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Year 12 Biology > 6. Cellular Signals > Flashcards

6. Cellular Signals Flashcards

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1
Q

Why do cells communicate?

A

Cells need to communicate with each other and responds to changes within their own intracellular fluid.
Cells need to maintain homeostasis to ensure that factors within the internal environment are maintained within narrow limits.

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2
Q

What characteristics do all signalling molecules share?

A
  • bind to sites on specific receptions on their target cells
  • the receptors are proteins that receive various signals
  • specific receptor or protein exists for each signalling molecule
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3
Q

What is long distance travel to target cells?

A

Hormones secreted by various endocrine glands are chemical signals that travel via the circulatory system over long distances .

Such as FSH that is secreted by pituitary gland cells that travel via blood to target cells in the ovary.

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4
Q

How do signalling molecules travel to nearby cells?

A

Some chemical signals are released by signalling cells and travel short distances to nearby target cells, diffusing through extra cellular space around cells. (Local mediators)

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5
Q

How does one cell send and receive a signal?

A

Chemical signals released by one cell may be received by the same cell.

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6
Q

What is an example of one cell sending a signal that the same cell receives?

A

In T cells when a foreign antigen is present, one kind of T cell responds to the signal created by the foreign antigen by producing a growing factor that binds to receptors on the same cell type, stimulating their replication.

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7
Q

What is direct cell to cell contact?

A

In some cases a signal can move directly from the cytosol of one cell to that of another through direct cell to cell contact, enabled through structural features of gap junction in animals or plasmodesmata in plants.

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8
Q

What are gap junctions?

A

In animal cells, they consist of protein lined pored in the plasma membranes of adjacent cells, allowing small molecules to pass between cells and electrical signal transmission.

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9
Q

What is plasmodesmata?

A

Cell to cell communication in plants is achieved through gaps through cell walls. The plasma membrane of cells is continuous and forms the lining of the plasmodesmata.

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10
Q

How do signalling cells carry signals to target cells?

A

Highly mobile signalling cells can deliver their signal to target cells.
Seen between cells of the immune system. The signalling cell carries chemical signal on its surface and receiving cell has specific receptor for this signal.

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11
Q

What is the definition of signal reception?

A

Process of detection of a signal from the external environment by a target cell involving the binding of a signalling molecule to a specific receptor.

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12
Q

What is the definition of signal transduction?

A

Signalling pathway in which a series of steps are triggered that is brought about by the change in receptor molecule.

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13
Q

What is the definition of cell response?

A

The result produced in a target cell in response to the reception and transduction of an extracellular signal., which can include, activation or inhibition of genes in the nucleus, activation of enzymes, rearrangement of the cytoskeleton.

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14
Q

What are the stages of cellular communication shown as a stimulus response model?

A

Stimulus: signal molecule (hormone)

Receptor: protein on the cell surface or inside the cell

effector: intracellular chemicals

Arrow transmission and amplification

Response: change in cell function

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15
Q

What occurs during signal reception?

A
  • the first step of cellular communication is the reception of a signalling molecule or ligand from the cells external environment. When the signalling molecule reaches the target cell it binds to a specific receptor.
  • the receptor is protein is specific due to each receptors having a particular signalling molecule binding to it, with complementary shapes.
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16
Q

Where can receptors be located?

A

Receptors can be located either on the plasma membrane of a specific target cell (cell surface receptors)
Receptors can be located either in the cytosol or nucleus of the specific target cell (intracellular receptors)

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17
Q

What generally occurs in signal transduction?

A
  • process that converts signal from outside the cell into a response within the cell.
  • signal received in one form, changed to another molecule and relayed to appropriate target within the cell that responds through an effector protein
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18
Q

How does transduction of a hydrophobic signal occur?

A

Steroid hormones are hydrophobic, able to cross the lipid bilayer of the plasma membrane through diffusion.
-inside the cell the steroid hormone binds with the specific receptor, a protein in solution either in the cytosol or the fluid component of the nucleus.

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19
Q

What is the transduction pathway of a hydrophobic signal?

A
  1. The binding of the steroid hormone to its specific receptor produces a change in the 3D shape of the receptor protein, exposing a region of the receptor that was previously within the molecule.
  2. The hormone receptor protein complex moves from the cytoplasm into the nucleus.
  3. The exposed segment of the receptor protein attaches to a target DNA sequence next to certain genes and activated those genes.
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20
Q

How does transduction of a hydrophilic signal occur?

