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Cellular Respiration & Photosynthesis - Coggle Diagram
Cellular Respiration & Photosynthesis
photosynthesis uses CO2 & H2O to make organic molecules & O2
Catabolic pathways yield energy by oxidizing organic fuels
energy enters ecosystems as light & exits as heat
chemical elements essential to life are recycled
cellular respiration uses O2 & organic molecules to make ATP; CO2 & H2O are produced as waste
release stored energy by breaking down complex molecules
electron transfer from food molecules to other molecules plays a major role in these pathways
chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or
redox reactions
oxidation
is the loss of electrons from substance
Reduction
is the addition of electrons to a substance
reducing agent
is the electron donor, it reduces the electron acceptor
oxidizing agent
the electron acceptor, it oxidizes the electron donor
Glycolysis & the citric acid cycle are major intersections to various catabolic & anabolic pathways
Feedback inhibition is the most common mechanism for metabolic control because it prevents wasteful production
Catabolism is controlled by regulating the activity of enzymes at strategic points in the pathway
plant & animal cells break down organic molecules by cellular respiration in the mitochondria
the chemical energy in food is transformed into chemical energy in ATP
Catabolic Pathways & Production of ATP
breakdown of organic molecules in exergonic
Cellular respiration
includes both aerobic & anaerobic respiration but is often used to refer to aerobic respiration
6CO₂ + 6H₂O <- 6O₂ + C₆H₁₂O₆
Fermentation
is a partial degradation of sugars that occurs w/o oxygen
Aerobic respiration
consumes organic molecules & oxygen & yields ATP
anaerobic is similar to aerobic but consumes compounds other than oxygen
Oxidation of Organic Fuel Molecules
during cellular respiration, fuel molecules are oxidized, & O2 is reduced
Cellular respiration is a redox process; energy is released as hydrogen and electrons are transferred to O atoms
oxidation of glucose transfers electrons from a higher energy stae to a lower energy state with O atoms
this releases energy that is used to synthesize ATP
Nicotinamide adenine dinucleotide,
NAD+
, is a coenzyme that functions as an electron carrier
enzymes remove a pair of hydrogen atoms from the substrate
the 2 electrons & 1 proton is transferred to NAD+ forming
NADH
the other proton is released as a hydrogen ion (H+) into the surrounding solution
cellular respiration uses an electron transport chain to break the fall of electron to O2 into several energy-releasing steps
Electron Transport Chain
consists of a series of molecules build into the inner membrane of the mitochondria
NADH
passes electron to the electron transport chain where they are transferred in a series of redox reactions, each releasing a small amount of energy
O2 captures the electron & the hydrogen nuclei (H+) forming H2O, energy yielded is used to regenerate ATP
Cellular Respiration Steps
1) Glycolysis: 1 Glucose > 2 Pyruvate
breaks down glucose, no oxygen required, occurs in the cytoplasm of cell
energy investment phase, 2 ATP are used to
split glucose into 2 three-carbon sugar molecules
energy payoff phase, 4 ATP are synthesized, 2 NAD+ are reduced to NADH, the small sugars are oxidized to form 2 pyruvate and 2 H2O
2 ATP are produced by substrate-level phosphorylation during glycolysis
does not release any CO2 & occurs whether or not O2 is present
P: 2 Pyruvate, 2ATP, 2NADH
2) Pyruvate Oxidation: 2 Pyruvate > 2 Acetyle COA
no ATP released, required oxygen, occurs in the matrix of mitochondria
P: 2 Acetyle COA, 2 Co2, 2NADH
most energy in glucose remains stored in the pyruvate molecules produced by glycolysis
pyruvate is converted to Acetyl CoA before entering the citric acid cycle
3) Kreb Cycle (Citric Acid) > 2 Acetyle COA
occurs in the matrix of the mitochondria, requires oxygen
P: 2 ATP, 2 CO2, 3 NADH, 1FADH} per turn > 4CO2, 6NADH, 2FADH
oxidized organic fuel derived from pyruvate
because 2 pyruvate are produced per glucose, the cycle runs twice per glucose molecule consumed
4) Oxidative Phosphorylation (ETC+ Chemiosmosis)
R: 10 NADH, 2 FADH2
P: ~ 28 ATP
occurs in the inner membrane of the mitochondria, requires O2
NADH & FADH2 donate electrons to the ETC, which powers ATP synthesis
the pathway of electron transport
molecules of the ETC are embedded in the inner mitochondrial membrane
membrane is folded into cristae to increase surface area for ETC
most molecules in the ETC are protiens
electrons are passed through a # of carrier molecules including several
cytochromes
Chemiosmosis: the energy-coupling mechanism
energy released as electrons are passed down the ETC is used to pump H+ from the mitochondrial matrix to the intermembrane space
H+ moves down its concentration gradient back across the membrane, passing though the protein complex
ATP Synthase
Total ATP: ~32 ATP (30-38 ATP)
During cellular respiration, most energy flows in this sequence: Glucose > NADH > ETC > proton-motive force > ATP
making about 32 ATP
Fermentation & Anaerobic respiration
most cellular respiration depends on electronegative oxygen to pull electrons down the transport chain
fermentation is an extension of glycolysis that oxidizes NADH by transferring electrons to pyruvate or it derivaties
2 types are
