Transcript Cellular Respiration: Harvesting Chemical Energy

UNIT 3
Chapter 9: Cellular Respiration
Chapter 10: Photosynthesis
Chapter 11: Cell Communication
The Basics

The sun is the
ultimate source of
energy for all living
things
 Light
energy trapped
in organic molecules
 Trapped energy
available to
autotrophs and
heterotrophs
Cellular Respiration & Fermentation

Catabolic pathways can proceed with or
without oxygen present
 Fermentation
occurs when oxygen is NOT
present
 Cellular respiration occurs with oxygen and is
much more efficient than fermentation

Most of cellular respiration occurs in the
mitochondria
Organic molecules + O2  CO2 + H20 + energy
ATP Hydrolysis & Redox Reactions
The removal of a
phosphate group
from ATP
releases energy
 Phosphorylation
is a common tool
used to power
reactions


Redox (reduction-oxidation) reactions
release energy when electrons are moved
 Loss
of electrons = oxidation
 Gain of electrons = reduction

Redox reactions are used to synthesize
ATP
 Creating
NaCl (table salt) is a redox reaction:
Na + Cl  Na+ + Cl-

The electron donor is called the reducing
agent and the electron recipient is called
the oxidizing agent
Na + Cl  Na+ + Cl-
The Function of Coenzymes

Glucose is not simply broken down in a
single step to yield energy
 Steps
to break down components of glucose
using specific enzymes
 Hydrogen atoms and electrons ripped off of
glucose and given to coenzymes like NAD+

Nicotinamide Adenine Dinucleotide
H-C-OH + NAD+  CO2 + NADH + H+
Steps of Cellular Respiration

Cellular
respiration
involves three
steps:
 Glycolysis
 The
Krebs cycle
 The Electron
transport chain
and oxidative
phosphorylation
Glycolysis – An Overview
Glycolysis occurs in the cytoplasm
 Glucose is split into two three-carbon
sugars

 Sugars
are oxidized and rearranged to form
pyruvate

10 steps of glycolysis are catalyzed by
specific enzymes
 Energy
phase
investment phase and energy payoff

Energy investment
 ATP
provides
energy to
phosphorylate
glucose


2 ATP per glucose
Energy payoff
4
ATP and 2 NADH
are produced per
glucose

Glycolysis produces a net of 2 ATP and 2
NADH
 Happens
with or without oxygen and no CO2
is produced
 However, if oxygen is present, pyruvate
molecules can move in to the Krebs cycle

NADH will play a role later in the process (the
electron transport chain)
The Krebs Cycle
Pyruvate still holds a lot of the original
glucose molecule’s chemical energy
 Pyruvate enters the mitochondria and is
modified

CO2
removed
to produce
acetyl CoA

Each pyruvate
used to produce:

1 acetyl CoA,
which is used to
produce:
1 ATP
 3 NADH
 1 FADH2 (an
electron
transport carrier
similar to
NADH)

The Electron Transport Chain (E.T.C.)
Respiration ultimately produces 38 ATP
(max), but so far, only 4 have been
produced
 8 NADH and 2 FADH2 molecules enter
the electron transport chain
 The electrons are used to power ATP
synthesis
 Each mitochondrion has thousands of
sets of the E.T.C. in the cristae

The electron transport chain shuttles
electrons from NADH towards increasingly
more electronegative atoms, ultimately to
oxygen
 Process occurs
in inner
membrane of
mitochondria

 Oxygen
“captures” eand H+ to
make water

Electrons from NADH and FADH2 are
ultimately passed off to oxygen
 For
every two electron carriers (4 electrons),
one O2 molecule is reduced  2 H2O

The electrons moving down the E.T.C. are
used to pump H+ ions into the inter
membrane space of the mitochondrion
H+ ion gradient is created and is referred
to as proton-motive force
 An

H+ ions diffuse back into the mitochondrial
matrix through ATP Synthase

As H+ ions move through ATP Synthase,
that protein shifts its conformation
 Shift

joins a phosphate group to ADP
That entire process is called
chemiosmosis
 Chemiosmosis
occurs in plants also, but it is
driven by light energy
Intermembrane Space
+
+
+
+
+
+
+
+
NAD+
O
+
+
Matrix
+
+
+
+
+
+
H
P P P P
H
+
+
Summary of Cellular Respiration
Fermentation
Some cells can produce ATP whether
oxygen is present (aerobic) or not
(anaerobic)
 Two types of fermentation exist:

