ENERGY, CELLULAR RESPIRATION

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ENERGY, CELLULAR RESPIRATION PHOTOSYNTHESIS

• AP Biology
• Beth Walker

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Review of Metabolism Energy

• Metabolic Pathways
• A. Catabolic Pathway ? releases energy by
• breaking down complex molecules into
• simple molecules
• Ex. Cellular Respiration
• B. Anabolic Pathways ? consumes energy
• to build complex molecules from simpler
  
• molecules
• Ex. Photosynthesis

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Energy Basic Principles

• Energy can be transferred from one form to
  another!
• Ex. Radiant energy of sunlight ? Chemical
  energy in the bonds of glucose
• 1st Law of Thermodynamics energy can be
  transformed transferred, but it cannot be
  created or destroyed!!

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Chemical Energy Life

• Exergonic Rxn
• a) net loss of free
• energy (-)
• b) rxn is energetically
• downhill
• c) spontaneous rxn
• d) energy-producing
• catabolic pathway

• Endergonic Rxn
• a) net gain of free
• energy ()
• b) rxn is energetically
• uphill
• c) non-spontaneous rxn
• d) energy-requiring
• anabolic pathway

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ATP Cellular Work

• Three Main Types of Work?
• 1) Mechanical Work muscle contraction, cilia
• movement, chromosome movement
• 2) Transport Work pumping substances
• across membranes
• 3) Chemical Work making polymers
• from monomers
• The immediate source of energy that drives
• cellular work is ATP!!!

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ATP Cellular Work
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Structure of ATP

• Adenine, Ribose 3 Phosphates

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How ATP Works

• The exergonic breakdown of
• ATP ? ADP P is coupled with enzymes
• Enzymes help the P move to another molecule
• The molecule receiving the P has been
  phosphorylated!
• This process is called energy coupling

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Energy Coupling
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Regeneration of ATP

• Energy needed to hook ADP P comes from catabolic
  reactions in the cell
• Cellular Respiration
• Muscle Cell 10 million ATPs used and remade
  per second per cell

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REDOX Reactions

• Reduction
• e
• H
• losing energy
• GER

• Oxidation
• -e
• -H
• producing energy
• LEO

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Energy Flow

• Photosynthesis
• H2O sunlight CO2 ? C6H12O6 O2
• Cellular Respiration
• O2 C6H12O6 ? CO2 H2O ATP
• See handout on energy flow

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Energy Flow Chemical Recycling
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Cellular Respiration

• Catabolic Production of ATP
• Final Electron Acceptor is oxygen
• Most efficient pathway ? more ATPs
• Harnesses energy in proteins, fats,
  carbohydrates
• Transfers E stored in food to molecules to ATP
• ATP ? ADP P release E

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Cellular Respiration Overview
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Cellular Respiration Overview

• Glycolysis
• 1) starts with glucose (6 Cs)
• 2) ends up with 2 pyruvates (3 Cs)
• 3) occurs in the cytoplasm of cells
• B. Krebs Cycle
• 1) occurs in the mitochondrial matrix
• 2) Acetyl CoA ? CO2, NADH, FADH2
• are all e-
  carriers

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Cellular Respiration Overview Continued

• C. Electron Transport Chain (ETC)
• 1) in mitochondrial matrix
• 2) accepts e-s from NADH FADH2
• 3) couples the slide of e-s to oxidative
• phosphorylation
• 4) generates 90 of ATP
• 5) O2 is the final electron acceptor

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Cellular Respiration Overview Continued

• Two Types of Phosphorylation
• 1) Substrate Level Phosphorylation
• makes ATP w/o the direct use of
• oxygen
• a) glycolysis
• b) Krebs Cycle
• c) ETC (Electron Transport Chain)
• 2) Oxidative Phosphorylation makes ATP
• with oxygen as the final e- acceptor
• a) Chemiosmosis/ETC

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Substrate-Level Phosphorylation
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Sequence of Cellular Respiration

1. Glycolysis
2. Production of Acetyl CoA
3. Krebs Cycle
4. Electron Transport Chain with Chemiosmosis

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Glycolysis w/ or w/o O2

• Starts w/ one glucose ? ends w/ 2 pyruvate
• Where? In the cytoplasm
• Energy investment is 2 ATPs
• Makes 4 ATPs
• Net gain of 2 ATP (substrate-level
  phosphorylation)

