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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