40. Anabolism

Question 1

how are catabolic and anabolic reactions coupled?

Answer 1

• catabolic reaction furnish energy necessary to drive anabolic reactions
• ATP made during catabolic processes used in cellular function and synnthesis of new cellular components
  – Lipids: cell membranes
  – amino acids: proteins/enzymes
  – purines and pyramidines: building blocks of DNA/RNA

Question 2

what is anabolism?

Answer 2

• polymerisation of building blocks into macromolecules
• rate of synthesis regulated
  – resources not expended on unncessary products
  – maintain orderly growth
• biosynthetic polymerisation reactions have requirement for energy input
  – pathways involve both ATP and reducing power

Question 3

what are the general principles governing biosynthesis?

Answer 3

• macromolecules synthesised from limited simple structural units (monomers)
  – saves genetic storage capacity, raw materials, energy
• many enzymes used both catabolism and anabolism
  – saves raw materials, energy
• some enzymes function one direction only
  – separate enzymes to catalyse two direction allows independent regulation
• breakdown of ATP coupled to certain reactions
  – anabolic pathways operate irreversibly
  – free energy released during breakdown of ATP drives synthesis reactions
• catabolic/anabolic pathways use different co-factors
  – catabolic generate NADH
  – NADPH electron donor in biosynthetic reactions
• catabolism/anabolism physicall separated in cell
  – compartmentalised/localised to certain regions

Question 4

what are the role of lipids?

Answer 4

• principle form of stored energy
• major constituents of cell membrane
• eg. pigments, cofactors, detergents etc…

Question 5

what type of lips are used?

Answer 5

• saturated
  – not one C=C
• monosaturated
  – one C=C
• polyunsaturated
  – more than 1 C=C

-most contain fatty acids / their derivatives
– monocarboxylic acids with long alkyl chains

Question 6

how are fatty acids synthesised?

Answer 6

• catalysed by fatty acid synthase complex
  – with acetyl-CoA and malonyl-CoA substrates and NADPH e- donor
  — acetyl-CoS formed during carbohydrate breakdown
  — malonyl-CoA product of carboxylation of acetyl-CoA
• acetate and maonate first transferred from coenzyme A to acyl carrier protein (ACP)
• synthase adds 2 C at a timw to growing chain
  – 2 stage process
  – requires 1 ATP, 2 NADPH

Question 7

what are the stages of fatty acid synthesis?

Answer 7

• malonyl-ACP reacts with fatty acyl-ACP
  – yields CO2 and fatty acyl-ACP thats 2 C longer
• Beta-keto group from condesation reaction is removed (3 step process)
  – two reductions and a dehyration

Question 8

how are lipids important in the cell membrane?

Answer 8

• phospholipids major component of eukaryotic/bacterial cell membranes
• complex lipids synthesised from products of:
  – fatty acid biosynthesis
  – glycolysis
  – amino acid biosynthesis

Question 9

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Answer 9

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Question 10

what is amino acid synthesis?

Answer 10

• AA derived from intermediates in glycolysis, citric acid cycle, pentose phosphate pathways
• nitrogen enters by way of glutamate or glutamine
  – derived from citric acid cycle intermediate (alpha-ketoglutarate)
• simple AA pathways
  – direct transamination
• complex AA pathways
  – multiple steps, branched
  – allow synthesis of family related AAs from single precursor

Question 11

what are nucleic acids?

Answer 11

• precursor of NAs are nucleotides
  – composed of nitrogenous base joined to phosphorylated 5-C sugar
• nitrogenous bases:
  – pyrimidines and purines, clyclic-N-containing molecules
  – joined by pentose sugar (de/oxyribose)
  – nucleoside with one/more phosphate groups joined to sugar (nucleotide)
• ribonucleotides are precursors for RNA synthesis
• ribonucleoties converted to deoxyribonucleotides
  – monomeric building blocks of DNA

Question 12

what are the types of nucleic acids?

Answer 12

• A
• C
• G
• T
• U

Question 13

what is the structure of nucleic acids?

Answer 13

• sugars and phosphate for alternating chaine
  – joined by phosphodiester bonds
  – backbone of moleccule
• RNA typically single-stranded
  – DNA double stranded bound by H bond

Question 14

what is petidoglycan?

Answer 14

• major component of bacterial cell walls
  – structure and osmotic pressure
• large and complex
  – ,ong polysaccharide chains made of alternating N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG) residues
  – pentapeptide chains attached to NAM
  – polysaccharide chains connected through pentapeptides/interbridges

Question 15

how is peptidoglycan synthesised?

Answer 15

• two carries
  – uridine diphosphate (UDP) involve in cytoplasmic rxns
  – bactoprenol phonsphate (undecaprenyl pyrophosphate) fxns at plasma membrane
• 3 stages
  – cytoplasm UDP derivatives of NAM and NAg formed. Amino acids added sequentially to UDP-NAM to form pentapeptide chain
  – cytoplasmic membrane, NAM-pentapeptide transferred to second carried which fxns as transport lipid. intermediate formed called Lipid I. UDP transfers NAG to bactoprenol-NAM-pentapeptide complex (Lipid I) generating Lipid II. Repeat unit flipped external side of cell membrane, incorperated into growing peptidoglycan chain by penicillin-building proteins (PBPs)
  – periplasmic space, PBPs catalyse transglycosylation and transpeptidation rxns. Result in polymerisation and corsslinking of glycan strands via flexible peptides.
• vulnerable to disruption by antimicrobial agens
  – inhibition at any stage weakens cell wall and result in somotic lysis