Cellular Respiration
• So, all living things need energy in order
to stay alive. The transformation of
energy and matter in the body is called
metabolism. Metabolism involves
anabolic (build-up) and catabolic (breakdown) reactions.
• When cells have extra resources such as
food and energy, anabolism occurs and
stores nutrients for later. If we need food
or energy, catabolism occurs and breaks
down stored nutrients for the body to use.
• Cellular respiration is a series of metabolic
processes that all living cells use to
produce energy in the form of ATP.
• Cellular respiration can take two paths:
aerobic and anaerobic.
• Aerobic respiration occurs when oxygen is
available and anaerobic occurs when
oxygen is not available.
• Remember …
• Autotrophs (producers) make glucose by
photosynthesis, whereas heterotrophs
(consumers) get energy by ingesting the
bodies or remnants of autotrophs or fellow
heterotrophs.
•
•
During cellular respiration, heterotrophs use
oxygen to break apart glucose molecules
(this is a combustion reaction).
When glucose is combusted, energy is
released. Electrons move from a higher
energy state in the C-H bonds of glucose and
O-O bonds of oxygen to a more stable state
in the C-O bonds of carbon dioxide and O-H
bonds in water.
ATP (Adenosine Triphosphate)
• Primary source of free energy in living cells
(free energy is energy that can do useful work)
• Made during cellular respiration and
photosynthesis
• When a cell requires free energy (to drive
endothermic reaction), it breaks down ATP with
a hydrolysis reaction to make ADP, Pi and 31
KJ/mol of energy (ADP and Pi are more
chemically stable)
ATP
• When the body makes ATP (during cellular
respiration), ATP is less stable and requires the
input of energy (endothermic).
• ATP stores energy in its bonds (especially
between ADP and Pi) and when the bonds break
later, the energy is released.
• In order to better understand ATP
production, it is recommended that you read
Chapter 2 – Section 2.2
• I will quickly go over it in class
Redox Reactions
• Redox reactions – chemical reaction
involving the transfer of one or more
electrons from one atom to another
(always involve oxidation and reduction)
• Cellular respiration requires the use of
redox reactions to make ATP
• Oxidation – chemical reaction in which an
atom loses one or more electrons. The
substance that loses the electrons is
oxidized and the substance that takes the
electrons is called the oxidizing agent
• Reduction – a chemical reaction in which
an atom gains one or more electrons.
Three goals of cellular respiration:
1.Break bonds between 6 carbon atoms of
glucose, resulting in 6 CO2
2.Move hydrogen from glucose to oxygen,
making 6H2O
3.Trap as much free energy as possible (that
has been released in the process to make
ATP)
• 4 stages of Cellular Respiration:
• Stage 1 – Glycolysis – 10 step process that occurs in
cytoplasm
• Stage 2 – Pyruvate Oxidation – one-step process
occurring in mitochondrial matrix
• Stage 3 – The Krebs Cycle – an 8-step cyclical process
occurring in mitochondrial matrix
• Stage 4 – Electron transport and chemiosmosis
(oxidative phosphorylation) – a multi-step process
occurring in the inner mitochondrial matrix
• We should also understand the two
different energy-transferring mechanisms
• Substrate-Level Phosphorylation
• Oxidative Phosphorylation
Substrate-Level Phosphorylation
• ATP made directly by enzyme-catalyzed
reaction
• A phosphate-containing compound
transfers a phosphate group directly to
ADP (makes 31 KJ/mol)
• For each glucose molecule processed, 4
ATP (2 net) molecules are generated this
way in glycolysis and 2 in Krebs cycle
Oxidative Phosphorylation
• ATP formed indirectly
• Requires a number of sequential redox
reactions, with oxygen being the final
electron acceptor
• Begins when NAD+ (nicotinamide adenine
dinucleotide) removes 2 hydrogen atoms
(2 protons and 2 electrons) from part of
original glucose molecule.
• 2 electrons and 1 proton attach to NAD+
making it NADH (remaining proton
dissolves)
• NAD+ is oxidized form
• NADH is reduced form
• NAD+ reduction occurs in one reaction in
glycolysis, during the pyruvate oxidation
step (stage 2) and in three reactions of the
Krebs cycle.
• Another coenzyme, FAD (flavin adenine
dinucleotide) is reduced by two hydrogen
atoms from part of the original glucose
molecule
• FADH2 is the reduced form (all protons
and electrons bond to it)
• FAD is reduced to FADH2 in one reaction
of Krebs cycle
• Reductions of these molecules are energyproducing and eventually will transfer their
energy to ATP molecules
• Substrate-level phosphorylation does not require
oxygen, while oxidative phosphorylation does.
See handout
http://www.copernicusproject.ucr.edu/ssi/HSBiolog
yResources.htm
TO Know!!!
• Cellular respiration is the process where the body takes
in glucose and oxygen to make ATP, CO2, and H2O
• Starts with glycolysis in the cytoplasm of the cell (takes
glucose and breaks it down to make pyruvic acid). In the
process energy is released. This causes ADP and P to
come together to make 2 ATP.
• Pyruvic acid changes into another molecule in the
mitochondiral matrix (called pyruvate oxidation).
• This new molecule goes into the mitochondria to enter
the Krebs cycle
• The Krebs cycle is a series of reactions that release
energy (makes 2 ATP and makes CO2 and H)
• Then hydrogen enters the electron transport chain
(mitochondrial membrane) and a series of redox
reactions happen. This yields 32 ATP and some water.