Download Chapter 8 Cellular Energy

Chapter 8 Cellular Energy
Biology
Section 8.1
How Organisms Obtain Energy
Main idea – All living organisms use
energy to carry out all biological processes
 Objectives

 Summarize
the two laws of thermodynamics
 Compare and contrast autotrophs and
heterotrophs
 Describe how ATP works in a cell
Transformation of Energy
All cellular activities require energy; the
ability to do work
 Thermodynamics is the study of the flow
and transformation of energy in the
universe

Laws of Thermodynamics
The 1st Law – “Law of conservation of
energy” – Energy can be converted from
one form to another, but it cannot be
created nor destroyed
 The 2nd Law – Energy that is “lost” is
generally converted to thermal energy –
“entropy increases”
 Entropy – measure of disorder or unusable
energy, in a system.

Autotrophs & Heterotrophs

Autotrophs – organisms that make their own
food
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Chemoautotrophs – uses chemicals as a source of
energy
Photoautotrophs – convert light energy from the
Sun into chemical energy
Heterotrophs – organisms that need to ingest
food to obtain energy
Metabolism
All of the chemical reactions in a cell are referred
to as the cell’s metabolism
 Metabolic pathway is a series of chemical
reactions in which the product of one reaction is
the substrate for the next reaction
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Catabolic pathways – releases energy by breaking
down larger molecules into smaller ones
Anabolic pathways –uses the energy released by
catabolic pathways to build larger molecules from
smaller molecules
The continual flow of energy within an organism
is the result of the relationship of catabolic and
anabolic pathways
Photosynthesis
Photosynthesis is the anabolic pathway in
which light energy from the Sun is
converted to chemical energy for use by
the cell
 6CO2 + 6H2O  C6H12O6 + 6O2

Cellular Respiration
Cellular Respiration is the catabolic
pathway in which organic molecules are
broken down to release energy for use by
the cells
 C6H12O6 + 6O2  6CO2 + 6H2O + ATP

Photosynthesis & Cellular Respiration
Form a Cycle
ATP: The Unit of Cellular Energy
Adenosine Triphosphate (ATP) is the most
important biological molecule that provides
chemical energy
 ATP is made of an adenine base, a ribose sugar,
and three phosphate groups
 ATP releases energy when the bond between
the second and third phosphate groups is
broken, forming adenosine diphosphate (ADP)
and a free phosphate group
 Energy is stored in the phosphate bond formed
when ADP receives a phosphate group and
becomes ATP

ATP: The Unit of Cellular Energy
Section 8.2 Photosynthesis
Main idea – Light energy is trapped and
converted into chemical energy during
photosynthesis
 Objectives

 Summarize
the two phases of photosynthesis
 Explain the function of a chloroplast during
the light reactions
 Describe and diagram electron transport
Overview of Photosynthesis
Photosynthesis is a process in which light energy
is converted into chemical energy
 6CO2 + 6H2O  C6H12O6 + 6O2
 Photosynthesis occurs in two phases

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Phase 1-Light-dependent reactions-light energy is
absorbed and then converted into chemical energy in
the form of ATP and NADPH
Phase 2-Light-independent reactions-the ATP and
NADPH formed in phase 1 is used to make glucose
Phase 1: Light Reactions

Chloroplasts – capture light energy in
photosynthetic organisms; disc-shaped
organelles that contain two main
compartments
 Thylakoids
are flattened saclike membranes
that are arranged in stacks (grana) and are
the location of light-dependent reactions
 Stroma are the fluid spaces outside the grana
and are the location of light-independent
reactions
Phase 1: Light Reactions
Pigments
Pigments are light-absorbing molecules
found in the thylakoid membranes of
chloroplasts
 Chlorophylls are the major light-absorbing
pigments in plants; reflecting green light
 Accessory pigments allow plants to trap
additional light energy

 Carotenoids
light
– reflect yellow, orange and red
Electron Transport

Activated electrons are passed from one
molecule to another along the thylakoid
membrane in a chloroplast. The energy
from electrons is used to form a proton
gradient. As protons move down the
gradient, a phosphate is added to ADP,
forming ATP
Electron Transport (cont.)
Light energy absorbed by photosystem II is used
to split a molecule of water. When water splits,
oxygen is released from the cell, protons (H+;
hydrogen ions) stay in the thylakoid space and
an activated electron enters the electron
transport chain
 As electrons move through the membrane,
protons are pumped into the thylakoid space
 At photosystem I, electrons are re-energized and
NADPH is formed

Electron Transport (cont.)
Chemiosmosis: Protons accumulate in the
thylakoid space, creating a concentration
gradient
 When protons move across the thylakoid
membrane through ATP synthase, ADP is
converted to ATP

