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Biology 3 > Cellular signalling > Flashcards

Cellular signalling Flashcards

1
Q

What are hormones?

A

Signalling chemicals produced in specialised cells.
They travel in the blood and bodily fluids.
They acts on specific target cells to cause a specific response.

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2
Q

What is the endocrine system?

A

A body system composed of different endocrine glands that secrete hormones that travel in the blood.

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3
Q

What are the functions of the hormones in the endocrine system?

A

Required for:

  • internal communication
  • regulation
  • maintaining homeostasis
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4
Q

What are target cells?

A

Cells which respond to stimulation by a hormone.

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5
Q

What type of hormones are insulin and glucagon?

A

Antagonistic hormones because they both regulate the concentration of glucose in the blood but have opposite effects.

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6
Q

What are the different categories of hormones? (3)

A
  • steroids
  • peptides
  • amine
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7
Q

Describe the structure and provide and example of a steroid hormone.

A

They are lipid and phospholipid derived and synthesised from cholesterol.
Eg. Testosterone and cortisol

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8
Q

Describe the structure and provide and example of a peptide hormone.

A

They consist of chains of amino acids.

Eg. insulin, growth hormone

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9
Q

Describe the structure and provide and example of a amine hormone?

A

They are derived from amino acids.

Eg. thyroxine, melatonin

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10
Q

What are cytokines?

A

Group of small proteins secreted by several types of cells in the immune system.
Signalling molecules.

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11
Q

What is the function of cytokines?

A

They are signalling molecules that enhance the immune response and are apart of the of the second line of defence.

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12
Q

What makes cytokines unusual?

A

They have both effector and regulatory activities.

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13
Q

What are neurotransmitters?

A

Are chemicals which diffuse across a synapse and bind to the photo-synaptic cell to transmit the nerve impulse and trigger a response.

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14
Q

What is a synapse?

A

The junction between two neurons. It allows an electrical or chemical signa pass an l to another neuron

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15
Q

What are the different forms of cell communication?

A

Endocrine, paracrine, autocrine and exocrine

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16
Q

What is reception?

A

The signalling molecule (ligand) binds to a specific receptor protein.

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17
Q

What is signal transduction?

A

Reception triggers conformational change in the receptor, activating intracellular molecules.
Reception sets off a phosphorylation cascade of
intracellular communication ‘molecules’ (enzymes, proteins).

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18
Q

What is the difference between signal transduction of hydrophilic and hydrophobic molecules?

A

A hydrophilic molecule cannot cross the PM, so it must bind to cell surface receptors that either elicit a response or activate second messenger, where as a hydrophobic signal can cross PM, and will be received by intracellular receptor.

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19
Q

How does a hydrophobic molecule undergo signal transduction?

A

The signalling molecule will pass through the plasma membrane, and bind to a receptor either in the cytosol or in the nucleus.

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20
Q

How does a hydrophilic molecule undergo signal transduction?

A

They cannot diffuse across the plasma membrane, so they bind to a membrane-bound receptor. This causes a shape change in the receptor, which activates a second messenger inside the cell. The second messenger causes signal cascade. At each step of the cascade the number of activated molecules increases, called signal amplification.

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21
Q

What is a ligand?

A

A small molecule that binds to the active site of a larger molecule

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22
Q

What occurs during signal transduction?

A

A signalling molecule binds to the receptor of the target shape and it then experiences a change in shape.

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23
Q

What is signal amplification?

A

One signal is amplified into thousands of signals.

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24
Q

What is a second messenger?

A

Small, NON-PROTEIN molecules or ions that are
usually water-soluble.
Carry the signal to the target organelle

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25
Q

What is an intracellular receptor?

A

A receptor found inside the cell (in cytoplasm). Usually receives hydrophobic signalling molecules.

26
Q

What is apoptosis?

A

A natural, regulatory process of programmed cell death, initiated after a cell receives a signal resulting in the removal of cells that are no longer needed or may be a threat.
This process is mediated by enzymes (caspases).

27
Q

What is the role of caspases?

A

They are enzymes involved in the process of apoptosis.

They cleave specific proteins in the cytoplasm or nucleus.

28
Q

What happens to a cell when it undergoes apoptosis?

