Microbiology-chapter 6 (exam 2) pt3
Regulation of Respiration
Example of feedback inhibition 2 key control points: -In glycolysis Phosphofructokinase is allosterically inhibited by ATP and/or citrate -In pyruvate oxidation Pyruvate dehydrogenase inhibited by high levels of NADH Citrate synthetase inhibited by high levels
The Role of Glutamate in Amino Acid Synthesis - Figure 6.30
Glutamate provides bacteria a mechanism for incorporation of nitrogen into organic material •Glutamate is synthesized in a single-step reaction that adds ammonia to α-ketoglutarate •Transamination can then generate other amino acids
Carbon Fixation
Incorporation of CO2 into organic compounds by chemolithoautotrophs and photoautotrophs •Light-independent reactions do this in photosynthetic organisms •Consumes a great deal of ATP, reducing power •Calvin cycle most common pathway to fix carbon but others are possible
Calvin Cycle
Three essential stages of Calvin cycle •Incorporation of CO2 into organic compounds •Reduction of resulting molecule •Regeneration of starting compound Six "turns" of cycle incorporate 6 CO2 molecules into one molecule of fructose-6-phosphate •Consumes 18 ATP, 12 NADPH per fructose molecule
Light-Dependent Reactions in Anoxygenic Photosynthetic Bacteria pt1
Light reactions in anoxygenic photosynthetic bacteria •Each has single photosystem •Cannot use water as electron donor, so anoxygenic •Bacteriochlorophylls - main light-harvesting pigments •Use electron donors such as hydrogen gas (H2), hydrogen sulfide (H2S), organic compounds
Cyclic and Non-cyclic Photophosphorylation pt 2
Non-cyclic photophosphorylation - produce both ATP and reducing power •Electrons from photosystem II establish proton motive force and are then donated to photosystem I •Photosystem II replenishes electrons by reducing H2O and generates oxygen (process is oxygenic) •Electrons from photosystem I reduce NADP+ to NADPH
Photosynthesis
Photosynthesis: harvest the energy of light power the synthesis of organic compounds from CO2 •Plants, algae, several groups of bacteria General reaction: where X indicates element such as oxygen or sulfur In cyanobacteria and photosynthetic eukaryotic cells the "X" is an atom of oxygen -"12H2X"=12 H2O & "12 X"=6O2 -Referred to as oxygenic because O2 is produced Purple and green bacteria use a molecule such as H2S instead of water -The process is "anoxygenic"
Photosynthesis pt1
Photosynthetic organisms contain pigments to capture light energy; colors due to reflected wavelength •Chlorophylls (plants, algae, cyanobacteria) •Accessory pigments absorb at additional wavelengths Pigments located in photosystems, protein complexes within membranes •In eukaryotic organisms, photosystems are located in chloroplasts
Photosynthesis pt2
Photosynthetic processes are considered in two stages. •The first stage, the light-dependent reactions, captures radiant energy and uses it to generate the following compounds needed to synthesize organic compounds from CO2: •ATP •Reducing power (NADPH or NADH)
Anabolic Pathways—Synthesizing Subunits from Precursor Molecules
Prokaryotes remarkably similar in biosynthesis processes •Synthesize subunits for lipids, amino acids, nucleotides using precursor metabolites formed in the central metabolic pathways •If enzymes are lacking, end product must be supplied •Fastidious bacteria require many growth factors
Aromatic Amino Acids pt2
Then the 7-carbon compound is modified through a series of steps until a branch point is reached -If synthesis proceeds in one direction, tryptophan is produced. -In the other direction, another branch point is reached; from there, either tyrosine or phenylalanine can be made.
Triglycerides (Lipid Catabolism)
-common energy sources -hydrolyzed to glycerol and fatty acids by lipases -glycerol degraded via glycolytic pathway -fatty acids often oxidized via β-oxidation pathway
Chemolithotrophs pt2
Chemolithotrophs extract electrons from inorganic energy sources -Pass electrons to an electron transport chain that generates a proton motive force. -Energy of gradient is used to make ATP *Chemolithotrophs generally thrive in specific environments where reduced inorganic compounds are found. *Thermophilic chemolithotrophs - grow near hydrothermal vents of the deep ocean and obtain energy from reduced inorganic compounds from the vents. *Unlike organisms that use organic molecules to fulfill both their energy and their carbon needs, chemolithotrophs incorporate CO2 into an organic form.
