Ch. 12 - Anabolism Flashcards
Principles of Anabolism
- these reactions are endergonic (requires input of chemical or light energy) **energy from catabolism is used for biosynthetic pathways**
- catalyzed by enzymes
- reduction reactions (most biosynthesis involves reductions)
- biosynthetic pathways are regulated by enzymes
Regulation:
cells would rather transport molecules in from exogenous source than make them (endogenous source). exogenous molecules provide more material usually and is more energy efficient because a cell doesn’t have to expend energy producing molecules it has to breakdown
- regulation includes regulating enzyme activity and regulating enzyme synthesis and amount of enzyme
- enzymes also synthesize monomers, polymers, and other cell structures
Anabolism of cell structures
Energy from catabolism is used for biosynthetic pathways:
- Using a carbon source and inorganic molecules, organisms synthesize new organelles and cells
- A great deal of energy is needed for metabolism
- energy for anabolic reactions is usually coupled to ATP breakdown to release energy for biosynthesis
Precursor Metabolites in Biosynthesis
Generation of precursor metabolites is critical in anabolism
- carbon skeletons are used as starting substrates for biosynthetic pathways
- these carbon skeletons are usually intermediates of the metabolic pathways like intermediate molecules of glycolysis and Tricarboxylic acid cycle
- most of these intermediates are used for the biosynthesis of amino acids
Biosynthesis of monosaccharides and polysaccharides
key molecule of carbohydrate is glucose
Sources of glucose:
- exogenous organic source (transport into cell) for heterotrophs
- synthesize glucose from CO2 via the Calvin Cycle for autotrophs or chemolithoautotrophs
Gluconeogenesis- synthesis of glucose from other molecules when exogenous glucose might not be as available (oxaloacetate can help synthesize an intermediate of glycolysis called phosphoenolpyruvate, which can help synthesize glucose. **functional reserve of glycolysis**
-ENERGY STORAGE polysaccharides (starches) and structural polysaccharides (peptidoglycan) are snythesized from different activated forms of glucose (intermediates)
Fixation of CO2 by autotrophs
carbon fixation= synthesis of organic molecules from CO2
-occurs in photolithoautotrophs
Possible carbon fixation cycles:
- Calvin Cycle (most common)
- Reductive TCA cycle
Calvin Cycle
- used by most autotrophs to fix CO2
- also called the reductive pentose phosphate cycle
- in eukaryotes, this process occurs in stroma of choloroplasts
DARK REACTION (does not require light and uses products from light reaction for glucose synthesis)
3 phases:
- Carboxylation phase
- Reduction phase
- Regeneration phase
OVERVIEW: CO2 is added to 5-carbon molecule of RuBP. this makes an unstable molecule that breaks up into two separate 3-carbon molecules with a phosphorus attached to both (phosphoglycerate). Using ATP and NADPH from the light reactions of the organism, phosphoglycerate is reduced by these molecules in a series of reactions that result in glyceraldehyde 3-phosphate. Some glyceraldehyde molecules are used to synthesize glucose, while others are used to regenerate the Calvin Cycle. the cycle needs to turn many times to produce alot of glucose because for every molecule of CO2 added to the Calvin Cycle, only one carbn is donated to glucose synthesis.
