Topic 11.1, 6.3 & 6.5 - Antibody production and vaccination/ Defense Against Infectious Diseases/ Neurons and Synapses

Question 1

A. The Immune System

1.Outline the role of the skin and mucous membranes in the prevention of infectious disease.

4+1 for skin and 4 for mucous membranes

Answer 1

• First layer of defense
• The skin and mucous is a physical barrier against pathogens
• Skin
  -Continuous: hard to find an opening
  -Many layers and tough
  -Natural organisms: competitive exclusion by non-harmful microbes, bacteria is covered on your body so it prevents any other from entering your body
  -pH and Oils
  –Sebum secretes oils with lactic and fatty acids, these make the surface acidic inhibiting bacterial growth (some types)
• Mucous membranes: nose, mouth, genitals
  -Sticky mucus: traps invaders
  -pH: not favorable to pathogens
  -Lysozyme: enzymes break down pathogens
  -Natural organisms: competitive exclusion by non-harmful microbes

Question 2

A. The Immune System

2.Outline the steps of blood clotting.

what is clotting (4) and how does blood clot 6 steps

Answer 2

Leukocytes: white blood cells, immune system
Erythrocytes: red blood cells, carry oxygen
Platelets: used in clotting
What is clotting
* When skin is cut, blood vessels are severed and start to bleed, clotting stops this wound from bleeding.
* Prevents loss of blood and blood pressure. Creates a barrier to infection by pathogens until new tissues are grown.
* Blood clotting involves many chemical reactions (metabolic pathway). They produce a catalyst for the next reaction.
* Cell fragments, called platelets, circulate in the blood along with erythrocytes and leukocytes. They begin the process.

How does blood clot?
1. Platelets aggregate at the cut site, forming a temporary plug.
2. They then release proteins called clotting factors.
3. The cascade of reactions that occur after the release of clotting factors quickly results in the production of an enzyme called thrombin.
4. Thrombin converts soluble fibrinogen into insoluble fibrin.
5. The fibrin forms a mesh that traps more platelets and red blood cells (erythrocytes)
6. The clot is initially a gel, but changes to a hard scab when exposed to air

Question 3

A. The immune system

3.Explain the link between blood clotting and coronary thrombosis.

Answer 3

• If deposits of plaque in coronary arteries rupture, blood clots form, blocking the flow of blood in the artery
• This is called coronary thrombosis
• If the artery is completely blocked, the heart is deprived of oxygen and nutrients. This leads to insufficient production of ATP (cell respiration).
• Contractions become irregular and uncoordinated (heart quivers = fibrillation)
• This is called a heart attack. The condition can be fatal.

Question 4

A. The Immune System

4.Explain antigens and how they are related to blood transfusion safety.

Answer 4

• Antigens: a substance or molecule, often found on a cell or virus surface, that causes antibody formation
• Any foreign molecule on the surface of pathogen cells that can trigger an immune response is called an antigen
• Antibody AKA immunoglobulins: a globular protein that recognizes a specific antigen and binds to it as part of an immune response. Antibodies are specific to certain antigens
• Lymphocytes are a special type of white blood cell (leukocytes) that produces antibodies.
• The ABO blood type classification system uses the presence or absence of certain antigens on red blood cells to categorize blood into four types. In this case, the antigens are glycoproteins.
• These glycoprotein antigens cause antibody production if a person does not naturally possess them.
  -O type - All blood types have the O glycoprotein antigen.
  -A type = N-acetyl-galactosamine added to the O glycoprotein
  -B type = galactose added to the O glycoprotein
• If a person with type A blood received a blood transfusion of type B or AB (non-self cells) for example, an immune response would be triggered and their B antibodies would bind to the antigens causing agglutination or the accumulation of antibodies which can render the blood impassable and could lead to death.

Question 5

A. The Immune System

5.Outline the role of phagocytes in non-specific immunity to diseases.

