Week 6 Flashcards
What is a nutrient and the 6 main nutrient groups?
A substance/chemical that an organism needs to live, grow, reproduce
6 main nutrient groups:
- Carbohydrate, lipids, protein, vitamins, minerals, water
Defintion of essential nutrient
Must be obtained from an external source,
- Either because the organism cannot synthesise it, or produce sufficient quantities
What are the four common micronutrient deficiencies?
- Iron
- Iodine
- Vitamin A
- Zinc
What are the eight micronutrient elements essential for higher plants?
Boron, chlorine, copper, iron, manganese, molybdenum, nickel and zinc
What are the two major groups of nutrients?
Macronutrients
- Large quantities
- Carbohydrates, proteins and lipids
Micronutrients
- Minute quantities
- Vitamins, minerals, and trace elements
What two forms are carbohydrates presented in?
Simple carbohydrates
- glucose, fructose, other sugars
Compound carbohydrates
- Starch in plants
- Glycogen in animals (liver and muscles)
- Polymers of glucose
- Metabolised to CO2 + H20 and energy
Structure of glycogen
- Branched biopolymer
- Linear chains of glucose residues
- Chains branching off every ten glucose or so
Structure of starch (amylum)
- Large number of glucose units joined by glycosidic bonds
- Large amount of compound carbohydrates
- Produced by all green plants as an energy store
- Staple foods:
- Potatoes, wheat, maize (corn), and rice
Function of proteins
- Building material for body parts
-Muscle, brain, blood, skin, hair, nails, bones and
body fluids. - Essential for growth, repair of worn-out tissues, and
resistance against infections.
What are the 9 essential amino acids for proteins?
histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine
Where can you source proteins?
Both animals and plant foods:
Animals:
- ‘Complete’
- Contain all amino acids
Plant Proteins:
- ‘Incomplete’
-Some low in amino acids (methionine, lysine, tryptophan)
- Supplement with grains, nuts, seeds, legumes
Structure of lipids
- Water-insoluble
- Triglycerides, phospholipids and sterols, such as cholesterol
What are lipids essential for?
− Brain, nerves and hormones, and
− Absorption, transport and storage of fat-soluble vitamins (A, D,
E and K)
How can triglycerides exist?
May be a FAT or an OIL:
Depends on predominant type of fatty acids it contains
− saturated, monounsaturated or polyunsaturated
FATS
• Predominant fatty acids = saturated and monounsaturated
-Solid at room temperature
• Triglycerides of land animal sources
OILS (Triglyceride)
- Polyunsaturated fatty acids predominate
- Liquid at room temperature
-Aquatic animals (marine fish) = polyunsaturated fatty
acids and their lipids
Triglycerides of plant sources
• Vegetable oils:
Mustard oil, soybean oil, sunflower oil, corn oil
However:
Coconut and palm oil contain large proportions of
saturated and monounsaturated fatty acids (solid at room
temp)
Vitamins
-Cannot be synthesized in body
-Essential for metabolism and utilization of carbohydrates,
proteins and lipids
- Function as co-enzymes
e.g. Vitamin C for collagen hydroxylation
Either Water soluble or fat soluble:
Water-soluble vitamins:
− B-complex vitamins (B1, B2, etc.) and vitamin C
Lipid-soluble vitamins:
− A, D, E and K
What three forms does vitamin A exist in?
Retinols
Beta-carotenes
Carotenoids
What is vitamin A needed for?
