Plant Metabolism Chapter 10 Slide 2 Outline Introduction Enzymes
and Energy Transfer Photosynthesis Respiration Additional Metabolic
Pathways Assimilation and Digestion Slide 3 Introduction
Photosynthesis - converts light energy to usable form Respiration -
releases stored energy Facilitates growth, development and
reproduction Metabolism - sum of all interrelated biochemical
processes in living organisms Animals rely on green plants for O 2,
food, shelter and other products Slide 4 Enzymes and Energy
Transfer Enzymes regulate metabolic activities Anabolism - forming
chemical bonds to build molecules Photosynthesis Catabolism -
breaking chemical bonds Cellular respiration
Photosynthesis-respiration Cycle involves transfer of energy via
oxidation-reduction reactions Slide 5 Enzymes and Energy Transfer
Oxidation-Reduction Reactions Oxidation - loss of electron(s)
Reduction - gain of electron(s) Oxidation of one compound usually
coupled with reduction of another H atom lost during oxidation and
gained during reduction O usually final acceptor of electron Slide
6 Photosynthesis Energy for most cellular activity = adenosine
triphosphate (ATP) Plants make ATP using light as energy source
Takes place in chloroplasts and other green parts of organisms 6CO
2 + 12H 2 O + light C 6 H 12 O 6 + 6O 2 + 6H 2 O Many intermediate
steps to process, and glucose not immediate 1 st product Slide 7
Photosynthesis CO 2 reaches chloroplasts in mesophyll cells by
diffusion (stomata -> leaf interior) Use of fossil fuels,
deforestation, and other human activities add more CO 2 to
atmosphere than is removed Has potential to cause global increases
in temperature May enhance photosynthesis Slide 8 Photosynthesis
Less than 1% of all H 2 O absorbed by plants used in photosynthesis
Most transpired or incorporated into plant materials H 2 O source
of e - in photosynthesis and O 2 released as by-product If H 2 O in
short supply or light intensities too high, stomata close and
reduce supply of CO 2 available for photosynthesis Slide 9
Photosynthesis ~40% of radiant energy received on earth visible
light Violet to blue and red-orange to red wavelengths absorbed
Green light reflected Leaves absorb ~80% of visible light reaching
them Light intensity varies with time of day, season, altitude,
latitude, and atmospheric composition Visible light passed through
prism Slide 10 Photosynthesis Plants vary considerably in light
intensities needed for optimal photosynthetic rates Temperature and
amount of CO 2 can be limiting Slide 11 Photosynthesis If light and
temps too high: ratio of CO 2 to O 2 inside leaves may change
Accelerates photorespiration - uses O 2 and releases CO 2 May help
some plants survive under adverse conditions If light intensity too
high: photooxidation - results in destruction of chlorophyll If H 2
O in short supply or light intensities too high: stomata close and
reduce supply of CO 2 available for photosynthesis Slide 12
Photosynthesis Several types of chlorophyll molecules Mg end
captures light Lipid tail anchors into thylakoid membrane Most
plants contain chlorophyll a (blue-green color) and chlorophyll b
(yellow-green color) Chlorophyll b transfers energy from light to
chlorophyll a Chlorophyll a molecule Slide 13 Photosynthesis Other
photosynthetic pigments include carotenoids (yellow and orange),
phycobilins (blue or red, in cyanobacteria and red algae), and
several other types of chlorophyll Ca. 250-400 pigment molecules
grouped in light- harvesting complex = photosynthetic unit Two
types of photosynthetic units work together in light-dependent
reactions Two phases of photosynthesis: Light-dependent reactions
Light-independent reactions Slide 14 Photosynthesis Major Steps of
Photosynthesis Light-Dependent Reactions: Thylakoid membranes of
chloroplasts H 2 O split apart, releasing e - and H + ; O 2
released e - pass along e - transport system ATP produced NADP
reduced to NADPH (used in light-independent reactions) Slide 15
Photosynthesis Major Steps of Photosynthesis Light-Independent
Reactions: Stroma of chloroplasts Utilize ATP and NADPH to form
sugars Calvin Cycle CO 2 combines with RuBP (ribulose bisphosphate)
and combined molecules converted to sugars (glucose) Uses ATP and
NADPH produced during light- dependent reactions Slide 16
