C2.1 Chemical Signalling Flashcards

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1
Q

Define ligand.

A

Ligands are signalling molecules that cause biochemical reactions that lead to a specific response.

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2
Q

Outline the structure and function of receptor molecules.

A

Structure:
- Receptor molecules exhibit specificity to ligands due to the structure of their binding sites

Function:
- Chemical signalling helps maintain homeostasis, development, immune response, neural function and metabolic regulation by receiving signals from outside the cell and passing the signals to the inside

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3
Q

Outline the relationship between receptor and a specific ligand.​

A

Receptors and ligands interact either directly or indirectly

Directly:
- involving cell-to-cell contact

Indirectly:
- occurs through the secretion of molecules by one cell that are transported to the target cells

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4
Q

Describe the 6 stages of chemical signalling in cells

A
  1. Synthesis and release of ligand from signalling cell
  2. Transport and diffusion - Ligand transports to target cell (for instance, in the blood)
  3. Receptor binding - Binds to receptor on target cell
  4. Signal Transduction - binding to receptor causes a series of reactions within the cell
  5. Cellular response - the cell produces a response (for instance, expressing certain genes)
  6. Signal termination - ligand is degraded in order to terminate the signal
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5
Q

Describe the process of quorum sensing in a population of bacteria, including the role of signaling molecules, receptors and a threshold for gene expression.

A
  • Bacteria involved in quorum sensing release small signalling molecules called autoinducers which diffuse in their environment
  • once the population threshold for bacteria is reached, the bacteria coordinate the expression of genes with the help of autoinducers binding to receptors and inducing or stopping gene expression.
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6
Q

What are the 2 different types of bacteria and what do they use to communicate

A

Gram +ve bacteria
- Use processes oligopeptides

Gram-ve bacteria
- Use Acylated homoserine lactones (generally)

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7
Q

What is an example of Quorum sensing in bacteria

A

Bioluminescence in Vibrio Fischeri

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8
Q

What type of bacterium is vibrio fischeri

A

Gram -ve

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9
Q

Outline the process of bioluminescence in Vibrio fischeri as an example of quorum sensing in bacteria (6 stages)

A
  • As a response to population density of the bacterium rising, VF releases an autoinducer called Acylated homoserine lactones
  • The autoinducer induces the lux operon which, thus, produces more autoinducers
  • When autoinducers get to a certain concentration, the enzyme luciferase is expressed also (it’s part of the lux operon)
  • Luciferase catalyses a reaction which oxidises luciferin to oxyluciferin. This releases light
  • As the release of light energy intensifies, this process ensures that light’s only released when numbers of bacteria are high
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10
Q

What are 3 applications of quorum sensing other than bioluminescence

A
  • Medicine: Blocking quorum sensing can prevent biofilms from forming. Quorum sensing blockers could be used as alternatives to antibiotics
  • Bioremediation: Which is being used to breakdown pollutants from the environment
  • Food Spoilage: Autoinducers can be blocked in bacteria which causes food spoilage and biofilms to form
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11
Q

What chemical triggers bioluminescence in Vibrio fischeri

A

Acylated homoserine lactones

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12
Q

List the 4 main categories of signalling molecules in animals

List 2 extra signalling molecules

A
  • Hormones
  • Neurotransmitters
  • Cytokines
  • Calcium ions

Extra:
- Phermones: Communicate with members of the same species
- cAMP: act as secondary messengers in the signalling cascade

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13
Q

WARLD of hormones (action etc) - a signalling molecule in animals

A

Hormones:
- What: Regulate metabolic functions of other cells
- Action: act on tissues which possess receptors
- Release: Hormones secreted by endocrine glands into extracellular fluid
- Location: Receptors may be intracellular or on the surface membrane
- Duration: Effects remain for a prolonged period of time

