Week 2 Infection and the Immune Response Flashcards
What are the different shapes of bacteria?
Spherical - cocci
Cylindrical - bacilli or rods
Helical - spirochaetes
What does the arrangement of bacteria depend on?
The plane of successive cell divisions
What are examples of bacteria arrangements?
Chains, Clusters, pairs, angled pairs or palisades
What does gram stain divide bacteria into?
Gram positive and gram negative
In which type of bacteria does the peptidoglycan form a thick layer external to the cell membrane?
Gram-positive bacteria
In which type of bacteria does the peptidoglycan form a thin layer with an overlying outer membrane?
Gram-negative bacteria
What are the principal molecules of the outer membrane?
Lipopolysaccharides and lipoproteins
What causes the peptidoglycan to be highly polar?
The polysaccharides and the charged amino acids
What is a function of the highly polar peptidoglycan membrane?
to form a thick hydrophilic surface
What does the property of hydrophilia allow?
It allows gram - positive organisms to resist the bile in the gut
Are gram negative bacteria hydrophilic or hydrophobic?
The outer membrane is hydrophilic but the lipid components give hydrophobic properties as well
what are the three main types of bacteria?
Bacillus (rod), Coccus (sphere), and spirallus (spiral)
What are pili?
Another form of bacterial surface protection. pili are more rigid than flagella`
What is the function of pilli?
Attachment either to other bacteria (sex pili) orto host cells (common pili)
What does bacterial growth rate depend on?
The environment they are in
What is the lag phase?
The initial period of adjustment
What is the log/exponential phase?
The period where the population doubles at a constant rate (generation time)
What is the death phase?
As nutrients are depleted and toxic products accumulate cell growth slows to a stop and cells eventually begin to die
What is the structure of the bacterial genome?
Circular
What is the origin of replication (OriC)?
The singular point on the circular bacterial genome where replication begins
Which enzymes are used to unwind and separate the two DNA strands?
helicases and topoisomerases
What do the separated DNA strands serve as?
Templates for DNA polymerase
What do the two copies of the genome consist of?
One parent strand and one daughter strand
What does the process of cell division involve?
-segregation of replicated genomes
-formation of a septum in the middle of the cell
-separation of the two cells
How is the septum formed?
An invagination of the cytoplasmic membrane and ingrowth of the cell wall
What is quorum sensing?
The mechanism by which specific gene transcription is activated in response to bacterial concentration.
What happens when quorum sensing bacteria reach appropriate numbers?
The signalling compounds they produce are at a sufficient concentration to activate the transcription of specific genes
What are endospores?
Highly resistant spores within bacterial cells
What are the functions of endospores?
To enable the bacteria to survive adverse conditions
When are endospores formed?
When the cells are unable to grow e.g. when the environment changes or when nutrients are exhausted but never by actively growing cells.
What is the structure of the bacterial spore?
A complex multi-layered coat surrounding a new bacterial cell
What gives the bacteria their extreme resistance to heat and chemicals?
The presence of Dipicolinic acid and high calcium content
How long do endospores remain dormant?
many years
When do endospores return to a normal bacterial state?
When the conditions improve a new bacterial cell emerges and resumes normal life
Why are viruses not considered to be alive?
They require a host cell to reproduce
How much smaller than bacteria are viruses roughly?
10x
What does the general structure of viruses include?
Nucleic acid, protein subunits, cell membrane and a vural envelope
What is most viral genetic material made of?
RNA but some do have DNA
What genetic material do retroviruses have?
Genetic material that swaps between RNA and DNA
What is the virus envelope?
A liquid bilayer that surrounds the virus.
What does the virus envelope contain?
virus proteins that are important for infecting other cells
How is the virus envelope formed?
When the virus buds from the surface of cells they acquire this extra layer.
What extra enzyme do viruses with RNA have?
They always have their own replicase as humans dont have enzymes to replicate RNA
What do viruses need in order to replicate?
A host cell to make copies of its genetic material and the proteins and enzymes it requires to replicate
What is the cellular process that all viral cells require?
