Chapter 6 – Pathways
Vocab
Free Energy (G) – Energy that is available for doing useful work, after allowance has
been made for the increase or decrease of disorder.
Endergonic – A chemical reaction in which the products have higher free energy than
the reactants, thereby requiring free energy input to occur.
Exergonic – A chemical reaction in which the products of the reaction have lower
free energy than the reactants, resulting in a release of free energy.
1st Law of Thermodynamics – The principle that energy can be neither created nor
destroyed.
2nd Law of Thermodynamics – The principle that when energy is converted from one
form to another, some of that energy becomes unavailable for doing work.
Phosphate level phosphorylation – A type of phosphorylation in which the
phosphoryl group is transferred from a donor compound (a phosphorylated reactive
intermediate) to the recipient compound
Oxidative phosphorylation – ATP formation in the mitochondrion, associated with
flow of electrons through the respiratory chain.
Chemiosmosis – Formation of ATP in mitochondria and chloroplasts, resulting from
a pumping of protons across a membrane (against a gradient of electrical charge and
of pH), followed by the return of the protons through a protein channel with ATP
synthase activity.
Oxidation – elative loss of electrons in a chemical reaction; either outright removal to
form an ion, or the sharing of electrons with substances having a greater affinity for
them, such as oxygen. Most oxidations, including biological ones, are associated with
the liberation of energy.
Reduction – Gain of electrons by a chemical reactant; any reduction is accompanied
by an oxidation
Pigment – A substance that absorbs visible light.
Photosystem – A light-harvesting complex in the chloroplast thylakoid composed of
pigments and proteins.
Questions:
1) - Chemical transformation happens in a series of reactions that form a metabolic
pathway
- A specific enzyme catalyzes each reaction
- Metabolic pathways are similar in all types of organisms
- Metabolic pathways in eukaryotes are compartmentalized
- A key enzyme, which can be activated or inhibited, controls each metabolic
pathway and determines the speed of reactions
2) Reduction is the gain of one or more electrons; whereas, oxidation is the loss of
one or more electrons. They must occur together because as one chemical is
oxidized the electron is transferred to another chemical, which reduces it.
3) Pyruvate oxidation doesn’t produce any ATP. While the citric acid cycle produces
2 ATP per FADH+.
4) Ammonia is toxic to mammals in high levels because it depletes the mitochondria
of ketoglutarate, which is key to the citric acid cycle. Without the keroglurate, the
cirtic acid cycle cannot produce enough ATP for the organism to operate and it
also prevents the electron transport chain.
5) CO2 has the lowest free energy because it is the most oxidized. CH4 is the most
reduced so it has the most free energy.
6) Top: oxidation because it losses electrons
Bottom: reduction because it gains electrons
7) In the inner membrane of the mitochondria O2 is reduced to water and NADH to
NAD+. In electron transport, through embedded proteins, the reactions release
energy used to transport H+ ions out of the mitochondria matrix. As a result, a
proton gradient is established across the inner membrane and chemiosmosis can
start.
8) The other 452 kcal become unusable for work due to the 2nd law of
thermodynamics.
9) Oxidative phosphorylation makes more than 50 kcal/mol of energy. Oxidative
phosphorylation yields more ATP than substrate phosphorylation. Each NADH
can produce two to three ATP molecules. The citric acid cycle yield 10 molecules
of ATP. Two molecules of acetyl CoA produced about 20 ATPs per molecule.
About 32 molecules of ATP produced per fully oxidized glucose.
10) Fermentation is the anaerobic degradation of a substance such as glucose to
smaller molecules such as lactic acid or alcohol with the extraction of energy. It
reoxidizes NADH to allow glycolysis to continue. In lactic acid fermentation,
NADH is used to reduce pyruvate to lactic acid. This regenerates NAD+ to keep
glycolysis going. In alcoholic fermentation, pyruvate is converted to
acetaldehyde, which releases CO2. NADH is used to reduce acetaldehyde to
ethanol, again regenerating NAD+ for glycolysis.
11) Lipids and proteins can be used to make Acetyl CoA for the citric acid cycle. The
lipids are broken down, and the glycerol is used to start glycolysis. The fatty acids
are converted to CoA to start the citric acid cycle. Protein can be hydrolyzed into
amino acids, which feed glycolysis and the CAC.
12) Light is a form of energy. It is a form of electromagnetic radiation in waves, and it
behaves as particles called photons. Shorter wavelengths have more energy.
Pigments are molecules that absorb photons with wavelengths in the visible
spectrum.
13)
14) In photosystem I at the P700 chlorophyll light energy is absorbed at 700nm and
passes and electron to NADP+, which causes it to reduce into NADPH. In
photosystem II at the P680 chlorophyll light energy is absorbed at 680nm and
produces ATP and oxidizes water. Cyclic electron transport is the flow of
electrons that produces ATP but no NADPH or O2 in photosynthetic light
reactions. This process is cyclic because an electron is passed from a chlorophyll
and is brought back to the same chlorophyll.
15) In photosynthesis energetic electrons are passed through a series of membranebound carriers to a lower energy level final acceptor. In a similar way to
mitochondria, a proton gradient is generated and is used by ATP synthase to store
energy in the bonds of ATP.
16) – Fixation of CO2 = a CO2 is added to a five-carbon ribose that produces a
molecule that breaks into two 3PG molecules.
– Reduction of 3PG to form G3P. Phosphorylation of a high energy phosphate
from an ATP and a reduction of NADPH from light reactions are used in this
reduction.
– Regeneration of the CO2 acceptor, RuBP = ATP is used to convert RuMP into
RuBP. One CO2 is fixed and the CO2 acceptor is regenerated.
17)
18) In photosystem I needs an electron form the last carrier in the electron transport of
photosystem II.
19) Having multiple ways of capturing light has an evolutionary advantage because it
allows the plants to receive and store more light. More light means more energy.
If a anytime the ability for a plant to receive light form the sun light from was
obstructed, like in the winter or when ash from a volcanic explosion blocks the
sun, plants that have more stored light will survive longer.
20) Since red light is absorbed in water, plants that photosynthesis waves lengths with
red light cannot live underwater.
21) Since rubisco makes up half of the plants proteins and plants are the most
abundant organisms on the plant by the transitive property rubisco is the most
abundant protein on the planet. Rubisco is a contraction of ribulose bisphosphate
carboxylase/oxygenase, the enzyme that combines carbon dioxide or oxygen with
ribulose bisphosphate to catalyze the first step of photosynthetic carbon fixation
or photorespiration, respectively.
22) Plants need both processes because they need cellular respiration to obtain energy
from glucose.
23) A. Complete, pH 3.8 without anything missing
B. Emit the row with pH 37.0
C. All groups where there was an element missing had a dramatic loss in Light
emission.
D. ATP went down in the absence of Pi because Pi is needed to make ATP
E. ATP production could be negative if more ATP is used than created.
F. Free energy that drives the production of ATP comes from hydrolysis of ATP