Cell Growth and Division. Chapter 10 and 11.4

Transcription

1 Cell Growth and Division Chapter 10 and 11.4

2 Let s Discuss When a living thing grows, what happens to its cells? Why does an animal get larger? What are some of the difficulties a cell faces as it increases in size? scale/

3 Information Overload Where is the critical information for a cell stored? DNA! A cell uses DNA to build the molecules needed for cell growth. As size increases, the demands on that information grow as well. If a cell were to grow without limit, an information crisis would occur. DNA s help is limited if cell gets too big.

4 Exchanging Materials The rate at which exchange of food, O 2 an waste are in and out of the cell 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.

5 Ratio of Surface Area to Volume Surface Area (l x w) x 6 sides Volume (l x w x h) Ratio of surface area to volume ratio Cube Size: 1cm Cube Size: 2cm Cube Size: 3cm 6 cm 2 24 cm 2 54 cm 2 1 cm 3 8 cm 3 27 cm 3 6:1 3:1 2:1

6 Traffic Problems It s like a traffic jam: 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.

7 Division of the Cell When a cell gets too large, it will split and create two new daughter cells in a process called cell division. Before cell division, the cell copies all of its DNA.

8 Division of the Cell It then divides into two daughter cells. Each daughter cell receives a complete set of DNA. Cell division reduces cell volume. It also results in an increased ratio of surface area to volume, for each daughter cell.

9 Cell Division and Reproduction How do asexual and sexual reproduction compare? Asexual Reproduction Single parent genetically identical offspring from a single parent Examples: hydra, bacteria Reproduction is quick and get large number of offspring Sexual Reproduction 2 parents inherit some of their genetic information from each parent Examples: most animals and plants Reproduction is longer and you get fewer offspring compared to asexual Genetic diversity helps ensure survival of species when environment changes

10 Chromosomes How long is DNA?? 3 meters! Package DNA in a carrier called a chromosome. Cell MUST copy its genetic info before the cell division begins. daughter cell gets its own copy of that genetic information.

11 Chromosomes Cells of every organism have a specific number of chromosomes. Humans: 46 Dogs: 39 Dolphin: 44

12 Compressed DNA In eukaryotic cells, chromosomes are located in the nucleus, and are made up of chromatin (DNA)

13 Compressed DNA DNA coils around histone proteins to form nucleosomes. Coiling action helps fit enormous lengths of DNA into the tiny space of the nucleus!

14 Types of Chromosomes Sex Chromosomes: Female: XX Male: XY Autosomes: all other chromosomes

15 The Cell Cycle Prokaryotes: Regular pattern of growth, DNA replication, and cell division. Copy DNA when it gets to a certain size When DNA replication is complete, the cells divide through a process known as binary fission.

16 The Cell Cycle Binary fission is asexual reproduction Ie: bacteria

17 The Cell Cycle Eukaryotes: 4 Phases: G1, S, G2, and M.

18 The Cell Cycle Interphase is the time between cell divisions Growth: G1, S, and G2 Cell Division: M Phase (Mitosis and Cytokinesis)

19 The Cell Cycle G 1 phase: cells increase in size and synthesize new proteins and organelles.

20 The Cell Cycle S (or synthesis) phase: new DNA is synthesized when the chromosomes are replicated.

21 The Cell Cycle G 2 phase: many of the organelles and molecules required for cell division are produced.

22 The Cell Cycle M Phase: Mitosis is the division of the cell nucleus. Cytokinesis is the division of the cytoplasm.

23 Important Terms 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

24 Mitosis: Prophase 1.Duplicated chromosome condenses and becomes visible.

25 Mitosis: Prophase 2. The centrioles move to opposite sides of nucleus and help organize the spindle.

26 Mitosis: Prophase 3. The spindle forms to prepare for separation of the chromatids

27 Mitosis: Prophase 4. The nucleolus disappears and nuclear envelope breaks down.

28 Mitosis: Metaphase 1. Centromeres of the duplicated chromosomes line up across the center of the cell.

29 Mitosis: Metaphase 2. The spindle fibers connect the centromere of each chromosome to the two poles of the spindle.

30 Mitosis: Anaphase Centromeres are pulled apart and the chromatids separate to become individual chromosomes. Chromosomes separate into two groups near the poles of the spindle.

31 Mitosis: Telophase 1. Chromosomes spread out into a tangle of chromatin. 2. A nuclear envelope re-forms around each cluster of chromosomes. 3. Spindle breaks apart, and a nucleolus becomes visible in each daughter nucleus.

32 Cytokinesis Need to split the cells after mitosis Animals: cell membrane is drawn in until the cytoplasm is pinched into two equal parts. Cleavage Furrow

33 Cytokinesis 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.

34 Review itemview? problemid= &frame=banner&openedf rom=itemlibrary&preview=assignitem bc_campbell_biology_7/media/ interactivemedia/activities/load.html?12&c

35 Chromosome Number Diploid Cells: cell that has a set of homologous chromosomes. Homologous: each of the chromosomes from the male parent has a corresponding chromosome from the female parent. 2N where N = # of chromosomes

36 Chromosome Number Haploid Cells: single set of chromosomes, therefore 1 set of genes. Gametes are haploid Represented by n

37 Mitosis Review One diploid parent cell (asexual) Occurs in somatic cells Two resulting daughter cells are diploid Daughter cells identical to parent cell

38 Meiosis What kind of cell is created by meiosis? How many chromosomes are there in each?

39 Meiosis Meiosis is a process in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell. 2 divisions, Meiosis I and II Diploid cell will become 4 haploid cells

40 Meiosis

41 Meiosis: Interphase I Chromosome Replication- DNA replicates to 46 single chromosomes

42 Meiosis: Prophase I The cells begin to divide, and the chromosomes pair up, forming a structure called a tetrad, which contains four chromatids.

43 Meiosis: Prophase I Tetrads undergo crossing-over. Chromatids of the homologous chromosomes cross over one another. Crossing-over = variation!

44 Meiosis: Metaphase I Tetrads (or paired homologous chromosomes) line up at the center of the cell Spindles attach to the tetrads

45 Meiosis: Anaphase I Spindle fibers pull each homologous chromosome pair toward opposite ends of the cell. At completion, separated chromosomes cluster at opposite ends of the cell.

46 Meiosis: Telophase I and Cytokinesis Telophase I: a nuclear membrane forms around each cluster of chromosomes. Cytokinesis: form two new cells.

47 Meiosis Only 1 set of chromosomes present

48 Meiosis I Two cells made from Meiosis I are different. Why? Meiosis II Cells do not undergo a round of chromosome replication before entering.

49 Meiosis: Prophase II Chromosomes, consisting of two chromatids become visible.

50 Meiosis: Metaphase II Chromosomes line up in the center of each cell. Chromatids attach to spindle fibers

51 Meiosis: Anaphase II Paired chromatids separate.

52 Meiosis: Telophase II and Cytokinesis Each of the four daughter cells produced in meiosis II receives two chromatids. Each cell has the haploid number (N) just two chromosomes each.

53 Meiosis

54 Compare Mitosis and Meiosis Mitosis Meiosis Have 2 sets of chromosomes Have 1 set of chromosomes 2 diploid cells in the end 4 haploid cells in the end Autosomal chromosomes Sexual chromosomes Exact copy of cell Genetic variations via crossing over 1 round of cell division needed 2 rounds of cell division needed