Organelles Ribosomes sites of protein synthesis Organelles Endoplasmic

Organelles • Ribosomes - sites of protein synthesis

Organelles • Endoplasmic reticulum network of membranes in the shape of flattened sacs or tubules - Rough ER - connected to the nuclear envelope, a series of flattened sacs, surface is studded with ribosomes, produces various proteins -Smooth ER - a network of membrane tubules, does not have ribosomes, synthesizes fatty acids and steroids, detoxifies certain drugs

Organelles • Golgi complex - consists of 3– 20 flattened, membranous sacs called cisternae. - Modify, sort, and package proteins for transport to different destinations. - Proteins are transported by various vesicles.

Golgi Complex

Processing and Packaging

Organelles • Lysosomes - vesicles that form from the Golgi complex and contain powerful digestive enzymes

Organelles • Peroxisomes – Smaller than lysosomes – Detoxify several toxic substances such as alcohol – Abundant in the liver • Proteasomes – Continuously destroy unneeded, damaged, or faulty proteins – Found in the cytosol and the nucleus

Organelles Mitochondria - the “powerhouses” of the cell – Generate ATP – More prevalent in physiologically active cells: muscles, liver and kidneys – Have inner and outer mitochondrial membranes similar in structure to the plasma membrane – Cristae - the series of folds of the inner membrane – Matrix - the large central fluid-filled cavity – Self-replicate during times of increased cellular demand or before cell division – Contain own DNA • Inherited only from your mother

Mitochondria

Organelles - Nucleus u Spherical or oval shaped structure u Usually most prominent feature of a cell u Nuclear envelope - a double membrane that separates the nucleus from the cytoplasm u Nuclear pores - numerous openings in the nuclear envelope, control movement of substances between nucleus and cytoplasm u Nucleolus - spherical body that produces ribosomes u Genes - the cell’s hereditary units, control activities and structure of the cell u Chromosomes - long molecules of DNA combined with protein molecules

Nucleus

Packing of DNA into a Chromosome of a Dividing Cell

Overview of Gene Expression

Transcription

Translation

Protein Synthesis Interactions Animation • Protein Synthesis You must be connected to the internet to run this animation.

Somatic Cell Division - Mitosis • The cell cycle is a sequence of events in which a body cell duplicates its contents and divides in two • Human somatic cells contain 23 pairs of chromosomes (total = 46) • The two chromosomes that make up each pair are called homologous chromosomes (homologs) • Somatic cells contain two sets of chromosomes and are called diploid cells

Cell Division • Interphase - the cell is not dividing - The cell replicates its DNA - Consists of three phases, G 1, S, and G 2, replication of DNA occurs in the S phase Mitotic phase - consists of a nuclear division (mitosis) and a cytoplasmic division (cytokinesis) to form two identical cells

The Cell Cycle

DNA Replication

Nuclear Division: Mitosis • Prophase - the chromatin fibers change into chromosomes. • Metaphase - microtubules align the centromeres of the chromatid pairs at the metaphase plate. • Anaphase - the chromatid pairs split at the centromere and move to opposite poles of the cell; the chromatids are now called chromosomes. • Telophase - two identical nuclei are formed around the identical sets of chromosomes now in their chromatin form.

Cytoplasmic Division: Cytokinesis • Division of a cell’s cytoplasm to form two identical cells • Usually begins in late anaphase • The plasma membrane constricts at its middle, forming a cleavage furrow • The cell eventually splits into two daughter cells. • Interphase begins when cytokinesis is complete.

Mitosis Centrosome: Centrioles Pericentriolar material 1 6 Nucleolus Nuclear envelope Chromatin Plasma membrane Cytosol LM all at 700 x (a) INTERPHASE 2 Kinetochore Centromere Chromosome (two chromatids joined at centromere (f) IDENTICAL CELLS IN INTERPHASE 5 Mitotic spindle (microtubules) Fragments of nuclear envelope Early Late (b) PROPHASE Metaphase plate 3 Cleavage furrow (c) METAPHASE 4 (e) TELOPHASE Cleavage furrow Chromosome Late Early (d) ANAPHASE

Mitosis

Reproductive Cell Division u. During sexual reproduction, each new organism is the result of the union of two gametes (fertilization), one from each parent. u. Meiosis - reproductive cell division that occurs in the gonads (ovaries and testes) that produces gametes with half the number of chromosomes. u. Haploid cells - gametes contain a single set of 23 chromosomes. u. Fertilization restores the diploid number of chromosomes (46).

Reproductive Cell Division • Meiosis occurs in two successive stages: meiosis I and meiosis II. • Each of these two stages has 4 phases: prophase, metaphase, and telophase. • Summary - Meiosis I begins with a diploid cell and ends with two cells having the haploid number of chromosomes; in Meiosis II, each of the two haploid cells divides, and the net result is four haploid gametes that are genetically different from the original diploid starting cell.

Meiosis and Cytokinesis

Comparison of Mitosis and Meiosis

Cell Division Interactions Animation • The Cell Cycle and Division Processes Interactions Animation You must be connected to the internet to run this animation.

Cellular Diversity u. The average adult has nearly 100 trillion cells. u. There about 200 different types of cells. u. Cells come in a variety of shapes and sizes. u. Cellular diversity permits organization of cells into more complex tissues and organs.

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