Download File E-Leraning : METABOLISME

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Enzim merupakan senyawa organik
bermolekul besar yang berfungsi untuk
mempercepat jalannya reaksi metabolisme di
dalam tubuh tumbuhan tanpa mempengaruhi
keseimbangan reaksi
Enzim tidak ikut bereaksi, struktur enzim
tidak berubah baik sebelum dan sesudah
reaksi tetap
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Enzim sebagai biokatalisator
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Bagian enzim yang aktif adalah sisi aktif dari
enzim
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Enzim diberi nama sesuai dengan nama substrat dan
reaksi yang dikatalisis
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Biasanya ditambah akhiran ase
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Enzim dibagi ke dalam 7 golongan besar
Klas
Oksidoreduktase
(nitrat reduktase)
Transferase
(Kinase)
Hidrolase
(protease, lipase,
amilase)
Tipe reaksi
memisahkan dan menambahkan elektron atau
hidrogen
memindahkan gugus senyawa kimia
Liase
(fumarase)
membentuk ikatan rangkap dengan
melepaskan satu gugus kimia
Isomerase
(epimerase)
Ligase/sintetase
(tiokinase)
Polimerase
(tiokinase)
mengkatalisir perubahan isomer
memutuskan ikatan kimia dengan
penambahan air
menggabungkan dua molekul yang disertai
dengan hidrolisis ATP
menggabungkan monomer-monomer
sehingga terbentuk polimer
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Komponen utama enzim adalah protein
Protein yang sifatnya fungsional, bukan
protein struktural
Tidak semua protein bertindak sebagai
enzim

Enzim terdiri dari 1 ata lebih rantai polipeptida
dan bagian yang bukan protein yang penting
untuk aktifitas katalitik (kofaktor)
Kofaktor:
1. gugus prostetik
2. koenzim
3. ion metal
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Gugus prostetik: senyawa organik yang mengikat
kuat pada apoenzim
Koenzim: senyawa organik yang berasosiasi
secara tidak permanen dengan apoenzim,
biasanya berupa vitamin.
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Beberapa contoh enzim yang memerlukan
kofaktor
1.
2.
3.
4.
5.
6.
NAD (koenzim 1)
NADP (koenzim 2)
FMN dan FAD
Cytokrom: cytokrom a, a3, b, b6, c, dan f
Plastoquinon, plastosianin, feredoksin
ATP: senyawa organik berenergi tinggi,
mengandung 3 gugus P dan adenin ribose
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Enzim dibentuk dalam protoplasma sel
Enzim beraktifitas di dalam sel tempat
sintesisnya (disebut endoenzim) maupun di
tempat yang lain diluar tempat sintesisnya
(disebut eksoenzim)
Sebagian besar enzim bersifat endoenzim
1.
2.
3.
4.
5.
6.
7.
8.
Enzim bersifat koloid, luas permukaan besar,
bersifat hidrofil
Dapat bereaksi dengan senyawa asam maupun
basa, kation maupun anion
Enzim sangat peka terhadap faktor-faktor yang
menyebabkan denaturasi protein misalnya
suhu, pH dll
Enzim dapat dipacu maupun dihambat
aktifitasnya
Enzim merupakan biokatalisator yang dalam
jumlah sedikit memacu laju reaksi tanpa
merubah keseimbangan reaksi
Enzim tidak ikut terlibat dalam reaksi, struktur
enzim tetap baik sebelum maupun setelah
reaksi berlangsung
Enzim bermolekul besar
Enzim bersifat khas/spesifik
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Suhu: optimum 300C, minimum 0 0C, maksimum
400C
Logam, memacu aktifitas enzim: Mg, Mn, Co, Fe
Logam berat, menghambat aktivitas enzim: Pb,
Cu, Zn, Cd, Ag
pH, tergantung pada jenis enzimnya (pepsin aktif
kondisi masam, amilase kondisi netral, tripsin
kondisi basa)
Konsentrasi substrat, substrat yang banyak
mula-mula memacu aktifitas enzim, tetapi
kemudian menghambat karena: penumpukan
produk (feed back effect)
Konsentrasi enzim, peningkatan konsentrasi
enzim memacu aktifitasnya
Air, memacu aktifitas enzim
Vitamin, memacu aktifitas enzim
Penghambatan aktifitas enzim :
1.
Kompetitif
2.
Non kompetitif
3.
unkompetitif
Penghambatan kompetitif
Penghambatan nonkompetitif
Penghambatan unkompetitif
Respirasi
Heterotrof
• Heterotrof membutuhkan molekul organik
sebagai makanan.
• Energinya diperoleh dari ikatan kimia di
dalam molekul makanan seperti
karbohidrat, lemak dan protein.