Alcohol Fermentation & Lactic Acid Fermentation
In
alcohol fermentation
pyruvate is converted to ethanol in two steps
1st: releases CO2 from pyruvate 2nd: produces NAD+ & ethanol
yeast is used in brewing, winemaking, and baking
Lactic Acid Fermentation
pyruvate is reduced directly by NADH to form lactate & NAD+
no release of CO2
by fungi & bacteria is used to make cheese & yogurt
both have some similarities
All use glycolysis (net ATP = 2) to oxidize glucose & harvest the chemical energy of food
In all three, NAD+ is the oxidizing agent that accepts electrons during glycolysis
Comparing fermentation w/Anaerobic & Aerobic Respiration
Fermentation
an organic molecule (pyruvate or acetaldehyde) acts as a final electron acceptor
produces 2 ATP by substrate-level
phosphorylation
electrons are transferred to the
electron transport chain
harvests much more ATP by oxidative phosphorylation-up to 32 ATP in aerobic respiration
Obligate anaerobes carry out fermentation or anaerobic respiration and cannot survive in the presence of O2
Yeast and many bacteria are facultative anaerobes, can survive using either fermentation or cellular respiration
Photosynthesis
feeds the biosphere
photosynthesis
is the process that converts solar energy into chemical energy within chloroplasts, it nourishes almost the entire living world directly or indirectly
process that feeds the biosphere:
Autotrophs
are "self-feeders" that sustain themselves w/o eating anything derived from other organisms
they are the producers, produce organic molecules from CO2 & other inorganic molecules
almost all plants are photoautotrophs, they use the energy of sunlight to make organic molecules
Heterotrophs
obtain organic material from other organisms; they are consumers
almost all heterotrophs depend on photoautotrophs for food & O2
Photosynthesis converts light energy to the chemical energy of food
plants & other photosynthetic organisms contain organelles called
chloroplasts
chloroplasts are found mainly in cells of the
mesophyll
, the interior tissue of the leaf
CO2 enters & O2 exits the leaf through the
stomata
stomata: an envelope of 2 membranes surrounding a dense fluid
chloroplasts split H2O into hydrogen & oxygen incorporating the electrons of hydrogen into sugar molecules and releasing O2 as a by-product
the structural organization of these organelles allows for the chemical reaction of photosynthesis
Thylakoids
are connected sacs in the chloroplast that compose a third membrane system
may be stacked in columns
Chlorophyll
resided in the thylakoid membranes
photosynthesis reverses the direction of electron flow compared to respiration
redox process in which H2O is oxidized & CO2 is reduced
it is endergonic process
Photosynthesis consists of the
light reactions & Calvin Cycle
Light reactions (in the thylakoids):
split H2O, providing electrons & protons(H+)
releases O2 as a by-product
reduce the electron acceptor
NADP+
to
NADPH
generate ATP from ADP by
photophosphorylation
Calvin Cycle make sugar from CO2 using ATP & NADPH
begins w/
carbon fixation
, incorporating CO2 into organic molecules
light rxns convert solar energy to chemical energy of ATP and NADPH
chloroplasts are solar-powered chemical factories
their thylakoids transform light energy into chemical energy of ATP & NADPH
Nature of Sunlight
light is electromagnetic energy (radiation)
this travels in rhythmic waves
Wavelength
: measure of distance between crests of electromagnetic waves
it can range from less than a nanometer to more than a kilometer
electromagnetic spectrum
: the entire range of electromagnetic energy
Visible Light
: (380nm-740nm) drives photosynthesis & produces the colors seen by the human eye
pigments are substances that absorb visible light; different pigments absorb different wavelengths & the wavelengths that are absorbed disapper
Spectrophotometer
: measures a pigment's ability to absorb various wavelength
absorption spectrum
: a graph plotting a
pigment’s light absorption versus wavelength
photosystem
consists of a reaction-center complex surrounded by light-harvesting complexes
Reaction-center complex
: an association of proteins holding a special pair of chlorophyll
a
molecules & a primary electron acceptor
Primary electron acceptor
in the reaction center accepts excited electrons and is reduced as a result
Light-harvesting complex
: consists of various pigment molecules bound to proteins
transfers the energy of photons to the chlorophyll
a
molecules in the reaction-center complex
there are
2 types of photosystems
(in the thylakoid membrane)
Photosystem II (PSII)
called P680 because its reaction-center chlorophyll a is best at absorbing light w/wavelength of 680nm
Photosystem I (PSI)
its P700 because its reaction-center chlorophyll a is best at absorbing light w/wavelength 700nm
Linear electron flow
: involves both photosystems & produces ATP & NADPH using light energy
1) photon hits a pigment in a light-harvesting complex PSII & its energy is passed among pigment molecules until it excites P680
2) electron from P680 is transferred to the primary electron acceptor
3) enzyme catalyzes the split of H2O into 2 electrons, 2 H+ & and oxygen atom
4) electron are passed in a series of redox reactions from the primary electron acceptor of PSII down an ETC to PSI
5) potential energy stored in the proton gradient drives production of ATP by chemiosmosis
1 more item...
