Chapter 6- Chromosomes and Cell Reproduction

1. Chapter 6- Chromosomes and Cell Reproduction

2. I. Chromosomes

3. A. New cells are formed by cell division. 1.An adult human body produces about 2 trillion cells EVERY day! This is about 25 million new cells per second! • 2.Cell division allows for this. • 3.Eukaryotic organisms undergoing growth, development, repair, or asexual reproduction divide by a different type of cell division.

4. Continued • 4. Gametes are reproductive cells (egg and sperm) undergo meiosis for cellular division.

5. B. Bacterial cells divide to reproduce 1.Bacteria reproduce by a type of cell division called binary fission. • 2.Binary fission is a form of asexual reproduction that produces identical offspring. 3. In asexual reproduction a single parent passes exact copies of its entire DNA to its offspring.

6. C. Eukaryotic cells form chromosomes before cell division • 1.A gene is a segment of DNA that codes for a protein or RNA molecule. 2. As a Eukaryotic cell prepares to divide, the DNA and the proteins associated with DNA coil into a structure called chromosomes.

7. Continued • 3. Chromosomes are squished together called chromatids. 4. The chromosome has two strands – one from mom and one from dad. A “twist tie” called a centromere holds them together. See page 119.

8. Centromere

9. D. Chromosome number and structure affect development. • 1.Each human somatic (any cell besides sex cells) normally contain two copies of 23 chromosomes for a total of 46 chromosomes. • 2.Each chromosome contains thousands of genes that play important roles in determining how a person’s body develops and functions.

10. Continued • 3. Each of the 23 pairs of chromosomes consists of two homologous chromosomes. • 4. Homologous chromosomes are chromosomes that are similar in size, shape and genetic content.

11. Continued • 5. All of the cells in the body, besides gametes have two pairs of chromosomes. (One from mom one from dad) they are called diploid. • 6. Sex cells only have DO NOT have a pair, they are called haploid (1/2 the amount of chromosomes)

12. Continued 7. A zygote is a fertilized egg cell. • 8. Look at figure 6-1 pages 121 to view number of chromosomes.

13. E. Chromosomes determine your sex. • 1.Of the 23 pairs of chromosomes in human somatic cells, 22 pairs are called autosomes • 2.Autosomes are chromosomes that are not directly involved in determining the sex of an individual. • 3.The sex chromosomes, one of the 23 pairs contain the gene that determines the gender. Males determine the gender of the human.

14. F. Change in chromosome number • 1.Sometimes a human could have different chromosome numbers. • 2.A karyotype is performed to view an individual’s chromosomes. • 3.Down syndrome is an extra copy on pair 21.

15. II. The cell Cycle A. The cell cycle describes the life of a Eukaryotic cell. • 1.The cell cycle is a repeating sequence of cellular growth and division during the life of an organism. • 2.A cell spends 90% of its time in the first three phases of the cycle-interphase.

16. Continued • 3. First growth (G1)phase- a cell grows rapidly and carries out its routine functions. Cells that are not dividing remain in the G1 phase. 4. Synthesis (S) phase- A cell’s DNA is copied during this phase. At the end of this phase, each chromosome consists of two chromatids attached at the centromere.

17. Contined • 5. Second growth (G2) phase-In the G2 phase, preparations are made for the nucleus to divide. 6. Mitosis-the process during cell division in which the nucleus of a cell is divided into two nuclei.

18. Continued • 7. Each nucleus ends up with the same number and kinds of chromosomes as the original cell. 8. Cytokinesis-the cytoplasm splits.

19. B. The cell cylce is carefully controlled • 1.If a cell spends 90% of its time in interphase how do cells “know” when to divide? • 2.Cell Growth (G1) checkpoint-This checkpoint makes the key decision of weather the cell will divide or not.

20. Continued • 3. DNA synthesis (G2) checkpoint-DNA replication is checked at this point by DNA repair enzymes. If this checkpoint is passed, proteins help to trigger mitosis. • 4. Mitosis checkpoint-will trigger the exit from mitosis.

21. C. When control is lost: cancer • 1.Certain genes contain the information necessary to make the proteins that regulate cell growth and division. • 2.If one of these genes is mutated, the protein may not function.

22. Continued • 3. Cancer is the uncontrolled growth of cells. • 4. Cancer is a disorder of cell division.

23. D. Mitosis • I Prefer Mangos And Tangerines Interphase (not really a phase) Prophase Metaphase Anaphase Telophase Cytokinesis

24. INTERPHASE • Interphase- is part of the cell cycle before mitosis. During Interphase • The cell grows • DNA is being copied • This period between cell division can be very long.

25. INTERPHASE

26. PROPHASE • Prophase- This is the longest phase. During this phase; • The nuclear envelope disappears. • The centrioles start to move to the opposite poles. • Spindle fibers start to form. • Chromosomes are becoming evident.

27. PROPHASE

28. METAPHASE • Metaphase-Metaphase is the shortest phase of mitosis. • The chromosomes line up in the middle of the cell.

29. METAPHASE

30. ANAPHASE • ANAPHASE- Begins when the centromere that join the sister chromatids start to split. • The chromosomes are being pulled to the opposite sides of the cell toward the Centrioles.

31. ANAPHASE

32. TELOPHASE • TELOPHASE-Final process of mitosis. • Chromosomes are at the opposite poles. • Nuclear envelope reforms.

33. TELOPHASE

34. CYTOKINESIS-Splitting of the cytoplasm.

35. Teacher note: http://www.cellsalive.com/mitosis.htm