Unit 3: Signatures of life Area of Study 2

Disease A disease is any change that impairs the function of an individual in some way – Non – infectious disease (genetic, nutritional) – Infectious disease (caused by a pathogen) Pathogens can be – Non – cellular – Cellular

Non-cellular agents PRIONS – Infectious agents made of protein – Normal prion protein occurs mainly in nerve cells – The shape of the protein is altered but the chemical make-up is still the same – A prion can convert normal proteins to the abnormal shape. – Cause Spongiform encephalopathy (sponge like brain) eg: Mad Cows Disease, CJD in humans

PRION

Bacteriophage replication

VIROIDS Smallest known infectious particle Short pieces of naked RNA At present only identified as plant pathogens.

Cellular Pathogens Prokaryotes – Bacteria Eukaryotes – Protozoa – Fungi – Endoparasites (tapeworms, flukes, nematodes) – Ectoparasites (Fleas, ticks, lice, mites)

Have a cell wall & a single circular chromosome Live in almost every habitat on Earth Important role in the Ecosystem Classified according to shape (coccus, rod- shaped, spiral shaped) Some have flagella, spores, capsule Have ribosomes but no membrane bound organelles. Cell wall structure is used to classify bacteria BACTERIA

Bacterial cell wall – Gram stain The cell wall structure of bacteria can be used to classify them: Gram-positive cell wall. Has many layers of peptidoglygan that retain the crystal of violet dye when the cell is stained. They look purple with this stain.(Often more susceptible to antibiotics) Gram-negative. A gram-negative cell wall is thin. The inside is made of peptidoglycan. The outer membrane is composed of phospholipids and lipopolysaccharides. They look pink with the gram stain.

Bacterial diseases Bacteria can cause a disease by: – Large numbers which cause a change in the normal functioning of the host. – Directly attacking & destroying tissue.(e.g. gangrene) – Producing a toxin which may kill or seriously affect the normal functioning of the host’s cells. Endotoxins part of cell wall of Gram –ve bacteria. Effective when cell dies e.g. Salmonella (heat stable) Exotoxins produced by Gram +ve bacteria during normal growth e.g. Clostridium botulinum, tetanus (heat sensitive but extremely toxic)

Treatment of bacterial diseases Chemotherapy (use of chemicals) Antibiotics – Alexander Flemming – Howard Florey – Narrow Spectrum – Broad Spectrum – Correct use of antibiotics

Sensitivity Test

Single-celled pathogens Examples include: – Protozoa e.g. Plasmodium falciparium which causes severe malaria (relies on the vector - the Anopheles mosquito) – Amoeba e.g. Entamoeba histolytica which causes amoebic dysentry (spread through contaminated food and water)

Lifecycle of Malaria

Fungi Heterotrophic Many are ectoparasites Some cause superficial infection of skin, nails e.g. Tinia, ringworm Yeast e.g. thrush infect mouth and vagina Some affect plants e.g. Wheat rust, mildew Treated with fungicides

Transmission

Parasites as vectors Parasites live on or in another organism (ectoparasite /endoparasite) Many parasites come into direct contact with body fluids so may act as vectors. Vector – an organism that transmits a pathogenic organism form one host to another. (e.g. Flea and Yersinia pestis)

Antigens Cells have antigens (protein molecules) which represent a recognition code for the organism. This enables the organism to recognise the cell as ‘self’ or ‘non-self’. Pathogens display antigens that are foreign to the host organism and are rejected by the host.