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HNC Applied Science in Biology and Chemistry > Cell Biology- Outcome 3 > Flashcards

Cell Biology- Outcome 3 Flashcards

Cellular Communication

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1
Q

what factors must be regulated and monitored to regulate a cells internal environment

A
  • nutrition
  • hormone regulation (temperature, metabolism)
  • excretion of waste and toxins
  • repair when damaged
  • identification
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2
Q

what are different ways of cells communicating?

A
  • directly with adjacent cells
  • different mechanisms with cells over a large distance
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3
Q

what are eukaryotic cells separated by?

A

extracellular matrix

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4
Q

what is an example of when cells are pressed together?

A

epithelia tissue

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5
Q

what are examples of junctions between animal cells?

A
  • desmosomes
  • tight junctions
  • gap junctions
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6
Q

describe desmosomes

A
  • 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
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7
Q

how do desmosomes form links between cells and what protein is involved in this?

A
  • through connecting intermediate filaments of the cytoskeleton
  • can be further linked by a family of proteins known as cadherins
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8
Q

how are desmosomes arranged?

A

they are localised along the cell membrane in areas known as plaques

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9
Q

what is the function of desmosomes?

A

to provide strength and stability

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10
Q

where are desmosomes found?

A

in cells subject to stress such as epithelia and cardiac tissue
- where stress can be communicated / shared between cells

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11
Q

what is the function of a tight junction?

A

not directly involved in cellular communication - function as a ‘sealing junction’

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12
Q

what do tight junctions form and what is the effect?

A

leak-proof seal between cells so that material has to enter the cell through transport mechanism

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13
Q

how are the membrane proteins which form at tight junctions arranged?

A

arranged like beads on a string that span the adjacent membranes of each thigh junction

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14
Q

what are examples of cells where tight junctions are found?

A

intestinal cells and bladder cells

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15
Q

describe the composition of gap junctions

A
  • 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
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16
Q

how is a gap junction formed?

A

when 2 connexons from adjacent cell membranes ‘dock’ together then a gap junction is formed

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17
Q

what is the function of a gap junction?

A
  • 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
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18
Q

what do gap junctions allow?

A
  • rhythmic contraction of the heart
  • neurones to communicate impulses
  • during labour - gap junction between smooth muscle allow passage of ions and therefore contractions occur
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19
Q

what is an example of a junction that allows communication between adjacent plant cells?

A

plasmodesmata

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20
Q

describe the arrangement of plasmodesmata and explains what this allows

A
  • 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

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21
Q

what is cytoplasmic streaming?

A

where the cytoplasms of neighbouring cells are linked and so allows exchange of small molecules between cytoplasm of both cells

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22
Q

how can the streaming of molecules in cytoplasmic streaming be regulated?

A

by constricting or dilating the openings at each end of the channel

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23
Q

when do cells use extracellular signalling mechanisms?

A

when cells are located at a significant distance away from each other

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24
Q

what are the tree main stages of cellular signalling?

A

reception, signal transduction, response

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25
Q

describe what happens during the reception stage of cellular signalling

A
  • target cell possesses a receptor molecule on its cell membrane which receives signal and converts it into response
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26
Q

what is a signal molecule called and what is its function?

A
  • called a ligand
  • can bind and activate a receptor molecule on the target cell membrane
  • ligand and receptor are a complimentary fit
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27
Q

what is a ligand said to be and what may it be?

A
  • 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
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28
Q

describe what happens during the signal transduction stage of cellular signalling

A
  • 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
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29
Q

what are examples of second messengers during the signal transduction stage?

A
  • cyclicAMP (cAMP)
  • calcium
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30
Q

describe what happens during the response stage of cellular signalling

A
  • 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
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31
Q

what are the two different forms of distance signalling?

A

chemical signalling and electrical signalling

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32
Q

what are examples of chemical signalling?

A

insulin signalling and growth hormone signalling

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33
Q

what is chemical signalling?

A

chemical messengers are released by specialised cells and have an effect on the target cell

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34
Q

what is an example of a chemical messenger?

A

any hormone

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35
Q

explain what happens during insulin signalling

A
  • 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
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36
Q

explain what happens during growth hormone signalling

A
  • 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
37
Q

what cells carry out electrical signalling?

A

neurons

38
Q

what are the function of neurones?

A

specialised cells which are capable of transmitting an electrical impulse either to another neurone cell, a muscle cell or endocrine cell

39
Q

what are the function of dendrites?

A

receives electrical signals from receptors

40
Q

what is the function of the cell body?

A

control centre contains nucleus ribosomes and most of the cytoplasm

41
Q

what is the function of the axon?

A
  • propagates signal to synaptic knobs
  • may be myelinated or unmyelinated
42
Q

what is the function of the synaptic terminal?

A

transmit signal via neurotransmitter

43
Q

what is the synapse?

A

functional region between adjacent neurones

44
Q

what is the synaptic cleft?

A

gap between one neurone and another

45
Q

what is the neuro-effector junction?

A

area between motor neurone effecter

46
Q

what is the pre-synaptic neurone?

A

neuron before gap

47
Q

what is the post-synaptic neurone?

A

neurone after gap

48
Q

what happens during electrical signalling?

