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Selamat pagi
Kuliah biokimia
Ke 6
Photosynthesis
Isi kuliah
• Metabolisme karbohidrat
• Pengertian fotosintesis
• Mekanisme fotosintesis
Metabolisme karbohidrat
Contoh
Anabolisme/Pembentukan/sintesa
Katabolisme/Penguraian/degradasi
fotosintesa respirasi
Glukosa, O2CO2, H2O, E
Pengertianphotosynthesis
• Photo means ‘light’ and synthesis means ‘to make’
• Process in which plants convert carbon dioxide and water into sugars using solar energy
• Occurs in chloroplast
Photosynthesis:
6 CO2 + 6 H2O C6 H12 O6 + 6 O2
carbon dioxide + water = sugar + oxygen
Tracking atoms STARCH
photosynthetic products often stored as starch
•Starch = glucose polymer
Mekanisme fotosintesis• Melalui 2 tahap reaksi
1.Tahap reaksi terang (reaksi Hill)
2.Tahap reaksi gelap (reaksi Blackman)
Reaksi terang memanfaatkan energi chy dan H2O untuk menghasilkan energi kimia (ATP dan NADPH) dan O2.
Energi kimia itu digunakan dalam reaksi gelap untuk mengubah CO2 menjadi glukosa (C6H12O6)
• A Photosynthesis Road Map
Chloroplast
Light
Stack ofthylakoids ADP
+ P
NADP
Stroma
Lightreactions
Calvincycle
Sugar used for
Cellular respiration
Cellulose
Starch
Other organic compounds
Fig. 10.1
Fig. 10.2a
Fig. 10.2b
Fig. 10.2c
Fig. 10.4
Different pigments absorb light differently
Why are plants green?
Reflected
light
Transmitted light
Fig. 10.6
Fig. 10.8
• Chloroplasts contain several pigments
Chloroplast Pigments
– Chlorophyll a – Chlorophyll b – Carotenoids
Figure 7.7
Reaksi terang / reaksi Hillada 5 tahap
1.Penyerapan energi chy oleh pigmen khloroplas
2.Pemindahan energi chy dari pigmen pelengkap ke khlorofil a
3.Aktifasi khlorofil a oleh energi chy
4.Fotolisis air dan pelepasan oksigen
5.Transport elektron dan pembentukan energi kimia ATP dan NADPH (fosforilasi)
Sistem transport elektron (photophosphorylation /
fotofosforilasi)
Ada 2 macam
Sistem transport elektron non siklik
Sistem transport elektron siklik
Fotofosforilasi non siklik
Perhatikan gambar berikut
Mulai dari fotosistem I (dihasilkan NADPH)
Kmd fotosistem II (dihasilkan ATP)
Sistem transport elektron siklik
Perhatikan gambar berikut
Melibatkan fotosistem I saja
tidak melibatkan fotosistem 2
Dihasilkan ATP
Cyclic Photophosphorylation • Process for ATP generation associated with some
Photosynthetic Bacteria• Reaction Center => 700 nm
Sekian dulu
• See you
Asimilasi karbon (reaksi gelap)
ada 3 macam
1.Siklus Calvin pada tanaman gol C3
2.Jalur Hatch-Slack dan siklus Calvin pada tanaman gol C4
3.Crassulacean acid metabolism (Jalur Hatch-Slack dan siklus Calvin) pada tan gol CAM
asimilasi karbon pada tanaman C3 (Siklus Calvin-Benson)
Perhatikan gambar berikut
Pada tanaman C3 terdapat enzim rubisco yang mengakibatkan tjd fotorespirasi
Fig. 10.20
Hasil dari Siklus Calvin-Benson
Hexose (six-carbon) sugars are not a product of the Calvin cycle. Although many texts list a product of photosynthesis as C6H12O6, this is mainly a convenience to counter the equation of respiration, where six-carbon sugars are oxidized in mitochondria. The carbohydrate products of the Calvin cycle are three-carbon sugar phosphate molecules, or "triose phosphates," namely, glyseraldehyde 3 phosphate (G3P
Fig. 10.17
Rubisco• Ribulose bisphosphate carboxylase oxygenase• (fixes CO2 & O2)• Enzyme in Calvin Cycle (1st step)• Most abundant protein on Earth
– Ca. 25% total leaf protein
Photorespiration
• When rubisco “fixes” O2, not CO2
• Lose 1/2 C as CO2;
• Only occurs in light
• Rate increases with temperature
Asimilasi karbon tanaman gol C4
Perhatikan gambar berikut
Jalur Hatch-Slack pada sel mesofil
Siklus Calvin pada sel selimut berkas pengangkutan (bundle sheat cells)
Fig. 10.21
Jalur Hatch-slack
Siklus Calvin
Asimilasi karbon tanaman gol CAM
Perhatikan gambar berikut
Jalur Hatch-Slack dan Siklus Calvin pada sel mesofil
Fig. 10.22
Type 1: C3 Photosynthesis
• Adaptive Value– More efficient under normal light, temperature,
and moisture.
