SNAB Biology- Topic 6


Health and dieases

Health- is a state of physical, mental and social wellbeing which includes the absence of disease and infirmity.

Disease- A condition that impains the normal functioning of an organism.

Disease's can be caused by different things such as:                                                                        * Genetic defects- Eg. Cancer                                                                                                            * Nutritional deficiences Eg malnutrition, obesity, amenia                                                                  * Environmental factors Eg. Toxic chemicals

Infectious diseasses can be passed between indviduals: Malaria, HIV, TB

Microrganisms- H type Eg. Fungi, Virus, Bacteria

Pathogen- Is an organism that can cause damage to the organism (Host) it infects. (Bacteria, Viruses and fungi. A pathogen causes diseases.

Parasite- Is an organism that lives on or is another organism (The Host)

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Bacteria includes: Plasma membrane, Ribosome, flagellum, Plasma DNA 1-3mm, Chromosomal DNA, Capsule.

Virus- Non- Living.

Transmittion of diease ( portals of entry)

- Respiratory tract    - Gastrointerinal tract    - Utinogential opening     - Breaking of skin

Models of transmission:

- Droplet -Sneeze  - Direct contact -Indirect contact - Ventricle transmission (Carried in H20+Blood) - animal Vecton - Eg. Mosquite

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Immune system

Bodies have the mechenism to defend and destroy against any foreign matter

- Primary defences help prevent pathogens and parasite from entering it 

- Primary defences include Skin and Mucus Membranes.

First Line of defence (Physical + Chemical barriers)

- Skin - Nasal passage and trachs are linked with Mucus (Made by globlet cells) and cillia. - Eye tears contain hysozymes  -Hcl acid  - Normal flora (Good micro-organisms) - expulsive relexes(sneeze)

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Immune system

Second line of defence: (Non- Specific). How it defends against pathogens.

Inflamation: Inflammotory response occurs to help destroy invading microbes.

Lysozyme : Tears help to wash out the foeigen material and attacks any bacteria on the surface of the eye. The enzyme lysozyme kills bacteria by breaking down their cell walls

Intelron: provides Non-specific defence against viruses and some bacteria.

Phagocytosis: White blood cells that engulfs bacteria and other foreign matter in the blood and tissue.

Phagocytes are white blood cells - Macrophages, Neutrophiles

Phagocytes recognise self antigens that engulf (pathogens)

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Macrophages- BIG eaters- also become ATP - Englulf a lot of bacteria (last longer) 

Neutrophiles -  Destroy little - Quick to resond 

Histamine- Leaks into the blood vessels/ dialated causes redness (swealling) it is a chemical and causes vasodilation which is the dilation of blood vessels which decreases blood pressure this increases the permeability of the capiliaries.

Histamines are chemicals that cause the arteriotes in the area to dialite increasing the bloodflow in the capillaries at the infected sight

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Secondary line of defence

Secondary line of defence - Non specifc 

1) cause - damage or infected tissue

2) Most cells secrete histamine (cell signalling molecule)

3) Increases blood flow to area - Vasodilation

4) Capillaries become leaky increasing tissue fluid and phagocytes to the infected area

5) Stimulates cells to secrete cytokines which promote phagocyosis by macrophages (phagocyte)

6) Cytokines also attract neutophiles to damaged infected area

7) Cells at the site release protein infection

8) Puss is collected due to dead white blood cells

(APC) Antigen presenting cells present the pathogen on the surface

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T- Cells

T- cell receptors or CD4 (mattures in the thymus) It must find a complemtary match or APC

Body cells: Proliferation (cell division mitosis)- Clonal expansions - Once t-cells bind to antigen, the receptor is complimentory to that spefic antigen. It activates it which causes the cell division to create t-cells for the specific ACP to kill the antigen (Cytokines are realsed)

Cell repetors: Helper cells - activates B-cells by releasing cytokines. 

Killer cells- Kills pathogens by releasing chemicals.

Memory cells- Remember antigens for next time.

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B-cells are made in the bone marrow, they are another type of white blood cells                             - Covered with antibodies,   - Antibodies bind to antigens  -Forms antigen AB complex                  

- Each B-cell has different shaped antibodies (AB)  

- Antibody on B-cell binds to complmentory antigen, so each B-cell will bond to different antigens

Differentiation - When B-cells become specialised into Memory and palsmid cells.

Activation- T-helper cells help by releasing cytokines where the B-cells respond, Directly through the receptors where they bind, the antigen and receptor.

Memory- Memory cells remember the same chogen fo a further reduction of antigens.

