Module 3 WK9+10+11 Flashcards
Which term describes the inactive form of an enzyme?
Apoenzyme
Which term describes the active form of an enzyme?
Holoenzyme
Which type of organic molecules are tightly or covalently bound to an enzyme?
Coenzymes
What are molecules that diffuse to and bind an enzyme for its catalytic activity then diffuse away?
Cosubstrates
What is the main function of B-group vitamins?
Haematopoiesis and energy production
Which type of molecules are metal ions loosely or tightly bound to an enzyme?
Cofactors
Most B-group vitamins are bioactive only as coenzymes.
true or false
true
B vitamins correct name to the corresponding vitamin.
Vitamin B1: thiamin
Vitamin B2: riboflavin
Vitamin B3: niacin
Vitamin B5: pantothenic acid
Vitamin B6: pyroxidine
Vitamin B7: biotin
Vitamin B9: folate
Vitamin B12: cobalamin
What is the coenzyme form of thiamin?
Thiamin diphosphate (TDP)
In what form is thiamin present in plant products?
Free thiamin
What is the role of thiamin diphosphate (TDP) in the oxidative decarboxylation of pyruvate?
TDP is a coenzyme for pyruvate decarboxylase
role of thiamin in the pentose phosphate pathway?
Thiamin is a coenzyme of transketolase in the pentose phosphate pathway
In which food product is mandatory fortification of thiamin required in Australia?
Bread-making flour
What are thiamin antagonists?
Chemical compounds that lower the bioavailability of thiamin
What is the name of the type of beriberi caused by alcohol use disorder?
Wernicke-Korsakoff syndrome
good animal source of thiamin?
Pork
coenzyme forms of riboflavin
The two coenzyme forms of riboflavin are flavin mononucleotide and flavin adenine dinucleotide
FMN and FAD in food need to be converted to riboflavin for absorption
What is the primary function of FAD and FMN in the body?
Act as electron carriers in oxidation-reduction reactions
What is the role of riboflavin in the synthesis of niacin?
Riboflavin acts as a coenzyme in the conversion of tryptophan to niacin
good dietary source of riboflavin?
Dairy products
sign of riboflavin deficiency?
Lesions on the corner of the mouth
Niacin can be endogenously synthesised from which amino acid?
Tryptophan
coenzyme form of niacin?
NADP, NAD+, NADH, NADPH
function of niacin?
Acts as an electron carrier in oxidation-reduction reactions
Niacin is found in animal products as…
Nicotinamide
Animal products (meat and fish) are better sources of niacin than plant products.
true or false
true
good plant source of niacin?
Peanut butter
Niacin deficiency can lead to pellagra. What are the symptoms of pellagra?
Dermatitis, diarrhea, dementia, and even death
What is the upper level (UL) for niacin based on preventing?
Peripheral vasodilation
What are the coenzyme forms of pantothenic acid?
4’-phosphopantetheine and coenzyme A
absorption of pantothenic acid?
The coenzyme forms of vitamin B5 must be converted to pantothenic acid for absorption
functions of 4’-phosphopantetheine?
To act as a coenzyme in fatty acid production
To convert folate to its coenzyme form
function of acetyl-CoA in the body?
Synthesis of cholesterol and steroid hormones
Synthesis of fatty acids and ketones
Modification of proteins through post-translational acetylation
Synthesis of acetylcholine, a neurotransmitter
pantothenic acid deficiency symptom?
Burning feet syndrome
Which is the most stable form of vitamin B6?
Pyridoxine
What is the coenzyme form of vitamin B6?
Pyridoxal phosphate
All 6 forms of vitamin B6 are found in food.
true or false
true
All forms of vitamin B6 can be converted to PLP in the liver.
true or false
true
What is the primary role of PLP as a coenzyme?
Amino acid metabolism
function of PLP?
Conversion of homocysteine to cysteine
Deamination of amino acids for energy production and gluconeogenesis
Synthesis of neurotransmitters from amino acids
Synthesis of non-essential amino acids
common symptom of vitamin B6 deficiency?
Microcytic, hypochromic anaemia
What can result from vitamin B6 toxicity?
Nerve damage
coenzyme form of Biotin
carboxybiotin
Biotin is a water-soluble vitamin that acts as a coenzyme in various…
carboxylase enzymes
Biotin can be found in food in its.. (form) … freed by… for absorption
free form or bound to lysine residues in protein to form biocytin, which is then freed by the enzyme biotinidase for absorption.
carboxybiotin function
several metabolic pathways. Biotin is important for the conversion of pyruvate to oxaloacetate in gluconeogenesis and the conversion of acetyl-CoA to malonyl-CoA in fatty acid synthesis. Biotin is also involved in the biotinylation of histone proteins, which promotes gene expression.