• How– Uses RUBISCO to collect CO2 during the day
and undergo photosynthesis
• Who: most plants
Type 2: C4 Photosynthesis• Adaptive Value 1
– Photosynthesizes faster under high light/heat conditions.
• How– Eliminates Photorespiration by using PEP
carboxylase (another enzyme) to collect CO2 during the day and hand delivering CO2 to RUBISCO so that it can’t react with O2.
– Many grasses and crops (e.g., corn, sorghum, millet, sugar cane)
Type 3: CAM Photosynthesis• Adaptive Values
1. Better water use efficiency• How
1. Stomata open during night
2. Uses PEP carboxylase to collect CO2 during the night stores the CO2 as acid, closes stomata during day when conducts photosynthesis.
3. Can keep stomata closed all the time, using CO2 from respiration to photosynthesize and O2 from photosynthesis for respiration.
– Advantage in arid climates• Who: cactuses, agaves, bromeliads, euphorbia
Sampai di sini fotosintesis
• Terimakasih
• Selamat siang
Global Environmental Change & Photosynthesis:
C3 vs. C4 vs. CAM
• Increasing CO2
• Increasing chronic and acute temperatures
• Increasing N (vs. decreasing C:N from increasing CO2)
• Changes in water
CO2 effects on photosynthesis
• C4 > C3 at low CO2
• But, C3 > C4 at high CO2
*At high CO2, C3 more efficient than C4 at all temps.(photosynthesis only, not other processes)
Photosynthetic N-use efficiency
• C4 plants need (have) less leaf N than C3
• Photosynthesis higher per unit N in C4
• Humans are increasing global N, which benefits C3 more than C4
• Increasing CO2 decreases leaf N content, more in C3 than C4
Photosynthetic water-use efficiency
• C4 plants use less water than C3
• (cause stomates open less)
• Water availability may increase or decrease in the future.
Predicting the future for plants
• How will increases in CO2, N, and chronic and acute heat stress affect photosynthesis?
• Who will win or lose? C3? C4?
• How will pollution (eg, ozone) interact?
• Current research in my lab an example.
Elevated CO2
Increased leaf C:N
Decreased Heat-shock proteins (Hsps)
Decreased thermotolerance
•High CO2 effects greater in C3 than C4 and CAM species.
•High CO2 effects greater on induced than basal thermotolerance.
Hypothesis
corn
0 1 2 3 4 5
0
10
20
30
40
corn
0 1 2 3 4 5
wheat
0 1 2 3 4 5
0
10
20
30
40
wheat
0 1 2 3 4 5
700ppm CO2
370ppm CO2
no-pre-hs pre-hs
Pn 0
10
20
30
40
sorghum sorghum
0
10
20
30
40
barley barley
Time (h) Time (h)
Heat stress decreased Pn in all species(not the result of stomatal closure).
Elevated CO2 had negative effects on Pn of C4 species, and positive effects on C3 species.
Pre-heat shock has a positive effect on Pn.
corn
0 1 2 3 4 5 6
corn
0 1 2 3 4 5 6
0.0
0.2
0.4
0.6
wheat
Y D
ata
0.0
0.2
0.4
0.6
700ppm CO2370ppm CO2
wheat
time (h)
0.0
0.2
0.4
0.6
no-pre-hs pre-hs
arabidopsis
0 1 2 3 4 5 60.0
0.2
0.4
0.6 arabidopsis
0 1 2 3 4 5 6
0.0
0.2
0.4
0.6
Barley Barley
0.0
0.2
0.4
0.6 sorghum sorghum
et
Heat shock decreased Фet of all
C3 and C4 species
There was negative CO2 effects on all species, except for wheat
There was positive Pre-HS effects on all species
SoyFACE: CO2 & ozone
phot
osyn
thet
ic e
lect
ron
tran
spor
t
0.0
0.2
0.4
0.6
0.8
controlheat-stressed
_______ambientCO2 &
ozone
_______elevatedCO2
_______elevated ozone
_______elevatedCO2 &
ozone