Download KATABOLISME KARBOHIDRAT

KATABOLISME KARBOHIDRAT
TUJUAN:
Setelah mempelajari bab ini diharapkan mahasiswa mampu:
1. Menjelaskan tahap-tahap reaksi yang terjadi dalam glikolisis
2. Menjelaskan energi yang digunakan maupun yang dihasilkan
pada proses glikolisis
3. Menjelaskan tahap-tahap reaksi pada siklus asam sitrat (daur
Krebs)
4. Menjelaskan energi yang dihasilkan dalam siklus asam sitrat
5. Menjelaskan rantai transport elektron pada respirasi/ proses
fosforilasi oksidatif
6. Menjelaskan jalur pentosa fospat
7. Menjelaskan glukoneogenesis
8. Menjelaskan jalur glioksilat
KATABOLISME KH (RESPIRASI SELLULER)
• Terjadi pada tiga seri reaksi:
1. Glikolisis
2. Siklus asam sitrat
3. Rantai transport elektron
• Menghasilkan:
1. CO2
2. H2O
3. ATP
Termasuk:
• Reaksi anaerob (tanpa O2)- menghasilkan sedikit ATP
• Reaksi aerob (memerlukan O2) – menghasilkan sgn besar ATP
Tahapan Oksidasi sempurna Glukosa
• Oksidasi glukosa dengan melepaskan H terjadi
4 tahap:
• Glycolysis – Pemecahan glukosa menjadi 2
molekul as. pyruvat di sitoplasma, tidak
membutuhkan oksigen, menghasilkan 2 ATP
• Reaksi transisi- pyruvate dioksidasi menjadi 2acetyl group yang dibawa CoA, dan CO2
dilepas; terjadi dua kali per /tiap molekul
glukosa.
Glycolysis
• 10 tahapan reaksi
• Memecah gluksosa menjadi 2 asam piruvat
• Terjadi di sitoplasma
• fase/tahap respirasi selluler anaerob
• Menghasilkan 2 ATP
Terjadi 3 aspek:
1. fosforilasi
2. Penguraian
3. produksi NADH dan ATP
4-13
Langkah – Menginvestasikan
Energi
• Pada awal glycolysis, 2 ATP digunakan
untuk mengaktifkan glukosa (6C), yang
akan dipecah menjadi 2 molekul berkarbon
3, yaitu PGAL.
• PGAL membawa fosfat dari ATP.
• Dimulai dari sini, masing-masing molekul
berkarbon 3 (3C) mengalami seri reaksi
yang sama.
Glycolysis
Tahap 1
- Fosporilasi
• 2 fospat ditambahkan
ke glukosa
• memerlukan ATP
Tahap 2 – penguraian
• 6-carbon glukosa
dipecah menjadi 2
molekul berkarbon 3
yaitu: Dihidroxiaceton
dan glyseraldehid
4-14
Langkah – pemanenan energi
• Terjadi oksidasi PGAL dgn melepaskan
elektron (H) yang kemudian ditangkap oleh
NAD+:
• 2 NAD+ + 4H → 2 NADH + 2 H+
• Oksidasi PGAL dan substrat berikutnya
menghasilkan 4 grup fosfat berenergi tinggi
yang digunakan untuk mensintesis ATP
pada fosforilasi substrat.
Glycolysis
Langkah ke 3- Produksi NADH dan
ATP
• atom hydrogen dilepas
• atom hidrogen berikatan dengan
NAD+ untuk menghasilkan
NADH
• NADH membawa atom H ke
rantai transport elektron jika
oksigen tersedia
• ADP difosforilasi menjadi ATP
• Dua molekul asam pyruvat
dihasilkan
4-15
Ringkasan Glycolysis
• Masukan:
• Glukosa
• 2 NAD+
• 2 ATP
• 4 ADP + 2 P
• Hasil:
• 2 pyruvat
• 2 NADH
• 2 ADP
• 2 ATP (net gain)
Reaksi Anaerob
Jika oksigen tidak
tersedia • Rantai transport
elektron tidak dapat
menerima NADH
• Asam piruvat
dikonversi menjadi
asam laktat
• glikolisis terhamabat
• Produksi ATP
menurun
4-16
Reaksi Aerob
Jika oksigen tersedia:
• asam piruvat
digunakan untuk
mengahsilkan acetyl CoA
• Siklus Asam sitrat
mulai
• Rantai transpor
elektron berfungsi
• CO2 dan H2O
terbentuk
• 36 molekul ATP
dihasilkan per mol
glukosa
4-17
Di Dalam Mitokondria
• mitochondria adalah organel sel yang memiliki dua lapis
•
membran, yaitu membran internal dan membran luar ,
terdapat ruang antara kedua membran.
Cristae adalah lipatan membran dalam ke arah matrix
matrix, The transition reaction and citic acid cycle occur
in the matrix; the electron transport system is located in
the cristae.
Transition Reaction
• The transition reaction connects glycolysis to the
•
•
citric acid cycle, and is thus the transition
between these two pathways.
