2) For each of the following pathogens, state whether they are prokaryotes or eukaryotes

• the plasmodium parasite that causes malaria.

• the tuberculosis bacterium

• the yeast that causes athlete's foot

We resemble our parents, but do not look exactly like either of them.

Law of genetics were worked out in 19th Century by Gregor Mendel.

DNA as the genetic material was only established in middle of 20th Century. Mendel's law's have been built on by subsequent researchers.

Key terms

gene - a sequence of bases in DNA that contains the information to make a polypeptide or protein.

DNA - deoxyribonucleic acid

RNA - ribonucleic acid

Genes consist of DNA. DNA hold the genetic information.

Genes control production of proteins by transferring the genetic information from DNA via RNA to the ribosomes where proteins are synthesised.

Proteins are what determine the characteristics of an organism.

Strong relationship between structure of the nucleic acids and their function.

Both RNA and DNA are polynucleotides.

Each nucleotide contains a

*pentose (5 carbon sugar)

*an organic base containing nitrogen

*a phosphate group

RNA

the pentose - is ribose (hence the name RNA)

organic bases - adenine (A), cytosine (C), guanine (G) or uracil (U)

DNA

the pentose - is deoxyribose (hence the name DNA)

organic bases - adenine (A), cytosine (C), guanine (G) or thymine (T)

The nucleotides are joined together in long chains by phosphodiester bonds between the pentose sugars - described as a sugar-phosphate backbone.

Phosphodiester bonds are formed in a condensation reaction.

The DNA molecule is a double helix where two long polynucleotide chains are held together, like a twisted ladder formation, with hydrogen bonds between complementary pairs.

A - T

C - G

This base pairing is central to how DNA stores and passes on genetic information , as well as how genes control protein synthesis.

RNA is a much shorter single strand polynucleotide chain.

Usually roughly cylindrical although there are other shapes such as rods and spirals.

Do not have membrane bound organelles - are prokaryotic cells.

Yeasts - including those that are used in fermentation to produce ethanol (an alcohol) are single cell organisms.

Yeast cells are bigger than bacteria - 4-12 micrometres.

Fungi are eukaryotes - they have chromosomes contained within a nucleus and other membrane bound organelles.

Do not contain organelles in the way that eukaryotic and prokaryotic cells do.

Consist of genetic material (RNA or DNA) surrounded by a protein coat.

Some viruses have an envelope of lipid bilayer and glycoprotein around the protein coat. This is originally from the cell in which the virus replicated,

Many shapes and sizes. Most viruses are very small 20-350 nanometre.

Very diverse group including some photosynthetic organisms such as algae.

Most protists are unicellular microorganisms.

Some are multicellular such as seaweeds.

Some protists are parasitic pathogens eg Plasmodium that causes malaria.

• Physical contact with an infected person eg skin to skin contact.

• contaminated surface eg. door handles, other hard surfaces.

• Sharing of needles can result in blood-borne pathogens.

• Pathogens such as hepatitis C or HIV can spread through transfusion with contaminated blood products.

• unprotected sexual contact can transmit STIs.

Airborne transmission

• carried by dust or droplets (aerosols) in the air.

• Some droplets can exist for many hours.

• Inhaling infected droplets can lead to infection.

• Covid 19 and Tuberculosis are spread this way.

Indirect transmission

• Vehicle transmission - when infected food or water are eaten/drunk (ingested).

• faecal-oral transmission is the result of poor hand hygiene.

• significant cause of food poisoning.

• Vehicle transmission can also be through infected blood on inanimate objects such as clothing/bedding.

• Indirect transmission can also include being bitten by an infected vector (the organism that transmits the pathogen from host to host). Insect bites for example.

• Malaria protist - Plasmodium. The vector is the Anopheles mosquito.

• Lyme disease - caused by a bacterium

• Zika fever - caused by a virus.

  
  

We can then understand how the spread can be prevented or minimised.

Inadequate sanitation

• a lack of access to clean water for washing.

• clean water is unlikely to carry water-borne diseases.

• inadequate sewage disposal increases risk of faecal-oral transmission of a range of pathogens.