Skin, hair, eyes
Increases resistance to infection
- Immune system: T cell differentiation
Vitamin A Deficiency
Xerosis cutis (dry skin)
- Retinoic acid (RA): growth factor for epithelial (and other)
cells
- RA can control gene transcription
Low resistance to infection
Vitamin A deficiencies ( Eye disorders)
xerophthalmia (eye fails to produce tears)
− Loss of goblet cells in conjunctiva
− no mucus, debris accumulates, Bitot’s spots
(keratin) form due to dryness
• Keratomalacia
− (atrophy of corneal epithelial cells)
− opaque cornea and blindness
Night blindness
− Retinal (Vitamin A) and opsin form
rhodopsin in retina
− Rhodopsin: pigment for low light detection
Thiamine (Vitamin B1)
-Found in all tissues, especially the liver
-Essential for tissues with High oxidative metabolism:
-Nervous system
- Heart
- Involved in metabolism of acetyl CoA in mitochondria
- Thiamine = Transport form
- Phosphorylated thiamine derivatives = Active forms
- thiamine pyrophosphate (TPP)
What can cause Thiamine (B1) deficiency?
- Caused by diets of mostly white rice (common in alcoholics)
- Depression
- Poor appetite
- Skin problems
- Beriberi
Neurological degeneration (‘Dry’)
− Numbness, confusion
Cardiovascular disease (‘Wet’)
− Tachycardia, cardiomegaly, and
congestive heart failure - Muscular wasting
- Edema
Niacin (vitamin B3
AKA Nicotinic acid
Conversion of carbohydrates→ glucose for energy
production
Niacin → nicotinamide → Nicotinamide adenine
dinucleotide (NAD) and NADPNAD and NADP are cofactors in many enzymatic reactions, including dehydrogenases (catabolism)
Sometimes used to lower blood lipids
-Reduced cardiovascular disease risk if on statins
-Raises HDL cholesterol
Niacin ( vitamin B3) deficiency
Pellagra
• Inflammed skin (Dermatitis)
• Diarrhoea
• Dementia
Light sensitivity
Skin lesions (bleeding and peeling, ‘broad collar’ rash
Skin darkens over time
Confusion and aggression
Ataxia
Dilated cardiomyopathy
Death
Vitamin B12
Cobalamin
• Water-soluble vitamin
• Metabolism of every cell of the
human body:
• Cofactor in DNA synthesis, and in both
fatty acid and amino acid metabolism
• Normal functioning of nervous system,
role in synthesis of myelin
• Maturation of developing red blood
cells in the bone marrow.
Vitamin B12 deficiency
Dietary or other cause
• Pernicious anemia (reduced number of blood cells)
− Due to inhibition of DNA synthesis
− Tiredness
− Neurological and heart problems
• Malabsorption of vitamin B12
− Atrophic gastritis - stomach lining thinned
− Conditions that affect small intestine:
▪ Crohn’s disease, celiac disease, bacterial
growth, or a parasite
− Immune system disorders
▪ Graves’ disease or lupus
What is pernicious anaemia?
Autoimmune condition
- Caused by an inability to absorb adequate amounts of Vitamin B12 from the digestive tract
- Deficiency of intrinsic factor (secreted by stomach)
Results in:
- Decreased rate of RBC production (erythropoiesis)
Treatment:
- Regular injections of vitamin B12
What is the molecular basis of Pernicious Anaemia?
Intrinsic factor secreted by parietal cells
• Found on outer wall of gastric gland
• Secrete HCl and intrinsic factor
• In absence of intrinsic factor, no vitamin
B12 is absorbed and results in anaemia
• Autoantibodies against intrinsic factor
prevent binding of B12 and hence its
absorption, resulting in vitamin B12
deficiency.
OR:
• Autoantibodies against H+
/K+ ATPase in
parietal cell plasma membrane (leads to
destruction of cells)
Vitamin C
- Ascorbic acid
- Growth and repair of tissues
- Collagen production
- Prevents auto-inactivation of lysyl and prlyl hydroxylase
- Two key enzymes in collagen biosynthesis - Potent antioxidant
Vitamin C deficiency
- Scurvy (ECM diseases)
- Bleeding gums
- Bruising
- Low infection resistance
Vitamin D
Vitamin D acts as a hormone
- Stimulates Ca2+ and PO43- (phospahte) absorption from intestine
- Supplemented by dietary intake
-Synthesised from cholesterol derivative when exposed to sunlight - Must be activated first in the liver and then the kidneys (hydroxylation)
Activation of vitamin D
Vitamin D from diet or from skin synthesis is biologically inactive.