A
  • 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
49
Q

what is THRESHOLD?

A

where a minimum number of neurotransmitters have to be released and hence post-synaptic receptors are activated in order to reach THRESHOLD

50
Q

what happens if threshold is reached?

A

target cell will be activated and response will be appropriate to cell type

51
Q

what happens at the point of threshold?

A
  • electrical stimuli will change electrical charge of cell membrane
  • this has an effect on membrane proteins (ion channels)
  • triggers action potential
52
Q

describe what happens during the FIRST HALF of action potential

A

depolarisation occurs
- electrical stimuli causes Na+ channels to open
- Na+ move into cell (positive charge)
- resultant change in potential: negative to positive

53
Q

describe what happens during the SECOND HALF of action potential

A

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)

54
Q

what is summation?

A

when many weak signals can have a cumulative effect and eventually reach threshold level where an action potential will be triggered

55
Q

what are two neurotransmitters that are an example of electrical signalling and how do they work?

A
  • noradrenaline and acetylcholine
  • they antagonise each other in function
56
Q

what is an example of chemical AND electrical signalling?

A

anti-diuretic hormone

57
Q

what is anti-diuretic hormone (ADH)?

A

a hormone which helps to regulate water balance in the body (osmoregulation)

58
Q

where is ADH stored and synthesised?

A
  • stored in posterior pituitary gland
  • synthesised in the hypothalamus
59
Q

what are osmoreceptors?

A

receptors located in the hypothalamus that detect changes to the osmolarity (solute content) of the blood

60
Q

what happens when osmolarity is low (low solute, high water)?

A
  • osmoreceptors are not activated
  • secretion of anti-diuretic hormone is suppressed
61
Q

what happens when the osmolarity is increased (high solute, low water)?

A
  • 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
62
Q

what happens when the water concentration of blood is very high in terms of the kidneys?

A
  • 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
63
Q

what happens when the water concentration of the blood is low in terms of the kidneys?

A
  • kidney tubules become more permeable
  • lots of water is reabsorbed into bloodstream
  • results in a small volume of concentrated urine being produced
64
Q

how can the osmoregulation pathway be triggered and what is the target response?

A
  • by baroreceptors sensing changes to blood pressure
  • response is to vasoconstriction blood vessels to increase blood pressure
65
Q

where can signalling errors occur in a pathway?

A
  • if the ligand is absent/mutated
  • is the receptor is absent/mutated/desensitised
  • if the cellular response is incorrect
66
Q

what is receptor affinity?

A

a term that describe the binding of a ligand to its receptor

67
Q

what happens if a ligand has high affinity?

A

ligand binds tightly to receptor

68
Q

what happens if a ligand has low affinity?

A

ligand doesn’t bind as strongly to the receptor

69
Q

what is internalisation?

A

where receptors can be removed from the cell membrane

70
Q

what are the fate of receptors that undergo internalisation?

A
  • 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
71
Q

what happens in type 1 diabetes?

A
  • 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
72
Q

what secondary complications and diseases can diabetes lead to over time?

A
  • heart disease
  • high blood pressure
  • nerve damage
  • kidney damage
  • eye and foot problems
73
Q

what are symptoms of type 1 diabetes?

A
  • increased urination
  • thirst
  • weight loss
  • fatigue
  • nausea
  • wounds taking longer to heal
  • blurred vision
74
Q

what are the treatments for type 1 diabetes?

A
  • 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
75
Q

what happens in type 2 diabetes?

A
  • 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
76
Q

what are symptoms of type 2 diabetes?

A
  • increased urination
  • thirst
  • weight loss
  • fatigue
  • nausea
  • wounds taking longer to heal
  • blurred vision
77
Q

what are the treatments for type 2 diabetes?

A

lifestyle changes and dietary control

78
Q

what is pituitary dwarfism a result of and what is this due to?

A
  • 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
79
Q

what are symptoms of pituitary dwarfism?

A
  • 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
80
Q

what is the treatment for pituitary dwarfism?

A
  • growth hormone replacement therapy
  • synthetic growth hormone administrated by injection maybe several times a week
81
Q

what is Parkinsonism?

A

a progressive deterioration of nerve cells in the substantia nigra

82
Q

what chemical messenger do the neurones in the substantia nigra produce?

A

dopamine

83
Q

what area in the brain do the neurones in the substantia nigra communicate with ?

A

corpus striatum

84
Q

what chemical messenger do the neurones in the corpus striatum produce?

A

acetylcholine

85
Q

what does communication between the corpus striatum and substantia nigra allow?

A

co-ordination of movement

86
Q

what happens under normal circumstances in muscle movement co-ordination?

A
  • 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
87
Q

what happens in Parkinson’s disease?

A
  • 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
88
Q

what are symptoms of Parkinsonism?

A
  • tremors
  • slow movements
  • rigidity
  • anxiety
  • memory problems
  • speech and communication problems
89
Q

what are treatments for Parkinsonism?

A

-drug therapy to boost levels of dopamine - levodopa and dopamine agonists

  • drug therapy to reduce activity of acetylcholine - anticholinergics

HNC Applied Science in Biology and Chemistry (6 decks)

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