Autotrof
• Autotrof merupakan organisme yang dapat
menggunakan sumber energi dasar (sinar
matahari) untuk membuat energi. Mis:
tumbuhan dan beberapa mikroorganisme
• 2 Types
– Photosynthetic autotrophs
– Chemosynthetic autotrophs
Chemosynthesis
• Chemosynthesis is a process used by
prokaryotic organisms to use inorganic
chemical reactions as a source of energy
to make larger organic molecules.
Aerobic Vs. Anaerobic
• Aerobic respiration requires oxygen.
• Anaerobic respiration does not require
oxygen.
Aerobic Respiration
• Aerobic cellular respiration is a specific
series of enzyme controlled chemical
reactions in which oxygen is involved in
the breakdown of glucose into carbondioxide and water.
• The chemical-bond energy is released in
the form of ATP.
• Sugar + Oxygen  carbon dioxide + water
+ energy (ATP)
Summary:
3 steps: 1st glycolysis
2nd Krebs cycle
3rd Electron Transport Chain (ETC)
A Road Map for Cellular Respiration
Cytosol
Mitochondrion
High-energy
electrons
carried
mainly by
NADH
High-energy
electrons
carried
by NADH
Glycolysis
Glucose
2
Pyruvic
acid
Krebs
Cycle
Electron
Transport
Figure 6.7
Glycolysis
Stage 1: splitting glucose molecule (C6) into
two PGALD (C3). 2 ATPs are used per
glucose metabolism.
• Stage 2: catalyzes the oxidation of PGALD to
pyrvate. Generate s 4 ATPs per glucose
metabolism.
glucose
ATP
Glycolysis
Hexokinase
ADP
glucose-6-phosphate
Phosphoglucose Isomerase
fructose-6-phosphate
ATP
Phosphofructokinase
ADP
fructose-1,6-bisphosphate
Aldolase
glyceraldehyde-3-phosphate + dihydroxyacetone-phosphate
Triosephosphate
Isomerase
Glycolysis continued
glyceraldehyde-3-phosphate
NAD+ + Pi
Glyceraldehyde-3-phosphate
Dehydrogenase
NADH + H+
Glycolysis
continued.
Recall that
there are
2 GAP per
glucose.
1,3-bisphosphoglycerate
ADP
Phosphoglycerate Kinase
ATP
3-phosphoglycerate
Phosphoglycerate Mutase
2-phosphoglycerate
Enolase
H2O
phosphoenolpyruvate
ADP
Pyruvate Kinase
ATP
pyruvate
6 CH2OH
5
H
4
OH
O
H
OH
H
2
3
H
OH
glucose
6 CH OPO 2
2
3
ATP ADP
H
H
1
OH
5
4
Mg2+
OH
O
H
OH
3
H
2
H
1
OH
Hexokinase H
OH
glucose-6-phosphate
1. Hexokinase catalyzes:
Glucose + ATP  glucose-6-P + ADP
The reaction involves nucleophilic attack of the C6
hydroxyl O of glucose on P of the terminal
phosphate of ATP.
ATP binds to the enzyme as a complex with Mg++.
6 CH OPO 2
2
3
5
H
4
OH
O
H
OH
3
H
H
2
OH
H
1
OH
6 CH OPO 2
2
3
1CH2OH
O
5
H
H
4
OH
HO
2
3 OH
H
Phosphoglucose Isomerase
glucose-6-phosphate
fructose-6-phosphate
2. Phosphoglucose Isomerase catalyzes:
glucose-6-P (aldose)  fructose-6-P (ketose)
The isomerization is an electron shift where 2 electron
from C2 carbon reduce the C1 aldehyde of the glucose6-phosphte molecule to an alcohol.
Phosphofructokinase
6CH OPO 2
2
3
O
5
H
H
4
OH
6CH OPO 2
2
3
1CH2OH
O
ATP ADP
HO
2
3 OH
H
fructose-6-phosphate
5
Mg2+
1CH2OPO32
H
H
4
OH
HO
2
3 OH
H
fructose-1,6-bisphosphate
3. Phosphofructokinase catalyzes:
fructose-6-P + ATP  fructose-1,6-bisP + ADP
This highly spontaneous reaction has a mechanism
similar to that of Hexokinase.
The Phosphofructokinase reaction is the ratelimiting step of Glycolysis.
.
2
1CH2OPO3
2C
O
HO 3C
H 4C
H
H
5
C
H
Aldolase
2
CH
OPO
2
3
3
OH
2C
OH
1CH2OH
2
CH
OPO
2
3
6
fructose-1,6bisphosphate
O
+
O
1C
H 2C OH
2
CH
OPO
3
2
3
dihydroxyacetone glyceraldehyde-3phosphate
phosphate
Triosephosphate Isomerase
4.Aldolase catalyzes: fructose-1,6-bisphosphate
dihydroxyacetone-P + glyceraldehyde-3-P
The reaction is an aldol cleavage, the reverse of an
aldol condensation.
