Cell Growth and Division Honors Biology Chapter 10

Cell Growth Living things grow larger due to an increase in cells Larger the cell, the more demands on the DNA and the more transport of water and nutrients across the membrane The surface area to volume ratio must also be maintained.

Cell Growth Before the cell gets too big in size, it must divide into 2 new daughter cells via a process known as cell division In order to divide, the cell must make a copy of its DNA so each cell has a set of instructions of how the body functions DNA Replication

Cell Division Occurs in 2 main stages 1. mitosis – division of nucleus 2. cytokinesis – division of cytoplasm Considered to be asexual since the two daughter cells are genetically identical to the parent cell Source of new cells as organism grows and develops

Chromosomes Made of DNA and proteins Cells of every organism have a specific number of chromosomes humans = 46 carrot = 18 fruit fly = 8 Chromosomes are only visible during cell division, these structures form to compact the DNA to make it easy to divide

Chromosome Structure Each chromosome consists of 2 identical “sister” chromatids When the cell divides, the sister chromatids separate from each other. One chromatid goes to each of the 2 new cells Each pair of chromatids are attached by the centromere. The centromere is usually located near the middle of the chromatid The human body contains 46 chromosomes and 46 centromeres, each of which contain 2 chromatids Short arm Long arm One chromosome with 2 identical sister chromatids

Cell Cycle 1. M Phase: (mitosis phase) mitosis and cytokinesis During the cell cycle, a cell grows, prepares for division, and divides to form 2 new identical daughter cells, each of which then begin the cycle again. The cell cycle consists of 4 phases 1. M Phase: (mitosis phase) mitosis and cytokinesis 2. G1 Phase: (gap phase) growth and activity 3. S Phase: (synthesis phase) DNA replication 4, G2 Phase: (gap phase) growth and activity G1, S and G2 all used to be group together and called interphase

Cell Cycle G1 Phase M Phase S Phase G2 Phase

Interphase Cell spends more time in interphase than M phase 1. G1 Phase – Most growing occurs. Cells increase in size and synthesize new proteins and organelles 2. S Phase – Chromosomes are replicated. Key proteins are synthesized 3. G2 Phase – Shortest of the three phases. Organelles and molecules required for division are produced. When the cell completes this phase it is ready to enter the M phase and begin the process of cell division

Mitosis Involves the centrioles (cell organelles made of proteins and microtubules) of the cell Occurs in four stages 1. prophase – chromosomes appear and nuclear envelope breaks down 2. metaphase – chromosomes line up across center of cell 3. anaphase - sister chromatids separate into separate cells 4. telophase – chromosomes gather at opposite ends of two cells and two new nuclear envelopes begin to form

Interphase During Interphase the chromosomes are not visible. The cell grows and replicates its DNA and centrioles Spindle forming Centrioles Chromatin Centromere Nuclear envelope Centriole Chromosomes (paired chromatids) Interphase Prophase Spindle Cytokinesis Centriole Metaphase Telophase Individual chromosomes Anaphase Nuclear envelope reforming

Prophase Longest phase of mitosis Chromatin condenses and chromosomes become visible The nuclear envelope begins to break down Centrioles separate and take positions on opposite sides of the cell The spindle, a microtubule structure that helps separate the chromosomes, begins to form

Prophase Interphase Prophase Cytokinesis Metaphase Telophase Anaphase Spindle forming Centrioles Nuclear envelope Chromatin Centromere Centriole Chromosomes (paired chromatids) Interphase Prophase Spindle Cytokinesis Centriole Metaphase Telophase Individual chromosomes Anaphase Nuclear envelope reforming

Metaphase Chromosomes line up across the center of the cell. Microtubules connect the centromere of each chromosome to the two poles of the spindle

Metaphase Interphase Prophase Cytokinesis Metaphase Telophase Anaphase Spindle forming Centrioles Nuclear envelope Chromatin Centromere Centriole Chromosomes (paired chromatids) Interphase Prophase Spindle Cytokinesis Centriole Metaphase Telophase Individual chromosomes Anaphase Nuclear envelope reforming

Anaphase The centromeres that join the sister chromatids of the chromosome split and allow the sister chromatids to separate and become individual chromosomes The chromatids continue to move until they have separated into two groups near the poles of the spindle Anaphase ends when the chromatids stop moving

Anaphase Interphase Prophase Cytokinesis Metaphase Telophase Anaphase Spindle forming Centrioles Nuclear envelope Chromatin Centromere Centriole Chromosomes (paired chromatids) Interphase Prophase Spindle Cytokinesis Centriole Metaphase Telophase Individual chromosomes Anaphase Nuclear envelope reforming

Telophase Final stage of mitosis Chromosomes begin to loosen and into a tangle of dense material Two new nuclear envelopes begin to reform around the two clusters of chromosomes The spindle begins to break apart and a nucleolus becomes visible in each daughter nucleus Mitosis is now complete, 2 nuclei are formed, but the cells are not yet separated

Telophase Interphase Prophase Cytokinesis Metaphase Telophase Anaphase Spindle forming Centrioles Nuclear envelope Chromatin Centromere Centriole Chromosomes (paired chromatids) Interphase Prophase Spindle Cytokinesis Centriole Metaphase Telophase Individual chromosomes Anaphase Nuclear envelope reforming

Cytokinesis Separation of cytoplasm within a single cell Typically occurs at the same time as telophase Cell membrane is drawn inward until the separation of the cytoplasm into two nearly equal parts Each part contains its own nucleus and organelles In plants, a cell plate forms midway between the divided nuclei and a cell wall begins to appear in the cell plate

Cytokinesis Interphase Prophase Cytokinesis Metaphase Telophase Spindle forming Centrioles Nuclear envelope Chromatin Centromere Centriole Chromosomes (paired chromatids) Interphase Prophase Spindle Cytokinesis Centriole Metaphase Telophase Individual chromosomes Anaphase Nuclear envelope reforming

Mitosis and Cytokinesis Video Segment ..\..\bio CD\Chapter 10A.mpg

Did you know???? KNOWLEDGE IS POWER!!!!!!!!!!! All of the DNA in an adult human body could fit inside one ice cube, but if unwound, stretched out and joined end to end, it could reach from the earth to the sun and back again approximately 400 more times.  KNOWLEDGE IS POWER!!!!!!!!!!!

Homework Assignment This will be due tomorrow, start it in class now because it is a long assignment!!! Suppose you were small enough to hitch a ride on a chromosome located in an animal cell that goes through mitosis and cytokinesis. Describe what you would see happening during EACH phase of the process