1. Cell Reproduction Chapter 4 Notes

2. Why is cell division important?  Many celled organisms grow because cell division increases the number of cells they have.  One-celled organisms reproduce using cell division.

3. The Cell Cycle  Like organisms have life cycles, cells have life cycles.  It is a series of events that takes place from one cell division to the next.  The time it takes to complete the cycle is not the same for all organisms or all cells in an organism.  Most of the time, a cell is in interphase. (Inter=between) (Between cell divisions). It is a period of growth and development. After that, cell division begins.  Study Figure 2 on page 97.

4. Mitosis  PART of cell division—the nucleus divides into two.  The two new nuclei will be identical because everything duplicates (copies) before it separates (during interphase). The chromosomes thicken into coils called chromatids and they attach to their pair at a spot called a centromere.  Steps of mitosis: (PMAT) prophase – nuclear membrane breaks down, chromatid pairs are visible, centrioles move to opposite ends of the cell prophase – nuclear membrane breaks down, chromatid pairs are visible, centrioles move to opposite ends of the cell metaphase – the pairs of chromatids line up at the center of the cell, centromere is attached to centriole by spindle fibers metaphase – the pairs of chromatids line up at the center of the cell, centromere is attached to centriole by spindle fibers anaphase – centromere divides, spindle fibers shorten and chromatids begin to move to opposite ends of the cell (now they are called chromosomes again) anaphase – centromere divides, spindle fibers shorten and chromatids begin to move to opposite ends of the cell (now they are called chromosomes again) telophase – new nucleus forms, chromosomes uncoil telophase – new nucleus forms, chromosomes uncoil

5. Cell Division  After mitosis, the cytoplasm divides and two new cells are created.  In animal cells, the cytoplasm pinches in (like a balloon with a string tied around it).  In plant cells, a cell plate forms and new cell walls grow on each side.  After the cytoplasm divides, the cell enters interphase again, the period of growth and development.

6. Asexual Reproduction  Some organisms with eukaryotic cells can reproduce asexually by using cell division. All cells will be genetically identical to the parent cell because of the duplication of the nucleus that happens in mitosis. All cells will be genetically identical to the parent cell because of the duplication of the nucleus that happens in mitosis.  Bacteria do not have a nucleus, so they can’t use mitosis/cell division to reproduce asexually. They use fission.  Budding – new organism growing from the body of a parent organism  Regeneration – process that uses cell division to replace lost body parts

7. Body Cells vs. Sex Cells  Two types of cells in your body—body cells and sex cells. (ALL cells except sex cells (sperm and egg) are body cells.)  Body cells – chromosomes are in pairs (diploid). Humans have 23 pairs (46 chromosomes).  Sex cells – have half the number of chromosomes as body cells (one from each pair). (23 for humans.)

8. Sexual Reproduction  Two sex cells come together—sperm (male) and egg (female).  The sperm cell enters the egg cell in a process called fertilization.  The resulting cell is called a zygote.

9. Meiosis  Meiosis is the process used to create haploid cells so that sexual reproduction can take place. Sex cells have half so that when they combine with another sex cell, which also has half, the result will be “whole.” [If two diploid cells combined, the offspring would have double the amount of chromosomes.] Sex cells have half so that when they combine with another sex cell, which also has half, the result will be “whole.” [If two diploid cells combined, the offspring would have double the amount of chromosomes.]  During meiosis, the nucleus divides twice (Meiosis I and Meiosis II).  Study diagrams and descriptions on pages 106- 107.

10. DNA (deoxyribonucleic acid)  Contains information that an organism needs to grow and function  Has a structure that resembles a twisted ladder sides are made up of sugar-phosphate molecules sides are made up of sugar-phosphate molecules rungs are made up of nitrogen bases (remember this later for nitrogen cycle) rungs are made up of nitrogen bases (remember this later for nitrogen cycle)  To duplicate itself, it unwinds, separates its sides, and then forms new sides.

11. Genes  Genes—sections of DNA on a chromosome (pieces of code) [Ex: like a slice is part of a loaf]  Contain instructions for making specific proteins  RNA carries codes for making proteins from the nucleus to the ribosomes in the cytoplasm Messenger RNA (mRNA), Ribosomal RNA (rRNA), Transfer RNA (tRNA) Messenger RNA (mRNA), Ribosomal RNA (rRNA), Transfer RNA (tRNA)  Cells use only the genes that direct the making of proteins needed by that cell (like a character in a play only reads the lines in the script for them)

12. Mutations  Any permanent change in the DNA sequence of a cell’s gene or chromosome. can change the traits of the organism can change the traits of the organism can be caused by outside factors like X-rays, sunlight, and some chemicals can be caused by outside factors like X-rays, sunlight, and some chemicals  Can be passed to offspring only if mutation is passed to a sperm or egg cell.