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U302 Cellular Signalling - Part 1 - Signal types, Apoptosis, Innate immune response
Terms in this set (61)
What is the process by which an organism converts an extracellular signal to a response?
1) Reception: The binding of the signal molecule (ligand) to its specific receptor
2) Transduction: The second messenger is formed or is released into the cytosol
3) Response: Activation of cellular process
What are the three stages of Signal transduction?
- Able to pass through membrane
- Binds onto receptors within the cytosol to initiate transduction
- Required a carrier protein for transport via blood
How do lipid-based signalling molecules act on target cells?
- Unable to pass through cell membrane
- Bind to receptors on the surface of the cell membrane
- Activates a secondary messenger within the cytosol to initiate transduction
- Leading to a change in cytoplasmic function or gene transcription
How do protein-based signalling molecules act on target cells?
Controlled and programmed cell death
What is Apoptosis
Too much can lead to neurodegenerative diseases such as Alzheimer's and Huntington's disease
What conditions can too much Apoptosis cause?
Too little can lead to the production of cancer
What conditions can too little Apoptosis cause?
- Mitochondrial pathway: signals from inside the cell
- Death receptor pathway: signals from outside the cell
What are the two main Apoptosis trigger pathways?
- Signals from inside the cell
- Occurs when there is serious damage inside the cell
- Example: Severe DNA damage/malfunction
Describe the Apoptosis Mitochondrial pathway
- Signals from outside the cell
- Received a signal due to cells that are not fully developed
- There are more cells than needed
- Cells have outlived their usefulness
Describe the Apoptosis death receptor pathway
1) Stimulus initiates Apoptosis
2) Cell shrinks and develops small bumps (blebs) on their surface
3) Caspase enzyme breaks down DNA and proteins in the nucleus and mitochondria
4) Blebs break apart and bind to receptors on phagocytic cells. These cells engulf these fragments.
Describe the process of Apoptosis
- It is the result of too little Apoptosis
- Cells posses the ability to ignore signals regulating growth and death signals
- Results in the formation of tumours
What types of cell signals are there?
They bind to the sites on specific receptors on their target cells
What characteristic do all signalling molecules share?
Any molecule that binds to a specific target to form a biologically active complex
What is a ligand?
Chemical signalling molecules for communication between members of one animal species.
What are pheromones?
Name 5 Plant growth hormones
Signalling molecules, mostly peptides or modified amino acids. Cannot pass through the plasma membrane, instead activates receptor on surface.
What are neurotransmitters?
Produced in Neurons and stored in Synaptic Vesicles
Where are neurotransmitters produced?
Synaptic vesicles fuse with cell membrane following an electrical signal, and neurotransmitters are released. The contents of the synaptic vesicle diffuse across the synaptic gap.
How are neurotransmitters transported?
- Dendrites of another neuron in order to continue an impulse
- Cells stimulated by neurons (muscles, glands)
What do neurotransmitters target?
Where are Pheromones produced?
Excreted into the environment
How are pheromones transported?
Stimulus -> Receptor -> Modulator -> Effector -> Response
Name the steps of the Stimulus-Response model
Proteins, Lipoproteins, Polysaccharides, lipopolysaccharides, lipids, nucleic-acids, some metals such as mercury.
What molecules can be or contain Antigens?
They identify bodily cells as 'self' to prevent the organisms own immune system from attacking it.
Self-antigen receptors stop cells from attacking other cells with self-antigens.
What role to self-Antigens / MHC markers play?
All cells within an organism
On what cells can you find Class 1 MHC markers?
Special white blood cells: T cells and B cells
On what cells can you find Class 2 MHC markers?
Any molecule that can initiate an immune response
Any molecule (or part of a molecule) that can stimulate a specific immune response, namely the production of antibodies.
All Antigens are Immunogens, but not all immunogens are antigens
What's the relationship between Antigens and Immunogens?
A type of antigen that produces an abnormally vigorous immune response to a perceived threat that would normally be harmless to the body.
An antigen which produces an abnormal immune response, typically producing antibodies that attack an organisms own cells (autoantibodies). Typically results in autoimmune diseases.
What are auto-antigens?
A biological agent that causes disease or illness to its host
What is a pathogen?
An infection is just the process of a pathogen gain entry to an organism and multiply. Disease is the effects resulting from damage caused by the pathogen.
What the difference between an infection and a disease?
