2. Cells Flashcards
1
Q
What is a Eukaryotic cell ?
A
A cell that has a distinct nucleus and possesses membrane-bound organelles
2
Q
What is the function of the nucleus?
A
- Control centre of the cell, through the production of mRNA and tRNA
- Contains the genetic material of the cell in the form of DNA and chromosomes
- Manufacture RNA
3
Q
What is the nuclear envelope?
A
-A double membrane surrounding the nucleus
-Outer membrane is continuous with the Endoplasmic Reticulum of the cell and will often have ribosomes on its surface
4
Q
What is the function of the nuclear envelope?
A
-Controls the entry and exit of materials
- Contains reactions taking place within it
5
Q
What are the function of the Nuclear Pores?
A
Allows passage of large molecules such as messenger RNA, out of the nucleus.
6
Q
What is Nucleoplasm
A
Granular, jelly-like material that makes up the bulk of the nucleus
7
Q
What is the nucleolus?
A
Small spherical region within the nucleoplasm
There may be multiple in the nucleus
8
Q
What is the function of the nucleolus?
A
Manufactures ribosomal RNA and assembles ribosomes
9
Q
Describe the structure of a chromosome
A
Consists of protein-bound, linear DNA
Chromatin is the material that makes up chromosomes
10
Q
What is the function of the mitochondria
A
Site of Aerobic Respiration
Responsible for the production of the energy-carrier molecule ATP
11
Q
What is the function of the double membrane of a mitochondrion?
A
Controls entry and exit of material
The inner membrane is folded to form extensions called Cristae
12
Q
What is the function of the Cristae?
A
Provide large surface area for attachment of enzymes and other proteins required in respiration
13
Q
What is the function of the matrix within the mitochondrion?
A
It contains proteins, lipids, ribosomes and DNA and controls the production of some of the mitochondrion proteins.
It is also the location of many enzymes involved in respiration
14
Q
Describe the structure of the Endoplasmic Reticulum
A
3D system of sheet-like membranes spread throughout the cytoplasm
Continuous with outer membrane of nucleus
Membranes enclose a network of tubules and flattened sacs called cisternae
15
Q
What is the function of the Rough Endoplasmic Reticulum?
A
Provide a large surface area for the synthesis of proteins and glycoproteins
Provide a pathway for transport of proteins throughout the cell
16
Q
Describe the difference in structure between the rough Endoplasmic Reticulum and the smooth Endoplasmic reticulum
A
RER has ribosomes on the outer surface of membranes and SER lacks ribosomes on its surface and is often more tubular in appearance.
17
Q
What is the function of the Smooth Endoplasmic Reticulum?
A
Synthesis, store and transport of lipids and carbohydrates
18
Q
Describe the structure of a ribosome
A
Small cytoplasmic granules found in all cells, either in cytoplasm or in RER
19
Q
What are the 2 types of ribosomes and what are the differences between the 2?
A
80s- found in eukaryotic cells
70s- found in prokaryotic cells & mitochondria. Also slightly smaller
20
Q
Describe the structure of the Golgi Apparatus
A
Similar to SER but more compact
Stacks of membranes that make up flattened sacs called cisternae, with small rounded hollow structures called vesicles
21
Q
What happens in the Golgi Apparatus
A
Proteins and lipids produced in ER are modified in the Golgi and then transported to the vesicles where they are regularly pinched off the ends of the cisternae.
These vesicles move to the cell surface, fuse with the membrane and release their content outside the cell
(PACKAGING AND PROCESSING)
22
Q
What are the functions of the Golgi Apparatus
A
Add carbohydrates to proteins to form glycoproteins
Form lysosomes
Produce secretory enzymes
Secrete carbohydrates
Transport, modify and store lipids
23
Q
What are lysosomes
A
Formed when vesicles produced by Golgi Apparatus contain enzymes
They isolate enzymes from the rest of the cell before releasing them outside the cell or into phagocytise vesicles within the cell
24
Q
What are the functions of the lysosomes
A
Hydrolyse material ingested by phagocytic cells
Exocytosis
Digest worn out organelles
Completely break down cells after they die (autolysis)
25
What is the function of the chloroplast
Site of photosynthesis
26
Describe the structure and function of the chloroplast envelope
Double plasma membrane
Highly selective in what leaves and enters
27
Describe the structure and function of the Grana
Structure: stacks of 100 disc-like structures called thylakoids
Function: location of first stage of photosynthesis - absorbs light
28
What are thylakoids?
Contain photosynthetic pigment - chlorophyll
Some have tubular extensions (lamella) which join ajecent grana.
29
Describe the structure and function of the Stroma
Structure: fluid filled matrix, within it are other structures such as Starch grains
Function: location of the seconds stage of photosynthesis (synthesis of sugars)
30
How is the chloroplast adapted for photosynthesis?
