Vitamins Flashcards
(183 cards)
1
Q
What is a vitamin and in what amounts are they needed?
A
Vitamins are essential organic substances needed in minute amounts to activate highly specific metabolic functions in the body
2
Q
Why are vitamins accessory nutrients?
A
Because they themselves supply no energy and form no structures but their deficiencies can be dangerous as well as toxic if some are in excess
3
Q
What are vitamins that must be consumed called?
A
Preformed vitamins
4
Q
What are vitamins that may be synthesised by the body using precursors called?
A
Pro-vitamins
5
Q
Vitamins can be classified, what are the two sub divisions?
A
Water soluble vitamins and lipid soluble vitamins
6
Q
How would you describe water soluble vitamins?
A
They are not stored in any tissues and excess is removed in urine
7
Q
Examples of some water soluble vitamins would include?
A
b1, b2, b3, b5, b6, b9, b12, vitamin c, biotin (vit h)
8
Q
Where are lipid soluble vitamins stored and can they be removed?
A
They are stored in the liver and adipose. The body has no way of removing them until they are used.
9
Q
Give some examples of some lipid soluble vitamins
A
Vitamins a, d, e and k
10
Q
Of the vitamins that are ingested, where do the majority originate from?
A
From plant sources (except b12) as byproducts of photosynthesis
11
Q
Give two examples of pro vitamins and from what they are synthesised
A
carotene –> vitamin a ultraviolet light –> vitamin d
12
Q
What are most vitamins converted into, for use inside the body? What is one of their main roles?
A
Most vitamins are converted into coenzymes - b12
13
Q
Some vitamins such as vitamin d and some metabolites of vitamin a have a different role other than coenzymes, what can they do?
A
They act more like hormones, binding to receptors and controlling gene expression and metabolism
14
Q
Some vitamins such as vit c and vit e act as ______, not as coenzymes or the control of gene expression and metabolism
A
antioxidants
15
Q
What is the role of antioxidants
A
Preventing or delaying some types of cell damage
16
Q
What is a coenzyme?
A
A coenzyme is a non protein compound that is necessary for the functioning of an enzyme
17
Q
Some coenzymes allow the substrate to react more readily, give some vitamin derivatives that allow this
A
CoA, pyridoxal phosphate, thiamin diphosphate and vitamin b12
18
Q
There are some oxidative coenzymes, what are these
A
NAD+, NADP+, FAD, lipoic acid
19
Q
What is the function of oxidative coenzymes?
A
To carry hydrogen atoms or electrons
20
Q
What is the protein part of the enzyme called?
A
The apoenzyme
21
Q
When the protein part of the enzyme is in combination with the coenzyme the catalytically competent enzyme is known as what?
A
As the holoenzyme
22
Q
Apoenzyme + coenzyme =
A
holoenzyme
23
Q
Vitamin b1 is
A
thiamine
24
Q
vitamin b2 is
A
riboflavin
25
vitamin b3 is
niacin
26
vitamin b5 is
pantothenic acid
27
vitamin b6 is
pyridoxine
28
vitamin b9 is
folic acid
29
vitamin b12 is
cobalamin
30
vitamin c is
ascorbic acid
31
vitamin a is
retinol
32
vitamin d is
calcitrol
33
vitamin e is
tocopherols
34
Where is thiamine/vitamin b1 derived from?
From a substituted pyrimidine and thiazole
35
Is thiamine water soluble or lipid soluble?
It is water soluble
36
How can one obtain vitamin b1/thiamine?
Through their diet from most grains
37
Where is a deficiency of b1 prevalent?
In South east Asia
38
What is the active form of thiamine?
Thiamin pyrophosphate - TPP
39
Where is thiamine converted to its active form of thiamin pyrophosphate?
In the brain and liver
40
What enzyme converts thiamin/vit b1 to thiamin pyrophosphate?
The enzyme thiamin diphosphotransferase
41
Why is thiamin pyrophosphate necessary in the body?
It is a key coenzyme for the pyruvate and a-ketoglutarate dehydrogenase catalysed reactions
42
What is the function of pyruvate dehydrogenase?
Part of a multi enzyme complex that acts to convert pyruvate generated in glycolysis into acetyl coA for entry into the krebs cycle
43
What is the function of a-ketoglutarate dehydrogenase?
regulation in the krebs cycle. Involved in the conversion of ketoglutarate to syccinyl coA
44
Thiamin pyrophosphate (TPP) is a necessary coenzyme for pyruvate dehydrogenase and a-ketoglutarate, what does TPP assist in in both cases?
