Biomi 2900 Wk 5

Front 1

Types of phototrophs

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1. photoautotroph
2. photoheterotroph

Front 2

Define: photoautotroph

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1. perform photosynthesis
2. use CO2 as the only source of carbon

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Define: photoheterotroph

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1. perform photosynthesis
2. use compounds other than CO2 as source of carbon (carbohydrates, fatty acids, etc.)

Front 4

Commonalities of all forms of photosynthesis

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1. antenna system
2. reaction center
3. energy carriers
4. electron transport system (electron transferred in a series of oxidation-reduction reactions)

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2 types of photosythesis

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1. oxygenic photosynthesis
2. anoxyenic photosynthesis

Front 6

Define: oxygenic photosythesis

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1. generates O2 as a product
2. done by cyanobacteria, algae, and green plants

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Define: anoxygenic photosynthesis

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1. does not generate O2 as a product
2. largely done by purple and green sulfur bacteria

Front 8

What is photosynthesis comprised of?

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1. light dependent reactions (aka light reactions)
2. light independent reactions (aka dark reactions)

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Define: light reactions

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light energy converted into chemical energy in the form of ATP and NADPH

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Define: dark reactions

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the ATP and NADPH formed in the light reactions reduce CO2 into carbohydrates

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Describe: light reactions

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1. take place along cell membrane
2. purple bacteria and cyanobacteria, light reactions occur on thylakoids (help photon uptake)
3. various pigments are involved (bacteriochlorophylls, chlorophylls, bacteriorhodospin)

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What does photoexcitation lead to?

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photolysis

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Define: photolysis

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the light-driven separation of an electron from a donor molecule

Front 14

Bacteriochlorophylls

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1. primary pigments in anoxygenic photosynthetic bacteria
2. donor molecule

Front 15

chlorophylls

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1. primary pigments in oxgyenic photosynthesizers
2. magnesium chromophore comprises the center of the molecule

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bacteriorhodopsin

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1. unique light absorbing protein found in some Archaea
2. purple pigment is clustered in abundance in the cell membrane
3. doubles as a proton pump (generating a PMF that is converted to chemical energy)

Front 17

What happens when an electron is passed to an ETS?

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NADPH and proton potential is produecd

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Define: antenna complex

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grouping molecules of cholorphyll to maximize light absorption

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niche stratification

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allows different organisms to thrive in various environments via wavelength-specificity of organisms

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Define: reaction center

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cluster of protein complexes and associated pigments in the membrane that catalyze the light reactions

Front 21

Describe process of reaction centers in photosystem I (PS I) and photosystem II (PS II)

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1. Pigments in PS I absorb photons
2. Electrons in PS II generated by splitting of water (In oxygenic photo.) are excited
3. excited electrons flow along ETS
4. as electrons flow, protons concentrate and create a PMF; ATP is made via ATPsythase
5. Again, pigments in PS I are absorbed an electrons are excited
6. Electrons can take either the non-cyclic photophosphorylation (aka Z scheme/pathway) AND cyclic phtotphosphorylation

Front 22

Define: non-cyclic photophosphorylation (aka Z scheme/pathway)

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he electrons consumed in the reduction of NAP+ to NADPH

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Define: cyclic photophosphorylation

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when an adequate amount of NADPH has been accumulated, the electrons are cycled back to PS II; more ATP produced, but no more NADPH is produced

Front 24

Where is PS I found?

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1. chlorobia
2. green sulfur bacteria

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Where is PS II found?

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1. alphaproteobacteria
2. purple non sulfur bacter

Front 26

iClicker Question: T/F - NADPH+ is the terminal electron acceptor for both PSI and PS II

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PS II alone does not have electrons with high enough energy to reduce NADP to NADPH

Front 27

Define: CO2 fixation

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an anabolic process that uses ATP and reducing power to fix CO2 into carbon intermediates for biosynthesis for cellular components - OR "conversion of gaseous CO2 to a solid state"

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What are the four known autotrophic CO2 fixation pathways in prokaryotes?

