Molbiol 2011-13-organelles
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Cell Theory
• The cell is the basic structural and functional unit of life
• Organismal activity depends on individual and collective activity of cells
• Biochemical activities of cells are dictated by subcellular structure
• Continuity of life has a cellular basis
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Figure 3.2
Secretion being releasedfrom cell by exocytosis
Peroxisome
Ribosomes
Roughendoplasmicreticulum
NucleusNuclear envelopeChromatin
Golgi apparatus
Nucleolus
Smooth endoplasmicreticulum
Cytosol
Lysosome
Mitochondrion
Centrioles
Centrosomematrix
Microtubule
Microvilli
Microfilament
Intermediate filaments
Plasmamembrane
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Plasma Membrane
• Separates intracellular fluids from extracellular fluids
• Plays a dynamic role in cellular activity• Glycocalyx is a glycoprotein area abutting the
cell that provides highly specific biological markers by which cells recognize one another
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Fluid Mosaic Model
• Double bilayer of lipids with imbedded, dispersed proteins
• Bilayer consists of phospholipids, cholesterol, and glycolipids– Glycolipids are lipids with bound carbohydrate– Phospholipids have hydrophobic and hydrophilic
bipoles
PLAY Membrane Structure
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Fluid Mosaic Model
Figure 3.3
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Functions of Membrane Proteins• Transport
• Enzymatic activity
• Receptors for signal transduction
Figure 3.4.1
PLAY Receptor Proteins
PLAY Enzymes
PLAY Transport Protein
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Functions of Membrane Proteins• Intercellular adhesion• Cell-cell recognition• Attachment to
cytoskeleton and extracellular matrix
Figure 3.4.2
PLAY Structural Proteins
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Plasma Membrane Surfaces
• Differ in the kind and amount of lipids they contain
• Glycolipids are found only in the outer membrane surface
• 20% of all membrane lipid is cholesterol
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Lipid Rafts
• Make up 20% of the outer membrane surface• Composed of sphingolipids and cholesterol• Are concentrating platforms for cell-signaling
molecules
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Membrane Junctions
• Tight junction – impermeable junction that encircles the cell
• Desmosome – anchoring junction scattered along the sides of cells
• Gap junction – a nexus that allows chemical substances to pass between cells
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Membrane Junctions: Tight Junction
Figure 3.5a
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Membrane Junctions: Desmosome
Figure 3.5b
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Membrane Junctions: Gap Junction
Figure 3.5c
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Membrane Potential• Voltage across a membrane• Resting membrane potential – the point where
K+ potential is balanced by the membrane potential– Ranges from –20 to –200 mV– Results from Na+ and K+ concentration gradients
across the membrane– Differential permeability of the plasma membrane
to Na+ and K+
• Steady state – potential maintained by active transport of ions
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Generation and Maintenance of Membrane Potential
PLAY InterActive Physiology ®: Nervous System I: The Membrane Potential
Figure 3.15
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Cell Adhesion Molecules (CAMs)
• Anchor cells to the extracellular matrix• Assist in movement of cells past one another• Rally protective white blood cells to injured or
infected areas
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Roles of Membrane Receptors• Contact signaling – important in normal
development and immunity• Electrical signaling – voltage-regulated “ion
gates” in nerve and muscle tissue• Chemical signaling – neurotransmitters bind to
chemically gated channel-linked receptors in nerve and muscle tissue
• G protein-linked receptors – ligands bind to a receptor which activates a G protein, causing the release of a second messenger, such as cyclic AMP
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Operation of a G Protein
• An extracellular ligand (first messenger), binds to a specific plasma membrane protein
• The receptor activates a G protein that relays the message to an effector protein
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Operation of a G Protein
• The effector is an enzyme that produces a second messenger inside the cell