Answer 5

• The second line of defense
• Phagocytes can ingest pathogens in the blood.
• They can also squeeze out through the walls of blood capillaries and move through tissues to sites of infections.
• They ingest pathogens by endocytosis (aka phagocytosis) and digest them with lysosome enzymes.
• Phagocytes are a category of leukocytes or white blood cells.
• There are many types of leukocytes and they have many different roles in keeping us healthy.
• Large numbers of phagocytes (and other leukocytes) at a site of infection form what we call “puss”
• Phagocytes give us what is called non-specific immunity to diseases because a phagocyte does not distinguish between pathogens – it digests any pathogen if stimulated to do so.
  *

Question 6

A. The Immune System

6.Outline the steps in antibody production and explain how it gives specific immunity.

context on doc and 5 steps

Answer 6

Steps of a Typical immune response:
Step 1: Antigen presentation
* A macrophage is a type of phagocyte (act as a messenger between specific and non-specific immune response systems)
* When a macrophage encounters a not-self antigen on a pathogen it engulfs it by phagocytosis but partially digests it
* Molecular pieces of the antigen are displayed on the cell membrane of the macrophage

Step 2: Activation of Helper T-cells
* Helper t-cells (lymphocytes) have antibody-like receptor proteins in their plasma membrane.
* These receptors recognize and bind to antigens being presented by phagocytes. It docks onto it, physically sensing the shape of the antigen. (There are many types of helper T cells but only a few will have receptor proteins that fit)
* When a T-helper lymphocyte docks onto a displayed antigen, the phagocyte passes a chemical signal to the T cell, making it active.

Step 3: Activation of B cells by helper T cells
* Inactive B-cells have antibodies in their plasma membrane.
* The activated helper T-cell then binds with an inactive B-cell with a matching antibody to the antigen.
* The activated helper T-cell also sends a chemical (protein) signal to the B-cell activating it.

Step 4: production of antibodies
* Several activated B lymphocytes then undergo rapid clonal expansion (cloning by mitosis) to produce numerous identical B cells, which can all produce the specific antibody required to find the invading pathogen. These new cells are called plasma cells.
* Activated B lymphocytes also create memory B cells which is give us immunity
* Extra diagram on slides

Step 5: Released Army of Antibodies Eliminate Pathogen
* The newly released antibodies circulate in the bloodstream, eventually find their antigen match (protein of the pathogen) and eliminate them.

Question 7

A. The Immune System

8.Outline how antibiotics work

Answer 7

Antibiotics work by disrupting structures (cell walls/membranes) or metabolic pathways in bacteria (also RNA polymerase/translation)

Question 8

A. The Immune System

9.Outline Florey and Chain’s experiments to test penicillin and how it would not be compliant with current protocols on testing.

9+4 concerns

Answer 8

• Antibiotics are chemicals produced by organisms to kill or control the growth of other organisms, typically bacteria.
• The most famous type of antibiotic (discovered by Alexander Flemming in 1928) is penicillin, a chemical made by the fungus Penicillium to kill bacteria.
• Florey and Chain sought to investigate the use of chemical substances to control bacterial infections
• They found that penicillin seems like the most promising bacteria to test was penicillin
• They developed methods for growing the fungus Penicillium, stimulating secretion, and isolating the antibiotic
• They found that the Penicillin worked on bacteria on agar plates.
• To test if they worked on living things they infected 8 mice with a bacteria that causes fatal pneumonia. The 4 mice that were treated with penicillin lived, but the other untreated mice died
• They then tested penicillin on a man close to death from a bacterial infection, but because it as the early stages and they only had a small amount of unpure penicillin, the man started to recover but then died from a relapse
• They produced larger quantities and tested it on 5 different bacterial infected patients. All except one were cured. Pharmaceutical companies in the U.S. then began mass-producing penicillin.

