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Home , Cell cycle, Cell division

The Cycle Objective # 1

„ In this topic we will examine the , the series of changes that a cell Compare the amount and goes through from one division to the organization of genetic material in next. prokaryotic cells with the amount „ We will pay particular attention to how and organization of genetic the genetic material is passed on from material in eukaryotic cells. parent cell to daughter cells during the cell cycle. 1 2

Objective 1 Objective 1

„ An average eukaryotic cell has about 1,000 times more DNA then an „ The DNA in a eukaryotic cell is average prokaryotic cell. organized into several linear „ have a single, circular . Each DNA molecule. It is sometimes called normally contains one DNA molecule “naked” because the DNA is not which is combined with special combined with . proteins called .

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Objective 1 Objective # 2 DNA Prokaryotes structure single, naked, many linear circular DNA chromosomes, Describe the process of cell molecule each made of 1 DNA molecule division in prokaryotic cells. joined with location in an area of the inside a called membrane-bound the nucleoid nucleus

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1 Objective 2 Objective 2 Prokaryotes use a type of cell 3) Finally, the cytoplasm divides in half, division called binary : producing 2 daughter cells which 1) First, the single, circular DNA each have one copy of the original molecule replicates, producing two DNA molecule. Therefore, the 2 identical copies of the original. new cells are genetically identical to 2) Next, the 2 DNA molecules move each other and to the original cell: to opposite ends of the cell.

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Objective 2 Objective # 3 Describe the structure of both unduplicated and duplicated eukaryotic chromosomes; and distinguish between chromosome, , , and .

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Objective 3 Objective 3

„Eukaryotic chromosomes are made ƒHow can such long molecules fit inside of chromatin, a complex of DNA a microscopic nucleus? and protein. ¾Every 200 nucleotide pairs, the DNA ƒEach unduplicated chromosome wraps twice around a group of 8 contains one DNA molecule, which proteins to form a nucleosome. may be several inches long. ¾Higher order coiling and supercoiling also help condense and package the chromatin inside the nucleus: 11 12

2 Objective 3 Objective 3

„For much of the cell cycle, most of the chromatin is loosely coiled. „During this time, the individual chromosomes cannot be seen inside the nucleus.

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Objective 3, Eukaryotic Nucleus Objective 3 „Prior to each chromosome duplicates itself. „All the duplicated chromosomes then condense into short rod-like structures that can be seen and counted under the :

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Objective 3 Objective 3

„ Because of duplication, each condensed chromosome consists of 2 identical joined by a centromere. „ Each duplicated chromosome contains 2 identical DNA molecules (unless a occurred during duplication), one in each chromatid:

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3 Objective 3 Objective 3

„ The centromere is a constricted point on the chromosome containing a specific DNA sequence, to which is bound 2 discs of protein called . „ Kinetochores serve as points of attachment for that move the chromosomes during cell division. 19 20

Objective 3 Objective # 4

Explain what are and how they are useful.

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Objective 4 Objective 4

„ The particular array of chromosomes in a eukaryotic cell is called its . „ To examine a karyotype, the chromosomes are photographed when they are highly condensed, then photos of the individual chromosomes are cut out and arranged in order of decreasing size:

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4 Objective 4 Objective # 5

„ Karyotypes are used to study the Distinguish between a haploid number and structure of the chromosomes present in a cell. cell and a diploid cell. Distinguish between identical „ They can also be used to detect chromosomal abnormalities that may chromosomes, homologous be associated with specific genetic chromosomes, and non- traits or defects. homologous chromosomes.

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Objective 5 Objective 5

„ In eukaryotes, every species requires a „ Cells that contain 1 complete set of specific number of chromosomes to chromosomes are called haploid. code for all the polypeptides produced „ n or N represents the number of by the . These chromosomes chromosomes in a haploid cell. make up 1 complete set. „ Cells that contain 2 complete sets of „ Each chromosome in a set controls chromosomes are called diploid. the production of a different group of „ 2n or 2N represents the number of polypeptides. chromosomes in a diploid cell. 27 28

Objective 5 Objective 5

„ For example, 23 different „ We will use different shapes to chromosomes are needed to code for represent the different chromosomes all the polypeptides produced by that make up a set, and different colors . to represent different sets of chromosomes. „ Therefore, in humans: N=23 2N = 46

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5 Objective 5 Objective 5 Unduplicated Chromosomes Duplicated Chromosomes

Haploid Cell, N = 3 Diploid Cell, 2N = 6 Haploid Cell, N = 3 Diploid Cell, 2N = 6 31 32

Objective 5 Objective 5

„ In a diploid cell, the chromosomes „ However, homologous chromosomes are occur in pairs. The 2 members of each not identical because they may code for pair are called homologous different forms of each trait: chromosomes or homologues. Red eyes Short wings Tan body „ Under the microscope, homologous chromosomes look identical. „ In addition, because they code for the same polypeptides, they control the White eyes Long wings Tan body same traits. 33 34

Objective 5 Objective 5

„ Identical chromosomes: „ Homologous chromosomes: ¾Look the same under the ¾Look the same under the microscope (have microscope (have the same shape the same shape but different colors on our and color on our diagrams) diagrams) ¾Control the same traits ¾Control the same traits ¾May code for different forms of each trait ¾Code for the same form of each trait ¾Independent origin - each was inherited from ¾Common origin – both descended a different parent from the same original chromosome 35 36