• The second messenger activates a kinase• The activated kinase can trigger a variety of
cellular responses
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Operation of a G Protein
Figure 3.16
Extracellular fluid
Cytoplasm
Inactivesecondmessenger
Cascade of cellular responses(metabolic and structural changes)
Effector(e.g., enzyme)
Activated(phosphorylated)kinases
First messenger(ligand)
Activesecondmessenger(e.g., cyclicAMP)
Membranereceptor
G protein
1
2
3 4
5
6
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Operation of a G Protein
Figure 3.16
Extracellular fluid
Cytoplasm
First messenger(ligand)
Membranereceptor
1
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Operation of a G Protein
Figure 3.16
Extracellular fluid
Cytoplasm
First messenger(ligand)
Membranereceptor
G protein
1
2
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Operation of a G Protein
Figure 3.16
Extracellular fluid
Cytoplasm
Effector(e.g., enzyme)
First messenger(ligand)
Membranereceptor
G protein
1
2
3
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Operation of a G Protein
Figure 3.16
Extracellular fluid
Cytoplasm
Inactivesecondmessenger
Effector(e.g., enzyme)
First messenger(ligand)
Activesecondmessenger(e.g., cyclicAMP)
Membranereceptor
G protein
1
2
3 4
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Operation of a G Protein
Figure 3.16
Extracellular fluid
Cytoplasm
Inactivesecondmessenger
Effector(e.g., enzyme)
Activated(phosphorylated)kinases
First messenger(ligand)
Activesecondmessenger(e.g., cyclicAMP)
Membranereceptor
G protein
1
2
3 4
5
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Operation of a G Protein
Figure 3.16
Extracellular fluid
Cytoplasm
Inactivesecondmessenger
Cascade of cellular responses(metabolic and structural changes)
Effector(e.g., enzyme)
Activated(phosphorylated)kinases
First messenger(ligand)
Activesecondmessenger(e.g., cyclicAMP)
Membranereceptor
G protein
1
2
3 4
5
6
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Cytoplasm
• Cytoplasm – material between plasma membrane and the nucleus
• Cytosol – largely water with dissolved protein, salts, sugars, and other solutes
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Cytoplasm
• Cytoplasmic organelles – metabolic machinery of the cell
• Inclusions – chemical substances such as glycosomes, glycogen granules, and pigment
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Cytoplasmic Organelles
• Specialized cellular compartments• Membranous – Mitochondria, peroxisomes, lysosomes,
endoplasmic reticulum, and Golgi apparatus• Nonmembranous– Cytoskeleton, centrioles, and ribosomes
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Mitochondria
• Double membrane structure with shelf-like cristae
• Provide most of the cell’s ATP via aerobic cellular respiration
• Contain their own DNA and RNA
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Mitochondria
Figure 3.17a, b
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Ribosomes
• Granules containing protein and rRNA• Site of protein synthesis• Free ribosomes synthesize soluble proteins• Membrane-bound ribosomes synthesize
proteins to be incorporated into membranes
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Endoplasmic Reticulum (ER)
• Interconnected tubes and parallel membranes enclosing cisternae
• Continuous with the nuclear membrane• Two varieties – rough ER and smooth ER
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Endoplasmic Reticulum (ER)
Figure 3.18a, c
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Rough (ER)
• External surface studded with ribosomes• Manufactures all secreted proteins• Responsible for the synthesis of integral
membrane proteins and phospholipids for cell membranes
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Signal Mechanism of Protein Synthesis
• mRNA – ribosome complex is directed to rough ER by a signal-recognition particle (SRP)
• SRP is released and polypeptide grows into cisternae
• The protein is released into the cisternae and sugar groups are added
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Signal Mechanism of Protein Synthesis
• The protein folds into a three-dimensional conformation
• The protein is enclosed in a transport vesicle and moves toward the Golgi apparatus
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Signal Mechanism of Protein Synthesis
Figure 3.19
Cytosol
Ribosomes
mRNA
Coatomer-coatedtransportvesicle
Transportvesiclebudding off
Releasedglycoprotein
ERcisterna
ERmembrane
Signal-recognitionparticle(SRP)
Signalsequence
Receptorsite
Sugargroup
SignalsequenceremovedGrowing
polypeptide
1
2
34
5
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Signal Mechanism of Protein Synthesis
Figure 3.19
Cytosol
mRNA
