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2. Immagini e concetti della biologia Sylvia S. Mader
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

3. A6 - Cell Duplication
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

4. Reproduction ASEXUAL REPRODUCTION SEXUAL REPRODUCTION
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

5. 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.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

6. Cell division
The process by which a parent cell divides into two or more daughter cells is called
cell division.
multicellular organisms
unicellular organisms
growth
reproduction
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

7. Reproduction in Prokaryotes
For unicellular organisms cell division is equivalent to reproduction and is called binary fission.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

8. 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.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

9. 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
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

10. Interphase G1 phase first growing phase
Production of proteins and enzymes.
Proteins and DNA in the nucleus replicate.
S phase
synthesis phase
The cell prepares for mitosis. DNA organizes into chromosome.
G2 phase
second growing phase
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

11. M-phase: mitosis and cytokinesis
PROPHASE ➡ METAPHASE ➡ ANAPHASE ➡ TELOPHASE
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
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

12. Chromosomes
In Eukaryotes, during cell division chromosome become visible.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

13. 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.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

14. Mitosis Mitosis maintains the original chromosome number
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

15. Mitosis
Prophase
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

16. Mitosis
Metaphase
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

17. Mitosis
Anaphase
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

18. Mitosis
Telophase
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

19. 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 cell
Plant cell
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

20. Cell cycle is controlled by checkpoints
If the cell misses one of the checkpoints, apoptosis (the programmed cell death) occurs.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

21. 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
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

22. Cell cycle is controlled by signals
Internal signals
kinases and cyclins combine and drive the cell cycle
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

23. 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.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

24. Homologous chromosomes
Chromosome pairs of the same length and centromere position with genes for the same characteristics.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

25. Meiosis
After meiosis, one chromosome from each homologous pair is in the haploid daughter cell.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

26. Meiosis: synapsis
The pairing of two homologous chromosomes is called synapsis and forms tetrads.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

27. Meiosis: crossing-over
After synapsis, DNA segments from one chromatid pass to another chromatid in the tetrad.
The result are two genetically new chromatids.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

28. Genetic variability
Crossing-over allows recombination of genes in chromosomes and contributes to the genetic variation of the offsprings.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

29. Meiosis requires two division cycles
Meiosis I: Homologous pairing and crossing-over occur
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

30. Meiosis requires two division cycles
Meiosis II: chromatids from meiosis I separate into 4 cells
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

31. 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).
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

32. Chromosomal abnormalities
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.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

33. Chromosomal abnormalities
Structural abnormalities may be caused by different mechanisms.
Deletion
Duplication
Inversion
Translocation
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018

34. Trisomy 21
Down syndrome, also known as “trisomy 21”, is a chromosomal condition caused by the presence of a third copy of chromosome 21.
Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2018