Download Chapter 8 and 9 Notes

Cellular Energetics
Chapters 8 (Photosynthesis) & 9 (Cellular Respiration)
I. Overview of Photosynthesis and Cellular Respiration:
PHOTOSYNTHESIS (AUTOTROPHS)
CO2
+
H2O
CARBON DIOXIDE WATER
C6H12O6
GLUCOSE
+
O2
OXYGEN
RESPIRATION (HETEROTROPHS and AUTOTROPHS)
II. Energy and Metabolism
METABOLISM – sum of all chemical reactions in an organism; reactions are organized into
pathways:
 CATABOLIC – Releases energy – break down complex molecules into simpler
molecules
o Ex. Hydrolysis (adding water to break),
o Ex. CELLULAR RESPIRATION (breaking down glucose for ATP)
 ANABOLIC – Requires energy to combine simpler molecules into more
complicated one
o Ex. Condensation Reaction/Dehydration Synthesis (removing water to
make),
o Ex. PHOTOSYNTHESIS (production of sugar “food” for plant)
EXERGONIC Reaction – spontaneous reaction, RELEASES energy “EXITS”
 Ex. Respiration
ENDERGONIC Reaction – non-spontaneous reaction, REQUIRES energy “ENTERS”
 Ex. Photosynthesis
III. Energy in Cells – ATP
ADENOSINE TRIPHOSPHATE – Energy Currency of the Cell – molecule with unstable
phosphate bonds that the cell breaks off to drive endergonic reactions
 Cell traps energy stored in ATP by transferring the last PHOSPHATE group
from ATP to other compounds
 ATP that lost P group = ADP (adenosine diphosphate)
o
o
ATP - Drives most cellular work
Components:
 Adenine
 Ribose
 3 phosphate groups
IV. CHAPTER 8 – PHOTOSYNTHESIS
PHOTO = LIGHT SYNTHESIS = TO MAKE : Anabolic process which converts solar E  “food”
(glucose) for survival. Occurs in the CHLOROPLASTS of AUTOTROPHS(producers).
Solar E is converted by the use of PIGMENTS, molecules that absorb certain wavelengths of
light and reflect (what we see) others.
Primary photosynthetic pigments:
 CHLOROPHYLL A: main photosynthetic pigment, absorbs RED & BLUE light,
reflects GREEN
Chlorophyll b & c absorb different wavelengths of blue & red
Accessory pigments:
 CAROTENES: absorb BLUE & GREEN reflect yellow and orange.
In fall, chlorophyll is broken down so we see the colors of the accessory pigments.
OVERVIEW OF PHOTOSYNTHESIS: USES ENERGY FROM THE SUN TO CONVERT
WATER AND CARBON DIOXIDE INTO HIGH ENERGY SUGAR AND OXYGEN
(light)
Overall Equation:
6CO2 + 6 H2O  C6H12O6 + 6O2
(chlorophyll)
PHASE I- LIGHT DEPENDENT REACTION energy captured from the SUN
 Occur in the THYLAKOID membranes – and involve PHOTOSYSTEMS - clusters
of chlorophyll and proteins that act like antennae to absorb sunlight.
 Light energy is used to produce the energy rich compound ATP and an electron
carrier NADPH. Electrons are given to NADP+ by breaking apart H2O molecules,
and stripping the Hydrogen atoms of their ELECTRONS. Also released as a waste
product by this breakdown is OXYGEN gas. (good for us!)
PHASE II- LIGHT INDEPENDENT REACTION: Energy from light reactions used to “fix”
CO2 into sugars (AKA Calvin cycle, or Carbon Fixation)
 Occurs in the STROMA
 Use the ATP and the NADPH from the Light Dependent reactions to produce high
energy SUGARS (like glucose – C6H12O6) from CARBON DIOXIDE.
 Does not require light, but will not occur if products from light reactions are not
being made.
NADP+ is an electron carrier – it can
accept a pair of high-energy electrons
and transfer them, along with most of
their energy to another molecule (When
carrying electrons is called NADPH)
PHASE I: LIGHT REACTIONS (AKA Photophosphorylation)
Occur in the thylakoid membranes of chloroplasts
Two Stages:
1) Light Absorption: Light energy is used to break apart H2O into three things:
 Oxygen atoms: diffuse out as waste
 H ions: used to make NADPH (a coenzyme: H carrier,
remember NADH from respiration?) and eventually ATP’s
 Electrons: used in photosystem I and II below
What is a photosystem? A combination of chlorophyll molecules plus accessory
pigments where light absorption occurs. Photosystems act like antennas, capturing
light energy and transporting electrons (an ETC) through the thylakoid membrane
2) Chemiosmosis: H+ diffuse across membrane fueling ATP synthesis – remember this from
respiration too?