CONCERNS:
* Florey and Chain’s research would not be regarded as safe enough today.
* Extensive animal testing of new drugs is first done to check for harmful effects.
* After successful animal testing small, then larger doses of the drug are used on healthy informed adults.
* Only then is the drug tested on patients with the disease. If small trials suggest that the drug is safe and effective, larger double-blind trials are carried out on patients to further test the drug’s effectiveness.

Question 9

A. The Immune System

10.Outline why antibiotics are not effective against viruses.

Answer 9

• Antibiotics have no effect on viruses as they have very different structures and no metabolism of their own
• Antibiotics do not work against viruses because viruses use host cell metabolism, they are protected by the host cell structure, and have different structures (ex protein coat instead of the cell wall)
• Also antibiotic resistance can occur rapidly leading to its ineffectiveness (see A11)

Question 10

A. The Immune System

11.Outline the causes of antibiotic resistance

Answer 10

• Indiscriminate (using many antibiotics without purpose) use of antibiotics can lead to antibiotic resistance
• For example through the evolution of natural selection (Gr.11). Bacteria can take in DNA from other bacteria or DNA that is loose in their environment via their pilus. This along with random mutations that can occur enable them to evolve very quickly creating multiple-resistant strains of bacteria and becoming ineffective against bacteria.
  –Grade 11 example was methicillin-resistant Staphylococcus aureus (MRSA). When a bacteria creates variations of itself some react and diminish with the antibiotic but then the bacterias start to variate to form a different dominant strain so that the initial antibiotic is no longer effective.
  –Another example is a multi-drug resistant tuberculosis (MDR-TB) which is another bacterial strain that has evolved immunity to antibiotics

How to avoid antibiotic resistance:
* Doctors prescribing antibiotics only for serious bacterial infections
* Patients completing courses of antibiotics to eliminate infections completely
* Hospital staff maintaining high standards of hygiene to prevent cross-infection
* Farmers not using antibiotics in animal feeds
* Pharmaceutical companies developing new types of antibiotics

Question 11

12.Outline the effects of HIV on the immune system and methods of transmission.

5 methods of transmission+1, 6 effects on the immune system

Answer 11

Human immunodeficiency virus (HIV) can lead to Acquired Immune Deficiency Syndrome (AIDS)

Context:
* All viruses must find a complementary protein membrane cell in the body to be effected.
* In a cold, the virus located the proteins on the mucous membrane in the nasal region and damages those cells

Methods of Transmission:
* HIV does not survive long outside the body and cannot be passed through skin—thus transmission is through the transfer of bodily fluids from an infected person to an uninfected person, for example:
* Through small cuts or tears in the reproductive system during sexual intercourse.
* In traces of blood on a hypodermic needle (needle that goes just below the first layer of skin) that is shared by IV drug users.
* Across the placenta from mother to baby, or through cuts during childbirth, or in milk during breastfeeding.
* In transfused blood, or in blood clotting factors used to treat hemophiliacs.
* After the HIV infection occurs, the cells remain alive allowing the virus to stay in the cells for years—this is called the latency period.
* Because of the latency period and the fact that viruses mutate quickly it is very difficult and essentially impossible to cure, at the moment.

Effects of HIV on the immune system:
* In HIV, the virus recognizes the membrane proteins on T-lymphocytes (AKA T-cells) and infects/damages those cells
* The HIV virus injects its RNA and the enzyme reverse transcriptase which allows a DNA copy of the viral RNA to be produced in the cell.
* With the T-cells being effected by HIV over a period of years, there was a significant decrease in the number of T-cells able to produce antibodies
* As such, antibodies would eventually no longer be produced and the non-functioning immune system leaves the body vulnerable to pathogens that would normally be controlled easily
* It is one or more of the secondary infections that ultimately take the life of someone with AIDS

Question 12

A. The Immune System

13.Explain immunity and how vaccines lead to immunity.

2 types of cell that create anitibodies/vaccine and the principals of it

Answer 12

• Immunity to a disease is due to either the presence of antibodies that recognize antigens associated with a disease or to memory cells that allow the production of these antibodies.

