week 10 - gastrointestinal system Flashcards
what is metabolism
sum of all chemical reactions in which energy is made available and consumed in the body
what does the body need energy for
Contraction of muscles for all movement
Accumulation of ions and other molecules against concentration gradients (nerve impulse transmission)
Biosynthesis and hence for the building of tissues
Waste disposal and hence for getting rid of the end products of bodily function
Generation of heat and hence maintenance of body temp
what is gibbs free energy and when is it positive and negative
it is usable energy or energy that is available to do work
deltaG = negative when the reaction gives out energy and is positive when the product contains more energy than the substrate
describe the structure of ATP
adenosine tri-phosphate is composed of adenine, ribose and three phosphate groups
ADP is only two phosphate groups
how is acetyl coenzyme A produced
glycolysis of glucose
beta-oxidation of fatty acids
transamination and oxidative deamination of amino acids
all of these reactions produce acetyl coA
vitamins and minerals play essential roles in these reactions
what kind of process is the TCA cycle
amphibolic meaning it has anabolic and catabolic components
steps of the TCA cycle
acetyl coA enters and condenses with oxaloacetate to produce citrate
decarboxylation phase - citrate is metabolised into succinyl coA (CO2 released)
reductive phase - succinyl coA to oxaloacetate
1 GTP produced
1 acetyl coA lead to 3 NADH and 1 FADH2 being produced
steps of the electron transport chain
NADH and FADH2 donate two electrons and one proton
electrons are passed along RADOX centres which have an increasing affinity for electrons - electrons moving along produces ATP
ATP used to pump protons against conc gradient from matrix through the inner mitochondrial membrane to the intermembrane space
protons return to matrix through ATP synthase as IMM is impermeable
as protons are driven through, ATP synthase rotates and ATP is produced
electrons at end of complex 4 are donated to molecular O2 with a proton to produce water
how are electrons passed between complexes in the ETC
As electrons reach end of RADOX centres in complex 1, they are passed via coenzyme Q to the next complex and so on… but from complex 3 to 4, cytochrome C passes electrons between complex
why is complex 2 different (in ETC)
it is not pump proteins
FADH2 joins at this complex
describe glycolysis
glucose is broken down to 2 pyruvate molecules in two phases
phase 1 - endergonic (2 ATP in) - glucose to glyceraldehyde-3-phosphate
phase 2 - exergonic - G-3-P is metabolised to pyruvate producing 4 ATP giving a net gain of 2 ATP
occurs in the cytosol
how is pyruvate converted into acetyl coA
Pyruvate undergoes further metabolism in the mitochondria where, on entry, the 3C pyruvate loses a carbon atom with the production of CO2 to form acetyl CoA by the action of pyruvate dehydrogenase - A molecule of NADH is also formed in this process and that can be fed into the electron transport chain
Acetyl CoA is then able to enter the TCA cycle
how is excess glucose stored in the body
in the form of glycogen mainly within the liver and also in muscle
what are lipids
highly efficient energy storage molecules and are important to the body’s ability to adapt to periods of fasting
examples - fats, oils, waxes, certain vitamins (such as A, D, E and K), hormones and most of the cell membrane that is not made up of protein
what are triglycerides and how can they be broken down
Fats are stored as triglycerides - triglycerides are three fatty acids attached to a glycerol backbone, these triglycerides can be broken down into their component parts of fatty acids and glycerol by an enzyme called lipase
how are fatty acids transported in the blood
Fatty acids are released and transported in the blood as a complex with albumin and are taken up by other cells for oxidation
they are hydrophobic so are transported within albumin which protects them from water
All enzymes required for fatty acid catabolism are within matrix of mitochondria but fatty acids need to be modified by the addition of acetyl coA molecule in order to enter the mitochondria
beta-oxidation occurs once they enter they matrix
describe fatty acid transportation into the mitochondrial matrix
addition of coA allows fatty acids to enter the mitochondria - forms fatty acyl coA
carnitine replaces coA to form fatty acyl carnitine - allowing it across the outer mitochondrial membrane
carnitine shuttle allows fatty acids to cross impermeable IMM into matrix
coA replaces carnitine to from fatty acyl coA and fatty acids can be degraded
describe fatty acid degradation
once in the matrix, beta-oxidation can occur
