Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Endocrine > Biochemistry of Thyroid > Flashcards

Biochemistry of Thyroid Flashcards

1
Q

What is the main physiological role of thyroid hormone?

A

To regulate cellular metabolism and energy homeostasis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the secretory unit of the thyroid? Where is thyroid hormone produced?

A

Thyroid follicle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the cells that surround the colloid called? What is the side of the cells that face the colloid called?

A

Thyroid follicular cells

Apical side

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What comprises colloid?

A

Thyroglobulin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the two sides of the thyroid follicle cells?

A

Apical and basolateral sides

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What side of the follicular cells is exposed to the bloodstream?

A

Basolateral side

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are the two biologically active thyroid hormones?

A

Thyroxine (T4)

3,5,3’-triiodothyronine (T3)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the basic structure of T3 and T4?

A

A tyrosine molecule linked to a phenyl ring

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How many phenyl rings are in T3 and T4?

A

Two

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

T3 has two iodine

atoms on its (phenyl or tyrosine) ring.

A

Tyrosine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the significance of removal of an iodine molecule from the tyrosine ring of T3?

A

Becomes 3,3,5’ triiodothyronine, (reverse T3, rT3) and has NO biological activity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Where does the synthesis of T3 and T4 occur?

A

T4 is solely in the thyroid gland, whereas T3 can occur in other tissues

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Why is it that T3 can be synthesized in many tissues, but T4 can only be synthesized in the thyroid?

A

T3 is generated by deiodination of T4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the major secretion of the thyroid gland: T3 or T4?

A

T4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Where in the thyroid does the biosynthesis of T3 and T4 occur?

A

On the surface of thyroglobulin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Where, besides fortified salt, does iodine come from the diet?

A

seafood

Plants

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is organification?

A

The process of iodine attachment to the thyroglobulin molecule

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is coupling? What is the enzyme that catalyzes this process?

A

The synthesis of MITs and DITs together to form T3/T4

TPO

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is the transporter that bring in iodine to the follicular lumen? Where is the transporter located?

A

Na/I symporter

Basolateral membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What does the Na/I symporter do? Is this active or passive?

A

Brings in one I for every two Na

Secondarily active–relies on Na/K ATPase the constant pumps Na out of the cytoplasm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What happens to the iodide once it enters the cell cytoplasm?

A

transported to the apical side of the cell, where it is transported by a membrane iodide channel protein

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is the iodide channel protein on the apical side of thyroid cells called? What happens to the iodide once it is transported into the colloid through this protein?

A

Pendrin

Goes into exocytotic vesicles fused with the apical cell membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Where does the organification of iodide occur?

A

In the exocytotic vesicles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What type of bond is the Iodine to tyrosine bond?

A

Covalent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is the enzyme that catalyzes the bond between iodine and thyroglobulin? Where is this found? What is the electrophile for this reaction?

A

Thyroid peroxidase
It is an integral protein of the apical membrane of follicular cells

H2O2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What percent of tyrosyl residues of thyroglobulin are iodinated?

A

20-30%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is the ratio of T4:T3 coupling?

A

5-7 : 1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What are the steps of thyroglobulin secretion?

A

Thyroglobulin is endocytosed, and then fuse with cell lysosomes forming phagolysosomes.

There, thyroglobulin is cleaved (hydrolyzed) to release T4 and
T3 but also DIT, and MIT.

They are then secreted.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Where does the conversion of thyroglobulin to T3/T4 take place?

A

In the phagolysosomes of the colloid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What happens to the MITs and DITs that are hydrolyzed off of thyroglobulin in the lysosome?

A

Deiodinated by a spseicifc deiodinase, and the iodide is transported back to the apical side of the follicular cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What happens to the thyroglobulin molecule when the iodines are taken off in the lysosome?

A

most sent back, but some undergo transcytosis, and are excreted

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What does an increase in serum thyroglobulin levels in indicate?

A

Thyroid pathology

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

What are the steps involved in the secretion of T3/T4 in terms of the HPA axis?

A

TRH from the hypothalamus signals the pituitary to release TSH. TSH acts on the thyroid to increase T3/T4 output.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What type of hormone is TRH? What are the components of this?

