BIO 103 JMU McMullen Exam 2 - topic 6

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