CELL GROWTH, DIVISION, AND REPRODUCTION

1. Section 10.1 CELL GROWTH, DIVISION, AND REPRODUCTION

2. Chapter Mystery: Pet Shop Accident Julia stared into the salamander tank in horror. As an assistant in a pet shop, Julia had mistakenly put a small salamander in the same tank as a large one. Just as she realized her error, the large salamander attacked and bit off one of the small salamander’s limbs. Acting quickly, Julia scooped up the injured salamander and put it in its own tank. She was sure it would die before her shift ended. But she was wrong! Days passed….then weeks. Every time Julia checked on the salamander, she was more amazed at what she saw. How did the salamander’s body react to losing a limb? As you read this chapter, look for clues to help you predict the salamander’s fate. Think about the cell processes that would be involved.

3. I. Exchanging Materials • Food, oxygen, and water enter a cell through the cell membrane • Waste products leave in the same way • The rate at which this exchange takes place depends on the surface area of a cell • The rate at which food and oxygen are used up and waste products are produced depends on the cell’s volume • The ratio of surface area to volume is key to understanding why cells must divide as they grow

4. II. Ratio of Surface Area to Volume Imagine a cell shaped like a cube. As the length of the sides of a cube increases, its volume increases faster than its surface area, decreasing the ratio of surface area to volume. a. If a cell gets too large, the surface area of the cell is not large enough to get enough oxygen and nutrients in and waste out.

5. III. Division of the Cell • Cell division: process in which a cell divides into two new “daughter cells” before it grows too large • Before cell division the cell copies all of its DNA • It then divides into two “daughter” cells • each daughter cell receives a complete set of DNA • Cell division: • reduces cell volume • results in an increased ratio of surface area to volume for each daughter cell

6. IV. Asexual Reproduction • Asexual reproduction: reproduction that involves a single parent producing an offspring i. The offspring produced are, in most cases, genetically identical to the single cell that produced them ii. a simple, efficient, and effective way for an organism to produce a large number of offspring iii. both prokaryotic and eukaryotic single-celled organisms and many multicellular organisms can reproduce asexually

7. b. Examples of Asexual Reproduction i. Bacteria reproduce by binary fission ii. Kalanchoe plants form plantlets iii. Hydras reproduce by budding

8. V. Sexual Reproduction • sexual reproduction: offspring are produced by the fusion of two sex cells – one from each of two parents • fuse into a single cell before the offspring can grow • offspring produced inherit some genetic information from both parents • most animals and plants, and many single-celled organisms, reproduce sexually

9. VI. Comparing Sexual and Asexual Reproduction Fill in the table below:

10. Mystery Clue #1 As its wound heals, the salamander’s body cells are dividing to repair the damage. In what way is this type of cell division similar to asexual reproduction?

11. Section 10.2 THE PROCESS OF CELL DIVISION

12. I. Chromosomes • The genetic information that is passed on from one generation of cells to the next is carried by chromosomes • Every cell must copy its genetic information before cell division begins • Each daughter cell gets its own copy of that genetic information • Cells of every organism have a specific number of chromosomes

13. II. Prokaryotic Chromosomes • Prokaryotic cells lack nuclei • Instead, their DNA molecules are found in the cytoplasm • Most prokaryotes contain a single, circular DNA molecule, or chromosome, that contains most of the cell’s genetic information.

14. III. Eukaryotic Chromosomes • In eukaryotic cells, chromosomes are located in the nucleus, and are made up of chromatin • Chromatin is composed of DNA and histone proteins. • DNA coils around histone proteins to form nucleosomes • The nucleosomes interact with one another to form coils and supercoils that make up chromosomes

15. IV. The Prokaryotic Cell Cycle a. a regular pattern of growth, DNA replication, and cell division b. most prokaryotic cells begin to replicate, or copy, their DNA once they have grown to a certain size c. when DNA replication is complete, the cells divide through a process known as binary fission

16. d. Binary fission: a form of asexual reproduction during which two genetically identical cells are produced e. For example, bacteria reproduce by binary fission.

17. V. The Eukaryotic Cell Cycle • The eukaryotic cell cycle consists of four phases: G1, S, G2, and M • Interphase: the time between cell divisions i. It is a period of growth that consists of the G1, S, and G2 phases • The M phase is the period of cell division.

18. d. G1 Phase: Cell Growth cells increase in size and synthesize new proteins and organelles

19. e. S Phase: DNA Replication new DNA is synthesized when the chromosomes are replicated

20. f. G2 Phase: Preparing for Cell Division many of the organelles and molecules required for cell division are produced

21. g. M Phase: Cell Division • In eukaryotes, cell division occurs in two stages: mitosis and cytokinesis. • Mitosis is the division of the cell nucleus. • Cytokinesis is the division of the cytoplasm.

