Exam 2 - Lecture 12 Flashcards
many _____________ _____________ are used as starting substrates for amino acids
precursor metabolites
what atom is a major component of protein, nucleic acids, coenzymes, and more?
nitrogen
what are potential sources of nitrogen used by cells?
- ammonia (NH3)*
- nitrate (NO3-)*
- nitrogen gas (N2)
- *most cells use these
why is ammonia easily incorporated into organic material?
it is more reduced than other forms of inorganic nitrogen
ammonia is added to ______-_____________ under high ammonia conditions to form ______________
alpha-ketoglutarate; glutamate
what enzyme transfers amino groups to carbon skeletons?
transaminases
what enzyme reduces nitrate to nitrite?
nitrate reductase
what enzyme reduces nitrite to ammonia?
nitrite reductase
what enzyme catalyzes the reduction of atmospheric nitrogen (N2) to ammonia?
nitrogenase
what organisms have nitrogenase?
only bacteria and archaea
how many ATP and electrons does it cost the cells to reduce N2 to NH3? what % of cellular ATP can this process consume?
- 16 ATP and 8 electrons
- up to 20% cellular ATP
which two amino acids have sulfur groups?
cysteine and methionine
what is an example of a coenzyme that contains sulfur?
coenzyme A
where is sulfur commonly obtained from?
- external sources
- intracellular amino acid reserves
sulfate (SO4,2-) has to be ________ in order to be incorporated into organic molecules
reduced
what is assimilatory sulfate reduction?
sulfate is reduced into hydrogen sulfide (H2S) and then is used to synthesize cysteine. cysteine is then used to make sulfur contained organic compounds
what is the first step in assimilatory sulfate reduction? how many ATP does it use?
- sulfate activation through the formation of PAPS (phosphoadenosine 5’-phosphosulfate)
- uses 2 ATP
what takes place after sulfate reduction in assimilatory sulfate reduction? how many NADPH are used?
- sulfate in PAPS is sequentially reduced to sulfite (SO3-) and H2S
- 2 NADPH used
what is the final step of assimilatory sulfate reduction?
H2S is used to create cysteine
how do fungi make cysteine? how about bacteria?
- fungi: H2S + serine
- bacteria: H2S+ O-acetylserine
what is transamination? what serves as the source of the amino group?
- the direct addition of amino groups to precursor metabolites to make some amino acids
- glutamate
glutamate + pyruvate = ?
alanine
glutamate + oxaloacetate = ?
aspartate
what is an amino acid biosynthetic pathway?
when the carbon skeleton is first modified in a precursor metabolite and that single precursor gives rise to several amino acids
what four amino acids can be made biosynthetically from oxaloacetate?
threonine, methionine, lysine, and isoleucine
what is a nucleoside?
nitrogenous base + 5 carbon sugar
what is a nucleotide?
nucleoside + phosphate
(base + sugar + phosphate)
which end of DNA has the phosphate? how about the hydroxyl?
- 5’-phosphate
- 3’-OH
what are the purines? are they made of one or two rings?
- adenine and guanine
- 2 joined, cyclic rings
what are the pyrimidines? are they made of one or two rings?
- cytosine, uracil, and thymine
- single ring
how many steps is the purine biosynthesis pathway?
11 complex steps
what is the base of all purine molecules?
ribose-5-phosphate
what is the first purine product formed? all initial products are _______________
- inosinic acid
- ribonucleotides
how are purine deoxyribonucleotides made from ribonucleotides?
by the reduction of the 2’-OH to a 2’-H
what are the first two pyrimidines made?
(deoxy)uridine and (deoxy)cytidine
what are the starting molecules for pyrimidine biosynthesis?
- aspartic acid
- high energy carbamoyl phosphate
- (and bicarbonate and glutamate)
what is the important difference between purine and pyrimidine biosynthesis?
- purine rings are synthesized while attached to ribose
- ribose is added AFTER synthesis of the pyrimidine ring
what % of Earth’s surface is water? what % of that water is freshwater and salt water?
- 70% of the surface
- 97.5% salt, 2.5% fresh
what are important physical factors for microbes in aquatic environments?
- dissolved O2 (most important)
- dissolved CO2
- temperature
- pH
- light penetration
in the very deep ocean, oxygen concentration __________ with depth
increases
in warm environments, oxygen may become _________ a few meters below the surface
limited
the constant exchange of CO2 at the water’s surface is called the:
carbonate equilibrium system
what is high levels of atmospheric CO2 causing in the carbonate equilibrium system? what does this do to the water?
- higher CO2 dissolution into seawater
- it decreases the pH
what is an estuary?
a semi-closed coastal region where a river meets the sea
what is the characteristic salinity profile of an estuary called?
a salt wedge
microbes in estuaries must be able to withstand large changes in salt concentration. what is their salt requirement?
halotolerant
are estuaries nutrient rich or poor?
rich
what is eutrophication? can this lead to algal blooms?
- enrichment of an ecosystem with chemical nutrients, typically compounds containing phosphorus and nitrogen, which can be caused by pollution
- yes
what are harmful algal blooms?
HABs are blooms that occur when a single microbial species (algae or cyanobacteria) grows at the expense of other members of the community
what toxins are released by cyanobacteria into the environment from the algal blooms in Lake Erie?
microcystins
drinking or swimming in algal blooms can cause _________
illness
what are two ways algal blooms harm other members in the community?
- strips all the oxygen from the water
- photosynthesizing microorganisms and plants can’t get light
what is the euphotic zone?
the range of water depth where light penetrates with enough intensity so that the rate of photosynthesis by microscopic autotrophs exceeds the collective rate of respiration
- basically there’s enough light for photosynthesis here
what microbe is the most numerous in marine ecosystems?
virioplankton