Dense populations

• lead to overcrowding in households.

• lack of social distancing outside the home.

• this increases the rate of transmission by direct, indirect and indirect routes.

Lack of information

• lack of accessible health promotion and information means that people may be less likely to take precautions to prevent the spread of infection.

• May be resistant to preventative measures such as vaccination.

All these factors are associated with deprivation worldwide.

Antigens are found on pathogens and on the surfaces of all body cells.

Antibody - a blood protein that it produced in response to a specific antigen. An antibody binds specifically to an antigen (in a similar way to an enzyme binding to a specific substrate.)

Inflammation - a local response to injury and/or infection.

Cell-signalling - the process whereby cells communicate with each other. Usually by release of chemicals such as histamine, cytokines or interleukins.

Phagocytes - produced in bone marrow and circulate in the blood. Some leave the blood and are present in the tissues.

Phagocytosis - the process of the phagocyte engulfing a pathogen or other foreign material.

Lymphocytes - small white blood cells. B lymphocytes (B cells) are responsible for antibody production. T Lymphocytes (T cells) play different roles in the immune response.

Plasma cells - release antibodies in response to antigens. Once a B cell becomes a mature plasma cell, it can release up to 2,000 antibodies per second. They have a shorter lifespan than memory cells.

The immune response is part of that process, but not the only part.

Physical and chemical barriers

• first line of defence.

• skin - significant external barrier

• mucous membranes - line the gut, airways, reproductive system.

• Goblet cells - produce sticky, thick mucous that helps to trap bacteria and other pathogens.

• Antimicrobial proteins and peptides - help to destroy pathogens and can also be involved in stimulating the immune system.

• Lysosome (an enzyme) - hydrolyses bonds in the cell wall components of some bacteria. This weakens the cell walls meaning the bacteria swell and burst. Lysosome is present in tears protecting the surface of the eyes. Also in breast milk providing protection to the infant as their immune system develops.

  
  

  
  

  Inflammation

• response to injury or infection.

• Area becomes red, hot and swollen due to increased blood flow.

• Mast cells respond to damaged tissue by secreting histamine.

• Histamine, a cell signalling compound, stimulates a range of responses - increased blood flow in the capillaries; capillaries begin to leak more allowing fluid to enter the tissue resulting in swelling; phagocytes leave the blood and enter the tissues where they can engulf foreign material.

• histamine also stimulates cells to release cytokines, including interleukins that lead to more inflammation.

• cytokines also lead to the promotion of phagocytosis.

Phagocytosis

• Chemicals released by pathogens, into the blood, attract phagocytes.

• Receptors on the surface of the phagocytes bind to antigens present on the surface of most pathogens.

• This leads to the phagocyte engulfing and digesting the pathogen.

• Macrophages (a type of phagocyte) do not completely digest the pathogen. Instead the antigens from the partially digested pathogen are processed and then appear on the plasma membrane of the macrophage. These are then known as APCs - antigen-presenting cells. These APCs then present the antigens to the T lymphocytes. This process of antigen presentation initiates the immune response. This is a slower, more specific and more effective stage of defence against infection.

Cell-mediated response

Activation of T cells leads to cell-mediated response.

T-cells destroy pathogens by destroying infected body cells. This means the pathogens can not replicate and infect more body cells.

Antibodies are not involved in the cell-mediated response.

Process -

• activated T-cells bind to non-self antigens on the infected cells

• the T-cells then destroy the infected cells

• this kills bacteria/virus that replicates inside the cells

• activated T-cells form memory T cells.

Antibody-mediated response

Activation of B cells leads to the antibody-mediated response.

B cells produce antibodies and it is these antibodies that destroy the pathogens. Some antibodies are known as antitoxins because they bind to toxins by pathogens and neutralise them.

Process -

• activated B cells produce antibodies

• These antibodies are specific to the antigens on the pathogens that led to the activation of the B cells.

• antibodies bind to the antigens on the pathogens and neutralise them.

• Activated B cells form memory B cells

Memory cells - lead to a stronger and quicker response if the body encounters the same antigen again. This can help prevent a second infection and forms the basis of vaccination.

