Respiration and
Photosynthesis
Cellular Energy
• Metabolism – chemical reactions in a cell
o Catabolic pathways – release energy by
breaking down larger molecules
o Anabolic pathways – use energy released by
catabolic pathways
• Photosynthesis – anabolic pathway in which light
from the Sun is converted to chemical energy
• Cellular respiration – catabolic pathway in which
organic molecules are broken down to release
energy
Thermodynamics
• Thermodynamics – study of the flow and
transformation of energy in the universe
o Laws of Thermodynamics –
1. Law of conservation of energy – energy can
be converted from one form to another, but it
cannot be created or destroyed
2. Energy cannot be converted without loss of
usable energy (usually thermal energy)
ATP AND BIOLOGICAL ENERGY
• Adenosine triphosphate (ATP), the energy
currency or coin of the cell
• ATP consists of the adenine nucleotide
(ribose sugar, adenine base, and
phosphate group
• ADP + Pi + energy ----> ATP
ATP Analogy: Rechargeable
Batteries
• ATP is the higher energy form (the recharged
battery) while ADP is the lower energy form (the
used battery). When the terminal (third)
phosphate is cut loose, ATP becomes ADP
(Adenosine diphosphate; di= two), and the
stored energy is released for some biological
process to utilize. The input of additional energy
(plus a phosphate group) "recharges" ADP into
ATP (as in the analogy the spent batteries are
recharged by the input of additional energy).
Cellular Respiration Equation
(Reverse for Photosynthesis)
C6H12O6 +
6 Carbon Sugar
6CO2
+
Carbon dioxide
6O2 =
oxygen
6H2O +
water
ENERGY
Electromagnetic
Spectrum
Outer
membrane
Inner
membrane
Stroma
1 μm
Intermembrane
space
Thylakoid
membrane
Thylakoid
lumen
Granum (stack of
thylakoids)
In the chloroplast, pigments necessary for the light-capturing
reactions of photosynthesis are part of thylakoid membranes,
whereas the enzymes for the synthesis of carbohydrate molecules
are in the stroma.
Fig. 9-4c, p. 194
Photosynthesis: an overview
•
•
2 major steps:
– Light reactions (“photo”)
In the Light Dependent Processes
(Light Reactions) light strikes
chlorophyll a in such a way as to
excite electrons to a higher energy
state. In a series of reactions the
energy is converted (along an
electron transport process) into
ATP and NADPH. Water is split in
the process, releasing oxygen as
a by-product of the reaction.
– Carbon fixation (Calvin Cycle):
The ATP and NADPH are used to
‘fix’ carbon from carbon dioxide to
make organics (sugar)
Photophosphorylation is the process
of converting energy from a lightexcited electron into the
pyrophosphate bond of an ADP
molecule.
Photosystems
• Light harvesting units of
the thylakoid membrane,
where light energy is
converted to chemical
energy
• Composed mainly of
protein and pigment
antenna complexes
• Antenna pigment
molecules are struck by
photons (light)
Noncyclic Electron Transport
• Light-dependent reactions
– form ATP and NADPH
Light Dependent Reactions
• Photosystem II - Light energy splits water and causes the removal of
an electron from Photosystem II. Two electrons are replaced from a
water molecule, breaking the water into H+ ions and 2 O- ions.
These electrons are "boosted" to a higher energy state and are
passed through a series of reactions and electron carriers (called an
electron transport chain), eventually attaching them to a molecule in
Photosystem I. These reactions result in the production of ATP.
• Photosystem I - Light acts on a molecule in Photosystem I, causing
2 electrons to be "boosted" to a still higher potential. These
electrons are passed again through a series of reactions (another
electron transport chain making more ATP). Eventually the electrons
are attached to NADP+ and H+ to form NADPH, an energy carrier
needed in the Light Independent Reaction. The electrons from
Photosystem II replace the excited electrons in Photosystem I.
There is thus a continuous flow of electrons from water to NADPH.
This energy (ATP) is used in Carbon Fixation.
