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HUNT241 > Nutrition Lecture 5: Zinc > Flashcards

Nutrition Lecture 5: Zinc Flashcards

1
Q

What are rich food sources of zinc?

A

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

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2
Q

What factors influence zinc bioavailability?

A
  • Host related factors
  • Enhancers and inhibitors
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3
Q

What happens to zinc absorption during pregnanacy?

A

Markedly increases

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4
Q

What are zinc absorption enhancers?

A

Animal protein - flesh protein, milk, cheese

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5
Q

What are inhibitors of zinc absorption?

A
  • High doses of iron
  • Phytate
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6
Q

What is phytate?

A

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

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7
Q

What is the structure of phytate?

A

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

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8
Q

What are inositol phosphates?

A

a group of 6 naturally occurring organic compounds derived from inositol

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9
Q

What inositol phosphate is not inhibitory of zinc absorption?

A

IP4

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10
Q

What inositol phosphate is inhibitory of zinc absorption?

A

IP6

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11
Q

How can we make IP6 not inhibitory?

A

get rid of the phosphates to make IP4

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12
Q

How do we remove phosphates from IP6?

A
  • 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
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13
Q

How does phytate inhibit absorption?

A

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

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14
Q

Where does zinc absorption happen?

A

In proximal small intestine

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15
Q

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

A
  1. Carrier-mediated transport (ZIP4)
  2. Diffusion (at high doses e.g., supplements)
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16
Q

What is ZIP4?

A

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

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17
Q

What happens to zinc inside cells (2 options)?

A
  1. Used (enzymes etc.)
  2. Stored
  3. Transported out into bloodstream
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18
Q

What is zinc stored as inside of cells?

A

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

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19
Q

How is zinc transported out of cells across basolateral membrane?

A

By ZnT1

20
Q

What is ZnT1?

A

A protein that is responsible for transporting zinc out of cells

21
Q

How is zinc transported in the blood?

A

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

22
Q

What is zincs main function?

A

Over 200 enzymes are zinc-dependent

23
Q

How does zinc influence enzyme function?

A
  • Stabilises protein structure by binding to amino acid residues
  • Participates in reaction at active site
24
Q

How is zinc involved in our genetic material?

A

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

25
Q

How is zinc involved in cell function?

A
  • Cell growth
  • Cell membrane integrity
  • Cell replication
26
Q

How is zinc involved in our immune function?

A

Skin integrity, cell-mediated and humoral immunity

27
Q

How many proteins use zinc fingers?

A

Used by 1,000’s of proteins

28
Q

What is the structure of zinc fingers?

A

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

29
Q

What is metallothionein?

A

a small, cysteine-rich protein that binds heavy metals

30
Q

How many zinc ions can metallothionein bind at a time?

A

Up to 7 zinc ions

31
Q

What are the main functions of metallothionein? (4)

A
  • Store zinc
  • Zinc transporter
  • Cell signalling
  • Protect against oxidative stress
32
Q

When were the first cases of zinc deficiency reported?

A

1960s

33
Q

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

A
  • Stunting
  • Little or no secondary sexual development
34
Q

What is acrodermatitis enteropathica?

A

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

35
Q

What mutation causes acrodermatitis enteropathica?

A

Mutation of SLC39A4 gene which encodes the ZIP4 transporter on enterocytes

36
Q

What are the symptoms of acrodermatitis enteropathica?

A

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

37
Q

What are the causes of zinc deficiency?

A
  • Inadequate dietary intake
  • High physiological requirement
  • Excessive losses
38
Q

What is the relationship between zinc and diarrhoea?

A

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

39
Q

What are the impacts of zinc deficiency?

A
  • Impaired growth
  • Impaired immune competence
  • Poor taste acuity
40
Q

What groups are at risk for zinc deficiency?

A
  • Infants/children
  • Pregnancy
  • Elderly
  • Vegetarians/vegans
  • Low income
  • Prolonged diarrhoea
41
Q

What does zinc supplementation do for diarrhoea?

A

Reduces the incidence of it

42
Q

What is the upper limit of zinc intake?

A

> 40mg/day

43
Q

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

A
  • Metallic taste
  • Nausea
  • GI stress
  • May be fatal
44
Q

Zinc absorption upregulates the production of what?

A

Metallothionein

45
Q

What does Metallothionein preferentially bind?

A

binds copper over zinc

46
Q

What is the EAR for zinc?

A

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

47
Q

What is the RDI for zinc?

A

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

HUNT241 (22 decks)

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