Good dietary sources of biotin
liver, soybeans, and eggs.
association between raw egg and biotin
raw egg consumption can lead to biotin deficiency due to the tight binding of biotin to the protein avidin in raw egg whites, which prevents its absorption.
symptoms of biotin deficiency
dermatitis, hypotonia, nervous system dysfunction, and alopecia.
Why is folic acid more efficiently absorbed than naturally occurring folate?
Folic acid contains only one glutamic acid residue, while naturally occurring folate typically contains three or more.
What is the digestive enzyme that converts the polyglutamate form of folate to the monoglutamate form for absorption?
Folate conjugase
What is the primary role of folate?
Providing one-carbon units for methylation reactions
functions of folate?
Pyrimidine synthesis
Amino acid metabolism
Purine synthesis
Methylation reactions
Which reaction requires 5-methyltetrahydrofolate (5-MTHF)?
The conversion of homocysteine to methionine
symptom of folate deficiency?
Megaloblastic anemia
Why is the upper level (UL) for folate set at 1000 μg?
Because high doses may mask vitamin B12 deficiency
Which of the forms of vitamin B12 are used in fortified foods and supplements?
Hydroxocobalamin and cyanocobalamin
two coenzyme forms of vitamin B12?
Methylcobalamin and 5-deoxyadenosylcobalamin
How long can the body’s stores of vitamin B12 last?
3-5 years
What are the two transport proteins for vitamin B12 in the circulation?
Transcobalamin II and haptocorrin
what is indicative of vitamin B12 deficiency?
High levels of homocysteine
High levels of methylmalonic acid
Megaloblastic anaemia
Severe nerve degeneration
good dietary source of vitamin B12?
Animal products
describe the digestion and absorption of vitamin B12.
vitamin B12 is released from food with the help of pepsin and HCl, Vitamin B12 bind to R proteins found in saliva and gastric juice, R protein is digested to release vitamin B12 in the alkaline environment of the duodenum, vitamin B12 binds and form a complex with intrinsic factor which was made by gastric parietal cells, in the ileum vitamin B12-IF complex bind to specific receptors and is internalised by endocytosis
Vitamin B12 + coenzyme form functions and deficiency
Methylcobalamin is required for the function of methionine synthase, an enzyme that catalyzes the conversion of homocysteine methionine using 5-methyl-THF as a methyl donor. Methionine is used for the synthesis of S-adenosylmethionine, a methyl donor required for many biological methylation reactions, including DNA methylation.
Vitamin B12 deficiency leads to elevated levels of homocysteine in the blood which is associated with an increased risk of cardiovascular disease.
Vitamin B12 is also required for the function of L-methylmalonyl-CoA mutase, which converts L-methylmalonyl-CoA to succinyl-CoA for energy production and heme synthesis.
5-deoxyadenosylcobalamin is the coenzyme form of vitamin B12 required for the function of this enzyme. In the absence of vitamin B12, L-methylmalonyl-CoA is converted to D-methylmalonyl-CoA and then to methylmalonic acid which is thought to lead to abnormal myelin synthesis.
Which form of vitamin C is biologically active?
L-ascorbic acid
function of vitamin C in the body?
Collagen synthesis
Assisting iron absorption
Antioxidant activity
Neurotransmitter synthesis
How does vitamin C function as an antioxidant?
By donating electrons directly to free radicals
By regenerating other antioxidant compounds
By maintaining metal ions in the reduced state in antioxidant metalloenzymes
What does vitamin C become after it has donated an electron to inactivate a free radical or reactive oxygen/ nitrogen species?