6 Objective 5 Objective 5 ƒNon-homologous chromosomes: Duplicated Chromosomes ¾Look different under the microscope (have different shapes on our diagrams) ¾Control different traits

Haploid Cell, N = 3 Diploid Cell, 2N = 6 37 38

Objective # 6 Objective 6

„ – a section of a DNA molecule that contains the code for making one Define and be able to use the polypeptide. following terms correctly: gene, „ Gene locus –the location of a gene gene locus, and allele. along the length of a chromosome „ Alleles – that can occupy the same gene locus (on different chromosomes)

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Objective 6 Objective # 7

Homologous Chromosomes

Red eyes Short wings Tan body Identify the stages of the eukaryotic cell cycle, and describe the events of each stage.

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7 Objective 7 Objective 7

„ The cell cycle refers to the sequence of „ is subdivided into 3 stages: events that occur as a cell grows and ¾ G1 is the primary growth phase of the divides. It is divided into 2 main stages: cell cycle ¾ Interphase – chromosomes are not ¾ S is when the cell synthesizes a copy of visible. Involves and its chromosomes (DNA duplication). duplication of the genetic material. ¾ G2 is the second growth phase, during ¾ Cell division – includes division of the which preparations are made for cell duplicated chromosomes () and division. division of the cytoplasm (). 43 44

Objective 7 Objective 7

„Mitosis is subdivided into 4 stages: ¾ ¾ ¾ ¾

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Objective # 8 Objective 8

„ Mitosis: ¾ some haploid and some diploid cells List, describe, diagram, and may divide by mitosis. identify the stages of mitosis. ¾ each new cell receives one copy of every chromosome that was present in the original cell. ¾ produces 2 new cells that are both genetically identical to the original cell. 47 48

8 Objective 8, Mitosis in a Diploid Cell (2N=6) Objective 8, Mitosis in a Haploid Cell (N=3)

DNA duplication during DNA duplication during interphase interphase

Mitosis Mitosis 49 50

Objective 8, Stages of Mitosis Objective 8, Mitosis in a Diploid Cell (2N=6)

„ Prophase: ¾ nuclear membrane disintegrates ¾ nucleolus disappears ¾ duplicated chromosomes condense ¾ mitotic spindle begins to form ¾ kinetochores begin to mature and attach to mitotic spindle Prophase 51 52

Objective 8, Stages of Mitosis Objective 8, Mitosis in a Diploid Cell (2N=6)

„Metaphase: ¾kinetochores attach duplicated chromosomes to mitotic spindle ¾chromosomes line up, in single file, along metaphase plate at equator of cell

Metaphase 53 54

9 Objective 8, Stages of Mitosis Objective 8, Mitosis in a Diploid Cell (2N=6) „ Anaphase: ¾ split so that each duplicated chromosome becomes 2 identical, unduplicated chromosomes ¾ kinetochore microtubules shorten, pulling identical chromosomes to opposite poles ¾ polar microtubules elongate preparing Polar Microtubule cell for cytokinesis 55 Anaphase 56

Objective 8, Stages of Mitosis Objective 8, Mitosis in a Diploid Cell (2N=6)

„ Telophase: ¾ chromosomes reach poles of cell ¾ kinetochores disappear ¾ polar microtubules continue to elongate, preparing cell for cytokinesis ¾ nuclear membrane reforms ¾ nucleolus reappears ¾ chromosomes decondense Telophase 57 58

Objective 8, Mitosis in a Haploid Cell (N=3) Objective 8, Mitosis in a Haploid Cell (N=3)

Metaphase Prophase 59 60

10 Objective 8, Mitosis in a Haploid Cell (N=3) Objective 8, Mitosis in a Haploid Cell (N=3) Kinetochore Microtubule

Polar Microtubule Anaphase 61 Telophase 62

Objective # 9 Objective 9

„ Cytokinesis refers to division of the cytoplasm during cell division, while Describe the process of mitosis refers to division of the genetic cytokinesis and distinguish material (chromosomes). between mitosis and „ Although cytokinesis generally follows cytokinesis. mitosis, this isn’t always the case.

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Objective 9 Objective 9

„ In cells and other eukaryotic cells that lack a , cytokinesis is achieved by means of a constricting belt of filaments. „ As the filaments slide past each other, they create a furrow which deepens and eventually pinches the cell in half:

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11 Objective 9 Objective 9

„ cells possess a cell wall which is too rigid to be squeezed in half by actin filaments. „ Instead, a new , called a cell plate, is assembled in the middle of the cell. As this expands outward, it effectively divides the cell in two.

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Objective # 10 Objective 10

„ is the uncontrolled growth and Explain what cancer is, and division of cells. describe how cancer can „ Most result from in result when control of the one of two types of growth-regulating genes: eukaryotic cell cycle breaks ¾ proto- down. ¾ tumor-suppressor genes

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Objective 10 Objective 10

„ Proto-oncogenes code for proteins „ Tumor-suppressor genes code for involved in stimulating cell division. proteins involved in inhibiting cell „ Mutated proto-oncogenes that division. stimulate a cell to divide when it shouldn’t are called oncogenes „ Mutated tumor-suppressor genes that (cancer-causing genes). do not inhibit cell division when they should can also cause cancer.

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