Nutrition Flashcards
Where are vitamins supplied from?
Diet, some can be synthesised (D - sun. B&K -gut bacteria)
What type of compounds are vitamins?
Organic
What type of functions do they have?
Co-enzymes, hormones, cell signalling, antioxidants, regulators of growth & differentiation
What can affect absorption of vitamins?
Properties of the food e.g. low in fat
pre-existing disease e.g. ceiliac - impaired fat absorption and gastritis (low acid- b12)
Drugs may compete for absorption and kill bacteria
What is RDA?
recommended daily allowance - an intake that is adequate to ensure the requirements of all health people are met
Which vitamins are fat soluble and which are water soluble?
Fat soluble: Vitamin A Vitamin D Vitamin E Vitamin K
Water soluble:
B vitamins
Vitamin C
What type of vitamins can be stored?
Fat soluble stored. water soluble not stored
What is the active form of vitamin A?
Retinoids
What pigments give retinoids?
Carotenoid pigments (e.g. B carotene)
What is the function of vitamin A?
binds to proteins (opsin) in the cells of the retina to form visual pigments
Nuclear modulator of gene expression:
Cell proliferation
Differentiation
(especially epithelia)
Development
What are the symptoms of a vitamin A deficiency?
Major cause of blindness in children under 5 in developing countries
impaired resistance to infection - differentiation and function of lymphocytes and neutrophils affected
mild deficiency = night blindness
severe deficiency = metaplasia and keratinisation of the conjuctiva epithelial cells and thickening of the cornea (xerophthalmia)
What process produces vitamin D endogenously?
(D3 -photolysis of 7-dehydrocholesterol)
What are the functions of vitamin D?
Maintenance of plasma Calcium concentration (along with parathyroid hormone and calcitonin)
Steroid hormone activating nuclear receptors and influencing > 50 genes
What is cholecalciferol?
Vitamin D3 which is made by the skin when exposed to sunlight
What is egocalciferol?
also known as vitamin D2 and calciferol, is a type of fat soluble vitamin D found in food and used as a dietary supplement
What is the role of vitamin D in bone metabolism?
- Vit D stimulates intestinal Calcium and phosphate absorption and renal Ca reabsorption - mineralisation of bone is controlled by the availabiliy of Ca and PO4
Osteoblasts have receptors for calcitriol (active metabolite of vitamin D)
Osteoclast activity/number (paradoxically) increased
= Promotes formation and mineralisation of bone
What condition is caused by Vit D deficiency?
Rickets and osteomalacia (the softening of the bones caused by impaired bone metabolism primarily due to inadequate levels of available phosphate, calcium, and vitamin D)
What is vitamin E?
Lipid soluble antioxidant - very active free radical trapping
What does vitamin E do?
Free radical trapping
Cell signalling (inactivates protein kinase C)
deficiency not normally a problem
What does vitamin K do?
Co-enzyme in postranslational carboxylation of glutamate to γ carboxy glutamate (gla)
Permits binding of proteins to membrane phospholipids
Klotting: vitamin K dependent proteins involved in blood coagulation (thrombin factors VII, IX and X, protein C, S, Z)
What are vitamin K antagonists?
Anticoagulants e.g. warfarin
What can vitamin K deficiency lead to?
Haemorrhagic disease
Name some of the B vitamins
Thiamin (B1), ribofavin (B2), Niacin (B3), B6, Folic acid (B9), B12, pantothenic acid (B5)
What are all B vitamins?
Co-enzymes (co-factors)
What does Thiamin (b1) do?
Co-enzyme in central energy yielding pathways (pyruvate & keto-glutarate dehydrogenase)
Co-enzyme in pentose phosphate pathway (transketolase: NADPH for biosynthesis & ribose for nucleotides)
Co-enzyme in catabolism of leu, isoleu & val
Regulates nerve chloride channels
What does defiency of Thiamin lead to?
Berberi-peripheral neuritis: weakness, stiffness
What does Riboflavin (b2) do?
Electron carriers in a variety of oxidation & reduction reactions central to metabolism (mitochondrial electron transport chain)
B2 remain bound to enzyme
FAD (flavin adenine dinuceotide), FMN (flavin mononucleotide) oxidising coenzymes which accept two H atoms
Deficiency common but rarely a problem - bacterial synthesis, conservation and re-utilisation
What does Niacin (B3) do?
Precursor of co-enzymes NAD (nicotinamide adenine dinucleotide) & NADP (phosphate)
Electron carriers in metabolic redox reactions
Where is B3 synthesised from?