A
  • cell shrinkage
  • blebbing
  • nuclear fragmentation
  • chromatin condensation
  • chromosomal DNA fragmentation
29
Q

State weather the following compounds bind to cell surface receptors:

a) protein
b) amino acid
c) steroid
d) peptide
e) cytokines

A

a) yes: too large
b)
c) no: hydrophobic
d) yes: hydrophilic
e) yes: hydrophilic

30
Q

What occurs during the signal transduction of neurons?

A

Neuron is stimulated
• Gated sodium and potassium ion channels on its membrane are opened
• The sudden movement of ions in and out initiates the action potential
Action potential travels the length of the axon of the neuron in a wave-like
sequence
• Other ion channels are opened along the membrane
An action potential is the reversal of potential difference across a membrane
or between the inside and outside of nerve fibres •
• Action potential eventually reaches the synaptic terminals of the axon
Causes Ca2+ • to enter the cell
Increased concentration of Ca2+ causes vesicles to fuse with a nearby
membrane and neurotransmitters are released into the synaptic gap via
exocytosis

31
Q

How is cellular signalling terminated?

A

Response is terminated quickly by the reversal of
ligand binding; once the signal is degraded or
released, the response will conclude.

32
Q

Why can not all cells receive and respond to all hormone?

A

A hormone can only be received by a receptor if it has a complimentary shape. This is because receptors are specific.

33
Q

What has to occur in order to activate a messenger molecule?

A

A signalling molecule activated a receptor on the plasma membrane. The activated receptor stimulated the production/activity of the messenger molecule

34
Q

What is the role of the messenger molecule?

A

The role of the messenger molecule is to activate/switch on a particular gene.

35
Q

What is a pheromone?

A

A signalling molecule secreted into the external environment that affects the behaviour of another member of the same species – produced by animals and secreted into the external environment to act on a target cell in another organism

36
Q

What is another name for plant hormones?

A

Plant growth regulators.

37
Q

How can the attachment of a molecule to a receptor bring about a response within a cell?

A

The complementary binding causes the receptor to change shape, triggering a range of events that carry the signal into the cell, such as the synthesis of a second messenger and a cascade of events occurring

38
Q

What does negative feedback do?

A

original stimulus is reduced by the response.

39
Q

Compare the nervous system to the endocrine system?

A

NS: fast, short, neurotransmitter.
ES: slow, long, hormone.

40
Q

Why apoptosis sometimes occurs during the cell cycle?

A
  • A fault may occur, such as spindles breaking or chromosomes failing to separate.
  • Cells produced may be unable to function or are not required.
41
Q

Why might apoptosis occur?

A
  • Cellular injury
  • DNA damage
  • Viral infection
  • Old age
  • Cell no longer needed
42
Q

Explain how apoptosis occurs through the mitochondria pathway?

A

A signal causes the mitochondria to release cytochrome C which activates caspases in the cell.
When mitochondria are damaged they release signals called cytochromes. They act as signalling molecules for intracellular receptors that initiate apoptosis.

43
Q

Explain how apoptosis occurs through the death receptor pathway?

A

Initiated by a signalling molecule binding to a death receptor, which causes the activation of enzymes called caspases.

44
Q

What malfunctions can occur as a result of apoptosis?

A
  • Apoptosis is involved in foetus development. It is how the webbing between our fingers and toes, and the slit that allows our eyelids to open are removed.
  • Cancer is caused by a damaged cell not undergoing apoptosis. These cells divide rapidly, creating large lumps called tumours. There are many reasons why apoptosis fails to occur.
  • Overactive apoptosis: Leads to diseases such as Huntington’s, Alzheimer’s, type 1 diabetes
  • Underactive apoptosis: Leads to diseases such as cancer.
45
Q

Where are the receptors for a neurotransmitter found?

A

Receptors for a neurotransmitter will be found on the membrane of its target cell.

46
Q

Suggest how apoptosis can be explained as an example of signal transduction.

A

Signal transduction involves a cascade of events within the cell in response to an external signal. Apoptosis may be caused by external factors such as a protein called ‘tumour necrosis factor’. This protein will attach to other proteins on the cell membrane and trigger a signal within the cytoplasm that causes a series of events to occur within the cell leading to cell death.

