Diversity of the Endocrine Sys (M1B1)

Question 1

hormones can act on adjacent cells (paracrine action) and on the cell in which they were synthesized (autocrine action)

Answer 1

…

Question 2

Several factors determine the response of a target cell to a hormone. These can be thought of in two general ways which are?

Answer 2

(1) as factors that affect the concentration of the hormone at the target cell
(2) as factors that affect the actual response of the target cell to the hormone

Question 3

Hormones are present at very low concentrations in the extra- cellular fluid, generally in the atto- to nanomolar range

Answer 3

…

Question 4

high degree of discrimination is provided by cell-associated recognition molecules called?

Answer 4

receptors

Question 5

A target cell is defined by its ability to selectively bind a?

Answer 5

given hormone to its cognate receptor

Question 6

A target cell is defined by its ability to selectively bind a given hormone to its cognate receptor. Several biochemical features of this interaction are important in order for hor- mone-receptor interactions to be physiologically relevant are?

Answer 6

(1) binding should be specific, ie, displaceable by agonist or antagonist; (2) binding should be saturable
(3) binding should occur within the concentration range of the expected biologic response.

Question 7

All receptors have at least two functional domains which are?

Answer 7

• A recognition domain binds the hormone ligand

- region generates a signal that couples hormone recognition to some intracellular function.

Question 8

The domains responsible for hormone recognition and signal generation have been identified in?

Answer 8

protein polypeptide and catecholamine hormone receptors

Question 9

Steroid, thyroid, and retinoid hormone receptors have several func- tional domains which are?

Answer 9

• one site binds the hormone
• another binds to specific DNA regions -a third is involved in the interaction with other coregulator proteins that result in the activation (or repression) of gene transcription
• a fourth may specify binding to one or more other proteins that influence the intracellular trafficking of the receptor

Question 10

The dual functions of binding and coupling ultimately define a receptor, and it is the coupling of hormone binding to signal transduction (called receptor-effector coupling) that provides the first step in amplification of the hormonal response.

Answer 10

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Question 11

insulin receptor is a heterotetramer
composed of two copies of two different protein subunits (α β ) 22
linked by multiple disulfide bonds in which the extracellular α subunit binds insulin and the membrane-spanning β sub- unit transduces the signal through the tyrosine protein kinase domain located in the cytoplasmic portion of this polypeptide.

Answer 11

…

Question 12

The receptors for insulin-like growth factor I (IGF-I) and epi- dermal growth factor (EGF) are generally similar in structure to the insulin receptor.

Answer 12

…

Question 13

Polypeptide hormone and cat- echolamine receptors, which transduce signals by altering the rate of production of cAMP through G-proteins, are charac- terized by the presence of?

Answer 13

seven domains that span the plasma membrane.

Question 14

hormones in group I are?

Answer 14

lipophilic

Question 15

process of linking certain kinds of external events to biochemical responses done by cells?

Answer 15

signal transduction

Question 16

generic signal transduction components?

Answer 16

signaling molecule (includeing GH) > receptor > second messenger > effector > response [includes, altered gender expression or cell differentiation or altered metabolism]

Question 17

hormones that traverse the plasma membrane of all cells and binds to their cytoplasmic or nuclear receptors only in the target cells?

Answer 17

second messenger of group 1 hormones

Question 18

example of group 1 hormones?

Answer 18

steroid hormones

Question 19

group 1 hormones bind it’s receptor forming?

Answer 19

hormone receptor complex

Question 20

i’m group 1 hormones, the activated hormone receptor complex migrates yo the nucleus and hinds to specific sequences of DNA called?

Answer 20

hormone response element (HRE)

this interaction inc or dec transcription, synthesis of mRNA, of the target genes

Question 21

steps of lipid soluble hormones?

Answer 21

1) lipid soluble hormone diffuses through plasma membrane
2) hormone bonds with receptor in the cytoplasm forming receptor hormone complex
3) receptor hormone complex enters the nucleus n triggers gene transcription
4) transcribed mRNA is translated into proteins that alter cell activity

Question 22

glucocorticoids enhance the transcription of the gene coding for the key enzyme of?

Answer 22

gluconeogenesis process

Question 23

In large doses, glucocorticoids decrease the transcription of osteocalcin gene in osteoblasts i.e that may lead to?

Answer 23

demineralization of bones.

Question 24

one of the side effects of prolonged

administration of large doses of glucocorticoids is risk of?

Answer 24

DM and osteoporosis

Question 25

According to the nature of the second messenger, group II is sub classified into?

Answer 25

• •Group II a : Includes hormones that use cAMP as 2nd messenger; e.g. TSH, FSH, LH, ADH and ACTH.
• •Group II b: Uses cGMP as second messenger e.g. Atrial Natriuretic factor
• •Group II c : Use calcium or phosphatidyl inositol or both as second messengers e.g. Thyrotropin releasing hormone, Gonadotropin releasing hormone , oxytocin and ADH.
• •Group II d : The second messenger is tyrosine kinase phosphorylation cascade e.g. Prolactin , Growth hormone and Insulin

Question 26

cAMP is derived from ATP through the action of the enzyme?

Answer 26

adenylate cyclase

Question 27

cAMP binds to and activates an enzyme called……………. a that activates phosphorylation of many enzymes and proteins leading to a specific required response

Answer 27

protein kinase

Question 28

G-proteins:

Answer 28

1- G-proteins consist of three polypeptide subunits α,β & γ (heterotrimer).

2-Under the basal conditions( resting state) the α
subunit is GDP bound

3- Following the interaction of the activated receptor
(i.e after hormonal stimulation) GDP is exchanged
with GTP, so the α subunit turned into α – GTP .

4- the active α –GTP subunit dissociates from the β
& γ -dimer, then it acts on its target protein
(adenylate cyclase) to stimulate the synthesis of cAMP

Question 29

Switch of the action of hormones that increase cAMP concentration can be done by?

Answer 29

Removal of the hormone stimulus (no
synthesis).

Hydrolysis of cAMP by phosphodiesterase (PDE) enzyme.

Inhibitors of phosphodiesterase include the
methylated xanthine derivatives e.g. caffeine.
They cause increase level of cAMP intracellular

Question 30

Components of signal
transduction pathway of TSH
A member of Group II a?

Answer 30

• Signaling molecule: TSH
• Receptor : G Protein Coupled Receptor( GPCR)
• Second messenger: cAMP
• Effector: PKA
• Response: Stimulation of T3 and T4 secretion
by thyroid gland