Assists in the decarboxylation of a small ketoacid
45
In addition to its uses in metabolism, list three other uses of thiamine/ vitamin b1.
1. Enhance circulation and blood formation 2. Maintenance of nervous system - biosynthesis of acetylcholin and GABA 3. Production of HCl in stomach - digestive role
46
What is a deficiency of b1 called?
Beriberi
47
Alchohol-related thiamin deficiency is caused by an
inadequate intake of thiamine as well as impaired absorption and storage
48
What are the early symptoms of beriberi
they are non specific and include fatigue, loss of appetite, irritability, abdominal discomfort
49
As the disease of beriberi progresses, what do patients tend to develop?
Burning sensations, tingling in the extremities, changes in sensation - numbness, may develop psychosis. Heart failure,
50
Is vitamin b2/riboflavin water soluble or lipid soluble?
Water soluble
51
What is vitamin b2/riboflavin synthesised by?
Microorganisms and plants
52
What types of food provide vitamin b2?
Milk, liver, cheese, green vegetables, almonds
53
What destroys vitamin b2?
Exposure to light
54
What is the active form of riboflavin?
Riboflavin is the precursor for the coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). So it is active as a coenzyme
55
The enzymes that require FMN and FAD as coenzymes are called?
Flavoproteins
56
Several flavoproteins also contain metal ions, what are these termed?
Metalloflavoproteins
57
Both FMN and FAD are involved in a wide range of
redox reactions and help the metabolism of carbohydrates, amino and fatty acids
58
Symptoms associated with a deficiency of vitamin b2/riboflavin include
sore throat, dermatitis, anemia, neuropathy and cataract formation
59
Where is b2/riboflavin deficiency observed?
In malnutrition or chronic alcoholism
60
The conversion of riboflavin to flavin mononucleotide is required for absorption and transport into many tissues. This conversion is inhibited by...
hypothyroidism and the structurally similar medications such as tetracycline and tricyclic antidepressants
61
What is hypothyroidism?
Thyroid produced less thyroid hormone than it should which causes the metabolism to run too slow
62
Is niacin water or lipid soluble
Water soluble
63
B3/ niacin can be synthesised by the body, how?
It can be synthesised in the liver from the essential amino acid tryptophan but the synthesis is inefficient
64
The synthesis of niacin within the human body is inefficient, so what types of food can you obtain vitamin b3/niacin from?
Proteins, meat, fish, milk, eggs, peanuts
65
What is the active form of b3/niacin?
Nicotinamide adenine dinucleotide NAD+ and nicotinamide adenine dinucleotide phosphate NADP+
66
What is the function of the active forms of b3/niacin (NAD+, NADP+)?
Both function as cofactors for numerous dehydrogenases
67
What is the role of the derivatives of NAD+/NADP+ that come from coenzymes from b3/niacin?
Energy metabolism
68
List two other functions of niacin in the body
Removing toxic chemicals from the body and assisting in the production of steroid hormones
69
What is the deficiency disease associated with a b3 deficiency?
Pellagra
70
What two ways could cause an individual to develop b3 deficiency?
Failure of the body to absorb niacin or trptophan
71
What are the symptoms of pellagra?
dermatitis, blackening of the tongue, scaly skin sores
72
Where were early cases of pellagra observed?
Europe shortly after the introduction of corn
73
Why did the consumption of corn cause niacin deficiencies?
The niacin in corn is not bioavailable unless treated with a strong base
74
Is vitamin b5/ pantothenic acid water soluble or lipid soluble?
It is water soluble
75
What is pantothenic acid formed from?
B-alanine and pantoic acid
76
Which foods can pantothenic acid / vit b5 be found in?
Whole grain cereals, legumes, meat, eggs
77
What is the active form of pantothenic acid?
Pantothenate is required for the synthesis of coenzyme a, co-a which is needed for acetyl coA
78
What is the function of acetyl coa?
Delivers the carbon atoms to the krebs cycle to be oxidised for energy
79
What does pantothenic acid/vit b5 enhance within the body?
Healthy skin and muscles, fights allergies, metabolism
80
Symptoms of a deficiency in b5 include...
Headaches, depression, tingling, frequent infections.
81
What types of people would benefit from b5 / pantothenic acid?
People who are overstressed or those who are predisposed to allergies.
82
Is vitamin b6/pyridoxine water soluble or lipid soluble?
Water soluble
83
What is the origin of pyridoxine?
Nitrogen fixing bacteria
84
What is the active form of pyridoxine/ vit b6?
Pyridoxal phosphate
85
What enzyme converts pyridoxine to pyridoxal phosphate?
