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Infection, Immunity & Forensics - Topic 6, A-Level Biology

Terms in this set (65)

What is Algor Mortis?
When the body temperature falls until it equals the temperature of the surroundings due to the slowing of metabolic reactions after death.
What is Rigor Mortis?
When about 4-6 hours after death, the muscles in a dead body start to contract and become stiff.
What are the 5 Stages of Rigor Mortis?
1. Muscles become starved of oxygen, so oxygen-dependent reactions stop.
2.Respiration in cells = anaerobic, producing lactic acid.
3. pH of cells fall, inhibiting enzymes.
4. ATP for muscle contraction no longer produced, so bonds between the muscle proteins become fixed.
5. Proteins can no longer move, fixing muscle and joint.
What is Autolysis?
When the boys enzymes from the digestive tract and lysosomes start to break down cells after death.
What is Forensic Entomology?
It is the study of the colonisation of insects on a dead body.
How Can Time of Death Be Estimated by Insects?
1. Flies = after a few hours.
2. Beetles = later stages.
3. Blowfly eggs = death no more than 24 hours ago.
What are the 5 Stages of Succession if a Dead Body is Composing Above Ground?
1. Immediately after = bacteria.
2. As bacteria decompose tissue, flies and larve are attracted.
3. Fly larve feed on dead body, making conditions favourable for beetles.
4. Body dries out, beetles remain.
5. No tissue remains = no organisms.
What is a DNA Profile?
A genetic fingerprint of an organisms DNA.
What are the Coding Blocks in DNA?
* Non-coding = 'introns' (intragenic regions).
* Coding regions = 'axons' (expressed regions)/
What are Short Tandem Repeats?
When short DNA sequences are repeated many times within introns.
What are the 5 Stages of DNA Profiling?
1. Obtaining the DNA.
2. Creating the fragments.
3. Polymerase chain reaction.
4. Separating the fragments.
5. Viewing the DNA.
How is DNA Obtained in DNA Profiling?
Sample taken from biological tissue is broken down in a buffer solution (salt & detergent). DNA is separated by centrifuging or filtering.
How are the Fragments Created for DNA Profiling?
Restrictions enzymes cut the DNA at 4-6 base pairs long. The restriction enzymes are 'target scissors', cutting a DNA sample into fragments only where their specific restriction sequence occurs.
What Happens in the Polymerase Chain Reaction? (DNA Profiling)
1. DNA mixture is heated to 95 degrees, breaking H bonds between the DNA strands.
2. Mixture is cooled, primers bind to strand.
3. Heated to 72 degrees, polymerase can work.
4. Poymerase lines up free nucleotides, cbp means new complementary strands are formed.
5. Two copies and one cycle is completed. The cycle restarts and all four strands are used as templates.
How are the Fragments Separated in DNA Profiling?
Gel electrophoresis is used, separating according to length. DNA is placed into a slab of gel and covered in a electrical conducting buffer solution. Current is passed through. DNA fragments are negatively charged, so they move to the anode. Short fragments move faster, so they separate according to length.
How is the DNA from DNA Profiling Viewed?
The DNA fragments appear as bands under UV light.
Describe Bacteria
Single-celled, prokaryotic (no nucleus) organism. Only a few micrometers long. Have a plasma membrane, cytoplasm, ribosomes and other features.
Describe Viruses
Nucleic acids surrounded by protein. Very tiny. Have no plasma membrane, no cytoplasm and no ribosomes, but do have nucleic acid.
What are the 2 Phases of TB?
1. Primary Infection.
2. Active tuberculosis.
What is Primary Infection in TB?
Mass tissues in response to infection are formed but with TB they are anaerobic with dead bacteria and macrophages in the middle - 'tubercles'. After 3-8 the infection is normally controlled.
What Makes TB Different to Other Infections?
TB can survive and breed inside macrophages, as well as being able to target the cells of the immune systems. Tuberculosis can suppress T-Cells, reducing antibody production and attack by T-Killer cells.
Describe the Active Tuberculosis Stage
Occurs if the patients immune system cannot contain the disease. The bacteria inside the lungs multiply rapidly, destroying the lung tissue.
What is the Role of the Fever in TB?