Precursor in skin (7-dehydrocholesterol) (sunlight), or dietary vitamin D
First hydroxylation occurs in liver, converts vitamin D to 25 hydroxyvitamin D (also known calcidiol)
The second hydroxylation occurs primarily in the kidney and forms the physiologically active 1, 25- dihydroxylvitamin D ( also known as calcitriol)
Vitamin D deficiency
- Rickets
Symptoms:
-Delayed growth, bowed legs, weakness and pain in
spine, pelvis and leg - Brittle bones
- Bone tenderness
- susceptibility to fractures - Hypocalcemia
- Low level of calcium in blood
= tetany - uncontrolled muscle spasms
-Dental problems
Vitamin E
Fat-soluble antioxidant
- Found in many oils e.g. sunflower, corn, soybean
- Can scavenge free radicals (ROS) in membranes
- ability to donate a hydrogen atom
Consists of tocopherols and tocotrienols
- Tocotrienols may function to protect neurons from
damage (antioxidant activity)
Vitamin E deficiency
- Rare in humans (not caused by diet deficiency)
- Caused by abnormalities in dietary fat absorption
- Neurological problems
- Neuromuscular problems
- Anaemia (due to oxidative damage of red blood cells)
- Muscle and heart problems
- Nose bleeds
- Skin infections
Vitamin K
• Group of structurally similar, fat-soluble
vitamins
• Required for complete synthesis of
proteins prerequisites for blood
coagulation
• Controlling binding of calcium in bones
and other tissues.
• Modification of proteins = allows binding of
calcium ions
What are the sources of Vitamin K?
•Green leafy vegetables (spinach, kale, lettuce etc.)
• Other vegetables, whole wheat products, animal foods (meat, eggs,
fish)
• Oils (olive, canola, soybean)
Symptoms of vitamin K deficiency
Uncontrolled bleeding
• Bruising, gum bleeding, nose bleeding
• Stomach pains
• Weaken bones → osteoporosis
• Calcification of arteries and other soft tissues
What is the composition of living organisms?
Bulk Elements
- Carbon, hydrogen, oxygen, nitrogen, phosphorus
- kg
Macrominerals
- Sodium, potassium, magnesium, calcium
- mM ( ~ 0.5g- ~4g/day)
Essential trace elements or microminerals
- Iron, Zinc, Copper, Iodine, selenium, manganese, molybdenum, cobalt,
fluorine, chromium
- Required in mg amounts in diet
- Present in living organisms in [mM to mM]
What are the non-essential and potentially toxic elements?
Lead, mercury, arsenic
How much iron is usually consumed in a day?
~10-20mg/day in diet
How is iron split in the body? ( percentage)
60-70% of iron:
- majority present in haemoglobin in circulating erthrocytes
- 2.5 g Fe in RBC
- 200 billion new erythrocytes per day
5-15%:
- Other haemoproteins:
- E.g. cytochrome b, catalase (breaking down hydrogen peroxide),
myoglobin (iron storage protein in muscles)
- proteins use Fe in other functional groups
- E.g. iron-sulfur (Fe-S) proteins, NADH dehydrogenase (REDOX)
10-20%:
- Stored in ferritin (and haemosiderin) in hepatocytes and
reticuloendothelial macrophages
- Transferrin: Fe transport in blood
What is iron bound to to prevent toxicity?
Ferritin
What is ferritin?
Ferritin is a universal intracellular protein that stores iron and releases Fe in a controlled fashion.
It helps to keep iron in a soluble and non-toxic form.
What is apoferritin?
Ferritin that is not combined with iron
What is hemosiderin?
Iron is stored in this protein
A complex of ferritin, denatured ferritin (ferritin broken down in the spleen, when RBC is broken down) and other material.
How long is RBC in circulation?
100-120 days
What can the breakdown of heme give rise too?