A

Peptide hormone

Pyroglutamyl-histidyl-proline residues

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

What is the precursor to TRH? How does this become TRH? Where does this occur?

A

proTRH peptide, which undergoes cleavage by the action of peptidases
and cyclization of glutamine

Paraventricular nucleus of the hypothalamus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

How does TRH get to the anterior pituitary?

A

Portal circulation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

What does TRH do to cause TSH release?

A

Gq coupled protein increased PKC.

IP3 stimulates the release of Ca, which stimulates the secretion of TSH

38
Q

What are the two products of PKC activation via Gq proteins?

A

phosphatidylinositol 4,5-
bisphosphate (PIP2) into other second messengers- diacylglycerol (DAG) and inositol
1,4,5-trisphosphate (IP3)

39
Q

What is the half life of TRH?

A

3 minutes

40
Q

What type of hormone is TSH? What are its components?

A

huge glycoprotein with an alpha and beta subunit

41
Q

What is the function of the alpha and beta subunit of TSH?

A

Beta is specific to TSH, while the alpha is not

42
Q

What is the G protein that TSH activates? What does this cause? (3)

A

Gs

This stimulates the iodide transport, transcription of thyroid peroxidase, and transcription of thyroglobulin

43
Q

What is the half-life of TSH?

A

65 minutes

44
Q

What does TSH do in terms of thyroid growth?

A

Stimulates growth

45
Q

Which is a more potent inhibitor of TRH and TSH release: T3 or T4?

A

T3

46
Q

What is the effect of T3 and T4 at the pituitary level?

A

both T4 and T3 inhibit TSH secretion by decreasing the synthesis and release of
TSH

47
Q

What is the effect of T3 and T4 at the hypothalamic level?

A

T3 inhibits
the gene expression of TRH.

Additionally, T3 down-regulates the synthesis of TRH receptor
thus reducing the ability of thyrotrophs to produce TSH in response to TRH stimulation

48
Q

What three major hormones can alter the serum concentration of TSH?

A
  • Somatostatin
  • Dopamine
  • Glucocorticoids
49
Q

What is the vast majority of T3/T4 transported as?

A

Bound to thyroid binding proteins

50
Q

What are the two major thyroid hormone binding proteins? Which binds more?

A

Globulin (70%)

Albumin (30%)

51
Q

Which has a higher affinity for thyroid binding globulin: T3 or T4? What is the significance of this?

A

T4

If thyroid secretion ceases, T4 stored in the serum serves to delay the onset of
hypothyroidism.

52
Q

What is the relative magnitude of the effect of a loss of albumin on T3 and T4 levels?

A

little effect

53
Q

What, besides globulin and albumin, binds thyroid hormones in the serum? Which do these have higher affinity for: T3 or T4?

A

Transthyretin and lipoproteins

T4

54
Q

Which is more biologically active: T3 or T4? Which is found in higher concentration in the serum? Why is there this discrepancy?

A

T3 is more active
T4 is found in higher concentration

Around 80% of T4 is deiodinated in the periphery to become T3

55
Q

What can happen to T4 and T3 in the periphery?

A

Sequential deiodination to T2 or rT3

56
Q

What is the biological activity of rT3? T2?

A

None

57
Q

What are the enzymes that catalyze the deiodination of T3/T4? What is the cofactor necessary for these?

A

Deiodinases

Selenocysteine

58
Q

What is the primary deiodinase responsible for the conversion of T4 to T3 or rT3 in the periphery? Where is this found (3 organs)? What regulates this?

A

Deiodinase I
Liver, kidney, thyroid
Regulated by TSH-stimulated cAMP production in the thyroid

59
Q

What is the role of type II deiodinase? Where is this found?

A

Vast tissue distribution–an important source of intracellular T3 in tissues that produce T3 themselves, rather than deriving it from the plasma

60
Q

What is the role of type III deiodinase? What two organs is this found in?

A

Converts T4 to rT3, and T3 to T2 (inactivating each)

Inactives thyroid hormone in the brain and placents

61
Q

What are the two main functions of deiodination?

