BIOCHEMICAL PATHWAYS

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CHAPTER 6 BIOCHEMICAL PATHWAYS
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BIOCHEMICAL REACTIONS

• Organisms obtain energy through enzyme-controlled
  biochemical reactions
• Release energy stored in chemical bonds
• The ultimate source of all energy is the sun
• Converted to chemical energy through
  photosynthesis
• Organisms convert this chemical energy (food)
  into usable energy through cellular respiration
• Controlled release
• Large organic molecules are broken down
• Photosynthetic organisms produce food for their
  own use and for others

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BIOCHEMICAL REACTIONS

• All organisms carry out cellular respiration
  which may be
• Aerobic uses oxygen
• Anaerobic does not use oxygen
• Organisms can be classified based on how they
  obtain nutrients
• Autotrophs make their own food (green plants,
  algae)
• Heterotrophs obtain food from their
  surroundings (all animals, fungi)

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BIOCHEMICAL REACTIONS

• Some bacterial cells can produce food through
  chemosynthesis (chemical reactions)
• Occur within the cytoplasm
• In eukaryotic cells, these reactions are carried
  out in specific organelles
• Photosynthesis chloroplasts
• Cellular respiration mitochondria

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BIOCHEMICAL PATHWAYS

• Can be classified two ways
• Catabolic reactions - breakdown of organic
  molecules releases energy
• Anabolic reactions - synthesis of new organic
  molecules requires energy
• Energy for these reactions is supplied by
  adenosine triphosphate (ATP)
• Energy is released when ATP is broken down into
  ADP
• Reformed when a phosphate group is added to ADP
  (phosphorylation reaction)

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Like charging a battery
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The actual process
AMP
ADP
ATP
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AEROBIC CELLULAR RESPIRATION

• The breakdown of glucose molecules in the
  presence of oxygen
• Carbon dioxide and water are produced
• C6H12O6 6 O2 ? 6 CO2 6 H2O energy
  (ATP heat)
• glucose oxygen ? carbon dioxide water
  energy

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AEROBIC CELLULAR RESPIRATION

• Begins in the cytoplasm and is completed in the
  mitochondria.
• Series of enzyme-controlled reactions that are
  divided into three pathways
• Glycolysis
• Krebs cycle (citric acid cycle)
• Electron transport system

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GLYCOLYSIS

• Glycolysis the breakdown of glucose occurs in
  the cytoplasm
• Glucose (6-carbon atoms) is broken into two
  3-carbon molecules called pyruvate (pyruvic
  acid).
• 2 ATP molecules are produced
• Electrons released from these reactions are
  transferred to the electron transport chain.
• Will be attached to oxygen atoms

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GLYCOLYSIS
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KREBS CYCLE

• The pyruvate produced in the cytoplasm moves into
  the mitochondria, releasing
• Carbon dioxide (remnants of pyruvate)
• Electrons
• 2 ATP molecules
• The electrons are transferred to NADH and FADH2
  (electron carriers), which take them to the
  electron transport system.

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KREBS CYCLE
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ELECTRON TRANSPORT CHAIN

• When electrons receive additional energy they
  move to a higher energy level.
• When the electrons fall back to their original
  position they give up that energy.
• Special molecules (NADH, NADPH, FADH2) capture
  these excited electrons and transfer them to
  other chemical reactions
• Tied to the formation of ATP
• Oxidation-reduction reactions
• Electrons usually come from hydrogen creating H
  (hydrogen nucleus)

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ELECTRON TRANSPORT SYSTEM

• Electrons are transferred through a series of
  reactions until they are accepted by oxygen
• Oxygen combines with hydrogen ions to make water.
• This process generates large amounts of ATP
• 32 ATP total

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Electron Transport System
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FERMENTATION(Anaerobic Respiration)

• Two main types of fermentation
• Alcoholic fermentation
• Lactic acid fermentation
• Alcoholic fermentation used by yeast cells in
  the absence of oxygen
• Pyruvate from glycolysis is converted to ethanol
  and carbon dioxide
• The yeast cells gain 2 ATP

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FERMENTATION

• Lactic acid fermentation pyruvate from
  glycolysis is converted to lactic acid
• 2 ATP molecules are produced
• In bacteria, the build up of lactic acid
  interferes with metabolic functions and they die.
• Humans use lactic acid waste products from these
  types of bacteria to make yogurt, cultured sour
  cream, cheeses, and other fermented dairy
  products.

