoclonal antibody production were are b cells take from in the mouse?
It’s spleen
244
Describe the process of monoclonal antibody production.
1. A mouse is immunised by injection of antigen X to stimulate the production of antibodies targeted against X. The antibody forming cells (B-cells/plasma cells) are isolated from the mouses spleen.
2. These cells are fused to myeloma (cancer) cells grown in culture. The resulting tissue is called a hybridoma.
3. Each hybridoma produces relatively large quantities of identical antibody molecules. By allowing the hybridoma to multiply in culture, it is possible to produce a population of cells, each of which produces identical antibody molecules.
4. Once a monoclonal antibody is made, it can be used as a specific probe to track down and purify the specific protein that induced its formation.
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What is active immunity?
A weakened form of the pathogen is injected into someone.
246
What is passive immunity?
Antibodies for a pathogen is injected into someone.
247
active immunity is ______ - _______.
Long - lasting
248
Passive immunity is _____ - _________
Short - lasting
249
What do helper T cells release?
Cytokines called interleukins
250
what do interleukins do?
trigger phagocytes to increase their rate of phagocytosis.
Stimulate B cells to divide by mitosis.
251
What is the role of cytotoxic T cells?
Identify abnormal or virally infected cells.
Release perforin.
Perforin forms holes in the cell membrane, killing the cell.
252
what is agglutination?
When antibodies stick pathogens together preventing them from spreading around the body.
253
What is are centrioles?
hollow cylinders containing a ring of microtubules arranged at right angles to each other. Centrioles are involved in producing spindle fibres for cell division.
