Chapter 12 Flashcards
Anabolism
Energy from catabolism is used for biosynthetic pathways
using a carbon source and inorganic molecules, organisms synthesize new organelles and cells
antibiotics inhibit anabolic pathways
a great deal of energy is needed for anabolism
Anabolism 2
Turnover
continual degradation and resynthesis of cellular constituents by nongrowing cells
Metabolism is carefully regulated
for rate of turnover to be balanced by rate of biosynthesis
in response to organism’s environment
Precurser metabolites
Generation of precursor metabolites is critical step in anabolism
Carbon skeletons are used as starting substrates for biosynthetic pathways
examples are intermediates of the central metabolic pathways
most are used for the biosynthesis of amino acids
heterotrophs
exogenous organic source, or can sometimes synthesize it from other organic molecules
autotrophs and chemolithotrophs
synthesize glucose from CO2 via the Calvin Cycle (or other)
gluconeogensis
synthesis of glucose from other molecules
Synthesis of glucose from phosphoenolpyruvate
Phosphoenolpyruvate can be synthesized from oxaloacetate
Calvin cycle
Used by most autotrophs to fix CO2
Also called the reductive pentose phosphate cycle
In eukaryotes, occurs in stroma of chloroplasts
In cyanobacteria, some nitrifying bacteria, and thiobacilli, may occur in carboxysomes
inclusion bodies that may be the site of CO2 fixation
Consists of 3 phases
the carboxylation phase
the reduction phase
the regeneration phase
Three ATPs and two NADPHs are used during the incorporation of one CO2
Takes a total of 18 ATP and 12 NADPH for one glucose
Carboxylation phase
Catalyzed by the enzyme ribulose 1.5-bisphosphate carboxylase, also called ribulose bisphosphate carboxylase/oxygenase (rubisco)
Rubisco catalyzes addition of CO2 to ribulose-1,5-bisphosphate (RuBP), forming 2 molecules of 3-phosphoglycerate
Reduction and Regeneration Phases
3-phospho-glycerate reduced to glyceraldehyde 3-phosphate
RuBP regenerated
Carbohydrates (e.g., fructose and glucose) are produced
The hydroxypropionate bi-cycle
used by some archaeal genera and the green nonsulfur bacteria (also anoxygenic phototrophs)
The 3-Hydroxypropionate/4-Hydroxybutyrate Pathway
First described in 2007 in an archeon
Uses 3-hydroxypropionate cycle
Uses unique reaction to produce 3-hydroxybutryate
Gluconeogenesis
Synthesis of glucose and related sugars from nonglucose precursors
glucose, fructose, and mannose are gluconeogenic intermediates or made directly from them
galactose is synthesized with nucleoside diphosphate derivatives
bacteria and algae synthesize glycogen and starch from adenosine diphosphate glucose
Functional reversal of glycolysis, but the two pathways are not identical
7 enzymes shared
4 enzymes are unique to gluconeogenesis
synthesis of monosaccharides
Several sugars are synthesized while attached to a nucleoside diphosphate such as uridine diphosphate glucose (UDPG)
Synthesis of Polysaccharides
Also involves nucleoside diphosphate sugars
e.g., starch and glycogen synthesis
ATP + glucose 1-P ADP-glucose + PPi
(glucose)n + ADP-glucose (glucose)n+1 + ADP
Amino acid biosynthesis
Carbon skeletons come from intermediates of glycolysis or citric acid cycle (slide 42)
The amino group typically comes from inorganic nitrogen source obtained from the environment (e.g., NH3) and is incorporated by glutamine dehydrogenase or glutamine synthetase
Nitrogen assimilation
Nitrogen addition to carbon skeleton is an important step
potential sources of nitrogen: ammonia, nitrate, or nitrogen from the environment
most cells use ammonia or nitrate
ammonia nitrogen (universal source) easily incorporated into organic material because it is more reduced than other forms of inorganic nitrogen
Ammonia Incorporation into Carbon Skeletons
Ammonia N can be directly assimilated by
transaminase activity from one aa to another
glutamate dehydrogenase
glutamine synthetase-glutamate synthase systems
Once incorporated, nitrogen can be transferred to other carbon skeletons by transaminases
Assimilatory nitrate reduction
Used by bacteria to reduce nitrate to ammonia and then incorporate it into an organic form
Nitrate reduction to nitrite catalyzed by nitrate reductase
Reduction of nitrite to ammonia catalyzed by nitrite reductase
nitrogen fixation
Reduction of atmospheric nitrogen to ammonia
Catalyzed by nitrogenase
found only in bacteria and archaea
Mechanism of nitrogenase activity
Occurs in 3 steps to reduce N2 to 2 molecules of NH3
Requires large ATP expenditure
Once reduced, NH3 can be incorporated into organic compounds
sulfar assimilation
Sulfur needed for synthesis of amino acids cysteine and methionine synthesis of several coenzymes Sulfur obtained from external sources intracellular amino acid reserves (-SH)
sulfate = main (universal) inorganic sulfur source
assimilatory sulfate reduction
sulfate reduced to H2S and then used to synthesize cysteine
cysteine can then be used to form sulfur containing organic compounds
purines
cyclic nitrogenous bases consisting of 2 joined rings
adenine and guanine
pyrimidines
cyclic nitrogenous bases consisting of single ring
uracil, cytosine, and thymine
nucleoside
nitrogenase base pentose sugar