Granal membranes provide large surface area for attachment of chlorophyll, electron carriers and enzymes required in the first stage of photosynthesis
Fluid in the stroma possesses all the enzymes need to make sugars in the 2nd stage
Chloroplasts contain both DNA and ribosomes to manufacture proteins for photosynthesis
31
What is the function of the cell wall
Provided mechanical strength to prevent cell from bursting due to pressure created by osmosis
Allows water to move throughout the cell
32
What is the function of the vacuole
Temporary food store
Support for plants by making them turgid
33
Describe the structure and function of circular DNA
Structure: DNA is free in the cytoplasm
Function: Possess the genetic information for the replication of bacterial cells
34
Describe the structure and function of plasmids
Structure: smaller pieces of DNA that can reproduce independently
Function: possess genes that may aid in the survival of bacteria in adverse conditions, can be used as vectors between bacteria
35
Which ribosomes are present in prokaryotic cells?
70s (slightly smaller)
36
What is the function of the flagella
Rotates to move the cell
37
Describe the structure and function of the cell wall of a **prokaryotic** cell
Made up of MUREIN
Functions to give strength and structure, protects against mechanical damage and osmotic lysis
38
Describe the structure & function of the capsule
Structure: A layer of slime around the cell wall
Function: Protects the bacterium from other cells and helps groups of bacteria stick together for further protection
39
What are the features of an optical (light) microscope
Optical uses beam of light to produce an image
Magnifies up to x2000
Lower resolution
Cheap & easy to use
Creates only 2D images
40
What are the features of an electron microscope
Uses beam of electrons focused by electromagnets to produce an image
Magnifies up to x2,000,000
Higher resolution
Extremely expensive and more difficult to keep
Creates both 2D and 3D images
41
Why does an optical (light) microscope have a lower resolution than an electron microscope
Wavelength of light is a lot longer
Can only distinguish between 2 objects if they are 0.2 μm or further apart
42
Why does an electron microscope have a higher resolution than an optical microscope
Electron beam has a very short wavelength
Can distinguish between two objects only 0.1 nm apart
43
Why must a near vacuum be created within the chamber of an electron microscope
Electrons are absorbed and deflected by the molecules in the air
44
What are the 2 types of electron microscope
Transmission and scanning
45
How does a transmission electron microscope work?
Consists of an electron gun - produces beam of electrons - focused onto specimen by a condenser electromagnet
Beam passes through thin sections of specimen
Denser parts absorb more electrons and appear darker
Image is produced on a screen and can be photographed to give a photomicrograph
46
What are the limitations of both a scanning and transmission electron microscope ?
Resolution of 0.1 nm cannot always be achieved due difficulties in preparing specimen
High energy electron became stronger required - may destroy specimen
Complex staining process
No colour images
Whole system must be in vacuum- living organisms can’t be observed
Images can contain artefacts
47
What is one difference in limitations between a scanning and transmission microscope
Specimen don’t have to be extremely thin in a scanning microscope as electrons don’t penetrate as beam of electrons are directed from above not below
Scanning can also produce 3D images unlike transmission
48
What are the disadvantages of a scanning microscope
Lower resolution
No view of internal structures
49
What two things do you use to measure specimens under a microscope?
Eye piece graticule & stage micrometer graticule
50
What is the equation for calculating length of internal organelles using scale bar
Image length of organelle
———————————— x actual length of scale bar
Image length of scale bar
51
What is cell fractionation
Process where cells are broken up and the different organelles are separated out
52
What is the order of pellets produced by the centrifuge in cell fractionation
Pellet 1: nucleus
Pellet 2: chloroplasts
Pellet 3: mitochondria
Pellet 4: Endoplasmic reticulum and lysosomes
Last pellet: ribosomes
53
Step by step of cell fractionation
**Tissue** we are extracting is **placed into ice cold, isotonic and buffered solution**
The **cells are broken up by a homogeniser** which releases the organelles - resulting fluid is the homogenate
**Homogenate is then filtered** to remove any complete cells or debris
Homogenate is then placed in test tube and **spun in centrifuge.** (ultracentrifugation)
It starts off being spun at low speeds to **compress the heaviest organelles into a pellet** at the bottom
The remaining fluid (**supernatant**) is then **transferred to another test tube and spun** in the centrifuge at a **faster speed** to compress the next heaviest organelles into a pellet at the bottom
54
What are the three stages of the cell cycle?
Interphase
Nuclear division (meiosis or mitosis)
Cytokinesis
55
What is the order of the phases in mitosis
Interphase
Prophase
Metaphase
Anaphase
Telophase
(Cytokinesis)
56
What is the importance of mitosis ?