Plasma Cells (Mature Antibody producing B Cells)
* these are the cells already discussed that produce and release large quantities of antibodies against the foreign antigen into the bloodstream
* after the pathogen has been destroyed, the plasma cells die off

Memory B Cells
* remain in the bloodstream to allow rapid production of antibodies if the same foreign antigen appears again
* Provide long term immunity.
* The primary response is launched the first time the pathogen invades.
* The secondary response occurs the second time a pathogen invades.
* Memory B-cells ensure that the second response produces more antibodies at a faster rate.

Vaccination
* A vaccine is a modified form of a pathogen that stimulates the body to develop immunity to the disease, without fully developing the disease
* Vaccines may contain weakened (attenuated) or killed forms of the pathogen, or chemicals produced by the pathogen that act as antigens
* This stimulates the primary immune response

The principle of vaccination
* After receiving a vaccination, antigens in the vaccine stimulate the production of antibodies against the disease.
* Often, two or more vaccinations are needed to stimulate the production of enough antibodies.
–The first vaccination causes a little antibody production and the production of some memory cells.
–The second vaccination (booster) causes a response from the memory cells and therefore, faster and greater production of antibodies. (secondary immune response)
* Memory cells should then persist to give long-term immunity.

Question 13

A. The Immune System

14.Outline how smallpox was the first infectious disease eradicated by vaccination.

Answer 13

• It is a disease caused by the variola virus that results in severe disfigurement and can sometimes result in blindness and death.
• It is the first infectious disease to be eradicated by humans thanks to a global initiative and worldwide vaccination program in the 1960s and 1970s.
• The last known case was in 1977 in Somalia.

Question 14

A. The Immune System

15.Outline the ethical implications of Jenner’s vaccine experiment

Answer 14

• Smallpox was also the first disease for which a vaccine was tested on a human.
• In 1796 Edward Jenner deliberately infected an 8-year-old boy with cowpox using pus from a blister of a milkmaid with the disease.
• Cowpox is a less virulent disease caused by a virus similar enough to smallpox that the antibodies work for both.
• He then tried to infect the boy with smallpox but found that he was immune.
• Jenner then tested his procedure on 23 others including himself.
• Today Jenner’s tests would be considered unethical as they involved a child too young to give consent and he had not first done tests to find harmful side effects.

Question 15

B. The Nervous System

20.Outline the role of neurons in the nervous system

Answer 15

Neurons: cells that conduct nerve impulses in the form of chemical and electrical signals.
* Sensory neurons: bring info in to the CNS
* Motor neurons: carry response info to the muscle.
* Relay neurons: link sensory and motor neurons

Nerves: many neurons group together in a single structure.
* Able to transmit information rapidly from one part of your body to another
* The information is passed along by electrical signals called impulses
* Ex. 1. Stimulus (receptor), 2. Sensory information transmitted to CNS (sensort neuron), 3. Relay neurons (relay info to motor neurons and to your brain, CNS), 4. Response (the motor neuron activated the muscle cell, effector)

Question 16

B.The Nervous System

21.Draw and label a diagram of a neuron

Answer 16

see diagram and practice

Question 17

B. The Nervous System

22.Outline the role of myelination in myelinated nerve fibers.

Answer 17

• In expectation 23, the action potential and propagation steps are for unmyelinated neurons (thinner neurons), like for a giant squid
• Humans have myelinated neurons: along the axon, there is a coating of myelin or layered phospholipid.
• Special cells called Schwann cells grow around the axon in order to deposit the myelin. There may be around 20 or more layers until the Schwann cell stops growing.
• Nodes of Ranvier: gaps between the deposited myelin.
• Saltatory conduction: When in myelinated nerve cells, the impulse jumps from one node to the next.
• Saltatory conduction is much faster than unmyelinated signal propagation
• Speed = ~200m/s (myelinated) vs. ~2m/s (unmyelinated)
• One estimate states that it would take 5000x more ATP for a non-myelinated neuron to keep pace with a myelinated one.

