Cell Division Life Cycle of the Cell Life Cycle of the Cell Mitosis Mitosis Meiosis Meiosis

Cellular Division Cell division is a process by which a cell, called the parent cell, divides into two or more cells, called daughter cells. Cell division is usually a small segment of a larger cell cycle. cell cycle cell cycle 3 major types of cell division

Cellular Division The size of the cell signals time for division. Cell Grows until it reaches a size large enough to start division.

Prokaryotic Division  Ex. Bacteria  Prokaryotic Division is called Binary fission, it is the division of a prokaryotic cell into 2 daughter cells  Consists of 3 stages: 1.The 1 chromosome in the cell makes a copy of itself (in a process that is similar to unzipping and then reforming each side) 2.Cell grows until it reaches twice its original size 3.A cell wall forms between the 2 chromosomes and the cell splits into 2 new cells Identical to Original cell

Eukaryotic Division  More complex than prokaryotic cells because of organelles (ex. Mitochondria, endoplasmic reticulum, golgi bodies, chloroplasts, etc.)  The life of the eukaryotic cell is diagrammed as the cell cycle – the repeating sequence of growth and division of eukaryotic cells (4 major phases)

Cell Life Cycle Organelles are copied here G 1,S, & G 2 all make up Interphase Therefore, the cell is usually in interphase Cytokinesis happens here

Cell Cycle Cell Cycle Animated Animated

Cell Cycle   The cell cycle is driven by a chemical control system that both triggers and coordinates key events in the cell cycle. The cell cycle control system is regulated at certain checkpoints.   Signals from inside the cell (internal signals) and from outside the cell (external signals) are involved in turning the process of cell division off and on. An internal signal involves the cell sensing the presence of chemicals, called enzymes, which are produced inside the cell An external signal involves the cell sensing the presence of a chemical (such as a growth factor) which was produced in other specialized cells.

Cell Cycle   Cells can also respond to physical signals from their environment. Cells sense when they are too closely packed and cell division is turned off. Cells sense when they are not in contact with a surface and cell division is turned on.   A checkpoint in the cell cycle is a critical control point where stop and go signals can regulate the cycle. The cell division mechanism in most animal cells is in the “off” position when there is no stimulus present. Specific stimuli are required to start the processes

Mitosis – is the process that results in two nuclei with the exact same information Interphase – pre-mitotic phase Prophase – 1 st phase Metaphase – 2 nd phase Anaphase – 3 rd phase Telophase – 4 th phase Cytokinesis – cell divides PMAT:

Chromosomes are copied (# doubles) Chromosomes are copied (# doubles) Chromosomes appear as threadlike coils (chromatin) at the start, but each chromosome and its copy(sister chromosome) change to sister chromatids at end of this phase Chromosomes appear as threadlike coils (chromatin) at the start, but each chromosome and its copy(sister chromosome) change to sister chromatids at end of this phase Longest phase of the cell cycle – G 1, S, & G 2 Longest phase of the cell cycle – G 1, S, & G 2 CELL MEMBRANE Nucleus Cytoplasm chromatin

Chromosomes A chromosome is an organized structure of DNA and protein that is found in cells. It is a single piece of coiled DNA containing many genes DNAprotein cells genesDNAprotein cells genes

Chromosomes

Animal Cell Plant Cell Photographs from:

Mitosis begins (cell begins to divide) – nucleus breaks down and nucleolus disappears Mitosis begins (cell begins to divide) – nucleus breaks down and nucleolus disappears Centrioles (or poles) appear and begin to move to opposite end of the cell. Centrioles (or poles) appear and begin to move to opposite end of the cell. Spindle fibers form between the poles. Spindle fibers form between the poles. Chromosomes condense & become visible Chromosomes condense & become visible Centrioles Sister chromatids Spindle fibers

Animal Cell Plant Cell Photographs from: There are no centrioles in plant cells they can divide without them

Chromatids (or pairs of chromosomes) attach to the spindle fibers. Chromatids line up at the equator (center of the cell) Chromatids (or pairs of chromosomes) attach to the spindle fibers. Chromatids line up at the equator (center of the cell) Centrioles Spindle fibers

Animal Cell Plant Cell Photographs from:

