Pages 280 - 340
Metabolism - total of all chemical reactions in a living system.
Anabolism- energy poor molecules are transformed into energy rich molecules absorbing energy
Catabolism - energy rich molecules are transformed into energy poor molecules releasing energy
Autotrophic/Heterotrophic type of nutrition. Look up definition in glossary of text.
ATP are molecules which are able to transfer energy directly to reactant molecules during chemical reaction within a cell.
ATP - chemical compound adenosine tri?phosphate.
The adenosine part of ATP is the main body of the molecule;
it is
composed of adenine (also a component of DNA) and a simple sugar,
ribose.
The tri- part of the name refers to the fact that ATP has three phosphate
groups linked to the main adenosine body of the molecule.
Cyclic phosphorylation: work
ATP ---------------------------------> ADP + (P) + E
ADP + (P) + E ------------------------ > ATP
respiration
C6H12O6 + ATP
----------> C6H11O6PO4
+ ADP
Refer to figures handed out in lecture.
ATP is not the only molecule that may be used to transfer biological energy from energy rich molecules. Three other molecules (coenzymes) are nicotinamide adenine dinucleotide (NAD+) and flavin adenine dinucleotide (FAD). During photosynthesis the coenzyme NADPH2 is used in place pf NADH2
See Handouts From Class
Both of these molecules may be reduced by various chemical reactions (respiratory).
Example: NAD + CH3CH2OH -----> NADH+H + CH3COOH
Note the NAD molecule removes hydrogen atoms.
Example: NADH+H + CH3COCOOH ---> CH3CHOHCOOH + NAD
Note the NADH+H molecule donates hydrogen atoms.
These are called coenzymes: coenzymes you need to know are NAD, FAD
and NADP
These two reduced forms (NADH+H and FADH2) can also
be transferred to the cytochrome system in a mitochondria where they will
be oxidized with the energy being released converted into working
ATP. Oxygen is required for this process.
O2 + ADP + P + NADH -----> NAD + ATP + HOH
ATP can be synthesized from energy rich molecules in two ways. (Look above)
1.Energy
is directly taken from a substrate to form ATP from ADP and (P).
This is called substrate phosphorylation. (single step process)
2.Energy
is taken from an energy rich molecule by reducing NAD+ or FAD
to NADH+H or FADH2 These molecules move to a cytochrome system in a
mitochrondrion where the reduced forms NADH+H or FADH2 are oxidized
to NAD+ or FAD and the accompanying energy being transferred to make
ATP. This is called oxidative phosphorylation. (two step process)
During photosynthesis the coenzyme NADPH + H is used in place of
NAD + H
See Handouts From Class
Cellular
respiration is the chemical process (oxidation) of breaking down
energy
rich molecules (C6H12O6)
into energy poor molecules (CO2 + H2O) with the
energy being converted
into biologically usable energy - ATP. This is a slow
process and requires
several reactions which can be categorized into steps.
Aerobic respiration has three stages: glycolysis,
citric acid cycle (Krebs
cycle), and electron transport system. A limited
amount of ATP is produced
directly from specific steps in gylcolysis and
the Kreb cycle (substrate
phosphorylation). However, the bulk of
ATP will be formed by the formation of
NADH+H and FADH via glycolysis and the
Kreb cycle which then must move to
the electron transport system to be transformed
into ATP using oxygen (oxidative
phosphorylation). The overall equation for aerobic
respiration is:
36ADP + 36P + C6H12O6 + 6O2
------> 6CO2 + 6H2 O + 36 ATP
Glycolysis is a series of chemical reactions which occur in
a step by step process.
During each step an organic molecule is converted to
a different molecule
associated with an energy change. These steps will resemble
a "road map "showing
changes in organic molecules and the involvement of biological
energy. The two forms
of chemical biological energy involved during these reactions are
ATP and
NADH + H.
Examine the Glycolysis and prepare an input/output box in your
notes
indicating what enters and leaves this pathway. Include
the organic molecules and
the biological energy.