Growth, Repair and Reproduction
57
Describe the interphase
Period before mitosis where the cell is not dividing and chromosomes are not visible.
The cellular activity that does take place, is…
DNA replication & the replication of organelles
58
Describe the structure of a chromosome after replication
2 chromatids held together by a centromere.
One short arm and one long arm
59
Describe the prophase
Chromosomes condense (shorten and thicken) to become visible
Nuclear envelope disintegrates and the nucleolus disappears.
Centrioles move to the poles and from them spindle fibres develop
60
What are spindle fibres collectively known as?
Spindle apparatus
61
Describe the metaphase
Spindle fibres form
Spindle fibres attaches the centromeres of chromosomes
Chromosomes line up at the equator by being pulled along the spindle apparatus
62
Describe the anaphase
Centromeres split
Chromatids are pulled by spindle fibres to opposite poles
Energy for this process is provided by mitochondria that gather around spindle fibres
63
Describe the telophase
Nuclear envelope reforms around the chromosomes at the poles
Nucleolus reforms
Spindle fibres disintegrate
Chromosomes are no longer visible
64
Describe cytokinesis
The cytoplasm divides to form two cells with genetically identical nuclei (mitosis)
65
What is binary fission
Asexual reproduction of a single celled organism such as bacteria
(Prokaryotes divide this way)
66
Describe the stages of binary fission
Circular dna replicates - both copies attach to cell membrane at opposite ends of the cell
Plasmids replicate
Cell membrane grows between dna and pinches inwards dividing the cytoplasm
New cell wall forms, dividing the original cell into 2 identical daughter cells
Each has a single copy of circular DNA and a variable number of plasmid copies
67
What is cancer
A group of diseases caused by the growth disorder of cells
68
What are the 2 types of tumour? How does a tumour become cancerous?
Benign and Malignant
A tumour becomes cancerous if it changes from benign to malignant
69
How can the rate of mitosis be affected
The environment of the cell and growth factors
70
What causes uncontrolled mitosis
A mutation to one of the genes
**Mutant cells formed** are usually structurally and functionally different from normal cells.
They are capable of dividing to form tumours
71
How can treatment of cancer affect cancerous cells?
Preventing dna from replicating
Inhibiting metaphase in mitosis by interfering with spindle formation
72
What are the effects of chemotherapy on normal cells
Normal cells that also divide rapidly can be vulnerable to same damage such as hair producing cells
73
How can you identify cancerous cells
Large variably shaped nuclei
Many dividing cells, disorganised arrangement
Variation in shape and size
Loss of normal features
74
How do you calculate mitotic index
(Number of cells with condensed chromosomes ÷ total number of cells) x 100
75
What can the mitotic index measure or help us predict
An elevated mitotic index indicates that more cells are dividing. This knowledge can be important in predicting survival and response to chemotherapy and cancer types
76
What’s the name of a membrane that’s around all types of cells
Plasma membranes
77
Why are phospholipids an important structure to cell membranes
**form a phospholipid bilayer**
-allows lipid-soluble substances to enter and leave the cell
-prevent water soluble substances entering and leaving
-make membrane flexible and self-sealing
78
What forms do proteins come in in the cell membrane
Protein channels - form water filled tubes to allow water-soluble ions to diffuse across
Carrier proteins - bind to molecules or ions (eg: glucose and amino acids) and change shape to move these across the membrane
79
The functions of the proteins in the cell membrane
-structural support
-act as channels (channel proteins) transporting water-soluble substances across it
-allow active transport across through carrier proteins
-form cell surface receptors for identifying cells
-help cells adhere together
-act as receptors (especially for hormones)
80
Are cholesterol molecules in the cell membrane hydrophobic or hydrophilic?
Very hydrophobic
81
Function of cholesterol molecules in the cell surface membrane
-reduce lateral movement of other molecules by pulling together fatty acid tails of phospholipids
-make membranes less fluid at high temperatures by adding strength
-prevents loss of water and dissolved ions by being very hydrophobic
82
How are glycolipids made
Made up of carbohydrate covalently bonded with a lipid
83
Function of glycolipids in the cell membrane
-act as cell recognition sites
-maintain stability of membrane
-help cells attach to each other for tissue formation
84
How are glycoproteins formed
Carbohydrate chains attaching to extrinsic proteins on the outer surface of membrane
85
Functions of glycoproteins in the cell membrane
-act as cell recognition sites
-help cells attach to one another to form tissue
-allows cells to recognise each other
86
Permeability of cell surface membrane:
Why don’t most molecules freely diffuse across it?
