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Cell Division: The Cell Cycle

Cell Division: The Cell Cycle. Cell Cycle is the pattern of division & growth of a cell. It involves the copy & distribution of the genome into 2 daughter cells. Genome is a cell’s total hereditary endowment or the entire genetic code (DNA) found within the nucleus of a cell.

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Cell Division: The Cell Cycle

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  1. Cell Division: The Cell Cycle • Cell Cycle is the pattern of division & growth of a cell. • It involves the copy & distribution of the genome into 2 daughter cells. • Genome is a cell’s total hereditary endowment or the entire genetic code (DNA) found within the nucleus of a cell. • It takes place inside the somatic cells of humans with the exception of red blood cells & certain nerve cells. • Somatic cells are all the body’s cells except the reproductive cells; egg & sperm. • Somatic cells contain 46 chromosomes. • Chromosomes are condensed chromatin into double rods (chromatids) of genetic material. • Chromatin • The mass of very long, thin fibers of DNA & proteins that are found unwound within the nucleus. • Chromatid • ½ of the double-rodded structure of a chromosome

  2. The cell cycle serves 3 main functions…. • Reproduction • In single-celled organisms, 2 separate individual organisms are the result of the cell cycle. • Growth & development • In multi-cellular organisms, rapid copying of cells via the cell cycle add to the growing organism. • Tissue & renewal • In multi-cellular organisms that have reached maximum growth, the cell cycle renews & replaces older cells to maintain and organism’s size & function.

  3. The Cell Cycle occurs in 3 stages. • Stage 1: Interphase (21 hours) • Interphase is the longest of the 3 stages of the Cell Cycle • Interphase is divided into 3 subphases: • G1 (1st gap) • S phase • G2 (2nd gap) • The cell begins to grow & enlarge during all 3 subphases of Interphase.

  4. The cell produces structures that will be used to help the cell divide into 2 new cells. • Centromere connects the chromatids or double rods of chromosomes. • Centrioles are organelles used to separate & pull chromosomes into new nuclei. • Spindle fibers are bands that extend from the centriole & attach to the chromosome & pull it into separate nuclei.

  5. The primary process that takes place during Interphase is the replication of DNA. • DNA (deoxyribonucleic acid) is the sequence of nitrogen base pairs that determines the structure of proteins and serves as the genetic code of life. • Replication is the process by which the DNA makes an exact copy of itself. • DNA (chromatin within the nucleus) replicates or copies itself only during the S phase of interphase. • Steps of DNA replication • Step 1: DNA unzips; bonds connecting nitrogen base pairs dissolves. • Step 2: RNA brings in & attaches new nitrogen bases to the now exposed nitrogen bases resulting in 2 sets of nitrogen base pairs (Adenine to Thymine & Guanine to Cytosine). • Step 3: Deoxyribose & Phosphate are brought in to complete the sides resulting in 2 exact copies of the DNA molecule.

  6. Stage 2: Mitosis (<50 minutes) • During Mitosis, 2 nuclei are created and 1 copy of the DNA created during Interphase is distributed to each of the nuclei. • This process is typically divided into 4 primary phases. • Phase 1: Prophase • Phase 2: Metaphase • Recently a new phase; Prometaphase, has been added in between Prophaseand Metaphase. • Phase 3: Anaphase • Phase 4: Telophase

  7. Stage 3: Cytokinesis (< 15 minutes) • The cytoplasm divides. • The 1st sign of cleavage is the appearance of a cleavage furrow. • A cleavage furrow is shallow groove in the cell surface near the old metaphase plate. • 2 new cell membranes form around the 2 new cells. • The new cells have an identical set of chromosomes and half of the organelles.

  8. Nucleic acids • Organic molecule that contains the instructions cells need to carry out all of the functions of life. • Composed of the elements Carbon, Oxygen, Hydrogen, Nitrogen & Phosphorus in various combinations. • There are 2 types of nucleic acids • Deoxyribonucleic acid • More commonly known by the acronym, DNA • Ribonucleic acid • More commonly known by the acronym, RNA

  9. RNA is responsible for carrying the genetic code from the DNA in the nucleus to Ribosomes. • Ribosomes are the cell organelle located within the cytoplasm that is responsible for protein production. • Proteins are large organic molecules made of carbon, hydrogen, oxygen, nitrogen & in certain cases, sulfur. • Amino acidsare the building blocks of proteins. • There are over 20 known amino acids • 10 essential; must be ingested • 10 non-essential; the body synthesizes or makes. • Proteins serve several functions within the body… • Building blocks for most cell organelles & body structures. • Hair, skin, fingernails, muscles, etc. • Proteins form parts of various cells membranes.

  10. Enzymes are specialized proteins that speed up or slow down chemical reactions within the body. • There are 2 types of RNA. • Type 1: Messenger RNA (mRNA) • mRNA: responsible for taking a copy of the DNA code from the chromosomes in the nucleus to the appropriate ribosome. • Type 2: Transfer RNA (tRNA) • tRNA: responsible for bring the appropriate amino acid to the ribosome to build the protein. • RNA, which stands for ribonucleic acid, contains the same nitrogen bases as DNA with the exception of one and is only 1 strand unlike the 2 in DNA. • Thymine is replaced with Uracil and matches up with Adenine.

  11. Steps to Protein synthesis • Messenger RNA production • DNA unzips • RNA bases match up along one of the unzipped DNA strands. • Genetic information is transferred from the DNA strand to the RNA strand. • Messenger RNA attaches to a Ribosome • The ribosome moves along the messenger RNA strand reading the genetic code 3 bases (codons) at a time. • Codon: a 3 letter combination of the 4 nitrogen bases that code for & match up to a specific amino acid. • Stop codons: 3 letter combination that tells the ribosome to stop adding amino acids to a growing protein chain.

  12. Transfer RNA attaches to Messenger RNA • Based on the specific 3 letter combination (codon) that is read the transfer RNA retrieves the amino acid that the codon matches. • The amino acid is then connected to the previous amino acid. • Protein production finishes • The protein chain continues to grow with each amino acid that is added. • The ribosome reaches a STOPcodon or 3 letter combination that tells the ribosome to stop adding amino acids to the protein chain. • The protein chain is then released and transported to the part of the body that it is needed.

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