Cyclic electron flow
: photoexcited electrons cycle back from Fd to the cytochrome complex instead of being transferred to NADP+
Electrons are passed to a P700 chlorophyll in the PS I reaction center via the plastocyanin molecule (Pc)
uses only Photosystem I
only produces ATP
Comparing Chemiosmosis in Chloroplasts & Mitochondria
Both generate ATP by chemiosmosis
Electron transport chains pump protons (H+) across a membrane as electrons are passed through carriers with progressively higher electron affinity
Chloroplasts
high energy electrons drop down the transport chain from water, while in mitochondria, they are extracted from organic molecules
protons are pumped into the
thylakoid space and drive ATP synthesis on the stroma side of the membrane as they diffuse back into the stroma
Mitochondria
transfer chemical energy from food to
ATP; chloroplasts transform light energy into the chemical energy of ATP
protons are pumped to the
intermembrane space and drive ATP synthesis as they diffuse back into the mitochondrial matrix
Calvin Cycle uses chemical energy of ATP & NADPH to reduce CO2 to sugar
The Calvin Cycle is anabolic; it builds sugar from smaller molecules by using ATP & reducing power of electrons carried by NADPH
carbon enters cycle as CO2 & leaves as
glyceraldehyde 3-phosphate (G3P)
for one G3P to be synthesis the cycle must take place 3x
Calvin Cycle has 3 phases: carbon fixation, reduction, and regeneration
1. Carbon Fixation
: binding of CO2 to 5-carbon RuBP is catalyzed by rubisco. the 6-carbon molecule is split into 2 molecules of 3 G3P
2. Reduction
: each molecule of 3 G3P is altered through phosphorylation by 6 ATP & reduction by 6 NADPH to produce a G3P sugar. every 3 CO2 molecules that enter the cycle 6 molecules of G3P are formed
3. Regeneration
: remaining 5 molecules of G3P are rearranged on complex series of reactions yielding 3 molecules of RuBP. 3 additional molecules of ATP are used to facilitate the regeneration of RuBP
3 turns of the Calvin Cycle = 1 G3P
2 G3Ps= 1 glucose
2 turns of the Kreb Cycle = breakdown of 1 glucose
Alternative Mechanisms: Carbon Fixation
Plants have metabolic adaptations to help conserve water, but often involve trade-offs
On hot, dry days, plants close stomata, which
conserves H2O but also limits photosynthesis
The closing of stomata reduces access to CO2 and causes O2 to build up
These conditions favor an apparently wasteful
process called
photorespiration
Photorespiration
rubisco binds w/O2 instead of CO2 producing a 2-carbon compound
costly because it consumes O2 & organic fuel w/o producing any ATP or sugar
may provide some protection from damaging products of the light reactions that build up when the Calvin cycle slows due to low CO2
in many plants, photorespiration it drains away as much as 50% of the carbon fixed by the Calvin cycle
C4 Plants
: minimize the cost of photorespiration by incorporating CO2 into a 4-carbon compound as the 1st product of the Calvin cycle
in hot dry weather C4 plants usually close their stomata, conserving water by reducing CO2
Crassulacean Acid Metabolism (CAM)
they open their stomata at night & incorporate CO2 into organic acids that are stored in the vacuoles
Stomata close during the day & CO2 is released from organic acids & used in the Calvin cycle
similar to the
C4
pathway
