Cell Size Limitations

Transcription

1 Cell Size Limitations Cells come in a wide variety of sizes and shapes. Considering this wide range of cells sizes, why then can t most organisms be just one giant cell?

2 Diffusion limits cell size Although diffusion is a fast and efficient process over short distances, it becomes slow and inefficient as the distances become larger. Because of the slow rate of diffusion, organisms can t be just one giant-sized cell.

3 DNA limits cell size The cell cannot survive unless there is enough DNA to support the protein needs of the cell.

4 Surface area-to-volume ratio 1 mm 2 mm 4 mm 4 mm 1 mm 1 mm SA = 6 mm 2 Vol = 1 mm 3 Ratio of 6:1 2 mm 2 mm SA = 24 mm 2 Vol = 8 mm 3 Ratio of 3:1 SA = 96 mm 2 Vol = 64 mm 3 Ratio of 1.5:1 4 mm As a cell s size increases, its volume increases much faster than its surface area (SA). If cell size doubled, the cell would require eight times more nutrients and would have eight times more waste to excrete.

5 Surface area-to-volume ratio 1 mm 2 mm 4 mm 4 mm 1 mm 1 mm SA = 6 mm 2 Vol = 1 mm 3 Ratio of 6:1 2 mm 2 mm SA = 24 mm 2 Vol = 8 mm 3 Ratio of 3:1 SA = 96 mm 2 Vol = 64 mm 3 Ratio of 1.5:1 4 mm The surface area (SA), however, would increase by a factor of only four. The cell would either starve to death or be poisoned from the buildup of waste products.

6 Cell Division Cell division is the process by which new cells are produced from one cell. Cell division results in two cells that are identical to the original, parent cell.

7 Structures, which contain DNA and become darkly colored when stained, are called chromosomes. Chromosomes are the carriers of the genetic material that is copied and passed from generation to generation of cells. Accurate transmission of chromosomes during cell Murdoch division Online upload 2014 is critical. Chromosomes

8 The large, complex chromosomes of eukaryotes duplicate with each cell division Chromosomes contain a very long DNA molecule with thousands of genes Individual chromosomes are only visible during cell division They are packaged as chromatin when visible Sister chromatids Centromere Centromere

9 The large, complex chromosomes of eukaryotes duplicate with each cell division Before a cell starts dividing, the chromosomes are duplicated This process produces sister chromatids Sister chromatids Centromere Centromere

10 double-stranded human chromosomes ready for mitosis

11 The Cell Cycle The cell cycle is the sequence of growth and division of a cell. The majority of a cell s life is spent in the growth period known as interphase. Interphase

12 The Cell Cycle Mitosis Following interphase, a cell enters its period of nuclear division called mitosis. Following mitosis, the cytoplasm divides, separating the two daughter cells.

13 Interphase: A Busy Time Interphase, the busiest phase of the cell cycle, is divided into three parts: G1,S, & G2 Interphase DNA synthesis and replication (S) Rapid growth and metabolic activity (G1) Cell prepares for division (G2)

14 Interphase: A Busy Time During the first part of interphase, (G1),the cell grows and protein production is high. Interphase (G1) Rapid growth and metabolic activity (G1)

15 Interphase: A Busy Time In the second part of interphase, (S),the cell copies its chromosomes. Interphase (S) DNA synthesis and replication (S)

16 Interphase: A Busy Time After the chromosomes have been duplicated, the cell enters another shorter growth period, (G2),in which mitochondria and other organelles are manufactured and cell parts needed for cell division are assembled. Interphase (G2) Cell prepares for division (G2)

17 Biology is the only subject in which multiplication is the same thing as division

18 MITOSIS: Making New Cells

19 Where it all began You started as a cell smaller than a period at the end of a sentence.

20 Getting from there to here Going from egg to fetus. the original fertilized ova (egg) has to divide and divide and divide and divide

21 Why do cells divide Single-celled organisms for reproduction amoeba asexual reproduction (identical clones) starfish

22 Why do cells divide Multi-celled organisms for growth & development amoeba from fertilized egg to adult for repair & replacement replace cells that die from normal wear & tear or from injury starfish

23 The Phases of Mitosis The four phases of mitosis are Prophase, Metaphase, Anaphase, and Telophase. PMAT

24 Prophase: The first phase of mitosis During prophase, the chromosomes coil to form visible chromatins. Spindle fibers Disappearing nuclear envelope Doubled chromosome

25 Prophase: The 1 st phase of mitosis The two halves of the doubled structure are called sister chromatids. Sister chromatids are held together by a structure called a centromere, which plays a role in chromosome movement during mitosis. Centromere Sister chromatids

26 Metaphase: The 2 nd stage of mitosis During metaphase, the chromatids move to the equator (middle) of the spindle.

27 Anaphase: The 3 rd phase of mitosis During anaphase, the centromeres split and the sister chromatids are pulled apart to opposite poles of the cell.