Photosynthesis A Closer Look: Light-Dependent Reactions Each
pigment has own distinctive pattern of light absorption =
absorption spectrum When pigments absorb light, energy levels of e
- raised Energy from excited e - released when drops back to ground
state In photosynthesis, energy stored in chemical bonds Slide 17
Photosynthesis A Closer Look: Light-Dependent Reactions Two types
of photosynthetic units: photosystem I and photosystem II
Photosystem II before photosystem I Both produce ATP Both
photosystem I and photosystem II needed to produce NADPH and O 2 as
result of e - flow Slide 18 Photosynthesis A Closer Look:
Light-Dependent Reactions Photosystem I = chlorophyll a, small
amount of chlorophyll b, carotenoid pigment, and P 700 P 700 =
reaction-center molecule which uses light energy Remaining pigments
= antenna pigments Gather and pass light energy to reaction center
Fe-S proteins - primary e - acceptors, first to receive e - from P
700 Photosystem II = chlorophyll a, B-carotene, small amounts of
chlorophyll b, and P 680 Pheophytin (Pheo) - primary e - acceptor
Slide 19 Photosynthesis A Closer Look: Light-Dependent Reactions
Slide 20 Photolysis - H 2 O-splitting, Photosystem II Light photons
absorbed by P 680, boosting e - to higher energy level e - passed
to acceptor molecule, pheophytin, then to PQ (plastoquinone), then
along e - transport system to photosystem I e - extracted from H 2
O replace e - lost by P 680 1 O 2, 4 H + and 4 e - produced from 2
H 2 O Slide 21 Photosynthesis A Closer Look: Light-Dependent
Reactions e - Flow and Photophosphorylation e - transport system
consists of e - transfer molecules Photons move across thylakoid
membrane by chemiosmosis Phosphorylation - ATP formed from ADP
Slide 22 Photosynthesis A Closer Look: Light-Dependent Reactions
Photosystem I Light absorbed by P 700, boosting e - to higher
energy level e - passed to Fe-S acceptor molecule, Fd (ferredoxin),
then to FAD (flavin adenine dinucleotide). NADP reduced to NADPH e
- removed from P 700 replaced by e - from photosystem II. Slide 23
Photosynthesis A Closer Look: Light-Dependent Reactions
Chemiosmosis Net accumulation of H + in thylakoid lumen occurs from
splitting of H 2 O molecules and e - transport H + gradient gives
ATPase in thylakoid membrane potential to move H + from lumen to
stroma Movement of H + across membrane = source of energy for ATP
synthesis Slide 24 Photosynthesis A Closer Look: Light-Independent
Reactions Calvin Cycle 6 CO 2 combine with 6 RuBP (ribulose 1,5-
bisphosphate) with aid of rubisco Results in 12 3-C molecules of
3PGA (3- phosphoglyceric acid) NADPH and ATP supply energy and e -
reducing 3PGA to GA3P (glyceraldehyde 3-phosphate) 10 of 12 GA3P
restructured, using 6 ATP, into 6 5-C RuBP Net gain of 2 GA3P ->
converted to carbohydrates or used to make lipids and amino acids
Slide 25 The Calvin Cycle Slide 26 Photosynthesis A Closer Look:
Light-Independent Reactions Photorespiration - competes with
C-fixing role of photosynthesis Rubisco fixes O 2 instead of CO 2
Allows C3 plants to survive under hot dry conditions Dissipates ATP
and accumulated e -, prevents photooxidation When stomata closed, O
2 accumulates and photorespiration more likely Produces 2-C
phosphoglycolic acid (processed in perioxisomes) Forms CO 2 and PGA
-> reenter Calvin cycle No ATP formed Slide 27 Photosynthesis A
Closer Look: Light-Independent Reactions C 4 Pathway - produces 4-C
compound instead of 3-C PGA during initial steps of
light-independent reactions C 4 plants - tropical grasses and
plants of arid regions Kranz anatomy Mesophyll cells with smaller
chloroplasts with well- developed grana Bundle sheath cells with
large chloroplasts with numerous starch grains Slide 28
Photosynthesis A Closer Look: Light-Independent Reactions C 4
Pathway CO 2 converted to organic acids in mesophyll cells PEP
(phosphoenolpyruvate) and CO 2 combine, with aid of PEP carboxylase
Form 4-C oxaloacetic acid instead of PGA PEP carboxylase converts
CO 2 to carbohydrate at lower CO 2 concentrations than does rubisco
No photorespiration Slide 29 Photosynthesis A Closer Look:
Light-Independent Reactions C 4 Pathway CO 2 transported as organic
acids to bundle sheath cells, released and enters Calvin cycle CO 2
