Principles of cellular physiology 4 Flashcards

1
Q

State the difference between cell surface receptors and intracellular receptors

A
  • CELL SURFACE Membrane receptors for: hydrophilic signalling molecules activate a wide variety of intracellular ‘signal transduction’ pathways e.g. gene regulation
  • INTRACELLULAR: most receptors for hydrophobic signalling molecules act as transcription factors in nucleus to regulate gene transcription
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2
Q

What are hormones?

A
  • First messengers and are classified as ‘steroid’ or ‘nonsteroid’
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3
Q

Describe steroid hormones.

A
  • Lipid soluble - derived from cholesterol
  • Relatively small so can pass through the plasma membrane
  • Enter target cells and bind to intracellular receptor and activate genes that produce new proteins
  • Slower acting than non steroid hormones
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4
Q

Describe non steroid hormones.

A
  • Water soluble - derived from amino acid
  • Binds to receptors on target cell membranes and activates signal transduction pathways that produces a chemical called a second messenger
  • Work through intermediate mechanisms to activate existing enzymes; small amount of hormone can produce a significant cellular change
  • Faster action than steroid hormones
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5
Q

Describe the hormone receptors pathway (steroid hormones)

A

Hormone - nuclear receptors - activate genes - synthesise new proteins or enzymes - cell responds

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6
Q

Describe the hormone receptors pathway (non steroid)

A

Hormone - membrane-bound receptors - receptors alter the activity of G proteins which opens or closes ion channels and activates existing enzymes - cell responds OR receptors alter the activity of intracellular enzymes which activates existing enzymes - cell responds

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7
Q

Name the ligands for intracellular-nuclear receptors

A
  • Androgens, Oestrogens and progesterone - produced by gonads
  • Corticosteroids, Glucocorticoids, Mineralocorticoids - produced by adrenal gland
  • Thyroid hormone
  • Vitamin D3
  • Retinoic acid
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8
Q

Where are corticosteroids produced?

A

Adrenal gland

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9
Q

Where are glucocorticoids (GR) produced and what does it stimulate?

A

Adrenal gland
Act to stimulate glucose production

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10
Q

Where are mineralocorticoids (MR) produced and what does it act on?

A

Adrenal gland
Act on kidney to regulate salt and water balance

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11
Q

Where are thyroid (TR) hormones produced and state its role

A

Synthesised from tyrosine in thyroid gland
Has an important role in development and regulation of metabolism

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12
Q

Describe the role of vitamin D3

A

Regulated Ca2+ metabolism, bone growth

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13
Q

What is retinoic acid (RAR) synthesised from and what is its role?

A
  • Synthesised from vitamin A
  • Play important roles in vertebrate development
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14
Q

Where is the receptor GR localised?

A

cytoplasm

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15
Q

Where is the receptor MR localised?

A

Cytoplasm

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16
Q

Where is the receptor Estrogen localised?

17
Q

Where is the receptor progesterone localised?

18
Q

Where is the receptor TR localised?

19
Q

Where is the receptor RAR localised?

20
Q

Describe the structure of nuclear receptors.

A
  • Transactivation domain (A/B & E)
  • DNA-binding/dimerization domain (C)
  • Nuclear localisation domain (D)
21
Q

What is the role of transactivation domain (A/B & E)?

A

Contains the ligand binding domain (E) which causes a change of conformation to the DNA, initiating transcription

22
Q

What is the role of DNA-binding/dimerisation domain (C)

A

Allows dimerisation of receptors and
binding to the DNA

23
Q

What is the role of nuclear localisation domain (D)?

A

Allows the receptor to enter the nucleus or to maintain the nuclear localisation

24
Q

Describe the mechanism of CYTOPLASMIC receptor activation.

A
  • Receptor located in cytoplasm
  • Ligand enters cell and causes receptor activation
  • Ligand binding dislodges regulatory/repressor protein
  • Ligand-Receptor complex enters nuclear and binds to specific DNA sequence (in promoter region)
  • Gene transcribed and translated, protein produced
  • Or gene expression inhibited
  • Can have latent period of several hours due to production of mRNA and protein
25
Describe the mechanism of action of NUCLEAR receptor activation.
1. lipid soluble hormones diffuse through the plasma membrane 2. Lipid-soluble hormones bind to nuclear receptors 3. The hormone-receptor complex binds to hormone response element on the DNA - acts as transcription factor 4. The binding of the hormone-receptor complex to DNA stimulates the synthesis of mRNA - codes for specific proteins 5. The mRNA leaves the nucleus, passes into the cytoplasm of the cell and binds to ribosomes - directs the synthesis of specific proteins 6. Newly synthesised proteins produce the cell's response to the lipid-soluble hormones
26
Describe the intracellular regulation of gene expression.
1. Steroid hormone binds to intracellular receptor 2. Inhibitor is released to expose DNA binding site of receptor 3. Receptor binds to DNA and activates gene expression
27
Name two hormones that also cause transcriptional activation.
- glucocorticoid - thyroid hormone
28
Give an example of steroid signalling.
- Na+ reabsorption depends upon epithelial Na+ channel (ENaC) in cortical collecting duct in the kidney - These cells express a protein called Nedd4-2 which can bind to ENaC and causes channels to be internalised - This limits rate of Na recovery allowing Na+ to be lost in urine
29
What happens if our body needs more Na+?
Aldosterone induces expression of protein kinase called serum - glucocorticoid- inducible kinase 1 (SGK1)
30
What is the role of SGK1 and state what this leads to.
- phosphorylates Nedd4-2 - Prevents protein binding to ENaC so it remains in membrane - Leads to increased Na+ retention