Cellular Energy Flashcards
Metabolism
refers to all the metabolic pathways (series of chemical reactions) that are happening in a given organism. 2 types:
1) Catabolic processes -
breaking down larger molecules for energy while
2) Anabolic processes - using energy to build
larger macromolecules.
To break down carbohydrates for energy, cells use either ______ or _______.
1) aerobic cellular respiration
(consumes oxygen, more energy produced), or
2) anaerobic cellular respiration (no oxygen
needed, but less energy produced).
Adenosine Triphosphate (ATP)
- an RNA
nucleoside triphosphate. It contains an adenine
nitrogenous base linked to a ribose sugar (RNA
nucleoside part), and three phosphate groups
connected to the sugar (triphosphate part). - cellular energy currency
because of the high energy bonds between the
phosphate groups. These bonds release energy
upon hydrolysis (breaking bonds), resulting in ATP
losing a phosphate group and becoming adenosine diphosphate (ADP). Because of the additional negatively-charged phosphate group,
ATP is less stable than ADP.
Reaction coupling
is the process of powering an energy-requiring reaction with an energy-releasing
one. It allows an unfavorable reaction to be powered by a favorable reaction, making the net Gibbs free energy negative (-ΔG = exergonic =
releases energy + spontaneous).
Mitochondria
are organelles that produce ATP through cellular respiration (catabolic process).
- have an outer membrane and an inner membrane with many infoldings called cristae.
- The intermembrane space is located between the
outer and inner membranes while the mitochondrial matrix is located inside the inner
membrane.
endosymbiotic theory
states that eukaryotes
developed when aerobic bacteria were internalized as mitochondria while the
photosynthetic bacteria became chloroplasts.
Evidence of Endosymbiotic Theory include similarities between mitochondria and chloroplasts:
● They are similar in size.
● They possess their own circular DNA.
● They have ribosomes with a large and small subunit.
● They reproduce independently of the host cell.
● They contain a double membrane.
Aerobic cellular respiration
- performed to
phosphorylate ADP into ATP by breaking down
glucose and moving electrons around (oxidation
and reduction reactions).
Aerobic cellular
respiration involves 4 catabolic processes:
1. Glycolysis
2. Pyruvate oxidation
3. Krebs cycle
4. Oxidative phosphorylation
Glycolysis
Glucose → 2 ATP + 2 NADH + 2 pyruvate
Glycolysis takes place in the cytosol and does not
require oxygen, so it is also used in fermentation.
- Involves substrate-level phosphorylation, energy investment phase and payoff phase,
Substrate-level phosphorylation
the process
used to generate ATP in glycolysis by transferring a
phosphate group to ADP directly from a
phosphorylated compound.
Energy investment phase and an energy payoff phase in glycolysis:
- Hexokinase uses one ATP to phosphorylate
glucose into glucose-6-phosphate, which
cannot leave the cell (it becomes trapped by
the phosphorylation). - Isomerase modifies glucose-6-phosphate into
fructose-6-phosphate. - Phosphofructokinase uses a second ATP to
phosphorylate fructose-6-phosphate into
fructose-1,6-bisphosphate. This is the key
regulatory step in glycolysis. - Fructose-1,6-bisphosphate is broken into dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (G3P), which
are in equilibrium with one another. - G3P proceeds to the energy payoff phase so
DHAP is constantly converted into G3P to maintain equilibrium. Thus, 1 glucose molecule will produce 2 G3P that continue into the next
steps. - G3P undergoes a series of redox reactions to
produce 4 ATP through
substrate-level-phosphorylation, 2 pyruvate
and 2 NADH.
Since 2 ATP are used up in the energy investment
phase and 4 ATP are produced in the energy payoff
phase, a net of 2 ATP is produced per glucose
molecule within glycolysis.
Pyruvate Oxidation
2 pyruvate → 2 CO2 + 2 NADH + 2 acetyl-CoA
_________ is an enzyme that carries out the pyruvate oxidation steps.
Pyruvate dehydrogenase
Steps of Pyruvate Oxidations include:
1) Decarboxylation
2) Oxidation
3) Coenzyme A (CoA)
Decarboxylation
- Pyruvate molecules (3
carbon molecule) move from the cytosol into
the mitochondrial matrix (stays in the cytosol
for prokaryotes), where they undergo
decarboxylation, producing 1 CO2 and one
two-carbon molecule per pyruvate.
Oxidation
- The two-carbon molecule is
converted into an acetyl group, giving
electrons to NAD+
to convert it into NADH.
Coenzyme A (CoA)
- CoA binds to the acetyl
group, producing acetyl-CoA.
Krebs Cycle
2 acetyl-CoA → 4 CO2 + 6 NADH + 2 FADH2 + 2GTP
The Krebs cycle is also known as the citric acid
cycle or the tricarboxylic acid (TCA) cycle.
Like pyruvate oxidation, kreb cycle occurs in the ________
and the _______ for
prokaryotes.
1) Mitochondrial Matrix
2) Cytosol
Steps in Kreb Cycle
- Acetyl-CoA joins oxaloacetate (four-carbon)
to form citrate (six-carbon). - Citrate undergoes rearrangements that
produce 2 CO2 and 2 NADH. - After the loss of two CO2, the resulting
four-carbon molecule produces 1 GTP through
substrate-level phosphorylation. - The molecule will now transfer electrons to 1
FAD, which is reduced into 1 FADH2. - Lastly, the molecule is converted back into
oxaloacetate and also gives electrons to
produce 1 NADH. - Two acetyl-CoA molecules produce 4 CO2 + 6
NADH + 2 FADH2 + 2 GTP.
Oxidative Phosphorylation
Electron carriers (NADH + FADH2) + O2 → ATP + H2O