Note that C atoms are renumbered in products of
Aldolase.
2
1CH2OPO3
2C
O
HO 3C
H 4C
H
H
5
C
H
Aldolase
2
CH
OPO
2
3
3
OH
2C
OH
1CH2OH
2
CH
OPO
2
3
6
fructose-1,6bisphosphate
O
+
O
1C
H 2C OH
2
CH
OPO
3
2
3
dihydroxyacetone glyceraldehyde-3phosphate
phosphate
Triosephosphate Isomerase
5. Triose Phosphate Isomerase (TIM) catalyzes:
dihydroxyacetone-P  glyceraldehyde-3-P
The dihidroxyacetone-P is isomerized to PGALD, thus
this stage produce 2 molecules PGAL pe 1 glucose
Triosephosphate Isomerase
H
H
C
OH
C
O
+
+
H H
CH2OPO32
dihydroxyacetone
phosphate
H
OH
H H
C
C
+ +
H
OH
CH2OPO32
enediol
intermediate
O
C
H
C
OH
CH2OPO32
glyceraldehyde3-phosphate
The ketose/aldose conversion involves acid/base
catalysis, and is thought to proceed via an enediol
intermediate, as with Phosphoglucose Isomerase.
Active site Glu and His residues are thought to extract
and donate protons during catalysis.
Glyceraldehyde-3-phosphate
Dehydrogenase
H
1C
O
OPO32
+ H+ O
NAD+ NADH 1 C
+ Pi
H 2C OH
H 2 C OH
2
CH
OPO
2
3
3
glyceraldehyde3-phosphate
2
CH
OPO
2
3
3
1,3-bisphosphoglycerate
6. Glyceraldehyde-3-phosphate Dehydrogenase
catalyzes:
glyceraldehyde-3-P + NAD+ + Pi 
1,3-bisphosphoglycerate + NADH + H+
Glyceraldehyde-3-phosphate
Dehydrogenase
H
1C
O
OPO32
+ H+ O
NAD+ NADH 1 C
+ Pi
H 2C OH
H 2 C OH
2
CH
OPO
2
3
3
glyceraldehyde3-phosphate
2
CH
OPO
2
3
3
1,3-bisphosphoglycerate
Exergonic oxidation of the aldehyde in glyceraldehyde- 3phosphate, to a carboxylic acid, drives formation of an
acyl phosphate, a "high energy" bond (~P).
This is the only step in Glycolysis in which NAD+ is reduced
to NADH.
Phosphoglycerate Kinase
O
OPO32 ADP ATP O
O
1C
H 2C OH
2
3 CH2OPO3
1,3-bisphosphoglycerate
C
1
2+
Mg
H 2C OH
2
3 CH2OPO3
3-phosphoglycerate
7. Phosphoglycerate Kinase catalyzes:
1,3-bisphosphoglycerate + ADP 
3-phosphoglycerate + ATP
This phosphate transfer is reversible (low DG), since
one ~P bond is cleaved & another synthesized.
The enzyme undergoes substrate-induced
conformational change similar to that of Hexokinase.
Phosphoglycerate Mutase
O
O
C
1
O
O
C
1
H 2C OH
2
3 CH2OPO3
H 2C OPO32
3 CH2OH
3-phosphoglycerate
2-phosphoglycerate
8. Phosphoglycerate Mutase catalyzes:
3-phosphoglycerate  2-phosphoglycerate
Phosphate is shifted from the OH on C3
to the OH on C2.
