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NUTR2101 > Week 9 and 10 > Flashcards

Week 9 and 10 Flashcards

1
Q

What is the difference between mandatory and voluntary fortification?

A

Mandatory
replacing nutrients lost by processing or where there is an obvious need

voluntary
manufacturers are allowed to add nutrients and decide which ones. this needs to fit in with regulations though.

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2
Q

Name all the B vitamins

A 
B1: thiamin 
B2: riboflavin 
B3: niacin 
B5: pantothenic acid 
B6: pyridoxine 
B7: biotin 
B9: folic acid 
B12: cobalamin
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3
Q

Which vitamins are water soluble?

A

B vitamins
vitamin C
Choline

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4
Q

what is a coenzyme?

A

when the prosthetic group of an enzyme is an organic compound

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5
Q

what is a cofactor?

A

when the prosthetic group of an enzyme or another protein is a metal ion

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6
Q

what does coenzyme do?

A

enable the specific enzymes to function

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7
Q

What the Thiamin coenzyme called?

A

thiamin pyrophosphate (TPP)

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8
Q

Describe the absorption of Thiamin?

A

Small intestine, sodium-dependent active or passive absorption
Only free thiamin is absorbed

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9
Q

How is Thiamin transported?

A

Transported by red blood cells (RBCs) in the coenzyme form: thiamin pyrophosphate (TPP)

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10
Q

How is Thiamin stored?

A

Small amount stored in muscles and the liver

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11
Q

How is Thiamin excreted?

A

Excess rapidly filtered by kidneys and excreted via the urine

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12
Q

What are the functions of thiamin?

A

Assists enzymes involved in carbohydrate and branched chain amino acids metabolism

Thiamin is needed for normal function of nervous system

Required in decarboxyl at ion reactions

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13
Q

What are the diseases that are associated with thiamin deficiency?

A

Beriberi

Wernicke-Korsakoff syndrome

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14
Q

which foods contain thiaminase enzymes that destroy Thiamin?

A

raw fish, shellfish

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15
Q

which foods contain compounds that oxidize Thiamin?

A

Brussel sprouts, and beets

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16
Q

Which vitamin was Once called “yellow enzyme”?

A

riboflavin

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17
Q

how is riboflavin released and absorbed? how much is absorbed?

A

HCl in stomach releases riboflavin bound to dietary compounds (e.g. protein)

Free riboflavin absorbed via active transport or diffusion depending on concentration

60-65% absorbed

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18
Q

How is riboflavin trasported?

A

by carrier proteins in the blood

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19
Q

what is riboflavins coenzyme?

A

FAD FNM

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20
Q

where is riboflavin stored?

A

kidneys, liver and heart

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21
Q

where is riboflavin excreted?

A

when in excess through urine

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22
Q

you have bright yellow urine, which vitamin might cause this?

A

riboflavin

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23
Q

what are the 7 functions of riboflavin?

A
  1. Part of 2 key redox enzymes as flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD)
  2. Key roles in energy metabolism and in the CAC + ETC: FMN shuttles hydrogen atoms into ETC
  3. In beta-oxidation: conversion of fatty acids to acetyl CoA requires fatty-acyl dehydrogenase, which requires FAD
  4. The formation of niacin (vitamin B3) from tryptophan requires FAD
  5. Formation of the vitamin B6 coenzyme form (PLP) requires FMN
  6. Riboflavin participates in folate metabolism
  7. The synthesis of glutathione (part of cellular antioxidant enzyme glutathione peroxidase) requires the activity of a FAD-containing enzyme: glutathione reductase
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24
Q

who are at risk of riboflavin deficiency?

A

chronic alcoholism, malabsorption syndromes, use of contraceptive pill, high stress, elderlies

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25
Q

What are the two coezyme forms of riboflavin?

A 
Flavin adenine dinucleotide (FAD)
Flavin mononucleotide (FMN)
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26
Q

Where and how is niacin absorbed

A

Some absorbed in stomach, but mainly in small intestine

active transport and passive diffusion depending on concentration available

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27
Q

where is niacin first transported to

A

first transported in portal vein to liver

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28
Q

where is niacin stored?

A

liver

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29
Q

how is niacin excreted?