Question 18

B. The Nervous System

23.Explain how an action potential is produced and propagated

3647

Answer 18

Resting potential:
* The sodium-potassium pump maintains concentration gradients of sodium and potassium ions by using energy from ATP to move three sodium ions out of the cell and move two potassium ions into the cell.
* This along with the fact that there are negatively charged protein ions (organic anions) permanently located inside the cytoplasm of the axon, the number of positive charges is higher outside of the cell.
* The electrical potential (voltage) across the plasma membrane of a cell that is not conducting an impulse is about -70 mV and is called the resting potential.

Depolarization (transmission of action potential):
* First stage of action potential
* A stimulus causes the cell to become slightly more positive inside the cell (approx. -50mV = what is called the threshold potential)
* Na+ channels then open (“gated” by voltage).
* Na+ ions then diffuse into the cell (down their concentration gradient), causing further depolarization.
* This creates a positive feedback loop: more depolarization → more Na+ channels open
* This raises the membrane potential to a positive value of about approx. 35mV.

Repolarization:
* The dramatic change in the membrane potential causes the Na+ channels to close and the K+ channels to open.
* K+ ions flow out of the cell (down their concentration gradient) in the opposite direction to Na+ flow.
* This then makes the inside of the neuron axon negative again relative to the outside.
* The potassium channels remain open until the membrane has fallen to below -70mV (hyperpolarization).
–This does not restore resting potential, as the concentration gradients of Na+ and K+ ions have not yet been re-established.
–Returning to the resting potential takes a few milliseconds (and active transport by the Na+/K+ pump!) and then the neuron can transmit another impulse.

Propagation:
A nerve impulse is multiple action potentials starting at one end of a neuron and then propagating along the axon to the end.
Local currents: The diffusion of Na+ ions along the axon
After depolarization, Na+ ions that have entered the axon diffuse along the axon to where the sodium ion concentration is still lower.
This causes the threshold potential (50mV) to be met at the adjacent part of the axon, causing another action potential (there are sodium and potassium channels all along the axon)
This process repeats itself, until the end of the axon is reached.
+
The refractory period is caused by hyperpolarization, which means that the membrane is more negative than the resting potential (last step of repolarization). This extra negative charge is what keeps the propagation of action potentials going in one direction for all humans and other vertebrates.
The propagation of a nerve impulse is an all-or-nothing situation: meaning if the threshold is passed, the action potential will occur, and it will be the same magnitude each time…regardless of the strength of the stimulus

Question 19

B. The Nervous System

24.Outline the structure and function of sodium–potassium pumps for active transport and potassium channels for facilitated diffusion in axons. (the Na-K pump part of the above expectation is for all)

ONLY SL PART-6 steps

Answer 19

SL part:
* The sodium-potassium pump follows a repeating cycle of steps that result in three sodium ions being pumped out of the neuron’s axon and two potassium ions being pumped in. Each time the pump goes around a cycle 1 ATP is used.
* This is active transport because it moves the molecules from a region of lower concentration to a higher concentration and uses ATP.

Steps:
1. The interior side (inside the axon—intercellular space) of the pump is open and 3 sodium ions enter the pump, attaching to the binding sites.
2. ATP transfers a phosphate group from itself to the pump (phosphorylation of the pump protein, and dephosphorylation of the ATP). This causes the pump to undergo a conformational change so that the interior opening is closed and the exterior side is open to the outside of the axon.
3. Since the exterior side is open, the 3 sodium ions release (to the extracellular space).
4. 2 potassium ions from outside (extracellular space) can now enter the pump and attach to the binding sites
5. Binding of the potassium stimulates the phosphate group to be released, causing a conformational change so that the protein is only open to the inside of the axon (intercellular space).
6. The 2 potassium ions are released inside the axon and the sodium ions re-enter and bind to the pump again.

Question 20

B. The Nervous System

25.Analyze oscilloscope traces showing resting potentials and action potentials.