-not lipid soluble so can’t pass through phospholipid belayer
-too large to pass through channel proteins
-have the same charge as channel proteins so are repelled
-polar so can’t pass through non-polar hydrophobic tails in bilayer
87
What is a polar molecule
An electrically charged molecule
88
What is the fluid mosiac model of the cell-surface membrane
They way molecules are combined and arranged into the structure of the cell membrane
89
Why is the fluid mosaic model called it
Fluid - individual phospholipid molecules are moving relative to each other so gives membrane flexibility to constantly change shape
Mosiac - proteins embedded in the phospholipid bilayer vary in shape size and pattern
90
Is diffusion active or passive transport
Passive
Doesn’t require energy from external sources like ATP
91
Why/how is simple diffusion a passive form of transport
-all particles are constantly in a random motion due to kinetic energy
-these particles are constantly bouncing off each other and off objects
So these particles move down a concentration gradient from area of high concentration to low
92
Define diffusion
Net movement of particles from an area of high concentration to an area of low concentration until evenly distributed
Down a concentration gradient
93
What types of molecules pass easily through cell membranes
Small non polar molecules like oxygen and co2
94
Define facilitated diffusion
Movement of large and/or polar molecules across the cell membrane facilitated by channel & carrier proteins
Passive process down a concentration gradient
95
How do protein channels contribute to facilitated diffusion
Form water-filled hydrophilic channels.
Allow water-soluble ions to pass through membrane
They’re selective and only open to specific ions
The ion binds with protein causing it to change shape so it closes on side and opens on the other
96
How do carrier protiens contribute to facilitated diffusion
Specific molecules (like glucose) bind to the carrier protein causing protein to change shape so that the molecule is released into the membrane.
No external energy (like ATP) is needed as the molecule moves from a area of high concentration to an area of low concentration by using kinetic energy from the molecules
97
Define osmosis
The net movement of water molecules from an area of high water potential (dilute solution) to an area of low water potential (concentrated solution) down a concentration gradient (passive transport).
Through a selectively permeable membrane
98
What Greek letter represents water potential and how’s water potential measured
letter ψ (psi)
Measured in units of pressure usually kiloPascals (kPa)
99
Define water potential
The pressure created by water molecules.
Under standard conditions of temperature and pressure (25°c and 100kPa)
100
What’s the water potential of pure water
0 kPa
101
(In osmosis) Will the addition of a solute to pure water lower or higher it’s water potential
Lower
The more solute that’s added (the more concentrated the solution) the lower (more negative) it’s water potential
102
In osmosis what motion are the solute and water molecules
Random motion due to their kinetic energy
103
What type of molecules does the partially permeable membrane allow to cross and not cross (osmosis)
Allows water molecules to cross
But not solute molecules
From a higher water potential to the lower water potential
104
What happens if red blood cells are put in pure water
It will absorb water by osmosis as it has a lower water potential
Until cell surface membrane bursts and releasing its contents (haemolysis)
105
In osmosis:
If water potential of external solution is higher (less negative) than the cell solution what happens
Net movement of water enters the cell
Cell swell and bursts/lysis (only bursts if it’s animal cell because they don’t have cell walls)
106
In osmosis
If water potential of external solution is equal than the cell solution what happens
Net movement of water neither enters or leaves the cell as it’s in equilibrium
State of cell doesn’t change
If red blood cell then cell is isotonic
If plant cell then incipient plasmolysis occurs
107
In osmosis:
If water potential of external solution is lower (more negative) than the cell solution what happens
Net movement of water leaves the cell
Cell shrinks / shrivels / plasmolysed
A red blood cell would be darker as haemoglobin is more concentrated
If plant cell then cell is just plasmolysed
108
Define active transport
Movement of molecules or ions from an area of lower concentration to an area of higher concentration using ATP and carrier proteins going against the concentration
109
How does passive and active transport differ
Active:
-needs metabolic energy from ATP
-it’s against the concentration gradient
-uses carrier protein molecules which act as ‘pumps’
-very selective
110
Describe the process of direct active transport of a single molecule or ion
-molecule/ion **binds to receptor sites** on the **carrier protein**
-on the inside of cell, **ATP binds to protein, causing it to split into ADP and a phosphate molecule**
-carrier protein **changes shape** and **opens opposite side** of its membrane
-**molecule/ions released** to other side of membrane
- the **phosphate molecules released** from protein causing it to **revert to its original shape**
-phosphate molecule and ADP resyntheisise into ATP during respiration
111
Describe the sodium-potassium pump
Sodium ions are actively removed from cell/organelle
While potassium ions are actively taken in
Simultaneously
112
What does cotransport use to move substances into and out of cells and which cells specifically
Uses ions
Particularly in epithelial cells of the ileum
113
Describe the process of co-transport in the ileum
- **Na+ ions are actively transported out** of epithelial cells **by sodium potassium pump** into the blood **through a specific carrier protein**
- leaving a **lower concentration of Na+ in the cell** than in the lumen
- Na+ ions **diffuse into epithelial cells down conc gradient through Co-transport protein** and **carries in glucose and/or amino acids with them**
- the glucose/amino acids **pass into blood by facilitated diffusion using another carrier**
114
What are the 2 ways can the rate of movement across membranes be increased in co-transport ?
