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BIOLOGI SEL: PENDAHULUAN

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Sejarah perkembangan• 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 dapatberasal dari materi-materinonselular

• Rudolf Virchow (1855) : selberasal dari pembelahan sel yang sudah ada sebelumnya

• Penggunaan sel dalam penelitianin vitro : HeLa (sel kankermanusia) – George Gey(1951)

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Karakteristik sel• Sel sangat kompleks

– Molekul-molekulsederhana –kompleks organel

selmisalnyaC, H, O, N, S, P asam amino protein misalnyasalah satu komponendalam mitokondriayang merupakanorganel dari sel

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Karakteristik sel• Sel memiliki informasi genetik

– Gen : blueprint untuk struktur sel, seluruhaktivitas dan fungsi sel

• Sel dapat ber-reproduksi

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Karakteristik sel• Sel memperoleh

dan menggunakanenergi

• Sel melakukanmetabolisme 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 selIstirahat 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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Persamaanantara eukaryot dengan prokaryot:

• konstruksi membran plasma sama

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Persamaanantara eukaryot dengan prokaryot

• informasi genetik dikodeoleh DNA, dengan kodegenetic yang identik

• mekanisme transkripsi dantranslasi

EukaryotesProkaryotes

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• reaksi metabolisme• apparatus yang sama untuk konversi energi kimiawi

– prokaryot membran plasma – eukaryot membran mitokondria

Persamaan antara eukaryotdengan prokaryot:

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• mekanisme fotosintesis yang sama (tumbuhan –sianobakteri)

• mekanisme sintesa dan penyisipan protein membran• konstruksi proteosom yang sama (archaebacteria

dengan eukaryot)

Persamaan antara eukaryotdengan prokaryot:

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Perbedaan antara organisme prokaryot denganeukaryot

Prokaryot EukaryotOrganisme Bakteri,

cyanobakteriProtista, jamur, tumbuhan dan hewan

Ukuran sel Umumnya 1-10 μm

Umumnya 5-100 μm

Metabolisme Anaerobic atauaerobik

Aerobik

Organel Sedikit Mitokondria, kloroplas, retikulum endoplasma, dll

Inti Tidak ada AdaDNA DNA sirkular

dalam sitoplasmaDNA linier dan sangatpanjang, memilikidaerah yang dikode(ekson) dan tidakdikode /intron (sangatbanyak); berada dalaminti

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Perbedaan antara organisme prokaryotdengan eukaryot

Prokaryot Eukaryot

RNA dan protein RNA dan protein disintesis padaruang yang sama

RNA disintesis dan diproses di intiProtein disintesis di sitoplasma

Sitoplasma Tidak mengandung sitoskeleton, tidak ada aliran sitoplasma dalamsel, tidak ada endositosis daneksositosis

Dalam sitoplasma terdapat sitoskeleton: filamen-filamen protein, ada aliransitoplasma dalam sel, ada endositosisdan eksositosis

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Perbedaan antara organisme prokaryot denganeukaryot

Prokaryot Eukaryot

Pembelahan sel Kromosom ditarik dengan carapelekatan pada membran plasma

Kromosom ditarik apparatus mitosis (komponen sitoskeleton)

Organisasi sel Umumnya uniselular Umumnya multiselular, dan terjadiproses diferensiasi / spesialisasi sel

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Virus– membawa

informasi genetic berupa rantaitunggal atau gandaRNA atau DNA

– Materi genetiknyamengkode :

• Protein kapsul / kapsid

– aktif jika beradapada sel hidup

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Bioenergetika

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• 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

The Chemistry of Life: A 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 6CO2 + 6H2O + Energy

• Anabolic pathways: Build complex molecules from simpler ones by consuming energye.g. Photosynthesis in plants

6CO2 + 6H2O + Light energy 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

• Bioenergetics – The study of how organisms manage their energy resources– to maintain its high level of activity, a cell must

acquire & expend energy

Water behind dams has potential energy because of altitude

Chemical energy stored in molecules as a result of the arrangement of the atoms in these molecules

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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 Conservationof 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 endothermic

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Couple of terms• System: Is used to denote the matter under

study and refer to the rest of the universe-everything outside the systems the surroundings1. Closed system: e.g. a liquid in a thermos bottle is

isolated from its surroundings2. 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)

• carchemical energy (gasoline) converted to kinetic energy + the disorder of itssurroundings 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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• An important renewable high energy compound that powers cellularwork

• 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

ATP: Adenosine Triphosphate

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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 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 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 O2to make H2O

• Substrate-level phosphorylation -phosphate group moved from a substrate to ADP 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