Genes and Gene Function Chapter 6 Cell Division Genes and Gene Function Chapter 6

Genes and Cell Division Genes- The cell’s blueprints. Contain information needed to build the cells and cell products Genes are stored in Chromosomes Chromosomes are kept in the nucleus

Cell Division Cell Division (binary fission) occurs when one cell (parent cell) divides to produce two new cells (daughter cells) Example- building a factory that is the exact same as an old one. When you build, the order you do things is important. Example: You wouldn’t build the roof of a building before the foundation. A cell needs to go through three stages to prepare to divide.

Cell Division Interphase (stage one) – the genes are copied. (DNA replication) Genes are on long thin chromosomes. Two identical strands (Sister chromatids). The new cell uses the info on these genes to create the new structures.

Cell Division Mitosis (stage two) – The equal distribution of the parent cell’s genes between the two daughter cells. Provides each new cell with a complete set of all the genes. This stage goes through FOUR specific phases…

Mitosis Phase 1 – Prophase Prophase is when the membrane around the nucleus disappears and the chromosomes begin to coil up. Spindle of fibers formed Sister chromosomes appear X shaped The spindle of fibers move the chromosomes through the next three phases

Mitosis Phase 2-Metaphase - Chromosomes are lined up at the center of the spindle. Phase 3- Anaphase – Each pair of sister chromatids separates. Phase 4- Telophase- New chromosomes reach the end of the spindle and begin to uncoil. As they do this, a new nucleus forms around each group of chromosomes, resulting in two new nuclei

Cell Division Cytokinesis (stage three) – provides each new daughter cell with some cytoplasm and organelles. This stage is the physical separation of the cell into two daughter cells. Since both daughter cells have a complete set of blueprints (genes), they can make additional cellular parts.

Why is Mitotic cell division important? Purpose of cell division is to ensure that each new cell has the genes identical to the parent cell. Our skin cells perform cell division several times each day, replacing dead cells that are constantly being rubbed off. Mitosis needed for growth and replacement.

Asexual Reproduction Asexual Reproduction – The reproduction by mitotic cell division. One Example- amoeba Unicellular organism. Every three days, it grows large enough to divide

Asexual Reproduction Budding –a type of asexual reproduction where a bulge develops on the outside of the cell; Mitosis takes place; one of the two new nuclei goes into the bulge, called the Bud The bud then grows as it receives cytoplasm from the cell. When it is completely grown, the bud may break off, or stay attached.

Asexual Reproduction Regeneration- The process of regrowing missing body parts. Example: Planarian cut in pieces; able to grow back and asexually reproduce. Regeneration can also be a method of repair or replacement instead of reproduction.

Asexual Reproduction Spore – a cell surrounded by a protective covering. Many organisms produce spores by mitotic cell division These organisms can create hundreds of spores that can grow into a new organism. Example: Bread mold

Sexual Reproduction Sexual Reproduction – occurs when two organisms each give a complete copy of their genes to form a new organism. Meiosis – process in which this occurs. Process starts like Mitosis – the genetic material is doubled, but then there is another step – the two daughter cells separate the genes into single copies. When meiosis is complete, there are four daughter cells. Main Idea behind Meiosis- there is ONE duplication, and TWO divisions.

Meiosis Why can’t cells perform mitosis instead of meiosis? Each offspring would have too many chromosomes.

Terms to know Haploid- a cell in which the nucleus has just one copy of each chromosome. (after meiosis has occurred) Diploid – a cell in which the nucleus has two copies of each chromosome. (normal state) Gamete- a haploid reproductive cell designed to transfer or receive chromosomes during sexual reproduction

Terms to know Egg- a female gamete Sperm – a male gamete Fertilization – the combining of an egg and a sperm Zygote- the new diploid cell formed when an egg and a sperm combine.

DNA history In 1953, James D Watson and Francis H.C. Crick worked out a model for the structure of deoxyribonucleic acid (DNA) Twisted ladder Double Helix

DNA is Coded Messages Ladder made up of units called nucleotides Four different types of nucleotides, each containing a sugar, phosphate, and a base Four Bases are: Adenine Thymine Cytosine Guanine

DNA Model Sugars and phosphates form the sides of the ladder and the bases form the rungs. Each rung made of two bases Bases paired such that: Adenine is always with Thymine Cytosine always with Guanine

DNA Replication Genes are specific sections of DNA. The two nucleotide bases of each “ladder rung” are held together by chemical bonds that can be broken up by enzymes. Broken up or “unzipped” into two halves. Inside the cell there are free nucleotides in the nucleus which line up with the unzipped “half – DNA molecules” (only join up with the normal pairing partners)

DNA In time, each half-DNA will have a new corresponding side. Produces two identical DNA molecules Picture on pg. 87

DNA Replication - process in which one DNA molecule forms two DNA molecules. Before a cell divides, the chromosomes make complete copies of themselves by DNA replication, providing each new cell with a complete copy of all the genes. This is the first step in Mitosis or Meiosis

Why is DNA so important? Why do genes matter? Among other roles, the genes produce proteins needed for everything! Genes specify the specific proteins needed.

RNA decodes the message The DNA contains its genetic information in a code. This code is the arrangement of bases in the DNA molecule. When decoded, these bases cause specific proteins to be made in the cell.

Decoding When a cell needs a certain protein, the section of DNA code (gene) for that protein makes a ribonucleic acid (RNA). RNA is made up of nucleic acid like DNA, but RNA has only a single chain of nucleotides. Instead of the base Thymine, it has Uracil

Decoding Because the RNA molecule contains a copy of the DNA’s coded message, it is called the messenger RNA (mRNA) Once RNA has been made, the two sides of the DNA join back together. Transcription – The process of making messenger RNA molecules.

The decoded Messages are Proteins Once messenger RNA is made in the nucleus, it carries a working copy of the DNA’s coded message to a ribosome in the cytoplasm. The ribosome reads the code and makes a protein. The enzymes necessary to put the amino acids together are in the ribosomes. Protein Synthesis – manufacturing of proteins inside a cell.

tRNA Transfer RNA (tRNA) Each kind of tRNA attaches to a different type of amino acid in the cytoplasm. The various tRNA molecules carry amino acids to the ribosome and mRNA. The sequence or the mRNA determines which amino acids to use. The tRNA brings the amino acids to the mRNA.

RNA Ribosomes move along the mRNA and read three bases of the mRNA code at a time. Each group of three bases is called a codon, and codes for a specific amino acid. When the two types of RNA line up, the specific amino acid is put into the proper place.

RNA summery Ok, confused?... Basically, a protein contains at least one chain of amino acids. Transfer RNA bring the amino acids to the messenger RNA and line them up according to the codon.