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How Glycolysis Works

• 2 NAD reduced to 2 NADH
• 1 glucose (from start of glycolysis) ? 2 NADH
• 2 H2Os are produced
• Exergonic process
• Occurs in fermentation (w/o O2) respiration
  (with O2)

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Glycolysis
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Glycolysis

• If O2 is present ?2 pyruvates move to
  mitochondria
• If O2 in NOT present ? 2 pyruvates stay in the
  cytosol

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Production of Acetyl CoA

• Oxidation of 2 pyruvates ? Acetyl CoA
• 2 pyruvates 2NAD 2 Coenzyme A
• 2 Acetyl CoA 2NADH 2 CO2
• Pyruvates carboxyl group is removed given off
  as CO2

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Production of Acetyl CoA

• Remaining 2 carbon fragment is oxidized (lose e-)
  to form acetate therefore..
• NAD ? NADH
• oxidized ? reduced
• Coenzyme A is attached by an unstable bond that
  makes the acetyl group highly reactive? Acetyl
  CoA

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Production of Acetyl CoA
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Production of Acetyl CoA

• NET RESULT
• 2 NADH
• 2 CO2
• 2 Acetyl CoA (2 C)
• 2 Acetyl CoA made from 1 initial glucose

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Krebs Cycle aka, Citric Acid Cycle
Tricarboxylic Acid Cycle

• 2 Acetyl CoA enter
• Produces CO2
• H released
• e- released NAD ? NADH
• 1 ATP made per turn of the cycle by
  substrate-level phosphorylation
• 3 molecules of NADH made per turn
• 1 molecule of FADH2 made per turn

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Krebs Cycle Summary

• Enters Cycle
• 2 Acetyl Co A

• Exits Cycle
• 1 ATP X 2 2 ATPs
• 3 NADH X 2 6 NADH
• 1 FADH2 X 2 2 FADH2
• 2 CO2 X 2 4 CO2

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Krebs Cycle Summary
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Electron Transport Chain (ETC)

• NADH FADH2 pass their e-s down the ETC
• Requires O2 as the final e- acceptor
• (O2 is very electronegative)
• Oxidative Phosphorylation transfer of e- from
  food to O2

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Electron Transport Chain

• Releases energy in small, usable steps instead of
  1 large, wasteful step
• Chain b/cs reduced when it accepts e- from
  uphill neighbor
• Chain b/cs oxidized when it loses e-s to down
  hill neighbor

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Chemiosmosis

• Definition couples e- flow down ETC to ATP
  synthesis
• Creates a proton gradient across the inner
  mitochondrial membrane
• Uses ATP synthase (enzyme embedded in the
  mitochondrial membrane) to attach ADP to P ? ATP

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Chemiosmosis Cont.

• Cristae- infoldings of the mitochondria increase
  surface area available for chemiosmosis to occur
• ETC uses exergonic flow of e-s to pump H across
  the mitochondrial membrane into the intermembrane
  space.

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Chemiosmosis Cont.

• New proton gradient
• Fall of H thru ATP Synthase
• Harnesses the energy of the fall
• phosphorylates an ADP
• ATP

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Chemiosmosis
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Total Yield - _at_ 32 ATP
Where? Phase? Yield?
Cytoplasm Glycolysis 2 ATP (substrate) 2 pyruvate 2 NADH x 2.5 5 ATP
B/w cytoplasm mitochondria Acetyl CoA 2 NADH x 2.5 5 ATP 2 CO2
Mitochondria Krebs Cycle 6 NADH x 2.5 15 ATP 2 FADH2 x 1.5 3 ATP 2 ATP (substrate) 2 CO2
Mitochondria ETC Chemiosmosis See yellow font above all ATP in yellow are oxidative
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ATP Yield

• In eukaryotic cells, the ATP yield is slightly
  lower b/c of the NADH made during glycolysis.
• Mitochondrial membrane is NOT permeable to NADH
  so it must be moved across the membrane
  therefore.
• e-s are received at a lower place on the ETC
  (near where FADH2 is received)

