final cellular energetics Flashcards
why does cellular metabolism occur in a series of small enzyme-catalyzed steps
it allows energy to be stored/extracted in useful ways
how do catabolic reactions extract energy
through the breakdown of larger molecules into smaller ones
how is glucose catabolized
by glycolysis and the citric acid cycle
what glycolysis
metabolism of glucose; happens in cytosol
what does the citric acid cycle do
allows for further oxidation of glucose using respiration; happens in mitochondria
what are the electrons from glycolysis and the citric acid cycle used for
to generate ATP vis the electron transport chain and oxidative phosphorylation
what is catabolism
chemical breakdown
where does energy for cellular processes come from
catabolism of nutrients
how is energy harvested in useful quantities
sugar/other nutrients are oxidized in small, enzyme-catayzed steps
what happens with oxidation
electrons are removed
how do enzymes allow energetically favorable reactions to occur
by coupling them with energetically unfavorable reactions
what are the two phases of coupling of reactions by enzymes
metabolism of food molecule releases some energy and enzymes will couple this with formation of activated carrier molecule, then carrier will interact with other reactions
what is glycolysis at its core
take one molecule of glucose and convert it to two molecules of pyruvate with the net production of 2 ATP molecules and 2 NADH molecules
why is NADH referred to as a reducing power
because it has electrons available to reduce something else
what is the first phase of glycolysis
investment (2 ATP are spent to overcome activation energy barriers and activate glucose)
what is the second phase of glycolysis
cleavage (glucose is split into 2 3-carbon sugars)
what is the third phase of glycolysis
energy generation (4 ATP molecules are generated from final oxidation of the 3-carbon sugars)
what is reduction
addition of electrons - opposite of oxidation
what are the two types of coupling reactions
catabolism - energetically favorable
anabolism - energetically unfavorable
both reactions are coupled for ATP
what happens in glycolysis
one molecule of glucose is converted to two molecules of pyruvate with the net production of 2 ATP and 2 NADH molecules (“reducing power”)
energetically unfavorable
why must cells use fermentation
in the absence of O2, cells must use fermentation to oxidize NADH or they will run out of NAD+ and be unable to do glycolysis
what are the details of glycolysis
- enzyme makes a covalent linkage with substrate
a high energy bond is then replaced with a phosphate, which is transferred to ADP to make ATP - the energy released by hydrolyzing this bond drives the reaction
what is substrate-level phosphorylation
organic molecule (substrate) phosphorylates ADP to ATP
what is oxidative phosphorylation
free phosphate is directly attached to ADP without organic compound intermediate
what are the two modes of fermentation
first leads to excretion of alcohol and CO2, second leads to excretion of lactate
how much ATP does glycolysis yield per glucose molecule
2 ATP. further pyruvate metabolism will generate more
what does glycolysis yield in addition to ATP
2 NADH molecules. in the presence of O2, they can be oxidized back to NAD+, which can cycle back to be used for more glycolysis
what is NAD+
electron acceptor and electron cofactor
what happens in the absence of O2
cells use fermentation to oxidize NADH, or they’ll run out of NAD+
what is fermentation
the mechanism cells use to regenerate NAD+ (two types)
what is alcoholic fermentation
microbes use it to oxidize NADH back to NAD+ so they can continue glycolysis
how does alcoholic fermentation occur
- glucose goes through glycolysis to make pyruvate and 2 NADH
- convert NADH to NAD+ by donating electrons back to pyruvate
- pyruvate is decarboxylated (2 protons are added are CO2 is given off)
- regenerate NAD by reducing aldehyde and taking electrons from NADH
- generates ethanol
what is lactic acid fermentation
generate pyruvate and 2 NADH and have to regenerate NAD+
how does lactic acid fermentation occur
- take electrons and put them directly back on pyruvate at carbonyl group to convert it into hydroxyl group
- pyruvate is converted to lactate
- lactate can be oxidized back to pyruvate, which can be reduced back to glucose by liver
what is the purpose of lactic acid fermentation
allows maintenance of high level of glucose for muscles when only have enough oxygen to do glycolysis
what are the two steps that aerobic organisms use to further oxidize pyruvate to CO2 and water
citric acid cycle (occurs in matrix) and electron transport chain (occurs in inner mitochondrial membrane)
what happens in the citric acid cycle
- 4-carbon molecule + 2-carbon molecule to get 6-carbon molecule
- then oxidize this and release CO2 to get a 4-carbon molecule again
- use energy from oxidation to generate NADH/FADH2 molecules and a GTP molecule
what does glycolysis need for rearranging
glucose and enzymes
what are the advantages of biochemical cycles
- greater possibilities for regulation bc there are many steps
- provides entry pointes for other molecules (in glycolysis, entry points only allow for things related to glucose)
- lots of molecules are generated that are difficult to make from scratch
what are the disadvantages of biochemical cycles (i.e. krebs cycle)
you need oxaloacetate for krebs cycle
what does the citric acid cycle generate
6 NADH and 2 FADH2 per glucose molecule (add that to the 2 NADH from glycolysis + 2 NADH from pyruvate -> Acetyl CoA) = 10 NADH, 2 FADH2
how can the energy used to reduce NAD+/FAD be used
it can be extracted to generate ATP, done by a proton pump that uses the energy of NADH/FADH2 oxidation to create a proton gradient across the inner mitochondrial matrix
what reduction helps drive the formation of the proton gradient
the reduction of O2 to H2O provides another energetically favorable reaction
what pumps protons out of the mitochondrial matrix
NADH and FADH2
what is oxidative phosphorylation
ADP -> ATP generation by ETC in mitochondria
putting it all together with catabolic metabolism
- generate pyruvate in cytosol via glycolysis
- pyruvate enters mitochondria and is converted to acetyl CoA, which passes thru citric acid cycle
- generate CO2, NADH
- electrons from NADH and FADH pass through electron transport chain
- use oxygen to generate water
- proton gradient makes ATP
