Topic 7 Flashcards
antigens
compounds foreign to the body that trigger an immune response
- may be molecule or part of a molecule
- surface of pathogen may have several different antigens/epitopes
- if antigen gains entry into persons internal environment, immune system recognises them as foreign and immune response initiated.
distinguishing self from non-self
- cells and molecules are identified as self antigens by our immune system- therefore not destroyed by our immune cells-by protein markers on the cell
- these protein markers are expressed due to information contained in DNA-unique in everybody
- foreign antigens are recognized by specific receptors on our immune cells as non-self and bind to these receptors- triggers an immune response through cascade of events
- group of genes that determines these protein markers is called MHC (major histocompatibility complex)
MHC Class 1 marker
found on all cells (apart from red blood cell)
MHC Class 2 marker
found on antigen presenting cells
Antigen presenting cells
cells that process foreign antigens, placing them on their cell membrane to other immune cells- stimulates immune response
disease
any condition that impairs normal activity of an organism
what causes disease symptoms
physical or chemical damage to host
- inadequate supply of food and nutrients to a host
- symptoms don’t appear immediately- time between infection and symptom onset- incubation period
virulence`
the degree to which a pathogen can cause disease
entry points for a pathogen
nose and throat to lungs
mouth into digestive system
urethra or genital opening
cut, punctures, burns, insect bites that penetrate skin
types of non-cellular pathogens
- prions
- viruses
prions
- do not contain any genetic material
- consist of PrP protein, smaller than viruses
- two forms:
- PrPc- found naturally in nerve cells and plays role in memory, learning and transmission of signals between cells
- PrPsc- disease causing form, usually enters body through infected meat- causes nervous system degeneration
- very resistant to high temperatures, UV radiation and strong enzymes- difficult for immune system to combat
prion reproduction
- PrPc can be transformed to harmful PrPsc prion by contact with harmful prion
- contact causes PrPc to unfold and refold abnormally- secondary structure is converted to that of harmful PrPsc prion
- each transformed prion can then make contact with other normal prions, transforming them into abnormal prions- sets up chain reaction that rapidly multiplies numbers of harmful prions
- not true biological reproduction
Viruses
- non-cellular pathogens
- can only replicate inside living cell- obligate intra-cellular parasites
- usually host specific- will only cause disease in one kind or organism as they recognise specific surface molecules on cell membrane of specific host
- either contain DNA or RNA surrounded by protein coat (capsid)- naked viruses
- in some, the nucleocapsid is surrounded by an envelope- outer envelope may have glycoprotein spikes- act as recognition and attachment to specific host
structure of retrovirus
- composed of RNA
- contains reverse transcriptase enzyme- allows virus RNA to be transcribed into DNA after entering host cell.
- retroviral DNA can then integrate with host cell’s chromosomal DNA- then is expressed
reproduction of viruses
- host cells have specific receptor sites which allow only specific viruses to bind to them- virus can only replicate inside suitable host cell
- host cell infected with virus becomes factory- produces multiple copies of the virus
- mode of release of viral particles from infected cell- lysis or budding
- enveloped viruses- released from infected cell by budding- virions are released until infected cell dies
- naked viruses commonly released by lysis- infected host cell explodes and plasma membrane disintegrates
- viral particles released into extracellular fluid- allows them to infect other cells.
process of budding
- virus becomes attached to target cell
- cell engulfs virus by endocytosis
- viral contents are released
- viral RNA enters nucleus where it is replicated by viral RNA polymerase
- viral mRNA is used to make viral proteins
- new viral particles are made and released into extracellular fluid by exocytosis
- cell is not killed in process, and continues to make new virus.
process of lysis
- virus attaches to target cell
- virus penetrates cell membrane-injects DNA/RNA into cell
- viral nucleic acid replicates using host cell machinery
- new viral DNA/RNA are packaged into viral particles
- the cell continues to make and package new viral particles until it swells-membrane bursts and viral particles are released into extracellular fluid.
retrovirus process
- virus binds to specific receptors on host cell
- viral RNA, reverse transcriptase, integrase and other viral proteins enter host cell
- viral RNA is reversed transcribed to make viral DNA
- viral DNA enters nucleus and integrates into host cells DNA
- host cell DNA with viral DNA is transcribed and translated- creating new viral proteins
- viral RNA and proteins are packaged and assemble at cell membrane
- viral particles are released via exocytosis
how do viruses cause cancer
- viruses that cause cancer are lysogenic
- viral DNA incorporates into hosts DNA and is inactive.
- viral DNA is copied when DNA replication of cell occurs
- passed to new cell during mitosis
- viral DNA can be activated, often when cell is stressed
- site of incorporation into host- may result in some cells becoming cancerous
bacteria
single-celled prokaryotic- DNA
- can live, reproduce and cause disease in organisms
- reproduce by binary fission
- can either live and reproduce inside or outside cell
- has cell wall made of peptidoglycan
characteristics present in all bacteria
DNA, cell wall, plasma membrane, cytoplasm, ribosomes
characteristics present in some bacteria
capsule, pilus, plasmid, flagellum
shape characteristics of bacteria
round- coccus
rod-like- bacillus
spiral- spirochaete
organisation characteristics of bacteria
single
in pairs- diplo
in chains- strepto
clustered- staphylo
oxygen requirement
requires oxygen
with or without oxygen- facultative anaerobe
must not have oxygen- obligate anaerobe
gram stain differences
gram positive- thick peptidoglycan (disaccharide and amino acid) cross linked layer+ techoic acid (polysaccharide)
-when treated with gram stain, they turn violet
-penicillin, sulfonamide are effective antibiotics
gram negative- thin peptidoglycan+ lipid
-when treated with gram stain, they remain pink
-resistant to penicillin, effective antibiotics include streptomycin and tetracycline
-phagocytosis by WBC difficult
exotoxin properties
- proteins produced by gram positive bacteria
- released as part of normal bacterial growth+metabolism
- most toxic compounds known
- can easily diffuse into circulatory system
- can be destroyed by heat
- small dose causes symptoms in infected person
endotoxin properties
- part of cell wall of gram- negative bacteria
- lipids and only take affect when bacteria die
- less toxic than exotoxins, but are heat resistant
- does to produce symptoms is high, but immune system can’t produce antitoxins against them
fungi
single/multi-cellular prokaryotic organisms
-secrete digestive enzymes to break down organic matter
-secreted substance causes the disease
have cell wall made of chitin and will grow on any organic matter with suitable temperature and moisture
protozoan
- unicellular eukaryotic organisms
- absorb nutrients from host
- reproduce both sexually/ asexually outside or inside the cell
Macro-parasites
- worms are endo/macro parasites
- once inside- use organisms resources to live and reproduce- causing disease to host
- arthropods are invertebrates with external skeletons
- cause disease by biting their hosts
how does immune system detect all pathogens
- all have either surface molecules made of glycoproteins or polysaccharides- or they produce toxins and other secretions
- these act as non-self antigens to trigger body’s immune system
allergens as non-self antigens
- antigens that cause allergic reactions-allergens
- specific type of immune response which immune system overreacts to normally harmless substance
- can produce minor symptoms or life threatening anaphylaxis
ways of avoiding immune system
antigenic variation shedding antigens antigenic mimicry protection from antibodies attacking immune system normal immune response doesn't occur in dying tissue