Groups of Chemolithotrophs
Chemolithotrophs fall into four general groups: •Hydrogen bacteria oxidize hydrogen gas. •Sulfur bacteria oxidize hydrogen sulfide. •Iron bacteria oxidize reduced forms of iron. •Nitrifying bacteria include two groups: •one oxidizes ammonia forming nitrite •another oxidizes nitrite producing nitrate
Light-Dependent Reactions in Cyanobacteria and Photosynthetic Eukaryotic Cells
Cyanobacteria, plants and algae: have two types of photosystems (photosystem I and photosystem II) •Work together to raise energy of electrons stripped from water •Both photosystems use chlorophyll a as a reaction-center pigment
Cyclic and Non-cyclic Photophosphorylation pt 1
Cyclic photophosphorylation - used to synthesize ATP, but not reducing power •Photosystem I produces ATP •Reaction-center chlorophyll emit high-energy electrons -Transferred to electron transport chain (ETC) to pump protons across membrane -returned to same reaction-center chlorophylls
Chemolithotrophs pt1
Prokaryotes unique in ability to use reduced inorganic compounds as energy sources Waste products of one organism may serve as energy source for another •Hydrogen sulfide (H2S) and ammonia (NH3) -Produced by anaerobic respiration when inorganic molecules (sulfate, nitrate) serve as terminal electron acceptors -Used as energy sources for sulfur bacteria and nitrifying bacteria
Photosystems - Figure 6.26
Reaction-center pigments donate excited electrons to electron transport chain •The energy of the electrons is used to pump protons across the membrane to generate a proton motive force •An ATPase uses that energy to synthesize ATP •The process called photophosphorylation to reflect its dependence on radiant energy.
Lipid Synthesis
Requires fatty acids and glycerol Fatty acids: 2-carbon units added to acetyl group from acetyl-CoA •Usually 14, 16, or 18 carbon atoms Glycerol: synthesized from dihydroxyacetone phosphate generated during glycolysis
Aromatic Amino Acids pt1
Synthesis of aromatic amino acids such as tyrosine and phenylalanine requires a multistep, branching pathway -Joining of phosphoenolpyruvate (3-carbon) and erythrose-4-phosphate (4-carbon)—to form a 7-carbon compound. -The precursors originate in glycolysis and the pentose phosphate pathway
Protease (Protein and Amino Acid Catabolism)
hydrolyzes protein to amino acids
Deamination
removal of amino group from amino acid -resulting organic acids converted to pyruvate, acetyl-CoA, or -TCA cycle intermediate -can be oxidized via TCA cycle -can be used for biosynthesis -can occur through transamination
Aromatic Amino Acids - Figure 6.31
•Amino acids are feedback inhibitors of enzymes that directs branch to its own synthesis •Amino acids also inhibit formation of original 7-carbon compound •Result is that cell does not make amino acids that are already present
Nucleotide Synthesis
•DNA, RNA initially synthesized as ribonucleotides which can be converted to deoxyribonucleotides •Purines: atoms added to ribose 5-phosphate to form ring •Pyrimidines: ring made, then attached to ribose 5-phosphate
Carbohydrates pt2
•Disaccharides and polysaccharides -cleaved by hydrolases or phosphorylases
Carbohydrates pt1
•Monosaccharides -converted to other sugars thTriat enter glycolytic pathway
Light-Dependent Reactions in Anoxygenic Photosynthetic Bacteria pt2
•Purple bacteria: photosystem similar to photosystem II of cyanobacteria and eukaryotes •Energy of electrons insufficient to reduce NAD+ -Instead expend ATP to use reversed electron transport NAD+ •Green bacteria: photosystem similar to photosystem I -Electrons can generate proton motive force or reduce NAD+