Enolase

O
O
C
1
H 2 C OPO32
3 CH2OH
H 
O

O
C
C
OH
O
O
C
1
OPO32
CH2OH
2C
OPO32
3 CH2
2-phosphoglycerate enolate intermediate phosphoenolpyruvate
9. Enolase catalyzes:
2-phosphoglycerate  phosphoenolpyruvate
+ H2O
O
O
Pyruvate Kinase
C
1
C
2
ADP ATP
O
O
C
1
OPO32
3 CH2
phosphoenolpyruvate
C
2
O
3 CH3
pyruvate
10. Pyruvate Kinase catalyzes:
phosphoenolpyruvate + ADP  pyruvate +
ATP
Krebs Cycle
• Makes ATP
• Makes NADH
• Makes FADH2
Conversion of pyruvate to Acetyl
CoA
NAD+ NADH
O
HSCoA
O
H3C
O
pyruvate dehydrogenase complex
pyruvate
• 2 per glucose (all of Kreb’s)
• Oxidative decarboxylation
• Makes NADH
CO2
O
SCoA
H3C
acetyl CoA
Net From Kreb’s
• Oxidative process
– 3 NADH
– FADH2
– GTP
• X 2 per glucose
– 6 NADH
– 2 FADH2
– 2 GTP
• All ultimately turned into ATP (oxidative
phosphorylation…later)
Citrate Synthase Reaction (First)
Aconitase Reaction
O
HO
O
O
C
CH2
C C
CH2
C
O
O
HO
O
O
citrate
aconitase
O
C
CH
HC C
CH2
C
O
O
O
O
isocitrate
• Forms isocitrate
• Goes through alkene intermediate (cis-aconitate)
– elimination then addition
• Hydroxyl moved and changed from tertiary to secondary
– (can be oxidized)
• 13.3kJ
Isocitrate Dehydrogenase
O
HO
C
CH
HC C
CH2
C
O
O
O
O
NADH
CO2
O
O
isocitrate
•
•
•
•
NAD
O
C
C O
CH2
CH2
C
isocitrate dehydrogenase
O
O
alpha ketoglutarate
All dehydrogenase reactions make NADH or FADH2
Oxidative decarboxylation
-20.9kJ
Energy from increased entropy in gas formation
α-ketoglutarate dehydrogenase
O
O
C
C O
CH2
CH2
SCoA
CoASH
CO2
NAD
C
CH2
CH2
C
NADH
C
O
O
alpha ketoglutarate
O
O
O
dehydrogenase
alpha ketoglutarate
•
•
Same as pyruvate dehydrogenase reaction
Formation of thioester
– endergonic
– driven by loss of CO2
• increases entropy
• exergonic
•
-33.5kJ
succinyl CoA
Succinyl CoA synthetase
SCoA
O
C
CH2
CH2
C
O
O
succinyl CoA
O
GDP
GTP
CoASH
succinyl CoA
synthetase
•
Hydrolysis of thioester
•
Coupled to synthesis of GTP
•
-2.9kJ
– Releases CoASH
– Exergonic
– Endergonic
– GTP very similar to ATP and interconverted later
O
C
CH2
CH2
C
O
O
succinate
Succinate dehydrogenase
O
O
O
C
CH2
CH2
C
O
O
FAD
FADH2
succinyl CoA
dehydrogenase
C
C H
H C
C
O
succinate
•
•
Dehydrogenation
Uses FAD
– NAD used to oxidize oxygen-containing groups
• Aldehydes
• alcohols
– FAD used to oxidize C-C bonds
– 0kJ
O
O
fumarate
Fumarase
O
C
C H
H C
C
O
O
O
O
H2O
fumarase
O
C
HC OH
CH2
C
O
fumarate
• Addition of water to a double bond
• -3.8kJ
O
malate
Malate Dehydrogenase
O
O
C
HC OH
CH2
C
O
O
malate
•
•
•
•
O
NADH
NAD
malate
dehydrogenase
O
O
C
C O
CH2
C
O
oxaloacetate
Oxidation of secondary alcohol to ketone
Makes NADH
Regenerates oxaloacetate for another round
29.7 kJ
Net From Kreb’s
• Oxidative process
– 3 NADH
– FADH2
– GTP
• X 2 per glucose
– 6 NADH
– 2 FADH2
– 2 GTP
• All ultimately turned into ATP (oxidative
phosphorylation…later)
INHIBITOR OF TCA CYCLE
1. Fluoroacetate
• Condensation with CoA
Fluoroacetyl-CoA
• Condensation FluoroacetylCoA with Oxaloacetate
Fluorocitrate
inhibit Akonitase enzyme
accumulation of citrate
• Fluoroacetate
pesticide
2. Malonate
suksinat dehydrogenase
enzyme
3. Arsenite
α-ketoglutarate dehydrogenase enzyme
REGULATION OF TCA CYCLE
REGULATION OF TCA CYCLE
Electron Transport System
• The electrons released from glycolysis and
the Krebs cycle are carried to the electrontransport system (ETS) by NADH and
FADH2.
• The electrons are transferred through a
series of oxidation-reduction reactions until
they are ultimately accepted by oxygen
atoms forming oxygen ions.
• 32 molecules of ATP are produced.
What is the electron
transport chain?
A chain of protein complexes embedded in
the inner mitochondrial membrane.
Transports electrons and pumps hydrogen
ions into the intermembrane space to
create a gradient.
Components of the electron
transport chain (ETC)






NADH dehydrogenase
Ubiquinone (Q)
Succinate dehydrogenase
Cytochrome b-c1
Cytochrome c
Cytochrome oxidase
 Arranged in order of increasing
electronegativity (weakest to strongest)
NADH produced
from glycolysis
VS
VS
NADH produced
from Krebs cycle
• NADH produced in the cytoplasm by glycolysis:
CAN diffuse from outer mitochondrial membrane
to
intermembrane space.
