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Energy in a Cell

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					Energy in a Cell
The Need for Energy
Cell Energy
  Autotrophs – make their
   own food
  Heterotrophs must get
   energy from consuming
   other organisms
Autotrophs – such as
 plants, make food from
 light energy
Light energy is
 transformed into
 chemical energy as
 chemical bonds
All chemical bonds
 store energy, some
 more than others
 There is a LOT of energy in a
  carbon to carbon bond (these
  are in organic molecules such
  as sugar)
 There is too much energy in a
  carbon-carbon bond for
  normal cell processes
 So…mitochondria break
  down organic compounds,
  like sugars and fats, and
  convert the energy into
  ATP or adenosine
  triphosphate
ATP
 Composed of:
  Adenine – amino acid
  Ribose – 5-carbon sugar
  3 phosphate groups
  The phosphate groups are
   charged particles
ATP
 It requires a lot of energy to
  force the phosphate groups
  to bond because of their
  same charges
 All that energy becomes
  available when the bonds
  are broken between the
  phosphates
ATP
 When ATP has the last
  phosphate broken off to
  release the energy, it
  becomes ADP
  (adenosine
  diphosphate)
Photosynthesis
Trapping the Sun’s Energy
The Photosynthesis
Equation
  Word equation:
  Carbon dioxide + water light>
   glucose + oxygen
  Chemical equation:
  6 CO2 + 6 H2O light>
    C6H12O6 + 6 O2
Light and Pigments
  Photosynthesis requires
   light-catching pigments
  Chlorophyll
  Accessory pigments
   include: xanthophyll and
   beta carotine
Reactions in the
Chloroplast
  Thylakoids – membrane sacs
   that contain clusters of
   pigment molecules called
   photosystems
  Grana- stacks of thylakoids
  Stroma – area outside the
   thylakoid
 Light dependent reactions
  happen in the thylakoids
  (that’s where the light-
  catching pigments are)
 Light independent
  reactions happen in the
  stroma
NADPH
 The process of capturing
  sunlight results in the
  formation of high energy
  electrons
 These high energy
  electrons require special
  carrier molecules
NADPH
  NADP+ is a carrier molecule.
  - nicotinamide adenine
  dinucleotide phosphate
• - accepts a pair of high
  energy electrons along with a
  hydrogen ion: H+
  - creates NADPH
Light Dependent
Reactions
  Requires Light
  Turns ADP and NADP     + into

   the high energy carriers
   ATP and NADPH
How does it work?
   Light is first absorbed by
    pigments in Photosystem II
    Absorbed light increases
      energy in electrons which
      are passed to electron
      transport chain
    New electrons for
      chlorophyll come from water
 High energy electrons travel
  from Photosystem II to
  Photosystem I on the Electron
  Transport Chain
 Electron Transport Chain
  drives transport H + across the

  membrane of the thylakoid
 Photosystem I reenergizes high
  energy electrons and transfers
  them to NADP+ which becomes
  NADPH after picking up H+
 Process creates a charge
  difference across the thylakoid
  membranes; restoring the
  charge balance drives ATP
  creation
H + concentration  is higher
 on one side of the
 thylakoid membrane than
 the other
Facilitated diffusion
 happens to correct charge
 imbalance
ATP synthase helps with
 facilitated diffusion of
 hydrogen ions, but uses
 their passage to create
 ATP
Drives ATP synthesis
The Calvin Cycle
 ATP and NADPH are not stable
  enough to store energy for long
 The Calvin Cycle converts less
  stable, high energy molecules
  into high energy sugars
  (glucose)
 Calvin Cycle is light-
  independent
How Does it Work?
 6 carbon dioxide molecules
  combine with 6 5-carbon
  molecules
 combine with six 5-carbon
  molecules which split
  creating twelve 3 carbon
  molecules
 3 carbon molecules are then
  converted to high energy form
  using the energy from ATP
  and NADPH
 2 of the twelve 3-carbon
  compounds are converted to
  similar molecules and
  combined to form a 6-carbon
  sugar
 The remaining ten 3-carbon
  compounds are recombined into
  5-carbon compounds and re-
  enter the cycle
 Plants use 6-carbon sugars for
  energy for growth and repair,
  and to construct complex
  carbohydrates like cellulose
Chap 9.2: Photosynthesis
(summary)
 Photosynthesis happens in 2
  stages; light-dependant reactions,
  and light-independent reactions in
  the chloroplast.
 Light-dependant reactions - energy
  is passed down the electron-
  transport chain to form ATP
 Photolysis of water releases O2
  and restores electrons for electron
  transport chain. NADPH forms for
  use in light-independent rxs.
 Light-independent reactions
  (Calvin Cycle) uses CO2 to form
  sugar in the stroma of the
  chloroplast.
Cellular Respiration
 Chapter 9.3: Big Ideas

