Biology Chapter 4 Notes: Energy
Energy: capacity to do work; two types are kinetic and potential energy; can be captured, converted, lost
in the form of heat; can change but never disappear; conversion of energy is not perfectly efficient and
invariably includes the transformation of some energy into heat
Kinetic energy: energy of moving objects
Potential energy: stored energy or the capacity to do work that results from an object's location or
position; ex. water dam; chemical energy (storage of energy in chemical bonds)
Adenosine triphosphate (ATP): must be captured in the bonds of this molecule; free-floating, found in
cells that act like a rechargeable battery; temporarily stores energy that can then be used for cellular
work; ATP connects the timing of energy needed/provided; small sugar molecule (ribose) + adenine + 3
phosphate groups; release of energy = separation of a phosphate; kinetic energy into potential when
phosphate group attaches to ADP
Photosynthesis
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Carbon dioxide + water + sunlight --> oxygen + sugar
Pigments: light-absorbing molecules
light energy (kinetic) made up of packets called photons --> primary photosynthetic pigment
(chlorophyll a) or chlorophyll b, carotenoids --> photons excite the electrons in the chlorophyll
--> electron gains energy, potential energy in chlorophyll molecule increases --> returns to
resting state or passed to another molecule (primary ways energy moves through cells)
"Photo" reactions: happens in the thylakoid; primary electron acceptor grabs them and sends
them to electron transport chain; water molecules are split and oxygen and hydrogen are
released as by-products to replace the electrons sent to transport chain; electrons move
through the chain and energy levels lower; energy powers proton pumps and move hydrogen
ions from stroma to thylakoid; protons rush out of thylakoid with great kinetic energy which can
be used to build ATP; electrons passed to second electron transport chain; in the end, electrons
passed to molecule called NADP+ creating NADPH
”Synthesis" reaction (calvin cycle): 1. fixation: rubisco (most common protein on earth) pluck
carbon from air and fix them to a visible organic (carbon-containing) molecule within the
chloroplast; 2. sugar creation: newly built molecule is chemically modified; phosphate from ATP
added and some high energy electrons from NADPH and creates glyceraldehyde 3-phosphate
(G3P); 3 carbon molecules from carbon dioxide must be fixed into G3P to synthesize six-carbon
sugars (glucose and fructose); 3. Regeneration: other G3P molecules are regenerated into the
original molecule in the chloroplast to which the carbon from CO2 is attached (requires energy
from ATP)
Synthesis of 1 G3P: fix 3 carbon molecules from carbon dioxide; consumes 9 ATP and 6 NADPH
generated in the "photo" reactions
Combating Water Loss
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combating water loss through evaporation: close stomata (pores on underside of leaves that
opens up for carbon and oxygen; although water is lost, carbon and oxygen cannot
enter/release
C4 Photosynthesis: adds extra set of steps to minimize water loss; has enzymes that attract
carbon dioxide strongly; binds to carbon when CO2 concentration is very low; requires more
energy than C3 photosynthesis; oxygen released at night
Carssulacean acid metabolism (CAM): used by cacti, pineapples, fleshy juicy plants that close
stomata during hot dry days; holding molecules store CO2 until needed; slower growth
Cellular Respiration
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oxygen + sugar --> carbon dioxide + water + ATP
glycolysis: splitting of sugar; splits into two molecules called pyruvate (2 ATP used); payoff after
split = 4 ATP + 2 NADH + water
Pyruvate molecule --> passes electrons to NAD+ into NADH; releases carbon dioxide --> the C2O
attaches to coenzyme A into acetyl-CoA --> ready to enter krebs cycle
Acetyl CoA adds to oxaloacetate into 6-carbon molecule --> NADH is made and 2 carbon dioxide
is exhaled --> 4 carbon molecule oxaloacetate is reformed --> ATP is generated --> electrons
passed to NADH and FADH2
ATP built in electron transport chain in Mitochondria
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90% of energy payoff is from NADH and FADH2
interspace membrane is studded with electron carriers (chain); NADH and FADH2 donate
electrons and hydrogen ions enter the intermembrane space; free hydrogen ions form water
and the rest are pushed back up into the mitochondrial matrix with great kinetic energy and
used to build ATP; cyanide prevents electron transport chain to bind with electrons; halting
production of ATP
Other Metabolisms
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acid buildup occurs when bodies are demanded of bursts of energies; oxygen deficiencies begin
and slowdown of ATP production occurs
Cellular resp w/o water: animals accept pyruvate and produce lactic acid while yeast accepts
acetaldehyde and end product is ethanol
Complete Diets
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Sugars: must be separated into simple sugars for glycolisis --> Acetyal-CoA production --> krebs
--> electron transport chain --> energy
Lipids: into fatty acid --> 1. acetyal-CoA
2. --> glycerol --> glycolysis --> acetyal-CoA
Proteins: into carbon compounds --> 1. glycolysis
2. krebs cycle
3. amino group