cell communication Flashcards
effector cells
respond to signalling molecules
what are the modes of transmission of signalling molecules?
Autocrine signalling:
Signalling molecules act on the cell that secreted them
Paracrine signalling:
Signalling molecules act on cells that are close to the secreting cell
Endocrine signalling:
Signalling molecules act of cells that are far away from the cell that secretes them.
animals hormones source, modes, hydrophilic/hydrophobic
source:
glands and organs
mode:
Autocrine
Paracrine- interstitial fluid between cells
Endocrine- via bloodstream
hydrophobic or hydrophilic:
“Hydrophobic steroid hormones
Hydrophilic peptide hormones
hydrophobic or hydrophilic amino-acid-derived hormones”
plant hormones source, modes, hydrophilic/hydrophobic
source:
Most plant cells are capable of producing a variety of them
mode:
Various including diffusion
hydrophobic or hydrophilic
Hydrophobic or hydrophilic phytohormones
neurotransmitters source, modes, hydrophilic/hydrophobic
source:
neurons
mode:
Paracrine- exocytosis into the synapse
hydrophobic or hydrophilic:
hydrophilic
cytokines source, modes, hydrophilic/hydrophobic
source:
Immune cells such as macrophages, B- and T-lymphocytes and mast cells
mode:
“Autocrine
Paracrine
Endocrine “
hydrophobic or hydrophilic:
hydrophilic
pheromones source, modes, hydrophilic/hydrophobic
source:
various cells
mode:
Communication between organisms by diffusion outside the organism
hydrophobic or hydrophilic:
“Hydrophobic pheromones
Hydrophilic pheromones “
what is a hormone? what properties does it have? what does it do?
Signalling molecule
Produced in tiny amounts
Long-lasting effect on target cells
Regulate growth and activity
what do animals hormones do? where do they come from?
Growth, metabolism, reproduction
Glands and organs that along with some tissues synthesis and secrete hormones into the bloodstream
Main glands and organs: pineal gland, hypothalamus, pituitary gland etc.
what are the three classes of animal hormone?
Lipid hormones: from fatty acids or cholesterol, hydrophobic, eg: testosterone, oestrogen, cortisol
Peptide and protein hormones: hydrophilic, peptide hormone: insulin, protein hormone: growth hormone
Amino-acid-derived hormones: hydrophobic or hydrophilic, eg: thyroxine, dopamine
abscisic acid: source, effector site, effects
From leaves (chloroplasts) and roots
Effector site: seeds, buds, guard cells, leaves and fruit
Transported in the xylem from roots and phloem from leaves
effects: seeds and bud dormancy, drought tolerance and apical dominance
auxins: source, effete site, transport, effect
source: shoot tip, seeds
Effector site: growing region of shoots and roots, developing fruit
Transported from cell to cell usually from shoots to roots
Effects: shoot tips towards light (phototropism), roots grow downwards (gravitropism), apical dominance
cytokinins: source, effete site, transport, effect
source: roots and developing fruits
Effector site: branch and leaf buds
Transported in xylem
Effect: growth of material branches
ethene: source, effete site, transport, effect
source: ripening fruits and other parts of plant
Effector site: most cells
Diffusion (it is a gas)
Effect: increase sugar content in fruit, fruit and leaf drop
gibberellins: source, effete site, transport, effect
Source: root and shoot apical meristems, growing leaves and seeds
Effector site: meristems, leaves, seeds and flowers
Usually used by the cell that made it or moved cell-to-cell by xylem and phloem
Effect: elongation of stems, leaf expansion, seed germination, fruit and flower maturation
how are bones made strong or weak?
Pressure one bones causes them to become thicker
Take pressure off bones, causes calcium to be reabsorbed into circulation
Calcitonin adds to bone’s calcium
Parathyroid hormone removes from bone’s calcium
where is the pituitary gland? what does it do? what does the hypothalamus do and how do they work together?
Base of brain
‘master gland’- produces many of the body’s hormones
Involved in growth, reproduction, lactation, kindness function, skin pigmentation, regulation of adrenal and thyroid glands etc.
Hypothalamus detects stimuli and monsters homeostasis.