 Cellular Respiration happens in
  3 stages:
  glycolysis,
  the citric acid cycle(Krebs
   cycle),
  the electron transport chain.
 Chapter 9.3: Big Ideas
 (cont)

Glycolysis- breaks down
 glucose to make pyruvic
 acid and ATP to start the
 respiration process.
 Chapter 9.3: Big Ideas
 (cont)

 Citric Acid cycle- breaks down
  Acetyl-CoA and forms ATP and
  CO2 in the Mitchondria
 Electron Transport Chain-
  Produces ATP and H2O
Cellular Resp. Overview

• Process used by cells to
  release energy from foods
  using oxygen
• oxygen + glucose  carbon
  dioxide + water + energy
Cellular Resp. Overview
(cont)
• 6 O2 + C6H12O6  6 CO2 + 6
  H2O + Energy
• Involves glycolysis and the
  Krebs or Citric Acid Cycle
Glycolysis

  Basically: one glucose (6-
   carbon sugar) is split into 2
   pyruvic acid (3-carbon
   molecules)
  2 ATP are needed to start
   process, but 4 ATP are
   produced
Glycolysis (cont)

  NAD+   is another high energy
   electron pair acceptor
  2 NADH are created by
   glycolysis; can be used to
   make ATP
  No oxygen needed
The Krebs Cycle and
Electron Transport
  Aerobic part of cellular
   respiration
  The Krebs cycle breaks
   pyruvic acid into carbon
   dioxide and water using
   oxygen
The Krebs Cycle
a.k.a. Citric Acid Cycle
  Pyruvic acid enters
   mitochondrion from the
   cytoplasm
  1 carbon is broken off as
   carbon dioxide; 2-carbon
   compound is left
 2-carbon compound binds with
  coenzyme A to form acetyl-
  coenzyme A (acetyl-coA)
 Acetyl-coA attaches to a 4-
  carbon compound to form citric
  acid ( hence the name Citric Acid
  Cycle )
 Through various intermediate
  stages; 2 more carbons are
  released as carbon dioxide
 A 4-carbon compound is left; this
  will attach to the next acetyl-coA
  and the cycle starts over
Electron Transport
  A series of molecules that
   uses high-energy electrons
   to convert ADP into ATP
Electron Transport
  High energy electrons are
   passed along the electron
   transport chain; at the end,
   there is usually an enzyme
   that transfers the electrons to
   oxygen and hydrogen to form
   water
 Every time a pair of electrons
  travels down the chain, their
  energy is used to send H+ across
  the membrane.
 This creates an area of high H+
  concentration and an area of low
  H+ concentration
 Facilitated diffusion occurs to try
  to bring H+ concentrations to
  equilibrium
 The carrier molecule is ATP
  synthase which make an ATP for
  every H+ that goes across the
  membrane
 1 pair of high energy electrons = 3
  ATP
The Totals
  Glycolysis =         2 ATP
  Krebs/Electron Trans=34ATP
  Total                36 ATP
Fermentation
  Anaerobic way to process
   food to get energy
  Everything starts with
   Glycolysis
Alcoholic Fermentation
  Pyruvic acid + NADH 
   alcohol + CO2 + NAD  +

  Yeast works on an
   alcoholic fermentation
   system
Lactic Acid Fermentation

  Pyruvic acid + NADH  lactic
   acid + NAD+
  Muscle cells can build up lactic
   acid when they are forced to
   work without enough of an
   oxygen supply
Photosynthesis and
Cellular Respiration
            Photosynthesis     Cellular
                               Respiration
Function    Energy storage     Energy release
Location    Chloroplasts       Mitochondria
Reactants   CO2 and H2O        C6H12O6 and O2
Products    C6H12O6 and O2     CO2 and H2O
Equation    6 CO2 + 6 H2O ->   6O2 + C6H12O6 -
            C6H12O6 + 6O2      > 6 CO2 + 6 H2O

				
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