A
  1. Trigger formation of biologically active hormones

2. Deactivate the thyroid hormones when their concentration increases above desirable levels

62
Q

What reaction do the phenolic hydroxyl groups of T4/T3 undergo to be secreted in the urine/bile?

A

Glucuronidation

Sulfation

63
Q

How does thyroid hormone get into cells?

A

Through specific high affinity transport proteins that is dependent on Na gradient

64
Q

Where are the thyroid hormone receptors located?

A

Nucleus, constitutively inhibiting transcription

65
Q

What are the DNA sequences that thyroid receptors sit atop?

A

Thyroid hormone response element (TREs)

66
Q

What are the two components of the thyroid receptor heterodimer?

A

Receptor region and the Retinoid X receptor (RXR)

67
Q

What is the function of the RXR region of the thyroid receptor?

A

Recruits HDAC activity to maintain chromatin in a condensed state, and prevent transcription

68
Q

What happens when thyroid hormone binds its receptor?

A

Conformational change, displacing the HDAC, and binding of a HAT complex.

69
Q

What is the function of HAT complexes?

A

Acetylate histones (makes available for transcription)

70
Q

Does thyroid hormone act outside the nucleus?

A

Yes–regulation of ion channels and protein kinase signaling cascades that increase cAMP

71
Q

There are thyroid hormone receptors in nearly all tissues. What is the significance of this?

A

Acceleration of the Basal metabolic rate

72
Q

How does thyroid hormone increase BMR? (2)

A

Stimulation of Na/K ATPase activity

Transcription of uncoupling mitochondrial proteins

73
Q

What is the effect of thyroid hormone on oxygen consumption by mitochondria? Why?

A

Increases d/t increase uncoupling agents

74
Q

What is the effect of thyroid hormone on adipose tissue?

A

Increases lipolysis and activating LPL

75
Q

What is the effect of thyroid hormone on glycogenolysis and gluconeogenesis?

A

Increase to balance the increased use of glucose as a fuel for thermogenesis

76
Q

What is the effect of thyroid hormone on bones?

A

Control osteoclast and osteoblast activity, and thus growth (slow growth vs osteoporosis)

77
Q

What is the effect of thyroid hormone on the CV system?

A

Increases cardiac output d/t increase in the transcription of Ca ATPase, myosin, and adenylate cyclase

78
Q

What is the effect of thyroid hormone on the liver?

A

Stimulate increased cellular uptake and metabolism of cholesterol and TAGs

79
Q

What is the effect of thyroid hormone on the pituitary (beside negative feedback)?

A

Stimulate GH production

80
Q

What is the effect of thyroid hormone on the brain?

A

Involved in the process of neurogenesis, neuronal migration, differentiation, and synaptogenesis

81
Q

What are some common causes of hypothyroidism?

A

Autoimmune disorders (e.g. Hashimoto’s thyroiditis)

82
Q

What are the autoantibodies found in Hashimoto’s thyroiditis? (3)

A

Thyroid peroxidase
Thyroglobulin
TSH receptors

83
Q

What happens to TSH levels in Hashimoto’s thyroiditis?

A

Increase

84
Q

What is the biochemical name of T3? rT3? T2?

A 
T3 = (3,5,3')
rT3 = (3, 3', 5')
T2 = (3, 3')
85
Q

What type of molecule is thyroglobulin? Where in the follicular cells is this synthesized?

A

homodimer glycoprotein

rER

86
Q

What percent of T3 and T4 does the thyroid synthesize?

A

20% of T3

100% of T4

87
Q

What are the subunits that comprise the G protein coupled receptors?

A

Alpha
Beta
Gamma

88
Q

What is the effect of T3/T4 on the pituitary?

A

Inhibits:

  • TSH transcription
  • TSH modification
89
Q

What is the effect of T3/T4 on the hypothalamus?

A

Inhibits:

  • TRH gene expression
  • TRH receptor synthesis
90
Q

Does thyroid hormone secretion impact thyroglobulin synthesis?

A

No

91
Q

Inner, outer, or dual ring activity: Type I, II, and III deiodinases?

A 
I = both
II = outer
III = Inner

Endocrine (32 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions