MOLECULAR ORGANIZATION OF EUKARYOTIC CELL
Dwi Ari Pujianto, Ph.D Departemen Biologi FKUI
PROKARYOTIC CELL
Major intracellular compartment of an animal cell
Genetic information is inside the chromosomes
Nucleosomes are a basic unit of eukaryotic chromosome structure
• The protein that bind to the DNA to form chromosome
• Histone
• Non histone
• Histones are responsible for the first and most basic level of chromosome packing
• Histone + DNA Nucleosome
+ Nuclear
DNA = Chromatin
Structural organization of The Nucleosome
Membrane functions
• Enclose cells and organelles
• Maintain specificity
• Ion gradient Molecules transport
• Sensor/receptor
Membrane Biology
• Lipid bilayer (5 nm), impermeable towards most of water-soluble molecules
• Protein molecules, function as
• Transport specific molecules
• ATP synthesis mitochondria
• Receptor
• Connect cytoskeleton with extracellular matrix
General structure of cell membrane
Electron micrograph of human RBC
Energy-generating metabolim in mitochondria
Lipid Bilayer
-Struktur dasar pada membran sel proporsi lipid = 50% dari total massa - membran lipid bersifat amphiphilic
Amphiphilic
Hydrophilic (water-loving) / polar
Hydrophobic (water-fearing) / non polar
- Lipid yang paling banyak adalah phospholipid yang tersusun oleh -Satu polar head group
-Dua hydrophobic hydrocarbon tail (fatty acids) 14 -24 atom carbon -Cis-double bond unsaturated small kink menentukan
membrane fluidity
Phosphoglycerides
-Mempunyai 3 atom carbon pada Glycerol backbone
- Dua rantai asam lemak (fatty acid) dihubungkan oleh ikatan ester pada glyserol, sedangkan atom ke 3 dari glyserol berhubungan dengan phosphate group
-Phosphate group berhubungan dengan salah satu head group Choline, ethanolamine, serine
-Kombinasi dari beberapa fatty acid dan head group - Phosphatidylethanolamine,
- Phosphatidylserine - Phosphatidylcholine
Phosphoglyceride utama Pada sel mamalia
Bagian-bagian dari molekul phosphogliceride
Prinsip membran transport
-Pada protein-free lipid bilayer
- Molekul berdifusi berdasarkan gradien konsentrasi (Tinggi Rendah) -Faktor yang menentukan laju difusi :
- ukuran molekul
- Kelarutan dalam minyak - Muatan
-Makin kecil ukuran molekul dan makin larut dlm minyak (makin hidrofobik dan makin non polar) makin cepat berdifusi dengan lipid bilayer
- Iipid bilayer highly impermeable terhadap molekul yg bermuatan (ion)
Relative permeability of synthetic lipid bilayer to different classes of molecules
Protein Membran
Lipid bilayer struktur dasar membran biologi
Protein membran berperan dalam fungsi spesifik
Myelin membran < 25% adalah protein (less functions)
Membran yg terlibat dlm produksi ATP 75% protein
Berbagai cara protein berasosiasi dengan lipid bilayer
Transmembrane Protein With hidrophobic & hidrophilic
regions
Peripheral membrane protein Integral membrane protein
Soluble protein In the cytosol
Glycosylphosphatidylinositol (GPI) anchor
Terdapat 2 klas utama Membran Transport Protein
Transporter (carrier atau permease)
- mengikat solute yang spesifik untuk ditransport
- Protein ini mengalami serangkaian perubahan konformasi untuk men- transfer solute yg telah terikat melewati membran
- Bisa aktif dan pasif Channel
- Interaksi dengan solute lemah
- Terbentuk aqueous pores terbuka specific solutes (inorganic ion dengan ukuran dan muatan yang sesuai) bisa lewat
- Pasif transport
Transporters and Channel Proteins
Organelles Functions (1)
• Nucleus, contains the genome
• Cytoplasm Cytosol and cytoplasmic organelles
• Endoplasmic reticulum rER, sER, protein
synthesis, produces most of the lipid, store Ca2+ ion
• Golgi apparatus Golgi cisternae, receives lipids and
proteins from ER and dispatches to various destinatios
after modifications
Organelles Functions (2)
• Mitochondria and chloroplast, generate most of the ATP
• Lysosomes digestive enzymes that degrades defunct organlles or endocytosed molecules