this process cleaves carbon backbone between alpha and beta carbons making the fatty acid smaller and smaller
each cleavage produces acetyl coA, 1 NADH and 1 FADH2 which can be fed into ETC
describe protein metabolism
transamination - removes amine group from AA and transfers it to an alpha ketoacid - when it accepts the amine group it transfers the keto group to the original AA
deamination - amine group removed from AA releasing the carbon backbone of the AA which can be regenerated into glucose, fatty acids or various TCA cycle intermediates - produces a side product of ammonium (toxic so kidneys exclude it)
describe glucogenic and ketogenic amino acids
glucogenic - breakdown products ultimately form glucose by conversion to pyruvate, or intermediates of TCA cycle
ketogenic - breakdown products form fatty acids via the intermediates of acetyl coA or acetoacetyl coA
sources of metabolic fuel in prolonged periods of starvation
fat - triglycerides in adipose tissue - sufficient to prolong life for 3 months
protein - provides approx. 14 days worth of energy but is spared for as long as possible to permit mobility
why is the BMI not always a good representation of an individual
does not take into account muscle mass or cardiovascular condition
factors influencing energy expenditure
menstruation, age, last three months of pregnancy and also lactation cause increase in expenditure
components of a balanced diet and their functions
carbohydrate - energy source
protein - repair and growth
fat - long term energy store, insulation
vitamins - A: vision C: antioxidant D: Ca absorption
minerals - Ca: bone mineralisation Fe: oxygen transport
fibre - effective bowel function
water - hydration
structure of triglycerides
glycerol and three fatty acids
where is cholesterol found
present in plasma membrane of cells but also serves as a precursor for the synthesis of a number of other molecules such as sex hormones, oestrogen and testosterone as well as bile salts and phospholipids
dietary sources for the components of a balanced diet
C - bread rice pasta potatoes p - meat fish dairy nuts fat - meat cheese cream fish v - A: sweet potato B: veg C: citrus D: oily fish m - Ca: milk Fe: red meat K: bananas f - plants
essential amino acids
9 AAs that cannot be produced by the body and must be obtained by the diet
types of carbohydrates and examples
monosaccharides - glucose, fructose, galactose
disaccharides - sucrose, maltose, lactose
polysaccharides - starch
bonds between monosaccharides in poly and disaccharides
glycosidic bonds
glands secreting saliva
parotid, submandibular and sublingual salivary glands
function of saliva in digestion
starts the digestion of carbohydrates by producing an enzyme called alpha-amylase
how alpha-amylase starts to digest carbohydrates
cleaves the 1-4 glycosidic bonds to produce maltose, a disaccharide, maltotriose, a trisaccharide and alpha limit dextrin
digestion in the mouth
alpha amylase starts carb digestion
Lingual lipase which breaks down triglycerides into fatty acids and glycerol is also present in saliva but most fat digestion takes place later in the small intestine
digestion in the stomach
start of protein digestion
secretion and activation going on in the stomach during digestion
chief cells secrete pepsinogen
parietal cells secrete HCl acid which denatures proteins and activates pepsin
pepsin then cleaves peptide bonds within the polypeptide chain to produce many smaller oligo peptides
what is a zymogen
some enzymes are synthesised as inactive precursors - these inactive precursors are called zymogens
exocrine function of the pancreas
pancreatic juice and alkali secretion
alkali secretions buffer any acid from the stomach and provide an optimal pH for. digestive enzymes in the duodenum
endocrine function of the pancreas
secretion of insulin and glucagon
function of the pancreatic secretions into the duodenum
Pancreatic secretions into the duodenum include a number of proteases such as trypsin and chymotrypsin and carboxypeptidase as well as other enzymes to digest elastin
function of liver in digestion
production and secretion of bile
role of bile in digestion
Stored in gallbladder and released into the duodenum after a meal
Important in the emulsification of fat particles so that fats are accessible for enzymes
Bile salts aid absorption of fats by forming complexes called micelles
properties of bile that allows it to help emulsify fats
Cholesterol derived potion of bile acid is hydrophobic and the amino acid conjugate is hydrophilic - bile acids are amphipathic
Due to these properties, bile salts have a detergent action of particles of dietary fat causing fat globules to break down or be emulsified into tiny droplets
why fats are emulsified
greatly increases the surface area of fat making it available for the digestion by lipases
