The Cell Cycles Mitosis and Meiosis. Essential question: How do cells reproduce and why?

Transcription

1 The Cell Cycles Mitosis and Meiosis Essential question: How do cells reproduce and why?

2 Objectives Section 10.1 Explain why cells divide in terms of growth and cell size

3 Review - Types of Cell Division 2 Types of cell division Asexual Several purposes Sexual One purpose

4 Review - Types of Cell Growth Individual Cell Size Increase Number of Cells Increases

5 10.1 Why Divide?

6 10.1 Cell Growth Limits to Cell Size: 1. DNA Overload What is the job of the DNA of a cell? A set amount of DNA is unable to meet the needs of an evergrowing cell.

7 2. Exchange of Materials How do substances get in and out of a cell? 10.1 Cell Growth As a cell grows larger, both the surface area (the cell membrane) and the volume (the cytoplasm and organelles) grow larger, but at different rates!

8 Calculating Surface Area to Volume Ratios 10.1 Cell Growth Which cat has the greatest surface area to volume ratio?

9 How do you increase surface area without decreasing overall size of the organism? Has the volume changed?

10 Calculating Surface Area to Volume Ratios Which cell has the biggest surface area to volume ratio? 2cm 8cm 2cm 2cm 8cm 8cm Surface area = 2cm x 2cm x 6sides = 24 cm 2 Volume = 2cm x 2cm x 2cm = 8cm 3 SA:V = 24:8 24/8 = 3:1 Surface area = 8x8x6 = 384 cm 2 Volume = 8x8x8 = 512cm 3 SA:V = 384: /512 = 0.75:1

11 Let s Practice Calculating Cell Size 1cm 5 cm 10 cm 20 cm 40 cm 80 cm

12 So as organisms get bigger their surface area/volume ratio gets smaller. It becomes more difficult for them to exchange materials with their surroundings. If the volume of a cell becomes too big for the surface area to support, substances such as food, O 2, and wastes cannot diffuse in and out fast enough.

13 Objectives Section 10.1 Explain why cells divide in terms of growth and cell size

14 10.1 Cell Growth Review 1. Give 2 reasons why cells divide that are not related to growth. The larger a cell becomes, the more demands the cell places on its DNA and the more trouble the cell has in moving enough nutrients and wastes across the cell membrane. 2. As a cell increases in size, which increases more rapidly, its surface area or its volume? Its volume. 6:1 3:1

15 3. Calculate the surface area, the volume, and the ratio of surface area to volume of an imaginary cubic cell measuring 4 cm on each side. 3 cm 3 cm Surface area: l x w # of sides: 3 x 3 x 6 = 54 cm 2 3 cm Volume: l x w x h: 3 x 3 x 3 = 27 cm 3 SA:V ratio: 54:27 = 6:3 (or 2:1)

16 How does surface area to volume affect the physiology of organisms? (Let s look at a related concept!) Is it better to be a large animal or a small one in cold climates?

17 Organisms also exchange heat with their surroundings. Large animals have an advantage in having a small surface area/volume ratio: they lose less heat than small animals. Why do penguins huddle?

18 Which animal has the greatest surface area to volume ratio? The MOUSE of course! How might the small surface area to volume ratio help the hippo in its natural environment?

19 Chapter 10.2 The Cell Cycle and Mitosis

20 Objectives Describe the main events of the cell cycle Explain each of the four phases of mitosis

21 Some Cell Division Terminology Don t panic Just sharpen your pencil!

22 Phases Each of the time periods of a cell s life are referred to as phases This is similar to the way you can breakdown your life into phases Certain events are associated with each phase and can be used for identification of the phase

23 Chromosomes Chromosomes are made up of DNA wound tightly around proteins called histones Histones + DNA = chromatin When a cell prepares for division it duplicates its DNA and condenses the chromatin into neat packages called chromosomes

24 Exist in homologous pairs One from mom One from dad Humans have 23 pairs 22 autosome pairs 1 sex pair (these determine the sex of the organism) Chromosomes

25 During replication (S phase) a pair of sister chromatids are made for each homolog of a chromosome pair Sister Chromatids

26 Chromosomes Are generally represented in their duplicated form A single duplicated chromosome has two parts, each called a chromatid Each chromatid is referred to as a sister and is attached at a centromere

27 Cell Cycle During the cell cycle, a cell grows, prepares for division, and divides to form 2 daughter cells, each of which then begins the cycle again. how_the_cell_cycle_works.html

28 It includes two major stages 1) Interphase G1, S, G2 2) M phase (nuclear and cellular division) Mitosis (division of the nucleus) Cytokinesis (division the cell) Cell Cycle