-epithelial cells in the ileum have microvilli which has a large surface area for insertion of carrier proteins for diffusion, facilitated diffusion and active transport
-increase number of protein channels and carrier proteins in any given area of membrane
115
Describe how exocytosis and endocytosis moves molecules through cell membranes
Transports large molecules
These particles are enclosed in vesicles made from cell membrane and transported into cell in endocytosis
In exocytosis, vesicles containing large particles are fused with cell membrane and released from cell
116
Rate of gas exchange by diffusion becomes more rapid as…
- surface area increases
- diffusion distance decreases
- diffusion gradient becomes steeper
- temperature increases
117
Define an infection
An interaction between the pathogen and the body’s various defence mechanisms resulting in individuals death or recovery from disease
118
How do you recognise your own cells
By lymphocytes distinguishing between self cells and non-self cells (foreign cells)
119
Difference between bacteria and viruses
Bacteria:
Prokaryotic cells - circular strand of DNA
Doesn’t need a host to survive
Bigger
Have: membrane, wall, cytoplasm and membrane bound organelles
Viruses:
Consists of just nucleic acid enclosed in a protein coat
genetic material in form of DNA or RNA
Require a host cell to survive
Smaller
Have no membrane bound organelles
120
3 Physical barriers to infection
Skin - consists of keratin
Stomach acid - HCl which kills bacteria
Guy and skin flora - natural bacterial flora competes with pathogens for food and space
121
Examples of Nonspecific responses of the body to infection
-inflammation
-lysozymes action
-interferon
-phagocytosis
122
What is done to minimise the effect of tissue rejection
Donor tissues for transplant are matched as closely as possible to the recipient (best matches come from relative that are genetically close)
Immunosuppressant drugs are often administered to reduce the keel of the immune response that still occurs
123
What are 2 examples of the non-specific immune response
Physical barriers
Phagocytosis
124
What are 2 examples of the specific immune response
Cell mediated response (involving t-lymphocytes)
Humoural response (involving b-lymphocytes)
125
What are the two types of white blood cell
Phagocytes and lymphocytes
126
When does phagocytosis occur and why?
If a pathogen tries to infect the body, the body’s first line of defence is the physical and chemical barriers - should this fail, the next line of defence is phagocytosis
127
Give the step by step process of phagocytosis
1. **Chemical products** of pathogens or dead, damaged and abnormal cells **act as attractants** causing **phagocytes to move towards the pathogen**.
2. The **receptors** on the cell surface membrane **of the phagocyte recognise and attach to chemicals on the surface of the pathogen**
3. They **engulf** the pathogen to form a **vesicle, known as a phagosome**
4. **Lysosomes** move towards vesicles and **fuse** with it
5. **Lysozymes** break down the pathogen by **hydrolysis**
6. The **soluble products** from the breakdown are **absorbed into the cytoplasm** of the phagocyte
128
Define immunity
The ability of organisms to resist infection by protecting against pathogens or their toxins that invade their bodies. Involves recognising foreign material (antigens)
129
Define agglutination
The clumping together of cells or particles caused by antibodies which assists phagocytosis
130
Define antibody
A protein specific to an antigen, produced by plasma cells
131
Define antigen
Foreign/non-self proteins on the surface of cells that stimulate an immune response.
132
Define pathogen
Microorganism that causes communicable diseases eg: bacteria, viruses, fungi, protists/protocista
133
Describe viral structure
- acellular
- non living
- smaller than bacteria
- contains nucleic acids such as DNA or RNA as genetic material, enclosed within a protein called the capsid
- can only multiply inside living host cells
- some like HIV have a lipid envelope. If not present the capsid has attachment proteins which are essential in allowing the virus to identify and attach to a host cell.
134
What are the two types of lymphocyte
B lymphocytes
T lymphocytes
135
Where do b lymphocytes mature
Bone marrow
136
Where do t lymphocytes mature
In the thymus gland
137
How can t-lymphocytes distinguish invader cells from normal cells
Antigens displayed on cell surface membranes
138
What are cells that display foreign antigens called ?
Antigen-presenting cells
139
What are the stages in the response of a t-lymphocyte to infection by a pathogen
(cell mediated immunity)
1. **Pathogens invade** body cells **or are taken in by phagocytes**
2. Phagocyte places **antigens** from the pathogen on its cell-surface membrane
3. **Receptors on a specific helper T cell are complimentary** to these antigens
4. This **attachment activates the T cell** to divide rapidly by **mitosis** and form **clones**
5. Cloned t -cells **destroy** the pathogen
140
What are the 4 ways the cloned t - cells can destroy pathogens ?
