Cellular Energy
The First Law of Thermodynamics
• first law of thermodynamics– Energy can be transferred and
transformed, but it cannot be created or destroyed
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
The Second Law of Thermodynamics
• second law of thermodynamics: – Every energy transfer or transformation
increases the entropy (disorder) of the universe
During every energy transfer or transformation, some energy is unusable, and is often lost as heat
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 8-3
(a) First law of thermodynamics (b) Second law of thermodynamics
Chemicalenergy
Heat CO2
H2O
+
Cell Energy
• Energy is essential to life• All living organisms must be able to
produce energy, store energy and use energy
• Cells need a a quick source of energy
• Cellular energy is stored in chemical bonds of the ATP molecule
ATP
• ATP = Adenosine triphosphate• Adenosine molecule with 3
phosphate groups attached
Adenosine P P P
Fig. 8-8
Phosphate groupsRibose
Adenine
ATP
• The charged phosphate groups act like the positive poles of two magnets, they repel each other
• Energy is contained in the bond that holds the phosphate molecules to the adenosine
• When a bond breaks, energy is released resulting in ADP (adenosine diphosphate)
• Refer to pg 229 fig 9.2
An organism’s metabolism transforms matter and energy, subject to the laws
of thermodynamics
• Metabolism is the totality of an organism’s chemical reactions
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Enzyme 1 Enzyme 2 Enzyme 3
DCBAReaction 1 Reaction 3Reaction 2
Startingmolecule
Product
A metabolic pathway begins with a specific molecule and ends with a product. Each step is catalyzed by a specific enzyme
Organization of the Chemistry of Life into Metabolic Pathways
• Catabolic pathways release energy by breaking down complex molecules into simpler compounds– Cellular respiration, the breakdown of
glucose in the presence of oxygen, is an example of a pathway of catabolism
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• Anabolic pathways consume energy to build complex molecules from simpler ones– The synthesis of protein from amino acids
is an example of anabolism
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Photosynthesis
• Absorbing light energy and converting it into stored chemical energy (plants & algae)
• Principal product = glucose (O2 – major by-product)
• Takes place in chloroplast
Photosynthesis cont.
• Sun – ultimate source of energy
• Because photosynthesis is the essential step between solar energy and life – it is one of the most important biological processes.
Photosynthesis
• To use the energy solar energy, plant cells must trap light energy and store it in a form that is readily usable by the cell (ATP)
• Because light is not available 24 hours a day, the plant must have some way to store energy for later use photosynthesis
Photosynthesis
• Photosynthesis happens in two phases– Light dependent reaction
• Conversion of light energy into chemical energy
• Produces ATP – ATP immediate use by the plant
– Light independent reaction• Uses ATP to produce glucose
– Glucose - stored energy for later use
Chemical equation for photosynthesis
chlorophyll
CO2 + H2O + light energy glucose + H2O + O2
Chlorophyll a
6CO2 + 12H2O + light energy C6H12O6 + 6O2 + 6H2OMost of us don't speak chemicalese, so the above chemical equation
translates as:six molecules of water plus six molecules of carbon dioxide produce
one molecule of sugar plus six molecules of oxygen
Chloroplast• Chloroplast – cell organelle where
photosynthesis occurs• Composed of Thylakoids in stacks
(Grana), with space around (Stroma)• Chlorophyll is found in the membranes of
the thylakoids
Chlorophyll
• A green-colored pigment• Primary catalyst of photosynthesis• There are at least 4 different types
of chlorophyll (a, b, c, d)• Found in Chloroplasts
Structure of Chloroplast
• Thylakoid is the structural unit of photosynthesis. Thylakoids are stacked like pancakes in stacks known collectively as grana. The areas between grana are referred to as stroma.