Name 4 cellular pathogens
Name 2 non-cellular pathogens
- Single celled Eukaryotic organisms
- Usually transmitted via a host or by drinking infected water
- DNA or RNA that encodes specific proteins once inside a host cell
- Self-replicating genetic material
What living features do Viruses possess?
- No metabolic activity
- Cannot reproduce independently
What non-living features do Viruses possess?
A protein shell, known as a caspid, surrounding the genetic material.
What simple non-cellular structure do all Viral particles include?
Infectious particles made of protein lacking nucleic acids - Prions are 'self proteins', so the body does not react against them.
What are Prions?
Physical and chemical barriers preventing pathogens from gaining entry into the body. INNATE.
What is the first line of immune defence?
Immune cells non-specific attack against pathogens gaining entry to the body. INNATE.
What is the second line of immune defence?
Specific attacks from immune cells and antibodies tailored to attack each invading pathogen. ADAPTIVE. Only comes into operation if second line of defence fails.
What is the third line of immune defence?
Inflammatory responses by secreting various cytokines
What do Macrophages initiate?
1) Pathogen identified by receptor and is engulfed
2) Pathogen is completely enclosed in a vesicle
3) Lysosomes fuse with the Phagosome and release toxic chemicals
4) Pathogen undergoes digestion
5) Indigestible material is discarded via exocytosis
Describe the process of phagocytosis
Multi-lobed nuclei that are the first to arrive at an infection site and identify non-self cells.
What are Neutrophils?
- Border guards
- Releases signal attracting other immune cells to infection site
- Involved in acute inflammatory response
- Contains granules rich in histamine and heparin
- Found in tissues close to external environments
What are Mast cells?
- Acts as an antigen presenting cells in lymph nodes
- Mobile cells that identify pathogens and secrete antiviral cytokines
- Migrates via lymphatic vessels
- Found in tissues, mainly skin epidermis, lining of airways and gut
What are Dendritic cells?
- Recognise and attack cells lacking a MHC self marker
- Degranulation releases proteases and perforin proteins, which insert holes in the plasma membrane of foreign cells or self infected cells
- Induces Apoptosis
What are Natural Killer cells?
The release of granules filled with anti-microbial and toxic molecules into target cells (e.g. pathogens or infected self cells)
What is Degranulation?
1) Released perforin molecules molecules make hole in plasma membrane of target cell
2) Proteases enter target cell and induce apoptosis
Describe the process of Degranulation
Proteins that 'interfere' with viral replication and signal to nearby cells to prepare for possible viral infection.
What are interferons?
- Induce transcription of a number of genes that encode production of inactive forms of antiviral enzymes that inhibiting protein synthesis and destroying RNA
- Make the plasma membrane less fluid
- Cause virus-infected cells to undergo apoptosis
- Activate immune cells, such as Natural Killer cells that eliminate infected cells by apoptosis.
Describe the functions of interferons
1st Stage: Vascular Stage -> Involves changes to the blood vessels
2nd Stage: Cellular stage -> involves actions of various immune cells
3rd Stage: Resolution stage -> Switches off the inflammatory response
What are the three stages of inflammatory response?
1) Bacteria enters body via a cut
2) Blood clots form
3) Histamines released by damaged cells attract phagocytes
4) Blood vessels increase in diameter and permeability in area of damage. Allows defensive substances to leak into tissue spaces.
5) Phagocytes reach damaged area within 1 hour of injury.
6) Abscess starts to form after a few days. This is a collection of dead phagocytes, damaged tissue and various body fluids. AKA Pus.
Give an example of what happens during an inflammatory response
- Dilation of blood vessels
- Increased permeability of local capillaries
What key processes occur in the vascular stage of inflammatory response?
- Escape of immune cells from capillaries
- Migration of neutrophils to infection site
- Phagocyte attack on bacteria
What key processes occur in the cellular stage of inflammatory response?
- Infection presence -> pro-inflammatory cytokines released
- Resolution: Reversal of all the processes that produced acute inflammation
> Reversal of capillary dilation
> Cessation of release of pro-inflammatory cytokines
> Release of anti-inflammatory cytokines and resolvin and protectin lipids
What key processes occur in the resolution stage of inflammatory response?
- Chronic inflammation
- Damaging to body
- Cause of several diseases
> Ulcerative colitis
> Rheumatoid arthritis
What happens if the inflammatory response does not resolve?
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