The atp requiring enzyme pyridoxal kinase
86
What is the function of pyridoxal phosphate?
Functions as a coenzyme in enzymes involved in transamination reactions - required for synthesis and catabolism of amino acids
87
What does a deficiency in b6/pyridoxine cause?
Skin disorders, poor coordination, insomnia,
88
\*Describe the structure of b9/folic acid.
A conjugated molecule consisting of a pteridine ring structure linked to para-aminobenzoic acid that forms pteroic acid. Folic acid itself is then generated through the conjugation of glutamic acid residues to pteroic acid
89
What types of food is folic acid/b9 obtained from?
From leafy vegetables, yeast, animal liver
90
What is the primary form of folic acid/ b9
Folic acid is reduced within cells to tetrahydrofolate THF
91
Which enzyme reduces folic acid / b9 to tetrahydrofolate - the active form of folic acid?
Dihydrofolate reductase
92
What is the function of tetrahydrofolate?
To carry and transfer various forms of one carbon units during biosynthetic reactions
93
\*In biosynthetic reactions, what is the one carbon unit that tetrahydrofolate helps to transfer?
Methyl, methylene, methenyl, formyl or formimino groups
94
What are carbon transfer reactions required in? Biosynthesis of what?
The biosynthesis of serine, methonine, glycine, choline and purine nucleotides
95
What is the most pronounced effect of a folate deficiency?
On DNA synthesis
96
What happens when a folate deficiency results in the inability to synthesis DNA during erythrocyte maturation?
Abnormally large erythrocytes - the disease is termed macrocytic anemia
97
Why do pregnant women need more folate?
Because there is an increased number of rapidly proliferating cells present in the blood
98
Describe the structure of vitamin b12 or cobalamin
Composed of a tetrapyrrol ring and a co ordinated cobalt ion
99
What organisms synthesis b12/cobalamin
Microorganisms.
100
B12 is found in the liver of animals bound to a protein known as
methycobalamin
101
Where does hydrolysis of methycobalamin occur
in the stomach by gastric acids or the intestines
102
Following absorption of vitamin b12, it is transported to the liver in the blood bound to what?
To transcobalamin II
103
What does vitamin b12 help in the production of?
Red blood cells
104
Explain how the catabolism of some fatty acids and amino acids requires vitamin b12 as a coenzyme
The enzyme in this pathway, methylmalonyl coa mutase requires vitamin b12 as a cofactor in the conversion of methylmalonyl coa to succinyl coa
105
Describe a second reaction which requires vitamin b12 as a coenzyme
Vitamin b12 catalyses the conversion of homocysteine to methionine and is catalysed by methionine synthase
106
Why are vegetarians at a high risk of developing vitamin b12 deficiencies
Because plants do not produce b12
107
A lack of vitamin b12 can lead to...
anemia
108
How is vitamin c derived?
from glucose via the uronic acid pathway
109
Why is ascorbic acid required in the diet?
Because the enzyme l-gulonolactone oxidase responsible for the conversion of gluconolactone to ascorbic acid is absent in primates
110
What is the active form of vitamin c?
Ascorbate acid
111
What is the main function of ascorbate acid?
A reducing agent in a number of different reactions
112
Vitamin c has the potential to _____ cytochromes a and c of the respiratiory chain as well as ___________ \_\_\_\_\_
reduce, molecular oxygen
113
What is the most important reaction requiring ascorbate as a cofactor?
The hydroxylation of proline residues in collagen
114
Because vitamin c serves as a coenzyme in the hydroxylation of proline residues in collagen, it is required for the maintenance of
normal connective tissue
115
Ascorbic acid is required for the reduction of iron 3 to iron 2 in the
gut, allowing iron to be absorbed into the bloodstream
116
Ascorbic acid is required for the catabolism of which amino acid?
tyrosine
117
Ascorbic acid is required for the synthesis of what?
1. synthesis of epinephrine from tyrosine 2. synthesis of bile acids
118
why is ascorbic acid required in the involvement in the process of steroidogenesis
The adrenal cortex contains high levels of vit c which are depleted upon adrenocorticotrophic hormone (acth) stimulation of the gland
119
What is a deficiency of vitamin c called?
scurvy
120
What is scurvy characterised by?
easily bruised skin, muscle fatigue, swollen gums
121
What is the cause of a deficiency?
a poor diet/ increased requirement
122
What is the primary physiological state leading to an increased requirement for vitamin c?
severe stress - this is due to a rapid depletion in the adrenal stores of the vitamin
123
When was scurvy common?