Hypothalamus regulates hormone production from pituitary gland
Together, they maintain homeostasis
are neurotransmitters hydrophilic or hydrophobic? where are they released? where are the made? want do they do? what are examples?
Hydrophilic
Secreted by neurones
Produced in synaptic terminals
Paracrine signalling
Secreted into the synapse
Electrical signal stimulates the release
Neurotransmitters diffuse and bind to receptors on the other side
Cause a transmission of electrical impulse
Involved in movement
Examples are dopamine, serotonin etc.
are cytokines hydrophilic or hydrophobic? what do they do? where are they released? what are some examples? where do they bind? mode?
Hydrophilic
Communication between immune cells
Coordinate aspects of the immune response
Released in response to damage or pathogens
Sources include macrophages, T lymphocytes and lymphocytes
Some cytokines such as interferons and interleukins regulate inflammation and immune responses to infection
Bind to target cell surface
Involved in paracrine or autocrine signalling
where are pheromones secreted? what do they do?
Excreted into the external environment
Influence behaviour and physiology of an individual (usually the same species)
Trigger alarm and aggressive responses, marking territory, marking food trails and attracting mates
how can pheromones be involved in insect control?
Flood crops with female pheromone which confuses males and makes mating hard
Not harmful to environment
Target more specifically
Insects cannot develop a resistance to them
what is signal transduction?
converting the original stimulus signal into a response.
what is the signal response model? what are the steps?
A way of considering signal transduction
steps:
Reception- detection of signalling molecule by receptor
Transduction- the relay of the signal in the cell
Cellular response- the activation of cellular response
what is reception? where are receptors? what are features of receptors?
Detection of signalling molecule
Receptors on the membrane, in the cytosol or in the nucleus (depends on hydrophobic or hydrophilic)
Receptors are specific for certain molecules (complementary)
what is transduction? how many steps?
Converting the signal into a form that can be relayed to its final destination (for a response) Can be single step (bind to receptor and produce response) Multi step (cascades)
what is the cellular response? where?
Gene expression, activation of enzymes, secretion of signalling molecules
Occur in the nucleus, cytosol and membrane
what is signal transduction of hydrophobic signalling molecules?
Hydrophobic are usually lipid-based eg. Steroids
Ones that enter nuclear pores act as transcription factors
what is signal transduction of hydrophilic signalling molecules?
Peptide hormones, neurotransmitters and cytokines
where are hydrophilic molecules reception?
Unable to diffuse through the membrane
Bind to receptors on the exterior (transmembrane proteins)
what is transduction of hydrophilic? what kind of response?
Intracellular domain of transmembrane protein which transfers the signal into the cell
Intracellular part changes shape which activates molecules inside the cell (cellular response)
Direct response
Indirect response activates such as second messengers or G proteins or both
what are secondary messengers of transduction for hydrophilic?
Small Non-proteins
Usually Water-soluble
Easily move through the cytosol, triggering and amplifying responses
what are transduction cascades (transduction of hydrophilic)?
Transduction cascades: series of events in which a change in one molecule causes a change in another, etc.
Molecules may be enzymes, channel proteins, of cell structure proteins
A signalling molecule may cause different responses in different cell types:
Different receptors for the same molecule may activate different cascades
Proteins can be specific to only some cells and will lead to specific responses in only those cells
Signalling molecules in low concentrations
Cascade allows for amplification or that signal leading to enough response molecules for that cell
what are G proteins (transduction of hydrophilic)
Intracellular protein
Coupled with receptors on the membrane
When activated the cause activity of proteins such as enzymes and are often second messengers to relay signals
what are cellular responses for hydrophilic?
Responses in the nucleus
Signalling molecule triggers gene expression
Causes gene regulation (only made when needed)
Cascade results in a functional transcription factor
Responses in the cytosol
Inhibition or activation of enzymes in the cytosol
Responses on the plasma membrane
Allow certain things to enter and exit
Ion channels
Type of transmembrane protein
Allow ions in or out
Can be opened or closed by signalling molecules
signal transduction in a neuron?
