Cell Growth, Division, & Reproduction

Transcription

1 Cell Growth, Division, & Reproduction

2 Two main reasons why cells divide rather than continue growing: A larger cell places more demand on the DNA. When a cell s size increases, its DNA does not & the extra demand placed on the DNA can lead to information overload. A larger cell is less efficient in moving nutrients & waste materials across the cell membrane. The rate at which food goes in & wastes leave the cell depends on the volume

3 By using ratio of surface area to volume, you can see how a cell s surface area grows compared to its volume. In a cell, surface area (cell membrane) does not increase as fast as the volume and this can cause serious problems.

4 Explain using town roads or library vs. people in the town

5 Cells have to divide before they get too large. The problem of increasing cell size is solved by cell division. Cell division The process by which a cell divides into 2 new daughter cells. Cells replicate or copy their DNA before they divide. This replication of the DNA solves the problem of information overload because each daughter cell gets a complete copy of genetic information (DNA).

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7 There are two types: Asexual reproduction Sexual reproduction

8 Production of genetically identical offspring from a single parent Bacteria reproduce by binary fission Hydras reproduce by budding Kalanchoe plants form plantlets.

9 Production of genetically diverse offspring from 2 parent organisms. Except identical twins, which are genetically the same.

10 ASEXUAL REPRODUCTION Advantages: Faster reproduction Having offsprings which are genetically identical if the environmental conditions are favorable. Disadvantage Having offsprings which are genetically identical if the environmental conditions are unfavorable. SEXUAL REPRODUCTION Advantages: Organisms are genetically diverse Enables species to adapt rapidly to new environmental conditions. Disadvantages: Slower (time needed to find mates, growth & development of offspring). Yeast can reproduce asexually & sexually

11 The Process of Cell Division

12 Cells have a lot of genetic information Ex. E. coli s DNA is 1.6mm in length, 1000x longer than E. coli itself. Scale- think of 300m rope stuffed in a backpack Cells can handle large molecules like DNA only by careful packaging. Genetic information is bundled into packages of DNA known as chromosomes.

13 Human genome contains 3 billion base pairs divided into 23 chromosomes. A single strand of DNA 3 billion base pairs long would be about 1.02 meters (over three feet) long, The DNA is divided into 23 separate pieces (chromosomes) averaging 4.5 cm,

14 Most prokaryotes contain a single-circular DNA chromosome.

15 Eukaryotes have more DNA than prokaryotes so they contain multiple chromosomes. Fruit flies have 8 xm/cell Humans have 46xm/cell Fruit fly Chromosomes

16 Eukaryotic chromosomes form a close association with histones. Histones proteins found in the chromosomes Chromosome &protein complex chromatin DNA tightly coiled around histones form beadlike structures called nucleosomes. Nucleosomes coils to form thick fibers. During cell division, the thick fibers condense & supercoils to form a duplicated chromosome.

17 Chromatids 2 identical halves of a chromosome Centromere constricted area of a chromosome that holds chromatids. Chromatids form as DNA makes a copy of itself before cell division

18 Chromosomes make it possible to separate DNA precisely during cell division.

19 Series of events when the cell grows, prepares for division, and divides to form 2 daughter cells

20 Binary fission division of a singlecelled organism to produce 2 genetically identical organism. Steps The chromosome copies itself The cell grows larger A cell wall forms in the middle of the cell & it divides.

21 Oyfs bdi

22 Consists of Interphase time between cell divisions. G1-gap 1 S-synthesis G2 gap 2 M-phase or cell division Mitosis cytokinesis Interphase Most of the cell s life time is spent in interphase

23 G1 Intense cell growth synthesize new proteins & organelles Cells do most of their growing in this phase.

24 S phase DNA replication. The cell now contains 2x as much DNA

25 G2 Shortest of the 3 phases of interphase Production of many of the cell s molecules & organelles is completed. Cell prepares to enter mitosis

26 Note Cells in the Central Nervous System stop dividing at maturity and never divide again They exit the cell cycle from G1 & enter G0 G0 cells do not copy the DNA or prepare for cell division

27 In eukaryotes, cell division occurs in two stages: mitosis and cytokinesis. Mitosis division of the cell nucleus. Cytokinesis division of the cytoplasm. In many cells, these 2 stages overlap

28 Divided into 4 stages 1. Prophase (P) 2. Metaphase (M) 3. Anaphase (A) 4. Telophase (T) PMAT Depending on the kind of cell, mitosis can take a few minutes to several days

29 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

30 Longest phase of mitosis Genetic material condenses. Duplicated chromosomes become visible Spindle fibers start to form. Nucleolus disappears & nuclear envelope breaks down

31 Shortest phase of mitosis Easiest to see with a microscope Centromeres of duplicated chromosomes line up across the center of the cell. Spindle fibers connect to the centromere of each chromosome to the 2 poles of the spindle

32 Chromosomes separate & spindle fibers move them to opposite sides ends of the poles. Each sister chromatid is now considered an individual chromosome

33 Chromosomes begin to unwind and a nuclear envelope forms Mitosis is complete

34 Completest the process of cell division divides the cell in 2 The area of the cell which pinches in is cleavage furrow

35 In plant cells, a cell plate is formed (Cell plate- membrane bound by cell wall).

36 4 ak0 Mitosis Flip Book oip8o