Chapter 4: Cell Reproduction

Aim: Why is cell division important?

The Cell Cycle Series of events that takes place from one cell division to the next Length of time to complete a cell cycle is different in all cells Most of the life of any eukaryotic cell is spent in interphase-period of growth and development Nerve and muscles cells are always in interphase (no longer divide)

During interphase, hereditary material is copied and the cell prepares for cell division Cell division begins after interphase Cells need to copy hereditary material before dividing so the new cells have a complete set of hereditary material to carry out life functions

Aim: What is the process of mitosis?

Mitosis Process in which the nucleus divides to form two identical nuclei New nuclei are identical to original nucleus Interphase: ◦ nucleus divides and chromosomes duplicate forming chromatids-two identical DNA strands

4 stages of mitosis: 1. Prophase: ◦ Chromatids fully visible ◦ Nucleolus and nuclear membrane disintegrate ◦ Centrioles move to opposite ends of cell (not in plants) ◦ Spindle fibers begin to form 2. Metaphase: ◦ Chromatids line up across the center of the cell ◦ Centromere of each chromatids attaches to spindle fibers from each side

3. Anaphase: ◦ Each centromere divides ◦ Chromatids separate and move to opposite ends of cell and become chromosomes 4. Telophase: ◦ Spindle fibers disappear ◦ Nucleus forms ◦ Cytoplasm being divided ◦ 2 new cells form:  Animal Cell-cell membrane pinches in middle  Plant Cell- cell plate appears forming a new cell wall

Results of Mitosis Each new nucleus has the same number and types of chromosomes as the original Humans: ◦ Every cell has 46 chromosomes-23 pairs, except sex cells ◦ All the trillion of cells have the same hereditary material ◦ Use DNA to become different types of cells ◦ Cell division allows growth and replaces damaged or worn out cells

Aim: What is asexual reproduction?

Asexual Reproduction New organism is produced from one organism New organism’s hereditary material is identical to the parent’s hereditary material 3 forms of Asexual Reproduction 1.Cellular:  Used by organisms with eukaryotic cells  Ex: sweet potato growing in jar of water (mitosis)  Bacteria reproduce asexually by fission  Can’t use mitosis because they don’t have a nucleus

2. Budding ◦ Bud grows from the body of the parent organism ◦ Made possible by mitosis 3. Regeneration ◦ Uses cell division (mitosis) to regrow body parts ◦ Examples: sponges, sea stars

Aim: What is sexual reproduction?

Sexual Reproduction Two sex cells come together Formed from cells in reproductive organs Sperm-male Eggs-female Fertilization-joining of egg and sperm ◦ Forms a zygote Following fertilization, cell division begins

Diploid Cells: ◦ Cells have pairs of similar chromosomes ◦ Human body cells-23 pairs, 46 chromosomes ◦ Skin, bones, tissues and organs form from diploid cells Haploid Cells: ◦ Do not have pairs of chromosomes ◦ Sex cells ◦ Have only 23 chromosomes-one from each of the 23 pairs

Aim: Why is meiosis needed for sexual reproduction?

Meiosis Produces hapliod sex cells After 2 haploid sex cells combine-a diploid zygote forms Two divisions of the nucleus occur ◦ Meiosis 1 ◦ Meiosis 2 Results in four sex cells

Meiosis 1 Chromosome is duplicated Prophase 1 Each duplicated chromosome comes near its similar duplicated chromosome Metaphase 1 ◦ Pairs of duplicated chromosomes line up in center of cell

Anaphase 1 ◦ Each chromatid pair attaches to one spindle fiber ◦ 2 pairs of chromatids move away to opposite ends of cell Telophase 1 ◦ Cytoplasm divides ◦ 2 new cells form ◦ Each new cell has one duplicated chromosome from each similar pair

Meiosis 2 Chromatids of each cell will be duplicated Prophase 2 ◦ Duplicated chromosomes and spindle fibers reappear Metaphase 2 ◦ Duplicated chromosomes move to middle of the cell ◦ Each centromere attaches to 2 spindle fibers instead of 1

Anaphase 2 ◦ Chromatids separate and move to opposite ends of the cell ◦ Chromatids now chromosomes Telophase 2 ◦ Spindle fibers disappear ◦ Nuclear membrane forms around the chromosomes After meiosis 2 cytokenisis occurs-the division of the cytoplasm

Aim: What are the parts of a DNA molecule?

DNA Deoxyribonucleic Acid Contains information for an organism’s growth and function DNA code is copied when the cell divides Rosalind Franklin discovered it is 2 chains of molecules in a spiral form 1953 DNA model created by James Watson & Francis Crick

Similar to a twisted ladder Each side of ladder is made up of sugar- phosphate molecules Rungs of ladder-made of nitrogen bases 4 kinds of nitrogen bases: 1.Adenine (A) 2.Guanine (G) 3.Cytosine (C) 4.Thymine (T) Cytosine=Guanine Adenine=Thymine These bases occur as pairs

Aim: What is the function and structure of RNA?

Genes Most of your characteristics depend on the kinds of proteins your cells make The instructions for making a specific protein are found in your genes Are a section of DNA on a chromosome Determine the order of amino acids in a protein Changing the order makes a different protein Found in the nucleus

Proteins are made on ribosomes Codes for making proteins are carried from the nucleus to the ribosomes by RNA RNA: ◦ Made in the nucleus on a DNA pattern ◦ 4 bases: adenine, guanine, cytosine and uracil (U) ◦ Molecules contain the sugar ribose ◦ 3 types of RNA

1. mRNA: ◦ Messenger RNA ◦ Protein production begins when it moves into the cytoplasm ◦ Carries codes to make the amino acids bond 2. rRNA: ◦ Ribsosomal RNA ◦ Ribosomes made of it 3. tRNA: ◦ Transfer RNA ◦ Bring amino acids to the ribosomes ◦ Attach with the mRNA to make a protein

Aim: How do mutations occur?

Mutations Happens when DNA is not copied correctly Are any permanent change in the DNA sequence of a gene or chromosome of a cell X-rays, sunlight, and some chemicals may cause mutations Examples: ◦ Having an extra chromosome ◦ Missing a chromosome

Without correctly coded proteins an organism can not grow, repair or maintain itself Can cause death Mutations in body cells may or may not be life threatening Mutations in sex cells cause all the cells that are formed to have the mutation Some mutations have no effect Some can be beneficial