Some heme containing Fe is broken down in the liver. It gives rise to bilirubin (also gives pee yellow colour).
It is excreted into the bile (in gallbladder) to intestines to faeces (where it gives it the brown colour)
Where is dietary iron mainly absorbed?
In duodenum
How can iron be lost through?
Bleeding, sweat, lactation, and through lost of intestinal mucosal and skin cells
Dietary iron occurs in what three forms:
Ferrous iron (Fe2+)
Ferric iron (Fe3+)
Heme iron (Fe2+ chelated as hemoglobin, myoglobin and enzymes
Which form of iron can cause damage interms of active oxygen species if it was allowed free in the body?
Ferrous iron (Fe2+)
Describe the process of Iron (Fe) uptake and release in gut
-Non-haem iron (Fe3+) in the duodenum is reduced by a ferric reductase in brush border to Fe2+ ( Not readily absorbed Fe3+ needs to be reduced to Fe2+)
- Transported into enterocyte (epithelial cells) through transmembrane iron transporter DMT1 (divalent metal transporter 1)
Once up-taken inside the cell:
- Fe2+ is either stored in ferritin (within the cell) or,
- Passes through basolateral membrane to reach blood and enters
circulation
- Membrane Fe2+ exporter= ferroportin
- Fe2+ re-oxidised by the plasma ferroxidase cerulopasmin (or its membrane- associated homologue, hephaestin) to form Fe3+
Free iron needs to be bound as it is toxic if it is not, so Fe3+ is bound by apo-transferrin and forms holo-transferrin
Holo-transferrin with bound Fe3+ circulates in plasma as serum transferrin.
Transferrin with Fe3+ binds to the transferrin receptor on cell membrane
Transferrin receptor complex internalises into endosomes
Fe3+ dissociates from transferrin in endosomes
Fe3+ transported out of endosome into cytosol by DMT1 (also known as Nramp2)
Iron is either stored or utilised by the cell
Name some factors that contribute to iron deficiency
- Dietary, bleeding
- Anaemia, decrease in number of erythocytes
- Microcytic anaemia
- Skeletal muscle, intestinal mucosa iron depleted before heart and liver iron
- Iron supplementation e.g. pregnancy
- Genetic deficiency disorders= rare
Iron toxicity (acquired)
e.g. transfusions
African Bantu who brew beer in iron containers (high iron intake)
- Now linked to polymorphism in ferroportin gene
- Associated higher ferritin levels
- Cell damage, liver, heart, pancreas increased indicidence of liver cancer and cirrhosis of liver
- Skin becomes pigmented due to iron deposition
Iron toxicity (Genetic)
- Results in increased absorption of iron (‘iron overload)
- Hemochromatosis
- Affects 1 in 250,000
- 5 main types identified with different gene mutations
- Imbalance of iron metabolism leading to increase in total body iron
store
Symptoms of hemochromatosis
- Chronic fatigue
- Accumulation of iron in liver, heart, pancreas, joints etc.
-Liver cirrhosis with increased risk of hepatocellular carcinoma - Joint pain and arthritis
- Diabetes (‘bronze diabetes’): accumulation of iron in pancreas beta cells (reduces or stops secretion of insulin)
Hereditary hemochromatosis (HHC)
Type 1: HFE gene (common C282Y mutation; 83% of cases)
• HFE regulates entry of iron into cell (mechanism complex and poorly
understood)
• HFE binds to transferrin receptor to regulate iron uptake
• Mutated HFE signals ‘low’ iron, body increases iron uptake
• Regulates production of another protein, hepcidin, considered
“master” iron regulatory hormone
• Hepcidin determines how much iron is absorbed from diet and
released from storage
Treatment of hemochromatosis
Phlebotomy (Bloodletting)
- Withdrawl of considerable quantities of blood from a patient to cure
or prevent illness and disease
Desferrioxamine mesilate
- Iron-chelating compound (bind iron to body and help remove it)