29 Stage 1 - Interphase In Between Interphase G1= cell grows S =chromosomes duplicate G2= organelles duplicate, DNA checked

30 Stage 2 Mitosis Nuclear Division First part of M Phase The division of the nucleus of somatic (body) cells during the cell cycle. Its divided into 4 phases. Remember Interphase and Cytokinesis are NOT part of Mitosis. mitosis_and_cytokinesis.ht ml

31 KEY CONCEPT The phases of the M Phase of the cell cycle do not occur in isolation The are a continuum starting with prophase and proceeding sequentially through metaphase, anaphase and finally telophase Sometimes it can be difficult to determine the phase a cell is in because it will appear to be transitioning from one phase to another

32 Prophase First stage of Mitosis Nuclear membrane breaks down Chromatin condenses into chromosomes Centrioles (animal cells only) separate and a spindle apparatus begins to form a cage like structure across the cell

33 Prophase

34 Metaphase Second Phase of Mitosis Each chromosome is connected to a spindle fiber at an area called the kinetochore on the centromere. the chromosomes line up in the middle of the spindle (called the metaphase plate)

35 Metaphase

36 Anaphase Third Phase of Mitosis The sister chromatids separate at the centromere into individual chromosomes and move apart to opposite ends of the cell. the spindle fibers shorten and pull the chromosomes to each end (aster)

37 Anaphase

38 Telophase Fourth and Final Stage of Mitosis Nuclear envelopes reform around each complete set of chromosomes Chromosomes unwind back into chromatin losing their distinct shape

39 Telophase

40 Final Step - Cytokinesis The last step of M phase The equatorial belt pinches cytoplasm in half Each daughter cell has an identical set of chromosomes

41 The Whole Cell Cycle Putting it all together!

42 So what is the END RESULT? One Parent Cell DIVIDES INTO Two identical Daughter Cells

43 Regulating the Cycle Proteins called cyclin help regulate the cell cycle in eukaryotic cells. They respond to internal and external events. These proteins are regulators.

44 When Things Go Wrong Some cells begin to grow without regulation They produce a mass of cells called a tumor Benign tumors do not cause damage to surrounding tissues Malignant tumors DO cause damage to tissues and may become cancerous Cancer cells do not respond to the signals that regulate the growth of most cells. As a result, they form masses of cells called tumors that can damage surrounding tissues. Brief animation!

45 11-4 Meiosis Cell Division for Sexual Reproduction

46 Homologous Chromosomes All sexually reproducing organisms inherit one set of chromosomes from each parent Each parental set contains exactly the same number of chromosomes The corresponding chromosome from each parent is called a homolog 2 homologs make a homologous pair

47

48 Chromosome Pair 1 Chromosome Pair 2 Chromosome Pair 3

49 Chromosome Number Diploid (2 N) Cells with a complete set of homologous pairs Haploid (N) Cells with one half the homologous chromosomes in a diploid cell Let s do a quick activity to investigate this.

50 What is Meiosis? A cell division cycle which reduces the number of chromosomes in new cells by half Diploid (2N) somatic (body) cells are reduced to haploid (N) gamete (sex) cells Chromosome reduction occurs by separation of homologous chromosomes

51

52 Meiotic Cell Division the Basics Meiosis involves 2 distinct phases Meiosis I Homologous pairs are separated 2 haploid cells are formed Meiosis II Sister chromatids are separated 4 haploid cells are formed End result is 4 genetically distinct haploid cells

53 Meiotic Cell Division the Basics Start with Interphase Meiosis I Prophase I Metaphase I Anaphase I Telophase I Cytokinesis 2 daughter cells result Meiosis II Prophase II Metaphase II Anaphase II Telophase II Cytokinesis Each daughter cells divides into 2 new daughter cells 4 daughter cells in total

54 A Closer Look at Meiosis I Meiosis I involves a special step that leads to genetic changes in duplicate sister chromatids During PROPHASE I Homologous chromosomes join together in a structure called a TETRAD

55 Tetrads and Crossing Over TETRAD formation (synapsis), the arms of one chromatid of each homolog CROSSOVER one another a gene segment from one parent chromosome is exchanged with an equal gene segment from the other parent chromosome

56

57

58 Cytoplasm distribution in human gamete formation Males Cytoplasm distribution is even Meiosis results in Four equal sperm cells Occurs in the testes Females Cytoplasm distribution is uneven Meiosis results in One large egg Three smaller polar bodies Occurs in the ovaries

59 Zygote Formation Fertilization The joining of a haploid egg and a haploid sperm cell Results in the formation of a ZYGOTE (a fertilized egg) What is the chromosome number of a zygote? Haploid or Diploid?