Chapter 2 - Cellular Respiration Flashcards
Glucose
glucose contains about 2800 kJ/mol of free energy that is slowly released in small redox reactions
converting ADP to ATP temporarily stores 31 kJ/mol of this energy
the energy then gets used for
active transport
synthesis of macromolecules
mechanical work
Gibb’s free energy
predicts the amount of useful energy released by a reaction
positive change in G = non-spontaneous and endergonic
negative change in G = spontaneous and exergonic
Reaction coupling
in metabolism, non-spontaneous reactions happen routinely
to do this, spontaneous reactions are coupled with non-spontaneous ones
as long as the overall change in G is negative, both reactions will proceed
ATP hydrolysis releases just the right amount of energy to power metabolic processes
more = inefficient, less = ineffective
Glycolysis
occurs in the cytoplasm of all organisms and is oxygen independent
requires the input of 2 ATP, but produces 4 ATP (per glucose)
consists of ten reactions grouped into 4 stages
4 stages of glycolysis
mobilization
cleavage
oxidation
ATP generation
Mobilization
glucose (6 carbons) gains potential energy
it is phosphorylated twice with the input of 2 ATP
Cleavage
the product of mobilization (fructose -1,6 - biphosphate) is split in half
two molecules of PGAL are formed (3 carbons each)
Oxidation
a pair of high energy electrons (and a proton) are removed from PGAL
these are used to reduce NAD+ to NADH
ATP Generation
each molecule is then converted to pyruvate
in the process, 2 ATP are generated from each by substrate level phosphorylation
substrate level phosphorylation = coupled reaction where, in this case, a phosphate is added to ADP
Free energy of glycolysis
all exergonic reactions require activation energy, in this case 2 ATP are invested
the first several steps of glycolysis increase the free energy of glucose
the largest release of energy is the oxidation
there are two smaller releases of energy during the production of ATP
Problem with glycolysis
glycolysis depletes the cell’s NAD+ reserves
the cell then requires other metabolic processes to regenerate NAD+
aerobic conditions = oxidative respiration
anaerobic conditions = fermentation
Mitochondria
made up of outer membrane, inner membrane, intermembrane space, and mitochondrial matrix
the folds in the inner membrane are called “cristae”
Oxidative decarboxylation of pyruvate (step 1)
transition step between glycolysis and Krebs cycle
step 1 = pyruvate enters mitochondria
Oxidative decarboxylation of pyruvate (step 2)
in mitochondrial matrix, pyruvate molecules are decarboxylated to form CO2 and an acetyl group
the acetyl group is added to the carrier molecule coenzyme A, forming acetyl-CoA
this step also reduces a molecule of NAD+ to NADH (per pyruvate)
Oxidative decarboxylation of pyruvate (step 3)
acetyl-CoA molecule (2 carbons) binds to oxaloacetate (4 carbons) to make citrate (6 carbons), the first substrate of Krebs cycle
coenzyme A is then released to go fetch another acetyl group