ch 10 bacterial metabolism Flashcards
aspects of metabolism common to all organisms
- life obeys the laws of thermodynamics
- the energy cells obtain from their environment is most often conserved as ATP
- oxidation-reduction (redox) reactions play a critical role in energy conservation
- the chemical reactions that occur in cells are organized into pathways
- each reaction of a pathway is catalyzed by an enzyme or a ribozyme
- the functioning of biochemical pathways is regulated
three major types of work
chemical work - synthesis of complex molecules
transport work - take up of nutrients, eliminate wastes, and maintain ion balances
mechanical work - cell motility and movement of structures within cells
substrate level phosphorylation
mechanisms for making ATP using molecules such a phosphoenolpyruvate (PEP) as a source of the phosphoryl group
phosphate transfer potential
anility to donate a phosphoryl group to other molecules
- ATP is high
electron transport chain (ETC)
system of electron carriers membrane-bound and organized
electron carriers
located in plasma membranes and intracytoplasmic membranes of bacterial and archaeal cells
localized in the internal membranes of mitochondria and chloroplasts in eukaryotic cells
- NAD, NADP, FAD, FMN, CoQ, cytochromes, nonheme iron proteins, ferredoxin
biochemical pathways
sets of chemical reactions performed by organisms that convert a starting substrate into one or more products
can be linear, cyclic, branching
metabolite flux
rate of turnover of a metabolite (rate at which a metabolite is formed and then used)
apoenzyme
protein component of an enzyme
cofactor
nonprotein component of an enzyme
holoenzyme
the complete enzyme consisting of the apoenzyme and its cofactor
prosthetic group
if the cofactor is tightly or covalently attached to the apoenzyme
coenzyme
if the cofactor is loosely attaching and can dissociate from the apoenzyme after products have been formed
six classes of enzymes
- oxidoreductase: oxidation-reduction reactions
- transferase: reactions involving the transfer of chemical groups btw molecules
- hydrolase: hydrolysis (break down) of molecules
- lyase: breaking of C-C, C-O, C-N and other bonds by a means other than hydrolysis
- isomerase: rearranges molecules to isomer form
- ligase: joining of two molecules using ATP (or the energy of other nucleoside triphosphates)
enzyme activity is significantly impacted by:
- substrate conc
- pH
- temp
competitive inhibitor
directly competes with binding of substrate to catalytic site and prevents the enzyme from forming product
noncompetitive inhibitor
binds enzyme at site other than active site
changes enzyme’s shape so that it becomes inactive or less active
ribozymes
catalytic RNA molecules
functions:
- splicing of pre-rRNA
- splicing of mitochondrial rRNA and mRNA
- splicing of chloroplast tRNA, rRNA and mRNA
- splicing of viral mRNA
metabolism
important for conservation of energy and materials
maintenance of metabolic balance despite changes in environment
3 major mechanisms:
- metabolic channeling
- regulation of the synthesis of a particular enzyme
- direct controlling of the activity of enzymes
metabolic channeling
influences pathway activity by localizing metabolites and enzymes to specific parts of a cell
uses compartmentation - the distribution of enzymes and metabolites among separate cell structures or organelles
posttranslational regulation
direct stimulation or inhibition of the activity of critical enzymes rapidly alters pathway activity, occurs after the enzyme has been synthesized
irreversible (cleavage) and reversible (allosteric regulation, covalent modification)
allosteric enzymes
an enzyme whose activity is altered by the noncovalent binding of a small molecule (allosteric effector) at a regulatory site separate from the catalytic site; effector binding prompts a conformational change in the enzyme’s catalytic site, causing enzyme activation or inhibition
covalent modification of enzymes
reversible on and off switch, usually occurs through the addition or removal of a particular chemical group
advantages:
- respond to more stimuli in varied/sophisticated ways
- regulation of enzymes that catalyze covalent modification adds second level of regulation
feedback inhibition/end product inhibition
ensures balanced production of a pathway end product
pacemaker enzyme - catalyzes the slowest or rate-limiting reaction in the pathway
- each end product regulates its own branch of the pathway
- each end product regulates the initial pacemaker enzyme
isoenzymes - different forms of an enzyme that catalyze the same reaction