Dehydroascorbic acid
function of vitamin C in collagen synthesis
Vitamin C acts as a cosubstrate in the hydroxylation of proline and lysine residues in collagen. Hydroxyproline provides more rigidity to the collagen; hyroxylysine allows for post translation modifications: glycosylation, phosphorylation to overall strengthen collagen fiber
Symptom of severe vitamin C deficiency
scurvy - easy bruising and slow wound healing
good source of vitamin C
citrus fruit
role of vitamin C in enzymes prolyl hydroxylase anf Lysyl hydroxylase
maintains Fe in reduced state
= collagen synthesis and strength
role of vitamin C in enzymes trimethyllysine hydroxylase 4-butyrobetaine hydroxylase
maintains Fe in reduced state
= carnitine synthesis for B-oxidation
role of vitamin C in enzymes para-hydroxyphenylpyruvate hydroxylase, homogentisate dioxygenase
maintains Fe in reduced state
= energy production from tyrosine catabolism
role of vitamin C in enzymes tyrosine hydroxylase
maintains tetrahydrobiopterin in reduced state
= L-dopa synthesis from tyrosine
role of vitamin C in enzymes dopamine beta-hydroxylase
maintains Cu in reduced state
= norepinephrine synthesis from dopamine
role of vitamin C in enzymes ten-eleven translocation methylcytosine dioxygenase
maintains Fe in reduced state
= gene expression
role of vitamin C in enzymes ten-eleven translocation methylcytosine dioxygenase
maintains Fe in reduced state
= gene expression
function of vitamin C: antioxidant
in the circulation, and in cells:
- Vitamin C donates electrons to free radicals, reactive oxygen- and nitrogen species to “inactivate” them,thus limiting the damage to DNA, polyunsaturated fatty acids, phospholipids, and amino acids in proteins
- Vitamin C regenerates other antioxidant compounds when they have been oxidised: e.g vitamin E,
- Vitamin C keeps ions in metalloenzymes in the reduced form: e.g. glutathione peroxidase, superoxide
dismutase
function of vitamin C: prooxidant
(although minimal), e.g.:
- Reducing free ferric iron to ferrous iron => favorable in the GIT to promote iron absorption, but in the circulation may cause cell damage by generating free radicals like superoxide (however most of the iron is transported bound to protein)
function of vitamin C: cytochrome p450 system function
Synthesis and function of enzymes involved in:
- Metabolism of cholesterol in the synthesis of bile
- Steroid hormones synthesis and metabolism (aldosterone and cortisol)
- Detoxification of carcinogens, food additives and pollutants etc., involving hydroxylation reactions
- Alcohol metabolism
how is niacin found in food and what can be done to make more bioavailable
animal products- nicotinamide, NAP, NAPD
plant - nicotinic acid
grains- niacin bound carbohydrate = niacytin or to protein = niacinogen -> decreases bioavailability of niacin for absorption (e.g. in corn)
made more bioavailable by soaking in lime water
what were the major minerals studied
sodium, potassium, chloride, calcium, phosphorus, magnesium
why does a vitamin B6 deficiency lead to microcytic hypochromic anemia
B6 is a cofactor in synthesis of heme. When this is impaired, hemoglobin synthesis is also decreased, and RBC therefore cannot mature properly, resulting in small and pale RBC instead
why is it better to consume a riboflavin supplement with food
riboflavin can be present either free or bound to protein as FMV and FAD. When bound to proteboin they need to be freed by HCl (bile) and converted toflavin to be absorbed
why can it be quite easy to reach a dose of B6 equal to UL
many hair/ nail, sports and body building products/ supplements contain vitamin B6 so its easy to consume to the UL
why is the RDI for niacin expressed in “niacin equivalents”
to include both dietary preformed niacin and the niacin made endogenously from tryptophan
why are paper and opaque plastic containers used for dairy milk and dairy products?
riboflavin in food is rapidly broken down by light” opaque containers should be used to package riboflavin rich foods (e.g. milk). resistant to heat, oxidation and acid
what is meant by ascorbic acid is a non-specific reducing agent
it can donate electrons to a wide variety of molecules thus participates in many different redox reactions
explain why folate and cobalamin are tightly linked in metabolism
one-carbon metabolism and DNA synthesis
THF- essential for synthesis of purines and pyrimidines
methylcobalamin - methionine synthase reactions -> catalyses transfer of a methyl group from THF to homocysteine
Deficiency of either results in megaloblastic anemia but B12 deficiency also results in severe permanent neurological damage if not addressed, high levels of circulating folate may mask B12 deficiency
Where is water absorbed?
Stomach
Jejunum
Ileum
Large intestine
What percentage of total body water loss occurs via the lungs and skin?
50%
In adults, approximately what percentage of body weight is water?
55%
The majority of the body’s water is contained in which compartment?
Intracellular compartment
function of water?
Maintaining cell shape and structure
Regulation of body temperature
Lubrication of joints and body tissues
Transport of nutrients and waste products
Recommended water intake is based on the EAR (estimated average requirement)
true or false
false
Recommended water intake is based on the AI (adequate intake). EAR is difficult to establish in the experimental setting as homeostatic mechanisms compensate for acute over or under-hydration status.
