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Three regions/structures Nucleus Largest organelle; genetic library with blueprints for nearly all cellular proteins Responds to signals; dictates kinds and amounts of proteins synthesized Most cells uninucleate; skeletal muscle cells, bone destruction cells, and some liver cells are multinucleate; red blood cells are anucleate Three regions/structures © 2013 Pearson Education, Inc.

Nuclear pores Nucleus Nuclear envelope Chromatin (condensed) Nucleolus Figure 3.29a The nucleus. Nuclear pores Nucleus Nuclear envelope Chromatin (condensed) Nucleolus Cisterns of rough ER © 2013 Pearson Education, Inc.

The Nuclear Envelope Double-membrane barrier; encloses nucleoplasm Outer layer continuous with rough ER and bears ribosomes Inner lining (nuclear lamina) maintains shape of nucleus; scaffold to organize DNA Pores allow substances to pass; nuclear pore complex line pores; regulates transport of large molecules into and out of nucleus © 2013 Pearson Education, Inc.

Surface of nuclear envelope. Figure 3.29b The nucleus. Surface of nuclear envelope. Fracture line of outer membrane Nuclear pores Nucleus Nuclear pore complexes. Each pore is ringed by protein particles. Nuclear lamina. The netlike lamina composed of intermediate filaments formed by lamins lines the inner surface of the nuclear envelope. © 2013 Pearson Education, Inc.

Dark-staining spherical bodies within nucleus Nucleoli Dark-staining spherical bodies within nucleus Involved in rRNA synthesis and ribosome subunit assembly Associated with nucleolar organizer regions Contains DNA coding for rRNA Usually one or two per cell © 2013 Pearson Education, Inc.

Threadlike strands of DNA (30%), histone proteins (60%), and RNA (10%) Chromatin Threadlike strands of DNA (30%), histone proteins (60%), and RNA (10%) Arranged in fundamental units called nucleosomes Histones pack long DNA molecules; involved in gene regulation Condense into barlike bodies called chromosomes when cell starts to divide © 2013 Pearson Education, Inc.

Figure 3.30 Chromatin and chromosome structure. 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) 3 Tight helical fiber (30-nm diameter) 4 Looped domain structure (300-nm diameter) 5 Chromatid (700-nm diameter) 6 Metaphase chromosome (at midpoint of cell division) consists of two sister chromatids © 2013 Pearson Education, Inc.

Defines changes from formation of cell until it reproduces Includes: Cell Cycle Defines changes from formation of cell until it reproduces Includes: Interphase Cell grows and carries out functions Cell division (mitotic phase) Divides into two cells © 2013 Pearson Education, Inc.

Period from cell formation to cell division Interphase Period from cell formation to cell division Nuclear material called chromatin Three subphases: G1 (gap 1)—vigorous growth and metabolism Cells that permanently cease dividing said to be in G0 phase S (synthetic)—DNA replication occurs G2 (gap 2)—preparation for division © 2013 Pearson Education, Inc.

G1 checkpoint (restriction point) Interphase S Growth and DNA Figure 3.31 The cell cycle. G1 checkpoint (restriction point) Interphase S Growth and DNA synthesis G2 Growth and final preparations for division G1 Growth M Mitosis Cytokinesis Prophase Metaphase Telophase Anaphase Mitotic phase (M) G2 checkpoint © 2013 Pearson Education, Inc.

Interphase Centrosomes (each Plasma has 2 centrioles) membrane Figure 3.33 Mitosis is the process of nuclear division in which the chromosomes are distributed to two daughter nuclei. (1 of 6) Centrosomes (each has 2 centrioles) Plasma membrane Interphase Nucleolus Chromatin Nuclear envelope © 2013 Pearson Education, Inc.

Meiosis - cell division producing gametes Mitotic cell division - produces clones Essential for body growth and tissue repair Occurs continuously in some cells Skin; intestinal lining None in most mature cells of nervous tissue, skeletal muscle, and cardiac muscle Repairs with fibrous tissue © 2013 Pearson Education, Inc.

Events Of Cell Division Mitosis—division of nucleus Four stages ensure each cell receives copy of replicated DNA Prophase Metaphase Anaphase Telophase Cytokinesis—division of cytoplasm by cleavage furrow © 2013 Pearson Education, Inc.

