Transcript Cell Energetics

CELL ENERGETICS
Photosynthesis and Cellular Respiration
Photosynthesis
 All energy for the planet comes from the sun.
 Photoautotrophs are organisms that can convert light
energy to chemical energy.
 This process is called photosynthesis and can be
summarized in the following equation:
light energy
6H2O + 6CO2
6O2+ C6H12O6
Photosynthesis
 Photosynthesis takes place in the chloroplasts of plant
cells and consists of 2 sets of reactions.
 Light dependent reactions take place in the
thylakoid and use water and light energy. Oxygen is a
product of these reactions.
 Light independent reactions take place in the stroma
and use carbon dioxide. Carbohydrates are a product
of this reaction.
Light Dependent Reactions
 Sunlight strikes chlorophyll molecules.
 The energy of sunlight splits water molecules
(photolysis).
 Oxygen atoms are released.
 Hydrogen atoms are stripped of their electrons, which
are passed to the electron carrier NADP+ forming
NADPH and H+.
 The concentration gradient of hydrogen is used to drive
an ATP synthase, making ATP.
Light Independent Reactions
 Carbon dioxide, ATP, and the electrons carried by
NADP+ are used to build sugar.
 The molecule RuBP rearranges carbon dioxide to form
an intermediate molecule called PGA .
 PGA is converted to PGAL, using ATP and the NADP+.
 Some PGAL is used to make glucose and some is used
to regenerate RuBP to continue the process.
Photosynthesis
CO2
Water
ADP + Pi
+ NADP+
RuBP
PGAL
ATP + NADPH
+ H+
Light Independent
Light Dependent
Reactions
Reactions
O2
Carbohydrates
Cellular Respiration
 Neither autotrophs nor heterotrophs can utilize the
energy of the carbohydrate as it is. Both types of
organisms must convert the carbohydrate to ATP, the
energy currency of the cell, in order to carry out
metabolic activity.
 This process is called cellular respiration and can be
summarized in the following equation:
C6H12O6 + 6O2
6H2O + 6CO2 + ATP
Cellular Respiration
 Cellular respiration takes place in the cytoplasm and
the mitochondria of eukaryotic cells and consists of 3
sets of reactions.
 Glycolysis occurs in the cytoplasm and breaks down
glucose to pyruvate, producing 2 molecules of ATP.
 The Kreb’s Cycle occurs in the mitochondrial matrix
and breaks down pyruvate, producing CO2 and 2
molecules of ATP.
 Oxidative phosphorylation occurs in the
mitochondrial matrix, uses oxygen, and produces 32
molecules of ATP.
Glycolysis
 Glycolysis breaks down glucose, a 6-carbon sugar, into
2 molecules of pyruvate, a 3-carbon intermediate.
 When glucose is broken down, some of the hydrogen
atoms are stripped of their electrons, which are passed
to the electron carrier NAD+, forming NADH and H+.
 An initial investment of 2 ATP are used to reconfigure
the glucose atoms, but 4 ATP are produced in the
process for a net total of 2 ATP.
Kreb’s Cycle
 Pyruvate is converted to Acetyl-Coenzyme A in the
cytoplasm of the cell.
 Acetyl-CoA moves into the mitochondrial matrix, and
through a series of reactions, carbon and oxygen
molecules are stripped, releasing CO2, and electrons
are passed to NAD+ and FAD, forming NADH and
FADH2 and many H+.
 These reactions generate 2 molecules of ATP.
Oxidative Phosphorylation
 The only substances that move into the mitochondrial
membrane are the electron carriers, NADH and FADH2,
and the hydrogen protons.
 The hydrogen electrons are passed through a series of
protein complexes and ultimately to oxygen, which
accepts them.
 Just like in the light dependent reactions of
photosynthesis, the hydrogen protons develop a steep
concentration gradient, which drives the production of
ATP by an ATP synthase. 32 molecules of ATP are
produced.
Cellular Respiration
Electrons carried
via NADH
GLYCOLYSIS
Glucose  Pyruvate
ATP
Electrons carried via
NADH and FADH2
KREB’S
CYCLE
ATP, CO2
O2
OXIDATIVE
PHOSPHORYLATION
ATP, H2O
Fermentation
 If oxygen is present, aerobic cellular respiration is
done.
 In the absence of oxygen, anaerobic respiration takes
place.
 Glycolysis occurs.
 Following glycolysis, the pyruvate is converted to either
lactic acid or ethanol. This is fermentation.
 Fermentation involves very few chemical reactions
(compared to cellular respiration) but only produces 2
molecules of ATP.