BIOLOGY                                                                                                                                        ENERGY INPUTS AND OUTPUTS

Concepts/Ideas/Facts:

  1. energy drives metabolism
  2. energy can’t be added to or lost – first law of energy
  3. All organized systems tend toward disorder – entrophy – the second law of energy
  4. Energy is continuously being resupplied by the sun
  5. Chlorophyll loses an electron when energized by light
  6. each NADH molecules yields 3 ATP molecules
  7. a total of 38 ATP molecule are produced during respiration: 2 by glycolysis, 2 by the Krebs cycle, and 34 by the electron transport chain.

DEFINITIONS:

1.   ATP - (adenosine triphoshphate) nucleotide consisting of a five-carbon sugar (ribose), a base(adenine), and three phosphate groups (P).  ATP is the main energy carrier for many reactions.  ATP, the energy currency or coin of the cell, transfers energy from chemical bonds to      enedergonic (energy absorbing) reactions within the cell.  When ATP gives up a phosphate group (P), ADP (adenosine diphosphate) forms.  Energy is given off.  ATP forms again when ADP binds to inorganinc phosphate (Pi) or to a phosphate group from a different molecule.

2.  ATP/ADP CYCLE – the breaking apart of ATP into ADP and the regenerating ATP again from  ADP and a Phosphate.  The chemical formula for the expenditure/release of ATP energy can be written as:

a.       ATP à ADP + energy + Pi  - that is Adenosine Triphosphate produces Adenosine  diphosphate + Energy + inorganic phosphate

We can write the chemical reaction for the formation of ATP as:

b.      ADP + Pi + energy ----> ATP  - that is Adenosine diphosphate + inorganic Phosphate +  energy produces Adenosine Triphosphate

Energy is stored in the covalent bonds between phosphates, with the greatest amount of energy in the bond between the second and third phosphate group.  This covalent bond is known as a pyrophosphate group.

3.      PHOSPHORYLATION – the giving up of a phosphate group to other molecules by ATP

4.     ENDERGONIC REACTIONS – end with a net increase in usable energy.   Endergonic means “energy in.”  Anabolic reactions use up energy. They are endergonic. In an anabolic reaction small molecules join to make larger ones.  Condensation reactions that occur in cells are anabolic.

5.      EXEGONIC REACTIONS - end with a net decrease or loss in usable energy.  Exogonic means “energy out”.  Catabolic reactions give out energy. They are exergonic. In a catabolic reaction large molecules are broken down into smaller ones.  Hydrolysis reactions are catabolic.

6.      METABOLISM - All living things must have an unceasing supply of energy and matter.  The transformation of this energy and matter within the body is called metabolism.

7.      CATABOLISM – (Catabolic reactions) Catabolism is destructive metabolism. Typically, in catabolism, larger organic molecules are broken down into smaller constituents. This usually occurs with the release of energy (usually as ATP).

8.      ANABOLISM – (Anabolic reactions) Anabolism is constructive metabolism. Typically, in anabolism, small precursor molecules are assembled into larger organic molecules. This always requires the input of energy (often as ATP).

9.      ELECTRON TRANSFER CHAINS – arrays of enzymes and molecules in membranes that accept and give up electrons in sequence.

10.  CHEMICAL EQUILIBRIUM – reactants and products are in a steady state of back and form equilibrium.

11.  GYCOLYSIS – (means “splitting sugars”) a nine step pathway for the breaking apart of glucose for energy and a six step pathway for building glucose back again.  When the cell needs energy glucose is split into two pyruvate molecules

12.  OXIDATION-REDUCTION REACTIONS or REDUX REACTIONS – the release of energy by electron transfers.

13.  OXIDATION REACTIONS - reactant losses one or more electrons, thus becoming more positive in charge (+)

14.  REDUCTION REACTIONS – reactant gains one or more electrons, thus becoming more negative in charge (-)

15.  RESPIRATION – the process, with the use of oxygen, by which the chemical energy of carbohydrates is transferred to ATP and is immediately made available to the cell.  It is the complete oxidation of glucose.