28 Telophase: The 4 th phase of mitosis During telophase, two distinct daughter cells are formed. The cells separate as the cell cycle proceeds into the next interphase. Nuclear envelope reappears Two daughter cells are formed

29 DNA must be duplicated DNA in chromosomes chromosomes in cell cell 4 single-stranded chromosomes nucleus duplicated chromosomes duplicated chromosomes cell 4 Murdoch double-stranded Online upload 2014 chromosomes nucleus

30 Mitosis: Dividing DNA & cells Stage 1: cell copies DNA Making new DNA during S phase of interphase DNA Copy DNA! cell Copying of DNA occurs during interphase S nucleus (interphase S)

31 Mitosis: Dividing DNA & cells Stage 2: DNA winds into chromosomes DNA is wound up into chromosomes to keep it organized. duplicated chromosomes Wind up! cell Organizing of DNA occurs during prophase nucleus (prophase)

32 Mitosis: Dividing DNA & cells Stage 3: Chromosomes line up chromatids line up in middle attached to protein cables that will help them move Line up! Lining of DNA along equator occurs during metaphase duplicated chromosomes line up in middle of cell (metaphase)

33 Mitosis: Dividing DNA & cells Stage 4: Chromosomes separate chromatids divide, separating pairs start moving to opposite ends Separate! Dividing & separating of DNA occurs during anaphase chromosomes divide & move to opposite ends (anaphase)

34 Mitosis: Dividing DNA & cells Stage 5: Cell starts to divide cell start to divide nucleus re-forms Divide! Cell division begins to occur during telophase (telophase)

35 Mitosis: Dividing DNA & cells Stage 6: DNA unwinds again Identical daughter cells separate now they can do their every day jobs The End! New cells are formed during the process of cytokinesis. (cytokinesis)

36 New daughter cells Get 2 exact copies of original cells same DNA clones

37 Cytokinesis Following telophase, the cell s cytoplasm divides in a process called cytokinesis. Cytokinesis differs between plants and animals. Toward the end of telophase in animal cells, the plasma membrane pinches in along the equator.

38 Cytokinesis Plant cells have a rigid cell wall, so the plasma membrane does not pinch in. A structure known as the cell plate is laid down across the cell s equator. A cell membrane forms around each cell, and new cell walls form on each side of the cell plate until separation is complete.

39 Results of Mitosis When mitosis is complete, unicellular organisms remain as single cells. In multicellular organisms, cell growth and reproduction result in groups of cells that work together as tissue to perform a specific function. Tissues organize in various combinations to form organs that perform more complex roles within the organism. Multiple organs that work together form an organ system.

40 Mitosis in whitefish blastula

41 Mitosis in plant cell

42 onion root tip

43 Overview of mitosis I.P.M.A.T.C. interphase prophase Please Make Another Two Cells cytokinesis metaphase anaphase telophase

44 Mitosis & Cancer: When Making New Cells Goes Wrong!

45 When is mitosis a good thing? When you have to add or replace cells growth & development repair replacement

46 When is mitosis a BAD thing When cells reproduce & they are not needed these cells take over organs, but don t do the right job they just keep making copies cancer Uncontrolled cell growth Damages organs

47 Why would cells just make bad copies? If DNA gets damaged, cells stop listening to correct instructions Mutations (wrongly constructed DNA strands) Some causes of mutations: UV radiation chemical exposure radiation exposure heat cigarette smoke pollution age genetics

48 Normal Control of the Cell Cycle Proteins and enzymes control the cell cycle The cell cycle is controlled by proteins called cyclins and a set of enzymes that attach to the cyclin and become activated. Occasionally, cells lose control of the cell cycle.

49 Normal Control of the Cell Cycle This uncontrolled dividing of cells can result from the failure to produce certain enzymes, the overproduction of enzymes, or the production of other enzymes at the wrong time. Cancer is a malignant growth resulting from uncontrolled cell division.

50 Normal Control of the Cell Cycle Enzyme production is directed by genes located on the chromosomes. A gene is a segment of DNA that controls the production of a protein.

51 Cancer: A mistake in the Cell Cycle Currently, scientists consider cancer to be a result of changes in one or more of the genes that produce substances that are involved in controlling the cell cycle. Cancerous cells form masses of tissue called tumors that deprive normal cells of nutrients.

52 Tumors Benign tumor abnormal cells remain at original site as a lump most do not cause serious problems & can be removed by surgery

53 Tumors Malignant tumor cells leave original site carried by circulatory systems to other tissues start more tumors damage functions of organs throughout body

54 Cancer: A mistake in the Cell Cycle In later stages, cancer cells enter the circulatory systems and spread throughout the body, a process called metastasis, forming new tumors that disrupt the function of organs, organ systems, and ultimately, the organism.

55 The causes of cancer The causes of cancer are difficult to pinpoint because both genetic and environmental factors are involved.

56 The causes of cancer Environmental factors, such as cigarette smoke, air and water pollution, and exposure to ultraviolet radiation from the sun, are all known to damage the genes that control the cell cycle. Cancer may also be caused by viral infections that damage the genes.

57 Cancer prevention Physicians and dietary experts agree that diets low in fat and high in fiber content may reduce the risk of many kinds of cancer. Vitamins and minerals may also help prevent cancer. In addition to diet, other healthy choices such as daily exercise and not using tobacco also are known to reduce the risk of cancer.