Download Plant Metabolism Chart

Plant Metabolic Pathways
The Leaf
Plant leaves are flattened to maximise the surface area for the absorption of light. The upper and lower surfaces are covered by a waxy cuticle which slows the loss of water
from the leaf. Beneath the cuticle lies the epidermis which provides some support for the leaf. The lower epidermis has small pores called stoma that allow for gaseous
exchange. During the day CO2 diffuses in and O2 out, during the night CO2 diffuses out and O2 in. Water vapour also escapes from the stomata and it is this loss that creates
the transpiration stream drawing mineral nutrients from the soil and up into the plant. The exchange of gases through the stomata is regulated by the guard cells which lie on
either side of it. The palisade mesophyll cells are elongated and contain many chloroplasts, this is the main photosynthetic area of the plant. The spongy mesophyll has
large air spaces to allow for the rapid diffusion of gases in and out of the leaf. The veins in the leaf contain vascular tissue, the xylem and phloem. The xylem provides
support as well as carrying water and mineral nutrients. The phloem carries away the products of photosynthesis, primarily sucrose, to the rest of the plant.
Metabolic Pathways
A metabolic pathway is a chain of
chemical reactions each step of
which is controlled by a specific
enzyme. The product of each enzyme
becomes the substrate for the next in
the chain. Each step involves small
changes in the substrates energy and
form thus making it easier for the cell
to control the reactions. Pathways
that build up molecules are said to be
anabolic e.g. photosynthesis.
Catabolic pathway breakdown
molecules e.g. respiration. Pathways
are like production lines in a factory
and allow the cell precise control.
T.S. Leaf
upper
epidermis
cuticle
Plant Cell
mitochondrion
cell wall
Glycolysis
Glycolysis is the oldest stage of respiration and takes place in the cytoplasm. Glucose a hexose sugar is first
phosphorylated twice by ATP to give it activation energy. The phosphorylated hexose sugar splits into two triose sugars
which are converted in several steps to pyruvic acid. Substrate level phosphorylation: In the process of conversion each
triose sugar (substrate) adds phosphate (phosphorylation) to each of two ADP's . This produces a net gain of two
ATP’s. Each triose also reduces the coenzyme NAD. In the absence of oxygen the pyruvate is converted to ethanol and
CO2 regenerating NAD and, allowing glycolysis to continue. In some organism e.g. mammals the pyruvate is converted
to lactic acid for the same reason. Glycolysis is the common pathway for both anaerobic and aerobic respiration.
Glycolysis
Chloroplast
Rough ER
Lipid
globule
Stroma
nucleus
Envelope
Palisade
mesophyll
Spongy
mesophyll
lower
epidermis
Grana
vacuole
chloroplast
Thylakoid
plasmodesmata
Light Stage
Lamella
NADP
DNA
Mitochondria
Starch
grain
Mitochondria
Mitochondria are surrounded by two
layers of membrane. The inner one is
Glucose, 6C
Starch
folded to increase its surface area and
form the cristae. The cristae are
ATP (x2)
covered by mushroom shaped stalked
particles. These stalked particles are
ADP (x2)
ATPase's manufacturing ATP. The
Hexose
mitochondria is filled by the matrix
phosphates
and its here that the Krebs cycle takes
6C
place.
Triose
Triose
The Link Reaction
phosphates, 3C In the link reaction the 3 carbon
phosphates, 3C
molecule pyruvate, the end product of
Inorganic Phosphate
glycolysis combines with coenzyme A
to produce acetylcoenzyme. In the
NAD
process one CO 2 is produced and
Glycerol, 3C
ADP
Oxidoreductase
NAD is reduced. The link reaction is a
Reduced
major crossroads in metabolism other
ATP
NAD
molecules such a fatty acids can enter
respiration at this stage.
Photosynthetic Pigments
Plants have a variety of different plant pigments. Each of these have
a different absorption spectra enabling the plant to harvest a wide
variety of different wavelengths of light. Chlorophyll a has two
peaks of absorption in the blue and red end of the spectrum, it does
not absorb strongly in the green wavelengths and as a result these
wavelengths are reflected and the plant will appear green. The
pigments are found in the grana of the chloroplast and arranged to
maximise the absorption of light.