See Handouts From Class
input/output box
(write in your notes and learn)
Organic Molecules: Input: glucose
Output: 2 pyruvic acid molecules
Energy Output: ATP ( 2 used during activation and 4 synthesized
= net of 2)
NADH (2 formed which may be converted into 2 ATP per NADH
thus a total of four ATP may be formed by these coenzymes)
Glycolysis produces a net of 2 ATP directly and 4 through
NADH, a total of 6
ATP per glucose.
Substrate phosphorylation refers to the ATP made directly.
Oxidative phosphorylation refers to the ATP synthesized through the
NADH
Aerobic respiration also involves the Kreb Cycle.
During this process pyruvic acid
which was formed during glycolysis is going to be oxidized into
carbon dioxide and
water producing ATP directly (by substrate phosphorylation)
and the coenyzmes
(NADH + H and FADH) which form ATP via cytochrome system
(oxidative phosphorylation).
Prepare an input/output box in your notes indicating what enters and leaves the Kreb Cycle pathway. Include the organic molecules and the biological energy.
See Handouts From Class
Organic Molecules : Input: pyruvic acid Output: 3 carbon dioxide molecules
Energy Output ? ATP - 1 via substrate phosphorylation,
NADH - 4 formed which
may be converted into 3 ATP per NADH, FADH – 1 formed which
may be
converted into 2 ATP per FADH. Total of 15 per Kreb
cycle.
The conversion of NADH, FADH into NAD,FAD forming ATP involves the
cytochrome
system utilizing oxygen. Cytochrome Electron Transport System
See Handouts From Class
Prepare an input/output box in your notes indicating what enters and leaves the CETS pathway.
No organic molecules are broken down.
NADH and FADH may enter the chain which provided energy to drive a proton pump. This pump forms a proton gradient in the crista lumen of the mitochondrion which allows the enzyme ATPase to to form ATP.
ADP + P -----à ATP + HOH
The end receptor of the hydrogen ions is oxygen. (oxygen is consumed)
Therefore this set of reactions is called oxidative phosphorylation.
Energy Output – 3 ATP per NADH + H and 2 ATP per FADH + H
The NADH+H produced during glycolysis has to move through mitochondrion;
therefore ATP is required for active transport. This is why these NADH
+ H produces only a net of two ATP where NADH + H is mitochondrion produces
three ATP.
Anaerobic Respiration
Includes glycolisis; however the pyruvate is reduced into ethanol
and
carbon dioxide. The reducing power comes from the NADH + H
produced during glycolysis; therefore they can not be used to produce ATP
via oxidative phosphorylation.
2ADP + 2P + C6H12O6 ---> 2CO2
+ 2C2 H5OH + 2 ATP
See Handouts From Class
Examine glycolysis and the reduction of pyruvate into carbon dioxide
and ethanol.
input/output box
(write in your notes and learn)
Organic Molecules - Input: glucose
Output: 2 ethanol and 2 carbon dioxide
Energy Output - ATP ( 2 used during activation and 4 synthesized
= net of 2)
NADH (2 formed which are used to reduce pyruvate)
Other catabolic reactions producing energy and carbon skeletons.
Pentose Phosphate Pathway
Forms energy and ribose sugars for DNA, RNA synthesis.
See Figures in text involving Pentose Phosphate Pathway
Respiration of Lipids
Lipids (triglycerides ae hydrolyzed into glycerol and fatty acids.
Glycerol can be converted into
pyruvate and metabolized.
Fatty Acids can be broken down
into acetates (2 carbon molecules) via beta
oxidation and enter the Kreb
Cycle.
See Figures in text involving break down of fat
Heat-generation reactions
Thermogenic reactions or cyanide resistant reactions.
