BIOLOGI SEL:
PENDAHULUAN
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Sejarah perkembangan
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•
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Robert Hooke : sel mati : sel dari
gabus
Anton van Leeuwenhoek : sel
hidup
Matthias Schleiden : sel pada
tumbuhan
Theodor Schwann (1839): Teori
sel
– Semua organisma terdiri dari satu
atau lebih sel
– Sel : unit struktural hidup
•
•
•
Schleiden & Schwann : sel dapat
berasal dari materi-materi
nonselular
Rudolf Virchow (1855) : sel
berasal dari pembelahan sel yang
sudah ada sebelumnya
Penggunaan sel dalam penelitian
in vitro : HeLa (sel kanker
manusia) – George Gey BISEL07-SITH/ITB-MIT/IR
(1951)
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Karakteristik sel
• Sel sangat kompleks
– Molekul-molekul
sederhana –
kompleks Æ organel
Æ sel
misalnya
C, H, O, N, S, P Æ
asam amino Æ
protein Æ misalnya
salah satu komponen
dalam mitokondria
yang merupakan
organel dari sel
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Karakteristik sel
•
Sel memiliki informasi genetik
– Gen : blueprint untuk struktur sel, seluruh
aktivitas dan fungsi sel
•
Sel dapat ber-reproduksi
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Karakteristik sel
•
•
Sel memperoleh
dan menggunakan
energi
Sel melakukan
metabolisme sel
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Karakteristik sel
•
Terdapat suatu aktivitas mekanis dalam sel yang
dinamis
– Misalnya perubahan bentuk sel akibat aksi dari
protein-protein dalam sitoplasma
•
Sel dapat memberi respons terhadap suatu stimulus
– Reseptor hormon, reseptor faktor tumbuh, reseptor
matriks ekstraselular, atau reseptor lainnya (G)
– Respons : misalnya metabolisme sel, proliferasi sel
atau gerakan sel
Istirahat
teraktivasi
retraksi
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Karakteristik sel
•
Sel mampu mengatur diri sendiri (self
regulation)
–
Misalnya pengaturan siklus sel
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Prokaryot -Eukaryot
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Persamaan
antara eukaryot dengan prokaryot:
• konstruksi membran plasma sama
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Persamaan
antara eukaryot dengan prokaryot
•
•
informasi genetik dikode
oleh DNA, dengan kode
genetic yang identik
mekanisme transkripsi dan
translasi
Eukaryotes
Prokaryotes
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Persamaan antara eukaryot
dengan prokaryot:
•
•
reaksi metabolisme
apparatus yang sama untuk konversi energi kimiawi
–
–
prokaryot Æmembran plasma
eukaryot Æ membran mitokondria
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Persamaan antara eukaryot
dengan prokaryot:
•
mekanisme fotosintesis yang sama (tumbuhan –
sianobakteri)
•
•
mekanisme sintesa dan penyisipan protein membran
konstruksi proteosom yang sama (archaebacteria
dengan eukaryot)
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Perbedaan antara organisme prokaryot dengan
eukaryot
Prokaryot
Eukaryot
Organisme
Bakteri,
cyanobakteri
Protista, jamur,
tumbuhan dan hewan
Ukuran sel
Umumnya 1-10
μm
Umumnya 5-100 μm
Metabolisme
Anaerobic atau
aerobik
Aerobik
Organel
Sedikit
Mitokondria, kloroplas,
retikulum endoplasma,
dll
Inti
Tidak ada
Ada
DNA
DNA sirkular
dalam sitoplasma
DNA linier dan sangat
panjang, memiliki
daerah yang dikode
(ekson) dan tidak
dikode /intron (sangat
banyak); berada dalam
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inti
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Perbedaan antara organisme prokaryot
dengan eukaryot
Prokaryot
Eukaryot
RNA dan protein
RNA dan protein disintesis pada
ruang yang sama
RNA disintesis dan diproses di inti
Protein disintesis di sitoplasma
Sitoplasma
Tidak mengandung sitoskeleton,
tidak ada aliran sitoplasma dalam
sel, tidak ada endositosis dan
eksositosis
Dalam sitoplasma terdapat sitoskeleton
: filamen-filamen protein, ada aliran
sitoplasma dalam sel, ada endositosis
dan eksositosis
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Perbedaan antara organisme prokaryot dengan
eukaryot
Prokaryot
Eukaryot
Pembelahan sel
Kromosom ditarik dengan cara
pelekatan pada membran plasma
Kromosom ditarik apparatus mitosis
(komponen sitoskeleton)
Organisasi sel
Umumnya uniselular
Umumnya multiselular, dan terjadi
proses diferensiasi / spesialisasi sel
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Virus
– membawa
informasi genetic
berupa rantai
tunggal atau ganda
RNA atau DNA
– Materi genetiknya
mengkode :
• Protein kapsul /
kapsid
– aktif jika berada
pada sel hidup
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Bioenergetika
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The Chemistry of Life: A network
of metabolic pathways
• Cell metabolism can
be compared to an
elaborate road map
of the thousands of
chemical reactions
that occur in the cell
It is an intricate
network of metabolic
pathways
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• Catabolic pathways: They
release energy by breaking down
complex molecules to simpler
compounds
– A major catabolic pathway found
in a cell is respiration which breaks
down sugar glucose and other
fuels into carbon dioxide and water
with release of energy
C6H12O6 + 6O2 Æ 6CO2 + 6H2O +
Energy
• Anabolic pathways: Build
complex molecules from simpler
ones by consuming energy
e.g. Photosynthesis in plants
6CO2 + 6H2O + Light energy Æ
C6H12O6 + 6O2 + 6H2O
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• Organisms Transform Energy:
– Energy: The capacity to do work
• Kinetic energy: The energy of motion possessed by
all moving objects e.g. water gushing through a dam
turns turbines
• Potential energy: Energy that matter possesses
because of its location or structure
Chemical energy stored in
molecules as a result of the
arrangement of the atoms in
these molecules
Water behind dams has
potential energy because