A
  • The peptide hormone binds to the specific receptor on the cell surface as it is hydrophilic and cannot cross the lipid bilayer of the plasma membrane.
  • The signal must be transferred from receptors on the cell surface to second messengers within the cytoplasm.
  • large numbers of molecules of a second messenger are produced which amplify the original signal by a factor of up to 1000 in order to transfer it from receptor to nucleus.
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21
Q

What are second messengers?

A

A second messenger is an intracellular signalling molecule produced during the process of signal transduction which are not enzymes but activate the a key enzyme at the start of an enzyme relay.

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22
Q

What is the signal transduction pathway of a hydrophilic signal?

A
  1. The binding of the peptide hormone to its cell surface receptor causes a change in the cell surface of the receptor protein that activates it.
  2. The receptor activates an enzyme embedded in the inner surface of the plasma membrane.
  3. This activated enzyme catalysed the production of multiple copies of a second messenger (cAMP) which amplifies the signal, because the binding of one external signalling molecule results in the production of multiple copies of second messenger molecules.
  4. The second messenger molecules activate the copies of a key enzyme (protein kinase) that activates the next enzyme in the relay and so on, further amplifying the signal.
  5. The signal is relayed to the nucleus where specific genes are activated and effector proteins such as enzymes are produced or may regulate the activity of enzymes already in the cytoplasm.
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23
Q

Solubility in water

A

PROTEIN AND PEPTIDE HORMONES: yes as they are hydrophilic and require no assistance to travel through the blood.

STEROID AND THYROID HORMONES: no as they are hydophobic and require a carrier protein for transport by the blood

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24
Q

Able to pass through cell membrane

A

PROTEIN AND PEPTIDE HORMONES: unable to pass through cell membrane, phospholipid bilayer because they are hydrophilic

STEROID AMD THYROID HORMONES: able to pass through the phospholipid bilayer because they are hydrophobic.

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25
Q

Location of receptor protein of target cell

A

P: cell surface

Steroid thyroid: intracellular, cytosol or nucleus

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26
Q

Signal transduction method

A

P: indirectly act on genes and second messengers are produced

S: directly regulate gene expression and have no second messengers

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27
Q

Duration of response

A

P: shorter period of response
S: longer lasting response

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28
Q

What occurs during the signal cellular response?

A
  • Effector proteins are produced by gene activity stimulated directly by steroid hormones, or indirectly by peptide or protein hormones.
  • These effector proteins produce the cellular response to the original external signal molecule.
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29
Q

What are some examples of cellular response to signals?

A

-cell migration entailing the production of structural proteins, such as the microtubules of the cytoskeleton
• changes in metabolism that involve either the production of specific enzymes or a regulated increase in enzyme activity
• cell division involving DNA synthesis and the action of enzymes such as DNA polymerase
• apoptosis or programmed cell death involving the production of caspase enzymes.

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30
Q

Do cellular signalling pathways stay switched on?

A

Once activated they do not stay switched on. After a limited period of time the system returns to its original state ready to receive and respond to the next signal.

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31
Q

How are hormones eliminated?

A

Once a hormone has delivered its message to target cells and an appropriate response has occurred the hormones are no longer needed and inactivated by cell enzyme and excreted via the kidney or faeces.

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32
Q

What are the four manor chemical signals in animals?

A

Hormones, neurotransmitters, pheromones and cytokines

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33
Q

What are the amino acid hormones?

A

Thyroxine and epinephrine

34
Q

What are the protein hormones?

A

Gastrin, lepton, growth hormone, glucagon, insulin

35
Q

What are the steroid hormones (lipid derivative)?

A

Testosterone

Vitamin D

36
Q

What are some factors that can stimulate or inhibit the secretion of a hormone?

A

Environmental changes
Other hormones
Neurons or mental activities
Plasma concentration of ions or nutrients

37
Q

Why is hormonal communication specific?

A
  • A particular stimulus will only be detected by a specific group of hormone secreting cells
  • Only cells with specific receptors are capable of responding to the hormone
38
Q

What is insulin and its role in blood glucose regulation?

A

It is released when blood glucose levels rise, causing more glucose to be taken from the bloodstream by the body’s cells

39
Q

What is glucagon?

A

It is released when blood glucose levels fall. Glucagon causes the liver to convert stored glycogen to glucose which enters the bloodstream.

40
Q

What is the stimulus response model for the chain of events if blood glucose levels RISE?