 Alcoholic
fermentation
 Lactic acid fermentation
In alcoholic
fermentation,
pyruvate is
ultimately converted
to ethanol
 In lactic acid
fermentation,
pyruvate is
converted into lactic
acid


Some organisms, like bacteria and yeast
can produce enough ATP to survive
 These
organisms are called facultative
anaerobes
 Human muscle cells can behave as
facultative anaerobes, for a very short time


Cori Cycle
The presence of oxygen allows for the
production of up to 38 ATP molecules, but
without oxygen, only 2 ATP are created
END
Chloroplasts Make Photosynthesis Possible

Any green part of a plant possesses chloroplasts
which contain a green photopigment:
chlorophyll
Chloroplasts
are found mainly
in the mesophyll cells in the
interior of the plant’s leaves
O 2
exits and CO2 enters
through pores called stomata
on the leaf ’s surface


Chloroplasts are doublemembrane organelles
around a central space:
stroma
In the stroma are
membranous sacs called
thylakoids
Internal space called
thylakoid space
 Stacked into grana

The Basics of Photosynthesis

The general reaction of photosynthesis:
SUN
6CO2 + 12H2O


C6H12O6 + 6H2O + 6O2
Basically, carbon is extracted from carbon
dioxide to make sugar, while oxygen is released
into the atmosphere
The Light Reactions & The Calvin Cycle

Photosynthesis is a two step process

Light reactions


Converts solar energy into chemical energy
Calvin cycle

Incorporates CO2 into organic molecules and uses
chemical energy from light reactions to create sugar

The light reactions – an overview
Water is split, hydrogen and electrons used to reduce
NADP+ to NADPH (an electron carrier)
 ATP is generated by photophosphorylation


The Calvin cycle – an overview
CO2 is incorporated into what will become sugar
during carbon fixation
 NADPH and ATP are used to create the new
organic molecule


The light reactions & Calvin cycle:
The Photopigments of Photosynthesis

A number of pigments exist in plants, but only
one, chlorophyll a, is directly involved in the
photosynthetic reactions

Accessory pigments can
funnel light energy to
chlorophyll a
Chlorophyll b
 Carotenoids
 Xanthophylls


Photons of light are absorbed by pigments in
thylakoid membranes

In the thylakoid membrane, a “light antenna”
called a photosystem channels light energy

Energy transferred
from molecule to
molecule until it
reaches the reaction
center chlorophyll a
Photosystems

Two types of photosystems work in the light
reactions of photosynthesis

Photosystem I & Photosystem II
Photosystem I (P700) absorbs light best at 700nm (far
red)
 Photosystem II (P680) absorbs light best at 680nm

1. An
P680
isis hit
by
lightare
and
2 electrons,
2.
3.
Water
Excited
electrons
split
creating
passed
½excites
O2, which
down
an
is joined
E.T.C.
4.
electron
acceptor
in
P700
captures
the
+
sending
itand
to the
electron
acceptor
with
(which
another
creates
½
ATP)
Oprimary
to
to
form
P700
O
electrons
uses
them
to
reduce
NADP
2
2

Electron flow takes electrons from water, and
uses them to reduce NADP+
ATP created on the way through E.T.C.
 O2 is a byproduct of splitting water

ATP Synthesis

Chloroplasts and mitochondria both create ATP
using chemiosmosis
Chloroplasts
transform light
energy into
chemical energy
The Calvin Cycle

The Calvin cycle uses ATP and NADPH to
create sugar



Not actually “glucose,” but glyceraldehyde-3phosphate (G3P), a 3-Carbon sugar
Each turn through the Calvin cycle fixes one
carbon
There are three phases to the Calvin cycle