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1. Calvin cycle
2. reverse (reductase) TCA cycle
3. reductive acetyl Co-A pathway
4. 3-hydroxyproprionate pathway

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Describe: Calvin cycle

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1. most widespread method of CO2 fixation
2. used by oxygenic phototrophic bacteria

Front 30

Describe: reverse (reductive) TCA cycle

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1. essentially the citric cycle run in reverse
2. method done mainly by anaerobic bacteria (green sulfur bacteria)
3. it utilizes 4 or 5 ATPs to fix 4 CO2 molecules

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Describe: reductive acetyl Co-A pathway

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method used by strictly Archaea

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Describe: 3-hydroxypropionate pathway

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method used by green (non-sulfur) bacteria

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Equation for Calvin Cycle

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6 CO2 + 18 ATP + 12 NADPH --> 6 "turns" --> fructose 6 - PO4

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How many times does the Calvin cycle run?

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6 times to produce the 6-carbon sugar

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What are the three steps of the Calvin cycle?

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1. carbon fixation
2. reduction
3. regeneration of BuBP

Front 36

Describe carbon fixation in the calvin cycle

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1. forms 12 PGA from 6 CO2 and 6 RuBP
2. catalyzed by RuBisCO

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Describe: RuBisCO

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1. catalyzes Carbon fixation in Cavin cycle
2. comprised of large and small subunits
3. found exclusivly in chloroplasts, cyanobacteria, and purple bacteria
4. reacts with both CO2 and O2 (when O2 conc. is high, RuBisCo's affinity for CO2 decreases)

Front 38

Describe: reduction steps in calvin cycle

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1. forms G3P via NADPH

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Describe: G3P

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1. considered the first "real" stable intermediate of Calvin cycle
2. intermediate in glycolysis

Front 40

Describe: regeneration of BuBP in Calvin cycle

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1. involves "complex rearrangement intermediates"
2. catalyze the synthesis of RuBP

Front 41

Define: carboxysomes

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organelles found in autotrophic bacteria that contain RuBisCO and concentrate CO2 so that RuBisCO can function most efficiently

Front 42

Other ways CO2 can be incorporated into cell other than Calvin cycle?

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1. reverse TCA cycle
2. 3-hydroxyproprionate cycle
3. reductive acetyl CoA pathway

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Describe: reductive acetyl CoA pathway

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1. CO2 incorporation pathway used by methanogens and anaerobic soil bacteria
2. Two CO2 molecules are reacted to form acetyl grp of acetyl CoA
2. H2 is reducing compound

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Define: catabolic reactions

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breaks down compounds into smaller units to create energy

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Define: anabolic reactions (biosynthesis)

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1. consume energy to build compounds from monomers created by catabolism

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What is required for biosynthesis

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1. essential elements (C, O, H, N)
2. reduction potential
3. energy
4. metabolites
4.

Front 47

Define: metabolite

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intermediate of metabolism necessary for biosynthesis

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Polyketides

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1. group of metabolites
2. synthesized by modular enzymes

Front 49

Describe: fatty acidy synthase complex

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regulates biosynthesis of fatty acids

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Describe: acetyl CoA

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1. gatekeeper of citric cycle
2. product of reductive acetyl CoA pathway

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Describe: dehnhydratase

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adds unsaturation (double bonds) to fatty acid chain

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In what environment is saturated fatty acid maximization preferred?

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1. hot environment
2. rigid cell membrane is favorable

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In what environment is unsaturated fatty acid maximization preferred?

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1. cold environment
2. fluid cell membrane favorable

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Describe: biosynthesis of fatty acid

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1. Acetyl CoA is carboxylated to malonyl CoA and then converted to malonyl ACP
2. Malonyl ACP molecules are added together forming a saturated fatty acid chain
3. nearly B oxidation in reverse
4. process is energy expensive and tightly regulated

Front 55

Describe: stringent response

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1. ribosmal activity stalls
2. due tot lack of nutrients (amino acids)
3. because tRNA cant attach to amino acids and bring them to ribosomes to be sythesized into polypeptides

Front 56

Ways nitrogen can be incorporated into living systems?

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1. direct usage of NH3 via glutamine synthetase or glutamate dehydrogenase
2. organic nitrogen --> NH3 with no change in oxidation state of nitrogen
3. NO3 --> NO2 via nitrate reductase
4. N2 reduced to NH3 by nitrogenase (nitrogen fixation)

Front 57

Describe: Nitrogen fixation

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1. N2 reduced to NH3
2. molybdenum and iron are in enzyme complex
3. oxygen is kept out of complex
4. 24 ATP needed per N2

Front 58

Chemical equation for Nitrogen fixation

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N2 + 8H+ + 8e + 16-24 ATP ===> 2 NH3 + H2 + 16-24 (ADP +Pi)