A

Stimulus: blood glucose
Receptor: beta cells of pancreas
Transfer of signal: increase in the production of insulin
Effector: body cells such as muscle or liver
Response: take up of glucose from blood lowering blood glucose levels

Negative feedback

41
Q

How does glucose regulation occur under negative feedback control?

A

When an increase in blood glucose is detected the response is to reduce the magnitude of this stimulus do that the direction of the change is reverse, a decrease in blood glucose.

42
Q

What occurs during type 1 diabetes?

A

A failure of the body to produce insulin so cells do not receive a signal to take up glucose from the blood. Too high levels of blood glucose in the blood.

43
Q

What happen in type 2 diabetes?

A

The cells of the muscle and liver do not response to insulin adequately a breakdown of the signal transduction pathway of the target cell occurs.

44
Q

How does signal transduction of glucose control occur?

A
  • When glucose levels rise, glucose becomes a signalling molecule which binds to a receptor on the cell membrane of beta cells in the pancreas.
  • The signal is transducer through the cytoplasm leading to the production of transcription factors which enter the nucleus and activate the gene controlling insulin production.
  • Insulin is produced which leaves the cells and enters the bloodstream. The released insulin opens protein channels in cells with specific receptors allowing glucose to enter these cells via facilitated diffusion.
  • The net result is that blood glucose levels fall
45
Q

What is the signalling pathway of thyroxine?

A
  • Although thyroxine is an amine based molecule, it’s small size and hydrophobic nature allows it to move through the phospholipid bilayer of the membrane by diffusion into the cytosol and nucleus.
  • The receptor for thyroxine is found in the nucleus
  • The thyroxine receptor complex binds to DNA and initiates transcription and thus the expression of genes, leading to the cell’s response.
46
Q

How is thyroxine production controlled?

A
  • Thyroxine needs to be secreted at a constant rate so that levels in the blood stream are sufficient to maintain metabolic rates.
  • A tightly controlled negative feedback system ensures that levels vary at times when the needs of the body change.
  • TSH (thyroid stimulating hormone) is produced by the hypothalamus which stimulates the pituitary gland to produce TSH.
  • If thyroxine levels increases then thyroxine acts on the hypothalamus and the pituitary gland to produce less TRH and TSH respectively, decreasing the live of thyroxine produced by the thyroid gland.
47
Q

What are neurotransmitters?

A

Neurotransmitters are chemical signalling molecules of nerve cells.

48
Q

What are action potentials?

A

Electrical signals in the nerve cell that transmit a nerve impulse along the axon of a neutron.
Produced by the local movements of charged particles (sodium ion in and potassium ions out)

49
Q

What is the synapse?

A

The point where one nerve cell connects with another cell, either another neuron, muscle of gland.

50
Q

Why do vesicles containing neurotransmitters occur only at the end of axons?

A

To ensure the nerve impulse is transmitted in one direction only.

51
Q

What are the steps involved in the action of neurotransmitters?

A
  1. The arrival of the nerve impulse at the end of the axon causes an influx of calcium ions which causes vesicles to move towards the presynaptic membrane and release their neurotransmitter via exocytosis into the synaptic cleft.
  2. The neurotransmitter diffuses across the synaptic cleft to specific receptors on the postsynaptic membrane (either another neutron muscle cell or gland).
  3. The neurotransmitter binds to specific receptors on postsynaptic membrane.
  4. Ion channels in the postsynaptic membrane open, causing an influx of Na+.
  5. If enough Na+ moves in to reach the threshold potential an action potential will be generated.
  6. This will cause the receiving cell to respond to the arrival of the neurotransmitter. The response of the cell will depend on the type of cell, for example a muscle cell will either contract or relax, an endocrine gland may release a hormone or an action potential may be generated in a neuron.
  7. Neurotransmitters are broken down by enzymes once the message has been delivered. Components of the neurotransmitter are actively reabsorbed back into the synaptic knob.
52
Q

What are pheromones?

A

Pheromones are chemical signalling molecules released by one animal to the external environment that can carry a signal to a second member of the same species, and if this pheromone signal is received the second animal produces a physiological or behavioural change.

53
Q

What are the types of pheromones?

A

Trail (ants)
Alarm (aphids)
Territorial (mammals)
Sex (Moths and butterflies)

54
Q

What are cytokines?

A

Cell signalling molecules that aid cell to cell communication in immune responses and stimulate the movement of cells towards sites of inflammation, infection and trauma.