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ATP Yield is an Estimate

• The following factors could influence yield
• 1) Mitochondrial membranes differ in
• permeability to protons.
• 2) Proton-motive force can be used for other
• types of cellular work/active transport.
• 3) Prokaryotes make a little more ATP, b/c
• there is no mitochondrial membrane
• separating glycolysis from the ETC.
• (about 38 ATP)

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Anaerobic Respiration

• Occurs in only a few bacterial groups that live
  in anaerobic environments
• Occurs in the absence of free O2 something else
  is the final e- acceptor
• Pyruvate is reduced and NAD is regenerated
• Uses ETC to make ATP

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Fermentation

• Starts w/ glycolysis ? makes 2 ATPs
• If no O2, pyruvate is reduced and NAD is
  regenerated by fermentation.
• Keeps the cell from depleting its supply of
  NAD, which is the oxidizing agent necessary for
  the continuation of glycolysis.
• Two Types Alcohol Lactic Acid

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Alcohol Fermentation
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Alcohol Fermentation

• Mainly occurs in yeast bacteria
• Pyruvate is converted to ethanol in two steps
• 1) Pyruvate loses CO2 and is converted
• to a 2 C compound (acetaldehyde)
• 2) NADH is oxidized to NAD and
• acetaldehyde is reduced to ethanol.

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Lactic Acid Fermentation
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Lactic Acid Fermentation

• Mainly occurs in fungi, bacteria, human muscle
  cells
• NADH is oxidized to NAD pyruvate is reduced to
  lactate
• Helps make cheese yogurt
• In humans, muscle cells switch from aerobic
  respiration to lactic acid fermentation when O2
  is low
• Eventually carried to the liver converted back
  to pyruvate

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Comparing Types of Respiration

• Aerobic O2 is final e- acceptor Uses ETC to
  make ATP most ATP is made by oxidative
  phosphorylation, some by substrate-level
• Anaerobic something other than O2 is final e-
  acceptor uses ETC to make ATP most ATP made by
  oxidative phosphorylation, some by
  substrate-level
• Fermentation no O2 required final e- acceptor
  is pyruvate ATP only made by substrate-level
  phosphorylation less efficient than respiration

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Photosynthesis

• Sunlight CO2 H2O ? C6H12O6 O2
• Occurs in plants or autotrophs (organisms that
  can make their own food)
• Happens in the chloroplast double membrane with
  an internal thylakoid membrane system surrounded
  by stroma

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Structure of the Chloroplast
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Chloroplast

• Chlorophyll pigment that absorbs light energy
  from the sun chlorophyll a b
• Stomata openings on the underside of a leaf
  where CO2 enters and O2 exits
• Thylakoid Membrane - where chlorophyll is found
  light rxns occur
• Stroma - surrounds the thylakoid membranes where
  dark rxns/Calvin Cycle occurs

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Photosynthesis Redox

• Similar to respiration, but e-s flow in the
  opposite direction
• e-s increase their potential energy as they
  travel from H2O to reduce CO2 to sugar
• Light provides the energy to move e-s

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Overview of Photosynthesis

• Light Reactions
• Solar E ? light E
• Chlorophyll absorbs light
• NADP accepts e-s hydrogen
• O2 releases
• ATP made ? photophosphorylation
• Occurs in thylakoid membrane

• Dark Reactions
• Aka, Calvin Cycle
• Carbon fixation
• Reduces fixed carbon to sugar by adding e-s
• Uses ATP from light rxns
• No steps DIRECTLY require light
• Occurs in stroma

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Nature of Light

• Visible Light ? 380 750 nm
• Photons ? particle of energy
• Blue Red Light ? most effective in absorbing
  photons
• Pigments ? absorb light
• Photoxidation of Chlorophyll ?
• a) e-s are elevated to another orbital
• where it has more potential energy
• b) ground state ? excited state

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What is a photosystem?