22. h. Important Cell Structures Involved in Mitosis • Chromatid – each strand of a duplicated chromosome • Centromere – the area where each pair of chromatids is joined • Centrioles – tiny structures located in the cytoplasm of animal cells that help organize the spindle • Spindle – a fanlike microtubule structure that helps separate the chromatids

23. VI. Prophase • the first phase of mitosis • the duplicated chromosome condenses and becomes visible • centrioles move to opposite sides of nucleus and help organize the spindle • spindle forms and DNA strands attach at a point called their centromere • The nucleolusdisappears and nuclear envelope breaks down

24. VII. Metaphase • the centromeres of the duplicated chromosomes line up across the center of the cell • the spindle fibers connect the centromere of each chromosome to the two poles of the spindle

25. VIII. Anaphase • the centromeres are pulled apart and the chromatids separate to become individual chromosomes • the chromosomes separate into two groups near the poles of the spindle

26. IX. Telophase • the chromosomes spread out into a tangle of chromatin • a nuclear envelope re-forms around each cluster of chromosomes • the spindle breaks apart, and a nucleolus becomes visible in each daughter nucleus

27. X. Cytokinesis a. Cytokinesis: the division of the cytoplasm b. The process of cytokinesis is different in animal and plant cells

28. c. Cytokinesis in Animal Cells • The cell membrane is drawn in until the cytoplasm is pinched into two equal parts. • Each part contains its own nucleus and organelles

29. d. Cytokinesis in Plant Cells • In plants, the cell membrane is not flexible enough to draw inward because of the rigid cell wall • Instead, a cell plate forms between the divided nuclei that develops into cell membranes • A cell wall then forms in between the two new membranes

30. The Stages of the Cell Cycle

31. Mystery Clue #2 How might the cell cycles of the cells surrounding the salamander’s wound be affected?

32. Section 10.3 REGULATING THE CELL CYCLE

33. The controls on cell growth and division can be turned on and off. For example, when an injury such as a broken bone occurs, cells are stimulated to divide rapidly and start the healing process. The rate of cell division slows when the healing process nears completion.

34. I. The Discovery of Cyclins a. Cyclins: a family of proteins that regulate the timing of the cell cycle in eukaryotic cells This graph shows how cyclin levels change throughout the cell cycle in fertilized clam eggs.

35. II. Regulatory Proteins • Internal regulators are proteins that respond to events inside a cell i. they allow the cell cycle to proceed only once certain processes have happened inside the cell • External regulators are proteins that respond to events outside the cell i. they direct cells to speed up or slow down the cell cycle • Growth factors are external regulators that stimulate the growth and division of cells i. they are important during embryonic development and wound healing

36. Mystery Fish #3 How might regulatory proteins be involved in wound healing in the salamander?

37. III. Apoptosis • Apoptosis is a process of programmed cell death • Apoptosis plays a role in development by shaping the structure of tissues and organs in plants and animals • For example, the foot of a mouse is shaped the way it is partly because the toes undergo apoptosis during tissue development

38. IV. Cancer • Cancer is a disorder in which body cells lose the ability to control cell growth • Cancer cells divide uncontrollably to form a mass of cells called a tumor i. benign tumor is noncancerous, it does not spread to surrounding healthy tissue ii. malignant tumor is cancerous, it invades and destroys surrounding healthy tissue and can spread to other parts of the body iii. The spread of cancer cells is called metastasis iv. Cancer cells absorb nutrients needed by other cells, block nerve connections, and prevent organs from functioning

39. V. What Causes Cancer? • Cancers are caused by defects in genes that regulate cell growth and division • Some sources of gene defects are smoking tobacco, radiation exposure, defective genes, and viral infection. • A damaged or defective p53 gene is common in cancer cells. It causes cells to lose the information needed to respond to growth signals.

40. VI. Treatments for Cancer • Some localized tumors can be removed by surgery • Many tumors can be treated with targeted radiation • Chemotherapy is the use of compounds that kill or slow the growth of cancer cells.

41. Section 10.4 CELL DIFFERENTIATION

42. I. Defining Differentiation • Differentiation: the process by which cells become specialized • During development, cells differentiate into many different types and become specialized to perform certain tasks. • Differentiated cells carry out the jobs that multicellular organisms need to stay alive.

43. One of the most important questions in biology is how all of the specialized, differentiated cell types in the body are formed from just a single cell. d. Biologists say that such a cell is totipotent, literally able to do everything, to form all the tissues of the body. e. Only the fertilized egg and the cells produced by the first few cell divisions of embryonic development are truly totipotent.

44. II. Human Development • After about four days of development, a human embryo forms into a blastocyst, a hollow ball of cells with a cluster of cells inside known as the inner cell mass. • The cells of the inner cell mass are said to be pluripotent, which means that they are capable of developing into many, but not all, of the body's cell types.

45. III. Stem Cells • Stem cells: unspecialized cells from which differentiated cells develop • There are two types of stem cells: embryonic and adult stem cells.

46. c. Embryonic Stem Cells • Embryonic stem cells are found in the inner cells mass of the early embryo • Embryonic stem cells are pluripotent • Researchers have grown stem cells isolated from human embryos in culture • Their experiments confirmed that embryonic stem cells have the capacity to produce most cell types in the human body

47. d. Adult Stem Cells • Adult organisms contain some types of stem cells • Adult stem cells are multipotent • They can produce many types of differentiated cells • Adult stem cells of a given organ or tissue typically produce only the types of cells that are unique to that tissue

48. IV. Potential Benefits • Stem cell research may lead to new ways to repair the cellular damage that results from heart attack, stroke, and spinal cord injuries. One example is the approach to reversing heart attack damage illustrated below.

49. V. Ethical Issues • Most techniques forharvesting, or gathering, embryonic stem cells cause destruction of the embryo. • Government funding of embryonic stem cell research is an important political issue. • Groups seeking to protect embryos oppose such research as unethical. • Other groups support this research as essential to saving human lives and so view it as unethical to restrict the research.

50. Mystery Clue #4 Some adult salamander cells never completely differentiate. What ability do these cells retain?