ORGANELLES OF THE CYTOPLASM Cytoplasm Located between plasma
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
Outer mitochondrial membrane Ribosome Mitochondrial DNA (a) Inner mitochondrial membrane Cristae Matrix (c) Enzymes (b) Figure 3. 17
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
Smooth ER Nuclear envelope Rough ER Ribosomes (a) Diagrammatic view of smooth and rough ER Figure 3. 18 a
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
1 Protein- containing vesicles pinch off rough ER and migrate to fuse with membranes of Golgi apparatus. Rough ER Phagosome ER membrane Proteins in cisterna Pathway C: Lysosome containing acid hydrolase enzymes Vesicle becomes lysosome 2 Proteins are modified within the Golgi compartments. 3 Proteins are then packaged within different vesicle types, depending on their ultimate destination. Plasma membrane Golgi apparatus Pathway A: Vesicle contents destined for exocytosis Secretory vesicle Secretion by exocytosis Pathway B: Vesicle membrane to be incorporated into plasma membrane Extracellular fluid Figure 3. 20
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 Ca 2+
Nucleus Nuclear envelope Smooth ER Rough ER Vesicle Plasma membrane Lysosome Golgi apparatus Transport vesicle Figure 3. 22
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
(a) Microfilaments Strands made of spherical protein subunits called actins Actin subunit Microfilaments form the blue network surrounding the pink nucleus in this photo. Figure 3. 23 a
(b) Intermediate filaments Tough, insoluble protein fibers constructed like woven ropes Fibrous subunits Intermediate filaments form the purple batlike network in this photo. Figure 3. 23 b
(c) Microtubules Hollow tubes of spherical protein subunits called tubulins Tubulin subunits Microtubules appear as gold networks surrounding the cells’ pink nuclei in this photo. Figure 3. 23 c
Centrioles • Involved in: cell division • Found within the centrosome
Centrosome matrix Centrioles (a) Microtubules Figure 3. 25 a
Cellular Extensions • Flagella • Whiplike, motile extensions on surfaces of certain cells • propel whole cells (tail of sperm) • Cilia move substances across cell surfaces
Outer microtubule doublet Dynein arms Central microtubule Cross-linking proteins inside outer doublets Radial spoke TEM A cross section through the Microtubules cilium shows the “ 9 + 2” arrangement of microtubules. Cross-linking proteins inside outer doublets Radial spoke Plasma membrane Basal body Triplet TEM A longitudinal section of a cilium shows microtubules running the length of the structure. The doublets also have attached motor proteins, the dynein arms. The outer microtubule doublets and the two central microtubules are held together by cross-linking proteins and radial spokes. Cilium TEM A cross section through the basal 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. Basal body (centriole) Figure 3. 26
Power, or propulsive, stroke 1 2 3 4 Recovery stroke, when cilium is returning to its initial position 5 6 7 (a) Phases of ciliary motion. Layer of mucus Cell surface (b) Traveling wave created by the activity of many cilia acting together propels mucus across cell surfaces. Figure 3. 27
Cellular Extensions • Microvilli • Fingerlike extensions of plasma membrane • Increase surface area for absorption
Microvillus Actin filaments Terminal web Figure 3. 28
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
Nuclear pores Nuclear envelope Chromatin (condensed) Nucleus Nucleolus Cisternae of rough ER (a) Figure 3. 29 a
Surface of nuclear envelope. Fracture line of outer membrane Nuclear pores Nucleus Nuclear lamina. The netlike lamina composed of intermediate filaments formed by lamins lines the inner surface of the nuclear envelope. (b) Nuclear pore complexes. Each pore is ringed by protein particles. Figure 3. 29 b
1 DNA double helix (2 -nm diameter) Histones 2 Chromatin (“beads on a string”) structure with nucleosomes Linker DNA Nucleosome (10 -nm diameter; eight histone proteins wrapped by two winds of the DNA double helix) (a) 3 Tight helical fiber (30 -nm diameter) 4 Looped domain 5 Chromatid structure (300 -nm diameter) (700 -nm diameter) (b) Metaphase chromosome (at midpoint of cell division) Figure 3. 30
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