Lecture 5 - Zinc Flashcards
what are food sources of zinc
- dairy (because we consume large amounts)
- oysters and seafood
- meat and poultry
- organ meats like liver and kidney (found in pate and stuff)
what factors affect zinc bioavailability
- host related factors
- enhancers and inhibitors in meal
when is zinc absorption enhanced
zinc absorption is enhanced during pregnancy
in terms of zinc bioavailability what are enhancers
- meat
- fish
- poultry
animal protein in general are good examples of zinc absorption enhancers
in terms of zinc bioavailability what are inhibitord
- if you are taking high doses of iron this will inhibit zinc absorption, especially if supplement is taken between meals
- phytate
- combination of phytate and calcium = together this even more inhibitory
what is phytate
the molecule that the way in which a plant can store phosphate groups that it will need in order to germinate
what contains phytate
anything that could germinate (seeds, nuts, wholegrains, legumes, brown rice)
what does phytate do to zinc
very powerful inhibitor
what is the structure of phytate
6 carbon ring structure = each has a phosphate attached to it
what is the phytate ring structure similar to
similar to glucose (also 6 carbon ring, but one of them is oxygen in the ring)
how is phytate formed
glucose is converted to inositol and the groups are replaced with phosphate groups attached
what are some inositol phosphates
IP6 and IP4
is IP6 inhibitory or not
powerfully inhibitory
why does phytate store phosphate for plants
so the plant has easy ways to take the phosphate off and use them
what can you do to food to change it from IP6 to IP4
germinate the food, use fermentation also canning foods
what kind of ion is zinc and why does link to phytate
divalent positively charged ion = Zn2+
- binds nicely to the two oxygen on the phytate
where is zinc absorbed
proximal small intestine
what are the two mechanisms for zinc absorption
- carrier mediated transport (ZIP4)
- diffusion (at high doses e.g supplements)
inside cells zinc is either … or ….
- used (enzymes etc)
- stored (part of meallothionein, or in vesicles, or trans-golgi network)
zinc is transported across basolateral membrane by
ZnT1
what does zinc bind to for transport
- albumin
- transferrin
if you don’t absorb all zinc what will happen with it
it will be excreted
main function of zinc
> 200 zinc dependent enzyme
how is zinc related to enzymes
- stabilises protein structure by binding to amino cid residues
- participates in reaction at active site
other zinc functions
- gene expression (zinc fingers)
- tissue and cell growth (regulate protein synthesis)
- cell membrane integrity
- cell replication
- bone formation
- immune function
- associated with insulin
- taste acuity
what are zinc fingers used by
1,000s of proteins
what is the structure of zinc fingers
2 Cys and 2 His close together in protein chain > + zinc > protein folds tightly around it
forms a stable structure
depending on the function of the particular protein what influence can zinc fingers have
enhance or repress gene transcription
what is metallothionein
small cytoplasmic proteins
what is metallothionein rich in
cysteine rich - bind up to 7 zinc ions at a time
what are the functions of metallothionein
- store zinc (high binding affinity for zinc)
- zinc transporter within cell
- cell signalling (especially within and between nerve cells)
- protect against oxidative stress
when and what were the first cases of zinc deficiency reported
1960’s in middle east = male adolescent “dwarfs”
what were the clinical features of the first zinc reported zinc deficiencies
- stunting = short for their age
- little or no secondary sexual development
what kind of disorder is acrodermatitis enteropathica
- autosomal recessive disorder (need the mutation from both parents)
what is acrodermatitis enteropathica caused by and what is the mutation that causes this
defective zinc absorption in small intestine
mutation of a gene that codes ZIP4 transporter on enterocytes
what are the symptoms of acrodermatitis enteropathica
diarrhoea,
alopecia,
dermatitis around the mouth, nostrils, eyes and on palms and soles
poor immune function
delayed healing
what are the inadequate dietary intake reasons for zinc deficiency
- low energy intake
- poor bioavailability
- environment - low soil zinc
what are the high physiological requirement reasons for zinc deficiency
- growth
- pregnancy
- infection = immune function
what are the excessive losses reasons for zinc deficiency
- diarrhoea
- surgery, burns
- excessive alcohol consumption
impacts of zinc deficiency of impaired growth
- infancy = poor weight gain
- children = poor linear growth
impacts of zinc deficiency of impaired immune competence
- increased morbidity : diarrhoea, pneumonia
- increased mortality
what are the groups at risk of zinc deficiency
- infants, toddlers and young children
- adolescents
- pregnant or lactating women
- “older people”
- vegetarians, vegans
- low socio economic status
- prolonged diarrhoea
what are the effects of zinc toxicity
- metallic taste in mouth
- nausea
- gastric distress
- may be fatal
intakes above the upper level of zinc lead to what
reduced copper status
what are extremely high doses of zinc
> 1g zinc/day
what are intakes above the upper level of zinc
> 40mg/day
what does matallothionine preferentially bind to
prefers to bind to copper over zinc
how does increased zinc lead to decreased copper
Zn upregulates the production of metallothionine, this will bind to copper if it is available and then it is stuck in storage and the copper won’t be absorbed into the bloodstream
what are the zinc recomendations for adult men
RDI : 14mg/day
EAR : 12mg/day
what are the zinc recomendations for adult women
RDI : 8 mg/day
EAR : 6.5 mg/day
what is the upper level of intake for zinc
40mg/day
