Chapter 6. Cell Reproduction

Transcription

1 Chapter 6 Cell Reproduction

2 Chromosomes The growth and development of your body are controlled by instructions contained in your DNA

3 DNA decides what you will be..

4 DNA & Chromosomes Very long molecules Wound around protein molecules Compacts during cell replication to form chromosomes

5 If you unraveled all your chromosomes from all of your cells and laid out the DNA end to end, the strands would stretch from the Earth to the Moon about 6,000 times.

6 Eukaryotic Chromosomes Made of chromatin Complex of DNA & protein DNA coils tightly and forms chromosomes when a cell is preparing to divide. DNA -- Overview

7 Karyotype a picture of your chromosomes Chromosomes are isolated and stained You have 46 chromosomes 23 pairs

8 Another type of karyotype

9 Diploid 2n=46 When human cells have 23 pairs of chromosomes they are diploid Nearly all cells are diploid

10 Haploid 1n=23 Haploid cells only have 1 copy of each chromosome Sperm and ova are haploid

11 Sex Chromosomes 1 pair of your 23 chromosomes determines your sex These are known as the sex chromosomes X and Y

12 Females have 2 X Chromosomes

13 Males have 1 X and 1 Y chromosome

14 Chapter 6.2 Mitosis and Cell Division

15 Cell Growth and Replication Cells grow to their maximum, efficient size. Remember..the surface to volume ratio is critical.

16 When a cell reaches maximum size. It may stop growing It may divide Both processes are controlled by the cell s DNA

17 Prokaryotic Cell Reproduction Bacteria have only 1 circular chromosome Bacterial cell reproduction is more simple than eukaryotic cell division

18 Eukaryotic Cell Division Eukaryotes contain more DNA the prokaryotes Eukaryotic cell reproduction is more complicated than prokaryotic cell reproduction Mitosis and cell division

19 Mitosis Process by which the nucleus of a eukaryotic cell divides to form two nuclei Each nucleus contains a complete set of chromosomes

20 4 Phases of Mitosis Prophase Metaphase Anaphase Telophase

21 But 1 st the DNA has to replicate Interphase

22 Interphase (DNA Replication) Cell carries on normal functions ***DNA replicates**** Chromosomes are not visible

23 Interphase (DNA Replication) ** No chromosomes are visible**

24 Prophase - Mitosis begins DNA coils into chromosomes Nuclear envelope breaks up Spindle fibers, network of protein cables, forms.

25 Prophase Early Prophase Late Prophase

26 Metaphase Chromosomes attach to the spindle fibers Line up across center of cell

27 Metaphase

28 Anaphase Chromosomes separate from one another Reeled to opposite sides of the cell Spindle fibers begin to break down.

29 Anaphase

30 Telophase & Cytokinesis Chromosomes reach opposite ends of the cell Nuclear membrane reforms Chromosomes uncoil Spindle fibers disappear Cell divides into 2 = cytokinesis

31 Telophase & Cytokinesis Early Telophase Late Telophase

32 Plant Mitosis Instead of pinching into 2, a cell wall is formed between the new cells.

33 Onion Root Tips

34 Brain Aerobics.. Every second ~25 million cells are produced by mitosis in the human body. How many cells are produced by mitosis in a day?

35 Brain Aerobics Answer.. 25 million/second x 60 sec x 60 minutes x 24 hours = 2.16 trillion cells/day!

36 The Cell Cycle Most of a cell s life time is spent growing NOT dividing. A cell cycles between periods of growth and division.

37 The Cell Cycle 5 phase sequence of growth and division in eukaryotic cells

38 Interphase is the most active part of the cell cycle Taking in food Converting energy Discarding wastes Growing Differentiating **Duplicating genetic material and organelles**

39 Interphase can be divided into 3 stages of the cell cycle G 1 Phase S Phase G 2 Phase

40 G 1 Phase Also known as 1 st Gap Time of intense growth Some cells spend most of their lives in G 1

41 S Phase S stands for synthesis DNA is copied

42 G 2 Phase Also known as 2 nd Gap Final stage of interphase Cell continues to grow Duplicates organelles Prepares for cell division

43 Cell Cycle

44 Controlling the Cell Cycle Cell cycles are controlled by special proteins called cyclins. S-cyclin stimulates DNA replication in S phase M-cyclin triggers mitosis

45 Cyclins are influenced by growth factors Can turn on a gene that makes a particular cyclin. Can block the action of a cyclin. Help to control cell cycles Growth Factor

46 What happens when the cell cycle malfunctions?

47 It can be disastrous even life threatening!

48 When cells don t stop dividing Cells begin to divide uncontrollably Produces a clump of cells Tumor

49 Benign Tumors Excess cell growth remains localized Usually harmless

50 Benign Eyelid Tumor Before & after Surgery

51 Malignant Tumors Excess cell growth invades other tissues Can be extremely serious Cancer

52 Cancer A disease characterized by invasive, uncontrolled cell division and growth

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54 Breast Cancer Every 12 minutes a woman in America dies of breast cancer.

55 Breast Cancer

56 Mammograms & Ultrasounds Breast X-rays and images used to detect tissue changes Often find a tumor before it can be felt!

57 Normal & Abnormal Mammograms

58 Breast Cancer Cell Usually round very mobile Can grow in liquids Abnormal proteins and lipids on cell membrane Doesn t react to chemical signals in a usual manner

59 How does a cell become cancerous? Loses regulated cell division Penetrates or maneuvers around protective membrane barriers Invades other tissues Maintains nutrient and oxygen supply

60 Why does a cell become cancerous? Cancer cells have defective cell cycle control genes These genes have changes or mutations.

61 Is cancer hereditary? Not usually. Cancer mutations generally occur in body tissues such as skin or lungs. BUT..if mutations occur in eggs or sperm, then there is a n increased likelihood of developing cancer later in life.

62 What factors contribute to cancer development? Radiation UV light Cigarette smoke Diet & obesity may also be factors

63 Radiation UV light

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66 Cigarette smoke Half of all teenagers who are currently smoking will die from diseases caused by tobacco if they continue to smoke.

67 It s your choice!

68 Diet & Obesity

69 6.3 How Gametes Form

70 Nearly all of your cells are diploid 2n 46 chromosomes 23 pairs Except

71 Gametes Reproductive cells 1n Haploid 23 single chromosomes

72 Meiosis A 2 staged form of cell division in which the chromosome number is halved 46 chromosomes 23 chromosomes

73 Meiosis begins by replicating the chromosomes This step is identical to mitosis.

74 The homologous chromosomes then pair. The centromeres and chromosomes do not split apart during the first stage of meiosis Meiosis I

75 The first division reduces the number of chromosomes by 1/2

76 The second division, Meiosis II, splits the chromosomes The centromeres and sister chromatids divide.

77 The End result

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79 Crossing-Over A source of Genetic Variation Chromosomes line up during first division of Meiosis Homologous chromosomes can cross over

80 The new chromosomes are no longer exactly like the parent chromosomes.. they are a combination.

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82 Advantages Great genetic diversity Genetic variation Enables natural selection to occur

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