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14
Q

WARLD of Neurotransmitters (action etc) - a signalling molecule in animals

A

Neurotransmitters:
- What: Transmit signals between neurones
- Action: Carry signals from one neurone to the other or from one neurone to a target cell like muscle cells
- Release: Released into the synaptic cleft
- Location: Signal is transmitted in only one direction
- Duration: Actions are short lived

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15
Q

WARLD of Cytokines (action etc) - a signalling molecules in animals

A

Cytokines:
- What: Small proteins involved in the immune response
- Action: They activate the lymphocytes at the site of inflammation.
- Release: Released by white blood cells
- Location: They activate lymphocytes at sites of infection
- Duration: Duration of action ranges from less than a second to several hours

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16
Q

WARLD of Calcium 2+ ions (action etc) - a signalling molecule in animals

A

Calcium 2+ ions:
- What: Act as ligands - can bind to proteins and activate them
- Action: They can bind and activate proteins
- Release: As they move in and out of cells via calcium pump in the plasma membrane
- Location: Can be found intracellular and extracellular
- Duration: Not considered

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17
Q

Outline the properties shared by all signalling chemicals.

A
  • Specificity
  • Reception
  • Transmission
  • Cellular Response
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18
Q

List the 3 main chemical categories of hormones.

A
  • Amine hormones
  • Peptide hormones
  • Steroid or Lipid-derived hormones
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19
Q

Properties of amine hormones

A
  • Small molecules derived from the amino acids tyrosine and tryptophan
  • Mostly not lipid soluble so they bind to receptors on surface of target cells
  • Bind to surface receptors
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20
Q

Give 3 main examples of amino acid derived hormones; If can, where they are secreted by too

A
  1. Noradrenaline and Adrenaline; Secreted by medulla of adrenal gland
  2. Thyroxin; Secreted by the thyroid gland
  3. Melatonin; Secreted by pineal gland situated in the brain - helps to maintain circadian rhythm
  4. Seratonin; Secreted by the tryptophan
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21
Q

Properties of peptide hormones

A
  • They are in the form of polypeptide chains, small proteins, glycoproteins
  • Not Lipid soluble
  • Bind to surface receptors
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22
Q

Give 4 main examples of peptide hormones; If can, where they are secreted by and what they do too

A
  1. Insulin; Secreted by the pancreas in response to blood glucose level and promotes the uptake of glucose
  2. Oxytocin
  3. FSH
  4. Growth hormone
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23
Q

Properties of Lipid-based hormones

A
  • Lipid Soluble
  • They are derived from cholesterol
  • Steroid hormones are insoluble: Require carrier proteins to be transported via blood
  • Remain in circulation for longer
  • Can cross membrane directly into the cell
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24
Q

Give 4 main examples of lipid-derived hormones; If can, where they are secreted by and what they do too

A
  1. Oestradiol; Secreted by female reproductive organs
  2. Testosterone; Secreted by male reproductive organs
  3. Cortisol and Aldosterone; Secreted by the cortex of the adrenal gland
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25
Q

What molecule has a dual function; It can act both as a hormone and a neurotransmitter. Where is it secreted from too

A
  • Epinephrine (also called adrenaline) which is secreted from the medulla of the adrenal glands
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26
Q

What are neurotransmitters

A
  • Neurotransmitters are chemicals that transmit signals across a synapse
  • They are synthesised in the neurones and stored in thin-walled sacs called synaptic vesicles.
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27
Q

List chemical categories of neurotransmitters.​

A
  • Amino acids
  • Gases
  • Esters
  • Amines (modified amino acids)
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28
Q

Properties of amino acid as neurotransmitters

A
  • Involved in fast synaptic transmission
  • Glycine, Glutamate and GABA are examples
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29
Q

Properties of peptides as neurotransmitters

A
  • Responsible for a number of physiological and homeostatic processes - increases the motivation to eat food
  • Neuropeptide Y is an example
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30
Q

