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Fall 2023 > Cell bio- Photosynthesis > Flashcards

Cell bio- Photosynthesis Flashcards

1
Q

what is the ultimate source of metabolic energy in plants and some bacteria?

A

photosynthesis

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2
Q

how many stages are in photosynthesis?

A

2: 1. light reactions
2. dark reactions

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3
Q

light reaction

A

energy
absorbed from sunlight drives the synthesis of ATP &
NADPH (a coenzyme similar to NADH)

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4
Q

dark reactions

A

ATP
& NADPH drives the synthesis of carbohydrates from
CO2 & H2O

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5
Q

T/F: Sunlight is absorbed by photosynthetic pigments, the
most abundant of which are the chlorophylls, in which
electrons are excited to a higher energy state

A

true

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6
Q

what is the arrangment of pigments in chloroplast

A

photocentric , each contains hundred of pigment molecules.

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7
Q

what is the role of each pigment molecules?

A

acting as antennae to absorb light and transfer energy of excited e to chlorophyl molecules that serves as a reaction center

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8
Q

chlorophyll

A

a reaction center

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9
Q

pheophytin

A

membrane carrier

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10
Q

what does pheophytin do ?

A

High-energy electrons are then transferred to an electron transport chain through a
membrane carrier called Pheophytin, which couples their energy to the synthesis of
ATP & NADPH.

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11
Q

what are the proteins involved in photosynthesis?

A

4 multi-protein complexes in thylakoid membrane of chloroplast:
Photosystem I & II: absorb light and transfer energy to reaction center chlorophylls

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12
Q

photosystems I & II

A

absorb light & transfer energy

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13
Q

T/F: in mitochondria electron transfers are coupled to the transfer of protons
into the thylakoid lumen, establishing a proton gradient across the membrane

A

true

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14
Q

what is the most important differences between e transport in chloroplast and mitochondria?

A

the energy derived from sunlight during photosynthesis is
converted into both ATP & NADPH, the latter of which is required for the conversion
of CO2 into glucose.

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15
Q

how does electron transfer through photosystems?

A

Electrons are transferred sequentially between the 2 photosystems, with
photosystem I (PS I) acting to generate NADPH & photosystem II (PS II) acting to
generate the proton gradient that drives the synthesis of ATP

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16
Q

T/F: The pathway of electron flow starts at PS II, where the energy derived from
absorption of photons is used to split H2O molecules to molecular oxygen (O2) &
protons in the thylakoid lumen that starts to establish a proton gradient

A

true

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17
Q

what happens in PSII?

A

the energy derived from
absorption of photons is used to split H2O molecules to molecular oxygen (O2) &
protons in the thylakoid lumen that starts to establish a proton gradient

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18
Q

what are the carriers that high energy electrons can go through?

A

Plastiquinone (PQ)( lipid soluble)

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19
Q

Plastiquinone

A

carries electrons from photosystem II to the Cytochrome bf complex,
within which electrons are transferred to the peripheral membrane protein
Plastocyanin (PC) & 4 additional protons are pumped into the thylakoid lumen

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20
Q

what happens in cytochrome of complex during photosynthesis?

A

electrons are transferred to the peripheral membrane protein
Plastocyanin (PC) & 4 additional protons are pumped into the thylakoid lumen

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21
Q

Plastocyanin

A

peripheral membrane protein, carries the electrons to PS I, where the absorption of additional photons
raises their energy level

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22
Q

PSI

A

the absorption of additional photons
raises their energy level in this system.
uses these high-energy electrons to reduce NADP+ to NADPH, in which the
electrons are carried through a series to Ferredoxin (Fd)

23
Q

Ferredoxin (Fd)

A

a small protein on the
outside of the thylakoid membrane that complexes with the enzyme NADP
reductase, which transfers electrons to NADP+ to reduce it into NADPH

24
Q

T/F: The ATP & NADPH generated by PS I & PS II are used in the Calvin cycle to convert
CO2 into glucose

A

true

25
Q

cyclic electron flow

A
  1. second electron transport pathway
  2. the light
    energy harvested at PS I is used for ATP synthesis rather than generating NADPH.
  3. e is transfered to cytochrome bf complex
26
Q

what happens to electrons in cytochrome bf complex?

A

they are coupled with the
establishment of a proton gradient across the thylakoid membrane.

27
Q

T/F: electrons after losing energy with lower energy are returned to PSI by Plastocyanin after establishing H gradient

A

true

28
Q

T/F: Electron transfer from PS I can thus generate either ATP or NADPH, depending on
the metabolic needs of the cell.

A

true

29
Q

for each pair of electron transported how many protons and atp are yielded?

A

2 Protons at PS II, 4 are trasferred at Cytochrome bf complex, making 1.5 atp

30
Q

T/F: Cyclic electron flow has a lower yield, corresponding to 1 ATP per pair of electrons
from the 4 protons transferred across the membrane at the Cytochrome bf complex

A

true

31
Q

where does the dark reaction occur?