G1 checkpoint (restriction point) Interphase S Growth and DNA Figure 3.31 The cell cycle. G1 checkpoint (restriction point) Interphase S Growth and DNA synthesis G2 Growth and final preparations for division G1 Growth M Mitosis Cytokinesis Prophase Metaphase Telophase Anaphase Mitotic phase (M) G2 checkpoint © 2013 Pearson Education, Inc.

Centrosomes separate and migrate toward opposite poles Prophase Chromosomes become visible, each with two chromatids joined at centromere Centrosomes separate and migrate toward opposite poles Mitotic spindles and asters form © 2013 Pearson Education, Inc.

Nuclear envelope fragments Prophase Nuclear envelope fragments Kinetochore microtubules attach to kinetochore of centromeres and draw them toward equator of cell Polar microtubules assist in forcing poles apart © 2013 Pearson Education, Inc.

Early Prophase Early mitotic spindle Aster Centromere Chromosome Figure 3.33 Mitosis is the process of nuclear division in which the chromosomes are distributed to two daughter nuclei. (2 of 6) Early mitotic spindle Early Prophase Aster Centromere Chromosome consisting of two sister chromatids © 2013 Pearson Education, Inc.

Late Prophase Spindle pole Polar microtubule Fragments of nuclear Figure 3.33 Mitosis is the process of nuclear division in which the chromosomes are distributed to two daughter nuclei. (3 of 6) Spindle pole Polar microtubule Late Prophase Fragments of nuclear envelope Kinetochore Kinetochore microtubule © 2013 Pearson Education, Inc.

Centromeres of chromosomes aligned at equator Metaphase Centromeres of chromosomes aligned at equator Plane midway between poles called metaphase plate © 2013 Pearson Education, Inc.

Metaphase Spindle plate Figure 3.33 Mitosis is the process of nuclear division in which the chromosomes are distributed to two daughter nuclei. (4 of 6) Metaphase plate Spindle © 2013 Pearson Education, Inc.

Polar microtubules continue forcing poles apart Anaphase Shortest phase Centromeres of chromosomes split simultaneously—each chromatid becomes a chromosome Chromosomes (V shaped) pulled toward poles by motor proteins of kinetochores Polar microtubules continue forcing poles apart © 2013 Pearson Education, Inc.

Anaphase Daughter chromosomes Figure 3.33 Mitosis is the process of nuclear division in which the chromosomes are distributed to two daughter nuclei. (5 of 6) Anaphase Daughter chromosomes © 2013 Pearson Education, Inc.

Begins when chromosome movement stops Telophase Begins when chromosome movement stops Two sets of chromosomes uncoil to form chromatin New nuclear membrane forms around each chromatin mass Nucleoli reappear Spindle disappears © 2013 Pearson Education, Inc.

Begins during late anaphase Cytokinesis Begins during late anaphase Ring of actin microfilaments contracts to form cleavage furrow Two daughter cells pinched apart, each containing nucleus identical to original © 2013 Pearson Education, Inc.

Telophase Cytokinesis Nuclear envelope forming Nucleolus forming Figure 3.33 Mitosis is the process of nuclear division in which the chromosomes are distributed to two daughter nuclei. (6 of 6) Nuclear envelope forming Nucleolus forming Contractile ring at cleavage furrow Telophase Cytokinesis © 2013 Pearson Education, Inc.

Control of Cell Division "Go" signals: Critical volume of cell when area of membrane inadequate for exchange Chemicals (e.g., growth factors, hormones) Availability of space–contact inhibition © 2013 Pearson Education, Inc.

Control of Cell Division To replicate DNA and enter mitosis requires Cyclins–regulatory proteins Accumulate during interphase Cdks (Cyclin-dependent kinases)–bind to cyclins  activated Enzyme cascades prepare cell for division Cyclins destroyed after mitotic cell division © 2013 Pearson Education, Inc.

Control of Cell Division "Go" signals G1 checkpoints (restriction point) most important If doesn't pass  G0–no further division Late in G2 MPF (M-phase promoting factor) required to enter M phase "Other Controls" signals Repressor genes inhibit cell division E.g., P53 gene © 2013 Pearson Education, Inc.