Properties of amines as neurotransmitters. Give 3 e.g. and explain them

A
  • They are modified amino acids that have different functions
  • Serotonin, an example, regulates the mood
  • Dopamine, an example, is involved in reward and movement regulation in the brain
  • Noradrenaline, an example, controls the fight or flight response
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31
Q

The one property of nitrous oxide as a neurotransmitter

A
  • Acts as a moderator of neuronal functions
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32
Q

What is the action of neurotransmitters

A
  • Electrical signal arrives at neuron terminal
  • Vesicles containing neurotransmitters move to cell membrane and are released by exocytosis
  • Diffuse across the synaptic cleft
  • Bind to receptors on the post-synaptic membrane
  • Generate electrical impulse on the neurone
33
Q

Explain the 5 types of cell signalling (PAJES)

A
  • Autocrine signalling: Cells secrete signalling molecules which act on the same cell
  • Paracrine signalling: The signalling molecules travel a short distance to reach the target cells
  • Endocrine signalling: The signals released by the cells travel a long distance to reach the target cells (these are hormones)
  • Juxtacrine signalling (contact-dependent): Occurs when 2 cells are in physical contact with one another and the signal is bound to the surface of the signalling cell.
  • Synaptic: Occurs when ions pass across one cell to adjacent cells through gap junctions (neurotransmitters)
34
Q

What are the 3 domains of a typical cell-surface receptor

A
  • Extracellular ligand-binding domain
  • Transmembrane hydrophobic domain
  • Intracellular domain
35
Q

Structure of transmembrane receptors, including distribution of hydrophobic amino acids.

A

Distribution of hydrophilic amino acids:
- Hydrophilic amino acids are located on either side of the membrane

  • hydrophilic signalling molecules can’t penetrate the cell membrane and thus, require transmembrane receptors with hydrophilic amino acids on the extracellular side of the membrane to bind and initiate a signalling cascade within the cell
36
Q

Structure of intracellular receptors, including distribution of hydrophobic amino acids.

A

Distribution of hydrophobic amino acids
- Composed of hydrophobic amino acids that span the cell membrane

  • hydrophobic signalling chemicals like steroid hormones can diffuse across the cell membrane and bind to intracellular receptors in the cytoplasm or nucleus
37
Q

Function of transmembrane receptors

A
  • Present on the cell membrane of target cells and are specific to individual cell types
  • responsible for transmitting signals from the outside of the cell to the inside
  • Bind to extracellular signalling molecules (hormones, cytokines, neurotransmitters) to initiate a signalling cascade leading to changes in gene expression
38
Q

Function of intracellular receptors

A
  • Receptors located inside target cells and their function may occur in the cytoplasm or the nucleus
  • Bind to lipid-derived signalling molecules (steroid hormones) which can cross the plasma membrane and bind to intracellular receptors
  • This forms a hormone-receptor complex which can move to the nucleus and directly affect gene expression
39
Q

Compare the ligands ability to enter the target cell for intracellular receptors. Give examples.

A

Intracellular receptors:
- They interact with ligand molecules that can cross the cell membrane and regulate gene expression by binding to transcription proteins (e.g. hormone response element)

40
Q

Compare the ligands ability to enter the target cell for extracellular receptors. Give examples.

A

Extracellular receptors:
- They recognise and bind to extracellular ligands - the ligand-receptor interaction triggers the intracellular signalling events which influences cellular processes without the ligand directly entering the cell

41
Q

Define signal transduction.

A

The transmission of molecular signals from a cell’s exterior to its interior

42
Q

Describe the signal transduction pathway that is activated when a ligand binds to a transmembrane receptors (RSSAC)

A

Receptor activation:
- Receptors present on cell membrane surface get activated when ligands bind to them (specific nature binding - a specific type of ligand can bind to a particular type of receptor)

Signal Amplification:
- activation of lots of downstream messengers after a conformational change in the receptor protein thus, a small amount of signal is capable of triggering a larger response

Second messenger production:
- They relay signals inside the cells - cAMP is a common second messenger

Activation of protein kinases:
- Protein kinases (enzymes that phosphorylate proteins by adding a phosphate group) get activated due to cAMP

Changes in gene expression or cellular function:
- Finally, there’s an alteration of cellular response - altering the gene expression by opening / closing ion channels (through binding of a neurotransmitter / binding of a hormone to a receptor) or by activating an enzyme

43
Q

Describe the signal transduction pathway that is activated when a ligand binds to an intracellular receptor.

