Chapter 9 Flashcards
Energy enters most ecosystems as…
sunlight
Energy leaves most ecosystems as…
heat
Cells harvest…
chemical energy stored in organic molecules that the mitochondria and eukaryotes use as fuel for cellular respiration
Catabolic pathways
yield energy by OXIDIZING and BREAKING down organic molecules
via
an exergonic process
Fermentation
a catabolic process
-a partial degradation of sugars that occurs in the absence of oxygen
Cellular Respiration
the most prevalent and efficient catabolic pathway
- consumes Oxygen and organic molecules such as glucose and yields ATP
Cells must regenerate ATP…
in order to keep working
Catabolic pathways yield energy based on …
their ability to cause a transfer of elections
Redox reactions
transfer elections from one reactant to another by oxidation and reduction
i.e. redox of table salt: Na+ is oxidized, Cl- is reduced
Oxidation
a substance loses elections, or is oxideized
Reduction
a substance gains elections, or is reduced
the “fall” of electrons during respiration is…
stepwise and occurs by an electron transport chain
Electron Transport Chain
found in inter membrane counter of mitochondria
During cellular respiration…
glucose is oxidized
oxygen is reduced
done through a series of steps, each of which is catalyzed by a specific enzyme
at Key Steps during cellular respiration
electrons are stripped from glucose and the electrons are transferred with a proton as a hydrogen atom
glucose + 6oxygen => 6CO2 + 6water + Energy
O: glucose => 6CO2
R: 6oxygen => 6water
During cellular respiration, glucose is oxidized in a…
series of steps and
the H atoms are not directly transferred to oxygen but are …
passed to a coenzyme called NAD+
NAD+
nicotinamide adenine dinucleotide
oxidized form
Dehydrogenase enzyme
2 H atoms from glucose are removed by this enzyme and then it transfers 2 electrons and 1 H+ (proton) to NAD+ (creating NADH) and the other proton is released into the solution
NADH => NAD+
NADH: the reduced form
passes e- to the “top” or high energy end of the electron transport chain
If the electron transfer is not stepwise…
a large release of energy occurs as in the reaction of hydrogen and oxygen to form water
Electron Transport Chain location
in the mitochondria membranes
Electron transport chain
“breaks the fall” of electrons by passing them in a controlled series of steps, and uses the energy from the electron transfer to form ATP
a the “bottom” or lower-energy end, oxygen captures the electrons along with hydrogen to form water
During cellular respiration, electrons follow a
“downhill” route
Stages of cellular respiration
1) Glycolysis
2) Citric Acid Cycle
3) Oxidative phosphorylation
Glycolysis
occurs in the cytoplasm
- breaks down glucose into two molecules of pyruvate (produces some ATP)
glucose => 2 pyruvate + 2 H2O + 2ATP + 2 NADH
Citric Acid Cycle
occurs in the mitochondrial membrane
- utilizes pyruvate and completes the breakdown of glucose
2 pyruvate => ATP, CO2, NADH, FADH2
Oxidative Phosphorylation
occurs in the inner mitochondrial membrane
- drives the synthesis of ATP by the transfer of electrons from NADH in electron transport chain
NADH + FADH2 => ATP
Glycolysis and the citric acid cycle can generate ATP by
substrate level phosphorylation
Substrate-Level phosphorylation
an enzyme transfers a phosphate group from an organic substrate to ADP, forming ATP
i.e. Pyruvate Kinase: transfers a phosphate (phosphorylates) ADP from phosphoenolpyruvate (PEP) to make ATP and pyruvate
Glycolysis
“splitting of sugar”
harvests energy by oxidizing glucose, a 6 carbon molecule to two, 3-carbon pyruvate molecules
2 major phases
1) energy investment (predatory) phase
2) energy payoff phase
Glycolysis input and output
input: glucose
output: 2 pyruvate, 2 H2O, 2ATP, 2 NADH
Citric acid cycle
- takes place in the matrix of the mitochondrion
- completes the energy-yielding oxidation of organic molecules
Pyruvate must be converted into
acetyl-CoA
which will link glycolysis to the citric acid cycle
input: 2 pyruvate
output: 2CO2, 2 NADH, 2 Acetyl-CoA
Citric acid cycle input and output
for each turn of the cycle
input: 2 acetyl-CoA, 3 NAD, FAD+, ADP
output: 2CO2, 3 NADH, FADH, ATP
after 2 turns: output: 4 CO2, 6 NADH, 2 FADH2, 2ATP
Starting with 1 molecule of glucose
produce 10 NADH at end of CAC
2 from glycolysis
2 from conversion of pyruvate
6 from CAC
NADH and FADH2
from glycolysis and CAC
account for the majority of energy extracted from food
- donate e- to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation
Electron transport chain electrons from NADH and FADH2
lose energy as they pass down the pathway until the electrons are passed to oxygen, forming water
ATP synthase
a large protein complex imbedded in the mitochondrial wall and is the enzyme that synthesizes ATP
“Jesus enzyme”
Proton (H+) gradient
as electrons move through the electron transport chain, the protein complexes pump H+ from the mitochondrial matrix to the inter membrane space creating this gradient
H+ gradient
stores energy and drives chemiosmosis through the ATP synthase in a process referred to as a proton-motive force
Chemiosmosis
an energy-coupling mechanism that uses energy in the form of a H+ gradient across a membrane to drive cellular work and the formation of ATP
Cellular Respiration overview
During respiration, most energy flows in they sequence: glucose to NADH to electron transport chain to proton-motive force to ATP
1 molecule of glucose => 6 CO2, 4ATP are generated during glycolysis and the CAC
EACH NADH from glycolysis and CAC may contribute enough energy to the proton-motive force to generate 3 ATP
1 molecule of glucose => 34 ATP by oxidative phosphorylation and 4 ATP from substrate level phosphorylation => ~36-38ATP
about 40% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making approximately 38 ATP
Without electronegative oxygen to pull electrons down there transport chain
oxidative phosphorylation ceases however fermentation enables some cells to produce ATP without the use of O2
Glycolysis can produce ATP
with or without O2, in aerobic or aerobic conditions and couples with fermentation to produce ATP
Fermentation
can generate ATP from glucose by substrate-level phosphorylation as long as there is a supply of NAD+ to accept electrons
Alcohol Fermentation
pyruvate is converted to ethanol in two steps, one of which releases CO2
Lactic acid Fermentation
pyruvate is reduced directly to NADH to form lactate as a waste product
Bother fermentation and cellular respiration use
glycolysis to oxidize glucose and other organic fuels to Pyruvate but
cellular respiration produces more ATP
Catabolic pathways funnel electrons
from many kinds of organic molecules into cellular respiration
carbohydrates, fats, proteins can be used as energy
Anabolism or biosynthetic pathways
the body uses small molecules to bind other substances that may come directly from food or through glycolysis or the CAC
Cellular respiration is controlled by
allosteric enzymes at key points in glycolysis and the CAC
i.e. PFK is inhibited by high levels of ATP and activated by high levels of AMP