concentration high in bundle sheath = little photorespiration C 4
plants photosynthesize at higher temps than C 3 plants Costs 2 ATP
for C 4 photosynthesis Slide 30 Photosynthesis A Closer Look:
Light-Independent Reactions CAM Photosynthesis - similar to C 4
photosynthesis as 4-C compounds produced during light-independent
reactions, however: Organic acids accumulate at night (stomata
open) Converted back to CO 2 during day for use in Calvin cycle
(stomata closed) Adaptation to limited H 2 O supply and high light
intensity habitat Slide 31 Respiration Respiration - release of
energy from glucose molecules broken down to individual CO 2
molecules Initiated in cytoplasm and completed in mitochondria
Aerobic respiration needs O 2 C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O +
energy Slide 32 Respiration Anaerobic respiration and fermentation
- carried on in absence of O 2 Release less energy than aerobic
respiration Fermentation equations: C 6 H 12 O 6 2C 2 H 5 OH + 2CO
2 + 2ATP C 6 H 12 O 6 2C 3 H 6 O 3 + 2ATP Slide 33 Respiration
Major Steps of Respiration Glycolysis - 1st phase In cytoplasm No O
2 required Glucose converted to GA3P (glyceraldehyde 3- phosphate)
2 ATP molecules gained Slide 34 Respiration Major Steps of
Respiration Citric Acid (Krebs) Cycle - 2nd stage In fluid matrix
of cristae in mitochondria High energy e - and H + removed NADH,
FADH 2, and small amount of ATP produced CO 2 produced as
by-product Electron transport - 3rd stage In inner membrane of
mitochondria NADH and FADH 2 donate e - to e - transport system
Produces ATP, CO 2 and H 2 O Slide 35 Respiration A Closer Look
Glycolysis 3 Steps: Phosphorylation - glucose becomes fructose 1,6-
bisphosphate Sugar cleavage - fructose 1,6-bisphosphate split into
2 3-C GA3P (glyceraldehyde 3-phosphate) molecules Pyruvic Acid
Formation - H +, energy and H 2 O removed leaving pyruvic acid
Before citric acid cycle, pyruvic acid loses CO 2 and converted to
acetyl CoA No O 2 = anaerobic respiration and fermentation H +
released during glycolysis transferred back to pyruvic acid,
creating ethyl alcohol or lactic acid Slide 36 Respiration A Closer
Look Citric Acid (Krebs) Cycle Acetyl CoA combines with oxaloacetic
acid (O.A.), producing citric acid Each cycle uses 2 acetyl CoA,
releases 3 CO 2 and regenerates O.A. O.A. + acetyl CoA + ADP + P +
3NAD + FAD O.A. + CoA + ATP + 3NADH + H + + FADH 2 + 2CO 2 High
energy e - and H + removed, producing NADH, FADH 2 and ATP. Slide
37 Respiration A Closer Look e - Transport and Oxidative
Phosphorylation Energy from NADH and FADH 2 released as H + and e -
passed along e - transport system H + build up outside
mitochondrial matrix = electrochemical gradient Chemiosmosis
couples transport of H + into matrix with oxidative phosphorylation
= formation of ATP O 2 = ultimate e - acceptor, producing H 2 O as
it combines with H + Produces net gain of 36 ATP and 6 CO 2 and H 2
O Slide 38 Respiration Slide 39 Slide 40 Factors Affecting the Rate
of Respiration Temperature Increase from 20 o C to 30 o C,
respiration rates double H 2 O Medium in which enzymatic reactions
take place Low H 2 O content - respiration rate reduced O 2
Reduction in O 2 - respiration and growth rates decline Slide 41
Additional Metabolic Pathways Other processes contribute to growth
development, reproduction and survival Includes production of sugar
phosphates, nucleotides, nucleic acids, amino acids, proteins,
chlorophylls, cytochromes, carotenoids, fatty acids, oils, and
waxes Secondary Metabolism - metabolic processes not required for
normal growth and development Enable plants to survive and persist
under special conditions Colors, aromas, poisons - give competitive
edge Codeine, Nicotine, Lignin, Salicin, Camphor, Menthol, Rubber
Slide 42 Assimilation and Digestion Assimilation - conversion of
organic matter produced in photosynthesis to build protoplasm and
cell walls Sugars transformed into lipids, proteins, or other
carbohydrates, such as sucrose, starch and cellulose Digestion -
conversion of starch and other insoluble carbohydrates to soluble
forms Nearly always hydrolysis process Slide 43 Review Introduction
Enzymes and Energy Transfer Photosynthesis Respiration Additional
Metabolic Pathways Assimilation and Digestion
