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Metabolism (Feeding, fasting & exercise (energy stores (gycogen…
Metabolism
Feeding, fasting & exercise
breakdown = catabolism
biosynthesis = anabolism
ATP - huge turnover of more than 100kg per day - continuously being produced and broken down - present within cells as a source of phosphate and energy
standard G0 = -31kJ/mol
fuels in the blood
fatty acids are bound to albumin in the blood, ketone bodies are made from fatty acids in the liver - conc is normally negligable but rise quickly during fasting
plasma glucose is maintained at 5-6mmol/L because the brain metabolises mostly glucose, erythrocytes metabolise only gluocse, reuired by renal medulla
plasma store is small, only liver glycogen can supply the plasma, glucose canno tbe made from fatty aicds, can be made from amino acids but all protein is gunctional
actual Gp = -60kJ/mol
ATP conc falls during exercise, AMP rises a lot more than ADP - myosine ATPase, creatine kinase, adenylate kinase/myokinase
NADP = nicotinamide adenine dinucleotide phosphate
pentose phosphate pathway - major pathway in NADP breakdown and the breakdown of glucose - it is a metabolic parallel to glycolysis
growth is very energy intensive therefore a baby requires more kJ/kg/day - this decreases with age
there are essential amino acids and essential fatty acids but no essential carbohydrates/sugars
energy stores
plasma glucose
can be used by all tissues, but the available store is very small (~5mmol/L)
recycling of glucose is called the cori cycle - 6ATP needed to convert lactate to glucose
it is limited because glucose is reactive - hyperglycaemia
gycogen
glucose polymer, rapidly moblised, can supply energy quickly and anaerobicaly
hydrated, so weight limits the size of the energy store
liver glycogen maintains plasma glycose but muscle glycogen is only used by the muscle
TAG
highly reduced and therefore a large energy yeild
not hydrated - no weight pentalty - the largest energy store in the body
cannot be metabolised anaerobically - fatty acids cannot be used by the brain
protein
big store - can be converted to glucose and ketone bodies - all functional so breakdown leads to loss of function
slow/white fibres are specialised for oxidative metabolism, fast fibres specialised for anaerobic metabolism
fuels for muscle contraction
anaeorbic - muscle ATP, creatine phosphate, muscle glycogen
creatine phosphate is a phosphogen - it tops up the ATP once it is hydrolysed i.e. rephosphorylates ADP - quite a lot is present in te muscle
fatty acids and plasma cluose for aerobic
rise in AMP swicthes on AMP kinase - tends to favour breakdown pathways and inhibit biosynthetic reactions - the route of several different types of diabetes
promotes glucose uptake, glycolysis, fatty acid oxidation, mitochondrial biogenesis, and inhibits gluconeogenesis, cholesterol synthesis, glucogen synthesis, fatty acid/protein synthesis
carbohydrate metabolism
carbohydrate meets up to 50% of the energy requirement, all dietary carbohyrates are convertible to glucose there are not essential dietary sugars
sucrose = glucose + fructose
lactose = gluocse + galactose
there are 2 isomers of glucose - alpha and beta - whcih is impotant in enzyme specificity
starch
amylose - unbranched straight chains of glucose - carbon 1 in alpha confirguation - alpha(1-4) links
amylopectin - branched chains - alpjha(1-4) and alpha(1-6) links - some branches where alpha 1 carbon bonds eith carbon 6 on the next molecule
starch digestion
amylase
endoglycoside - hydrolyses alpha1-4 links to produce oligosacchardies
present in the saliva and secreted by the pancreas into the duodenum
glucoamylase
present on the intestinal wall
exoglycoside hydrolysing alpha1-4 links in oligosaccharides, trisacchardies, maltose
starch is degraded all of the way to glucose and then glucose is taken up
isomaltase
present on the intestinal wall
hydrolses alpjha1-6 link in isomaltose
alpha-dluocsidase inhibitors - can be given to dibaetic pateints orally to slow down the rate of starch degradation and therefore slow the rate that glucose is absorbed into the blood
miglitol, voglibose, acaebose
finding sucrose in the blood is bad - probably reached the blood via a gastric ulcer
sucralose i.e. splenda is an artificisl sweetner than cannot be hdylordes so is excreeted
protein digestion and nitrogen metabolism
nitrogen balance = total nitrogen ingested - total nitrogen excreted
disturbances of balance -
positive nitrogen balance - growth, pregnancy - more amino acids converted to body protein than in the amino acid pool
negative nitrogen balance
protein deprivation - less amino acids available to put into body protein
essential amino acid deficiency
trauma, disease - more amino acids in the amino acid pool/being broken down than used for growth
kwashiorkor - protein malnutrition but adeuqate energy intake
maramus - protein and energy deficiency
not all proteins are nutritionally equal - NPU net protein utilization - a measure of the ablity of a protein ot sustain growth - the weight of amino acids incorporated into a protein divided by the weight of those supplied in the diet
essential amino acids cannot be synthesised within the body so must be supplied in the diet
degradation of intracellular proteins - ubiwuitin targets proteins for degradation by bidning, proteasome, then ubiquitin released along with fragmented protein
gastric wall
chief cell
secretion and activation of pepsinogen - stimulated by acetylcholine - zymogen is modificed and packaged into veseil - converted to pepsinogen which is activated by the acidic conditions to pepsin
parietal/oxynitic cell
gastric acidification
trypsin, chymotrypsin, elastase, carboxypeptidase A/B, elastase
trypsinogen is converted to acitvwe trpysin by enteropeptiade , whcih activates downstream a number of other proteases
oligopeptides
urea
very soluble in water
electrically neutral
48% nitrogen by weight
synthesised by the liver and not further metabolised
plasma conc rises is renal failure - uraemia - and falls in liver cirrhosis
plasma ammonia is normally low but rises if the urea cycle is inhibited e.g in liver cirrhosis - ammonia is toxic - partciulary ot the cns
pancretic proteinases are specific to particular bones in amaino acids