Photosystem II  Electron Transport Chain  Photosystem I  short ETC  Chemiosmosis
http://www.science.smith.edu/departments/Biology/Bio231/ltrxn.html
PHASE II: CARBON FIXATION (AKA - CALVIN cycle, LIGHT INDEPENDENT reactions,
C3cycle, DARK REACTIONS)
Occurs in the STROMA OF CHLOROPLASTS
CO2 enters the stroma with the help of RUBISCO (most plentiful enzyme on earth) which
binds the CO2 to RIBULSOSE BIPHOSPHATE (RuBP) a 5-Carbon sugar, creating an unstable
6-Carbon compound.
Energy from ATP and NADPH (products of light RXN)
Combine six carbon dioxide molecules with six 5-carbon compounds and then…
Produce twelve 3-carbon compounds
Midcycle
Two 3-carbon molecules are removed (called G3P)
These become the building blocks of sugars, lipids, amino acids, etc.
Finally
Ten 3-carbon molecules are converted back into six 5-carbon molecules – go on to repeat
the cycle
FACTORS AFFECTING RATES OF PHOTOSYNTHESIS
LIGHT:
Increases then level off bc light rxns are
proceeding as fast as possible and Calvin cannot
keep up
CO2:
Same as light… will level off bc light rxns cannot
keep up
TEMPERATURE:
Low
High
Increase in temp makes molecules move faster but
if too hot  stomata close, decreasing rate of
photo.
O2:
x
x – atmospheric oxygen
Too much = photorespiration
Photorespiration interferes with successful performance of Calvin Cycle, which is undesirable
in plants.
WHY? B/C Rubisco (enzyme that binds CO2 to RuBP) can bind to either CO2 or O2.
In photosynthesis: Rubisco binds with CO2
CO2
RuBP
glucose (sugars)
rubisco
In photorespiration: Rubisco binds with O2
O2
RuBP
CO2 released – does not produce as much glucose
rubisco
Therefore, photorespiration reduces/decreases the amount of glucose made by plants.
 In high concentrations of carbon dioxide, photosynthesis is dominant process.
 In high concentration of oxygen, photorespiration is dominant process.
V. CHAPTER 9 CELLULAR RESPIRATION & FERMENTATION

A series of chemical reactions that release ENERGY by breaking down GLUCOSE and
making CO2 and H2O.
Overall Reaction:
C6H12O6 + 6O2  6CO2 + 6H2O

GLUCOSE is the primary source of ENERGY at the cellular level. The stored energy in
its bonds will be converted to cellular energy in the form of ATP.

Most of the process takes place in the MITOCHONDRIA of all cells. (Not just animal
cells – remember plant cells have mitochondria too!)
Anatomy of a Mitochondrion
 Mitochondria have two membranes, an outer membrane covering the organelle, and an
inner, folded membrane.
 Folds are called CRISTAE and they increase surface area for the reactions of cellular
respiration to occur.
 The inner membrane creates a fluid filled cavity called the MATRIX, where some of the
reactions of cellular respiration take place.
Reactions of Glycolysis and Respiration
Equation:
C6H12O6 + 6O2  6CO2 + 6 H2O
4 main stages
AEROBIC
o Glycolysis
o Prep for Citric Acid (Krebs) Cycle/Formation of Acetyl CoA
o Citric Acid/Krebs Cycle
o Electron Transport Chain and Chemiosmosis (Oxidative Phosphorylation)
GLYCOLYSIS – occurs in cytoplasm, breakdown of glucose into 2 molecules of
pyruvate aka pyruvic acid (does not require oxygen)
(2NAD+  2 NADH)
GLUCOSE
(C6H12O6)
2ATP
2PGAL (G3P)
(3C)
END PRODUCTS:
o 2 pyruvate (each containing 3 C – Glucose has 6)
o 2 NADH (electron carriers)
o NET gain of 2 ATP
4 ATP
2 pyruvate
(3C)
If Oxygen is PRESENT:
2. PREPARATION for CITRIC ACID CYCLE – pyruvate enters mitochondrion matrix
(2NAD  2 NADH)
2 pyruvates
(3C)
2 acetate
(2C)
2CO2
2 Acetly CoA
(2C)
2 CoA
END PRODUCTS:
o 2 NADH
o 2 Acetyl CoA
o 2 CO2 - waste (what do you exhale???)