A

in urine

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30
Q

What are the functions of niacin

A

Required in oxidation-reduction reactions as NAD+ and NADP+

Pharmacological use to lower cholesterol

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31
Q

what are the four stages of niacin deficiency?

A

Dermatitis, diarrhea, dementia, death

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32
Q

How can niacin be synthesised other then dietary intake?

A

Niacin can be endogenously synthesised from tryptophan in dietary protein

33
Q

how much and how is B5 absorped?

A

Only 40-60% of intake is bioavailable

Active transport and passive diffusion depending on concentration available

34
Q

when is pantothenic acid formed?

A

CoA forms when pantothenic acid combines with a derivative of ADP and the amino acid cysteine in any cells requiring it.

35
Q

How is pantothenic acid transported around the body?

A

Transported around the body freely and bound to RBCs

36
Q

how is pantothenic acid excreted?

A

urine

37
Q

what is the main function of pantothenic acid?

A

Essential as coenzyme A for the formation of acetyl CoA in all energy production pathways (entry into the CAC)

38
Q

why is pantothenic acid deficiency rare?

A

it is found in a large variety of foods

39
Q

what is the coenzyme form of pyridoxine?

A

pyridoxal phosphate (PLP)

40
Q

where is pyridoxine stored?

A

muscle tissue

41
Q

how is pyridoxine excreted?

A

urine

42
Q

what happens if no B6 is available?

A

all amino acids become essential as you cannot synthesise them

43
Q

what are the functions of pyridoxine?

A
  • amino acid metabolism
  • amino acid transamination for the synthesis of non-essential amino acids
  • required in glycogenesis
  • Gene expression regulation
  • Modulation of effects of steroid hormones
  • Immune function
  • Requiredinthesynthesisofimportantmetabolic compounds
44
Q

What are the effects of pyridoxine deficiency?

A

Oilydermatitis

Microcytic hypochromic anemia (small and pale RBC: due to reduced haeme and hemoglobin synthesis)

Convulsions, depression, confusion (due to altered neurotransmitters synthesis)

45
Q

what does having toxic levels of pyridoxine risk?

A

permanate nerve damage

46
Q

Describe how biotin might be absorbed?

A

in food as free biotin or biocytin (bound to lysine in protein)
then Biotinidase unbinds biotin for absorption then Free biotin absorbed by active transport (sodium dependent carrier)

47
Q

What are the functions of biotin?

A

Required in carboxylation reactions: co-enzyme (as biotin) of carboxylase enzymes (add CO2 )

Carboxylation of acetyl-CoA to form malonyl CoA, the beginning of fatty acid synthesis

Required for metabolism of carbohydrates, fats and proteins, CAC intermediates

Catabolism of branched-chain amino acids: ketogenic BCAA used to make acetyl-CoA

Involved in DNA folding in the nucleus as it binds to proteins facilitating the folding: role in gene stability

48
Q

Why might biotin deficiency occur?

A

Biotinidase enzyme deficiency (genetic polymorphism)

Excessive consumption of raw egg-white (>12 per day)

49
Q

what is the difference between folate and folic acid?

A

folate: food source: 50-80% bioavailable

folic acid: synthetic source: 100% bioavailable

50
Q

where does folate absorption occur?

A

small intestine

51
Q

what is the main form of folate found in circulation

A

5-methyl THFA is the main form found in the circulation

52
Q

where is folate stored?

A

liver

53
Q

how is folate excreted?

A

urine or feaces

54
Q

What are the functions of folate?

A

cell division, proliferation, and maintenance of new cells

DNA synthesis and repair

Amino acid metabolism

55
Q

what are the folate deficiency signs and symptoms?

A

DNA synthesis and repair impaired

Affects especially the rapidly dividing cells: RBC and GIT cells

In bone marrow: precursor cells cannot form new DNA, affect blood cells:

GIT cells: poor absorption of nutrients, as cells are poorly replaced or formed

56
Q

what are some causes of folate deficiency?

A

Methotrexate (anti-cancer-recurrence medication) is a folate antagonist: reduces the proliferation of cancer cells; but will affect healthy cells too

Poor intake or poor absorption (e.g due to polymorphism in folate conjugase: enzyme splitting poluglutamates to monoglutamate for absorption)

Polymorphism in dihydrofolate reductase (enzyme converting folate /folic acid to THFA, the active form of the vitamin)

Alcoholism: alcohol interferes with folate conjugase

Vitamin B12 deficiency (to recycle THFA)

Pregnancy increases needs due to increased cell division

57
Q

what can folate deficiency in early pregnacy lead to?

