Cell bio- Photosynthesis Flashcards
what is the ultimate source of metabolic energy in plants and some bacteria?
photosynthesis
how many stages are in photosynthesis?
2: 1. light reactions
2. dark reactions
light reaction
energy
absorbed from sunlight drives the synthesis of ATP &
NADPH (a coenzyme similar to NADH)
dark reactions
ATP
& NADPH drives the synthesis of carbohydrates from
CO2 & H2O
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
true
what is the arrangment of pigments in chloroplast
photocentric , each contains hundred of pigment molecules.
what is the role of each pigment molecules?
acting as antennae to absorb light and transfer energy of excited e to chlorophyl molecules that serves as a reaction center
chlorophyll
a reaction center
pheophytin
membrane carrier
what does pheophytin do ?
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.
what are the proteins involved in photosynthesis?
4 multi-protein complexes in thylakoid membrane of chloroplast:
Photosystem I & II: absorb light and transfer energy to reaction center chlorophylls
photosystems I & II
absorb light & transfer energy
T/F: in mitochondria electron transfers are coupled to the transfer of protons
into the thylakoid lumen, establishing a proton gradient across the membrane
true
what is the most important differences between e transport in chloroplast and mitochondria?
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.
how does electron transfer through photosystems?
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
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
true
what happens in PSII?
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
what are the carriers that high energy electrons can go through?
Plastiquinone (PQ)( lipid soluble)
Plastiquinone
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
what happens in cytochrome of complex during photosynthesis?
electrons are transferred to the peripheral membrane protein
Plastocyanin (PC) & 4 additional protons are pumped into the thylakoid lumen
Plastocyanin
peripheral membrane protein, carries the electrons to PS I, where the absorption of additional photons
raises their energy level
PSI
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)
Ferredoxin (Fd)
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
T/F: The ATP & NADPH generated by PS I & PS II are used in the Calvin cycle to convert
CO2 into glucose
true
cyclic electron flow
- second electron transport pathway
- the light
energy harvested at PS I is used for ATP synthesis rather than generating NADPH. - e is transfered to cytochrome bf complex
what happens to electrons in cytochrome bf complex?
they are coupled with the
establishment of a proton gradient across the thylakoid membrane.
T/F: electrons after losing energy with lower energy are returned to PSI by Plastocyanin after establishing H gradient
true
T/F: Electron transfer from PS I can thus generate either ATP or NADPH, depending on
the metabolic needs of the cell.
true
for each pair of electron transported how many protons and atp are yielded?
2 Protons at PS II, 4 are trasferred at Cytochrome bf complex, making 1.5 atp
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
true
where does the dark reaction occur?
stroma of chloroplst
what happens druing dark reactions?
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
how many ATPs are needed for calvin ? how many NADPH ?
18 ATP, & 12 NADPH for each molecule of glucose synthesized
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.
true
how does each can be obtained? amino acid , glycerol, glucose
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
glucogenesis
involves
the conversion of pyruvate to
glucose (essentially the
reverse of glycolysis).
T/F: Glucose is synthesized from
2 molecules of pyruvate at a
cost of 4 ATP, 2 GTP & 2
NADH.
True
how does glucose stored in animals & plants?
glycogen & starch, in the form of polysaccharides
T/F: synthesis of polysaccharides requires energy.
true
why does the formation of a glycosidic
bond must be coupled to an energy-yielding reaction?
the condensation reaction linking 2 sugars together is
energetically unfavorable,
how to fix the unfavorably energetic condensation reaction?
use of nucleotide sugars as
intermediates in the synthesis of polysaccharides
what is the nucleotide sugar process?
- Glucose is first phosphorylated in an ATP-driven reaction to form
Glucose-6-Phosphate, which is then converted to Glucose-1-
Phosphate. - 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 - chemical energy in the form of ATP &
UTP drives the synthesis of polysaccharides
from simple sugars
how does lipids made?
series of reactions during which coupled to the expenditure
of energy (in the form of ATP) & reducing power (in the form of NADPH)
How does fatty acids are synthesized?
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
where does fattty acid biosynthesis occurs?
in the cytosol of eukaryotic cells, the
major product of which is the 16-C
fatty acid palmitate
T/F: The principal components of cell
membranes are then synthesized
from fatty acids in the endoplasmic
reticulum
True
how does organisms perform nitrogen fixation?
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.
how does most bacteria, fungi, & plants can use nitrate to perform nitrogen fixation?
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
how to make organic compound from NH3?
synthesis of the amino acids
Glutamate (Glu) & Glutamine
(Gln), which are derived from the
citric acid cycle intermediate α-
Ketoglutarate.
how Gln & Glu help with synthesis?
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
where can we get raw material for amino acid synthesis?
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)
protein biosynthesis
- 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.