Chromatids (or pairs of chromosomes) separate at the centromere and begin to move to opposite ends of the cell. Chromatids (or pairs of chromosomes) separate at the centromere and begin to move to opposite ends of the cell. Centrioles Spindle fibers

Animal Cell Plant Cell Photographs from:

Spindle fibers disappear Spindle fibers disappear Two new nuclei form. Nucleolus returns to the inside of each nucleus Two new nuclei form. Nucleolus returns to the inside of each nucleus Chromosomes uncoil and appear as chromatin (threads rather than rods). Chromosomes uncoil and appear as chromatin (threads rather than rods). Mitosis ends. Mitosis ends. Nuclei Chromatin

Animal Cell Plant Cell Photographs from:

Cell membrane or cell plate moves inward to create two daughter cells – each with its own nucleus with identical chromosomes. Cell membrane or cell plate moves inward to create two daughter cells – each with its own nucleus with identical chromosomes. - animal cells → cleavage (pinching) furrow forms in the cell membrane to separate the cell. - plant cells → cell wall forms to separate cell.

Animal Mitosis -- Review Interphase Interphase Prophase Prophase Metaphase Metaphase Anaphase Anaphase Telophase Telophase Cytokinesis Cytokinesis

Plant Mitosis -- Review Interphase Interphase Prophase Prophase Metaphase Metaphase Anaphase Anaphase Telophase Telophase Cytokinesis Cytokinesis Cell wall plate

Mitosis Song

Meiosis

Meiosis  Meiosis – the process that divides the # of chromosomes in cells in half  2 successive nuclear divisions (goes through PMAT twice)  Before 1 st division, DNA is copied just like in mitosis  However, DNA is not copied before 2 nd division

Meiosis  Broken down into 2 parts – Meiosis I and Meiosis II  Meiosis I – homologous chromosomes separate into 2 diploid cells  Meiosis II – Each Cell Sister chromatids separate into 2 haploid cells Diploid Meiosis I Meiosis II Haploid DNA Copied  1 Diploid Cell = 4 Haploid Cells

Difference between Animals & Plants  In Animals – meiosis makes gametes (reproductive cells / sex cells – sperm & eggs)  In Plants – meiosis makes spores

2 Unique Events of Meiosis: 1. Crossing Over: Homologous chromosomes pair up next to each other Homologous chromosomes pair up next to each other Arms of chromosomes exchange segments (same sized) of DNA Arms of chromosomes exchange segments (same sized) of DNA 2. Skipping Replication: Only 1 replication of DNA, but 2 divisions → meiosis halves the number of chromosomes Only 1 replication of DNA, but 2 divisions → meiosis halves the number of chromosomes

Meiosis I 1. Prophase I: a. Chromosomes condense (become thick) and become visible b. Nuclear envelope breaks down c. Homologous chromosomes pair up d. Crossing over occurs 2. Metaphase I: a. Pairs of homologous chromosomes move to the equator (center) of the cell 3. Anaphase I: a. Homologues separate b. Chromosomes of each pair pull apart and move to the poles (opposite ends) of cell

Meiosis I 4. Telophase I: a. Chromosomes gather at each of the 2 poles b. Cytoplasm divide, forming 2 new cells. c. Each cell produced now contains the same number of chromosomes as the original cell d. Meiosis I often called reduction division Skipping Replication – DNA does not copy between meiosis I and meiosis II Meiosis II Is just like meiosis I except : we calls stages Prophase II, Metaphase II, Anaphase II, and Telophase II we calls stages Prophase II, Metaphase II, Anaphase II, and Telophase II 4 new haploid cells are created instead of 2 diploid cells 4 new haploid cells are created instead of 2 diploid cells

Genetic Recombination  The formation of new combinations of genes  2 chromatids of chromosomes no longer contain identical genetic material  Provides a source for genetic variation, which impacts the rate of evolution in organisms

Mitosis vs Meiosis Mitosis 1. PMAT Once 2. Ends with 2 diploid cells that are identical to parent cell 3. Somatic Cells (Body cells) undergo this cellular reproduction Meiosis 1. PMAT Twice 2. Ends with 4 haploid cells that are different from the parent 3. Gametes (Sex cells) undergo this cellular reproduction

Mitosis vs Meiosis