Plasma - secrete loads of antibodies specific to the antigen in the blood.  - tooled up for massive synthesis and secretion of antibody.  - From antigen to antibody complex

Antibodies are Proteins

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Antibodies help to clear infections by:

aggulatinating pathogens: Each antibody has 2 binding sites, so an antibody can bind to 2 pathogens at the sam time - the pathogens become clumped together. Phagocytes then bind to the antibodies and phagocytose a lot of pathogens at once.

Neutralising toxins- Antibodies can bind to the toxins produced by pathogens. This presents the toxins from affecting human cells,so the toxins are neutalised (inactivated). The toxin antibody complexs are also phagocytosed.

Preventing the pathogen binding to human cells- When antibodies bind to the antigens on payhogens, they may block the cell surface membrane receptors that the pathogens need to bind to the host cells. This means the pathogen cant attach or infect the host cells.

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Viral infections

When T-killer cells come in contact with antigens they kill it off.

1) Virus attaches to the receptor by recptor mediated endocytosis. There must be a complimentary match with the receptor and attachment proteins.

2) The lyzosome organelle breaks down the virus envelope (capsid)

3) The virus DNA enters the nucleus via the nucleus pores so transcription occurs making mRNA with RNA polymerase.

4) mRNA leaves the nucleus and are made into proteins.

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Splicing- How one gene can give rise to move more than one protein

* exams are genes that are expressed and introns are not expressed and do not code for amino acids

* Pre MRNA is an inimature strand of MRNA before introns are removed

Splicing is when the Introns are removed of Mrna and the extrons are expressed

Alternative splicing is when specific introns are removed to have a differnt MRNA (only some introns are removed)

It is used to synthesise antibodies as receptors.

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Immune response

Primary response: Is the first time an immune system is exposed

Secondary response: Is memory cells that can destroy the pathogen quicker

Primary response enters for the first time,cells are activated the speed of response is slow B+T cells are people experience symptoms.

Secondary response: pathogen enters for the second time the speed of the response is fat and cells are activated are Memory cells the person experiences No symptoms.

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Immune response

Immunity: is when you do not suffer from a disease and pathogens, and are immune to the development of dieseases as it has already been infected with the same pathogen. There are 2 types of immunity.

Active- when you make memory cells and antibodies - natrual and artifical

Passive- When you do not make memory cells or antibodies.

Active natural: exposure to pathogen when you become immune after catching the disease.

Artificial- Vaccination where injected with dead pathogens or antigens.

Passive natrual: Become immune due to anti-bodies Eg. breast milk

Artifical : Injected with antibodies

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HIV (Human Immunodeficiency Virus)

Hiv infects and destroys a type of white blood cell called the T Helper cell, which acts as a host cell for the virus. T helper cells acivate other immune activate other immune system cells *** they are important in the immune response. Hiv Leads to Aids.

- Aids is a condition in the immune system where it makes the immune system deteriorate.

How is it transmitted.

Bodily fluid- Mother to baby through placenta.

- Breaking of skin through shraing needles.

- Mucus membrane through sexual intercorse.

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viral protein

1) CCRS helps the precetor to fuse with the membrane of virus cell.

2) Rna has to be turned into DNA, using reverse transcriptase enzymes.

3) Intergraze enzymes with the HIV, DNA with the most cell nucleus.

4) Viral DNA uses host cells, RNA (transcription) polymerase to make viral RNA.

5) Viral RNA goes to most cells, ribosomes to make viral proteins.

6)  Viral proteins leave through exocytosis which it takes the membrane with it to create an envolope. Finds another receptor on T-cell to multiply.

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HIV symptoms

People with HIV are classed as having AIDs. When symptoms of their failing immune system start to appear or their T-helper ceel count drops. People start to expereince:                                


Sore Throat,

Body rashes,


Swollen glands

Antiviaral drugs can help inhibit the HIV, so it soes not develop into aids.

Hiv has a high rate of mutation in the genes that code for antigen proteins. The mutation chnages the structure of the antigen and this forms new strands of the virus. This is caused Antigenic Variation

Therefore Memory cells produced for one strain of HIV wont recognise other strains with different antigens.

The immune system has to produce primary response agaisnt each new strain.

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Aids symptoms

-Weight loss



-Skin problems

This is because there are not t-helper cells to release Citokines to activate B-cells, T-Killer or Macrophages to clear away infections

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Tuberculosis (TB)

Mycobacterium tuberculosis- causes the disease (TB)

Inflammation- At the site of infection, is where a pathogen enters the body (The site of infection) usually becones Red, Warm, Swollen and pain full

Infection occurs when tiny drop;ets containg the bacteria are inhaled into the lung.

