Principles+of+Biosynthesis Anabolism:+The+Use+of …crcooper01.people.ysu.edu/3702Ch12-2016.pdf · BIOL 3702: Chapter 12 AY 2015 -2016 Dr. Cooper 2 Photosynthetic+CO 2 Fixation Most&microbescan&incorporate,&or&fix,&CO

BIOL 3702: Chapter 12 AY 2015-2016

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Slide No. 1

Anabolism: The Use ofEnergy in Biosynthesis

BIOL 3702: Microbiology (Spring 2015)Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.

Principles of Biosynthesis

u Anabolism (= biosynthesis) vCreation of more complex molecules from simpler ones, but requires energy input

vCarefully balanced with catabolic processesvEnergy required in terms of ATP is enormous

Slide No. 2BIOL 3702: Microbiology (Spring 2015)Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.

Principles of Biosynthesis (cont.)

u Biosynthesis is shaped by several guiding principles:vAll macromolecules are derived from about 30 small precursors

vMany of the same enzymes used in both catabolism and anabolism

vEnd product regulation is generally more important in anabolic pathways



vTo be efficient, anabolic pathways must operated irreversibly and are usually coupled with the breakdown of ATP

v In eukaryotes, compartmentation permits different pathways to operate simultaneously and independently

vAnabolic and catabolic pathways typically use different co-factors, for example:Ø Catabolism produces NADHØ NADPH used as electron donor for anabolism



u Generation of precursor metabolites is critical step in anabolism


Fig. 12.2


u Carbon skeletons are used as starting substrates for biosynthetic pathwaysvExamples are intermediates of the central metabolic pathways

vMost are used for the biosynthesis of amino acids


BIOL 3702: Chapter 12 AY 2015-2016

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Photosynthetic CO2 Fixation

u Most microbes can incorporate, or fix, CO2via anaplerotic or other pathways

u Only autotrophs use CO2 as a sole carbon source and, therefore, utilize one of three different reductive pathways to do so

u Energy for these pathways comes from photosynthesis or lithotrophy


Photosynthetic CO2 Fixation (cont.)

u Five pathways to fix CO2vCalvin Cycle (reductive pentose phosphate cycle)

vReductive Tricarboxylic Acid Pathway - used by some Archaea

vAcetyl-CoA Pathway - used by acetogens, methanogens, and sulfate reducers

vHydroxypropionate cyclev3-hydroxypropionate/4-hydroxybutyrate pathway


Autrophic CO2 Fixation (cont.)

u Calvin Cycle (reductive pentose phosphate cycle)vPresent in photosynthetic eukaryotes and most photosynthetic prokaryotes

vAbsent in Archaea, some prokaryotic obligate anaerobes and microaerophiles

vOccurs in:Ø Chloroplast stroma (eukaryotes)Ø Carboxysomes (prokaryotes)

Slide No. 9BIOL 3702: Microbiology (Spring 2015)Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr. Slide No. 10BIOL 3702: Microbiology (Spring 2015)

Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.

To view this video, go to Chapter 12 Animations of Prescott's Microbiology Companion Site (9th ed.) located at the following URL: http://highered .mhe du cati on. com/si tes /0 073 40 24 00 /st ude nt _vie w0/i nd ex. ht ml

Autotrophic CO2 Fixation (cont.)

vThree phasesØ Carboxylation

§ CO2 is incorporated into ribulose 1,5-bisphosphate (RuBP;; 5 carbon molecule) to form two molecules of 3-phosphoglycerate (PGA;; 3 carbon molecules)

§ Catalyzed by the enzyme ribulose-1,5-bisphosphate carboxylase

Ø Reduction Phase§ PGA is reduced to glyceraldehyde 3-phosphate§ Requires one molecule of ATP and one molecule of NADPH for this reduction process to occur



Fig. 12.4

The Calvin Cycle

BIOL 3702: Chapter 12 AY 2015-2016

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Ø Regeneration Phase§ RuBP is regenerated via a series of reactions that resemble the pentose phosphate pathway

§ Also generates a number of different carbohydrate structures that can be used elsewhere in the cell

vTotal energy expenditure (provided by photosynthesis or chemotrophy):Ø 2 ATP moleculesØ 3 NADPH molecules



u Summary

Slide No. 14

6 CO2 + 18 ATP + 12 NADPH + 12 H+ + 12 H2O↓

glucose + 18 ADP + 18 Pi + 12 NADP+



Fig. 12.4

The Calvin CycleGluconeogenesis

u Non-photosynthetic microbes synthesize sugars from reduced organic molecules

u Synthesis of glucose using noncarbohydrateprecursors is termed gluconeogenesis

u Gluconeogenic pathway is remarkably similar to reverse glycolysis


Slide No. 17

Gluconeogenesis


Fig. 12.7

Gluconeogenesis (cont.)

u Gluconeogenic pathwayvShares seven (7) enzymes with glycolysisvThree steps are irreversible

u Some sugars are synthesized as nucleotide diphosphates which play a role in polysaccharide formation


BIOL 3702: Chapter 12 AY 2015-2016

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Anaplerotic Reactions

u The demand for intermediates of pathways can lead to a depletion of these compounds, thus disrupting the particular metabolic process, e.g., use of oxaloacetate from the TCA cycle to make amino acids

u Microbes have developed reactions, termed anaplerotic reactions, to replace these lost intermediates


Anaplerotic Reactions (cont.)

u Most microbes will replace TCA cycle intermediates by CO2 fixation - NOT the same as the Calvin Cycle or other pathways that fix CO2 to produce carbohydratesvCO2 is added to another compound that forms an intermediate

vFunctions as a replacement process, not for cellular growth

vMaintains the operation of the TCA cycle


Anaplerotic Reactions (cont.)

u Some microbes use the glyoxylate pathway to maintain the operation of the TCA cycle as well as to grow on two-carbon sources (e.g., acetate)v Essentially a modified TCA cyclev Two key enzymes:

Ø Isocitrate lyaseØ Malate synthase

v Pathway is essential for the survival of some pathogenic microbes in vivo



The GlyoxylateCycle

Fig. 12.24

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Principles+of+Biosynthesis Anabolism:+The+Use+of …crcooper01.people.ysu.edu/3702Ch12-2016.pdf · BIOL 3702: Chapter 12 AY 2015 -2016 Dr. Cooper 2 Photosynthetic+CO 2 Fixation Most&microbescan&incorporate,&or&fix,&CO