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Energy Metabolism: Photosynthesis (Light-dependent reactions (Nature of…
Energy Metabolism: Photosynthesis
Photosynthesis
produces complex organic compounds
light energy to chemical energy
endergonic reactions
driven by ATP
IMPORTANT TO USE ABUNDANT COMPOUNDS
Very stable and little energy
can put more energy in
reactants + products = nontoxic :<3: :<3:
Environmental and Internal Factors
Quality of sunlight
colors/wavelengths
sunlight~pure white~entire visible spectrum
chlorophyll absorbs red and blue
Quantity of sunlight
light intensity or brightness
clear sky days are preferred
low branches receive less
near equator is good
Duration of sunlight
hours sunlight is there :sun_with_face:
equator ~ 12 hours
summers - days are longer and brighter :sunny:
connection
Concepts
Entropy
disorder-increasing
Photoautotrophs
all green plants, cyanobacteria, & few bacteria
build their own molecules
using CO2, water, nitrates, sulfate, and other minerals
energy from sunlight
Heterotrophs
take in organic molecules
all animals, all completely parasitic plants
all fungi and nonphotosynthetic prokaryotes
Advantage
materials --> construction materials instead of fuel
some organic materials--> build into polymers
the rest respire for energy
Tissues & Organs
either photoautotrophs or heterotrophs
Chlorophyllous leaves + stems
photoautotrophic
roots, wood, flowers
heterotrophic
live on carbohydrates
imported through phloem
Energy and Reducing Power
Energy Carriers
pigments enter every reaction necessay
Energized pigments are large molecules
too energtic
can react w/ anything
aren't every mobile
never move across membranes
pigments make less energtic intermediates
photosynthetic RXN makes ATP
can makes almost any RXN
enter almost every reaction
If ATP can't enter
Guanosine triphosphate goes in
Photophosphorylation
:forbidden:animals, fungi, + nonchlorophyllous pant tissue
respire some high energy compounds
consumed as food/imported by phloem
ADP-->ATP
occurs only in chloroplasts in :explode:
substrate-level phosphorylation
high-energy phosphate groups are made
force phosphate onto ADP
Oxidative phosphorylation
ADP phosphorylated to ATP
Reducing Power
oxidized
doesn't carry as many electons
covalent and ionic
CO2 --> Carbon = +4 -
oxidation state
oxidation RXN
increases +charge
oxidizing agent
oxidize material they react w/
NADP+ & NAD+
Reduced
electrons added to atom
reduction RXN
reduces the + charge
Oxygen -- pull electrons away
reducing power
force e- onto compounds
important for plants
take in CO2 & water
convert it to macromolecules
reducing agent
place e- onto other molecules
NADH & NADPH
Redox Potential
accept or donate electrons
connection
other electron carriers
Cytochromes
protein, contains cofactor, heme
heme holds an iron atom
iron carries e-
intrinsic membrane proteins
Plastoquinones
transport e- over short distance
hydrophobic
dissolve easily into lipid
:
Plastocyanin
protein, carries e- on metal atom
metal - copper
+2 --> oxidzed
+1 --> reduced
Light-dependent reactions
aka thylakoid reactions
create intermediates ATP & NADPH
by water + light
The Nature Of Light
Electromagnetic radiation spectrum
gamma rays, X-rays, UV light
infrared light, microwaves, radio waves, visible light
quanta aka photons
a set of waves
radiations differ in wavelengths and energy
shorter wavelengths - high energy
gamma rays, UV light, cosmic rays
long wavelengths - little energy
infrared, microwaves, radar, radio waves
humans see visible lights only
390 nm to 760 nm
Nature of Pigments
pigment
absorbs certain wavelengths + distinctive color
protect
photosynthetic pigments
transfer absorbed light :explode: to e-
chlorophyll a
absorbs only some red/blue lights
visible lights have just right amount
ground state to an excited state
chlorophyll doesn't use high energy quanta
would throw away e-
some have too little energy
like infrared
can't boost enough energy
release of lights
fluorescence
Absorption spectrum :red_flag:
graph
shows which wavelengths are strongly absorbed
to start process, :fire:must be absorbed
Action spectrum
graph
shows which wavelengths are most effective
Accessory pigments
strongly absorb wavelengths
not absorbed by chlorophyll a
Reaction center :red_flag:
several proteins, pigments, cofactors
Stroma Reactions
Calvin/Benson Cycle or C3 cycle
CO2 conversion to carbohydrate
Acceptor molecule
ribulose-1, 5-bisphosphate: RuBP
reacts w/ CO2
2 identical molecules are formed
3-phosphoglycerate or PGA
contains 3 carbons
done by enzyme called RuBP carboxylase
1, 3-diphosphoglycerate
ATP gives high energy e- to this molecule
later reduced by NADPH
3-phosphoglyceraldehyde is made
some 3-phosphoglyceraldehyde comes out of chloroplast
used to make macromolecules
Thylakoid Reactions
CONNECTION
Photosystem I
excites e- of P700
absorbs 700 nm most efficiently
Ferredoxin
NADP+ --> NADPH
Reduced ~ strong reducing agent
small protein
Photosystem II
REDUCES P700 to P680
cytochrome b6/f complex
donates e- to PSII
gets it from plastoquinone
receives e- from
Q
Q ~ molecule of quinone
receives e- from phaeophytin
gets the chlorophyll a from water in PSII
e- stripped away, protons used, oxygen in the stomata
10 quanta to break water down
electron transport chain
2 times
back to PSI
energy boosted by light again
Anabolic Metabolism
build complex biomolecules
storage
short term storage
ATP & NADPH
intermediate- term storage
glucose and disaccharide
stable to move from cell to cell
weeks or months :smiley:
cause cells to absorb water by osmosis :warning:
long-term storage
starch
more stable than glucose
lasts for years
does not cause cells to absorb water
LIPIDS EVEN BETTER
The synthesis of Polysaccharides
Gluconeogenesis ~ synthesis of glucose
PGAL converted to dihydroxyacetone phosphate
then back to 3-phosphoglyceraldehyde
makes fructose-1, 6-bisphosphate
lost phosphate makes fructose-6-phosphate
Some becomes glucose-6-phosphate
in plants becomes: amylose, amylopectin, or cellulose
starch degradation is important
Environmental and Internal Factor
Leaf structure and water
palisade prenchyma above and spongy mesophyll below
:+1: for absorbing CO2
:-1: conserving water
reduce external surface by means of cylindrical leaves
dry, hot area; close stomata
reduced water loss, but hard to dissolve C02
C4 Metabolism
plant's water use efficiency
protoplasmic conc.
Photorespiration
energy- wasting process
carbon from CO2
use in sugar + other biomolecules
CAM
Crassulacean Acid Metabolism
conservation of water
PEP is carboxylated
makes oxaloacetate
night time