Dietary tryptophan
What deficiency is Niacin B3?
Pellegra - demention, diarrhea and dermatitis
What does vitamin B6 do?
Amino acid metabolism (transamination)
deficiency virtually unkown
What does vitamin B12 and folate (b9) do?
Co enzymes
DNA and myelin synthesis
What does deficiency of vitamin B12 and folate b9 lead to?
Anaemia and neurological damage
What role does vitamin C play?
Specific role in two enzyme classes:
Dopamine β-hydroxylase: synthesis of adrenaline and noradrenaline (Cu + dependent)
Lysine and proline hydrolyases: maturation of connective tissue (collagen)
Iron uptake: keeps iron as Fe2+, chelates it which increases absorbtion
Why may dentists be the first to spot a vitamin deficiency?
Rapid turnover of epithelium makes it sensitive to nutritional deficiencies
Vitamins involved with: wound healing, bleeding, resistance to infection, bone/tooth Ca2+
What facial manefestations of vitamin deficiencies are there?
Malar pigmentation (niacin, B vitamins), nasiolabiial seborrhea (niacin, riboflavin, b6 iron), lack of colour (malnutrition)
Lips - angular fissues (niacin, b6, riboflavin, iron), cheilosis (niacin, b6, riboflavin)
Gingiva - Spongy, bleeding, abnormal redness - vitamin C
Tongue - glossitis (folate, niacin, iron, b6, b12)
pale, atrophic, smooth/slick filiform papillary atrophy (iron, folate)
Magenta colour - riboflavin
What are triacylglycerols used for?
Fuel
What are glycerophospholipids used for?
Membranes
What is cholesterol used for?
Membranes
Bile salts: lipid digestions
steroid hormones: communication
What are triacylglycerols composed of?
3 fatty acids and glycerol joined by ester bonds
fatty acids have variable length and can be saturated or unsaturated (c=c)
efficient form to store energy
What are the sources of lipids?
Diet
make fat from carbohydrates (in liver)
Which type of lipid is a main dietary lipid?
Triacylglycerols
What do bile salts do?
Emulsify lipids into smaller droplets
What do lipases do?
Break down fatty acids from triacylglycerols and then form micelles, absorbed by epithelial cells
These are packaged as chylomicrons in the cells by the RER and golgi complex
What is the fate of chylomicrons?
Packaged back into triacylglycerols
The triacylglycerols in them get digested by lipoprotein lipase (LPL)
The fatty acids are absorbed by cells and the other remnants are absorbed by liver
LPL is produced by adipose, muscle and lactating mammary gland cells which is regulated by insulin
Why are chylomicrons packaged with an outer layer of phospholipids?
Hydrophobic so keeps the water out
What is an apoprotein?
a protein which together with a prosthetic group forms a particular biochemical molecule such as a hormone or enzyme.
What can LPL recognise?
The apoproteins so grab the circulating chylomicrons
What is predominantly the remnants of chylomicrons?
cholesterol and glycerol
Where are fatty acids synthesised mainly?
Liver - reactions in the cytoplasm
What can endodogenous lipids be packaged with to form VLDL (very low density lipoprotein)?
Proteins
What is the fate of VLDL?
The triacylglycerols in it are digested by LPL regulated by insulin
fatty acids absorbed by the cells
vldl remnant remains - mainly cholesterol
same fate as chylomicrons (dietary fat)
What becomes the main energy source during fasting?
fatty acids
Where are long chain fatty acids released from and what is it stimulated by?
Long chain fatty acids released from adipose tissue, stimulated by reduced insulin and increased glucagon
What is the main fatty acid oxidation pathway?
B-oxidation
How do fatty acids enter tissues?
Diffusion
What are the fatty acids activated to using ATP?
fatty acyl coA (INTERMEDIATE)
Where is the fatty acyl coA transported to?
Mitochondrial matrix
What is the fatty acyl coA converted to in mitochondria
Acetyl coA producing NADH AND FAD2H
What does the acetyle coA enter then?
TCA cycle
Why do fatty acids produce a lot of energy?
2 carbons used each time the process happens and chains have many carbons so lot of energy produced continously
What can fatty acyl coA’s be used to produce?
Convert bacj to triacyglycerols for storage
energy - b oxidation ketogenesis
membrane lipids - phospholipids, sphingolipids
Fed state
Packaged chylomicrons produced
lots of glucose coming in - VLDL produced
insulin increased
fatty acids taken to tissues intrinsically and extrinsically
Fasting state
Release of fatty acids
put through b oxidation to produce energy and ketone bodies - more energy
generate glucose in the liver
Where does cholesterol come from?
synthesised or from diet
Why is cholesterol important?