47
Q

Which statement is correct regarding cytokines?

a) Cytokines are small molecules of protein.
b) Animal reproductive cells produce cytokines.
c) Cell division in roots of plants is stimulated by cytokines.
d) Cytokines trigger a response in the cells of another individual.

A

The correct statement regarding cytokines is ‘ Cytokines are small molecules of protein.’

48
Q

A tissue that has been responsive to a hormone may, over time, lose its response to hormone. Suggest why.

A

The tissue may become less responsive to the hormone as the number of receptors for the hormone may decrease.
OR
If there is no change in receptor number there may be a change in the signalling system within the cell (for example a reduction in production of one of the secondary messenger molecules) to reduce the response to the hormone.

49
Q

Most water-soluble signalling molecules initiate responses within their target cells by…?

A

Attaching to receptors on the membranes of their target cells.

50
Q

If too much apoptosis occurs, what happens?

A

The number of cells decreases.

51
Q

The process of apoptosis or programmed cell death can result in what type of disease?

A

Autoimmune diseases if it occurs at too low a level.

52
Q

Describe how the attachment of a molecule, such as epinephrine, to a receptor, can bring about a response within a cell.

A

The hormone binding to the receptor causes the receptor to change shape in such a way that it then triggers a cascade of events inside the cell, involving second messengers that lead to a cellular response.

53
Q

How can a signalling molecule produce a different response in a different cell?

A

There may be different receptors or different secondary molecules.

54
Q

Explain how transport of a neurohormone compares with the transport of a neurotransmitter? (2)

A
  • Passage along nerves is electrical/faster than this type of transport
  • This transport of hormones is chemical/slower than the electrical transmission along a neuron.
55
Q

Why does a hormone that reaches two different cells, only produce a response in one of them?

A

The cell which responded had receptors specific for that particular hormone.

56
Q

Human and plant hormones are similar in that all are…?

A

Signalling molecules that act on receptor molecules.

57
Q

Is a neurotransmitter a hormone?

A

No, it is a signalling molecule that belongs to the nervous system, not the endocrine system.

58
Q

One feature that contrasts the action of nerves and hormones is the length of time that each acts for. Explain the characteristics of each system that lead to this difference in time of action.

A

Neurotransmitters travel extremely small distances to reach their target. Their action takes place in a very short period of time. A neurotransmitter is degraded as soon as it has acted and its parts returned to their source for reassembling and reuse.
In contrast, hormones are generally much slower to reach their targets and may continue to circulate in the blood, sometimes for days, before they are degraded. During this period a hormone continues to diffuse from the bloodstream to appropriate target tissues.

59
Q

What is the role of the messenger molecule?

A

The role of the messenger molecule is to activate/switch on a particular gene.

60
Q

What is the process of apoptosis via the mitochondria pathway?

A
  1. Cellular stress stimulates the mitochondria.
  2. Pores form on the outer membrane of the mitochondria and cytochrome C is released from the mitochondria and into the cytoplasm of the cell
  3. Cytochrome C activates Caspase-9 (the initiator caspases) by chopping a fragment of the inactive procaspase-9 molecule
  4. Caspase 9 then initiates a cascade of reactions and activate other caspases (the executioner caspases)
  5. The executioner caspases breakdown and fragment the DNA, nucleus, the cytoskeleton and other organelles to form blebs (apoptotic bodies)
  6. The blebs are removed by phagocytic activity (without affecting nearby cells)
61
Q

What is the process of apoptosis via the death receptor pathway?

A
  1. A death receptor ligand (signalling molecule) binds to a death receptors on the plasma membrane of a cell.
  2. The death receptor changes shape and
    this activates the inactive procaspase-8 molecule and converts it to caspase-8 (the initiator)
  3. Caspase-8 then begins to cleave and activate the executioner caspases and which breakdown the cell content and produce blebs
  4. Blebs are removed by phagocytic activity
62
Q

Compare extrinsic and intrinsic pathways of apoptosis.

A

Intrinsic: Initiated by factors inside the cell, dependent of cytochrome C (located in the mitochondria), mitochondria receives signal when a cell is damaged or stressed
Extrinsic: Initiated by factors outside the cell, occurs in cells that are no longer required, death Receptor Ligand: FaSL, death Receptor: FaSR

Biology 3 (10 decks)

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