Develop into memory cells
Stimulate phagocytes to engulf pathogens by phagocytosis
Stimulate b-cells to divide and secrete antibodies
Activate cytoxic T cells
141
How do cytoxic T cells kill infected cells?
Produce a protein called PEFORIN that makes holes in the cell surface membrane
Allows cell membrane to become freely permeable to all substances and as a result the cell dies
142
Why is humoral immunity called humoral immunity ?
Because it involves antibodies that are soluble in blood and tissue fluid of the body
143
Describe the function of plasma cells
Secrete antibodies into blood plasma that lead to the destruction of the antigen
Survive for only a few days
Can secrete around 2000 antibodies each second
144
What aspect of the immune response are plasma cells responsible for
Immediate defence - PRIMARY immune response
145
What aspect of the immune response are memory cells responsible for
SECONDARY immune response
146
What do memory cells do
Live considerably longer than plasma cells - long term immunity
When they encounter the SAME antigen at a later date they divide rapidly and develop into plasma cells and more memory cells
The plasma cells produce antibodies to destroy the pathogen
147
Give the step by step process that explains the role of B lymphocytes
(humoral immunity)
1. The surface antigens of an invading pathogen are taken up by a b-cell by endocytosis
2. The B cell processes and presents the antigens
3. Activated tH cells attach to processed B cells, thereby activating it
4. B cell divides by mitosis to give clones of plasma cells
5. The cloned plasma cells produce and secrete the specific antibody
6. The antibody attaches to the antigens on the pathogen and destroys it
148
Describe the binding sites of an antibody
Each antibody has 2 identical binding sites complimentary to a specific antigen.
The variable region
149
What is the variety of antibodies down to
The binding site consists of a sequence of amino acids that form a specific 3D shape that binds directly to a specific antigen
150
Describe the structure of an antibody
Made up of 4 polypeptide chains
- chains of one pair are long and called heavy chains
-chains of the other pair are shorter and called light chains
Each antibody has a specific binding site (known as the variable region)
The rest of the antibody is known as the constant region
151
How can the antibody lead to the destruction of the pathogen in a bacterial cell
-Cause agglutination of the bacterial cells making it easier for phagocytes to locate them
-Serve as markers that stimulate phagocytes to engulf bacterial cells to which they are attached
152
What is a monoclonal antibody
Clones of one specific antibody produced by B cells
153
How are monoclonal antibodies useful in medical **diagnosis**
Example -prostate cancer in men
Men with prostate cancer produce more of a protein called PSA leading to unusually high levels of it in the blood
By using a monoclonal antibody which interacts with this antigen, it is possible to obtain a measure of the level of PSA in the blood.
(Although not enough to diagnose the disease itself it gives early warning)
154
Give the step by step process of how monoclonal antibodies are formed
1. A mouse is exposed to the non-self material against which an antibody is required
2. The B cells in the mouse produce a mixture of antibodies which are extracted from its spleen
3. To enable the B cells to divide outside the body they are mixed with cancer cells
4. Detergent is added to the mixture to break down the cell surface membranes of both types of cell and enable them to fuse - HYBRIDOMA
5. The hybridoma cells are separated under a microscope and each single cell is cultured to form a clone
6. Each clone is tested to see whether it produces the required antibody
7. Any clone that does, is grown on a large scale and the antibodies are extracted from the growth medium
155
How are monoclonal antibodies used in direct monoclonal antibody therapy
Targets medication to specific cells
- attach a therapeutic drug to an antibody
-monoclonal antibodies can be produced that are specific to antigens on cancer cells
-antibodies are given to patient and they attach themselves to receptors on cancer cells
-they block chemical signals that stimulate uncontrolled growth
156
What are the advantages of antibodies
Highly specific & non toxic so have fewer side effects
157
How are monoclonal antibodies used in indirect monoclonal antibody therapy
Radioactive / cytotoxic drug is attached to monoclonal antibody which attaches to cancer cells and kills them
158
How do pregnancy tests work?
3 components : reaction site , test site & control site
Relies on presence of hormone hcG produced by the placenta & found in urine
159
Why is the presence of a fixed antibody at the control site of the test strip important ?
Prevents false negative results
If **no antigen antibody complex is formed** then the **free antibody & dye substrate** will continue to travel up the stick **not binding to any hcG protein**.