A

stroma of chloroplst

32
Q

what happens druing dark reactions?

A

utilize the ATP &
NADPH produced from the
light reactions to drive the
synthesis of glucose in a
series of reactions known as
the Calvin cycle

33
Q

how many ATPs are needed for calvin ? how many NADPH ?

A

18 ATP, & 12 NADPH for each molecule of glucose synthesized

34
Q

T/F: 2 electrons are needed to
convert each molecule of
NADP+ to NADPH, thus 24
electrons must pass through
the electron transport chain,
which also generates the 18
ATPs that are required.

A

true

35
Q

how does each can be obtained? amino acid , glycerol, glucose

A

amino acid: derived from the breakdown
of proteins
glycerol: produced from the
breakdown of lipids
glucose: (gluconeogenesis)
usually starts with lactate
(produced from anaerobic
glycolysis

36
Q

glucogenesis

A

involves
the conversion of pyruvate to
glucose (essentially the
reverse of glycolysis).

37
Q

T/F: Glucose is synthesized from
2 molecules of pyruvate at a
cost of 4 ATP, 2 GTP & 2
NADH.

A

True

38
Q

how does glucose stored in animals & plants?

A

glycogen & starch, in the form of polysaccharides

39
Q

T/F: synthesis of polysaccharides requires energy.

A

true

40
Q

why does the formation of a glycosidic
bond must be coupled to an energy-yielding reaction?

A

the condensation reaction linking 2 sugars together is
energetically unfavorable,

41
Q

how to fix the unfavorably energetic condensation reaction?

A

use of nucleotide sugars as
intermediates in the synthesis of polysaccharides

42
Q

what is the nucleotide sugar process?

A
  1. Glucose is first phosphorylated in an ATP-driven reaction to form
    Glucose-6-Phosphate, which is then converted to Glucose-1-
    Phosphate.
  2. Glucose-1-Phosphate reacts with Uridine
    Triphosphate (UTP), yielding UDP-Glucose,
    which is an activated intermediate that
    donates its glucose residue to a growing
    polysaccharide chain in an energetically
    favorable reaction
  3. chemical energy in the form of ATP &
    UTP drives the synthesis of polysaccharides
    from simple sugars
43
Q

how does lipids made?

A

series of reactions during which coupled to the expenditure
of energy (in the form of ATP) & reducing power (in the form of NADPH)

44
Q

How does fatty acids are synthesized?

A

by the
stepwise addition of 2-C units
derived from Acetyl-CoA to a
growing chain, with each addition
requiring the expenditure of 1 ATP
& 2 NADPH

45
Q

where does fattty acid biosynthesis occurs?

A

in the cytosol of eukaryotic cells, the
major product of which is the 16-C
fatty acid palmitate

46
Q

T/F: The principal components of cell
membranes are then synthesized
from fatty acids in the endoplasmic
reticulum

A

True

47
Q

how does organisms perform nitrogen fixation?

A

Some bacteria can use atmospheric N2 by a process call Nitrogen fixation, in whch
N2 is reduced to ammonia (NH3) at the expense of energy in the form of ATP.

48
Q

how does most bacteria, fungi, & plants can use nitrate to perform nitrogen fixation?

A

most
bacteria, fungi & plants can use nitrate (NO3-), which is a common constituent of soil,
by reducing it to NH3 via electrons derived from NADH or NADPH

49
Q

how to make organic compound from NH3?

A

synthesis of the amino acids
Glutamate (Glu) & Glutamine
(Gln), which are derived from the
citric acid cycle intermediate α-
Ketoglutarate.

50
Q

how Gln & Glu help with synthesis?

A

serve as
donors of amino groups during the
synthesis of the other amino
acids, which are also derived from
central metabolic pathways
including glycolysis & the citric
acid cycle

51
Q

where can we get raw material for amino acid synthesis?

A

raw material for amino acid
synthesis is thus obtained from
glucose, with the amino acids
being synthesized at the cost of
both energy (ATP) & reducing
power (NDAPH)

52
Q

protein biosynthesis

A
  • Protein polymerization requires energy because peptide bond formation is energetically unfavorable.
  • Amino acids undergo activation before being utilized in protein synthesis, similar to polysaccharide synthesis.
  • A gene specifies the unique sequence in which amino acids are assembled into proteins.
  • The nucleotide sequence of a gene dictates the protein’s amino acid sequence through the process of translation with messenger RNA as a template.
  • Amino acids are first bonded to specific tRNA molecules in an ATP-dependent reaction.
  • The amino acid is then added to the growing peptide chain’s C terminus, expending 2 GTP for each addition.
53
Q
A

Fall 2023 (15 decks)

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