Unit C: Cell Division, Genetics and Molecular Biology Chapter 17 Sec. 17.1 – The Cell Cycle

Why are you so good looking? Why cell division? How does it work? What is haploid? What is diploid?

Application Questions: What is a ‘germ’ cell? Is it haploid or diploid? What does it mean to ‘culture’ cells? Why do people culture cells? What is the purpose? What is a stem cell? Where do stem cells come from? Are there any ethical/moral problems with stem cell research? What is your opinion? What is a differentiated cell? How does a cell become differentiated? How does it relate to the ‘genes’ or DNA in the cell?

Introductory Video http://www.youtube.com/watch?v=3kpR5RSJ7SA

The Cell Cycle The cell cycle is the sequence of stages through which a cell passes from one cell division to the next. During the cell cycle the cell: Grows Duplicates its DNA And divides to form a new cell

The Cell Cycle Cont’d The cell cycle consists of 2 main phases: Interphase which can be divided into 3 stages: G1 (Growth 1) S (Synthesis) G2 (Growth 2) Division phase which consists of 1stage: M (Mitosis and Cytokinesis)

Chromosome Structure Before looking at the stages of the cell cycle it is important to understand the structure of chromosomes. The DNA of animals and humans is divided among a number of chromosomes. Each chromosome contains sections of DNA and proteins.

Chromosome Structure Cont’d The combination of DNA and proteins together is called chromatin. Chromosomes can be either uncondensed or condensed. Uncondensed chromosomes are long, thin strands that cannot be seen under a microscope. Condensed chromosomes are shorter, fatter strand that can usually be seen under a microscope.

Chromosome Structure Cont’d Chromosomes can either be unduplicated or duplicated. When a chromosome becomes duplicated, it means that it’s DNA has been copied. Duplicated chromosomes are held together by a centromere. When a chromosome’s DNA has been duplicated, the two duplicated parts are now known as sister chromatids.

Interphase Cells spend most of their lives in interphase. Cells are not dividing. G1 (Growth 1) Rapid growth. Chromosomes are unduplicated. S (Synthesis) Chromosomes duplicate their DNA.

G2 (Growth 2) Cell grows again. Completes its preparations for division.

Division Phase Prophase Metaphase Anaphase Telophase M (Mitosis and Cytokinesis) Parent cell divides to form two identical daughter cells. Mitosis can be divided into 4 stages: Prophase Metaphase Anaphase Telophase

The Full Cell Cycle

Prophase First phase in mitosis. Duplicated chromosomes condense by thickening and shortening. Centrioles move to opposite poles (ends) of the cell. Centrioles are small protein bodies found in the cytoplasm that provides attachment for spindle fibres during cell division.

Prophase Cont’d Spindle fibres are protein structures that guide chromosome movement during cell division. Spindle fibres attach to centromeres of duplicated chromosomes to help them move. Nuclear membrane that surround the nucleus starts to dissolve.

Prophase

Metaphase Second phase of mitosis. Chromosomes move to the center of the cell. This center area is called the equatorial plate. Nuclear membrane completely dissolves.

Metaphase

Anaphase Third phase of mitosis. Centromeres divide and sister chromatids separate. The sister chromatids are referred to a chromosomes now that they are separated. Chromosomes start to move to opposite poles of the cell.

Anaphase

Telophase Fourth and last stage of mitosis. Chromosomes reach opposite poles of the cell and begin to lengthen. Spindle fibres dissolve. Nuclear envelopes start to form around each mass of chromosomes.

Telophase

Cytokinesis Following the telophase of mitosis, cytokinesis occurs. Cytokinesis is the splitting of the cytoplasm between the two masses of chromosomes to form two separate cells.

A Cell Clock Cells have an internal biological clock determining how many times a cell can divide before it dies. Depending on the type of cell, some undergo more mitosis than others. More specialized cells such as heart, muscle and nerve cells cannot divide as many times as unspecialized ones. Unspecialized cells such as skin cells, are being damaged and dying off on a regular basis, so they are able to divide more than specialized cells.

http://www.youtube.com/watch?v=3kpR5RSJ7SA