The AI (adequate intake) for water was established based on the mean population intake in the 1995 National Nutrition Survey of Australia
true or false
false
Like all AIs, the AI for water is based on the MEDIAN population intake
how much fluids should men drink each day to meet the AI for water
2.1L
The AI for water is set on the basis that 80% of water intake comes from beverages while 20% comes from food. On this basis, men should consume ~2.1L (0.8 * 2.6) of fluids each day to meet the AI, with the remaining 20% (0.5L) of their water intake coming from foods
homeostatic response and system to correct dehydration
The acute homeostatic response to correct dehydration involves the activity of antidiuretic/anti-diuretic hormone and the renin-angiotensin-aldosterone/renin angiotensin aldosterone/RAAS system.
Dilution of which electrolyte in particular leads to symptoms of water intoxication?
sodium
The risk of death from dehydration increases with losses of greater than:
10% body weight
Where is the majority of sodium found in the body?
Extracellular fluid (ECF)
What is the function of sodium in the body?
Helps maintain osmotic pressure for fluid balance
What is the importance of the electrochemical gradient established by the Na+/K+-ATPase in the body?
Important for nerve transmission and muscle contraction
What is the recommended sodium intake in the Sodium Dietary Target (SDT)?
2000mg
What is the basis for the Sodium Dietary Target (SDT)?
Link between sodium and hypertension
What percentage of hypertensive patients are sodium sensitive?
25-50%
What percentage of sodium intake in the Western diet comes from processed foods?
75%
Sodium content must be listed on the Nutrition Information Panel (NIP).
true or false
true
What is the maximum amount of sodium per 100mL/100g that a food can contain in order to be considered “low salt”?
120 mg
What does an elevated plasma sodium concentration indicate?
Dehydration
what leads to hyponatremia?
Overhydration
Association between sodium intake and calcium loss?
Sodium intake >2g/day may increase urinary calcium losses
Where is the majority of potassium found in the body?
Intracellular fluid (ICF)
What is the primary way that potassium is absorbed?
Passive diffusion
functions of potassium
Helps maintain acid-base balance
Maintains water balance
Maintains the cell’s resting membrane potential
Involved in the conversion of phosphoenolpyruvate to pyruvate
potassium and insulin association
Insulin promotes potassium uptake into liver and muscles
What happens to potassium levels in the blood when they are high?
The kidneys excrete more potassium into the urine
What is the risk of both hypo- and hyperkalemia?
Cardiac arrhythmia and muscle weakness
increases the risk of potassium deficiency?
Diarrhea
Vomiting
Diuretic medications
Chronic excess alcohol intake
What is the main dietary source of chloride?
Sodium chloride
function of chloride in the body?
Contributes to the transmission of action potentials in nerves
What is the role of chloride in maintaining electrical neutrality in the body?
It balances the positive charge of sodium
What is the role of chloride in protein digestion as part of hydrochloric acid?
It converts pepsinogen to pepsin
describe the function of the chloride shift?
Chloride is exchanged for bicarbonate across the membrane of red blood cells to facilitate exhalation of CO2 via the lungs
What is the serum concentration of chloride dependent on?
Hydration status
In whom has chloride deficiency been observed?
Infants given chloride-deficient formula
Which mineral form gives bone and teeth their strength?
Hydroxyapatite
function of calcium in the body?
Blood clotting by binding and activating prothrombin
Muscle contraction by binding to troponin
Triggering release of vesicles containing neurotransmitters
Vasorelaxation effect on smooth muscle cells
What is the condition resulting in soft bones in adults due to calcium deficiency?
Osteomalacia
What is the condition resulting in brittle, porous bones at increased risk for fracture?
Osteoporosis
describe calcium homeostasis
A drop in blood calcium concentration is sensed by the parathyroid gland which releases parathyroid hormone into the blood. In the kidneys, parathyroid hormone promotes the transcription of 1-hydroxylase which hydroxylates 25-hydroxycholecalciferol to calcitriol. Calcitriol increases intestinal absorption of calcium by interacting with vitamin D receptors to promote the expression of calcium transporters in enterocytes. Calcitriol also increases renal reabsorption of calcium by promoting expression of necessary proteins. Elevations of parathyroid hormone and calcitriol in the blood stimulates bone resorption and release of calcium by activating osteoclasts. When blood calcium rises to normal levels, the parathyroid gland stops secreting parathyroid hormone. An increase in blood calcium concentration is sensed by the
thyroid gland which releases calcitonin into the blood. Calcitonin inhibits parathyroid hormone secretion, decreases bone resorption and intestinal calcium absorption, and promotes urinary calcium excretion.
primary source of phosphorous?