A

neural tube defect: Spina Bifida

58
Q

how much folate leads to toxicity?

A

1mg daily

59
Q

What are the two coenzyme forms of cobalamin?

A
  1. methyl cobalamin

2. 5-deoxy-adenosyl-cobalamin

60
Q

where does the conversion of cobalamin to coenzyme form occur?

A

in the liver

61
Q

describe the absorption process of cobalamin

A

Cobalamin is bound to protein in food, e.g. meat

Cobalamin released by action of HCl and pepsin in the stomach

Free cobalamin binds to R-protein (from salivary cells + gastric cells)

In the small intestine, pancreatic proteases release cobalamin from R-protein

Free cobalamin binds to intrinsic factor (IF) (from parietal cells)

IF + B12 travel to and are absorbed in the terminal ileum by endocytosis

Absorption is increased with increased intake

62
Q

where and how much cobalamin is stored in the body?

A

liver

enough for 2-3 years ~2500μg

63
Q

where is cobalamin excreted?

A

urine

but most is recycled in enterohepatic recirculation

64
Q

B12 is required as a coenzyme to which two enzymes?

A
  1. L- methylmalonyl-coenzyme A mutase

2. methionine synthase

65
Q

what does a cobalamin deficiency lead to?

A

Pernicious anemia: megaloblastic and macrocytic: death within 2-5 years due to a lack of RBC

66
Q

What are some of the possible causes for cobalamin deficiency?

A

Absence of R-protein (from stomach and saliva) Poor binding of the IF-B12 complex (receptor error) Presence of B12 consuming bacteria in the ilium

Anti-acid medications: reduced HCl production

Atrophic gastritis (with ageing, resulting in reduced HCl as parietal cells loose function)

Crohn’s and Coeliac‘s disease

Vegan /vegetarian diets without supplementing or using fortified products

Metformin (T2DM medication): interference with B12 absorption

67
Q

where and how is choline absorbed?

A

small intestine via transport protein

68
Q

where is choline transported in the body after absorption?

A

Circulates to the liver via the portal vein
From the liver, circulates to other tissues, uptake by diffusion and via carrier proteins such as in the blood-brain barrier

69
Q

where is choline stored?

A

liver

70
Q

How is choline excreted?

A

oxidized in the liver as betaine

Excess excreted via the urine

71
Q

What are the functions of choline?

A

Is part of phospholipids, lipoproteins, cell membranes in all cells, sphingomyelin, phosphatidylcholine.

A precursor of acetylcholine: essential in brain function and muscle function

Decreases homocysteine: methyl donor in the conversion of homocysteine to dimethylglycine

72
Q

what is the other name for vitamin C?

A

ascorbic acid

73
Q

What form is vitamin C found in as food?

A

Dehydro-ascorbic acid: oxidized form that needs to be “regenerated”

74
Q

Where is vitamin C absorbed?

is vitamin C absorbed differently between the two forms Ascorbic acid and Dehydroascorbic acid

A

Small intestine

Ascorbic acid: active transport

Dehydroascorbic acid: facilitated diffusion, then reduced to ascorbic acid

75
Q

How is vitamin C transported?

A

As ascorbic acid in the blood

76
Q

Where is vitamin C stored and how much is there in the body?

A

Pituitary gland, adrenal glands, WBC, eyes, brain

Body pool of 300 to 400mg

77
Q

how is vitamin c excreted?

A

Excess filtered by kidneys and excreted via the urine

78
Q

What are the functions of vitamin C?

A
  • Electron donor
  • Collagen synthesis
  • Protects lipids from peroxidation
  • Carnitine biosynthesis
  • Assists in non-heme iron absorption (conversion to ferrous form)
  • Synthesis of neurotransmitters, cholesterol, corticosteroids, bile acids, aldosterone, adiponectin
  • Protects immune cells from destruction via antioxidant action
79
Q

what disease occurs due to vitaminc C deficiency?

A

scurvy

NUTR2101 (14 decks)

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