ERcisterna
ERmembrane
Signal-recognitionparticle(SRP)
Signalsequence
Receptorsite
1
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Signal Mechanism of Protein Synthesis
Figure 3.19
Cytosol
mRNA
ERcisterna
ERmembrane
Signal-recognitionparticle(SRP)
Signalsequence
Receptorsite Growing
polypeptide
1
2
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Signal Mechanism of Protein Synthesis
Figure 3.19
Cytosol
Ribosomes
mRNA
ERcisterna
ERmembrane
Signal-recognitionparticle(SRP)
Signalsequence
Receptorsite
SignalsequenceremovedGrowing
polypeptide
1
2
3
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Signal Mechanism of Protein Synthesis
Figure 3.19
Cytosol
Ribosomes
mRNA
Releasedglycoprotein
ERcisterna
ERmembrane
Signal-recognitionparticle(SRP)
Signalsequence
Receptorsite
SignalsequenceremovedGrowing
polypeptide
1
2
34
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Signal Mechanism of Protein Synthesis
Figure 3.19
Cytosol
Ribosomes
mRNA
Transportvesiclebudding off
Releasedglycoprotein
ERcisterna
ERmembrane
Signal-recognitionparticle(SRP)
Signalsequence
Receptorsite
Sugargroup
SignalsequenceremovedGrowing
polypeptide
1
2
34
5
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Signal Mechanism of Protein Synthesis
Figure 3.19
Cytosol
Ribosomes
mRNA
Coatomer-coatedtransportvesicle
Transportvesiclebudding off
Releasedglycoprotein
ERcisterna
ERmembrane
Signal-recognitionparticle(SRP)
Signalsequence
Receptorsite
Sugargroup
SignalsequenceremovedGrowing
polypeptide
1
2
34
5
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Smooth ER• Tubules arranged in a looping network• Catalyzes the following reactions in various
organs of the body– In the liver – lipid and cholesterol metabolism,
breakdown of glycogen and, along with the kidneys, detoxification of drugs
– In the testes – synthesis of steroid-based hormones
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Smooth ER• Catalyzes the following reactions in various
organs of the body (continued)– In the intestinal cells – absorption, synthesis, and
transport of fats– In skeletal and cardiac muscle – storage and
release of calcium
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Golgi Apparatus
• Stacked and flattened membranous sacs• Functions in modification, concentration, and
packaging of proteins• Transport vessels from the ER fuse with the cis
face of the Golgi apparatus
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Golgi Apparatus
• Proteins then pass through the Golgi apparatus to the trans face
• Secretory vesicles leave the trans face of the Golgi stack and move to designated parts of the cell
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Golgi Apparatus
Figure 3.20a
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Role of the Golgi Apparatus
Figure 3.21
Secretion by exocytosisExtracellular fluid
Plasma membrane
Vesicle incorporatedinto plasma membrane
Coatomercoat
Lysosomes containing acidhydrolase enzymes
PhagosomeProteins in cisterna
Membrane
Vesicle
Pathway 3
Pathway 2
Secretory vesicles
Proteins
Pathway 1
Golgi apparatus
CisternaRough ER
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Role of the Golgi Apparatus
Figure 3.21
Secretion by exocytosisExtracellular fluid
Proteins in cisterna
Membrane
Vesicle
Secretory vesicles
Proteins
Pathway 1
Golgi apparatus
CisternaRough ER
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Role of the Golgi Apparatus
Figure 3.21
Secretion by exocytosisExtracellular fluid
Plasma membrane
Vesicle incorporatedinto plasma membrane
Coatomercoat
Proteins in cisterna
Membrane
Vesicle
Pathway 2Golgi apparatus
CisternaRough ER
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Role of the Golgi Apparatus
Figure 3.21
Extracellular fluid
Plasma membrane
Lysosomes containing acidhydrolase enzymes
PhagosomeProteins in cisterna
Membrane
Vesicle
Pathway 3
Secretory vesicles
Golgi apparatus
CisternaRough ER
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Role of the Golgi Apparatus
Figure 3.21
Secretion by exocytosisExtracellular fluid
Plasma membrane
Vesicle incorporatedinto plasma membrane
Coatomercoat
Lysosomes containing acidhydrolase enzymes
PhagosomeProteins in cisterna
Membrane
Vesicle
Pathway 3
Pathway 2
Secretory vesicles
Proteins
Pathway 1
Golgi apparatus
CisternaRough ER
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Lysosomes
• Spherical membranous bags containing digestive enzymes
• Digest ingested bacteria, viruses, and toxins• Degrade nonfunctional organelles• Breakdown glycogen and release thyroid
hormone
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Lysosomes
• Breakdown nonuseful tissue• Breakdown bone to release Ca2+