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ANAEROBIC RESPIRATION

• In humans, red blood cells produce energy through
  lactic acid fermentation
• They dont have mitochondria
• Muscle cells can use aerobic and anaerobic
  respiration.
• For anaerobic respiration, lactic acid
  accumulates resulting in fatigue, cramping, and
  pain.
• Must stop the activity or muscles will die
• When enough oxygen is available, lactic acid is
  converted to pyruvic acid Krebs cycle will
  proceed.

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ANAEROBIC RESPIRATION
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RESPIRATION
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FAT RESPIRATION

• Fats and proteins can also be used as a source of
  energy.
• Fats are digested to fatty acids and glycerol
• Proteins are digested to amino acids
• Requires several more complex steps.
• In fats, fatty acids and glycerol are broken down
  through the Krebs cycle in the mitochondria.
• Can produce more ATP than carbohydrates
• Serve as long term energy storage
• Twice as much energy per gram of fat than gram of
  carbohydrate

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PROTEIN RESPIRATION

• After proteins are broken down to amino acids,
  the amino group is removed.
• The carbon skeleton enters the respiratory cycle
  as acetyl, pyruvic acid, or other molecules found
  in the Krebs cycle.
• The removed amino group is converted to ammonia.
• Excreted as ammonia, uric acid, or urea (very
  toxic must be eliminated)
• Proteins cannot be stored, so they are converted
  to fat or carbohydrates.

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PHOTOSYNTHESIS

• Process in which energy from sunlight is
  converted to chemical energy.
• Anabolic process
• Used by plants, algae, and some bacteria
• The green pigment chlorophyll absorbs sunlight.
• Takes place in chloroplasts, which have 2
  regions
• Granum stacks of membranous sacs (thylakoids)
  that contain chlorophyll
• Stroma - the space between the membranes

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PHOTOSYNTHESIS

• Can be summarized by the following equation
• Light energy 6 CO2 6 H2O ? C6H12O6 6 O2
  
• carbon dioxide water? glucose
  oxygen
• Opposite of cellular respiration!

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PHOTOSYNTHESIS
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PHOTOSYNTHESIS

• Three separate events
• Light-capturing events
• Light-dependent reactions
• Light-independent reactions
• Visible light is a combination of different
  wavelengths of light seen as different colors.
• Chlorophyll absorbs red and blue light, reflects
  green
• Pigments called carotenoids (yellow, orange, red)
  also capture light, produce excited electrons
  visible in the fall

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PHOTOSYNTHESIS

• Light-capturing events
• Pigments capture light energy which causes some
  electrons to become excited
• Pigments are arranged into clusters called
  photosystems helps concentrate energy
• Light-dependent reactions
• Take place in the thylakoid membranes of the
  grana
• Excited electrons are passed through an electron
  transport system, producing ATP and NADPH
  (electron carrier)
• Some electrons split water producing oxygen gas,
  hydrogen ions, and additional electrons

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PHOTOSYNTHESIS

• Light-independent reactions
• Occur in the stroma
• Energy from excited electrons is used to make
  glucose, lipids, phospholipids, steroids, and
  other organic molecules from carbon dioxide
• Some of these molecules may also be used to
  produce DNA, RNA, or ATP

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OTHER ASPECTS OF PLANT METABOLISM

• Plants produce carbohydrates, fats, proteins, and
  nucleic acids from the products of photosynthesis
• Can produce some toxins and organic molecules
  that are used as medicines
• May also produce vitamins for themselves and
  other organisms
• Produce oxygen in photosynthesis which is used
  for cellular respiration by all living things

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AUTOTROPHS AND HETEROTROPHS

• All living things need oxygen for cellular
  respiration
• Green plants produce oxygen in photosynthesis,
  but they also use it in cellular respiration
• Produce more than enough and release the rest
• Animals are dependent on plants not only for
  oxygen, but also for essential nutrients to
  maintain metabolism and construct tissues
• Animals supply materials needed by plants and
  vice versa.
• Essential to life on Earth

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Need to Know

• What is cellular respiration?
• What are the 3 steps?
• How much ATP is formed at each step?
• Where in the cell do these occur?
• What is ATP?
• What is photosynthesis?
• What are the 3 steps?
• Where do these processes occur in a cell?

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CHAPTER 6 BIOCHEMICAL PATHWAYS
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AMP
ADP
ATP
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PHOTOSYNTHESIS
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CHAPTER 6 BIOCHEMICAL PATHWAYS
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AMP
ADP
ATP
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PHOTOSYNTHESIS
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