PH1123 Vitamins and Coenzymes Flashcards
how does taking unnecessary vitamin supplements effect health ?
One in three women and one in four men in the UK take dietary supplements for health reasons. But a review of 14 trials of vitamin pills taken by 170,000 people found they increased the death rate by 6 per cent. While they offered no explanation as to what caused the deaths, they discovered that the supplements offered no protection against cancers of the gut.
The researchers, writing in The Lancet, estimate that for every one million people taking the supplements, 9,000 would die prematurely as a result. The figure takes account of the background level of premature death in the population.
what’s an apoenzyme ?
the large protein molecule that forms the bulk of the enzyme molecule. In isolation it may be able to bind substrate but not able to catalyse its reaction
Whats a co factor ?
non-protein molecule or metal ion that binds to the apoenzyme to form the holoenzyme. The cofactor may be bound at the active site or at a distant site on the apoenzyme.
Whats a holoenzyme ?
Holoenzyme – the catalytically active form of the enzyme.
Whats the substrate ?
Substrate – the substance upon which an enzyme acts
Define a coenzyme
Definition: A non-protein organic compound, produced in living cells, which is involved in the activation of enzymes.
Co-substrates are altered during the course of the reaction and then dissociate from the enzyme. They are then regenerated by another enzymatic reaction.
Prosthetic groups remain bound to the enzyme but still need to be regenerated.
An enzyme is a protein that acts as a catalyst to increase the biochemical reaction rate without altering itself in the process, while a coenzyme is an organic non-protein molecule that is required by an enzyme to perform its catalytic activity.
Unlike enzymes, the coenzyme is often structurally altered during an enzyme-catalysed reaction.
Whats the definition of a vitamin ?
Definition: General term for any of several organic substances essential for normal metabolic processes and which, when absent in the diet, produce deficiency states as THEY ARE NOT PRODUCED NATURALLY BY THE BODY.
Many coenzymes are synthesised from dietary precursors - these dietary precursors are often vitamins.
describe the differences between water soluble and lipid soluble vitamins
WATER SOLUBLE
readily excreted via kidney in urine
required daily (in small amounts)
e.g. Vitamins B & C
LIPID SOLUBLE
stored in the body
(usually in liver)
excessive intake can
cause toxicity
e.g. Vitamins A, D, E & K
state general information for B group vitamins
Originally thought to be a single vitamin but now understood to be multiple vitamins – all of which form coenzymes
Some can be synthesised within the body by intestinal flora (note: this is different to being produced by the body)
State the sources, function and coenzyme produced by vitamin B1
Sources:
Found in cells therefore present in all whole natural foods e.g. whole cereal grains, beans, fruits and yeast
Coenzyme produced: Thiamine pyrophosphate (TPP)
Function:
Coenzyme to several enzymes in carbohydrate metabolism pathways (helping to release energy from food)
Also involved in conduction of action potentials in neurons and neuro-muscular transmission
What is the deficiency state of vitamin B1 and in whom is it most prevalent?
Deficiency state
Prevalent in eastern Asia (white rice contains little thiamine) and in chronic alcoholics (severely malnourished). Athletes and pregnant/lactating women may require supplements (increased carbohydrate consumption)
Beriberi can affect different organ systems
Wet beriberi affects the cardiovascular system and presents with cardiac failure, dyspnoea and oedema
Dry beriberi affects the peripheral nervous system and presents with peripheral neuritis, paralysis and wastage. A severe form of dry beriberi is known as Wernicke–Korsakoff syndrome and is characterised by paralysis of eye movement, unusual movements and impaired mental function.
State the sources, function and coenzymes produced by vitamin B2
Name: Vitamin B2 [A.K.A. riboflavin]
Sources:
Dairy products, eggs, green vegetables and almonds
Flavin mononucleotide (FMN) Flavin adenine dinucleotide (FAD)
Function:
Heterocyclic system acts as a H acceptor (or donor)
Coenzymes act as prosthetic groups on a family of mainly oxidoreductase enzymes known as flavoproteins
Involved in the metabolism of fats, carbohydrates and proteins
Also acts as a coenzyme in the processing of other vitamins (e.g. conversion of vitamin B6 into its coenzyme)
What is the deficiency state of vitamin B2 ?
Deficiency state
Rare in developed countries due to fortified foods but common in developing countries (due to malnutrition)
SYMPTOMS INCLUDE INFLAMMATION OF THE MOUTH AND LIPS (STOMATITIS) WHICH IS SIMILAR TO PELLAGRA BUT WITHOUT THE WIDESPREAD SKIN LESIONS (PELLAGRA SINE PELLAGRA)
It can also reduce iron absorption leading to anaemia with the size and haemoglobin content of red blood cells remaining normal (normochromic normocytic anaemia)
State the sources, function and coenzymes produced by vitamin B3
Name: Vitamin B3 [A.K.A. nicotinamide (niacinamide); niacin (nicotinic acid)]
Sources:
Meat, fish and nuts
Nicotinamide also used in acne treatments
Coenzymes produced:
Nicotinamide adenine dinucleotide (NAD)
Nicotinamide adenine dinucleotide phosphate (NADP
Function:
Important in oxidoreductase enzyme reactions: NAD(P)+ is an oxidising agent whilst NAD(P)H is a reducing agent
NADPH is important in anabolic processes (e.g. lipid and nucleic acid synthesis) whilst NAD+ is vital to catabolic processes (e.g. metabolism of energy sources like fatty acids and glucose)
What is the deficiency state of vitamin B3
Deficiency state
Body not entirely dependant on dietary intake as nicotinic acid can be produced from dietary tryptophan in vivo
Deficiency common in areas in which maize is the principal foodstuff (as it is low in both nicotinic acid and tryptophan)
Pellagra – characterised by ‘dermatitis, diarrhoea and dementia’.
Chronic alcoholics also at risk of deficiency
What is the toxicity state of vitamin B3 ?
Toxicity state
Skin flushes, liver damage (mainly seen with niacin supplementation; nicotinamide may be given as alternative supplement)