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CELL DIVISION What is cell division? All species pass on their genetic information by producing offspring. Both prokaryotes and eukaryotes use a process known as cell division to make new cells. Cell division is when a parent cell divides into two daughter cells. Prokaryotes use cell division to reproduce. Eukaryotes use cell division for growth and maintenance of cells, as well as for reproduction.

What are the types of cell division? There are three main types of cell division: 1. Binary Fission – prokaryotes use this type of cell division to reproduce 2. The Cell Cycle/Mitosis – eukaryotes use this type of cell division to make new cells 3. Meiosis – this is a special type of cell division used by organisms that sexually reproduce

exp!ore LAB SCIENCE CELL DIVISION IN Bacterial cell Origin of PROKARYOTES replication

Centromere • Binary fission involves the replication of the prokaryotic chromosome to Centrioles produce new cells.

• In bacteria, this chromosome is a circular double-stranded DNA molecule. Chromosomes

• This circular DNA molecule constitutes the entire genome of the bacteria.

• The reproduction of bacteria is clonal, Double-stranded Terminus of replication meaning each cell produced is an DNA (bacterial chromosome) identical copy of the parent cell. Spindle fibers exp!ore LAB SCIENCE BINARY FISSION Binary fission is the cellular reproduction mechanism used by single-celled prokaryotes, like bacteria. It occurs in five main steps:

1. Replication of the 2. Starting at the 3. The cell elongates 4. A new membrane 5. When the septum is circular bacterial DNA origin of replication, as the DNA is and cell wall begin to complete, the cell begins at the origin of the replication replicated. grow and form a pinches in two. Two replication. enzymes make copies septum at the midpoint daughter cells are of each strand of of the cell. formed, each DNA. The enzymes containing a bacterial continue until they DNA molecule. meet at the terminus of replication.

exp!ore LAB SCIENCE THE CELL CYCLE Cell division in eukaryotes occurs in a cycle that consists of five phases. This cycle is called the cell cycle. Phases of the Cell Cycle:

G1 (gap phase 1): this is the primary growth phase in which the cell prepares for DNA replication

f S (synthesis): during this phase, the cell synthesizes a replica

G1 S of its DNA f G2 Mitosis G2 (gap phase 2): this is the second growth phase in which Cytokinesis microtubules begin to form a spindle in order to prepare for separation of the replicated DNA

f Mitosis: during this phase, the replicated DNA separates

f Cytokinesis: during this phase, the cytoplasm separates, and two daughter cells are formed exp!ore LAB SCIENCE EUKARYOTIC Sister chromatids REPLICATION STRUCTURES Centromere

• Nucleus: a structure located in the center of all eukaryotic cells that contains genetic Centrioles information in the form of chromosomes • Chromosomes: structures located in the nucleus of a cell; they contain the genetic information of the organism (DNA) and protein • Sister chromatids: two identical copies of a Chromosomes chromosome that are attached to each other by a centromere Nucleus • Centromere: a structure that connects two sister chromatids and serves as a point of attachment for spindle fibers • Spindle fibers: filaments that pull sister chromatids apart during cell division • Centrioles: structures that assist in the formation of spindle fibers exp!ore Spindle fibers LAB SCIENCE MITOSIS Mitosis is the cell division process used by eukaryotes in which a single cell divides into two identical daughter cells. Mitosis allows organisms to grow and replace old cells. Mitosis is divided into five phases: interphase, prophase, metaphase, anaphase, and telophase.

Interphase Prophase Metaphase Anaphase Telophase

The cell’s DNA The chromosomes The The The cell replicates. condense and the mitotic chromosomes chromosomes Microtubules elongates and spindles form. The nuclear align in the are pulled to the begins to divide begin to extend envelope also begins to center of the opposite sides into two from the disintegrate. cell. of the cell. centrioles. identical daughter cells. exp!ore LAB SCIENCE 1 PROPHASE I The chromosomes begin to condense and crossing over occurs. SEXUAL REPLICATION The spindle begins to form.

VIA MEIOSIS 2 METAPHASE I The pairs of homologous chromosomes align at the equator of the cell.

• Meiosis is separated into two parts – 3 ANAPHASECentromere I Meiosis I and Meiosis II. The homologous pairs of chromosomes are pulled apart.

• Each part consists of prophase, metaphase, I MEIOSIS 4 CentriolesTELOPHASE I & CYTOKINESIS anaphase, and telophase. The separated homologues cluster at each end of the cell. The cell is split, forming two new cells, each with half the number of chromosomes as the original • A key feature of Meiosis is the crossing cell.

over that occurs in Prophase I. 5 PROPHASE II • Crossing over is what gives us genetic A new spindle forms in each cell and the nuclear envelope breaks down. Chromosomes variation. 6 METAPHASE II • Homologues are separated during Chromosomes are joined at the centromere and align at the equator of the cell. 7 Meiosis I and sister chromatids are ANAPHASE II The sister chromatids are pulled apart.

separated during Meiosis II. II MEIOSIS 8 TELOPHASE II & CYTOKINESIS • The steps of Meiosis are listed to the The separated sister chromatids cluster at each end of the cell. The cells are both split, forming four genetically diverse cells. right. Spindle fibers exp!ore LAB SCIENCE MEIOSIS Telophase I Telophase II Interphase Prophase I Metaphase I Anaphase I Prophase II Metaphase II Anaphase II & Cytokinesis & Cytokinesis

exp!ore LAB SCIENCE REFERENCES

Mason, K. Understanding Biology. McGraw-Hill Education; 1st edition, 2014.

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