Pyruvate is converted to a C2 acetyl group
attached to coenzyme A (CoA), and CO2 is
released.
During this oxidation reaction, NAD+ is converted
to NADH + H+; the transition reaction occurs
twice per glucose molecule.
Citric Acid Cycle
• The citric acid cycle is a cyclical metabolic
•
•
pathway located in the matrix of the
mitochondria.
At the start of the citric acid cycle, CoA carries
the C2 acetyl group to join a C4 molecule, and C6
citrate results.
Each acetyl group received from the transition
reaction is oxidized to 2 CO2 molecules.
Siklus Asam Sitrat
3. Siklus asam sitrat – satu seri reaksi oksidasi yang
melepaskan CO2 dan mengahsilkan ATP; terjadi 2 kali
per glukosa.
4. Rantai Transport Elektron – Satu seri senyawa
organik yang menerima dan melepas elektron yang
dilepas dari glukosa dan melewatkannya dari satu
karier ke karier berikutnya hingga sampai pada elektron
receptor terakhir yaitu O2. Dihasilkan air; Energi
dilepas untuk mensintesis 32 – 34 ATP.
• Jika oksigen tidak tersedia, terjadi fermentasi di
sitoplasma.
• During the cycle, oxidation occurs when NAD+
•
•
•
accepts electrons in three sites and FAD accepts
electrons once.
Substrate-level phosphorylation results in a gain of
one ATP per every turn of the cycle; it turns twice per
glucose.
During the citric acid cycle, the six carbon atoms in
glucose become CO2.
The transition reaction produces two CO2, and the
citric acid cycle produces four CO2 per molecule of
glucose.
Citric Acid Cycle
• begins when acetyl CoA
combines with oxaloacetic
acid to produce citric acid
• citric acid is changed into
oxaloacetic acid through a
series of reactions
• cycle repeats as long as
pyruvic acid and oxygen are
available
• for each citric acid
molecule:
• one ATP is produced
• eight hydrogen atoms
are transferred to NAD+
and FAD
• two CO2 produced
4-18
Citric acid cycle
SIKLUS ASAM SITRAT/ SIKLUS ASAM
TRIKARBOKSILAT
Citric acid cycle inputs and
outputs per glucose molecule
• Inputs:
• 2 acetyl groups
• 6 NAD+
• 2 FAD
• 2 ADP + 2 P
• Outputs:
• 4 CO2
• 6 NADH
• 2 FADH2
• 2 ATP
• Oxygen receives energy-spent electrons at
the end of the electron transport system.
• Next, oxygen combines with hydrogen, and
water forms:
• ½ O2 + 2 e- + 2 H+ → H2O
• When NADH carries electrons to the first
carrier, enough energy is released by the
time electrons are accepted by O2 to produce
three ATP; two ATP are produced when
FADH2 delivers electrons to the carriers.
Overview of the electron
transport system
Organization of Cristae
• The electron transport system is located in the
•
•
cristae of the mitochondria and consists of three
protein complexes and two mobile carriers.
The mobile carriers transport electrons between
the complexes, which also contain electron
carriers.
The carriers use the energy released by
electrons as they move down the carriers to
pump H+ from the matrix into the intermembrane
space of the mitochondrion.
• A very strong electrochemical gradient is
•
•
established with few H+ in the matrix and many
in the intermembrane space.
The cristae also contain an ATP synthase
complex through which hydrogen ions flow down
their gradient from the intermembrane space
into the matrix.
The flow of three H+ through an ATP synthase
complex causes a conformational change, which
causes the ATP synthase to synthesize ATP
from ADP + P.
• Mitochondria produce ATP by
chemiosmosis, so called because ATP
production is tied to an electrochemical
gradient, namely an H+ gradient.
• Once formed, ATP molecules are
transported out of the mitochondrial
matrix.
Organization of cristae
Electron Transport Chain
• NADH and FADH2 carry electrons to the ETC
• ETC series of electron carriers located in cristae of
mitochondria
• energy from electrons transferred to ATP synthase
• ATP synthase catalyzes the phosphorylation of ADP to ATP
• water is formed
4-19
Energy Yield from Glucose
Metabolism
• Per glucose molecule, there is a net gain
of two ATP from glycolysis, which occurs in
the cytoplasm by substrate-level
phosphorylation.
• The citric acid cycle, occurring in the matrix
of mitochondria, adds two more ATP, also
by substrate-level phosphorylation.
• Most ATP is produced by the electron
transport system and chemiosmosis.
• Per glucose molecule, ten NADH and two
FADH2 take electrons to the electron transport
system; three ATP are formed per NADH and
two ATP per FADH2.
• Electrons carried by NADH produced during
glycolysis are shuttled to the electron transport
chain by an organic molecule.
Accounting of energy yield per
glucose molecule breakdown
Summary of Cellular
Respiration
4-20
Rantai Transpor Elektron/ Fosforilasi oksidatif