Protein translation on the ribosomes
Where does replication of DNA/RNA take place?
In most cases the nucleus but for some viruses in the cytoplasm
What is the final stage of viral replication?
the assembly and release of the new virus
Where is the nucleocapsid formed?
Either the nucleus or cytoplasm of the host cell
How are viruses released?
-Budding through the cell membrane
-Cell lysis
-Cell death
What is cell lysis?
When a cell bursts
Why do viruses with RNA have a lot of mutations?
RNA polymerase makes a lot of mistakes
What is a lytic infection?
When the virus causes the host cells to burst when the virus replicates
What is a persistent infection?
When the virus is released slowly and consistently by the cell.
In these infections people can be symptomless for a long time but still carry and spread the virus
What is a latent infection?
The virus’ genetic material may be dormant in the host cells cytoplasm or even incorporated in its genome until it is triggered
What is malignant transformation?
When viruses cause ‘normal’ host cells to turn into tumour or cancer cells
Do cancer inducing viruses have DNA or RNA?
They can have either DNA or RNA
What is Hepatitis A?
A virus that can impair liver function. It is most common in countries with poor sanitation
How can Hep A be prevented?
Travellers are advised to be vaccinated. Generally the illness doesn’t present severe symptoms
What is Cholera?
Caused by a bacteria that leads to an acute gastrointestinal infection.
It is spread through un-sanitary water and food due to poor sanitation
How can Cholera be prevented?
Travellers are advised to be vaccinated as cholera can be very severe and sometimes even be fatal
What is Typhoid?
Can be caused by some strains of salmonella and is prevalent in india,S/SE Asia, some parts of Africa and Central America
How can typhoid be prevented?
Travellers should be vaccinated
What is Shigellosis?
Caused by a bacteria this causes symptoms like nausea,diarrheoa and abdominal cramps.
This is mostly in countries with poor sanitation but has been know to occur in the UK
How can illnesses that are caused by poor sanitation be avoided?
-Using bottled water
-Don’t have ice in your drink
-Only eat salad/fruit if you prepared it yourself
-Avoid eating unpasteurised dairy products
What is Zika virus?
An infection transmitted by an infected female mosquito. It is common in Brazil and other American countries.
The symptoms are not severe unless pregnant, it can then have a severe effect on the baby
What is Malaria?
Transmitted through the bite of a parasite. Mainly found in Africa, some parts of Asia and South America. The effects of malaria are more severe in pregnant women, children, and the elderly
How can Malaria be prevented?
Anti-malarial medication should be taken
What is Dengue fever?
Caused by a viral infection that is spread by mosquitos. It is mainly found in S/SE Asia, Africa and the Carribean. It causes flu-like symptoms.
How can mosquito transmitted illnesses be prevented?
-Stay indoors between dusk and dawn
- Use products containing DEET as a repellent
-Wear loose fitting clothes
-sleep under a net
-try not to go to highly infested areas
What are neutrophils?
The most common WBC, they make up 50-60% of WBCs
What is the function of neutrophils?
They phagocytose pathogens and infected cells and play a big part in inflammation
What is the function of Lymphocytes?
Lymphocytes are divided into T&B lymphocytes. They produce antibodies which play a big part in the bodies defence against infection. They can also recognise antigens and destroy them
What are monocytes?
When the monocytes are in tissue they are known as macrophages.
They are formed in the bone marrow and then are released into the blood and tissue
What is the function of monocytes?
Phagocytose pathogens
What are eosinophils?
They are usually found in tissue.
What is the function of eosinophils?
Combat parasitic infection and to phagocytose antibody-antigen complexes
Describe the structure of bacteria
Single-celled prokaryotes with characteristic cellular organisation
Describe gram-positive bacteria
has peptidoglycan ;ayers on the outside of the cell wall
stains purple
Describe gram-negative bacteria
has one layer of peptidoglycan between the two membranes
stains pink
Describe natural flora in the gut
normal flora is acquired soon after birth and changes with age. Benefits - competition and bi-products inhibit establishment of infection
vitamins (K&B) in the gut are produced by bacteria
the rate at which bacteria grow and divide depends on the nutritional state of the environment.
