Micro Exam 3 - Nitrogen Fixation, Anabolism: Lipids and Polysaccharides

What are the two ways nitrogen enters biological systems?

directly through premade amino acids and as ammonia attached to glutamate

What is the two step method that nitrogen enters biological systems?

glutamine synthetase pathway

What is glutamine synthetase pathway?

glutamate --(ATP, NH4+)--> glutamine --(NADPH, NH3)--> 2 glutamate

What is the one step method that nitrogen enters biological systems?

glutamate dehydrogenase pathway

What is glutamate dehydrogenase pathway?

α keto-glutamate --(NADPH, NH4+)--> glutamate

What is diazotrophy?

nitrogen fixation to produce ammonia

Energetically, what does diazotrophy require?

4 NADPH and 18 ATP, extremely expensive

What does diazotrophy require?

nitrogenase enzyme

What is nitrogenase?

complex of 2 subunit pairs

What 2 subunit pairs are in nitrogenase?

Fe protein and FeMo protein

What does the Fe protein do?

deliver electron

What does the FeMo protein do?

reduce nitrogen

What is the problem with diazotrophy?

function is disrupted by O2 because it reacts with iron in active site to form rust

What are solutions to O2 reacting in diazotrophy?

anaerobic conditions, extremely rapid respiration, heterocysts

Describe the process of fatty acid biosynthesis.

1 - fatty acid subunits must be activated by attaching a protein (ACP), 2 - malonyl-ACP donates 2 carbons to primer and liberates CO2 and elongates chain by 2 carbons, 3 - chain is reduced twice, 4 - repeat cycle

How do fatty acids vary?

primer and saturation introduction

What are fatty acid primer variations?

acetyl-ACP: even carbon chain, propionyl-ACP: odd carbon chain, isovaleryl-ACP: odd carbon chain with branch on end

What are two possible mechanisms for introducing unsaturation?

skip reduction step or monooxygenase

Explain how skipping the reduction step introduces unsaturation.

reducing enzyme fails at low temperatures so that double bond is preserved during synthesis

Explain how monooxygenase introduces unsaturation.

enzyme is made at lower temperatures and adds oxygen to reintroduce a double bond after chain is completed

Describe the process of polysaccharide biosynthesis.

1 - monosaccharide activation by attaching nucleotides, 2 - polysaccharide polymerization in cytoplasm

Describe the process of extracellular polysaccharide biosynthesis.

1 - NAM activated by UDP, 2 - 5 amino acids attached sequentially to NAM, 3 - NAM-peptide transferred to membrane carrier lipid and lipid carrier becomes new monomer activator, 4 - NAG activated with UDP, 5 - NAG attached to NAM-pentapeptide, 6 - lipid carrier and bound NAM-NAG-pentapeptide are flipped to opposite side of membrane catalyzed by MurJ, 7 - NAG-NAM-pentapeptide polymerized onto existing chain in wall, 8 - pentapeptides crosslinked by PBPs