slide 9 Flashcards
Life Requires Energy
Energy flows into an
ecosystem as sunlight
and leaves as heat.
Cellular respiration
is
the set of processes that
break down sugars to
produce ATP
Waste products of
respiration
(CO2 and H2O)
are raw materials for
photosynthesis
Photosynthesis
-anabolic
• endergonic
Respiration
-catabolic
• exergonic
Energy from
catabolism (exergonic,
energy-releasing
processes)
Energy for cellular
work (endergonic,
energy-consuming
processes
The breakdown of organic molecules
is exergonic.
anaerobic respiration
Some breakdown of sugars to produce ATP
can occur without oxygen and is referred to
as anaerobic respiration.
Aerobic respiration
consumes organic
molecules and oxygen and yields ATP more
efficiently than anaerobic metabolism
Cellular respiration
includes both aerobic and
anaerobic respiration but is often used to refer
specifically to aerobic respiration.
Although carbohydrates, fats, and proteins are all
consumed as fuel,
it is helpful to trace cellular
respiration with the sugar glucose.
In the breaking down of fuel molecules, hydrogen atoms (electrons and protons) are passed from molecules that donate electrons (electron donors)
to molecules that accept electrons (electron acceptors) in redox reactions.
electron transport chain.
Energy is released each time an electron is passed from an
interaction with high potential energy to one with lower
potential energy down an electron transport chain.
electron donor sodium
electron acceptor chlorine
oxidizing agents
Electron acceptors are called oxidizing agents
reducing agents
Electron donors are called reducing agents
because electrons are negative
Some redox reactions do not completely transfer electrons
from one substance to another
but just change the degree of
electron sharing in covalent bonds between the substances.
During cellular respiration,
the fuel (such as glucose) is oxidized, and O2 is reduced. Electrons are passed along a series of molecules between the fuel and O2 , the final electron acceptor.
Reactions of an electron transport chain
control the release
of energy so that it can be harnessed in the production of ATP.
In cellular respiration, glucose and other organic
molecules are broken down in a series of steps.
Electrons from organic compounds are usually first
transferred to NAD+.
Each NADH (the reduced form of NAD+ )
represents stored energy that is tapped to
synthesize ATP
NAD+ is a good electron transporter because
it can
cycle easily between oxidized and reduced states.
The Stages of Cellular Respiration
Harvesting of energy from glucose has three stages:
– Glycolysis (breaks down glucose into two
molecules of pyruvate)
– The citric acid cycle (completes the
breakdown of glucose)
– Oxidative phosphorylation (accounts for
most of the ATP synthesis)
Digestion
n breaks down large molecules
but does not yield useable energy
Digestion of carbohydrates produces
glucose molecules.
Glycolysis
is the nearly
universal pathway through which
glucose is first broken down to
two molecules of pyruvate.
Glycolysis occurs in the cytoplasm in two phases:
– Energy investment phase
– Energy payoff phase
Glycolysis occurs whether or not
O2
is present
substrate-level phosphorylation
is the
means of ATP production in the process of glycolysis
One way to produce ATP is to directly transfer
a phosphate
group from a sugar molecule to a molecule of ADP
Glycolysis yields
two molecule of ATP and two NADH
in aerobic metabolism
the two molecules
of pyruvate enter a mitochondrion.
in aerobic metabolism
the two molecules
of pyruvate enter a mitochondrion.
The citric acid cycle takes the products of glycolysis and yields
CO2
,
electron carriers (NADH and FADH2
), and one molecule of ATP.
Electron carriers from glycolysis and the citric acid cycle enter
the electron
transport chain of oxidative phosphorylation to produce the majority of ATP
