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2 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Sylvia S. Mader Immagini e concetti della biologia

3 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 A6 - Cell Duplication

4 ASEXUAL REPRODUCTION Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Reproduction SEXUAL REPRODUCTION

5 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Reproduction During ASEXUAL REPRODUCTION each daughter cell receives a copy of the parental cell DNA. During SEXUAL REPRODUCTION two gametes (an egg and a sperm cell) unite and the offspring receive a combination of its parents DNA.

6 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Cell division The process by which a parent cell divides into two or more daughter cells is called cell division. multicellular organisms growth unicellular organisms reproduction

7 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Reproduction in Prokaryotes For unicellular organisms cell division is equivalent to reproduction and is called binary fission.

8 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 The cell cycle INTERPHASE: the cell performs the functions that make it unique and prepares to division. MITOSIS: the cell divides into two daughter cells.

9 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Somatic cells and stem cells Somatic cell: any cell forming the body of an adult organism. Stem cell: cell that can divide and differentiate into diverse specialized cell types. Stem cells act as a repair system for the body

10 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Interphase G 1 phase first growing phase S phase synthesis phase G 2 phase second growing phase Production of proteins and enzymes. Proteins and DNA in the nucleus replicate. The cell prepares for mitosis. DNA organizes into chromosome.

11 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 M-phase: mitosis and cytokinesis The nuclear material (chromatin) becomes visible Chromosomes organize in the center of the cell Chromosomes separate and move into each new cell Cytokinesis: the cytoplasm divides into two separate cells PROPHASE ➡ METAPHASE ➡ ANAPHASE ➡ TELOPHASE

12 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Chromosomes In Eukaryotes, during cell division chromosome become visible.

13 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Haploid or diploid? Somatic cells are diploid (2n): have two sets of chromosomes. Gametes are haploid (n): the sperm and egg cells contain only one chromosome of each kind. During S phase DNA is copied, so two copies of each chromosome exist.

14 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Mitosis maintains the original chromosome number Mitosis

15 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Mitosis Prophase

16 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Mitosis Metaphase

17 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Mitosis Anaphase

18 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Mitosis Telophase

19 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Cytokinesis divides the cytoplasm In animal cells, cytokinesis occurs when the cell membrane forms a cleavage furrow. In plant cells, cytokinesis involves the formation of a cell plate from vesicles and a cell wall. Animal cellPlant cell

20 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Cell cycle is controlled by checkpoints If the cell misses one of the checkpoints, apoptosis (the programmed cell death) occurs.

21 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Cell cycle is controlled by signals Checkpoints respond to specific signal molecules that stimulate or inhibit the cell cycle. Internal signal molecules Kinases and Cyclin External signal molecules Growth factors and hormones Contact inhibition when two cells come in contact the cells arrest the growth

22 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Cell cycle is controlled by signals kinases and cyclins combine and drive the cell cycle Internal signals

23 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Cell cycle is controlled by signals External signals 1. Signaling molecules come from outside the cell to a receptor. 2. The signal is transmitted to the nucleus. 3. The control system in the nucleus receive the signal.

24 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Cancer cells have anomalies in the cell cycle Cancer cells lack differentiation and have abnormal nuclei. Cancer cells undergo metastasis when form tumors far from the original site.

25 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Homologous chromosomes Chromosome pairs of the same length and centromere position with genes for the same characteristics.

26 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Meiosis After meiosis, one chromosome from each homologous pair is in the haploid daughter cell.

27 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Meiosis: synapsis The pairing of two homologous chromosomes is called synapsis and forms tetrads.

28 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Meiosis: crossing-over After synapsis, DNA segments from one chromatid pass to another chromatid in the tetrad. The result are two genetically new chromatids.

29 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Genetic variability Crossing-over allows recombination of genes in chromosomes and contributes to the genetic variation of the offsprings.

30 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Meiosis requires two division cycles Meiosis I: Homologous pairing and crossing-over occur

31 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Meiosis requires two division cycles Meiosis II: chromatids from meiosis I separate into 4 cells

32 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Meiosis requires two division cycles The life cycle of most multicellular organisms include both mitosis and meiosis. Mitosis is involved in growth. Meiosis is involved in the production of gametes (spermatogenesis and oogenesis).

33 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Nondisjunctions occur when there are anomalies in the separation of chromosomes (meiosis I) or chromatids (meiosis II). Those mistakes can lead to monosomy (2n-1) or trisomy (2n+1) conditions. Chromosomal abnormalities

34 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Structural abnormalities may be caused by different mechanisms. Translocation Chromosomal abnormalities Deletion DuplicationInversion

35 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012 Down syndrome, also known as “trisomy 21”, is a chromosomal condition caused by the presence of a third copy of chromosome 21. Trisomy 21