EXAM #1: NORMAL BIOCHEMISTRY AND PHYSIOLOGY Flashcards Preview

Endocrine > EXAM #1: NORMAL BIOCHEMISTRY AND PHYSIOLOGY > Flashcards

Flashcards in EXAM #1: NORMAL BIOCHEMISTRY AND PHYSIOLOGY Deck (36):
1

What is the precursor of the thyroid hormones?

Tyrosine

2

What is the active form of thyroid hormone? Which is more active?

T3* and T4

*T3 is more active

3

What are the biologicaly inactive forms of the thyroid hormones?

T2 and rT3

4

Where are thyroid hormones synthesized?

Thyroid follicle

5

What direction does the apical side of the follicular cell face? Basal?

Apical= colloid

Basal= bloodstream

6

What is the platform for T3 and T4 synthesis?

Thryoglobulin

7

What is exogenous substance is required for the synthesis of thyroid hormones?

Iodine

8

What has virtually eliminated iodine deficiency in the US?

Iodized salt

9

How is iodine transported into the thyroid follicle?

Na+-I cotransporter (symporter)

10

What is organification?

Adding iodine to thyroglobulin

11

What is the site of organification?

Exocytotic vesicles in the colloid

12

Outline the process of organification.

Thyroid peroxidase oxidizes and attaches iodide to the tyrosyl residues

*Uses hydrogen peroxide

13

What is the outcome of organification?

Formation of MIT and DIT

*MIT= 1 iodine
DIT= 2x iodine

14

What is the next step after organification?

Coupling

15

What enzymes is responsible for coupling?

Thyroid peroxidase (TPO)

16

How is thyroglobulin released via the lysosomal pathway?

1) Endocytosis
2) Hydrolysis in the lysosome/ proteolysis
3) Diffusion into the circulation

17

What happens to thyroglobulin after cleavage of T3 and T4 during release?

1) Recycled to colloid
2) Transcytosis into the circulation

18

Describe the composition of TRH.

Pyroglutamul-histidyl-proline residues

19

What is the mechanism of TRH signaling in the anterior pituitary?

GPRC via
- PLC
- IP3
- Ca++

20

What is the mechanism of TSH signaling in the thyroid gland?

GPRC via
- cAMP protein kinases

21

Specifically, what does TSH stimulate?

1) Iodide transport
2) Transcription of thyroglobulin
3) Transcruption of tyroid peroxidase (TPO)

22

What thyroid hormone is preferentially bound to serum proteins?

T4

23

What enzymes catalyze the metabolism of T3 and T4?

Deiodinases

24

What are the functions of deiodinases?

1) Formation of active T3 from T4
2) Deactivation of T3 and T4 when their concentrations are too high

25

What form of deiodinase is active against T3?

Type III

*Thus, this is the major enzyme that deactivates thyroid hormones

26

What is the function of Type I deiodinase?

Outer/ inner ring vs. T4

27

Where is Type I deiodinase located?

Liver, kidney, thyroid

28

What are the products of Type I deiodinase?

T3 or rT3

29

What is the function of Type II deiodinase?

Outer ring vs. T4

30

What is the location of Type II deiodinase?

Diffuse

31

What is the product of Type II deiodinase?

Intracellular T3

32

What is the function of Type III deiodinase?

Inner ring vs. T4 and T3

33

Where is Type III deiodinase located?

Brain and placenta

34

What are the products of Type III deiodinase?

rT3 and T2

35

Describe the mechanism of action of the thyroid hormones in the nucleus.

1) TR binds DNA with RXR
2) TR/RXR recruits HDAC, repressing transcription
3) Binding of T3 or T4 displaces HDAC for HAT*

HAT complex turns target genes ON

36

What is stimulated by T3/T4 in regards to cellular metabolism?

1) Increased oxygen consumption/ heat production
2) Increased adipose tissue lipolysis
3) Increased glycogenolysis and gluconeogenesis