of altitude
• Bioenergetics – The study of how organisms
manage their energy resources
– to maintain its high level of activity, a cell must
acquire & expend energy
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Conversion of Energy from
one form to the other:
• Thermodynamics study of the changes
in energy that
accompany events
in the Universe
• Two laws of
Thermodynamics
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The First Law of
Thermodynamics
•
energy can be neither created nor destroyed (Law of Conservation
of Energy); total energy in Universe remains constant (regardless of
transduction process)
– Energy can, however, be transduced - burning fuel, polysaccharide
breakdown, photosynthesis
• Several organism communities are independent of photosynthesis –
communities residing in hydrothermal vents on ocean floor; depends on
energy obtained by bacterial chemosynthesis
• Some animals (fireflies, luminous fish) convert chemical energy back into
light
• ΔE = Q – W, where Q = heat energy & W = work energy
Reactions that result in heat lost
to the environment are called
exothermic;
those that result in heat gained
from the environment are called
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endothermic
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Couple of terms
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System: Is used to denote the matter under
study and refer to the rest of the universeeverything outside the systems the
surroundings
1. Closed system: e.g. a liquid in a thermos bottle is
isolated from its surroundings
2. Open system: Energy (&often matter) can be
transferred between the system and its
surroundings e.g. organisms
•
•
Entropy: A measure of disorder or
randomness
Free energy: Is the portion of a system’s
energy that can perform work when
temperature is uniform through out the system
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The Second Law of
Thermodynamics
• Every energy transfer or transformation
increases the entropy of the universe
(no machine is 100% efficient which
would be necessary)
• Some energy is inevitably lost as machine
works (same is true of living organism)
• car
chemical energy (gasoline) Æ converted to
kinetic energy + the disorder of its
surroundings will increase in the form of heat
and small molecules that are the breakdown
products of gasoline
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• Together the 1st & 2nd laws of thermodynamics show
that the energy of the universe is constant, but that
entropy continues to increase toward a maximum
• Gibbs combined concepts inherent in 1st & 2nd Laws to
get equation: ΔH = ΔG + TΔS
where:
1. ΔG is the change in free energy (the change during a process in
energy available to do work)
2. ΔH - change in enthalpy (total energy content of system; equivalent
to ΔE for our purposes)
3. T - absolute temperature (°K; °K = °C + 273)
4. ΔS - change in entropy of system
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•
Rearrange to ΔG = ΔH - TΔS - can predict direction in
which process will proceed & the extent to which the
process will occur
1. ΔG size shows the maximum amount of energy that can
be passed on for use in another process
2. Spontaneous process has -ΔG (exergonic) & proceeds
toward state of lower free energy; such a process is
thermodynamically favored
3. Non-spontaneous process, +ΔG (endergonic); cannot
occur spontaneously; it is thermodynamically unfavorable;
make it go by coupling to high -ΔG (energy-releasing)
reaction
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ATP:
Adenosine Triphosphate
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•
An important renewable high energy compound that powers cellular
work
ATP hydrolysis is used to drive most cellular endergonic processes
A. ATP is used for diverse processes because its terminal phosphate
group can be transferred to a variety of different types of molecules
(amino acids, lipids, sugars, & proteins)
B. In most coupled reactions, phosphate group is transferred in initial step
from ATP to one of above acceptors & is subsequently removed in
second step
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Enzymes: Biocatalysts
• A catalyst is a chemical agent that changes the rate of
reaction without being consumed by the reaction
• An enzyme is a catalytic protein
– Enzymes are substrate-specific (key-lock relationship)
– Enzymes are sensitive to temperature, pH and to some
chemicals
• Some Enzymes need
co-factors/coenzymes
to function
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Enzymes:
Biocatalysts
• Substrates can
compete with other
substrates to bind
on the same
position of the
same enzyme Î
interrupt the
reaction
• Enzymes can be
inhibited by the
addition of
inhibitors
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Enzymes: Biocatalysts
• Feed back inhibition of
enzymes: Feed inhibition is the
switching off of a metabolic
pathway by its end product
which acts as an inhibitor of an
enzyme within the pathway
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•
ATP formed 2 ways in cell:
– oxidative phosphorylation Æ inner
membrane of mitochondria
– substrate-level phosphorylation
•
Oxidative phosphorylation dehydrogenases move 2 electrons &
proton to NAD+ to make NADH
1. High energy NADH donates electrons to
other molecules at electron transport (ET)
chain
2. Because NADH transfers electrons so
readily, it is said to have high electron
transfer potential
3. As electron travels down ET system, it loses
energy used to make ATP & is added to O2
to make H2O
•
Substrate-level phosphorylation phosphate group moved from a
substrate to ADP Æ ATP
1. ATP formation is not that endergonic,
formation of other molecules is more
endergonic
2. Such molecules can donate their
phosphates to ADP to make ATP
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