bacterial metabolism - notes and lecture Flashcards
how does bacterial metabolism compare with eukaryotic metabolism?
in general, the same - but we’re focusing on glucose metabolism
what occurs in glycolysis?
glucose is oxidized to pyruvate
how does glycolysis allow for energy generation?
transfer of electrons from the glucose allows for production of ATP via direct, substrate-level phosphorylation
other electrons transfered to NAD+ to make NADH
what is the molecular equation for the formation of NADH?
NAD+ + 2e- + H+ –> NADH
what is the energy requirement and production of glycolysis?
for every mole of glucose, 2 moles ATP consumed, 4 moles of ATP produced, and one equivalent of NADH if formed from NAD+
what is the tricarboxylic acid cycle?
liberates reducing equivalents that drive ATP formation via oxidative phosphorylation
what is the glyoxylate shunt?
similar to krebs cycle but lacks many krebs cycle enzymes
consumes acetyl CoA, which is generated from acetate
goes from icoselate to malate
what is the major product when microbes grow on FA?
acetate (this pathway generally absent in mammals)
describe the electron transport chain in bacteria.
NADH donates electrons
transfer of electrons through electron transport chain converts energy of electrons into a proton gradient
proton gradient used to make ATP
what is the terminal electron receptor in the electron transport chain?
in aerobic respiration = O2
O2 + 2e- => H2O
in some bacteria, can respire anaerobically - use terminal electron acceptor other than O2, such as NO3-
what is oxidative phosphorylation? where does it occur?
production of ATP by electron transport chain process
in mammalian cells happens in mitochondria
in bacteria occurs across cytoplasmic membrane
when does fermentation occur? what is the process?
when there’s a lack of O2 => ETC and TCA cycles “back up” => some of the pyruvic acid made from glucose during glycolysis is reduced using NADH => NAD+ regeneration and fermentation product
how does fermentation produce energy?
ATP made by transfer of high-energy phosphate to ADP
no respiratory chain involved
via substrate-level phos only
how do the different forms of energy production compare in terms of efficiency? what are the equations for these processes?
aerobic respiration yields more energy per mole of glucose than fermentation does aerobic respiration: glucose + 6O2 --> 6CO2 + 6 H2O -deltaF = 688,000 cal fermentation: glucose --> 2 lactic acid -deltaF = 58,000 cal
what is the most simple fermentation pattern?
lactic acid fermentation
direct reduction of pyruvic acid by NADH and lactic dehydrogenase enzyme
what is the role of NADH in respiration and fermentation?
in respiration: donates its electrons to teh ETC in cytoplasmic membrane => NAD+ and proton gradient => ATP generation
in fermentation: NADH donates electrons to carbon-based substrate to generate fermentation product that’s excreted - NAD+ generated, but no additional ATP made in this step
which types of phosphorylation make ATP in respiration and in fermentation?
in respiration, oxidative phos
in fermentation, substrate level pho
what happens to the carbon from the growth substrate in respiration and fermentation?
in respiration, either as CO2 or assimilated into cellular material - nearly completely oxidized
in fermentation - reduced fermentation products in order to regenerate NAD+
what is the advantage of lactic acid production?
resulting low pH => discourages growth of competing microbes
where are lactobacilli found in the human body and what is their biological role?
in high numbers in vaginal tract and intestine
produce lactic acid => low pH
thought to be particularly important in protecting against yeast infections (candida albicans)
how do vaginal lactobacilli levels change over the course of a woman’s life?
prepubertal and post menopausal women don’t have them - vagina pH is neutral at these times
how are lactobacilli involved in food production?
ferment foods, such as saurkraut, yogurt, cheeses
what types of fermentation do clostridia do?
butyric acid fermentations, butanol-acetone fermenations
make butyric acid and acetic acid, CO2 and H2 from fermentation of sugars
may also form small amounts of EtOH and isopropanol
how would you identify the presence of clostridium in tissue?
hydrogen gas or butyric acid in tissue
what is the biological importance of butyric acid?
in animal models, seems to have protective effect against intestinal pathogens
what bacteria do propionic acid fermentation?
corynebacteria, propionibacterium and bifidobacterium
what are the products and reactants of propionic acid fermentation?
ferments lactate to acetic acid, CO2 and propionic acid
what food is propionic acid fermentation used to make?
swiss cheese - distinct flavor of propionate and acetate and holes due to entrapment of CO2
what is the biological significance of propionibacterium?
found in deeper follicles in dermis
implicated in pathogenesis of acne
propionic and butyric acid thought to keep other microbes from growing in these niches
what bacteria are included in the enterobacteriaceae group?
e coli and salmonella
what type of fermentation do enterobacteriaceae do?
mixed acid fermentations
what are the products and reactants of mixed acid fermentation?
pyruvic acid is converted to a two-carbon compound to formic acid
formic acid converted to CO2 and H2 gas if enzyme present
how does bacterial metabolism impact the host?
lactic acid fermentation can change pH - important in maintaining the pH of the vagina
gas gangrene - O2 limitation => microorganisms can grow => produces gasses
what are obligate aerobes?
many can’t grow in presence of O2 and require reducing conditions for growth
cannot grow via fermentation and can only respire with O2 as the terminal e- acceptor
found in gut, abscesses, deep puncture wounds
lack enzymes to detoxify reactive O2 species, which can damage many cell components
no ECT enzymes either
what are facultative anaerobes?
organisms that have both a functional respiratory system and fermentative capacity
growth occurs regardless of O2 availability
many, common, versatile pathogens are facultative anaerobes
what is catalase?
hemoprotein enzyme present in most aerobes which decomposes H2O2 into H2O and O2 gas
obligate anaerobes don’t have it
what is superoxide dismutase?
breaks down superoxide = highly reactive free radical reactive form of O2, formed by flavoenzymes
2 O2- + 2H+ –> H2O2 + O2
anaerobes don’t have it
what are aerotolerant anaerobes?
no functional respiratory system capable of oxidative phos
growth by fermentation exclusively
indifferent to O2 so can grow in air or without air
what are microaerophiles?
require low concentrations of O2 - 5%
what occurs in ethanol fermentation?
pyruvic acid is converted to CO2 and ethanol using NADH and alcohol dehydrogenase
what is the stickland reaction?
specialized fermentation by clostridia where energy is generated by fermentation of pairs of AA
one AA is the electron donor and other is electron acceptor
under what conditions do facultative anaerobes grow better?
more ATP generated during respiration than during fermentation so grow better aerobically than anaerobically
why do obligate anaerobes require reducing conditions for growth?
many have respiratory-like enzymes with flavins = electron carriers - produce H2O2 when O2 is present
results in reactive O2 species from the H2O2 that damage DNA and proteins
therefore need reducing conditions to prevent cell damage since they don’t have catalase or superoxide dismutase
where are anaerobic regions in the host? where can anaerobes grow in the body?
mouth, urinary tract
surface tissue also because there’s other bacteria present of the host tissues are using up all of ht eO2
anaerobes can also grow in the presence of O2 if there’s reducing agents
discuss the use of carbohydrates by bacteria (which bacteria are more likely to use them, which ones are more likely to be used)
most microbial pathogens use glucose as growth substrate
enteric organisms in intestine generally good at using carbs
can use lactose if have enzyme to cleave it, since it’s a disaccharide
how would you determine if a strain could ferment a certain substrate?
use pH indicators and gas detection systems - if there’s a change, it’s fermenting that substance