3. Citric Acid Cycle/Krebs occurs in the mitochondrial matrix, complete breakdown of
glucose and release of carbon dioxide. Remember there were 2 molecules of pyruvate,
therefore the Citric Acid Cycle must make TWO turns before you get the products from
the breakdown of the two pyruvate molecules
END Products
o 3 NADH
o FADH2
o ATP
o 2 CO2
End Products so far
Process
Glycolysis
Prep for Krebs
Krebs Cycle
TOTAL
NET End Products
6 NADH
2 FADH2
2 ATP
4 CO2
ATP
2 (Net)
0
2
4
(substrate level
phosphorylation)
NADH
2
2
6
10
FADH2
0
0
2
2
4. Electron Transport Chain – produces energy that drives the synthesis of ATP in
oxidative phosphorylation, ETC consists of proteins embedded in the inner membrane
of the mitochondrion, oxygen is the final electron acceptor
FADH2 and NADH are “cashed in” – oxidized (lose H ions), NAD+ and FAD are free to pick
up more Hydrogen Ions
ETC does not make ATP, it provides a source of energy for the production of ATP by chemiosmosis.
Chemiosmosis – embedded in the mitochondrial membrane (along with ETC) are protein
complexes called ATP synthases. These phosphorylate ATP from
ADP + Pi, ATP synthases use energy from a proton gradient – built up by the ETC
ATP synthases are built into
inner membrane of the
mitochondria – act like miniturbines, when H ions pass
through them they “spin”
which generates energy to
create ATP
End Products: Approximately 32-34 ATPs are generated for every glucose
Glycolysis
ATP
NADH
FADH2
CO2
Formation
of Acetyl
CoA
2
2
0
0
0
2
0
2
Citric
Acid
Cycle
2
6
2
4
ETC &
Chem.(NADH
TOTAL
and FADH2 are
cashed in)
See below
3 ATP/ NADH
2 ATP/FADH2
4
30
4
38 ATP
If No Oxygen is Present – Anaerobic Respiration (still begins with glycolysis,
therefore start with pyruvate)
DOES not produce ATP (ATP is made during glycolysis), regenerates NAD+ so
glycolysis can continue
Fermentation- enables some cells to produce ATP without the use of oxygen
1. Alcoholic (plants & fungi)
CO2
Pyruvate
(3C)
NADH
Acetylaldehyde
NAD+
ethyl alcohol
(2C)
2. Lactic Acid (animals & some bacteria)
NADH
Pyruvate
NAD+
lactic acid
Occurs in some bacteria and muscle cells (that is why you feel the BURN!)
PATHWAYS OF GLYCOLYSIS & RESPIRATION
GLUCOSE
C6H12O6
IF O2 PRESENT
GLYCOLYSIS (“glucose breaking”)
Glucose (6C)  2 Pyruvate (3C)
Yields: 2 ATP (Net)
2 NADH
IF O2 ABSENT
Cytoplasm
PREP FOR CITRIC ACID CYCLE
Pyruvate (3C)  Acetate (2C) joins
with CoA Acetyl CoA
Yields: 2NADH
Releases 2 CO2
FERMENTATION
Breakdown of pyruvate in absence of
O2 (regeneration of NAD+ so
glycolysis can continue)
cytoplasm
Matrix of Mitochondria
ALCOHOLIC
FERMENTATION
(plants & fungi)
CITRIC ACID CYCLE (Kreb’s Cycle)
Acetyl CoA  Krebs Cycle
Complete breakdown of glucose
Yields: 2 ATP, 6 NADH, 2 FADH2
Releases 4 CO2
Matrix of Mitochondria
LACTIC ACID
FERMENTATION
(animals & some bacteria)
Pyruvate  alcohol
+ CO2
Pyruvate  lactic acid
Important to
bakers and
brewers
Us: causes muscles to
BURN when working out
Bacteria: used to make
cheese and yogurt
ELECTRON TRANSPORT & ATP SYNTHESIS
NADH and FADH2 are “cashed in”
e- travel thru ETC generating a H+ ion gradient; H+ ions will pass
thru ATP synthase generating lots of ATP
Oxygen is final electron acceptor  water
Yields: 32-34 ATP
2
ATP/glucose
Inner membrane of mitochondria
36-38
ATP/glucose
Aerobic Respiration
Anaerobic Respiration