How does bacteria replicate?
The genomic DNA replicates from the origin of replication and must be accurate
formation of a septum in the middle of a cell
division of the cell to give separate daughter cell
How do bacteria cause virulence in the body?
they colonise, invade and release toxins
describe some examples of other microbial defences of bacteria
antigenic mimicry, antigenic masking, encapsulation, invasion of the host’s immune response
How does bacteria enter the body?
coughs, sneezes, vomit, bites from infected animals, exposure to infected body fluids through sexual intercourse or from sharing hypodermic needles
What are viruses?
obligate intercellular parasites
why do some viruses have an envelope?
they acquire a lipid bilayer as they bud from the surface of the cell
What is the genetic material of a virus contained in?
A coat or capsid, made up from a number of protein molecules.
How do viruses invade?
via inhaled water droplets
food or water
direct transfer from other infected host
from bites of vector arthropod
Describe the life cycle of a virus
virus attaches to cell
virus penetrates the cell membrane and injects nucleic acid (RNA or DNA) into the cell
viral nucleic acid replicates itself using host cell machinery
new viral nucleic acids are packaged into viral particles and released from the cell. The host cell may be destroyed in the process
what is the most common type of WBC?
phagocytes
how do phagocytes kill pathogens in extravascular tissue?
enter the extravascular tissue, ingest microbes then die within hours
where are macrophages found?
healthy macrophages are found in all tissues and organs
what are macrophages?
differentiated monocytes found in tissue that can survive for long periods of time
What do macrophages do?
they initiate and regulate inflammation, ingest microbes, clear dead tissue and initiate tissue repair
What are dendritic cells?
Link between the innate and adaptive immunity
antigen presenting cells
they also produce cytokines for inflammation and stimulate adaptive immune responses
What are mast cells?
found in the skin in the mucosal epithelium
both innate and adaptive
cytoplasmic granules - vasoactive amines e.g. histamines cause vasodilation and increased capillary permeability
proteolytic enzymes kill bacteria or inactivate toxins
synthesise lipid mediators and cytokines
What are natural killer cells?
secrete cytokines that activate macrophages
contain granules which are released into the extracellular space at the point of contact with the infected cell and bring about apoptosis
usually kills viral cell
What do eosinophils do?
many functions - inflammatory processes, trapping substances, killing cells, mainly anti-parasitic functions
allergy
Describe the function of lymphocytes
each lymphocyte binds to a specific antigen
once activated, lymphocytes multiply to produce clones
some B lymphocytes differentiate to plasma cells which produce antibodies
helper t cells produce cytokines which stimulate antibody production
cytoxic t cells bind to and kill infected cells and cancer cells
memory b cells
B cells also display antigens and secrete cytokines
What are lymph nodes for?
the site of immune response activation
What is the function of the spleen?
blood-borne antigens are captured by antigen-presenting cells in the spleen
What are the three outcomes from the complement cascade?
recruitment of inflammatory cells
opsonisation of pathogens
killing of pathogens
what are the three complement cascade pathways?
classical pathway
MB-lectin pathway
alternate pathway
What activates the classical pathway?
antigen:antibody complexes
what activates the MB-lectin pathway?
lectin binding to pathogen surfaces
What activates the alternate pathway
pathogen surfaces
What are the primary lymphoid organs?
bone marrow
thymus
what are the secondary lymphoid organs?
lymph nodes, spleen
What is the role of the thymus?
maturation of T lymphocytes - CD4+ “helper” and CD8+ “killer”
selection of auto reactive cells for removal to prevent autoimmunity
Export a repertoire of T cells for life
What are the 5 types of antibody?
IgM (5), IgA (2), IgD (1) ,IgG (1) , IgE (1)
From the afferent lymph vessels to the efferent vessels, in what order does the lymph pass immune cells?
B cells
T cells
Plasma cells and macrophages