16.  AEROBIC- with oxygen

17.  ANAEROBIC – without oxygen

18.  FERMENTATION – the extraction of energy from organic compounds without the use of oxygen.  Alcoholic fermentation converts pyruvic acid to ethyl alcohol.  Alcohol fermentation occurs in the cytoplasm.

19.  MNEMONIC – “OIL RIG”   Oxidation is a loss (OIL) of electrons; Reduction is a gain (RIG) of electrons.

20. METABOLIC PATHWAYS – the sequential use and storage of substances in an orderly, enzyme-mediated  reaction.

a.       Biosynthetic pathways, also called anabolic pathways, small molecules are assembled into glucose, starch, proteins and other molecules of higher bond energies. These anabolic pathways need energy and the main biosynthetic pathway is photosynthesis

b.       Degradative Pathways, or catabolic pathways, are exergonic.  They break down large molecules to smaller ones of lower bond energy.  Aerobic respiration, the main one, breaks down glucose to carbon dioxide and water with the release of a large amount of usable energy.

c.       Cyclic Pathways – is a non-linear pathway where the last step regenerates a reactant that is the cycles point of entry

d.      Branched Pathways – reactants are sent to two or more different reaction sequences

                                                                                                                                                     Three Steps in Respiration:

  1. Glycolysis – a nine step, anaerobic process that occurs in the ground substance of the cytoplasm that begins when the six-carbon glucose molecule is broken down to a pair of three-carbon molecules of pyruvic acid (pyruvate).  As the glucose molecule is oxidized, some of its energy is extracted in a series of small, discrete steps and is stored in the phosphoanhydride bonds of ATP.  Biologically, glycolysis maybe considered a primitive process, in that it most likely arose before the appearance of atmospheric oxygen and before the origin of cellular organelles.
  2. Krebs Cycle (citric acid cycle), (tricarboxylic acid cycle -TCA) – occurring in the matrix of the mitochondria and using oxygen, it is the breaking down of the pyruvate molecule into carbon dioxide and water, and the passing of the resulting electrons to the electron transport cycle. It begins with the formation of an organic acid (citrate).
  3. Electron Transport Chain – the final stage of aerobic respiration occurring in the cristae, which involves a series of electron carriers and enzymes embedded in the inner membrane of the mitochondria.  It is a series of biochemical steps by which energy is transferred in steps from a higher to a lower level.  Each step involves a specific electron carrier that has a particular energy level, with the carriers organized in a sequence of decreasing energy.  Thus more energy is released than is required to initiate the next process.                                                        

Steps in ATP Production (pg 108) – ATP is generated from the sequential dismantling of absorbed nutrient molecules in three steps: glycolysis, citric acid cycle (Kreb'sCycle), electron transport chain

