2) Energy production ~ carbohydrates Flashcards
(17 cards)
describe the structure of a monosaccharide
3-9 carbon atoms long
majority have asymmetric carbon atoms - they have 4 different groups attached to them and so are stereoisomers
have d and L forms ( D= natural form)
what is galactosaemia and how can it be caused
a rare condition where the body fails to metabolise galactose properly and it can be caused by an excessive amount of galactose in the blood
explain the key role of pyruvate dehydrogenase
it is an enzyme that converts pyruvate into acetyl coenzyme A so that it can enter the TCA cycle in the 3rd stage of metabolism
the reaction is not reversible, making it a key regulatory step for the TCA cycle.
explain the roles of the tricarboxylic acid cycle in metabolism
the main function of the cycle is to break the C-C bond in acetyl and oxidise the carbons to release CO2
the TCA cycle can produce approx. 32 molecules of ATP for every molecule of glucose
the cycle can produce a lot of intermediates that are necessary for other metabolic pathways - eg. C5 and C4 intermediates are used for synthesis of non essential amino acids, C4 intermediates are also used for synthesis of haem and glucose and C6 intermediates can be used for synthesis of fatty acids
how is the TCA cycle regulated
it is controlled by the rate of ATP usage.
ATP/ADP ratio and NADH/NAD+ ratio both regulate the cycle
NADH is a non competitive inhibitor for isocitrate dehydrogenase which catalyses an early step in the cycle that’s irreversible. the enzyme is activated by ADP
where does oxidative phosphorylation occur
at the inner mitochondrial membrane
outline the events that take place in stage 4 of metabolism
oxidative phosphorylation
NADH and FADH2 are re oxidised and lose protons and electrons. the electrons get transferred along carrier proteins and lose energy along the way to O2. the energy released is used to actively pump the protons across the membrane to create a proton gradient
what are the differences between oxidative phosphorylation and substrate level phosphorylation
oxidative phosphorylation:
- requires membrane associated complexes
- energy coupling occurs indirectly and uses a proton motive force
- needs oxygen
- its a major process for ATP synthesis for cells that need a lot of energy
substrate level:
- requires soluble enzymes
- energy coupling occurs directly through the formation of a high energy of hydrolysis bond
- can work without oxygen to a limited extent
- minor process of ATP production in cells that need a lot of energy
explain how the electron transport chain and ATP synthesis are coupled in phase 4 of metabolism
when conc of ATP is high, it means the conc of ADP is low, which is the substrate needed for ATP synthase. so ATP synthase cannot function due to a lack of substrate, so protons do not re enter mitochondria and so the proton conc outside increases to the point where it stops protons from being pumped and so the electron transport chain stops.
when ATP conc is low the opposite happens
how are dietary carbohydrates digested and absorbed
hydrolysed by glycosidase enzymes, releasing glucose. starts in the mouth with salivary amylase and continues in duodenum with pancreatic amylase.
what is lactose intolerance
when body has low activity of lactase so less able to digest lactose.
lactose goes to colon and broken down by bacteria. its presence causes increase is osmotic pressure in colon and draws water into in, causing diarrhoea. patients feel bloating and discomfort.
why is the pentose phosphate pathway important
starts from glucose 6 phosphate
- produces NADPH which is needed for reducing power for biosynthesis, maintenance of GSH levels and detoxification reactions
- produces C5 sugar ribose needed for nucleotides, DNA and RNA
no ATP made, CO2 released
what is the rate limiting enzyme for the pentose phosphate pathway
glucose 6 phosphate dehydrogenase
explain fructose metabolism
metabolised in liver
fructokinase converts it to fructose 1 phosphate
what does fructose in the urine mean
fructokinase is missing
describe fructose intolerance
aldolase enzyme is missing
fructose 1P builds up in liver
cells become depleted of inorganic phosphate so cannot make ATP
this leads to liver damage
managed by removing fructose and sucrose from diet