1st phase- No symptoms inflammatory response, phagocyes engulf TB but fail to destroy it as the TB has a Thick, Waxy cell wall. The bacteria can lie dormant for years.

2nd Phase- (Active tuberculosis) occurs if there are too many bacteria for the immune response to deal with. The bacteria multiply rapidly and destroy the lung tissues by crreating holes.

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How does the infection occur

Infection occurs when tiny droplets containg the bacteria (from an infected person) are inhaled into the lungs.

Macrophages engulf the MTB but some survive 

1st phase 1) Phagocytes englf the TB but they survive 

2) They are sealed off in Turbercles

3) They become dormant

2nd Phase 1) TB reactivates and starts to destroy the lungs, which stops the function of the immune system and weakens it.

The first phase occurs for months where the tubercles are formed.

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Symptoms of primary infection of TB

- Fever -General weakness -Severe choughing (caused by inflammation)

Symptoms of active TB

*weight loss *Coughing *fever *Loss of appetite

Role of fever in response to TB?

Fever and night sweats

This occurs as part of the imflammatory response fever causing substances are released from neutaphiles and macrophages. The chemicals affect the hypothalomus and alter the set point for the core body tempture to a higher temperature.

-effectors act to warm the body up to the new set point 

-Raised temperature enhances phagocytosis and immune system.

- Reduces reproduction of pathogens.

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Why HIV patients more likely to develop TB

Hiv stops T-helper cells from being made, therefore B-cells, T-Killer cells and macrophages cant be made. 

This then leads to the immune response to be weaker; consequently there are less chances of stoppping Tuberculosis.

Factors that can increase the chances of TB 

- Weak immune systems

- No immunisations (Vaccines)

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Antibiotics only work on bacteria (infections) - Antibiotic discovery

- sir alexander Flemming -1928

-Discovered by accident

-Bacteria on agar dish overnight 

-Contaminated with mold

-There was no growth of bateria around the mould on the agar dish.

What are antibotics?

Antibiotics are chemicals that kill or inhibit the growth of macro-organisms 

Bacteriocidal- antibiotics kill the bacteria  - Bacteriostatic antibiotics prevernt bacteria growth

Antibiotics- A drug that kills the entire bacteria

Antieptic- Destroys bacteria in the surface area

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How antibiotics work

Antibiotics work by inhibiting bacteria metabolsim

-Some antibiotics inhibit enzymes that are needed to move the chemical bonds in the bacterial cell walls. This prevents the bacteria from growing properly. It can also lead to cell deactivation, the weakened cell wall cant take the pressure as water moves into the cell by osmosis. This can cause the cell to burst.

- Some antobiotics inhibit protein production by binding to bacterial ribosomes. All enzymes are proteins so if the cell cant make proteins it cant make enzymes. This means it can not carry out important metabolic processes that are needed for growth and development

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How bacteria evolves

How does bacteria evolve to agigenic variation to avoid the secondary immune response?

1) Theres a random mutation on the antigen of an invading pathogen in the primary response.

2) The mutation leads to a change in the data sequence, which leads to the wrong MRNA strand with mutant base transcribed (Transcription)

3) amino acids change, so the polypeptide chain changes, with the mutated gene.

4) Protein structure also changes and leads to a different folding of the gene for the antigene.

5) Antigenic variation has occured which leads to a different antigen on the surface due to the mutated gene.

6) Memory cells in the secondary immune response cant remeber the mutant antigen and the antibodies cannot find and kill the pathogen so it survives.

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Antibiotic resistence

Evolution by natural selection.

-Certain characteristics that are advantages mutations are passed on to offspring. These mutations allow the offspring to eveolve and adapt.

Selection pressure

- something in an environment which favours some individuals more than other individuals (Disease, competition, preditors) Might make it harder to survive but they adapt to survive with their characteristics.

Bacteria evolve by mutations which make them resistant to antibodies

The sequence of protein structure chnages so the right enzyme cannot be matched.

-Bacteria reproduce quickly and in large numbers therefore random mutations are more likely 

- Antigenic variation will allow pathogens to help avoid detection of memory cells and secondary response.

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Microbial decomposition+ time of death

Microorganisms decompose organic matter 

- WHen plants and animals die, microogranisms on and in them secrete enzymes that decompose the dead organic matter into small molecules they can respire.