• Endosomes, provide environment for endocytosed materials to be sorted before entering lysosomes
• Peroxisomes, contains enzymes used in various
oxidative reactions
Evolution of Eukaryotic Cell and its internal membrane
Family of organelles based on their evolution
1. Nukleus dan cytosol Communication via nuclear pore complexes
2. Organelles that belong to the secretory and endocytic pathways ER, Golgi apparatus, Endosomes, lysosomes, transport vesicles, peroxisomes
3. Mitochondria/Plastids
= Topologically equivalent
1. Gated transport = proteins migrate between cyitosol dan nukleus through nuclear pore
2. Transmembrane transport = protein tranlocators move molecules between
compartments which are NOT topologically equivalent, e.g. Cyitosol to ER lumen or Citysol to Mitochondria
3. Vesicular transport = Molecule transports via vesicle formation. That is from lumen of an organele to other organele which are topologically equivalentt , e.g. From ER to Golgi Apparatus
Mechanism of transport molecules among the organelles
Typical of an Eukaryotic Cell
To function properly, cells must
Organize in space
Interact mechanically with environment Correctly shaped
Physically robust
Properly structured internally
Cytoskeleton
Cytoskeleton
• Intermediate filaments Mechanical strength
• Microtubules determine position of
membrane-enclosed organelles and direct intracellular transport
• Actin filaments Determine the shape of cell’s
surface, whole-cell locomotion
Comparison of three major types of Protein filaments
The Cytoskeleton
Microtubules (green) Actin filaments (red)
Accessory proteins
• Link the filaments to other cell components as well as to each other
• Essential for controlled assembly of the
cytoskeletal filaments in particular locations
• Accessory proteins motor protein that convert
ATP hydrolysis into mechanical forces
Cytoskeletal filaments are dinamic and adaptable
• Microtubules can rearrange into bipolar mitotic spindle during mitosis, cilia, flagella
• Actin filaments lamelipodia, filopodia,
contractile ring during mitosis
Microtubules (green) Actin filaments (red)
Major motor proteins of the spindle
Notes :
Kinesin-5 proteins have 2 motor domain, move toward the plus end forcing the poles apart Kinesin-4 and 10 associated with chromosome move chromosome away from the pole Kinesin-14 minus-end directed motors tends to pull the poles together
Dynein responsible for organizing microtubules
Cytoskeletal filaments are constructed from smaller protein subunits
Neutrophil’s cytoskeletal rearragement
in pursuit of bacteria
The cytoskeleton can also form stable structures
• Occur in cells that have achieved a stable, differentiated morphology (remodelled and replaced every 48 hr)
• Microvilli and Cilia maintain a constant location
• Maintain cellular polarity
Organization of the cytroskeleton in polarized epithelial cells
LOCALIZATION of The MOLECULES in the CELL:
The Signal Sequence
Typical Signal Sequences
Eukaryotic Cell Division
The Cell Cycle Control System
Two key components of the cell-cycle control system
Without cyclin, Cdk is inactive
Four Classes of Cyclin
• G1/S-cyclins : Activate Cdks in late G1
• S-cyclins : Stimulate chromosome duplication
• M-cyclins : Activate Cdks that stimulate entry into mitosis at G2/M checkpoint
• G1-cyclins : Help govern the activities of the
G1/S-cyclins
Cyclin-Cdk complexes in the cell-cycle control system
Anaphase-promoting complex Or
Cyclosome
Summary
• Eukaryotic cells are enclosed by biological membrane to maintain specificity
• Genetic information is organized into chromosomes and package into nucleosomes
• Each organelle has a specific function
• Transport molecules among the organelles: Gated, transmembrane or vesicular transport
• Cytoskeleton support the shape and transport molecules inside the cell
• Eukaryotic cells undergo cell division to reproduce