If NADH breaks down to NAD, a large amount of energy is liberated;
and if this powerful exergonic reaction is not coupled to any endergonic
reaction, all the energy is converted to heat. (ex. Skunk cabbage)
See Figures in text involving thermogenic reactions
Photosynthesis
Photosynthesis is a chemical process where energy poor molecules
(CO2 and
H2O) are converted to energy rich molecules (C6H12O6)
with the energy to
synthesize the energy rich molecule coming from light. The overall
equation is:
light
6CO2 + 6H2O ------------------->
C6H12O6 + 6O2
Chlorophyll
Photosynthesis has two stages: light dependent reactions and the light independent reactions (dark reactions) or Calvin Cycle . ATP and NADPH+H are produced during the light dependent reactions and carbon dioxide is fixed into glucose during the dark reactions.
Light Dependent Reactions:
Light – red (P680, P700) and blue are utilized
Pigments: chlorophyll “a”, chlorophyll “b”, carotenoids
(carotene and
xanthophylls); water insoluble
anthocyanin is a red water soluble pigment not used during
photosynthesis.
See Handouts From Class
Absorption Spectrum
See Handouts From Class
Action Spectrum
See Handouts From Class
Photosystem I and Photosystem II are used to convert light energy
into chemical energy (1) by passing electrons through a cytochrome
system which generates ATP; (2) reducing NADP to NADPH.
Photosystem I:
Uses P700 chlorophyll (absorbs red light at 700 nm range) to excite
electrons
Electron acceptor “X Fe4S4”
This reduced molecules passes electron to ferrodoxin which
reduces NADP to NADPH
Phototsystem II:
Uses P680 chlorophyll (absorbs red light at 680 nm range) to excite
electrons
Electron acceptor “phaeophytin”
Passes electron down a cytochrome system (b6/f) generating ATP
Plastocyanin passes electron to P700 chlorophyll
Water is split to replace the electrons lost.
See Handouts From Class
Input: light, ADP, NADP, water
Output: ATP, NADPH+H, oxygen
Photophosphorylation ATP is generated utilizing light energy (compare to substrate and oxidative phosphorylation)
How does cytochrome system generate ATP? Uses chemicl
energy from NADH or FAD received from glycolysis
or Kreb.
See Handouts From Class
Compare this to how ATP was generated during oxidative phosphorylation.
Two parts to oxidative phosphorylation
1) Uses energy from NADH and FADH (formed during glycolysis
and Krebs) to drive proton pump
2) The proton gradient formed by pump runs the ATPase
enzyme
which generates ATP.
See Handouts From Class
Two parts to photophosphorylation
1) Uses energy from light to drive proton pump
forming a hydrogen
gradient
2) The proton gradient formed by pump runs the ATPase
enzyme
which generates ATP.
Review aerobic respiration using input/out boxes.
The carbon, hydrogen and oxygen atoms of glucose are converted into
which molecules?
Some energy is transferred into ATP directly.
Some energy is transferred into NADH and FADH which will be oxidized to generate ATP (oxidative phosphorylation).
NADH and FADH (from glycolysis and Krebs cycle) supplied the power to form ATP.
Light supplies the power to form ATP during photophosphorylation.
Light Independent, Dark or Calvin Cycle Reactions
Utilize the energy (ATP and NADPH+H) formed in the light to reduce
carbon dioxide into glucose
The main enzyme is RUBISCO - RuBP
carboxylase
See Handouts From Class
12 ATP 12 ADP
Draw:
6 RuBP + 6 CO2
-----------> 12 PGA----------> 12 PGAL
5 carbon 1
carbon
2 (3carbon molecule)
12 NADPH+H
12 NADP
See Handouts From Class
2 of the PGAL move through glycolysis backwards to form 1 glucose
molecule and the remaining 10 PGAL recycle to reform the RuBP
input: carbon dioxide, (sugar ribulose biphosphate is recycled), ATP, NADPH+H
output: glucose, ATP, NADP
Light is not directly needed for this process; however, the ATP and
NADPH+H formed during the light reactions are required.
RUBISCO - RuBP This enzyme also fixes oxygen into
phosphoglycolate etc.