A
  • Binding to intracellular receptors results in the formation of an active ligand-receptor complex
  • This complex regulates gene expression by binding to DNA at specific sites thus, promoting or inhibiting the transcription of particular genes
44
Q

What are the 3 possible outcomes of electrical signals depending on the neurotransmitter?

A

Excitatory neurotransmitters:
- They excite the neurone and cause it to send the message forward at great speed to next target cell

Inhibitory neurotransmitters:
- Block or prevent neuronal excitability by inhibiting nerve transmission

Modulatory neurotransmitters:
- Act as neuromodulators which can create both excitatory and inhibitory effects depending on the receptors they bind to

45
Q

Outline the mechanism of synaptic transmission occurring at a post-synaptic cell, including the role of the neurotransmitter, transmembrane receptor, gated ion channel, threshold potential and action potential.

A

At a neuromuscular junction (a synapse between a neuron and a muscle cell) this mechanism takes place:

  1. Vesicles containing acetylcholine from presynaptic knob are released into synaptic cleft by diffusion through synapse and bind to its receptors on the postsynaptic knob

2 Once released, acetylcholine stays in cleft and can continually bind and unbind to postsynaptic receptors

  1. Enzyme acetylcholinesterase continuously breaks down acetylcholine to give choline and acetate molecules where choline is reabsorbed into the presynaptic knob
  2. This triggers Na+ channels (not voltage-gated Na+ channels) in postsynaptic knob to open
  3. Na+ ions enter into the cells resulting in depolarisation of the postsynaptic knob
  4. When threshold potential reaches, an action potential is generated
46
Q

What happens when a neurotransmitter binds to a receptor on the postsynaptic membrane

A

This can cause a change in the membrane potential

47
Q

What is the most common neurotransmitters in both invertebrates and vertebrates and what is it used for

A
  • Acetylcholine
  • Used as the neurotransmitter in many synapses including between neurons and muscle fibers.
48
Q

Describe the structure and function of the G-protein coupled receptors.

A

Structure:
- GPCRs consist of 3 subunits (alpha, beta, gamma) and in its inactive state, the alpha subunit’s bound to Guanine Diphosphate (GDP)

Function:
- GPCR is specific to a particular function; Being responsible for our sense of taste, smell, behaviour, mood.

  • They are also important in medicine mechanism of action as they are the target sites of many medicinal drugs
49
Q

List ligands of the G-protein coupled receptors.

A
  • Light sensitive compounds
  • Odours
  • Pheromones
  • Hormones
  • Neurotransmitters
50
Q

Outline the activation of the signal cascade triggered by the G-protein subunits.

A
  • Alpha subunit of G-protein is inactive as GDP is bound to it
  • Ligand binds to the receptor, causing conformational changes to the transmembrane receptor
  • This displace GDP from the Alpha subunit allowing GTP to bind which activates the G-protein
  • Alpha subunit disassociates
51
Q

What glands are epinephrine secreted by and what for

A
  • epinephrine is secreted by adrenal glands
  • In order for preparation for vigorous activity; stress/danger.
52
Q

Describe the activation of the cAMP second messenger system by the epinephrine receptor.

A
  • Epinephrine ligand binds onto the GPCR
  • alpha subunit from GPCR disassociates with gamma and beta subunits to activate adenylate cyclase which causes ATP to convert to cAMP
  • cAMP binds to Protein Kinase causing it to activate
  • This causes another enzyme, phosphorylase, get activated
  • This breaks down glycogen to glucose
  • Epinephrine ligand disassociates and GPCR goes back to original shape
53
Q

Outline the effects of epinephrine on a body.

