Cell Biology- Outcome 3 Flashcards
Cellular Communication
what factors must be regulated and monitored to regulate a cells internal environment
- nutrition
- hormone regulation (temperature, metabolism)
- excretion of waste and toxins
- repair when damaged
- identification
what are different ways of cells communicating?
- directly with adjacent cells
- different mechanisms with cells over a large distance
what are eukaryotic cells separated by?
extracellular matrix
what is an example of when cells are pressed together?
epithelia tissue
what are examples of junctions between animal cells?
- desmosomes
- tight junctions
- gap junctions
describe desmosomes
- localised patches that hold 2 cells together
- act like rivets and are also known as anchoring junctions
- tightly joined but there are still gaps between them
how do desmosomes form links between cells and what protein is involved in this?
- through connecting intermediate filaments of the cytoskeleton
- can be further linked by a family of proteins known as cadherins
how are desmosomes arranged?
they are localised along the cell membrane in areas known as plaques
what is the function of desmosomes?
to provide strength and stability
where are desmosomes found?
in cells subject to stress such as epithelia and cardiac tissue
- where stress can be communicated / shared between cells
what is the function of a tight junction?
not directly involved in cellular communication - function as a ‘sealing junction’
what do tight junctions form and what is the effect?
leak-proof seal between cells so that material has to enter the cell through transport mechanism
how are the membrane proteins which form at tight junctions arranged?
arranged like beads on a string that span the adjacent membranes of each thigh junction
what are examples of cells where tight junctions are found?
intestinal cells and bladder cells
describe the composition of gap junctions
- specialised areas of the cell membrane connecting the cytoplasm of adjacent cells
- intracellular chancels made up of 4 transmembrane protein called connexins
- 6 connexins make up a connexon channel
how is a gap junction formed?
when 2 connexons from adjacent cell membranes ‘dock’ together then a gap junction is formed
what is the function of a gap junction?
- allows passage of ions and small molecules such as amino acids and sugars (means they don’t have to go through plasma membrane)
- because ions can flow through the junction - allows changes in membrane potential from cell to cell
what do gap junctions allow?
- rhythmic contraction of the heart
- neurones to communicate impulses
- during labour - gap junction between smooth muscle allow passage of ions and therefore contractions occur
what is an example of a junction that allows communication between adjacent plant cells?
plasmodesmata
describe the arrangement of plasmodesmata and explains what this allows
- cylinder-like bridges connecting one cell with another
- bridge links the cell walls and is actually lined by plasma membrane
-cytoplasms of neighbouring cells are linked - allows exchange of small molecules such as salt, sugars and amino acids between the cytoplasm of both cells
what is cytoplasmic streaming?
where the cytoplasms of neighbouring cells are linked and so allows exchange of small molecules between cytoplasm of both cells
how can the streaming of molecules in cytoplasmic streaming be regulated?
by constricting or dilating the openings at each end of the channel
when do cells use extracellular signalling mechanisms?
when cells are located at a significant distance away from each other
what are the tree main stages of cellular signalling?
reception, signal transduction, response
describe what happens during the reception stage of cellular signalling
- target cell possesses a receptor molecule on its cell membrane which receives signal and converts it into response
what is a signal molecule called and what is its function?
- called a ligand
- can bind and activate a receptor molecule on the target cell membrane
- ligand and receptor are a complimentary fit
what is a ligand said to be and what may it be?
- ligand said to be first messenger
- ligand may be a hormone which has been secreted in one part of the body and travel to another organ to perform its function
describe what happens during the signal transduction stage of cellular signalling
- binding of ligand results in conformational change in receptor
- change in shape of receptor triggers intracellular events leading to production of second messengers which amplify the signal
what are examples of second messengers during the signal transduction stage?