• Chlorophyll is found in the grana
Light Dependent Reaction AKA:Photo Phase
• Step 1: Light energy is absorbed and energizes a chlorophyll molecule
• Step 2: Water molecules are split– Photolysis: breaking apart of a water molecule
by energized chlorophyll
• Step 3: Oxygen is released• Step 4: Hydrogen is bonded to hydrogen
acceptor (NADP)• Step 5: ATP molecule is made (energy
is stored in ATP)
Biology, Sixth Edition
Chapter 8, Photosynthesis: Capturing Energy
The Electron Transport Chain and Chemiosmosis
Light Independent Reaction AKA: Dark Phase
• Step 1: CO2 is bonded to RuBP– RuBP (ribulose biphosphate) – 5 carbon sugar with 2 phosphates– Resulting 6-carbon sugar is unstable and breaks to form 2
molecules of PGA (phosphoglyceric acid)– PGA is a 3-carbon sugar with a phosphate attached to it
• Step 2: PGA is converted to PGAL– PGA receives hydrogen and is energized by energy and
phosphate from and ATP molecule
• Step 3: Water is given off• Step 4: PGAL is converted to
glucose
Biology, Sixth Edition
Chapter 8, Photosynthesis: Capturing Energy
The Calvin Cycle:Phases 1 & 21. Carbon uptake
– Adds carbon dioxide to 5C ribulose bisphosphate (RuBP)
– Catalyzed by RUBISCO; ribulose bisphosphate carboxylase
2. Carbon reduction phase– Citrate is made and broken
to form phosphoglycerate (PGA)
– PGA is rearranged and phosphorylated by ATP
– NADPH reduces the backbone further to form glyceraldehyde-3-phosphate (G3P)
Biology, Sixth Edition
Chapter 8, Photosynthesis: Capturing Energy
The Calvin Cycle: Phase 3
3. Reformation of RuBP:– G3P is rearranged,– & phosphorylated – With further
investment of ATP… – To make RuBP, a
bisphosphorylated compound
• Alternatively, – G3P is shuttled out of
the cycle to produce glucose and other carbohydrates elsewhere
Biology, Sixth Edition
Chapter 8, Photosynthesis: Capturing Energy
Partition of Function in the Chloroplast
• The light-dependent reactions (the harvesting of light) occur on thylakoid membranes
• The carbon fixation reactions (formation of carbohydrate) occur in the stroma
Conditions for photosynthesis
• Adequate supply of light• Temperature affects the rate of
photosynthesis– Proper temperature for photosynthesis
varies from plant to plant
• Lack of water will cause a plant to stop photosynthesis
• Cell’s ability to absorb sufficient CO2
Classification of organisms according to how they obtain
energy• Autotrophs
– “self-feeders” (producers) – organisms that make their own food (photosynthesis)
– All green plants, certain bacterial and protozoa
• Heterotrophs– “other-feeders” (consumers) – organisms
that must obtain their nutrition from source outside themselves
– Animals, humans, fungi, most bacteria
Biology, Sixth Edition
Chapter 8, Photosynthesis: Capturing Energy
Engelmann’s Experiment: 1883
• Engemann sought to determine the wavelengths of light most important for production of oxygen
• He illuminated a strand of Spyrogyra (a green alga) with the spectrum of light from a prism while observing through a microscope
• Aerobic bacteria were attracted to the regions of high oxygen production: i.e. regions of photosynthesis
Aerobic bacteria
Biology, Sixth Edition
Chapter 8, Photosynthesis: Capturing Energy
Absorption vs. Action Spectra• Chlorophyll appears green because it absorbs most
strongly in the red and blue.• The action spectrum is the result of the interaction of
accessory pigments with chlorophyll.