  1. Glycolysis – enzyme initiated chemical process occuring first in the cytosol involving 10 separate sequential reactions that break down simple six-carbon sugar molecules, glucose, into two pyruvic acid molecules each of which contains three carbons.  The breakdown of glucose is not very efficient, only yielding two molecules of ATP per molecule of glucose, and most of the energy is still locked up in the pyruvic acid molecule.  The first part of the cylce requires no oxygen (anaerobic).  There is a net gain of 2 ATP molecules.  Each glucose molecule yields two molecules of acetyl-CoA which enters the Krebs Cycle.
  2. Citric Acid Cycle (Krebs Cycle or Tricarboxylic Acid Cycle) – The Citric Acid Cycle consists of a cyclical series of eight separate biochemical reactions directed by enzymes in the mitochondria.  Pyruvic acid produced by glycolysis in the cytosol is transported into the mitochondrial matrix where it is further broken down into a two-carbon molecule, acetic acid, by enzymatic removal of one of the carbon in the form of carbon dioxide (CO2) later removed as waste.  This acetic acid combines with a coenzyme A (a B vitamin) producing the compound acetyl coenzyme A (acetyl Co A).  A hydrogen atom is also release to be used later in the process.  The acetyl Co A, two-carbon molecule combines with oxaloacetic acid, a four carbon molecule forming a six-carbon citric acid molecule.  As the cycle continues the molecules are further modified releasing CO2 which is a waste product and hydrogen (at 4 conversion steps in the cycle) which is used in the electron transfer chain.  These hydrogen are captured by nicotinamide adenine dinucleotide (NHD) and flavine adenine dinucleotide   (FAD) and converted to NADH and FADH2 respectively.  The Krebs cycle produces 2 ATP molecules
  3. Electron Transport Chain (ETC) (respiratory chain) – final stage of aerobic respiration, occurs when NADH and FADH2 enter the electron transport chain, high-energy electrons are extracted from the hydrogen held in NADH and FADH2 in a series of step within the cristae.  As a result both NADH and FADH2 are converted back to NAD and FAD and are now free to pick up more hydrogen atoms released during glycolysis and the citric acid cycle.  The high-energy electrons progressively move to lower and lower energy levels, releasing energy, until they pick up an oxygen and create water.  NAD and FAD serve as the link between the citric acid cycle and the electron transfer chain.  A total of 34 ATP molecules are yield by the electron transport chain.
  4. ATP Synthase – energy enzyme, located on the surface of the inner membrane of the mitochondria that makes ATP by chemiosmosis, which converts ADP + Pi to ATP yielding 32 more ATP molecules for each glucose processed.  ATP is transported out of the mitochondria for use by the cell.  The generation of ATP by chemiosmosis occurs in chloroplasts and mitochondria as well as in some bacteria.

Glycolysis: anaerobic process that occurs in cytosol

  1. C6H12O6 à 2 Pyruvic Acids  + energy  à  2 ADP + energy  à 2 ATP + energy

                                                                                     (Kreb’s Cycle)

  1. each pyruvic acid has 3 carbons each (CH3COCO2H)
  2. if no O2 is available, pyruvic acid turns to lactic acid

Kreb’s Cycle: occurs in matrix of mitochondria and oxygen is required.  It begins where glycolysis

ends.  2 Pyruvic acids enter Kreb’s Cycle.  Pi is inorganic phosphorous.

  1. ADP + Pi à ATP (twice)
  2. As pyruvic acid breaks down NAD, a carrier molecule already in the matrix, picks up hydrogen converting NAD à NADH.  FAD, also a carrier molecule does the same thing, picking up hydrogen but converting to FAD à FADH2.  I ATP is generated per pyruvic acid but overall 2 ATP molecules are generated per glucose molecule! - (because gycolysis produces two pyruvic acids).  CO2 is generated as a waste product.

Electron Transport Chain:  aerobic process that occurs in the mitochondria and inner membrane when an electron (-) is stripped from hydrogen in the Kreb’s Cycle

  1. NADH and FADH2 transport H from Kreb’s cycle to Electron Transport Cycle (ETC)
  2. e- stripped from H makes H+
  3. electron is now passed down to lower and lower energy levels releasing energy
  4. energy is used to bond Pi to ADP to generate ATP (32 times per glucose molecule)
  5. Final e- is accepted by O2 which later combines with H to form H2O

Main Categories of Cell Activities Requiring Energy: (pg32)

  1. Synthesis of New Chemical Compounds – protein synthesis by ER (75% use of ATP)
  2. Membrane Transport – selective transport of molecules across a membrane such as the transport of molecules across the kidney tubules during the process of urine formation. (80% use of ATP)
  3. Mechanical Work – contractions of muscles such as heart or skeletal muscles

Formulas:

Cellular Respiration – C6H12O6  + O2 à CO2  + H2O   +   ATP   +    Heat

                                       (Raw Fuel)                                            (refined fuel)  

Photosynthesis – 6CO2  +  6 H2O à C6H12O6  + 6 O2

                                   (inorganic)              (organic)

ATP WEBSITES                        

http://faculty.clintoncc.suny.edu/faculty/Michael.Gregory/files/Bio 100/Bio 100 Lectures/Enzymes/energy.htm 

http://www.brookscole.com/chemistry_d/templates/student_resources/shared_resources/animations/oxidative/oxidativephosphorylation.html                                     

ATP MOLECULE