• Made up of chlorophyll, accessory pigments,
  proteins, other small molecules
• Where? In the thylakoid membrane
• All energy from photons are transferred thru the
  complex to a chlorophyll a molecule in the
  reaction center
• Chlorophyll a loses an e- to the primary e-
  acceptor in the rxn center

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Chlorophyll Molecule
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Types of Photosystems

• Photosystem I
• P700
• Best at absorbing light w/ a wavelength of 700 nm
• 1st photosystem discovered

• Photosystem II
• P680
• Best at absorbing light a/ a wavelength of 680 nm
• 2nd photosystem discovered

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Photosystem
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Light Reactions of Photosynthesis

• Converts solar E to chemical E
• Consists of cyclic non-cyclic electron
• flow
• Involves P700 P680 photosystems

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Cyclic Electron Flow

• Photosystem I (P700)
• Only makes ATP
• Simplest pathway
• Cyclic? b/c e-s leave the rxn center of
  chlorophyll and returns

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Cyclic Electron Flow
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Steps of Cyclic e- Flow

• 1) Light hits the rxn center
• 2) Moves e-s to an excited state
• 3) Accepted by the primary e-
• acceptor(PEA)
• 4) PEA suplies the e- to the ETC
• 5) Proton-motive Force (gradient) across the
  thylakoid membrane
• 6) ATP Synthase P ADP ? ATP
• photophosphorylation driven by klght E

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Non-cyclic Electron Flow

• Involves Photosystem I II
• Makes ATP NADPH
• Splits H2O photolysis
• Fills the e- holes left in Photosystem I

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Steps of Non-cyclic e- Flow Photosystem I (P700)

• 1) Light E excites e-s
• 2) e-s move down the ETC are stored
• in NADPH
• 3) e- holes are created in Photosytem I
• (P700)
• 4) Holes will be filled by Photosystem II
• (P680)

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Steps of Non-cyclic e- Flow Photosystem II (P680)

• 1) Light E hits the rxn center e-s are
• excited
• 2) PEA accepts e-s
• 3) e-a move down the ETC
• (proton gradient ? ATP)
• 4) e-a fill holes in photosystem I

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What fills the e- holes in Photosystem II?

• Photolysis splitting of H2O
• Forms 2 e-, 2 H, and O
• e-s are transferred to Photosystem II

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Important Point !!!

• Non-cyclic e- flow produces equal quantities of
  ATP NADPH, but the Calvin Cycle consumes more
  ATP than NADPH therefore, cyclic e- flow makes
  up the ATP debt for the Calvin Cycle

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Chemiosmosis Mitochondria vs. Chloroplast

• Mitochondria
• e-s n ETC come from oxidation of food molecules
• Spatial organization? protons are pumped from
  matrix to the intermembrane space
• Oxidative phosphorylation

• Chloroplast
• e-s come from light energy of sun
• Protons pumped from the stroma into the thylakoid
  compartment
• photophosphorylation

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Chemiosmosis
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Dark ReactionsCalvin Cycle

• CO2 enters
• Uses ATP as an E source
• Consumes NADPH to reduce e- to make sugar
• Occurs in the stroma
• Makes sugar (C6H12O6)
• Three Phases Carbon Fixation, Reduction,
  Regeneration

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Steps of the Calvin Cycle

• 1) An enzyme, rubico, combines CO2
• with RuBP (ribulose biphosphate)
• 2) 6 C intermediate splits in half to make
• 2 molecules of 3-phosphoglycerate
• 3) ATP ? ADP P the P group is
• transferred by an enzyme from
• 3-phosphoglycerate to
• 1-3-diphosphoglycerate

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Steps of the Calvin Cycle Continued

• 4) Pair of e-s donated from NADPH
• reduces 1-3-diphosphoglycerate to
• glyceraldehyde phsophate
• 5) Glyceraldehyde phosphate is a sugar
• 6) 5 molecules of glyceraldehyde
• phosphate combines w/ the
• breakdown of 3ATP to form 3
• molecules of RUBP

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Calvin Cycle

• 3 molecules of CO2 ? 6 molecules of
  glyceraldehyde phosphate (sugar)
• 5 molecules of glyceraldehyde phosphate ? 3
  molecules of RuBP
• Total of 9ATPs 6 NADPHs yield 1
  glyceraldehyde phosphate

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Photosynthesis Review