Component of cell membranes
precursor of bile salts
precursor of steroid hormones
precursor of vitamin D
What is cholesterol a major component of?
Blood lipoproteins
How is cholesterol taken up
Mainly by diffusion in gut enterocytes- not good for you
Why does cholesterol entry have to be regulated?
cannot be fully metabolised
but excess can be transported back into gut to be excreted
Where is cholesterol synthesised?
cytosol in liver
What molecule is mainly used to start cholesterol synthesis?
Acetyl coA
Which enzyme is a good drug target for cholesterol reduction?
HMG- coA reductase
statin - lowers cholesterol in blood, comeptitively inhibits the enzyme so this can be designed to look like its substrate - higher affinity for the enzyme
What are the 4 steps for cholesterol synthesis?
Acetyl coA - mevalonate
mevalonate - isoprenes
isoprenes (5c) - squalene (30c)
squalene - cholesterol
What happens to leftover cholesterol?
Converted to bile salts - stored in gallblader, secreted into gut
converted to biliary cholesterol into gut and can be reabsorbed
can be converted to cholesterol esters and packaged into VLDL to go to tissues
Why are bile salts effective as detergents?
Because they carry charge - electrons around them
What affects the recycling of cholesterol to the liver?
interact with bacteria that chemically alter them which deconjugate and dehydroxylate slightly so less able to reabsorb the cholesterol
What are cholesterolr and cholesterol esters transported in?
Lipoproteins (cholesterol helps stabilise them)
how does cholesterol enter the cell?
VLDL remnant left behind
these are converted to IDL (intermediate) and LDL (low)
LDL contain a lot of cholesterol and cholesterol esters
this can be returned to liver to make more VLDL or taken up by other cells needing cholesterol
- e.g. membrane synthesis - e.g steroid hormone synthesis
How are LDL endocytosed?
Recognised by the apoproteins on their surface by the LDL receptors
What happens to excess LDL?
Endocytosed by macrophages (scavenger receptors - recognise some apoproteins)
the ldl causes some of the macrophages to change into foamy cells - cause bumps in the vessels, blood rushes by and causes small thrombus to form, blood clot gets bigger etc which can cause inflammation and contribute to atherosclerosis
Why is maintenance of blood glucose levels essential?
Blood glucose too high = causes release of water from tissues - dehydration and death
Blood glucose too low - lack of fuel to produce ATP
brain depends on glucose as fuel - coma
red blood cells low on ATP, can’t provide oxygen to tissues - death
What happens to insulin and glucagon levels when glucose increases after eating a meal?
Insulin increases and glucagon decreases
Insulin allows uptake of glucose
What does glucagon do?
Increase in glucagon causes release of glucose
decrease in glucagon causes uptake and storage of glucose
Where do the three main sources of glucose come from?
Diet
Glycogen degradation
gluconeogenesis
Which sources of glucose are critical during fasting?
Glycogen degradation
Gluconeogenesis
What is glycogen?
Major storage form of glucose in humans in liver and muscle
What is the structure of glycogen?
Branched chains of glucose joined by alpha 1-4 linkages with branching by alpha 1-6 linkages
one carbon is joined to protein - glycogenin (reducing end)
forms huge polymers
What are the differences in processes in muscle and liver of glycogen?
Muscle - glycogen undergoes glycolysis mainly so that ATP is produced for energy
Liver - glycogen undergoes gluconeogenesis mainly to produce glucose which is released into the blood to raise blood glucose
What does glycogen synthesis require?
Energy in the form of UTP (uridine triphosphate)
What are the steps of glycogen synthesis?
- Glucose is transerred from UDP glucose to glycogenin (enzyme that polymerises first few molecules)
- Glycogen synthase transfers glucose from UDP glucose to growing chain
- This forms a 1-4 linkages
- When 11 residues are reached, 6-8 cleaved off and rejoined by alpha 1-6 linkages by branching enzyme.
Which two enzymes is glycogen degradation carried out by? and what do they do?
Glycogen phosphorylase - removes glucose molecules at end of chains
Debranching enzyme - acts as transferase, removing glucose molecules near branch point
- also cleaves branch point
What hormones regulate glycogen degradation in the liver and what are their effects?
- insulin decreases degradation
- glucagon increases degradation
- adrenaline increases degradation
What stimulates glycogen degradation in the muscles?
Low ATP (high AMP)
Calcium and adrenaline