Cell Reproduction Chapter 3, Section 5

Maintaining our bodies Why do cells reproduce? Growth Healing Maintaining our bodies

Chromosomes Structures inside the nucleus that contains genetic information. Chromosomes are made from long strands of DNA.

Parts of a Chromosome Chromatid- Identical strands of DNA. Centromere- Connects the chromatids of each chromosome.

Numbers of Chromosomes Organisms have different numbers of chromosomes. Humans have 23 pairs of chromosomes, 46 in all.

Mitosis The process in which the nucleus of a cell divides to form two identical nuclei.

Cell Cycles Cells do not live forever! The cell cycle is a series of stages a cell goes through before it divides.

Pre Mitosis - Interphase A period of growth and development. Most of the cell’s life is spent in Interphase. chromosomes are copied!

Steps of Mitosis Prophase Metaphase Anaphase Telophase

Step 1 - Prophase Nucleus disappears. Chromosomes thicken Spindle fibers stretch across the cell.

Thread-like structures that pull the chromosomes apart. Spindle Fibers Thread-like structures that pull the chromosomes apart.

Spindle Fibers attach to the centromere. Step 2 - Metaphase Chromosomes line up along the center of the cell. Spindle Fibers attach to the centromere.

to opposite sides of the cell. Step 3 - Anaphase The spindle fibers pull the chromosomes apart to opposite sides of the cell.

Step 4 - Telophase Spindle fibers disappear. The nuclei reforms. Chromosomes unwind.

Cytokinesis The cell pinches along the middle and becomes two new cells!

Interphase I Prophase Metaphase Cytokinesis Anaphase Telophase

Results of Mitosis One nucleus becomes two nuclei. Our cells have 46 chromosomes (23 pairs). After mitosis, a new nucleus with 46 chromosomes (23 pairs) is made.

DNA (Deoxyribonucleic Acid) Chromosomes are made out of DNA. DNA looks like a twisted ladder (called a double helix) DNA codes for the creation of proteins.

Structure of DNA DNA is made up of a: Sugar Group Phosphate Group Nitrogen Base

Guanine, Cytosine, Adenine, and Thymine, Four Nitrogen Bases Guanine, Cytosine, Adenine, and Thymine, These bases make up the “steps” in the DNA ladder.

Chargaff’s Base Pairing Rules Guanine always binds to Cytosine G----C Adenine always binds to Thymine A----T

DNA Replication In order for mitosis and meiosis to occur, DNA must replicate! The DNA strand “unzips” and two new strands of DNA forms.

Hydrogen bond between the two bases breaks and the strands separate Free floating nucleotides in the nucleus come and join with their complementary base pairs This makes two strands of DNA that are identical to the original