CANNOT diffuse from inner membrane to matrix.
• NADH produced from Krebs cycle:
Already in the matrix.
What to do?
• Cytosolic NADH (NADH that are produced by
glycolysis) pass electrons to shuttles
• Glycerol-phosphate shuttle:
Transfers electrons from cytosolic NADH to FAD to
produce FADH2
• Aspartate shuttle:
Transfers electrons from cytosolic NADH to NAD+ to produce
NADH
Complex I: NADH
dehydrogenase
• NADH dehydrogenase oxides NADH back to
NAD+
NADH + H+  NAD+ + 2H+ + 2e• The electrons are transferred to flavin
mononucleotide (FMN) which reduces to FMNH2
FMN + 2H+ + 2e-  FMNH2
• The electrons are then passed to iron-sulphur
proteins (FeS) located in NADH dehydrogenase
Complex I Continued…
• Electrons are accepted by Fe3+ which is reduced to
Fe2+
2Fe3+ + 2e-  2Fe2+
• These two electrons are then given to ubiquinone (Q)
• The two hydrogen ions are pumped into the
intermembrane space
*One hydrogen ion is pumped per
electron transferred
Ubiquinone (Q)
• A mobile electron carrier
2Fe2+ gives 2e- to Q
Q is reduced to QH2 (ubiquinol) and
2Fe2+ is oxidized 2Fe3+
• Carries electrons to complex III,
cytochrome b-c1
Interactive
Animation:
http://www.brookscole.com/chemistry_d/
templates/student_resources/shared_re
sources/animations/oxidative/oxidativep
hosphorylation.html
Complex II: Succinate
Dehydrogenase
• oxidation of succinate from Krebs cycle
to fumarate
Succinate + FAD  Fumarate + FADH2
FADH2 then tries to oxidize back into FAD by
passing its electrons to 2 Fe2+
2Fe3+ + 2e-  2Fe2+
Complex II Continued...
• These electrons from 2Fe2+ are then stolen by
ubiquinone (Q), which carries them to complex III.
•
2+
3+
Q + 2Fe
 2Fe + QH2
• Unlike complex I, complex II doesn’t have enough
free energy for active transport of the hydrogen
ions (protons) from FADH2 across the
intermembrane . This is why oxidation of FADH2
only yields 2 ATP molecules instead of 3 ATP
molecules like NADH.
Complex III: cytochrome b-c1
• Contains cytochrome b, cytochrome c1,
and FeS proteins.
• QH2 passes two electrons to cytochrome b
causing Fe3+ to reduce to Fe2+
• Same way from cyt b to FeS protein and
then to cyt c1
Cytochrome C (c)
• I’m a protein and like Q...
• I am also a water soluble mobile electron
carrier. I transport electrons one at a time
from complex III to complex IV.
Complex IV: Cytochrome Oxidase
(The End of the Line)
• This is the end of the line for electrons from
NADH or succinate.
• Oxygen (breathed in) is reduced and when
combined with these electrons, they form...
WATER
½ O2 (g) + 2H+ + 2e-  H2O (l)
THIS REACTION IS EXPLOSIVE! It’s highly
exergonic, releasing large amounts of energy.
Electrochemical gradient
• A concentration gradient created by pumping ions into a
space surrounded by a membrane that is impermeable
to the ions.
• Two components: electrical and chemical
• Proton-motive force (PMF) moves protons through an
ATPase complex on account of the free energy stored in
the form of an electrochemical gradient of protons
across a biological membrane.
Chemiosmosis
• Peter Mitchell – Nobel Prize in Chemistry in 1978
• A process for synthesizing ATP using the energy of an
electrochemical gradient and the ATP synthase enzyme.
• “osmosis”
• After chemiosmosis, ATP molecules are transported through
both mitochondrial membranes.
Connections!
• Electrons from NADH and FADH2 were passed down
the ETC
• As the electrons move down, energy released moves
protons to create electrochemical gradient
• Protons move through proton channels, and release
energy to synthesize ATP from ADP and Pi
• The many processes of ATP synthesis are all
continuous
Fermentation
• Fermentation describes anaerobic
pathways that oxidize glucose to produce
ATP.
• An organic molecule is the ultimate
electron acceptor as opposed to oxygen.
• Fermentation often begins with glycolysis
to produce pyruvic acid.
Anaerobic Cellular
Respiration
• Anaerobic respiration does not require
oxygen as the final electron acceptor.
• Some organisms do not have the
necessary enzymes to carry out the Krebs
cycle and ETS.
• Many prokaryotic organisms fall into this
category.
• Yeast is a eukaryotic organism that
performs anaerobic respiration.