- Microoganisms respire, Methane (CH4 and Co2) (recycles carbon back into atmosphere)

Scientists can estimate the Time Of Death of a body (TOD)

Body temperature - From the TOD metabolic reactions slow down and eventually stop, causing body temp to fall untill surrounding temperature -algor mortis

Human bosies cool at at rate of 1.5 c- 2.0 c per hour 

- Air tempture, clothing and body weight can affect the cooling rate of the body Clothed body will be slower than one without as it is insulated.

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Degree of muscle contraction

Degree of muscle contraction

4 to 6 hours after death muscles start to contract and become stiff (Rigor mortis)

-Muscle cells become deprived of oxygen 

- Respritation takes place but it is Anaerobic causing a build up of Lactic acid.

The PH of cells decrease due to lactic acid inhibiting enzymes that produce ATP

No ATP means that bonds between myosin and actin in muscles become fixed and the body stiffens. 

Rigor mortis occur quickly at higher tempture because of chemical reactions.

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Forensic Entomology

The Body is quickly colonised by a variety of different insects 

- TOD can be estimated by identifying the type of insects

- Diffrent conditions will affect an insects life cycle, drugs, humidity, oxygen and temperature.

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Extent of decomposition

Hours to a few days- Cells and tissues are being broken down by the body's own enzymes and bacteria. Skin turns greenish

Few days to a week- Microorganisms decompose tissue and organs. Produce gass makes body bloated.

Few weeks- Tissues begin to liquidfy and seep out into the area around the body.

Month to a year- Only the skeleton remains

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stages of succession

The types of organisms found in a dead body chnage over time going through a number of stages called- succession.

If body is above ground it follows stages of:

- Immediately after, conditions in the dead body are most favourable for bactera.

- As the bacteria decompose tissues, condions in the body become favourable for flies and their larvae.

- When fly larve feed on a dead body makes conditions favourable for beetles 

-As the body dries out conditions become less favourable for flies, they leave the body whe beetles remain as they can decompose dry tissues.

-When no tissue remains, conditions are less favouable for most organisms.

The stage of succession of a dead body is affected by many things including location such as above or below ground in water or dealed away.

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DNA profiling

A DNA profile is a Genetic fingerprint of an organism's DNA.

Everyones DNA is different (except identical twins) so your DNA is unique to you.

DNA profiling can be used to idenify people and to determine genetic realtionships between humans, between animals and plants.

How a DNA profile is made

1) A sample of DNA is obtained from the organism the the DNA profile is being made for (Blood, Saliva.

2) PCR  is used to amplify the DNA. The polymerase chain reaction is used to make millions of copies of specific regions of the DNA in a few hours. The DNA needs to be amplifed so there is enough to make a DNA profile.

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How PCR works

1) A reaction mixture is set up that contains the DNA sample, free nucleotides, primers and DNA polymerase.

Primers- Short pieces of DNA that are complemtary to the bases at the start of the fragment you want.

DNA polymerase is an enzyme that creates new DNA strands

2) The DNA mixture is heated to 95c to break the hydrogen bonds between two strands of DNA.

3) The mixture is then cooled to between 50 and 65c so primers and bind to the strand.

4) The reaction is heated to 72c so DNA polymerase can work 

5) The DNA polymerase lines up free DNA nucleotides alongside each template strand . Complentary base pairing means new complentary stands are formed.

6) Two new copies of the fragment of DNA are formed and one cycle of PCR is complete 

7) The cycle starts again.

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DNA profiling

A fluorescen tag is added to all the DNA fragments so they can be viewed under a UV Light 

Gell electrophoris is used to separate out the DNA fragments accorsing to their length.

1) The NDA is placed into a well in a slab of gel and is covered in a buffer solution that conducts electricty.

2) An electrical current is passed through the gel- DNA fragments are negativily charged so they move towards the positive electrodes at the far end of the gel.

3) Short DNA fragments move faster and travel further through the gel so DNA fragments seprate according to length.

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DNA profiling

Forensic scientis use DNA profiling to compare samples of DNA collected from a crime scenes such as blood, semen, skin cells, hair. they compare this to possible suspects, to link them to the crime scene.

Determine genetic realtionships in humans.

1) we inherit DNA from our parents- roughly half comes from each parent

2) More bands on two DNA profiles that match, the more closely related thoses people are.

3) Paternity tests are used to determine the biological father of a child by compairing the DNA profiles.

Animals and Plants 

DNA profiling can be used on animals and plants to prevent interbreading which causes health, productivity and reproductive problems.

Inbreeding decreases the gene pool- the number of different alleles in a population this can lead to an increased risk of genetic disorders leading to health propblems.

DNA can be used to identify how closely related individuals are.

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