Absorption curves: chlorophylls a & b The action spectrum of photosynthesis
Cellular Respiration
Cellular Respiration
• Glucose is produced during photosynthesis and is used in cellular respiration
• Cells need energy– Cells obtain the needed energy by
subjecting glucose to a chemical process that is very similar to burning
A Comparison of burning and Cellular Respiration of
sugar• Both give off water and CO2
• Both require oxygen• Both require activation energy• As the glucose is “burned” the energy
that it contains is released for the use by the cell, just as the burning of wood releases heat energy
• This process of burning food to release energy from it is called cellular respiration
Cellular Respiration
• The breaking down of a food substance into usable cellular energy in the form of ATP
Aerobic Cellular Respiration
• Basically, cellular respiration is the opposite of photosynthesis (they are not the reverse of each other)
• Aerobic Cellular respiration breaks down glucose to form water, carbon dioxide and energy
Cellular Respiration Equation
C6H12O6 + 6 O2 6 CO2 + 6 H2O and
energy
As a result of respiration, energy is released from the chemical bonds
found in complex organic molecules (food).
Aerobic Cellular Respiration
enzymes• Glucose + oxygen ATP (energy) + water + carbon
dioxide
enzymes
• C6H12O6 + 6O2 38ATP + 6H2O + 6CO2
• Respiration takes stored chemical energy and converts it to a ready-to-use chemical energy (ATP)
Three phases of aerobic cellular respiration
• Glycolysis– Requires an input of glucose and ATP– Breaks glucose into 2 smaller molecules– Takes place in the cytoplasm– Doesn’t require oxygen– Net gain of 2 ATP
• Citric Acid Cycle (Krebs Cycle)– Produces 3CO2, and hydrogen– Occurs in the mitochondria– Net gain of 2 ATP
• Electron Transport Chain– Requires an input of hydrogen and oxygen– Occurs in the mitochondria– Forms water– Forms 34 ATP
Efficiency of cellular respiration
• Aerobic cellular respiration of glucose traps approximately 50-60% of the energy in the glucose molecule– This breakdown of sugar is one of the most
efficient energy processes know
• Cars – only 20% of energy available in the fuel is used, most of the rest radiates as heat
Two types of cellular respiration
•Aerobic Requires oxygen
Most cells carry on aerobic cellular
respiration
All three Respiration steps
•AnaerobicDoes not require
oxygen
Some bacteria and fungi
Glycolysis only
Anaerobic Cellular Respiration
• Some cells exist in environments that do not have oxygen available
• Many bacteria in the lower layers of swamps, lakes, or the ocean do not have oxygen
• Cellular fermentation: the breakdown of food (usually glucose) without oxygen– Produces only 2 ATP
Fermentation
• Uses only Glycolysis. • An incomplete oxidation - energy
is still left in the products (alcohol or lactic
acid).
• Does NOT require O2
• Produces ATP when O2 is not available.
Two Types of Cellular Fermentation
• Lactic acid fermentation– Formation of lactic acid from glucose– Bacteria that form yogurt and cottage cheese
• Alcoholic fermentation– The formation of alcohol and CO2 from glucose
– Preformed by yeast cells (baking evaporates the alcohol of bread dough and CO2 causes dough to rise)
Lactic Acid Fermentation
• Done by human muscle cells under oxygen debt.
• Lactic Acid is a toxin and causes soreness and stiffness in muscles.
Strict vs. Facultative Respiration
• Strict - can only carry out Respiration one way… aerobic or
anaerobic.• Facultative - can switch respiration
types depending on O2 availability. Ex - yeast
Importance of Respiration• Alcohol Industry - almost every society has a fermented beverage.
• Baking Industry - many breads use yeast to provide bubbles to raise the
dough.
Matching
Sugar Cane GinBarley SakiGrapes TequilaJuniper Cones VodkaAgave Leaves BeerRice WinePotatoes Rum
Comparing Photosynthesis and Cellular respiration
• Photosynthesis– Food accumulated– Energy form sun
stored in glucose– CO2 taken in– O2 given off– Goes on only in light
– Occurs only in presence of chlorophyll
• Cellular Respiration– Food broken down– Energy of glucose
released
– CO2 given off
– O2 taken in
– Goes on day and night
– Occurs in all living cells
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