55
Q

How do cytokines signal to produce a response in cells?

A

Once cytokines are produced and released from the signalling cell, the cytokines diffuse to nearby target cells where each binds to a specific cell-surface receptor. The binding of a cytokine to its specific receptor triggers a signal transduction pathway in the cytoplasm. This process involves the production of second messenger molecules (such as cAMP) and enzyme activation. The signal is finally transduced to a specific cell response that is brought about by changes in gene transcription, in which cytokine-related genes are switched ‘on’ or ‘off’.

56
Q

What kind of effects can cytokines have?

A

stimulatory, inhibitory and regulatory

57
Q

What factors influence plant growth and development?

A

internal factors include chemical substances such as plant hormones and external factors include environmental facts such as light intensity, temperature, day length and gravity.

58
Q

In what ways are plants hormones similar to animal hormones?

A
  • Both produced in response so a stimulus and bind with specific receptor proteins and initiate a sequence of events within target cells leading to a response
  • Are produced in particular parts of the body of the animal or plant and travel to target cells
  • Produced in relatively small amounts
  • The same hormone may produce different responses in various tissues
59
Q

How do plant hormones differ from animal hormones?

A
  • Plant hormone cause different responses at different concentrations
  • Plant cells produce and secrete the chemical message in the right conditions in the growing regions of roots and shots as they do not possess specialised secretory organs/cells.
  • Distribution of hormones occur through diffusion from cells through extracellular fluid or transported through xylem and phloem
  • Plants do not monster or maintain a stable internal environment
60
Q

What are the five groups of plant hormones?

A

Auxin
Cytokinins
Gibberellins= promote growth
Abscisic acid and ethylene inhibit growth

61
Q

Where is auxin produced?

A

Growing tips (apical bud), developing seeds, leaf primordia

62
Q

Where are cytokinins produced?

A

Actively dividing meristematic regions of stems, roots and leaves

63
Q

Where are gibberellins produced?

A

roots young leaves seeds

64
Q

Where is ethylene produced?

A

Most parts of a plant with highest concentrations during senescence, leaf abscission and fruit ripening

65
Q

Where is abscisic acid produced?

A

roots

terminal buds

66
Q

What does auxin do?

A
  • Regulates embryonic growth and form
  • Promotes flowering and fruit development
  • Promote stem and coleoptile elongation
  • Produce trophic responses to light and gravity
  • Induce formation of xylem and phloem
  • Induce formation of adventitious roots
  • Prevent leaf drop (abscission)
67
Q

What do cytokinins do?

A
  • Promote cell division
  • Regulate growth and form (with auxin)
  • Promote root growth
  • Delay senescence (ageing)
  • Stimulate leaf expansion
  • Stimulate growth of lateral buds
  • Regulate development and activity of chloroplasts
68
Q

What do gibberellins do?

A
  • Promote rapid stem elongation (bolting)
  • Stimulate shoot growth’
  • Break dormancy of some seeds
  • Promote germination
  • Mobilise food stores in seeds
  • Promote flowering fruit and leaf growth
  • Stimulate production of seedless fruits
69
Q

What does ethylene do?

A
  • STimulates shoot and root growth
  • Promotes flower opening and fruit ripening
  • Promotes abscission of leaves and fruit
  • Stimulates leaf and flower senescence
70
Q

What does abscisic acid do?

A
  • Inhibits growth of shoots
  • Blocks seed germination
  • Promotes dormancy
  • Promotes synthesis of storage proteins in seeds
  • Promotes stomatal closure (in times of water stress)
71
Q

What happens when there is an even distribution of light on a growing shoot?

A

An even distribution of light results in an even distribution of auxin in the shoot (coleoptile). Cells in the tip of the stem contain light receptors. Cells on both sides of the shoot grow at the same rate so the shoot grows straight up.

72
Q

What happens when this is an uneven distribution of light?

A

If light shines from one side, auxin moves to the shaded side of the shoot (coleoptile) and causes the elongation of cells in the shaded area.

  • Cells in the shade have a higher concentration of auxin therefore the cells grown at a faster rate compared to cells in full light.
  • This causes an uneven growth rate causing the shoot to bend towards the light. Positive phototropism
73
Q

How does auxin affect the growth of roots?