• First step in anaerobic respiration is also glycolysis
Diagram
Anaerobic Respiration
Cytoplasm
C6H12O6
glucose
Alcoholic fermentation
Bacteria, Yeast 2 ATP
glycolysis
Aerobic Respiration
Lactic acid fermentation
Muscle cells
2 ATP
Krebs
Cycle
ETC
Mitochondria
Alcoholic Fermentation
• Alcoholic fermentation is the anaerobic
pathway followed by yeast cells when
oxygen is not present
• Pyruvic acid is converted to ethanol and
carbon-dioxide.
• 4 ATPS are generated from this process,
but glycolysis costs 2 ATPs yielding a net
gain of 2 ATPs.
•Alcoholic fermentation—occurs in bacteria and
yeast
Process used in the baking and brewing
industry—yeast produces CO2 gas during
fermentation to make dough rise and give bread
its holes
glucose
ethyl alcohol + carbon dioxide + 2 ATP
ALCOHOL FERMENTATION
Lactic Acid Fermentation
• In Lactic acid fermentation, the pyruvic
acid from glycolysis is converted to lactic
acid.
• The entire process yields a net gain of 2
ATP molecules per glucose molecule.
• The lactic acid waste products from these
types of anaerobic bacteria are used to
make fermented dairy products such as
yogurt, sour cream, and cheese.
• Lactic acid fermentation—occurs in muscle cells
Lactic acid is produced in the muscles during rapid
exercise when the body cannot supply enough oxygen
to the tissues—causes burning sensation in muscles
glucose
lactic acid + carbon dioxide + 2 ATP
LACTIC ACID FERMENTATION
PHOTOSYNTHESIS
photosynthesis
• Photo artinya cahaya dan sintesis artinya
membuat
• Proses di dalam tanaman yang mengubah
carbon dioksida dan air menjadi gula dan
oksigen
• Terjadi di dalam kloroplas
Photosynthesis:
6 CO2 + 6 H2O
carbon dioxide + water =
C6 H12 O6 + 6 O2
sugar + oxygen
photosynthetic
products often
stored as
starch
•Starch = glucose
polymer
Tracking atoms
STARCH
Carbon Fixation
• Penggabungan karbon dioksida
menjadi senyawa organik disebut
juga fiksasi karbon.
• Fiksasi karbon terjadi selama reaksi
yang tidak bergantung adanya
cahaya/ siklus calvin/ reaksi gelap.
Fig. 10.20
Calvin Cycle – Reminder of Steps!
 Karbon dioksida berdifusi masuk kedalam stroma
kloroplas.
 Enzim , RibuloseBifosfatase ( Rubisco)
memungkinkan karbon dioksida untuk bergabung
dengan gula berkarbon 5 (Ribulose biphosphate).
 Senyawa beratom karbon 6 tersebut sifatnya
UNSTABLE dan dipecah menjadi 2 gula
berkarbon 3 (3-PGA)
 2 3-PGA kemudian diubah menjadi G3P
 1 G3P akan menjadi glukosa
 Lainnya diregenerasi kembali menjadi
RibuloseBiphosphatase.
Fig. 10.17
Types of photosynthesis
• C3
– Kebanyakan tanaman
• C4
– CO2 untuk sementara disimpan dalam bentuk
asam organik 4-C.
– Berguna: penyinaran yang lama, suhu tinggi,
kurang CO2
– Rerumputan dan tanaman pertanian(e.g., jagung,
sorgum, tebu)
•CAM
•Stomata terbuka pada malam hari
•Berguna dalam kondisi iklim kering
•Kebanyakan kaktusan (e.g., cacti, euphorbs,
bromeliades, agaves)
C3!
• Siklus calvin dikenal sebagai lintasan
C3
PGA
• Contoh tumbuhan C3:
C3 Plants
• stomata TERBUKA pada siang hari dan
TERTUTUP pada malam hari.
• Ketika stomata terbuka, karbon dioksida
dapat masuk dan Oksigen dapat keluar.
• Pada saat cuaca panas, kering dan
kehilangan air(transpirasi) menjadi
MASALAH.
Problem
• Ketika stomata tertutup, karbon dioksida
tidak dapat masuk ke dalam daun dan
oksigen tidak dapat keluar dari daun.
• Oksigen berkompetesi dengan karbon
dioksida di dalam siklus calvin.
• Ketika terlau banyak oksigen di dalam
daun, oksigen akan berikatan dengan
RUBISCO (ribulose biphosphase) ini
disebut sebagai fotorespirasi.