Biosynthesis of Amino Acids and Nucleotides
Chemoorganoheterotrophs can use exogenous or endogenous amino acids, chemolithoautotrophs and photolithoautotrophs use only endogenous sources
- all microbes synthesize their own nucleotides (endogenous source) for “safety” reasons
- often involves long, multistep pathways
Amino Acid biosynthesis
- carbon skeletons used in biosynthesis come from intermediates of glycolysis or Tricarboxylic acid cycle
- the amino group typically comes from inorganic nitrogen source obtained from the environment (ex. ammonia-NH3) and is incorporated by enzymes like glutamine dehydrogenase
Nitrogen assimilation in amino acid biosynthesis
-nitrogen addition to carbon skeleton is an important step to make an amino acid
potential sources of nitrogen: NH3, NO3, N2 from the environment (most cells use ammonia or nitrate)
-ammonia is easily incorporated into organic material because it is the more reduced form of inorganic nitrogen
Ammonia incorporation into carbon skeletons
ammonia (NH3) is more reduced form of N and can be directly assimilated into carbon skeletons by different enzyme activity like glutamate dehydrogenase (GDH) and glutamine synthetase
-once incorporated into a carbon skeleton, nitrogen can be transferred to other carbon skeletons by transaminase enzyme
Nitrate reduction paired with ammonia assimilation
- used by bacteria to reduce nitrate to ammonia and then incorporate it into an organic form (carbon skeleton)
- nitrate reduction to nitrite; catalyzed by nitrate reductase
- reduction of nitrite to ammonia catalyzed by nitrite reductase
Nitrogen fixation
- reduction of atmospheric nitrogen (N2) to ammonia **used to make amino group**
- catalyzed by the enzyme nitrogenase
**this occurs only in bacteria and archaea**
Sulfur assimilation into carbon skeletons to help for certain amino acids
sulfur is needed for:
- synthesis of amino acids cysteine and methionine
- sulfur is incorporated into the synthesis of several coenzymes
sulfur is obtained from:
- external sources (exogenous)
- intracellular amino acid reserves (endogenous)
Use of sulfate as a sulfur source
Sulfate = main inorganic sulfur source for assimilation process
Assimilatory sulfate reduction:
- sulfate is reduced to H2S and then used to synthesize cysteine
- cysteine can then be used to form sulfur containing organic compounds
Synthesis of Purines, Pyrimidines, and Nucleotides
(purines and pyrimidines are the nitrogenous bases of nucleotides)
-microbes synthesize their own purines and pyrimidines
Purines:
-cyclic nitrogenous bases consisting of 2 joined rings (adenine and guanine)
Pyrimidines:
-cyclic nitrogenous bases consisting of a single ring
Nucleoside= nitrogenous base + pentose sugar (pentose sugar is either ribose or deoxyribose)
Nucleotide= nucleoside + phosphate
Phosphorus Assimilation into organic material
- phosphorus is found in nucleic acids, proteins, phospholipids, ATP, and some coenzymes
- most common phosphorus source is inorganic phosphate (PO43-)
Inorganic Phosphate (Pi):
- incorporated through the formationof ATP by
1. photophosphorylation
2. oxidative phosphorylation
3. substrate-level phosphorylation
Purine biosynthesis
- complex pathway in which several different molecules contribute parts to the final purine skeleton
- initial products are ribonucleotides, but deoxyribonucleotides are formed from the reduction of ribonucleotides (removal of the second hydroxyl group) and replacing it with a hydrogen
- different purine nucleotides start off as inosinic acid and differentiate into adenonise or guanine
Pyrimidine Biosynthesis
Begins with aspartic acid and high energy carbamyol phosphate
-ribonucleotides are initial products, and deoxyribonucleotide forms of Uracil and Cytosine are formed by reduction of ribose to deoxyribose
Lipid synthesis
PICTURE: phospholipid
Lipids: (strictly hydrophobic)
- major required component in cell membranes
- most bacterial and eukaryal lipids contain fatty acids
Fatty Acids: (long hydrocarbon tails with polar acid heads)
-synthesized then added to other molecules to form other lipids such as triglycerides and phospholipids
PICTURE: triglyceride
Fatty Acid Synthesis
synthesized from intermediates like acetyl-CoA and reducing power molecules like NADPH
- during synthesis, the Coenzyme A is replaced by an Acyl carrier protein (ACP)
- requires input of 1 ATP and HCO3- (bicarbonate) to change acetyl-CoA and then the new compound will keep being reduced by NADPH and carbons and hydrogens will keep being added by NADPH adding hydrogens so water can be released and compound can keep being modified until the carbon chains become most stable at CH2 and CH3. Malonyl ACP is also added to contiuned synthesis of the fatty acid
Triacylglycerols (triglycerides) and phospholipids
-eukaryotic microbes and some gram + bacteria can store carbn and energy as triglycerides
(made from fatty acids and glycerol phosphate)
Phospholipids:
- major components of eukaryotic and bacterial cell membranes
- synthesized from phosphatidic acid by forming CDP-diacylglycerol, then adding an amino acid