- cyclicAMP (cAMP)
- calcium
describe what happens during the response stage of cellular signalling
- cellular response depends on signalling molecule and the function of the target cell
- response may be:
Gene Regulation
Inactive to active enzyme
Enzyme Catalysis
Muscle cell contraction
Growth & developmental of the cell
what are the two different forms of distance signalling?
chemical signalling and electrical signalling
what are examples of chemical signalling?
insulin signalling and growth hormone signalling
what is chemical signalling?
chemical messengers are released by specialised cells and have an effect on the target cell
what is an example of a chemical messenger?
any hormone
explain what happens during insulin signalling
- insulin is secreted from Beta cells in the pancreas
- insulin travels through bloodstream and reaches many target cells such as
hepatocytes
muscle cells
brain cells
adipocytes
macrophages - each target cell will have receptor protein which is complimentary to shape of insulin
- once receptor is activated it will initiate a signalling cascade where response will be open to glucose channel - allows entry of glucose inside cell and effectively remove glucose from bloodstream
explain what happens during growth hormone signalling
- release of growth hormone from anterior pituitary gland is under control of hypothalamus
- target cells may be liver as well as cartilage, bone and muscle cells and adipocytes
- response in target cells is o stimulate cell growth and division
- at cellular level this can lead to
actin rearrangement
increased glucose metabolism
increase protein synthesis
what cells carry out electrical signalling?
neurons
what are the function of neurones?
specialised cells which are capable of transmitting an electrical impulse either to another neurone cell, a muscle cell or endocrine cell
what are the function of dendrites?
receives electrical signals from receptors
what is the function of the cell body?
control centre contains nucleus ribosomes and most of the cytoplasm
what is the function of the axon?
- propagates signal to synaptic knobs
- may be myelinated or unmyelinated
what is the function of the synaptic terminal?
transmit signal via neurotransmitter
what is the synapse?
functional region between adjacent neurones
what is the synaptic cleft?
gap between one neurone and another
what is the neuro-effector junction?
area between motor neurone effecter
what is the pre-synaptic neurone?
neuron before gap
what is the post-synaptic neurone?
neurone after gap
what happens during electrical signalling?
- electrical impulse will pass along axon and reach synaptic terminals
- neurotransmitters are packaged in vesicles at synaptic terminals
- electrical impulse mobilises the vesicles to move towards cell membrane and releases neurotransmitters into synaptic cleft (exocytosis)
- neurotransmitter crosses cleft and reaches receptor on post-synaptic neuron
what is THRESHOLD?
where a minimum number of neurotransmitters have to be released and hence post-synaptic receptors are activated in order to reach THRESHOLD
what happens if threshold is reached?
target cell will be activated and response will be appropriate to cell type
what happens at the point of threshold?
- electrical stimuli will change electrical charge of cell membrane
- this has an effect on membrane proteins (ion channels)
- triggers action potential
describe what happens during the FIRST HALF of action potential
depolarisation occurs
- electrical stimuli causes Na+ channels to open
- Na+ move into cell (positive charge)
- resultant change in potential: negative to positive
describe what happens during the SECOND HALF of action potential
depolarisation occurs
- initiated after peak depolarisation (+35mV)
- Na+ channels close and K+ channels open
-K+ ions move down concentration gradient out of cell
- cell becomes more negative and approaches RMP
- depolarisation occurs for longer due to K+ pumps taking longer to close (hyperpolarisation)
what is summation?
when many weak signals can have a cumulative effect and eventually reach threshold level where an action potential will be triggered
what are two neurotransmitters that are an example of electrical signalling and how do they work?
- noradrenaline and acetylcholine
- they antagonise each other in function
what is an example of chemical AND electrical signalling?
anti-diuretic hormone
what is anti-diuretic hormone (ADH)?
a hormone which helps to regulate water balance in the body (osmoregulation)
where is ADH stored and synthesised?
- stored in posterior pituitary gland
- synthesised in the hypothalamus
what are osmoreceptors?
receptors located in the hypothalamus that detect changes to the osmolarity (solute content) of the blood
what happens when osmolarity is low (low solute, high water)?
- osmoreceptors are not activated
- secretion of anti-diuretic hormone is suppressed
what happens when the osmolarity is increased (high solute, low water)?
- osmoreceptors stimulate the neuron’s of the hypothalamus
- electrical signals from neurons then stimulates the posterior pituitary gland to release ADH into bloodstream
- response from target cells is to cause kidney tubules to become more permeable and increase water reabsorption
what happens when the water concentration of blood is very high in terms of the kidneys?
- very little ADH is produced by pituitary gland
- almost no water is reabsorbed in distal convoluted tubule and collecting duct
- produces a large volume of dilute urine
what happens when the water concentration of the blood is low in terms of the kidneys?