• Secretory lysosomes are found in white blood cells, immune cells, and melanocytes
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Endomembrane System
• System of organelles that function to: – Produce, store, and export biological molecules– Degrade potentially harmful substances
• System includes:– Nuclear envelope, smooth and rough ER,
lysosomes, vacuoles, transport vesicles, Golgi apparatus, and the plasma membrane
PLAY Endomembrane System
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Endomembrane System
Figure 3.23
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Peroxisomes
• Membranous sacs containing oxidases and catalases
• Detoxify harmful or toxic substances• Neutralize dangerous free radicals– Free radicals – highly reactive chemicals with
unpaired electrons (i.e., O2–)
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Cytoskeleton
• The “skeleton” of the cell• Dynamic, elaborate series of rods running
through the cytosol• Consists of microtubules, microfilaments, and
intermediate filaments
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Cytoskeleton
Figure 3.24a-b
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Cytoskeleton
Figure 3.24c
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Microtubules
• Dynamic, hollow tubes made of the spherical protein tubulin
• Determine the overall shape of the cell and distribution of organelles
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Microfilaments
• Dynamic strands of the protein actin• Attached to the cytoplasmic side of the
plasma membrane• Braces and strengthens the cell surface• Attach to CAMs and function in endocytosis
and exocytosis
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Intermediate Filaments
• Tough, insoluble protein fibers with high tensile strength
• Resist pulling forces on the cell and help form desmosomes
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Motor Molecules
• Protein complexes that function in motility• Powered by ATP• Attach to receptors on organelles
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Motor Molecules
Figure 3.25a
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Motor Molecules
Figure 3.25b
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Centrioles
• Small barrel-shaped organelles located in the centrosome near the nucleus
• Pinwheel array of nine triplets of microtubules• Organize mitotic spindle during mitosis• Form the bases of cilia and flagella
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Centrioles
Figure 3.26a, b
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Cilia
• Whip-like, motile cellular extensions on exposed surfaces of certain cells
• Move substances in one direction across cell surfaces
PLAY Cilia and Flagella
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Cilia
Figure 3.27a
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Cilia
Figure 3.27b
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Cilia
Figure 3.27c
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Nucleus
• Contains nuclear envelope, nucleoli, chromatin, and distinct compartments rich in specific protein sets
• Gene-containing control center of the cell• Contains the genetic library with blueprints for
nearly all cellular proteins• Dictates the kinds and amounts of proteins to
be synthesized
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Nucleus
Figure 3.28a
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Nuclear Envelope
• Selectively permeable double membrane barrier containing pores
• Encloses jellylike nucleoplasm, which contains essential solutes
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Nuclear Envelope
• Outer membrane is continuous with the rough ER and is studded with ribosomes
• Inner membrane is lined with the nuclear lamina, which maintains the shape of the nucleus
• Pore complex regulates transport of large molecules into and out of the nucleus
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Nucleoli
• Dark-staining spherical bodies within the nucleus
• Site of ribosome production
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Chromatin
• Threadlike strands of DNA and histones
• Arranged in fundamental units called nucleosomes
• Form condensed, barlike bodies of chromosomes when the nucleus starts to divide
Figure 3.29
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Figure 3.30
Cell Cycle• Interphase– Growth (G1),
synthesis (S), growth (G2)
• Mitotic phase– Mitosis and
cytokinesis
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Interphase• G1 (gap 1) – metabolic activity and vigorous
growth• G0 – cells that permanently cease dividing• S (synthetic) – DNA replication• G2 (gap 2) – preparation for division
PLAY Late Interphase