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
________ and
________ work together to produce ATP in
oxidative phosphorylation.
1) electron transport chain (ETC)
2) chemiosmosis (ions moving down electrochemical gradients)
ETC goal:
Regenerate electron carriers and create
an electrochemical gradient to power ATP
production.
The ____________ is the
location of the ETC for _______ while the __________ is the location of the ETC for
___________.
1) mitochondrial inner membrane
2) Eukaryotes
3) Cell membrane
4) Prokaryotes
_________ are responsible for
moving electrons through a series of
___________ reactions in the
ETC. As the series of redox reactions occurs,
__________ are pumped from the mitochondrial matrix to the intermembrane space, forming an electrochemical gradient. This is the reason the __________ is highly acidic.
1) Four protein complexes (I-IV)
2) oxidative/reduction
3) Protons
4) intermembrane space
_______ is more effective than ______ and drops electrons off directly at _______, regenerating ______.
1) NADH
2) FADH2
3) complex-1
4) NAD+
FADH2 drops _______ off at protein complex-II, regenerating FAD. However, this results in the pumping of ______ protons due to the bypassing of complex-I.
1) electrons
2) fewer
Chemiosmosis goal:
Use the proton electrochemical gradient (proton-motive force) to synthesize ATP.
ATP synthase
is a channel protein that provides a
hydrophilic tunnel to allow protons to flow down their electrochemical gradient (from the
intermembrane space back to the mitochondrial matrix). The spontaneous movement of protons generates energy that is used to convert ADP + Pi into ATP, a condensation reaction that is endergonic (requires energy + nonspontaneous =
+ΔG).
ATP Yield of Aerobic Cellular Respiration
Aerobic respiration is exergonic, with a ΔG = -686 kcal/mol glucose.
NADH produces 3 ATP (NADH from glycolysis
produces less)*
*The 2 NADH from glycolysis produce 4-6 ATP
because a varying amount of ATP must be used to shuttle these NADH from the cytosol to the mitochondrial matrix. However, prokaryotes do not need to shuttle their NADH, so they will
produce 6 ATP.
FADH2 produces 2 ATP.
S-L = substrate-level
STAGE NET PROD YIELD NET ATP
Glycolysis 2 ATP (S-L) 2 ATP
2 NADH 4-6 ATP
2 PYR oxid 2 NADH 6 ATP
2 Kreb Cycle 2 GTP (S-L & ATP equiv.) 2ATP
6 NADH 18 ATP
2 FADH2 4 ATP
Total 36-38 ATP
Fermentation
an anaerobic pathway (no oxygen) that only relies on glycolysis by converting the produced pyruvate into different molecules in order to oxidize NADH back to NAD+.
Regenerating NAD+ means glycolysis can continue to make ATP. Fermentation occurs within the cytosol. The two most common types of fermentation are lactic acid fermentation and alcohol fermentation.
2 Types:
1) Lactic Fermentation
2) Alcohol Fermentation
Lactic acid fermentation
uses the 2 NADH from glycolysis to reduce the 2 pyruvate into 2 lactic acid. Thus, NADH is oxidized back to NAD+ so that glycolysis may continue. This happens frequently in muscle cells and occurs continuously in red blood
cells, which do not have mitochondria for aerobic respiration.
Cori cycle
is used to help convert lactate back
into glucose once oxygen is available again. It
transports the lactate to liver cells, where it can
be oxidized back into pyruvate. Pyruvate can then be used to form glucose, which can be used for more ideal energy generation.
Alcohol fermentation
uses the 2 NADH from glycolysis to convert the 2 pyruvate into 2 ethanol. Thus, NADH is oxidized back to NAD+ so that glycolysis may continue. However, this process has an extra step that first involves the decarboxylation of pyruvate into acetaldehyde, which is only then reduced by NADH into ethanol.
Types of organisms based on ability to grow in
oxygen:
1) Obligate aerobes
2) Obligate anaerobes
3) Facultative anaerobes
4) Microaerophiles
5) Aerotolerant organisms
Obligate aerobes
- only perform aerobic
respiration, so they need the presence of
oxygen to survive.
Obligate anaerobes
- only undergo anaerobic
respiration or fermentation; oxygen is poison
to them.
Facultative anaerobes
- can do aerobic
respiration, anaerobic respiration, or
fermentation, but prefer aerobic respiration
because it generates the most ATP.
Microaerophiles
- only perform aerobic
respiration, but high amounts of oxygen are
harmful to them.
Aerotolerant organisms
- only undergo anaerobic respiration or fermentation, but oxygen is not poisonous to them.
Molecules other than ______, such as other types of _____, _____, and _____ can be
modified to enter ________ at various
stages for energy generation.
1) glucose
2) Carbs, fats, and proteins
3) Cellular respiration
Other ________ mostly enter during
glycolysis. _________ describes the release of glucose-6-phosphate from glycogen, a highly branched polysaccharide of glucose. Disaccharides can undergo ______ to release two carbohydrate monomers, which can enter
glycolysis.
1) carbs
2) Glycogenolysis
3) hydrolysis
_______are the preferred energy source
since they are easily catabolized and are high yield (4 kcal/gram).
1) Carbs
Glycogenesis
refers to the reverse process - the
conversion of glucose into glycogen to be stored in the liver when energy and fuel is sufficient. Glycogen is stored in the liver and muscle cells.
_____ are mostly present in the body as
triglycerides. ______ are required to first digest fats into ______ and _____ through a
process called _____. These digested pieces
then can be absorbed by enterocytes in the _______ and reform triglycerides.
1) Fats
2) lipases
3) Free FA and alcohol
4) Lipolysis
5) small intestine
Adipocytes
are cells that store fat (triglycerides)
and have hormone-sensitive lipase enzymes to
help release triglycerides back into circulation as lipoproteins or as free fatty acids bound by a protein called albumin.
Chylomicrons
lipoprotein transport structures
formed by the fusing of triglycerides with proteins, phospholipids, and cholesterol. They leave enterocytes and enter lacteals, small lymphatic vessels that take fats to the rest of the body.
Low-density lipoproteins (LDLs)
low density of proteins, considered unhealthy because they transport cholesterol to the peripheral tissues, where it can cause vessel blockage.
High-density lipoproteins (HDLs)
- high density of proteins, considered healthy because they bring cholesterol to the liver to make bile.
When a ______ molecule travels to the ______, it can undergo a conversion to enter glycolysis or make new glucose via _______ at the liver.
1) glycerol
2) liver
3) gluconeogenesis
Free fatty acids undergo _______ to be
converted into acetyl-CoA. Beta-oxidation occurs in the _______ of eukaryotic cells and
requires an initial investment of ATP; the fatty
acid chain is then continuously cleaved to yield ________ molecules (which can be used in the Krebs cycle for ATP generation) and electron carriers (NADH + FADH2 - produces more ATP).
1) B-oxidation
2) mitochondrial matrix
3) two-carbon acetyl-CoA
Proteins
the least desirable energy source
because the processes to get them into cellular respiration take considerable energy and proteins are needed for many essential functions in the body.
______ are broken down into amino acids, which must first undergo _________
(removal of NH3) before being shuttled to various parts of cellular respiration.
1) Proteins
2) oxidative deamination
Ammonia (NH3)
toxic; must be converted
into uric acid or urea depending on the species
and excreted from the body. For example, humans convert ammonia into urea, which is excreted as urine
