organelles of the cytoplasm. cytoplasm located between plasma membrane and nucleus cytosol water...
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ORGANELLES OF THE CYTOPLASM
Cytoplasm• Located between plasma membrane and nucleus• Cytosol• Water with solutes (protein, salts, sugars, etc.)
• Cytoplasmic organelles• Metabolic machinery of cell
Cytoplasmic Organelles
• Membranous• Mitochondria• Peroxisomes• Lysosomes• Endoplasmic reticulum• Golgi apparatus
• Nonmembranous• Cytoskeleton • Centrioles • Ribosomes
Mitochondria
• Double-membrane structure with shelflike cristae• Provide most of cell’s ATP via aerobic cellular respiration• Contain their own DNA and RNA
Figure 3.17
Enzymes
Matrix
Cristae
Mitochondrial DNA
Ribosome
Outer mitochondrial membrane
Inner mitochondrial membrane
(b)
(a)
(c)
Ribosomes
• Site of protein synthesis• Free ribosomes synthesize soluble proteins • Membrane-bound ribosomes synthesize proteins destined for
membranes or secretion
Endoplasmic Reticulum (ER)
• System of Interconnected tubes and parallel membranes enclosing cisternae• Continuous with nuclear membrane• Two varieties:• Rough ER• Smooth ER
Figure 3.18a
Nuclearenvelope
Ribosomes
Rough ER
Smooth ER
(a) Diagrammatic view of smooth and rough ER
Rough ER
• External surface studded with ribosomes• Manufactures all secreted proteins• Synthesizes membrane integral proteins and phospholipids
Smooth ER
• Its enzymes catalyze reactions involved with:• In the liver-Lipid metabolism, cholesterol synthesis, synthesis of lipid
components of lipoproteins• In testes: Synthesis of steroid-based hormones (testes)• In skeletal & cardiac muscle—storage & release of calcium
Golgi Apparatus
• Stacked and flattened membranous sacs• Modifies, concentrates, and packages proteins and lipids• Proteins exit via secretory vesicles
Figure 3.20
Protein-containing vesicles pinch off rough ERand migrate to fuse with membranes ofGolgi apparatus.
Proteins aremodified withinthe Golgi compartments.
Proteins arethen packagedwithin differentvesicle types, depending ontheir ultimatedestination.
Plasmamem-brane
Secretion byexocytosis
Vesicle becomeslysosome
Golgiapparatus
Rough ER ERmembrane
Phagosome
Proteins incisterna
Pathway B:Vesicle membraneto be incorporatedinto plasmamembranePathway A:
Vesicle contentsdestined for exocytosis Extracellular fluid
Secretoryvesicle
Pathway C:Lysosome containing acid hydrolaseenzymes
1
3
2
Lysosomes
• Spherical membranous organelles containing digestive enzymes (acid hydrolases)• Can degrade/breakdown:• Ingested bacteria, viruses, and toxins• Nonfunctional organelles• Break down and release glycogen• Break down bone to release Ca2+
Figure 3.22
Golgiapparatus
Transportvesicle
Plasmamembrane
Vesicle
Smooth ER
Rough ER
Nuclear envelope
Lysosome
Nucleus
Peroxisomes
• Membranous sacs containing powerful oxidases and catalases• Detoxify harmful or toxic substances• Neutralize dangerous free radicals
Cytoskeleton• Elaborate series of rods throughout cytosol• Microtubules -hollow tubes, mostly radiating from a
centrosome; determine overall shape of cell and distribution of organelles• Microfilaments -actin strands attached to cytoplasmic
side of plasma membrane; Involved in cell motility, change in shape, endocytosis and exocytosis• Intermediate filaments-Tough, insoluble ropelike protein
fibers ;Resist pulling forces on the cell and attach to desmosomes
Figure 3.23a
Strands made of sphericalprotein subunits called actins
(a) Microfilaments
Actin subunit
Microfilaments form the blue networksurrounding the pink nucleus in thisphoto.
Figure 3.23b
(b) Intermediate filaments
Tough, insoluble protein fibersconstructed like woven ropes
Fibrous subunits
Intermediate filaments form the purplebatlike network in this photo.
Figure 3.23c
(c) MicrotubulesHollow tubes of spherical protein
subunits called tubulins
Tubulin subunits
Microtubules appear as gold networkssurrounding the cells’ pink nuclei inthis photo.
Centrioles
• Involved in: cell division• Found within the centrosome
Figure 3.25a
Centrosome matrix
(a)
Centrioles
Microtubules
Cellular Extensions
• Flagella• Whiplike, motile extensions on surfaces of certain cells• propel whole cells (tail of sperm)
• Cilia move substances across cell surfaces
Figure 3.26
Plasmamembrane
Outer microtubuledoublet
Dynein arms
Centralmicrotubule
Radial spoke
Radial spoke
TEM
TEM
Triplet
Basal body(centriole)
Cilium
Microtubules
Plasmamembrane
Basal body
Cross-linkingproteins insideouter doublets
Cross-linkingproteins insideouter doublets
A longitudinal section of acilium shows microtubules running the length of thestructure.
The doubletsalso have attached motor proteins, the dynein arms.
The outermicrotubule doublets and the two central microtubules are held together by cross-linking proteins and radial spokes.
A cross section through thebasal body. The nine outer doublets of a cilium extend into a basal body where each doublet joins another microtubule to form a ring of nine triplets.
A cross section through thecilium shows the “9 + 2”arrangement of microtubules.
TEM
Figure 3.27
(a) Phases of ciliary motion.
(b) Traveling wave created by the activity ofmany cilia acting together propels mucusacross cell surfaces.
Power, orpropulsive,stroke
Layer of mucus
Cell surface
Recovery stroke, whencilium is returning to itsinitial position
1 2 3 4 5 6 7
Cellular Extensions
• Microvilli• Fingerlike extensions of plasma membrane• Increase surface area for absorption
Figure 3.28
Microvillus
Actinfilaments
Terminalweb
Nucleus
• Genetic library with blueprints for nearly all cellular proteins• Responds to signals and dictates kinds and amounts of proteins to be
synthesized• Surrounded by nuclear envelope (perforated for exit of material)• Contains threadlike strands of DNA (30%), histone proteins (60%),
and RNA (10%) called chromatin• Also contains nucleoli : dark-staining spherical bodies involved in
ribosome assembly
Figure 3.29a
Chromatin (condensed)
Nuclear envelope Nucleus
Nuclear pores
Nucleolus
Cisternae of rough ER
(a)
Figure 3.29b
Nucleus
Nuclearpores
Fractureline of outermembrane
Nuclear pore complexes.Each pore is ringed byprotein particles.
Surface of nuclear envelope.
Nuclear lamina. The netlikelamina composed of inter-mediate filaments formed bylamins lines the inner surfaceof the nuclear envelope.
(b)
Figure 3.30
Metaphasechromosome(at midpointof cell division)
Nucleosome (10-nm diameter; eight histone proteins wrapped by two winds of the DNA double helix)
Linker DNA
Histones
(a)
(b)
1 DNA doublehelix (2-nm diameter)
2 Chromatin(“beads on a string”) structurewith nucleosomes
3 Tight helical fiber(30-nm diameter)
5 Chromatid(700-nm diameter)
4 Looped domain structure (300-nm diameter)