A
  • In the root the cell on the underside grows slower compared to cells on the upper side causing roots to grow towards the pull of gravity. Auxin accumulates on the lower side of the root and inhibits growth. negative phototropism
  • In the shoot the cells on the lower side grow faster compared to cells on the upper side causing the shoot to grow away from the pull of gravity. Auxin accumulates on the lower side of the shoot and promotes growth.
74
Q

What is the signal transduction pathway of auxin?

A
  1. Auxin increases the activity of proton pumps.
  2. The cell wall becomes more acidic.
  3. Wedge shaped expanses, activated by low pH, separate cellulose microfibrils from cross linking polysaccharides. The exposed cross linking polysaccharides are now more accessible to cell wall enzyme.
  4. The enzymatic cleaving of the cross linking polysaccharides allows the microfibrils to slide. The extensibility of the cell wall is increased. Turgor causes the cell to expand.
75
Q

What is the action of abscisic acid?

A
  • THe hormone ABA triggers a signalling cascade in guard cells that results in the stomatal closure and inhibits stomatal opening.
  • -Stomatal closure is mediated by turgor reduction in guard cells which is caused by removal of potassium ions and anions from guard cells.
  • ABA triggers guard cells to become more permeable to Ca ions which in turn opens K+ channels allowing it to leave guard cells which decreases ion concentrations in the guard cell, net movement of water out the guard cells causing guard cells to shrink and become flaccid, closing the stoma.
76
Q

How do gibberellins affect seed germination?

A
  • When water enters a seed, cells of the plant embryo release gibberellic acid (GA), which diffuses to the aleurone, the layer of cells that surrounds the starchy endosperm.
  • The GA binds to a specific receptor on the plasma membrane of aleurone cells; this is a G protein coupled receptor.
  • The binding of GA to the receptor starts the signal transduction pathway.
  • The end result of the signal transduction pathway is the activation of a gene that encodes the instructions for the enzyme α-amylase. α-amylase is an enzyme that breaks down starch.
  • α-amylase is secreted from the aleurone cells into the endosperm where it catalyses the breakdown of starch molecules into their glucose sub-units. The glucose molecules then diffuse to the embryo and provide it with an energy source for the initial stages of growth of a new plant.
77
Q

What is the mitochondrial pathway of apoptosis?

A
  • Internal cell signals are activated when Dna is severely damaged, malfunction of oxidation enzymes, virus
  • Proteins of the surface of mitochondria are activated and the mitochondria membrane breaks.
  • Caspases are enzymes which once activated enter the nucleus and break DNA into smaller pieces
78
Q

What is the death receptor pathway of apoptosis?

A
  • A cell is given a message from outside the cell to self destruct if the cell may not have developed fully, excessive cells, no longer required
  • Cell membranes have death receptors that receive messages for self destruction. Once a message is received a cascade of events occurs.
79
Q

What steps are involved in the cascade of events for apoptosis?

A

!. Many different caspases are activated within the cell and at the same time a message goes out to phagocytes in the area.

  1. All cells that have received the death signal begin to shrink and develop small bumps (blebs) on their surface.
  2. Caspases enter through the nuclear membrane pores, the DNA and proteins in the nucleus are degraded and the mitochondria break down.
  3. Organelles other than the nucleus and the mitochondria and generally preserved as the cell breaks into small membrane enclosed fragments, recycled.
  4. The small fragments bind to receptors on the phagocytic cells that have responded to messages from the dying cell. These phagocytes then engulf the fragments. Secrete cytokines which inhibit inflammation so surrounding cells are not damaged in the way that neighbouring cells are with necrosis.
80
Q

What is necrosis?

A

Necrosis is unplanned cell death that occurs when cells suffer trauma and die prematurely

81
Q

What happens in uncontrolled necrotic death?

A

The dying cells swell, the plasma membranes rupture and cell contents our out into the surrounding tissue causing local inflammation.
-If extensive volume of cells undergoes necrotic cell death and the blood supply is cut off gangrene can develop.

82
Q

How can apoptosis be related to disease?

A

Too much apoptosis in neurodegenerative diseases such as Parkinson’s and Alzheimer’s and AIDS.
Too little apoptosis: cancer, rheumatoid arthritis. Many cases of cancer appear to be the result of too little apoptosis. Mutations present in cancer cells enable these cells to grow in an uncontrolled fashion, crowding out normal healthy cells, and forming tumours. This situation arises because the cancer cells do not respond to the normal apoptotic signal to self-destruct.

Year 12 Biology (13 decks)

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