Regeneration
electrons
Cytochrome Chain
Carb
ox
y
electrons
tion
uc
Absorption
Energy potential
Air
Reduced
Stoma Guard cell High
DNA
space
The Light Stage
NADP
The light stage of photosynthesis Structure of Chlorophyll
takes place in the grana of the
x
chloroplast. Light energy is absorbed
Cristae
by pigments which are arranged into
Light
Light
Fat/Oil
elect
ron t
structures called the light harvesting
Porphyrin head
Glycerate phosphate, 3C
ransf
Light
er ch
Matrix
antennae. These funnel the energy
with magnesium
ain
harvesting
ATP
towards a central core called
centre
ADP
complex
Ethanol
Inner
photosystem II. Electrons in the
Photophosphorylation
PSI
Fatty
2C
chlorophyll of photosystem II are
ATP
membrane
Photosystem I
acids
ADP
Anaerobic
excited by the light energy and the
Pyruvate, 3C
Light
respiration
Light
X= CH3 in chlorophyll a
chlorophyll oxidised. The excited
CHO in chlorophyll b
Outer Link Reaction
electron is passed to a series of
CO2
Light
carriers and the energy is used to
membrane
harvesting
NAD
generate ATP, the process is called
complex
CO2
Reduced O
Oxidative Phosphorylation
photophosphorylation. Having given
PS II
Hydrocarbon
NAD
up some of its energy the electron is
Photosystem II
Acetyl coA
tail
Low
passed to photosystem I where it is
x2H+ + electrons + O = H2O
Krebs Cycle
excited again by light energy giving
+
Proteins
ADP
4OH = 2H2O + 2O2
H2O = OH + H
it enough energy to reduce NADP. To
ATP
+
Photolysis
excretion
replace the electron lost by the
Phosphate
other
o x i d a t i o n o f c h l o r o p h y l l i n Chlorophyll + light = Chlorophyll+ + electron Light Independent Stage
Mitochodrial
amino
acids
photosystem II water is split. This
6 Carbon
4 Carbon
Matrix
Absorption
+
o
ATP
releases an electron and a Hydrogen
Molecule
Molecule
Transamination
H
isc
ADP + P
Spectrum for
GP
ub
ion (H+). The electron reduces the
+
R
Amino acid
Re d
n
chlorophylls
H H+
tio
chlorophyll and the hydrogen ion
Reduced
electrons
CO2
+
la
Re
te
a,
b
and
H
a
s
r
pirato subst
combines with the excited electron
NADP
ry
+
+
Cristae
carotene
H H
O
from photosystem I to reduce NADP.
Reduced
b
a
Ammonia,NH3
C3
Oxygen is released from water as a
NADP
NAD
x3
Reduced
+
+
Cycle
carotene
Reduced
x2
H
H
waste product of the process and
RUBP
NAD
NAD/FAD
H+
TP
CO2 NAD
O
some of this will diffuse out of the
Nitrite,NO2Glucose
protons
Reduced
ATPase
plant. The two useful products of the
O
ADP
ATP
400
500
600
700
Rege
FAD
light stage are ATP and reduced
FAD
neration
Violet Indigo Blue
Green Yellow Orange Red
Starch
NADP and these will be used in the
Wavelength nm
ATP
Outer mitochondrial membrane
Nitrate, NO3O = Oxidoreductase
light independent stage.
The Light Independent Stage
The C3 cycle takes place in the stroma of the chloroplast. The cycle has three important stages. Carboxylation: The pentose sugar ribulose
1:5 bisphosphate combines with carbon dioxide to form x2 of the three carbon sugar Glycerate phosphate (GP). This is done with the help of
the enzyme Rubisco. Reduction: The reduced NADP is oxidised and Glycerate phosphate reduced and converted to another triose sugars. In
this step ATP is converted to ADP and phosphate, the ATP providing activation energy for the process. Regeneration: The triose sugars are
converted in several steps to back to RUBP . This process requires the triose sugars to be phosphorylated by ATP. Every three times the cycle
goes around three carbons will be added and one surplus triose sugar will be made. The surplus triose sugars are used to make other organic
molecules such as glucose, sucrose and starch. Amino acids also require the addition of nitrogen. It will take six turns of the cycle to produce
one completely new molecule of glucose and twelve for the disaccharide sucrose..
Amino acids
Nitrates absorbed by the roots are
reduced first to nitrites and then to
ammonia. The Ammonia is then
combined with a Krebs cycle acid to
make an amino acid such as glutamic
acid. Other types of amino acid are
made by moving the amino group
from one molecule to another.
Krebs Cycle
The Krebs cycle takes place in the
matrix of the mitochondria. The
acetylcoenzyme A combines with a 4
carbon molecule (oxaloacetate) to
produce a 6 carbon molecule (citrate).
In a series of reactions the 6 carbon
molecule is converted back to the 4
carbon molecule releasing two
molecules of CO2 as it does so. These
stages produce four reduced NAD’s,
one reduced FAD and an ATP.
Oxidative Phosphorylation
The reduced NAD’s and reduced FAD
in the mitochondria pass their
hydrogen's and electrons to a chain of
cytochrome carriers found in the
cristae of the mitochondria. The
cytochromes are alternately reduced
and oxidised as they gain and lose
electrons. This process separates the
H+ from the electrons creating a proton
gradient across the cristae. The H+ pass
back through the membrane through
the stalked particles which are ATPase
enzymes. So ultimately the energy
contained in the reduced coenzymes is
used to phosphorylate ADP toATP, the
final acceptors for the Hydrogen being
oxygen which combines producing
water. The whole process is called
oxidative phosphorylation. Oxidative
phosphorylation in combination with
the Krebs cycle and glycolysis form
the pathways of aerobic respiration.
This is much more efficient than
anaerobic producing about 38 ATP as
opposed to the net gain of 2 produced
by anaerobic respiration.