May occur as part of the inflammatory response. Fever-causing substances are released from neutrophils and macrophages.
How can Tuberculosis be Tested For?
1. Skin & blood tests.
2. Identification of bacteria.
3. Chest X-rays.
What is AIDS?
Acquired immune deficiency syndrome is caused by infection with the human immunodeficiency response, HIV.
Describe HIV
Structurally complex, enveloped virus, consisting of RNA and surrounded by a 20-sided protein capsid. It is enclosed in a layer of viral protein.
How Does HIV Invade T-Helper Cells?
Glycoprotein molecules on the virus surface, bind to the CD4 receptors on the T-helper cells. The envelope around the virus fuses with the T-helper cell membrane, enabling virus RNA to enter the cell.
How Does HIV Hijack a Cells Protein Synthesis?
The first step is to reverse transcribe and manufacture DNA from the RNA template, using reverse transcriptase. Once the HIV DNA strand is produced, it is integrated into the hosts DNA by intergrase. Once inside, it can then be transcribed and translated to produce new virus proteins.
What is mRNA Splicing?
Between transcription and translation, non-coding introns can be removed. The remaining sequences are axons (that will be expressed), meaning several proteins are formed from one length of mRNA if spliced in different ways.
How Do New Virus Particles in HIV Destroy T-Helper Cells?
The new HIV proteins, glycoproteins and nuclear material are assembled into new viruses that bud out of the T-cell, taking some of the membrane with it, killing the cell as they leave. As the number of viruses increase, the number of T-helper cells decreases, meaning T-Killer cells, macrophages and B-cells aren't activated.
Describe the Acute Phase of HIV Infection
1. HIV antibodies in blood after 3-12 weeks.
2. Rapid replication of virus and loss of T-helper cells.
3. Infected T-helper cells are recognised by T-killer cells, which starts to destroy them, reducing the rate of virus replication.
Describe the Chronic Phase of HIV Infection
1. Virus continues to reproduce rapidly but is kept under control by immune system.
2. May be no symptoms and can last for 20 years or more.
Describe the Disease Phase of HIV Infection
1. Eventually, the increased number of viruses in circulation (viral load) and declining number of T-helper cells = immune system very vulnerable.
2. Opportunist infections occur - pneumonia, TB.
What is the Difference Between Non-Specific Responses and Specific Immunity?
Non-specific responses help to destroy any invading pathogen, whereas specific immunity is always directed at a specific pathogen.
What Does Inflammation Do in terms of Immune Response?
Inflammatory response helps destroy invading microbes. Damaged white blood cells release chemicals such as histamine. Infecting microbes can be attacked by the white blood cells.
What Does Histamine Do in the Inflammatory Response?
The chemical causes arterioles to dilate, increasing blood flow in capillaries at infected site. Increase permeability of capillaries, which can cause an oedema.
What Happens in Phagocytosis & Lysosome Action?
1. Phagocyte recognises antigens on a pathogen & cytoplasm of phagocyte engulfs it into phagocytic vacuole.
2. Lysosome fuses with phagocytic vacuole, breaking down the pathogen.
3. Phagocyte presents the pathogens antigens on its surface to other immune system cells - 'antigen presenting cell'.
What Does an Interferon Do?
1. Its an antimicrobial protein.
2. Provides non-specific defence against viruses.
3. When cells are infected they produce interferons to prevent viruses spreading.
4. Inhibit viral proteins, preventing viral replication.
5. Activate cells in the specific immune response.
6. Activate non-specific immune response.
What is an Antigen-Antibody Complex?
When antibodies bind to the antigens on the surface of the pathogen.
What 3 Ways Do Antibodies Clear Infections?
1. Agglutinating proteins.
2. Neutralising toxins.
3. Prevent pathogen binding to human cells.
How Do Antibodies Agglutinate Proteins?
Antibody has 2 binding sites, so can bind to 2 pathogens at once. Phagocytes bind to antibodies and phagocytose lots of pathogens at once.
How Do Antibodies Neutralise Toxins?
Antibodies bind to the toxins produced by pathogens, preventing them from affecting human cells, so they are inactive/neutralised.
How Do Antibodies Prevent Pathogens Binding to Human Cells?