The **fixed antibody** at the control site **traps the free antibody & dye substrate** and produces a coloured line
160
Describe how a positive pregnancy test is acquired
The **hcG antigens bind with the antibodies**, the **hcG antibody colour complex** moves along the strip until it’s **trapped by a different type of antibody** which produces a coloured line
161
3 uses of monoclonal antibodies that raise ethical issues
- production of it involves use of mice - involves injecting tumour cells into mice, inducing cancer. Questions whether animals should be used this way
- there’s been deaths associated with their use in treatment of multiple sclerosis. Important that patients know risks and benefits of the drugs and there’s informed consent
- testing for safety of new drugs present certain dangers. Issues about the conduct of drug trials involving them.
162
What are the 2 types of immunity
Passive
Active
163
What are the 2 types of active immunity
Natural active immunity:
Individual becomes infected with disease under normal circumstances. Body produces own antibodies and continues to do so for many years
Artificial active immunity:
Forms basis of vaccination (immunisation).
Involves inducing an immune response in an individual, without them suffering the symptoms of disease
164
Define vaccination
Introduction of dead or **inactive pathogens with its antigens** (or mRNA) to **stimulate an immune response** and provide **long term immunity** by stimulating production of **memory cells**
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Step by step response to vaccination
-vaccine contains the specific antigen
-antigen is displayed on surface of an antigen presenting cell (eg: phagocytes)
-specific T-helper cells with complimentary receptor binds to the antigen
-this activates B-cells with complimentary antibody
-B-cells form many clones through dividing by mitosis
-differentiate to form plasma cells which produce antibodies
-some T-cells and B-cells develop into memory cells for a secondary immune response
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Features of a successful vaccination programme
- economically available in sufficient quantities to immunise most of the vulnerable population
- few side effects
- means of producing, storing and transporting the vaccine
- means of administering the vaccine properly at the appropriate time
- ability to vaccinate the vast majority of vulnerable population to produce herd immunity
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Describe the primary immune response in vaccinations
- first immune response to a pathogen/antigen
-longer lag time (slower) - no memory cells present
-phagocytosis, T-cells and B-cells involved - clonal selection
-pathogens multiply and damage host cells - feel symptoms
- T-cells and B-cells become memory cells
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Describe secondary immune response in vaccinations
-secondary infection by the same pathogen/antigen
-shorted lag time (faster)
-more antibodies produced
-**rate of antibody production is faster**
-memory T-cells and B-cells become Killer T-cells and plasma cells by clonal expansion
-don’t feel symptoms
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Reasons for vaccination failure
- fails to induce immunity in certain individuals eg: people with defective immune systems
- may develop disease immediately after vaccination, before immunity levels are sufficient enough = potential to then infect others
- pathogen may mutate frequently - antigens change suddenly - vaccines ineffective (antigenic variability)
- many varieties of a particular pathogen = impossible to develop a vaccine effective against them all.
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Define herd immunity
Arises when a **sufficiently large amount of population has been vaccinated** to make it **difficult for a pathogen to spread** within that population (as pathogens are passed from individual to individual when in close contact.)
It’s highly improbable that a susceptible individual will meet an infected individual = those that are immune are also protected
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Define clonial expansion
The production of many genetically identical daughter cells through cell division of the activated B or T lymphocyte after clonial selection
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Define clonal selection:
Process of matching the antigens on antigen presenting cells with the receptors on B/T lymphocytes
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What’s the MMR vaccine?
A combined vaccine for measles, mumps and rubella.
Replaces 3 separate vaccines
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How is passive immunity produced ?
produced by the introduction of antibodies into an individual **from outside source** = no direct contact with pathogen or antigen is necessary to induce immunity. (acquired immediately)
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Why is passive immunity not long lasting ?
Antibodies aren’t being produced by the individual themselves.
Antibodies aren’t replaced when they’re broken down
no memory cells are formed
= no lasting immunity.
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Describe the structure of the HIV virus
Outside- lipid envelope which has attachment proteins embedded
Inside the envelope- capsid that encloses the 2 single strands of RNA & some enzymes
One of these enzymes - reverse transcriptase (means the virus is part of a group called retroviruses)
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What is reverse transcriptase
Catalyses the production of DNA from RNA
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Give the steps in the replication of the HIV virus
- HIV enters the bloodstream & circulates
- HIV readily binds to protein called CD4 (on tH cells)
- the protein capsid fuses with the cell surface membrane (rna &enzymes of HIV enter the tH cell)
- reverse transcriptase coverts the HIV viruses RNA into DNA
- New DNA is moved to tH cell’s nucleus where it’s inserted into the cell’s dna
- the HIV DNA creates **mRNA** which contains instructions for making **new viral proteins**
- mRNA passes out of the nucleus through pores and **uses the cell’s protein synthesis mechanisms to make HIV particles**
- HIV particules break away from tH cell with a piece of its cell surface membrane which forms the lipid envelope
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How does HIV cause the onset of AIDS
HIV specifically attacks tH cells & interferes with their normal functioning leading to the onset of AIDS
An uninfected person normally has 800-1200 tH cells per mm^3 of blood wheras in a person suffering from AIDS this number can be as low as 200
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In AIDS, what is the negative effect of having a low number of tH cells and how is it caused ?