A

It increases heart rate and blood flow, leading to a physical boost and heightened awareness

54
Q

Define phosphorylation and kinase.

A

Phosphorylation: The production of ATP by the light dependent reactions - it can be a cyclic or non-cyclic process. This adds a PO4 3- group onto a specific molecule

Kinase: An enzyme that adds a PO4 3- from ATP to a specific molecule

55
Q

Describe the action of receptors with tyrosine kinase activity.

A
  • Receptors get activated by the binding of hormones
  • Tyrosine Kinase enzymes have 2 tails that extend into the cytoplasm
  • Binding of a hormone causes the 2 tails of the tyrosine kinase enzymes to connect (forming a dimer) and autophosphorylate
  • This causes a signalling cascade as secondary messenger proteins get activated
56
Q

What is insulin secreted by and when is it secreted

A

Insulin is secreted by pancreas cells when blood glucose levels are high.

57
Q

Describe the cause and effect of the activation of the insulin receptor.

A

Cause:
- Insulin is a hormone that gets secreted by the pancreas
- Insulin receptor gets activated due to insulin binding to it.

Effect:
- Tyrosine Kinase Phosphorylates itself and other signalling molecules like insulin receptor substrate proteins (IRS proteins)

58
Q

Describe the mechanism of steroid hormone action.

A
  • Steroid hormones diffuse across the plasma membrane
  • They bind to receptors in either the cytoplasm or nucleus of target cell to form an active receptor-hormone complex which leads to the production of cAMP (secondary messengers)
  • cAMP activates protein kinase A which phosphorylates various proteins
  • The signalling cascade results in the activation of a transcription factors which results in transcription of genes
  • Finally, a cellular response occurs which inhibits or activates gene transcription
59
Q

List example steroid hormones.

A
  • Estrogen
  • Cortisol
  • Progesterone
  • Testosterone
60
Q

Outline one example of a steroid hormone promoting transcription of a specific gene.

A
  • Example steroid hormone: Estradiol
  • Estradiol binds to G-protein coupled estrogen receptor (GPER) located on cell membrane
  • This activates the estradiol receptor interacting protein which leads to the production of cAMP (secondary messengers)
  • cAMP activates protein kinase A which phosphorylates various proteins
  • The signalling cascade results in the activation of a transcription factors which results in transcription of genes (the cellular response)
61
Q

Outline 2 steroid hormones

A

oestradiol and progesterone

62
Q

Describe the role of oestradiol in the regulation of the release of FSH and LH from the anterior pituitary, including the role of the hypothalamus, the oestradiol receptor, transcription factor and gonadotropin releasing hormone.

A
  • Oestradiol acts in the ovary & uterus and acts on the brain, helping to regulate the release the reproductive hormones
  • Oestradiol promotes the proliferation of uterine lining or inhibits the release of GnRH by hypothalamus
  • Gonadotrophin-releasing hormone (GnRH) is released by hypothalamus which triggers the release of LH and FSH from anterior pituitary
  • Oestradiol is a steroid hormone that diffuses through membrane of uterine cells and binds to a receptor in the cytoplasm
  • The hormone receptor complex then enters the nucleus to interact with DNA as a transcription factor therefore affecting gene expression
  • Oestradiol triggers LH and inhibits FSH
63
Q

Describe the role of progesterone in the formation and maintenance of the endometrium, including the progesterone receptor, transcription factor and growth factor protein.

