Zinc (Part1)

Question 1

Where is zinc mainly found?

Answer 1

Shellfish, beef

Question 2

How is Zinc absorbed?

Answer 2

Mainly in the small intestine

• Carrier-mediated which is saturable. It is separated into two parts, the apical and basolateral membrane transport
• Passive which is non-saturable by parracellular diffusion

Question 3

How is Zinc absorption regulated?

Answer 3

Increased dietary zinc = decrease absorption = increase fecal loss

Question 4

How is zinc homeostasis mainly regulated?

Answer 4

By how much you absorbed

Question 5

What proteins are involved in Zinc absorption and transport in the intestine?

Answer 5

Zip4 = uptake 
ZnT1 = transport

Question 6

ZnT1 knockout mice do not exist because…

Answer 6

It is embryonic lethal

Question 7

What is Acrodermatitis enteropathica (AE)?

Answer 7

A disease of zinc malabsorption 
Zinc -responsive inborn error of metabolism
Symptoms include
-dermatitis 
-impaired immunity
-impaired wound healing 
-hair loss 
-anorexia 
- impaired taste acuity

Question 8

AE is caused by?

Answer 8

A mutation in Zip4

Question 9

Who does AE mainly affect?

Answer 9

Young infants

Question 10

How do you treat AE?

Answer 10

Providing 20-30 mg Zn supps/ Day

Question 11

What enhances Zinc absorption?

Answer 11

Amino Acids such as histidine, methionine, cysteine

Organic acids such as citrate

Question 12

What are inhibitors of Zinc absorption?>

Answer 12

Phytate and Iron

Question 13

How is Zinc transported in the plasma?

Answer 13

Mainly bound to albumin in circulation

Question 14

There are a few tissues that take up more zinc than others such as…?

Answer 14

The pancreas

Question 15

Why does the pancreas take up a lot of zinc

?

Answer 15

Because the insulin producing B-cells take up a lot of zinc because they need zinc to make and secrete insulin

Question 16

Besides absorption and excretion how else can zinc be regulated?

Answer 16

By the pancreas excretions of bile

Question 17

How is Zinc excreted?

Answer 17

Mainly fecal

but in diseases of muscle catabolism urinary excretion may increase

Question 18

What are the Zip proteins?

Answer 18

Importers

Question 19

What are the ZnT proteins?

Answer 19

Exporters

Question 20

Why are there so many Zinc transporters?

Answer 20

Because they are expressed in different tissues

Question 21

How much zinc is stored and where is most of it located?

Answer 21

Total zinc content is 1.5-2.5g and the skeletal muscle holds most of it.

Question 22

What is metallothionein?

Answer 22

A zinc storage protein and Copper storage

Question 23

How many AA does MT have and how many of those are cystienes?

Answer 23

61 and 20 are Cysteines

Question 24

How many atoms of Zinc /copper can bind to MT for storage?

Answer 24

7

Question 25

What are the functions of Zinc?

Answer 25

1. Catalytic
   - greater than 300 known Zn metalloenzymes
2. Structural
   - Zinc finger proteins
3. Regulatory
   - Zinc finger proteins

Question 26

Zn Metalloenzymes

Answer 26

Alkaline phosphatase, RNA polymerases, Alcohol dehydrogenase