Nutrition Lecture 5: Zinc

Question 1

What are rich food sources of zinc?

Answer 1

Meat, poultry, shellfish, fish, liver, kidney, peas, beans, legumes

Question 2

What factors influence zinc bioavailability?

Answer 2

• Host related factors
• Enhancers and inhibitors

Question 3

What happens to zinc absorption during pregnanacy?

Answer 3

Markedly increases

Question 4

What are zinc absorption enhancers?

Answer 4

Animal protein - flesh protein, milk, cheese

Question 5

What are inhibitors of zinc absorption?

Answer 5

• High doses of iron
• Phytate

Question 6

What is phytate?

Answer 6

The molecule that plants use to store phosphate groups
- Anything that can germinate contains phytate
(Nuts, seeds, legumes)

Question 7

What is the structure of phytate?

Answer 7

6 carbon ring structure - each carbon has a phosphate group on it

Question 8

What are inositol phosphates?

Answer 8

a group of 6 naturally occurring organic compounds derived from inositol

Question 9

What inositol phosphate is not inhibitory of zinc absorption?

Answer 9

IP4

Question 10

What inositol phosphate is inhibitory of zinc absorption?

Answer 10

IP6

Question 11

How can we make IP6 not inhibitory?

Answer 11

get rid of the phosphates to make IP4

Question 12

How do we remove phosphates from IP6?

Answer 12

• Germinate the thing (bean, seed etc.) so it uses the phosphate groups
• Fermentation (bread is a fermentation process)
• Canning will also reduces the amount of phytate

Question 13

How does phytate inhibit absorption?

Answer 13

Zinc is a divalent positively charged ion
- It binds nicely to oxygens on the phytate
- Once bound it is stuck there and cant be absorbed in the gut

Question 14

Where does zinc absorption happen?

Answer 14

In proximal small intestine

Question 15

What are the two mechanisms that zinc enters enterocytes through the brush border?

Answer 15

1. Carrier-mediated transport (ZIP4)
2. Diffusion (at high doses e.g., supplements)

Question 16

What is ZIP4?

Answer 16

ZIP4 is responsible for uptake of zinc from the intestine. It facilitates the transport of zinc across the cell membrane into enterocytes (intestinal cells)

Question 17

What happens to zinc inside cells (2 options)?

Answer 17

1. Used (enzymes etc.)
2. Stored
3. Transported out into bloodstream

Question 18

What is zinc stored as inside of cells?

Answer 18

Part of metallothionein, or in vesicles, or trans-golgi network

Question 19

How is zinc transported out of cells across basolateral membrane?

Answer 19

By ZnT1

Question 20

What is ZnT1?

Answer 20

A protein that is responsible for transporting zinc out of cells

Question 21

How is zinc transported in the blood?

Answer 21

By binding to proteins in the blood such as albumin and transferrin

Question 22

What is zincs main function?

Answer 22

Over 200 enzymes are zinc-dependent

Question 23

How does zinc influence enzyme function?

Answer 23

• Stabilises protein structure by binding to amino acid residues
• Participates in reaction at active site

Question 24

How is zinc involved in our genetic material?

Answer 24

“zinc fingers” play a significant role in gene expression by binding to DNA, RNA, or proteins

Question 25

How is zinc involved in cell function?

Answer 25

- Cell growth - Cell membrane integrity - Cell replication

Question 26

How is zinc involved in our immune function?

Answer 26

Skin integrity, cell-mediated and humoral immunity

Question 27

How many proteins use zinc fingers?

Answer 27

Used by 1,000's of proteins

Question 28

What is the structure of zinc fingers?

Answer 28

2 Cys and 2 His close together in a protein chain + zinc - protein folds tightly around it

Question 29

What is metallothionein?

Answer 29

a small, cysteine-rich protein that binds heavy metals

Question 30

How many zinc ions can metallothionein bind at a time?

Answer 30

Up to 7 zinc ions

Question 31

What are the main functions of metallothionein? (4)

Answer 31

- Store zinc - Zinc transporter - Cell signalling - Protect against oxidative stress

Question 32

When were the first cases of zinc deficiency reported?

Answer 32

1960s

Question 33

What were the clinical features of the first zinc deficiency cases?

Answer 33

- Stunting - Little or no secondary sexual development

Question 34

What is acrodermatitis enteropathica?

Answer 34

a rare genetic disorder that causes defective zinc absorption in small intestine

Question 35

What mutation causes acrodermatitis enteropathica?

Answer 35

Mutation of SLC39A4 gene which encodes the ZIP4 transporter on enterocytes

Question 36

What are the symptoms of acrodermatitis enteropathica?

Answer 36

Poor immune function, wound healing, alopecia, diarrhoea and dermatitis around mouth

Question 37

What are the causes of zinc deficiency?

Answer 37

- Inadequate dietary intake - High physiological requirement - Excessive losses

Question 38

What is the relationship between zinc and diarrhoea?

Answer 38

The longer you have diarrhoea, the lower your serum zinc will be

Question 39

What are the impacts of zinc deficiency?

Answer 39

- Impaired growth - Impaired immune competence - Poor taste acuity

Question 40

What groups are at risk for zinc deficiency?

Answer 40

- Infants/children - Pregnancy - Elderly - Vegetarians/vegans - Low income - Prolonged diarrhoea

Question 41

What does zinc supplementation do for diarrhoea?

Answer 41

Reduces the incidence of it

Question 42

What is the upper limit of zinc intake?

Answer 42

>40mg/day

Question 43

What happens when someone consumes extremely high doses of zinc (>1g/day)?

Answer 43

- Metallic taste - Nausea - GI stress - May be fatal

Question 44

Zinc absorption upregulates the production of what?

Answer 44

Metallothionein

Question 45

What does Metallothionein preferentially bind?

Answer 45

binds copper over zinc

Question 46

What is the EAR for zinc?

Answer 46

Men = 12mg/day Women = 6.5mg/day

Question 47

What is the RDI for zinc?

Answer 47

Men = 14mg/day Women = 8mg/day