They block cell surface receptors.
Describe the Different Types of Antibodies
Can be membrane-bound or secreted. Membrane bound = extra section of protein that anchors them to B-cell membrane. Both are heavy chain proteins, coded for by single gene.
What are Plasma Cells?
Clones of the B-cells and secrete loads of antibodies into the blood.
What are Lymphocytes?
They are white blood cells that help defend the body against specific diseases. They circulate in the blood and lymph and gather in large numbers at the site of infection. Part of specific immune response. 2 types: B-Cells & T-Cells.
Describe B Lymphocytes
Produced in bone marrow with one specific type of antigen receptor. Activated when receptor binds to antigen with a complementary shape. Once activate, secretes antibodies which bind to antigens, allowing phagocytes to recognise and destroy the cell.
Describe T Lymphocytes
Produced in bone marrow and mature in thymus gland. Have on specific type of antigen receptor. Two types: T-helper cells & T-killer cells.
What do T-Helper Cells Do?
Stimulate B-Cells to divide and become cells capable of producing antibodies. Also enhance activity of phagocytes.
What do T-Killer Cells Do?
Destroy any cells with antigens on their surface membrane that are recognised as foreign. This also includes tissues received from transplants.
Describe the Activation of T-Helper Cells in Primary Response
Binds to antigen, becoming activated. Each T-helper cell divides to produce a clone of active T-helper cells and a clone of T-memory cells.
Describe the Cloning of B-Cells in Primary Response
Complementary base receptors bind to foreign antigens. They then bind with active, cloned T-helper cells and then release cytokines, which stimulate the division and differentiation of B-Cells.
What Clones Do B-Cells Divide to Produce Under the Influence of Cytokines?
1. B-effector cells - produce plasma cells which release antibodies into blood and lymph.
2. B-memory cells - enable quicker response if invaded again.
What is the Role of T-Killer Cells in the Primary Response?
They bind to the antigen on the body cell and divide to form an active alone, stimulated by cytokines. T-Killer cells release enzymes, creating pores in membrane of infected cell, allowing ions and water in so it swells and bursts, meaning the pathogens are released. Pathogens can then be labelled as targets for destruction by macrophages.
What is the Secondary Response?
Involves memory cells and take 2-7 days. B-memory cells produced in primary response differentiate to produce plasma cells and release antibodies.
What is Alternative Splicing?
When certain axons are removed, forming different mRNA strands. Therefore, there is more than one amino acid sequence, and so more than one protein can be produced from one gene.
How Can Pathogens Enter the Body?
1. Open wounds.
2. Digestive system.
3. Respiratory system.
4. Mucosal surfaces.
What Barriers are there to Prevent Infection in the Body?
1. Stomach acid.
2. Skin.
3. Gut and skin flora.
4. Lysozyme.
What is Active Immunity?
When your immune system makes its own antibodies after being stimulated by an antigen.
* Natural = immune after catching a disease.
* Artificial = immune after a vaccine.
Gives long term protection.
What is Passive Immunity?
When you are given antibodies made by a different organism.
* Natural = baby becomes immune due to antibodies from mother.
* Artificial = injected with antibodies.
Immediate, short term protection.
What is HIVS Evasion Mechanism?
Kills the cells that it infects, reducing immune system cells in body, reducing chance of being detected. Has a high rate of mutates which change the structure of antigens, forming new strains of the virus. The memory cells won't recognise it. HIV also disrupts antigen presentation.
What is Mycobacterium Tuberculosis's Evasion Mechanism?
Produces substances that prevent the lysosome fusing with phagocytic vacuole, meaning bacteria aren't broken down and can multiply undetected. Also disrupts antigen presentation, so it will not be recognised.
What are Bactericidal Antibiotics?
Destroy bacteria.
What are Bacteriostatic Antibiotics?
Prevent multiplication of bacteria. The hosts own immune system can then destroy the pathogens.
What are the 5 Ways Antibiotics can Interfere with Bacterial Cell Growth and Division?
1. Inhibition of bacterial cell wall synthesis.
2. Disruption of cell membrane.
3. Inhibition of nucleic acid synthesis.
4. Inhibition of protein synthesis.
5. Inhibition of specific enzymes.
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