CH 9 - glycolysis and fermentation Flashcards
oxidation numbers
O>C>H (electronegativity)
C(-1)——–H(+1)
O(-1)——–H(+1)
O(-1)——–C(+1)
C—C O—O electrons shared equally
if the molecule is not an ion, total should add to 0
burning methane
exergonic –> electrons are being towards a more electronegative element (away from C to O)
what is broken down to make ATP
glucose
starting with glucose, aerobic respiration includes… (slide 9-19)
glycolysis or an alternative
oxidative decarboxylation
the citric acid cycle (aka Krebs cycle)
oxidative phosphorylation
if we start with glucose, what gets oxidized? reduced?
reduced = O2
oxidized = Carbon, exergonic = energy released
aerobic respiration
oxygen is the final electron acceptor
anaerobic respiration
something else serves as the final electron acceptor
fermentation
glycolysis plus a few more steps to regenerate NAD
glycolysis (Fig 9-7, p. 233)
glykos - sweet lysis - split = splitting sugar
takes place in cytosol
glucose –> pyruvate
sequence of ten reactions in which glucose is catabolized to pyruvate with a single oxidative reaction and two ATP-generating steps
key events of glycolysis
first phosphorylation step traps product in cell - keeps low [glucose] in cell
splitting produces two three carbon molecules from one with six carbons
oxidation-reduction step (Gly-6) and ATP synthesis (Gly-7) –> carbon is oxidized, exergonic; NAD+ is is reduced
NADH carries two electrons and one proton from two Hs. What matters is the electrons as they will be delivered to the electron transport chain and eventually oxygen.
Another ATP is synthesized later –> put a little ATP in to get more out later
end of glycolysis = pyruvate
substrate level phosphorylation
how ATP is synthesized in glycolysis
direct transfer of P to ADP from a phosphorylated intermediate
in Gly-7, the exergonic reaction that drives endergonic ATP synthesis is oxidation of carbon in Gly-6
during glycolysis…
is any O consumed? no
was any CO2 produced? no
how many ATPs consumed? 2
how many ATPs produced? 4
net ATP production? 2
how many NADH produced? 2
can other carbohydrates enter glycolysis?
yes, but must be in the form of monosaccharides
prokaryotes have two alternatives to glycolysis
Entner-doudoroff
oxidative pentose phosphate
since glycolysis consumes no O, will we run out of ADP and Pi if we use glycolysis alone?
no, ATP is constantly breaking down
BUT would run out of NAD which is regenerated in the electron transport
in lactic acid fermentation, what is oxidized? reduced?
oxidized? Carbon
reduced? middle Carbon
two reasons food are fermented (by bacteria or fungi)
preservation
addition of flavor
steps to fermentation of food
bacteria and fungi –> secrete enzymes –> break down molecules in their surroundings –> take up products via membrane transport –> cause decomposition
Ex: milk + bacteria –> lactose –> lactic acid –> lowers pH –> casein –> denatured –> precip (curds)
sauerkraut/pickles –> high salt + low pH kills undesirable bacteria
role of allosteric regulation
matches rate of glycolysis to metabolic needs
phosphofructokinase is inhibited by its substrate ATP. the active site has a high affinity for ATP but the allosteric site has a low affinity for ATP. at low ATP concentrations, which is most likely to bind ATP? high ATP concentrations?
low ATP concentrations, active site is most likely to bind ATP
high ATP concentrations, enzyme is inhibited
synthesis of glucose
in between meals, our skeletal muscle breaks down glycogen to pyruvate and releases it. it can’t release glucose because it’s phosphorylated and won’t bind to the facilitated diffusion carrier. the liver converts pyruvate into glucose and releases it, providing glucose between meals. the liver does the same with lactic acid produced during intense anaerobic exercise.
gluconeogenesis
process of converting pyruvate to glucose
CONSUMES ATP
what controls whether a cell engages in glycolysis or gluconeogenesis?
Le Chatelier’s Principle - can shift equilibrium by changing concentration
some steps in glycolysis occur near equilibrium and are easily reversed
lots of glucose and little pyruvate?
glycolysis
lots of pyruvate and little glucose?
gluconeogenesis
some steps in glycolysis are so exergonic they are irreversible. this is why gluconeogenesis is endergonic overall. Those steps are either:
- different enzyme, different reaction
2. drive with ATP + GTP
how many ATPs are consumed to drive endergonic gluconeogensis
4
GTP is converted to GDP as a way of releasing energy, how many GTPs are used in gluconeogenesis
2
endosymbiotic theory for the origin of mitochondria and plastids
glycolysis –> cytosol
rest of respiration –> mitochondria
large ancestral eukaryotic cell engaged in fermentation, little ATP. engulfed ancestor of mitochondria engaged in the Entner-doudoroff pathway and the rest of aerobic respiration. Entner-doudoroff cycle lost evolutionarily.
hydrogenosomes and mitosomes
some anaerobic single-celled eukaryotes carry out a few more steps beyond pyruvate and make a little more ATP via substrate-level phosphorylation. they do so inside organelles called hydrogenosomes and mitosomes. These are thought to be evolutionary derived from mitochondria because:
- they have inner and outer membranes
- mitochondrial targetting sequences work