Competing Reactions
• Rubisco dapat bereaksi dengan CO2
(Carboxylase Reaction) – bagus untuk
produksi glukosa 
CH2OPO32-
C O
H C OH
H C OH
CH2OPO32Ribulose 1,5-bisphosphate
CO2
O-
O
C
H C OH
CH2OPO323-Phosphoglycerate
O-
O
C
H C OH
CH2OPO 323-Phosphoglycerate
Competing Reactions
• Rubisco dapat juga bereaksi dengan O2
(Oxygenase Reaction)
– Tidak bagus untuk produksi glukosa
CH2OPO32C O
H C OH
H C OH
CH2OPO32Ribulose 1,5-bisphosphate
O2
O-
O
CH2OPO32-
C
H C OH
CH2OPO323-Phosphoglycerate
C
O
O-
Phosphoglycolate
• Ketika oksigen berikatan dengan Rubisco
kemudan akan berkombinasi dengan gula
berkarbon 5 dan dirombak.
• Siklus Calvin terhenti: gula berkarbon 5
tidak bisa menjadi gula dan dirombak
menjadi air dan karbon dioksida.
• Rubisco bereaksi dengan O2 dibanding
CO2
• Terjadi dlam kondisi:
– Konsentrasi oksigen tinggi
– Kondisi panas
• Fotorespirasi dipetkirakan menurunkan
efisiensi fotosintesis sampai25%.
Solusi
Photorespiration
Alternative Pathways
Pada kondisi panas dan kering,
tumbuhan harus melakukan
lintasan alternatif.
C4 dan CAM
Fig. 10.21
C4 Pathway
• Pada lintasan C4
fotosintesis terjadi pada
mesofil dan selubung
berkas pembuluh.
– Reaksi terang di mesofil
– Siklus calvin di
Selubung berkas pembuluh
Image taken without permission from
C4 Pathway
• CO2 difikasi menjadi
molekul berkarbon 4
• Enzim tambahan–
PEP Carboxylase
that initially traps CO2
instead of Rubisco–
makes a 4 carbon
intermediate
C4 Pathway
• The 4 carbon
intermediate
“smuggles” CO2 into
the bundle sheath cell
• The bundle sheath cell
is not very permeable
to CO2
• CO2 is released from
the 4C molecule 
goes through the
Calvin Cycle
C3 Pathway
How does the C4 Pathway
limit photorespiration?
• Bundle sheath cells are far from the
surface– less O2 access
• PEP Carboxylase doesn’t have an
affinity for O2  allows plant to collect a
lot of CO2 and concentrate it in the
bundle sheath cells (where Rubisco is)
CAM Pathway
• Fix CO2 at night and
store as a 4 carbon
molecule
• Keep stomates
closed during day to
prevent water loss
• Same general
process as C4
Pathway
• Has the same leaf
anatomy as C3
plants
How does the CAM Pathway
limit photorespiration?
• Collects CO2 at night so that it can be
more concentrated during the day
• Plant can still do the calvin cycle during
the day without losing water
Fig. 10.22
Sintesis Sukrosa dan Pati
Synthesis of Starch and
Sucrose
Photosynthetic cell
•
CO2
chloroplast
Sukrosa: produk penting
dari fotosintesis
–
PGA
RuBP
1,3 bisPGA
•
Cadangan gula yg penting
–
starch
–
Triose P
sucrose
•
tap root of carrots and sugar
beet (up to 20% dry weight)
and in leaves, eg 25% leaf dry
weight in ivy
Bentuk utama translokasi C
–
–
RuBP = ribulose 1,5-bis-phosphate (pentose)
3-PGA = 3-phosphoglycerate
1,3 bisPGA = 1,3 bis-phosphoglycerate
accounts for most of CO2
absorbed
from photosynthetic leaves
(source leaves)
in germinating seedlings after
starch or lipid breakdown
Sugar Translocation is
Essential
•
Gula diperlukan dalam
proses metabolisme
– all the time, in all tissues
•
Sugars produced only
– by source tissues
•
Translokasi terjadi pada:
– source to sink over short term
– from storage tissues to young
tissues over long term
Sugar composition of phloem
sap
• > 500 different species (100 families) of dicots
(Zimmermann & Ziegler, 1975)
Most families
Aceraceae (maple)
Anacardiaceae (cashew)
Asteraceae (aster)
Betulaceae (birch)
Buddleiaceae (butterfly bush)
Caprifoliaceae (honeysuckle)
Combretaceae (white mangrove)
Fabaceae (legume)
Fagaceae (beech & oak)
Moraceae (fig)
Oleaceae (olive)
Rosaceae (rose)
Verbenaceae (verbena)
Sucrose
++++
++++
+++
+
++++
++
+++
+++
++++
++++
++++
++
+++
++
Raffinose Stachyose Sugar alcohols
+
+
Tr
Tr
Tr
Tr
Tr
Tr
++
++
+++
++++
++
Tr
++