Among sailors in the days when only non perishable foods could be stocked aboard ships
124
What three biologically active molecules does vitamin a consist of?
Retinol, retinal and retinoic acid
125
What plant precursor molecule is vitamin a derived from?
b-carotene
126
What does b-carotene consist of
two molecules of retinal linked at their aldehyde ends
127
What is b-carotene referred to as
the provitamin form of vit a
128
Ingested b carotene is cleaved in the lumen of the small intestine by what enzyme to yield what produce
b-carotene dioxygenase to yield retinal
129
How is retinal reduced to retinal?
by retinaldehyde reductase within the intestines
130
Retinol can then be esterified to palmitic acid and delivered to the
blood
131
Where is palmictic acid stored
stored in the liver as a liver ester with lipocytes
132
The transport of retinol from the liver to extrahepatic tissues occurs how
by binding of retinol to aproretinol binding protein
133
Where is the retinol-rbp complex transported to?
to the cell surface within the golgi complex and secreted
134
How is plasma transport of retinoic acid accomplished
by binding to albumin
135
The photoreceptor of most mammalian visual cells if a protein called
rhodopsin or visual purple
136
What is rhodopsin a complex made of
scotopsin and the 11-cis-retinal form of vitamin a
137
where is rhodopsin embedded
rhodopsin is a receptor embedded in the membrane of the rod cell
138
when rhodopsin is exposed to light what happens?
it is bleached, releasing the 11-cis-retinal
139
How is retional necessary for mucous production
it functions in the synthesis of certain glycoproteins and mucopolysaccharides
140
where is vitamin a stored?
in the liver
141
What are the symptoms of a vitamin a deficiency?
night blindness
142
How does deterioration of the eye tissue due to a lack of vitamin a occur?
progressive keratinization of the cornea, a condition called xerophthalmia
143
There is an increased risk of cancer when vitamin a is low, why?
Because vitamin a is thought to be a very effective antioxidant
144
Excess accumulation of vitamin a in the liver can lead to
toxicity
145
Vitamin d is what type of hormone
a steroid hormone
146
what is the function of vitamin d
to regulate specific gene expression following interaction with its intracellular receptor
147
what is the biologically active form of the hormone
vitamin d3 calcitriol
148
what is the function of the biologically active hormone of vitamin d calcitriol?
functions primarily to regulate calcium and phosphorous homeostasis
149
Where is active calcitriol derived from in plants?
from ergosterol which is produced in plants
150
Where is active calcitriol derived from in humans?
from 7-dehydrocholestrol which is produced in the skin
151
Ergocalciferol (vitamin d2) is formed by
uv irridation of ergosterol
152
In the skin 7-dehydrocholestrol is converted to vitamin d3 following what?
irradiation
153
Viamin e is a mixture of several related compounds known as
tocopherols
154
what is the most potent molecule out of the tocopherols
the a-tocopherol
155
vitamin e is absorbed from where
the intestines
156
where is vitamin e delivered to once absorbed from the intestines
to the liver
157
vitamin e has a lipophilic nature which means it accumulates where?
in cellular membranes, fat deposits and other circulating lipoproteins
158
Where is the major site of vitamin e storage?
in the adipose tissue
159
what is the function of vitamin e as a natural antioxidant
scavenging free radicals and molecular oxygen
160
what is the major symptom of a vtiamin e deficiency in humans in relation to red blood cells?
it leads to an increase in red blood cell fragility
161
What is the dietary requirement of pathothenic acid
10-15mg/day
162
What is the dietary requirement of biotin
0.15-0.3mg/day
163
What is the dietary requirement of thiamin
0.23mg or more per 1000kcal of food, min 0.8mg/day
164
What is the dietary requirement of vitamin b6
1.5-2mg/day
165
What is the dietary requirement of nicotinamide
7.5mg/day
166
What is the dietary requirement of riboflavin
0.2-0.4mg/day
167
What is the dietary requirement of vitamin b12
2 µg/day
168
What is the dietary requirement for vitamin c
50-200mg/day
169
What vitamin is this
Vitamin b1
170
What vitamin is this
vit b2
171
what is this
active form of b2 fmn flavin mononucleotide
172
What is this
active form of vit b2 - flavin adenine dinucleotide
173
what is this
niacin
174
what is this
pantothenic acid
175
what is this
acetyl coa
176
what is this
pyridoxine
177
what is this
pyridoxal phosphate
178
what is this
b9/folic acid
179
what is this
cobalamin
180
what is this
arcorbic acid
181
what is this
vit a
182
what is this
vitamin d
183
what vit is this
e