(photorespiration). Therefore, there is competition by oxygen and
carbon dioxide for this enzyme. inefficient
Where do these reactions occur?
Chloroplast (double membrane structure with liquid part stroma and
membrane sacs called grana)
Light dependent reactions occur in the thylakoids of grana and stroma; the Calvin Cycle enzymes located in the stroma.
The above reactions are called C-3 because the first product is PGA
Another type of carbon fixing pathway is termed C- 4
(found in tropical grasses – corn, sedges, etc)
The pathway uses an enzyme PEP carboxylase to fix carbon dioxide
into malate
PEP + CO2 --------------->
malate (OAA)
3 carbon 1 carbon
4 carbon
PEP carboxylase has a high affinity for carbon dioxide and does not
show photorespiration, therefore no competition with oxygen.
PEP carboxylase has a high affinity for carbon dioxide; the carbon
is fixed in the mesophyll cells of the leaf;
See Handouts From Class
Plants (C-4 plants) have Kranz anatomy (well developed bundle sheath
cells); the malate (OAA) is formed by PEP carboxylase in the mesophyll
cells. The malate moves into the bundle sheath cells where it is decarboxylated
forming carbon dioxide. In the bundle sheath cells the carbon dioxide(high
amounts) is fixed into glucose via RuBP carboxylase. Basically carbon dioxide
can be efficiently fixed in mesophyll cells by PEP carboxylase (C-4), move
to bundle sheath cells in the form of malate, decarboxylated in bundle
sheath cells forming a high concentration of carbon dioxide which is converted
into glucose by RuBP (C-3 metabolism).
See Handouts From Class
Why have a C-4?
1. PEP carboxylase is much more efficient in fixing carbon dioxide
2. C-3 plants have photorespiration where oxygen competes for
the RuBP carboxylase enzyme oxidizing PGA into carbon dioxide (wasteful
reaction)
(see figure)
See Handouts From Class
CAM plants uses the metabolism involved in C-4 plants but the timing
for each pathway is
different to conserve on water (stoma are closed during day).
(desert succulents Agave, Cacti. Bromeliads, Orchids)
These plants will have stomata closed during day and open at night
to conserve on water. During the night (stomata open, carbon dioxide
may enter) PEP carboxylase fixes carbon dioxide into malate (C-4 metabolism).
During the day (stomata closed to conserve water, carbon dioxide may not
enter) malate is decarboxylated forming carbon dioxide. RuBP
fixes the carbon dioxide into glucose via C-3 pathway.
See Handouts From Class
FILL OUT THE TABLE BELOW COMPARING THREE TYPES OF LIGHT INDEPENDENT REACTIONS
C-3 C-4 CAM
Main
Carboxylating
Enzyme
Location
Of Enzymes
When are Stomata
Open
When are Carboxylating
Enzymes Functioning
When are Light Dependent
Reactions Functioning
Type of Plants Exhibiting
This Pathway
Environmental Requirements for Respiration and
Photosynthesis
Light Quality - Which wavelengths reach the plant will have an effect on how the plant grows.
Light Quantity - The intensity of light which reaches the plant will have an effect on plant growth.
Light compensation point – The light intensity
where photosynthesis =
respiration.
Light saturation point – The light intensity
where an increase in light intensity
will not cause an increase in the photosynthetic
rate.
See Handouts From Class
Temperature
Between the temperatures 5 and 25 C an increase of 10
degrees causes a doubling
of the reactions. (Both photosynthesis and respiration)
Oxygen - Low oxygen concentration will cause respiration to
switch from aerobic to
anaerobic respiration. During anaerobic respiration the pyruvic acid
formed during glycolysis will be reduced into ethanol and carbon dioxide.
The reason for this is that lack of oxygen inhibits the cytochrome system
which oxidized NADH to NAD; therefore, in the absence of oxygen the
NAD will not be generated to be used to reduce the organic compounds of
the Krebs cycle.