Phase 2: Calvin Cycle
Light-independent Reactions

Calvin Cycle –
the second
phase of
photosynthesis
in which energy
is stored in
organic
molecules such
as glucose
Calvin Cycle (cont.)
First step – carbon fixation - 6CO2 + 6
RuBP (ribulose 1,5-biphosphate a 5carbon compound) to form 12 3-PGA (3phosphoglycerate, a 3-carbon molecule)
 Second step – the chemical energy stored
in 12 ATP and 12 NADPH is transferred to
the 12 3-PGA to form 12 G3P
(glyceraldehyde 3-phosphate, high energy
molecules)

Calvin Cycle (cont.)
Third step – 2 G3P leave the cycle to form
glucose and other organic compounds
 Final step – An enzyme called rubisco
converts the remaining 10 G3P into RuBP.
 Plants use the sugars formed during the
Calvin Cycle both as source of energy and
as building blocks for complex
carbohydrates, including cellulose, which
provides structural support for the plant

Alternative Pathways
Many plants in extreme climates have alternative
photosynthesis pathways to maximize energy
conversion
 C4 plants minimize water loss by closing stoma in
hot days as they fix carbon dioxide into 4-carbon
compounds instead of the 3-carbon molecules
during the Calvin Cycle
 CAM plants (crassulacean acid metabolism)
occurs in water-conserving plants as CO2 enters
leaves at night fixing it into organic molecules.
During the day, CO2 is released and enters the
Calvin Cycle

8.3 Cellular Respiration
Main idea – Living organisms obtain
energy by breaking down organic
molecules during cellular respiration
 Objectives

 Summarize
the stages of cellular respiration
 Identify the role of electron carriers in each
stage of cellular respiration
 Compare alcoholic fermentation and lactic
acid fermentation
Overview of Cellular 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
 C6H12O6 + 6O2  6CO2 + 6H2O + ATP

Cellular Respiration (cont.)

Two main parts

Glycolysis
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Anaerobic process – do not require oxygen
Aerobic Respiration
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Krebs cycle & electron transport
Aerobic process – requires oxygen
Glycolysis
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Glucose is broken down in the cytoplasm
through the process of glycolysis, refer to Figure
8.12 on p. 229
First, 2 phosphate groups are joined to glucose
Second, the 6-carbon molecule is broken down
into 2 G3P
Next, two phosphates are added and electrons
and hydrogen ions combine to produce 4 ATP
and 2 NADH, respectfully
Last, the 2 G3P are converted into 2 pyruvate
molecules
Glycolysis has a net yield of 2 ATP molecules
Krebs Cycle
The series of reactions in which pyruvate
is broken down into carbon dioxide is
called the Krebs cycle or tricarboxylic acid
(TCA) cycle.
 This cycle is known as the citric acid cycle,
too
 The Krebs cycle occurs inside the
mitochondria of cells.

Krebs Cycle (cont.)
Prior to the Krebs cycle, pyruvate reacts
with coenzyme A (CoA) to form acetyl CoA
 At the same time CO2 is released and
NAD+ is converted into NADH
 The reaction results in the production of 2
CO2 molecules and two NADH
 The cycle begins with acetyl CoA
combining with a 4-carbon compound to
form citric acid, a 6 carbon compound

Krebs Cycle (cont.)
Then, citric acid is broken down in the next
series of steps, releasing 2 molecules of CO2 and
generating one ATP, three NADH, and one
FADH2. FAD is another electron carrier similar to
NAD+ and NADP+
 Finally, acetyl CoA and citric acid are generated
and the cycle continues
 The net yield from the Krebs cycle is 6 CO2
molecules, 2 ATP, 8 NADH, and 2 FADH2.
 NADH and FADH move on to play a significant
role in the next stage of aerobic respiration

Krebs Cycle
Electron Transport
Refer to Figure 8.14 on p. 231
 Electrons move along the mitochondrial
membrane from one protein to another
 Electrons are transported to oxygen to form
water
 Electron transport produces 24 ATP
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Each NADH molecule produces 3 ATP
Each group of 3 FADH2 produces 2 ATP
In eukaryotes, one molecule of glucose yields 36 ATP
In prokaryotes, one molecule of glucose produces 38
ATP
Anaerobic Respiration
The anaerobic pathway that follows
glycolysis is anaerobic respiration, or
fermentation
 Fermentation occurs in the cytoplasm and
regenerates the cell’s supply of NAD+
while producing a small amount of ATP
 Two types

 Lactic
acid fermentation
 Alcohol fermentation
Lactic acid fermentation &
Alcohol fermentation

Lactic acid fermentation
 Enzymes
convert the pyruvate made during
glycolysis to lactic acid
 When oxygen is absent or in limited supply,
fermentation can occur
 Skeletal
muscles during strenuous exercise
 Microorganisms to produce cheese, yogurt & sour
cream

Alcohol fermentation
 Occurs
in yeast and some bacteria when
pyruvate is converted to ethyl alcohol and CO2
Photosynthesis & Cellular Respiration
Processes cells use to obtain energy
 Metabolic pathways that produce and
break down simple carbohydrates
 The products of Photosynthesis are
oxygen and glucose – the reactants
needed for cellular respiration
 The products of cellular respiration –
carbon dioxide and water – are the
reactants for photosynthesis