Carbon fixation, Reduction, Regeneration of the
CO2 acceptor
ATP
isG3P
used
to
add
another
phosphate
group
Net new
cost
per
G3P
9 3modified
ATP
+
6into
NADPH
+
3 to
COby
Some
sugars
are
by
3the
ATP
NADPH
isattached
used
to=
remove
one
ofsugars
phosphates
3CO
to
5-Carbon
(RuBP)
The
sugars
split
6,more
3-carbon
2
2 are6-Carbon
EACH
of to
the
3-Carbon
sugars
molecules
regenerate
from
each
sugar,
creatingRuBP
a G3P sugar
rubisco
sugars
The Calvin Cycle: CARBON FIXATION
ADP
P
P C C C ATP
P C C C C C P
P C C C P
ATPRuBP
ADP
P C C C ATP
P
ADP
P C C C C C P
RuBP
ATPP C C C P
ADP
rubisco
O C O
O C O
rubisco
rubisco
O C O
ATP
P C C C P
ADP
P C C C C C P
P C C C P
ATP
RuBP
ADP
The Calvin Cycle: REDUCTION
G3P
G3P
P C NADP+
C C P
G3P
G3P
P C NADP+
C C P
P C NADP+
C C P
G3P
P C NADP+
C C P
EXITS
CYCLE
P C NADP+
C C P
G3P
P C NADP+
C C P
NADPH
NADPH
NADPH
NADPH
NADPH
NADPH
The Calvin Cycle: REGENERATION OF THE CO2 ACCEPTOR (RuBP)
ADP
P
P C C C C C P ADP
P C C C
P C C C
P C C C C C P
ADP P C C C C C P
P C C C
P C C C
P C C C
15 Carbons
5 Phosphates
P
Two G3P molecules
will be combined to
form one glucose
molecule.
G3P
P C C C
15 Carbons
6 Phosphates
3 RuBP molecules
The Need for Alternative Methods of
Carbon Fixation


The Calvin cycle is not the only way plants fix
carbon
Dehydration is a huge problem for plants since
water can evaporate through the stomata


Hot dry days  plants close stomata
Most plants, called C3 plants, fix CO2 to RuBP
using rubisco

On hot, dry days, C3 plants close their stomata
CO2 levels drop as it’s used in the Calvin cycle
 O2 levels rise as it cannot escape the leaf
 Rubisco will then fix O2 to RuBP, which then
degrades and produces no G3P


This process is called photorespiration and can
severely affect the productivity of
photosynthesis in a plant
Avoiding Photorespiration


A number of plants, called C4 plants, will first fix
CO2 to a 4-carbon compound (organic acid)
PEP carboxylase has a high affinity for CO2 and
is much more efficient than rubisco


4-carbon compound moved to bundle sheath cells
where the Calvin cycle can take place
C4 plants are usually found in very hot regions
with intense sunlight

A second strategy for avoiding photorespiration
can be found in CAM plants


Cacti, pineapples, succulents
CAM plants close their stomata during the day,
and open them at night
Night: plants fix CO2 into organic acids in the
mesophyll cells
 Day: CO2 released from organic acids and light
reactions create ATP and NADPH



In C4 plants,
carbon fixation
and the Calvin
cycle are spatially
separated
In CAM plants,
carbon fixation
and the Calvin
cycle are
temporally
separated
END
Stages of Signal Transduction
• The three stages of signal transduction are:
• Reception, transduction, response
• Cells can communicate with other cells they
are physically connected to
• Across great distances using hormones
• Target cell is intended recipient for signal
Reception
• A Chemical signal called a ligand binds to
protein in the target cell’s membrane
• Protein changes conformation
• Change in conformation sets in motion a
series of other changes inside the cell
Transduction
• Transduction relays signals from reception to
cellular responses
• At each step, the signal is transduced in a
different form
• Usually a protein changing its comformation
• Kinases are a common group of intracellular proteins
Cellular Response
• Response can include activities within the
cell or stimulate transcription in the nucleus
• Can increase or decrease metabolism within a
cell
• Protein synthesis may be induced to create
proteins needed
• Certain pathways help to amplify responses
• Various cells may receive the same signal,
but have different responses
• Ex. adrenalin in heart muscle cells triggers
rapid heartbeat; adrenalin in liver cells triggers
release of glucose into the blood
END