6 points–see graph on doc

Answer 20

The changes in resting and action potentials can be traced using an oscilloscope which measures voltage change over time
1. From 0 to 1 millisecond the voltage within the axon is at -70mV= resting potential
2. It rises to -50mV either due to local currents or a neurotransmitter at the synapse
3. The membrane depolarizes due to voltage-gated Na+ channels opening and Na+ ions diffusing in.
4. The membrane repolarizes due to voltage-gated K+ channels opening and K+ ions diffusing out.
5. The K+ channels close slowly, which leads to hyperpolarization. This makes a refractory period where the neuron cannot be further stimulated.
6. The membrane returns to the resting potential due to pumping Na+ ions out and K+ ions into the axon, rebuilding the concentration gradients.

Question 21

B. The Nervous System

27.Outline the role of acetylcholine in synaptic transmission.

Answer 21

• Acetylcholine is a neurotransmitter between many synapses, including those between motor neurons and muscle fibers.
• It is produced by combining 2 parts: acetyl (from respiration) and choline (from diet)
• It travels across the synapse to bind its receptor
• However, the enzyme acetylcholinesterase rapidly breaks down acetylcholine in the synapse (into choline and acetate) so it only binds for a short time.
• After binding, one action potential is initiated.
• Choline is absorbed by the presynaptic neurons and re-used to make more acetylcholine.
• synapses that use acetylcholine are known as cholinergic synapses

Question 22

B. The Nervous System

28.Outline how neonicotinoids work by blocking synaptic transmissions.

Answer 22

• Neonicotinoids = an insecticide (a toxic substance that is used to kill insects)
  –Its synthetic chemical is similar to nicotine
• binds to the acetylcholine receptor in the CNS of insects.
• Acetylcholinesterase does not break it down, so it binds irreversibly.
• With the receptor blocked, it leads to paralysis and death
• Most widely used insecticide in the world because it is safe for mammals
• However, it is non-specific, so it also kills helpful insects (like bees).

Question 23

B. The Nervous System

29.Explain threshold potentials.

Answer 23

• An action potential will not occur unless the threshold potential (TP) has been reached (usually around -50 mV)
• once the TP voltage has been reached, depolarization begins - the start of an action potential
• the increase in charge from the resting potential (usually around -70mV) is typically due to an influx of sodium ions but if there isn’t a sufficient amount to reach the TP, no action potential will occur
• usually (especially within the brain and spinal cord) the dendrites of a neuron are connected (via synapses) to multiple other neurons (pre-synaptic) and so reaching the TP requires more than one of the neurons to have an influx of sodium.

Question 24

B. The Nervous System

26.Define synapse and list the steps of synaptic transmission.

9 steps

Answer 24

• Synapse: name of the area between the axon terminal of the pre-synaptic neuron and the dendrite of the post-synaptic neuron (neuron that is receiving the signal)
• Synapses occur between receptor → sensory → relay → response neurons etc.

Steps of Synaptic transmission:
1. A nerve impulse is propagated along the presynaptic neuron until it reaches the terminal end of the neuron and the pre-synaptic membrane.
2. Depolarization of the presynaptic membrane causes calcium ions (Ca2+) to diffuse through channels inside the neuron through the membrane.
3. Influx/rush of calcium causes vesicles containing neurotransmitters to move to the presynaptic membrane and fuse with it (the membrane).
4. Neurotransmitter is released into the synaptic cleft by exocytosis.
5. Neurotransmitter diffuses across the synaptic cleft and binds to neurotransmitter receptors on the postsynaptic membrane.
6. Binding of neurotransmitter to receptors cause sodium ion channels to open next to it.
7. Sodium ions diffuse down their concentration gradient into the postsynaptic neuron, causing the postsynaptic membrane to reach the threshold potential.
8. An action potential is triggered in the postsynaptic membrane and is propagated along the neuron.
9. The neurotransmitter is rapidly broken down and removed from the synaptic cleft.