- kidney tubules become more permeable
- lots of water is reabsorbed into bloodstream
- results in a small volume of concentrated urine being produced
how can the osmoregulation pathway be triggered and what is the target response?
- by baroreceptors sensing changes to blood pressure
- response is to vasoconstriction blood vessels to increase blood pressure
where can signalling errors occur in a pathway?
- if the ligand is absent/mutated
- is the receptor is absent/mutated/desensitised
- if the cellular response is incorrect
what is receptor affinity?
a term that describe the binding of a ligand to its receptor
what happens if a ligand has high affinity?
ligand binds tightly to receptor
what happens if a ligand has low affinity?
ligand doesn’t bind as strongly to the receptor
what is internalisation?
where receptors can be removed from the cell membrane
what are the fate of receptors that undergo internalisation?
- to be destroyed by lysosome degradation or to be recycled by endocytosis
- if receptor not on cell surface then they cannot detect ligand
- no signalling cascade triggered and no cellular response
what happens in type 1 diabetes?
- body cannot store and use fuel in the form of glucose for energy
- to utilise glucose the body requires the hormone insulin
- body self-destructs its own pancreatic β-cells that make and secrete insulin
- in absence of ligand signalling pathway doesn’t get switched on
- if no signalling pathway activated, no activation of glucose transporter at cell membrane
- as a result, cells are starved of energy, glucose remains circulating in blood stream and individual becomes hyperglycaemic
what secondary complications and diseases can diabetes lead to over time?
- heart disease
- high blood pressure
- nerve damage
- kidney damage
- eye and foot problems
what are symptoms of type 1 diabetes?
- increased urination
- thirst
- weight loss
- fatigue
- nausea
- wounds taking longer to heal
- blurred vision
what are the treatments for type 1 diabetes?
- insulin therapy either by injection using a syringe or insulin pen with prefilled insulin cartridge
- insulin pumps may also be used which are linked to a catheter under skin of abdomen
what happens in type 2 diabetes?
- pancreatic β-cells are functioning normally and are secreting insulin
- error in signalling pathway is that receptor no long responds to insulin
- receptor became desensitised to insulin due to persistent over exposure and stimulation
- no signalling pathway switched on, no activation of glucose transporter
- blood glucose levels remain high and individual becomes hyperglycaemic
what are symptoms of type 2 diabetes?
- increased urination
- thirst
- weight loss
- fatigue
- nausea
- wounds taking longer to heal
- blurred vision
what are the treatments for type 2 diabetes?
lifestyle changes and dietary control
what is pituitary dwarfism a result of and what is this due to?
- deficiency of growth hormone
- due to anterior pituitary gland failing to produce enough hormone
- lack of ligand to activate signalling pathway which stimulates cellular, tissue and bone growth
what are symptoms of pituitary dwarfism?
- proportional dwarfism - arm and lim sizes are proportional for height
- height below third percentile on SPGC
- growth rate slower than expected for age
- delayed or no sexual development during adolescence
what is the treatment for pituitary dwarfism?
- growth hormone replacement therapy
- synthetic growth hormone administrated by injection maybe several times a week
what is Parkinsonism?
a progressive deterioration of nerve cells in the substantia nigra
what chemical messenger do the neurones in the substantia nigra produce?
dopamine
what area in the brain do the neurones in the substantia nigra communicate with ?
corpus striatum
what chemical messenger do the neurones in the corpus striatum produce?
acetylcholine
what does communication between the corpus striatum and substantia nigra allow?
co-ordination of movement
what happens under normal circumstances in muscle movement co-ordination?
- muscle movement brought about by acetylcholine stimulating muscle cells
- if acetylcholine released constantly, muscles move all the time
- dopamine inhibits acetylcholine release
- as a result balancing act between neurotransmitters which ensure co-ordinated smooth muscle movement
what happens in Parkinson’s disease?
- little/no dopamine produced due to death of neuron’s in substantia nigra
- acetylcholine release is left unchecked
- means smooth control of muscle is lost and symptom of tremors develop
what are symptoms of Parkinsonism?
- tremors
- slow movements
- rigidity
- anxiety
- memory problems
- speech and communication problems
what are treatments for Parkinsonism?
-drug therapy to boost levels of dopamine - levodopa and dopamine agonists
- drug therapy to reduce activity of acetylcholine - anticholinergics
