bio lesson 8

autotrophs

-converts Sun’s energy to chem energy (ATP) and as chem bonds in inorganic molecules

-prod their own ATP and organic molecules through photosynthesis (plants, algae, bacteria)

heterotrophs

-live on organic molecules prod by autotrophs and survive by converting chem energy into ATP (animals, fungi, protists, prokaryotes)

-can extract the chem energy from organic molecules

cells oxidize organic molecules to extract energy

-all orgs use cell respiration to extract from the chem bonds of organic molecules

-cell respiration involves series of enzyme-catalyzed reactions

1. oxidation: loss of electrons

2. dehydrogenation: loss of protons

harvested electrons undergo a series of redox reactions

-electrons harvested from organic molecules possess energy

-redox reactions transfer electrons and associated energy

1. electrons lose some energy w/ each transfer

2. released energy may be lost as heat or may eventually be converted into ATP

-after multiple redox reactions, energy-deleted electrons are transferred to final electron acceptor molecule to complete harvesting

electron carriers

-cells rely on various electron carriers to facilitate the transfer of electrons harvested from covalent bonds of organic molecules

-transfer often involves cofactors (small chemicals that assist enzymes) working as electron carriers

-all are easily and reversibly oxidized and reduced

-NAD+ accepts 2 electrons and 1 proton to become NADH (reversible, as NADH is able to donate the 2 electrons to a substrate molecule and thereby reduce that other molecules, simultaneously returning the carrier to its oxidized NAD+ state so it can pickup other electrons

-NAD+ accepts a pair of electrons and a proton from an oxidized substrate and is converted to the reduced NADH

-nicotinamide group of NADH is the active part of molecule

-NAD+ to NADH= reduction

NADH to NAD+= oxidation

aerobic respiration of glucose

-final electron acceptor is oxygen

-deltaG= 686 kcal of glucose

-energy must be harvested in small steps, which involve electron carriers (NAD+, NADH)

-allows cells to convert about half of the energy stored in bonds of a glucose molecule into energy in the form of ATP

glucose oxidation

1. glycolysis (cytosol)

2. pyruvate oxidation (mitochondrial matrix)

3. krebs (matrix)

4. ETC and chemiosmosis (inner membrane), where ATP is synthesized

-prokaryotes conduct these reactions in cytosol/plasma membrane

2 phases of glycolysis

-converts 1 glucose to 2 pyruvates

1. energy input in the form of ATP must be supplied by cell

2. energy production: energy is prod in 2 forms, energy input and energy prod

*glycolysis doesn’t require oxygen and the conversion of glucose to pyruvate will occur whether or not oxygen is present

first phase of glycolysis

-glucose is converted to 2 G3P molecules

-generation of glyceraldehyde-3-phosphate (G3P) requires energy input

1. hydrolysis of 2 ATP molecules

2. needed to prime cleavage of glucose backbone

2nd phase of glycolysis

-each G3P molecule is converted to pyruvate

-G3P is oxidized (NAD+ to NADH)

-inorganic phosphate is added to G3P

-subsequently each Pi (4 total) will be transferred to ADP

-prod of glycolysis

1. 2ATP (net)+ 2NADH

ATP synthesis during glycolysis

-occurs via substrate level phosphorylation

-direct transfer of Pi from another molecule (PEP) to ADP, creating ATP

-the reaction is carried out so that the energy in the phosphate bond is maintained and will release the standard amt of energy when the ATP molecule is hydrolyzed to drive other chem reactions

pyruvate oxidation during aerobic respiration

-occurs in:

1. mitochondrial matrix of eukaryotes

2. plasma membrane of prokaryotes

3. catalyzed by pyruvate dehydrogenase

-each pyruvate is used to generate

1. 1 CO2

2. 1 NADH

3. 1 acetyl-CoA (fed into krebs)

krebs

-oxidizes the acetyl group generated by pyruvate oxidation

-occur in matrix of mitochondria

-pathway of 9 steps divided into 3 parts

1. acetyl-CoA + oxoloacetate yields citrate

2. citrate rearrangement and decarboxylation (2 CO2 released)

3. regeneration of oxaloacetate

-for each Acetyl-CoA entering:

1. release 2 CO2

2. reduce 2 NAD+ to 3 NADH

3. reduce 1 FAD (electron carrier) to FADH2

4. prod 1 ATP

5. regenerate oxoloacetate