Microbiology - Chapter 15 - Biosynthesis

biosynthesis, or anabolism

building of complex biomolecules

biosynthesis, or anabolism, requires

- essential elements

- reduction

- energy

biosynthesis, or anabolism, essential elements

C, H, O, N, and other essential elements

biosynthesis, or anabolism, reduction

reducing agents such as NADPH

biosynthesis, or anabolism , energy

coupling reactions to ATP hydrolysis, NADPH oxidation, or ion flow down a transmembrane concentration gradient

what does many substrates for biosynthesis arise from?

glycolysis and the TCA cycle

succinyl-CoA molecules

serve as the foundation of several amino acids, as well as vitamin B12

glycerol 3-phosphate

provides the glyceride backbone of lipids

pyruvate

provide the backbone of c=several amino acids with aliphatic side chains

are glucose catabolism and the TCA cycle reversible?

no

the synthesis for glucose

gluconeogenesis

gluconeogenesis

reverse most of the enzymes of glycolysis

in biosynthesis spending energy, what do enzymes couple synthetic reactions to?

reactions releasing energy

what are the several strategies that the genomic and energy costs of biosynthesis lead microbes to evolve?

- regulation

- competition

- genome and cooperation

what role does carbon dioxide fixation play?

essential roles in soil, aquatic and wetland ecosystems

CO2 fixation requires

tremendous energy input and a large degree of reduction to incorporate hydrogen atoms

CO2 fixation removes

our atmosphere's most potent greenhouse

a major form of carbon sequestration

CO2 fixation removing our atmosphere's most potent greenhouse

calvin cylce responsible for

the majority of earths biomass

reductive pentose phosphate cycle

calvin cycle

reductive pentose phosphate cycle organisms

- oxygenic phototrophic bacteria

- chloroplasts of algae and plants

- facultatively anaerobic purple bacteria

- some lithoautotrophic bacteria

intermediates of calvin cycle first identified using

14^C radiolabeling and paper chromatography

calvin cycle condenses

CO2 and H2O with the intermediate ribulose 1,5-biphosphate

ribulose 1,5-biphosphate

derived from the pentose phosphate cycle

rubisco

ribulose 1,5-biphosphate carboxylase/oxygenase

the reaction of pentose phosphate cycle is catalyzed by

rubisco

most abundant enzyme on earth

rubisco

three main phases of each turn of the calvin cycle

1. carboxylation and splitting:6C -> 2[3C]

2. reduction of PGA to G3P

3. regeneration of ribulose 1,5-biphosphate

What is the result of ribulose 1,5-biphosphate condensing with CO2 and H2O?

Formation of a 6C molecule

What happens to the 6C molecule immediately after it forms?

It splits into two 3-phosphoglycerate (PGA) molecules

carboxylation and splitting:6C -> 2[3C] reactions catalyzed by

rubisco

What molecule is phosphorylated in the reduction of PGA to G3P?

The carboxyl group of PGA

What is the source of the phosphate group in the reduction of PGA to G3P?

ATP

What molecule is reduced to form G3P in photosynthesis?

PGA

What molecule is used as a reducing agent in the reduction of PGA to G3P?

NADPH

What happens to one out of every six G3P molecules during regeneration of ribulose 1,5-biphosphate

It is available for biosynthesis of sugars and amino acids.

What happens to the other five G3P molecules during regeneration of ribulose 1,5-biphosphate

They enter a series of reactions that regenerate three molecules of ribulose 1,5-bisphosphate.

why is concentrating CO2 an important problem

CO2 diffuses readily through phospholipid membranes

where do many organisms contain the rubisco comlpex?

within carboxysomes

carboxysome structures

polyhedral

what does carboxysome take up?

bicarbonate (HCO3-)

what happens immediately after carboxysome take up bicarbonate (HCO3-)

converted to CO2 by carbonic anhydrase

after converted to CO2 by carbonic anhydrase

the CO2 is then fixed by rubisco

alternative CO2 fixation pathway

the reductive, or reverse, TCA cycle

what enables the assimilation of small amounts of CO2

reversible amounts of TCA cycle

regeneration steps of TCA cycle

anaplerotic reactions

example of anaplerotic reactions

PEP +CO2 -> oxaloacetate

what allows the reduction of CO2 to regenerate acetyl-CoA and build sugars

some bacteria and archaea having the entire TCA cycle functions in reverse

what does the reductive, or reverse TCA cycle use?

4-5 ATPs to fix four molecules of CO2 and generate one molecule of oxaloacetate

how is reductive, or reverse, TCA cycle reduction (addition of 2H+ + 2e-_ performed?

by NADPH or NADH and by reduced ferredoxin (FdH2)

what is the reductive acetyl-CoA cycle used by?

anaerobic soil bacteria, autotrophic sulfate reducers, and methanogenic archaea

are are two CO2 molecules condensed through in the reductive acetyl-CoA pathway

converging pathways to form the acetyl group of acetyl-CoA

what is an intermediate of two CO2 molecules condensed through in the reductive acetyl-CoA pathway converging pathways to form the acetyl group of acetyl-CoA

carbon monoxide

reductive acetyl-CoA pathway reducing agents

H2 instead of NADPH

Why is anaerobic photosystem II unable to directly reduce NAD(P)

to NAD(P)H?

Its antenna complex only absorbs low energy infrared wavelengths

Which of the following is the reducing cofactor typically used in

biosynthesis

NADPH

Which of the following is NOT a strategy used by microbes to control the energetic costs of biosynthesis

Gene duplications to allow for redundancy in biosynthetic pathways

does rubisco catalyze the addition of CO2 to xylulose 5 phosphate?

no

How many turns of the Calvin cycle does it take to feed one

molecule of glyceraldehyde-3-phosphate into the biosynthesis of

glucose

6

Nitrogen fixation is found only in a few organisms and is tightly

regulated because

nitrogen fixation is energy-intensive

The level of nitrogen fixation is highest under what conditions?

low levels of O2 and low levels of NH4+

most bacteria assimilate NH4+ into which two amino acids?

glutamate and glutamine