A
  • Progesterone produced by corpus luteum outside the ovary and maintains uterine lining to support a developing fetus
  • Progesterone can inhibit proliferation (growth) or promote the release of GnRH by hypothalamus
  • Gonadotrophin-releasing hormone (GnRH) is produced and released by hypothalamus which triggers the release of LH and FSH from anterior pituitary
  • Progesterone is a steroid hormone that diffuses through membrane of uterine cells and binds to a receptor in the cytoplasm
  • The hormone receptor complex then enters the nucleus to interact with DNA as a transcription factor therefore affecting gene expression
  • One of the genes that get activated is an insulin-like growth factor contributing to the maintenance of the endometrium lining (in uterus)
  • Progesterone triggers FSH and inhibits LH
64
Q

What effect does progesterone have on target cells in the endometrium?

A

Inhibits proliferation (growth) of endometrial cells

65
Q

Compare the processes and consequences of positive and negative feedback.

A

Process of positive feedback:
- End-product of a pathway amplifies starting point so more product is produced

Consequences of negative feedback
- End-product inhibits its own production

66
Q

Outline one example each of hormonal regulation via positive feedback and negative feedback.

A

E.g. of hormonal regulation via positive feedback:
- Blood clotting; platelets are activated by a signal to form a clot then, the platelets release chemicals that further activate near platelets resulting in amplification of clotting response.

E.g. of hormonal regulation via Negative feedback:
- Insulin regulates the blood glucose level; when blood glucose levels rise, insulin is secreted from the pancreas and binds to insulin receptors which activates them thus, causing glucose to be taken up and stored by the cells as glucose.
- When blood glucose levels falls, it inhibits the release of insulin allowing a balance of glucose in blood to be maintained.

67
Q

Identify which type of receptor is associated with positive feedback in cell signalling pathways

A

Transmembrane receptors

68
Q

Name 3 functions of G Protein-Coupled Receptors

A
  • Controlling muscle movement
  • Regulating heartbeat
  • Sensing light in the retina
69
Q

Similarities in transmembrane and intracellular receptors (3 marks)

A
  • Both involved in cell signalling
  • Both involve conformational changes when a ligand binds
  • Both have binding sites for ligands
70
Q

Differences in transmembrane and intracellular receptors (3 marks)

A
  • Transmembrane receptors located in plasma membrane whereas intracellular receptors are found in the cytoplasm or nucleus
  • Transmembrane receptors are specific to hydrophilic ligands whereas intracellular receptors are specific to hydrophobic ligands
  • Signals in transmembrane receptors stays outside the cell whereas signals in intracellular receptors penetrate the cell
71
Q

Explain the mechanism by which transmembrane receptors bring out responses using a named hormone (3 marks)

A
  • Insulin activates transmembrane tyrosine kinase receptors by binding to their extracellular domain
  • Intracellular domain of transmembrane tyrosine kinase receptors gets autophosphorylated
  • Signal transduction occurs
72
Q

Explain the mechanism by which intracellular receptors bring out responses using a named hormone (3 marks)

A

-Oestradiol diffuses through the cell membrane into the cell

  • Oestradiol binds to the intracellular receptors
  • The complex moves from the cytoplasm to the nucleus
  • Gene transcription is influenced
73
Q

4 Examples of hormones using the cAMP secondary messenger system

A
  • ACTH
  • Epinephrine
  • Glucagon
  • ADH
74
Q

Explain the 2 types of intracellular receptors

A

Type I:
- Located in cytoplasm and are translocated to the nucleus upon ligand binding

Type II:
- Located in nucleus and are directly involved in gene transcription

75
Q

5 ways in which the signal gets terminated

A
  • Degradation
  • Diffusion of signalling molecules
  • Reuptake
  • Inactivation of receptor
  • Feedback inhibition
76
Q

How is the resting potential maintained by a pump protein compared to in a neuron (axon)

A

pump protein:
- 3 Na+ out, 2K+ in

Neuron:
- 3 Na+ in, 2K+ out

77
Q

What’s the role of the g-protein in the function of a transmembrane receptor

A

it can regulate a specific metabolic reaction

78
Q

How does the insulin alter the function of a membrane

A

insulin causes an increase in glucose transporter proteins in the membrane

79
Q

State the function of the g-protein

A
  • Causes disassociation of alpha subunit