+
+++
Tr
Tr
Tr
Tr
+
++
++
+++
Tr
Tr
++++
+
++++
-
• most families transport sucrose
• concentration in phloem sap can reach 1 M
Starch is made in photosynthetic and nonphotosynthetic cells
Sel fotosintetik
• cadangan sementara
starch
Triose P
chloroplast
•Pada daun hijau
sucrose
Sel non-fotosintetik
• penyimpanan dalam jangka lama
• akar, umbi, biji
sucrose
starch
amyloplast
 Starch is the dominant storage polysaccharide in most plants
Sunflower
after
47 chloroplasts
min photosynthesis
 In leaves - transitory
starch
- in

high percentage of CO2 assimilated goes directly into starch
Carbon absorbed (mg)
7.87
Hexose accumulated
1.17
Sucrose
4.20
Starch
1.84
• Pada sel non-fotosintetik- pati disimpan dalam amiloplas
– storage organs
– herbaceous
– trees
bananas, tubers (up to 80% dry weight),
cereal grains (75% dry weight)
roots, underground stems, bulbs perennials
young twigs, roots, parenchyma of bark xylem & phloem
Composition of Starch
• Amilopektin
–  -1,4 &  -1,6-glucan
– 10,000 - 100,000 glucose units
– highly branched, 20 - 25 glucoses/branch
•
Amilosa
–  -1,4-glucan
– ~1000 glucose units
acceptors
for addition
of further
glucose units
polymer of glucose units
start
(reducing end)
• Butir pati
– Water insoluble,
– size & shape is
species specific
potato: oval,
100 µm in diameter
rice: angular,
10 µm in diameter
Fruktan
• Beberapa tanaman menyimpan senyawa lain
• Biasanya dalam bentuk fruktan
– water-soluble, non reducing polymers of fructose
– 5 - 300 fructose units, joined to one glucose
• daun, bunga dan organ penyimpanan yg terletak
dalam tanah
– Asteraceae (dahlias, jerusalem artichokes)
– Liliaceae (onions, asparagus)
– Iridaceae (irises)
• Daun pada beberapa Gramineae
– C3 grasses - barley, oats, rye grass
– major feedstuff for cattle & sheep in temperate zones
– But store starch in the seed
How are Sucrose and Starch
Synthesised?
Sukrosa dan pati disintesis pada
tempat berbeda
Pati dalam kloroplas
Sukrosa dalam sitosol
SINTESIS SUKROSA
1. Uridine-triphosphate (UTP) + Glucose-1-phosphate (G1P) ---> UDP-glucose +
Pyrophosphate (PPi)
2. UDP-glucose + PPi + Fructose-6-phosphate (F6P) ---> UDP + sucrose-6(F)-phosphate
(S6P)
3. Sucrose-6(F)-phosphate (S6P) + H2O ---> PPi + Sucrose
SINTESIS UDP-Glukosa
UTP
CH2OH
O
OH
Glucose 1-P
PPi
OH
UDP-G
pyrophosphorylase
O
O
O-P-O-P-O-uridine
OH O- O-
PENGURAIAN SUKROSA
Enzymes of Sucrose
Metabolism
Fructose 6P
UDP-Glucose
UDP
Sucrose P
Sucrose P Synthase
Sucrose P
Phosphatase
Pi
Sucrose
Invertase
Fructose
+
Glucose
UDP
Sucrose Synthase
Fructose
+
UDP-Glucose
polymer of glucose units
start
(reducing end)
acceptors
for addition
of further
glucose units
BIOSINTESIS
PATI
PGI: phosphoglucose isomerase. PGM: Phosphoglucomutase;
AGPase, ADPglucose pyrophosphorylase; SS, starch
synthase; BE, branching enzyme; DBE, debranching enzyme;
Glc-1-P, glucose-1-phosphate
Enzymes of Starch Synthesis
ATP
ADPglucose
Glucose 1-P
PPi
ADPG PPiase
 1,4 glucann
Glucose 1-P
 1,4 glucann
Starch
synthase
 1,4 glucann+1
Pi
Starch
phosphorylase
Starch
Branching Enzyme
• Branching enzyme forms the -1,6 links
start
starch synthase
start
-1,4 link
branching enzyme
-1,6 link
PENGURAIAN PATI
Starch is catabolized by 5 enzymes: α-amylase, βamylase, α-glucosidase, starch phosphorylase, and αdextrin 6-glucanohydrolase (debranching enzyme)
Genetic or biochemical modifications of starch are or
may be used for...
+ amylose
• fried snacks
(crispness / browning)
• thickener /
gelling agent
• biodegradable
packing material
• film coating
Modified starch
modified
starch
• Phosphate content
• water absorbency
• improve starch
granule integrity
(cross linker)
+ amylopectin
• Improve freezethaw of frozen food
• paper strength
• adhesive
• livestock feed
addition