Neuron stimulates, gate opens, potassium and sodium enter and action potential is initiated
Action potential moves along the axon and opens other gates
cellular response in a neutron?
Action potential reaches terminals which causes calcium ion to enter
Increased calcium causes vesicles to fuse with membrane and expel neurotransmitters
what is apoptosis?
Apoptosis: programmed cell death, self-destruction, regulates number of cells.
how Is apoptosis triggered? reasons? what does caspases do?
Apoptosis is receptor-mediated
Triggered by signalling molecules inside or outside of the cell
Reasons: cell ageing, cell obsolescence (cell no longer needed), damaged DNA
Enzyme called caspases are responsible for apoptosis
Caspases are produced and stores as inactive precursors
Binding of a signalling molecule activates the caspases precursor
Caspase stimulates the activation of other caspases which leads to cell death
Caspase-3 is a protease that causes fragmentation of actin filaments in the cytoskeleton and inactivates DNA repair
Caspase-3 causes a cascade in apoptosis
Caspase-3 causes neurone death in Alzheimer’s
what are the roles of caspases? can these processes be reversed?
Cleaved of DNA into characteristic fragments
Cleavage of proteins in the nuclear membrane
Degradation of nuclear proteins leading to condensation of chromatin
Dismantling cytoskeleton causing protrusion of membrane (bleb)
Breakdown of proteins in cytosol
Breakdown and fragmentation of organelles
Once triggered, apoptosis cannot be stopped or reversed.
what are major steps of apoptosis?
Separation from adjacent cells
Collapse of cytoskeleton
Cell shrinkage
Breakdown of organelles and nucleus
Blebbing of plasma membrane
Budding of plasma membrane bound vesicles (apoptotic bodies) which prevent toxic or immunogenic substances from leaking when a-optic bodies are phagocytosed
Phagocytosis of apoptotic bodies by specialised cells (usually macrophages) without spilling contents or triggering an inflammatory response
what is necrosis?
Cells may be damaged by injury, infection, toxins or loss of blood supply
Cells lyse or spill contents, triggering an inflammatory immune response
Accidental
what are the pathways of apoptosis?
intrinsic or mitochondrial and extrinsic
how does intrinsic pathway work?
Signal for apoptosis from inside cell
Damage by radiation, viral infections, toxins or damaged DNA
Stimulate transcription and translation of genes into proteins (signalling molecules) that activate the mitochondrial pathway
what are the Bel-2 proteins in the intrinsic pathway?
Control mitochondrial apoptosis
Promote (pro-)
Inhibit (anti-)
To promote, they relocate from the cytoplasm to to the surface of the mitochondria
Pores open and release cytochrome c (involved in electron transport chain) into the cytoplasm
Cytochrome c forms a complex (apoptosome) with protein Apaf-1 (apoptotic protease activating factor)
Apoptosome activates a cascade of caspases causing apoptosis
what is the extrinsic pathway of death receptor pathway?
From outside the cell
Transmembrane proteins called death receptors (specific to different cytokines)
Bind to death receptor, signal transduction in the cell which initiates a cascade of caspase that leads to apoptosis
excess apoptosis?
Can cause degenerative diseases such as alzheimers, Parkinson’s and motor neurone disease
inhibited apoptosis?
Example is when skin between fingers is not removed (syndactyly)
cancer
Unregulated and abnormal cell growth and division
Caused by increased rate of division or suppression of apoptosis
Growth of tumours
cancer: B-cell lymphoma
Excessive amounts of anti-apoptotic Bel-2 proteins are produced
No cytochrome c released, so no apoptosomes
Mutated B cells cannot be removed and replicate, forming cancer
Occurs most in the spleen and lymph nodes and can spread to liver and bone marrow
other defects that cause cancer?
Mutations in caspases that stops them functioning
Defects in Apaf proteins that prevent apoptosomes forming
what is the tumour suppressor gene, p53?
Some mutations are detected and repaired by enzymes in the nucleus
Tumour suppressor proteins are found in the cell cycle and check for damaged DNA
If it cannot be fixed, apoptosis happens
Mutations in tumour suppressor genes such as tumour suppressor 53 can cause many cancers
