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all living organisms
take in energy and materials from the environment
the nutritional mode of an organism is based on
what energy source it uses
what carbon source it uses
plants
energy source is light (light energy is converted to chemical energy via photosynthesis)
carbon source is inorganic carbon (CO2 is reduced to form organic compounds, used to make ATP)
eukaryotes
energy source is chemicals taken from the environment (energy is gained from the oxidation of reduced carbon compounds such as glucose)
carbon source is organic, reduced carbon molecules such as glucose (taken from the environment, reduced carbon compounds are used to make ATP)
photosynthesis
carbon dioxide, water light, chlorophyll
carbon dioxide
CO2, enters a plant through stomates in the leaves, moves by diffusion into the leaf cells, and then into chloroplasts
water
h2o, enters a plant through the roots, oxidization occurs (oxygen separates from the hydrogen and is released into the atmosphere)
light
visible (white) light is made up of many different colors (wavelengths)
range from violet to red
each type of light is composed of particles of energy
violet has the shortest wavelength (400 nm, high energy photons)
red has the longest (750 nm, low energy photons)
both colors used in photosynthesis
chlorophyll
photosynthesis begins when light energy is absorbed by photosynthetic pigments
organisms take on the color of the wavelength of light that are not highly absorbed (reflected)
chlorophyll absorbs violet, blue, and red light
several types (a, b, c, d, e)
all have a magnesium atom surrounded by four nitrogen atoms
pigments
grouped within photosystems, each containing 250-400 pigments
most of these serve as antenna pigments ( absorb light energy and pass it on to a special pair of chlorophyll a molecules)
the energy-capturing or light reactions
photochemical (light) reactions of photosynthesis convert light energy into the chemical energy of ATP
the biochemical reactions
the chemical energy produced in the previous reactions is used to reduce CO2 to carbohydrates in a series of steps aka the biochemical reactions
respiration
how cells use sugars (glucose) and an electron acceptor (o2) to make energy in a form (ATP) that can be used to power the cell’s reactions
ATP
adenosine triphosphate, the energy currency
energy stored in the terminal phosphate bond is produced by the breakdown (oxidation) of a glucose molecule
when the ATP molecule itself is hydrolyzed, it releases energy that can be used to drive other reactions
glycolysis
takes place in a series of ten reactions, each catalyzed by a specific enzyme
glucose → atp, nadh, pyruvate
substrate phosphorylation
the production of ATP molecules during glycolysis
a phosphate group is transferred from a high energy substrate molecule to ADP forming ATP
there is a net energy yield of 2 ATPs and 2 NADHs
2 pyruvic acid molecules contain a large amount of potential energy
reaction can’t stop now, because the cell would run out of NAD+ and cell would stop making ATP
for glycolysis to continue, there must be a source of free NAD+, fermentation produces these molecules, this provides the glycolysis pathway with NAD+ when oxygen is not available
anaerobic pathways: fermentation
pyruvic acid can follow several pathways, two are anaerobic
alcohol and lactate fermentation
alcohol fermentation
yeast cells and most plant cells can form ethanol and carbon dioxide
for yeast on grapes: when the sugar is exhausted or when the ethanol content becomes toxic, the yeast cells cease to function… at this point, the alcohol concentration is between 12 and 17 percent
lactate fermentation
lactate is formed by a variety of bacteria, fungi, protists, and animal cells when oxygen is scarce or absent
as lactate accumulates in the muscle cells during exercise, it lowers the pH of the cells and reduces the capacity of muscle fibers to contract, producing sensations of fatigue
cellular respiration
each glucose molecule (C6H12O6) is split (oxidized) and H combines with O2 (reduced) to form h2o
the oxidation of pyruvic acid
the two pyruvates from glycolysis are transferred to the mitochondrial matrix
there they are oxidized, forming NADH, CO2, and Acetyl CoA which enters the Krebs Cycle
a total of 4 NADH molecules have been formed from one glucose molecule so far
krebs cycle
the 2C acetyl group enters the Krebs cycle and joins with a 4C compound (Oxaloacetic acid) to produce a 6C compound
during the krebs cycle, ATP (Substrate Phosphorylation), NADH, FADH2, and CO2 are produced
Electron transport
at this point most of the glucose molecule’s energy is stored in the electrons of the NADH and FADH2 molecules, which have high energy levels
during electron transport these electrons are passed along carrier molecules (grouped into three protein complexes) to the low energy level of oxygen, and combine with protons to form h2o
this energy forms ATO through oxidative phosphorylation
each time a pair of electrons passes from NADH to oxygen, 3 molecules of ATP are formed from ADP and phosphate
each time a pair of electrons passes from FADH2 to oxygen, 2 molecules of ATP are formed
overall energy harvest (respiration)
glycolysis: 2 ATP, 2 NADH (4ATP) = 6 ATP
pyruvic acid to acetyl CoA: 2 NADH = 6 ATP
krebs cycle: 2 ATP, 6 NADH (18 ATP), 2 FADH2 (4 ATP) = 24 ATP
1 glucose total = 36 ATP