tH cells are important in cell mediated immunity
Without a sufficient number of tH cells the immune system cannot stimulate B cells to produce antibodies or tC cells that can kill cells infected by a pathogen
Memory cells may also become infected and destroyed
As a result the body is unable to produce an adequate immune response & as a result becomes more susceptible to other infections & cancers
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What is the ELISA test
Uses antibodies to not only detect the presence of a protein in a sample but also its quantity.
Extremely sensitive & can detect very small amounts of a molecule
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Give the step by step process of how the ELISA test works (eg. We are looking for a protein and in this case an antigen)
- Apply the sample to a surface (slide), to which all the antigens in the sample will attach
- Wash the surface multiple times to remove unattached antigens
- Add the antibody that is specific to the antigen we are trying to detect & leave to bind together
- Wash the surface to remove excess antibody
- Add 2nd antibody that binds with the 1st antibody (The 2nd will have an enzyme attached)
- Add the colourless substrate of the enzyme - the enzyme will act on this to change it into a coloured product
- The amount of antigen that’s present is relative to the intensity of the colour that develops
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How do antibiotics work (bacterial cell walls specifically)
Antibiotics can **prevent bacteria from making normal cell walls**
In bacteria cells (like plants) water enters constantly by osmosis
The cell doesn’t burst due to the murein cell wall (inelastic)
**Antibiotics such as penicillin inhibit certain enzymes required for synthesis & assembly of peptide cross-linkages in bacterial cell walls**
This **weakens the walls** making them **unable to withstand pressure** - cell burst & bacterium dies
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Why are antibiotics ineffective against viral diseases like AIDS ?
Viruses rely on a host cell to carry out their metabolic activities & therefore **lack their own metabolic pathways and structures= there are no metabolic mechanisms / structures for antibiotics to disrupt**
Viruses also have a protein coat instead of a murein cell wall & do not have sites where the antibiotics can work.
In any case, **when viruses are within an organisms own cells, antibiotics cannot reach them**
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Why is it best to vaccinate a population at one specific time to increase herd immunity ?
As it interrupts the spread of the pathogen
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Why is herd immunity important
Important as not everyone can be vaccinated eg: young children and people with allergies to the vaccination
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What was the controversy associated with the MMR vaccine & what did it result in?
a study suggested there was a higher incidence of autism among children who had recieved the MMR vaccine than those who recieved the 3 separate vaccines
Lots of parents opted for their child to have no vaccine (leaving their child unprotected) or the 3 separate vaccines
Many scientists suggest it was just a correlation between 2 factors
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How can AIDS lead to death
The body can’t produce an adequate immune response so is susceptible to infections and cancers
Pathogens will therefore reproduce, damage cells and release toxins
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Why does the fact that HIV rapidly enters host cells mean a vaccine is harder to develop and be effective ?
HIV enters the cells before antibodies can bind to it and are therefore not able to reach the HIV and destroy it
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Compare scanning electron microscope and transmission electron microscope
TEM:
Higher resolution
Produces image of internal structures only
Produces 2D image
Selections must be thin - one cell thick
SEM:
Lower resolution
Produces image of external structures only
Produces 3D image
Sections can be thicker than TEM
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Compare optical and electron microscope
Electron:
Uses a beam of electrons
Much greater resolution
Focused using magnets
Smaller structures are visible
Specimen must be dead
Image not in colour
Optical:
Uses a beam of light
Relatively low resolution
Focused using glass lenses
Smaller structures are not visible
Specimens can be living
Image in colour
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What’s a macrophage cell
Type of white blood cell (phagocyte) which presents antigens on its surface to present them to B or T cells
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What are the properties of molecules that can diffuse through the phospholipid bilayer quickly without transport proteins
Lipid soluble
Small
Non-polar (not charged)
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Give the reasons why the tissue must be placed into a solution with the following properties:
Ice cold, Isotonic & Buffered
(Cell fractionation)
**Ice cold** - reduces/ prevents enzyme activity that might break down organelles
**Isotonic** - prevents organelles from bursting or shrinking through osmosis
**Buffered** - so the pH doesn’t fluctuate as this could alter the structure of organelles & the function of enzymes
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What are the benefits of indirect monoclonal antibody therapy?
- can be used in smaller doses as targeted to specific sites
- cheaper and reduces side effects
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What are microvilli
Folded cell membrane