Protein-rich foods
factor contributing to the low bioavailability of phosphorous in grains and legumes?
The presence of phytic acid
How is phosphorous absorbed?
As inorganic phosphate
Serum phosphorous concentration is a good indicator of tissue concentration.
true or false
false
Which hormone increases phosphorous absorption?
Calcitriol
where is magnesium stored
bone
Where is phosphorous primarily found in the body?
In the bones and teeth
function of phosphorous in the body?
Contributes to bone and teeth mineralisation as part of hydroxyapatite
Involved in energy transfer and storage as part of ATP and creatine phosphate
Regulates enzyme activity through phosphorylation
Forms part of the backbone of nucleic acids
What is the role of calcitriol in magnesium absorption?
It promotes expression of TRPM6 channels, increasing magnesium absorption
function of magnesium in cardiovascular health?
Decreases blood pressure by dilating blood vessels
Magnesium is a cofactor in which metabolic pathways?
Energy metabolism
Protein synthesis
DNA and RNA synthesis
What are the symptoms of both severe magnesium deficiency and toxicity?
Cardiac, muscular, and CNS symptoms
is there is a UL for magnesium from food sources?
no
compare nutritional composition (foods, diet quality, nutrients, energy) of typical high potassium vs high sodium diet
Food Sources:
High Potassium Diet: Rich in fresh fruits, vegetables, legumes, dairy, nuts, seeds, and whole grains.
High Sodium Diet: Predominantly composed of processed and fast foods, cured meats, and salty snacks.
Diet Quality:
High Potassium Diet: Generally higher in essential nutrients, fiber, and antioxidants.
High Sodium Diet: Lower in essential nutrients, fiber, and often high in unhealthy fats and sugars.
Nutritional Benefits vs. Risks:
High Potassium Diet: Associated with improved blood pressure regulation, heart health, and bone health.
High Sodium Diet: Linked to increased risk of hypertension, cardiovascular diseases, bone density loss, and kidney issues.
Energy Content:
High Potassium Diet: Moderate to high, but typically more nutrient-dense and lower in unhealthy fats and sugars.
High Sodium Diet: Often high, with many calorie-dense, nutrient-poor options.
What are 7 nutrients you have studied thus far that are involved in good bone health? briefly explain their specific role
- Calcium
Bone Structure: Calcium is the primary mineral component of bone, giving it strength and structure. About 99% of the body’s calcium is stored in the bones and teeth.
Bone Remodeling: It is essential for the constant remodeling process of bones, involving resorption by osteoclasts and formation by osteoblasts.
- Vitamin D
Calcium Absorption: Vitamin D enhances the absorption of calcium from the intestine, ensuring that sufficient calcium is available for bone mineralization.
Bone Growth and Remodeling: It regulates calcium and phosphate levels in the blood, promoting normal bone growth and remodeling
.
3. Vitamin K
Bone Mineralization: Vitamin K is necessary for the carboxylation of osteocalcin, a protein that binds calcium and is essential for bone mineralization.
Bone Density: Adequate levels of vitamin K are associated with higher bone density and reduced risk of fractures.
- Phosphorus
Bone Formation: Phosphorus is a critical component of hydroxyapatite, the mineral complex that makes up bone and tooth enamel.
Bone Strength: It works with calcium to give bones their strength and rigidity.
- Magnesium
Bone Matrix: Magnesium is involved in the structural development of bone. About 60% of the body’s magnesium is found in the bones.
Calcium Metabolism: It plays a role in the regulation of calcium and vitamin D metabolism, essential for maintaining bone integrity.
- Vitamin C (Ascorbic Acid)
Collagen Synthesis: Vitamin C is essential for the synthesis of collagen, a major protein in bone that provides a framework for mineral deposition.
Bone Repair: It aids in the repair and maintenance of bones and teeth by supporting collagen production.
- Vitamin A
Bone Growth: Vitamin A is important for normal bone growth and development. It influences the activities of osteoblasts and osteoclasts, the cells responsible for bone remodeling.
Bone Remodeling: Adequate vitamin A is necessary for the proper functioning of these cells, ensuring balanced bone resorption and formation.
explain why salt intake may be an issue for people at risk of hypertension
For people at risk of hypertension, high salt intake can lead to increased blood volume, greater vascular resistance, hormonal imbalances, impaired kidney function, and endothelial dysfunction. These factors collectively raise blood pressure and increase the risk of developing or worsening hypertension. Therefore, managing salt intake is crucial for individuals at risk of or managing hypertension.