Vaccines - The secondary immune response is the basis of how vaccines work. A vaccine will stimulate the primary immune response without exposure to the pathogen. When later exposed to that pathogen the body has already memory cells in response to the vaccine.

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Trauma - is defined as injury that has a potential to cause disability or death.

The body responds in the same way initially but as trauma is more severe the response becomes greater.

• automatic

• similar to response to infection

and involves

• increased blood flow

• increased metabolic rate

• redness at site of injury due to increased blood flow and rupture of blood vessels around the injury site.

• pain caused by pressure on pain receptors due to accumulation of fluid.

• oedema - swelling caused by increased accumulation of fluid in the tissue at the injury site.

• loss of organ function (may stop working in a particular way, or stop working completely).

• bone structure deformity, damage or loss. (eg a fracture or amputation)

• haemorrhaging 1) bleeding when the skin is broken and blood vessels are ruptured 2) skin bruising (bleeding under intact skin).

The greater severity of trauma means that the inflammatory response is greater. Inflammation can become a disease process and can lead to multi organ failure or even death.

Provided the trauma/subsequent shock does not prove fatal then the body goes through a similar proliferation phase as described as per injury above.

• uses a powerful magnet to generate a strong magnetic field.

• Water molecules contain hydrogen and oxygen; each hydrogen nucleus consists of a single proton.

• the protons behave like tiny magnets that line up in the magnetic field of the MRI scanner (like a compass needle line up with the earth's magnetic field).

• short bursts of radio waves then knock the protons out of alignment.

• When the radio waves are switched off the protons become aligned again.

• In the process the protons send out radio signals that are picked up by the scanner.

• These signals show the exact location of the protons in the body.

• Computers use this data and create an image of the area scanned.

• Water molecules are in all soft tissues of the body.

• a bed moves the patient through the tube of the scanner (containing the large magnets). The computer creates a detailed 3 dimensional image of inside the body. The scan can take 15-90 minutes depending on the area being scanned and the level of details required.

Considerations of use.

• a person can normally eat, drink and take medication on the day of the MRI scan.

• Patient may be asked to be Nil By Mouth 4 hours prior to the scan.

• Patient can be asked to drink water and not pass urine before the scan if a full bladder is needed.

• Past medical history required, especially in relation to whether they have any magnetic materials in the body as these would be drawn to the powerful magnets in the scanner.

• examples of metal implants or fragments include - pacemaker or implantable cardioverter-defibrillator (ICD) used to control irregular heartbeat ; metal plates, wires or screws used in dental or orthopaedic surgery for fractures; cochlear implants; drug pump implants; eye implants used to hold the retina in place; IUD (intrauterine device/coil) which is a contraceptive device that is fitted inside the uterus and has copper round the outside; shrapnel/bullets; artificial joints/knee or hip replacements; tattoos or permanent make up that contains traces of metal.

This list is not exhaustive. The person may still be able to have an MRI scan but will depend on further information, type of scanner and procedure.

The medical history and preparing the patient for the scanner are very important to ensure the scan is as safe as possible. External metallic objects must be removed, eg jewellery.

The goal - remove damaged tissue and any associated toxins or waste products.

The site of injury may be bridged by a blood clot - reduces blood loss and prevent pathogens entering the wound. Clotting process - helps to bind the edges of the wounds and creates scar tissue.

Dead or damages body cells - removed by phagocytes.

Growth of new tissue to replace damaged tissue. Replacement of collagen lost by injury. Angiogenesis (growth of new blood vessels) means that new tissue is supplied with blood vessels (vascularisation).

New connective tissue is formed, remodelling the wound.

The maturation stage is the final stage of wound healing.

• reduction in vascularisation

• scar begins to fade

• collagen laid down forms cross links which decreases the risks of a wound pulling apart.

• following injury

• due to excessive bleeding

• due to a severe allergic reaction

• due to infection of the blood.

It results in the decrease in supply of oxygen and nutrients to the tissues.

Ischaemic shock - is a severe of ischaemia that can lead to organ failure and death if not treated correctly.