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 Nuclear envelope 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 ER and migrate to fuse with membranes of Golgi apparatus. Proteins are modified within the Golgi compartments. Proteins are then packaged within different vesicle types, depending on their ultimate destination. Plasma mem- brane Secretion by exocytosis Vesicle becomes lysosome Golgi apparatus Rough ER ER membrane Phagosome Proteins in cisterna Pathway B: Vesicle membrane to be incorporated into plasma membrane Pathway A: Vesicle contents destined for exocytosis Extracellular fluid Secretory vesicle Pathway C: Lysosome containing acid hydrolase enzymes 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 Golgi apparatus Transport vesicle Plasma membrane 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 spherical protein subunits called actins (a) Microfilaments Actin subunit Microfilaments form the blue network surrounding the pink nucleus in this photo.

Figure 3.23b (b) Intermediate filaments Tough, insoluble protein fibers constructed like woven ropes Fibrous subunits Intermediate filaments form the purple batlike network in this photo.

Figure 3.23c (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.

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 Plasma membrane Outer microtubule doublet Dynein arms Central microtubule Radial spoke TEM Triplet Basal body (centriole) Cilium Microtubules Plasma membrane Basal body Cross-linking proteins inside outer doublets Cross-linking proteins inside outer doublets 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. 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. A cross section through the cilium shows the “9 + 2” arrangement of microtubules. TEM

Figure 3.27 (a) Phases of ciliary motion. (b) Traveling wave created by the activity of many cilia acting together propels mucus across cell surfaces. Power, or propulsive, stroke Layer of mucus Cell surface Recovery stroke, when cilium is returning to its initial position

Cellular Extensions Microvilli Fingerlike extensions of plasma membrane Increase surface area for absorption

Figure 3.28 Microvillus Actin filaments Terminal web

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 Nuclear pores Fracture line of outer membrane Nuclear pore complexes. Each pore is ringed by protein particles. Surface of nuclear envelope. Nuclear lamina. The netlike lamina composed of inter- mediate filaments formed by lamins lines the inner surface of the nuclear envelope. (b)

Figure 3.30 Metaphase chromosome (at midpoint of 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 double helix (2-nm diameter) 2 Chromatin (“beads on a string”) structure with nucleosomes 3 Tight helical fiber (30-nm diameter) 5 Chromatid (700-nm diameter) 4 Looped domain structure (300-nm diameter)

cell GROWTH AND REPRODUCTION

The Cell Life Cycle Includes: Interphase and Cell division (mitotic phase)

Interphase Period from cell formation to cell division Chromatin is spread out in the cell for DNA replication Interphase has three subphases: G 1 (gap 1)—growth and metabolism S phase (synthetic phase)—DNA replication G 2 (gap 2)—preparation for division

Figure 3.31 G 1 Growth S Growth and DNA synthesis G 2 Growth and final preparations for division M G 2 checkpoint G 1 checkpoint (restriction point)

Figure 3.33 Centrosomes (each w/ 2 centrioles) Nucleolus Interphase Plasma membrane Nuclear envelope Chromatin Interphase

DNA Replication Occurs During the S- phase of Interphase Helicase untwists the double helix and exposes complementary chains Each nucleotide strand serves as a template for building a new complementary strand DNA Polymerase positions complementary nucleotides along the template strand and then covalently links them together

DNA Replication End result: two DNA molecules formed from the original This process is called semiconservative replication

Figure 3.32 Adenine Thymine Cytosine Guanine Old (template) strand Lleading and lagging strands are synthesized in opposite directions DNA polymerase Lagging strand Leading strand Free nucleotides Template for synthesis of new strand Chromosome Helicase unwinds the double helix and Exposes bases Old DNA Replication fork

Cell Division (Mitosis) Mitotic (M) phase of the cell cycle Essential for body growth and tissue repair Does not occur in most mature cells of nervous tissue, skeletal and cardiac muscle

Cell Division (Mitosis) Cell Division Includes two distinct events: 1.Mitosis—four stages of nuclear division: Prophase Metaphase Anaphase Telophase 2.Cytokinesis—division of cytoplasm by cleavage furrow

Figure 3.31 G 1 Growth S Growth and DNA synthesis G 2 Growth M

Prophase Chromosomes condense and become visible Centrioles migrate toward opposite poles Mitotic spindles and asters form Nuclear envelope fragments Microtubules attach to centromeres and draw them toward cell equator

Figure 3.33 Early mitotic spindle Early Prophase Centromere Aster Chromosome consisting of two sister chromatids Early Prophase

Figure 3.33 Spindle pole Kinetochore microtubule Polar microtubule Late Prophase Fragments of nuclear envelope Late Prophase

Metaphase Centromeres of chromosomes are aligned at the equator Metaphase plate = The plane midway between the poles of the cell

Figure 3.33 Spindle Metaphase plate Metaphase

Anaphase Shortest phase Centromeres of chromosomes split simultaneously— each chromatid now becomes a chromosome Chromosomes are pulled to opposite poles by microtubules

Figure 3.33 Anaphase Daughter chromosomes Anaphase

Telophase Begins when chromosome movement stops The two sets of chromosomes uncoil to form chromatin Nuclear membrane forms around each chromatin mass Nucleoli reappear and spindle disappears

Cytokinesis Begins during late anaphase Ring of actin microfilaments contracts to form a cleavage furrow Two daughter cells are pinched apart, each containing a nucleus identical to the original

Figure 3.33 Contractile ring at cleavage furrow Nuclear envelope forming Nucleolus forming Telophase Telophase and Cytokinesis