Chemiosmosis
• Chemiosmosis is the diffusion of ions across a
selectively-permeable membrane. More specifically, it
relates to the generation of ATP by the movement of
hydrogen ions across a membrane
• In photosynthesis - As electrons are passed from
chlorophyll to NADP+, more hydrogen ions are pumped
across the membrane. Inside of membrane becomes
positively charged and outside negatively charged.
Difference in charge provides the energy to make ATP
o ATP synthase in membrane allows hydrogen ions to
pass through it. As the ions pass through, the protein
spins like a turbine catalyzing the combination of ADP
and a phosphate group.
Chemiosmosis
The Calvin Cycle
Calvin Cycle (Light Independent)
• 6 carbon dioxide molecules eneter cycle from
atmosphere and combine with 6 5 carbon molecules to
make 12 3 carbon molecules
• Energy from ATP and NADPH is used to convert the 12 3
carbon molecules into high energy forms
• 2 of the 12 3 carbon molecules are removed from the
cycle to be used by the plant to produce sugars, lipids,
amino acids, etc. A single 6 carbon sugar is produced.
• Remaining 10 3 carbon molecules are converted back
into 6 5 carbon molecules
Overview of Respiration
• Organisms obtain energy in a process
called Cellular Respiration.
• The function of cellular respiration is to
harvest electrons from carbon compounds,
such as glucose, and use that energy to
make ATP. ATP is used by cells to do
work.
Cellular Respiration Process
Overview
• STAGE 1: GLYCOLYSIS
– IT DOES NOT REQUIRE OXYGEN (ANAEROBIC)
•
STAGE 2: THE PRODUCTS OF GLYCOLYSIS CAN
FOLLOW EITHER OF TWO MAIN PATHWAYS,
DEPENDING ON WHETHER THERE IS OXYGEN IN
THE CELL.
– AEROBIC RESPIRATION PATHWAY INCLUDES THE KREBS
CYCLE AND ELECTRON TRANSPORT AND REQUIRES
OXYGEN
– ANAEROBIC RESPIRATION PATHWAY IS CALLED
FERMENTATION (ALCOHOL OR LACTIC ACID
FERMENTATION) AND DOES NOT REQUIRE OXYGEN
Aerobic Respiration
• Glycolysis occurs in the cytoplasm
• All other stages in the mitochondria
Cellular respiration
• Glycolysis: cytosol;
degrades glucose into
pyruvate
• Kreb’s Cycle (Citric Acid):
mitochondrial matrix;
pyruvate into carbon
dioxide
• Electron Transport Chain:
inner membrane of
mitochondrion; electrons
passed to oxygen
Glycolysis
• 1 Glucose --->
2 pyruvate molecules
• Energy investment
phase: cell uses ATP
• Energy payoff phase:
ATP and NADH are
produced
• Net energy yield per
glucose molecule: 2 ATP
plus 2 NADH; no CO2 is
released; occurs
aerobically or
anaerobically
Glycolysis
Glycolysis I
Glycolysis II
Citric Acid Cycle
Citric Acid Cycle
Citric
Acid
Cycle
Electron transport chain
• NADH & FADH2 are used as
carriers in the electron
transport chain; oxygen is the
final acceptor
• ATP synthase:
produces ATP by using the H+
gradient (proton-motive force)
pumped into the inner
membrane space from the
electron transport chain; this
enzyme harnesses the flow of
H+ back into the matrix to
phosphorylate ADP to ATP
(oxidative phosphorylation)
Electron Transport Chain
Summary of Glycolysis and Cellular
Respiration
ATP Total Yield
• Glycolysis produces 2
ATP; aerobic
respiration produces
34 more ATP
Review: Cellular Respiration
•
•
•
•
Glycolysis:
ATP
Kreb’s Cycle:
ATP (substrate-level
phosphorylation)
Electron transport & oxidative
phosphorylation:
2 NADH (glycolysis) = 6ATP
2 NADH (acetyl CoA) = 6ATP
6 NADH (Kreb’s) = 18 ATP
FADH2 (Kreb’s) = 4 ATP
38 TOTAL ATP/glucose
2
2
Aerobic and Anaerobic Pathways
• In the absence of oxygen, fermentation
reactions produce alcohol or lactic acid but
no additional ATP.
Anaerobic Pathways