SCIENCE

• Living things are made up of Cells, which are the basic building blocks of all living things.
• Cells vary depending on the type, structure, and function that they perform.
• Three basic parts of the cell :

  1. Cytoplasm
  2. Cell Membrane
  3. Nucleus
• 1. Cytoplasm - a part that holds the organelles in place where most cell activities take place.

  Organelles :

  * Mitochondria

  * Lysosomes

  * Golgi Bodies

  * Endoplasmic reticulum

  * Ribosomes

  * Vacuole
• 2. Cell membrane - surrounds the cytoplasm, and decides what materials should be kept in and out of the cell.
• 3. Nucleus - the brain of the cell, where the chromosomes are located.
• Chromosomes are threadlike materials that hold the organism's genetic material called DNA or deoxyribonucleic acid.
• Other organelles of the cell :

  1. Centriole
  2. Centromere
  3. Cytoskeleton
  4. Ribosome
  5. Nucleolus
• Centriole

  • located in animal cell
  • One pair of celullar organelles near the nucleus
  • Made up of Cylinder of microtubule pairs
  • Helps in the formation of spindle fibers, which are the filaments that form protein structure that separates the chromosomes during cell division.
• Centromere

  • Located in plant, and animal cell
  • Part of the chromosome
  • Specialized DNA sequence of a chromosome that joins the sister chromatids - the two identical copies of chromatids that form the chromosomes
  • For microtubule attachment
  • Responsible for movement of the replicated chromosome into two daughter cells during cell division
• Cytoskeleton

  • Located in all types of cells
  • Network of fine filaments of fibers of protein that are present in the cytoplasm
  • Gives shape to the cell
  • Supports and facilitates movement through it's components - microfilament, intermediate filament, and microtubules.
• Ribosome

  • located in all cells
  • Not a membrane-bound structure
  • In prokaryotes - can be found floating freely in the cytosol; slightly smaller than the eukaryote's ribosomes
  • In eukaryotes - Small bodies that are free or attached to the endoplasmic reticulum
  • Produces or synthesizes protein
• Nucleolus

  • All cells except prokaryotes
  • Inside the cell's nucleus
  • Can be more than one
  • Disappears during cell division
  • Produces and assembles the cell's ribosomes
  • Contains building blocks of mRNA, tRNA, rRNA
  • Transcribes rRNA and combines it with protein
• Prokaryotes - are mostly unicellular organisms, consists of only one cell. Examples are, blue-green algae, and bacteria
• Eukaryotes - which are mostly multicellular organisms, consist of multiple number of cells. examples are plants, animals, and fungi
• cell cycle - is an ordered cycle of cell growth DNA replication, and cell division that leads to the formation of two daughter cells.
• Cytokineses - is the process in cell division that leads to the eventual division of the cytoplasm, resulting into two new cells.
• two important stages in cell cycle

  1. Interphase
  2. Cell division
• Interphase - is the nondividing phase, it serves as the resting stage.
• interphase is divided into four phases : Gap 1, Synthesis, Gap 2, and Gap 0
• Gap 1 - is the primary growth phase of the cell.
• Synthesis - DNA replication occurs
• Gap 2 - the cell continues to carry out it's usual functions, to grow, and to produce new proteins.
• Gap 0 - when cells stop dividing and leave the cycle as early as in G1
• the three cell divisions

  1. Mitosis
  2. Meiosis
  3. Cytokinesis
• cytokinesis is the division of cytoplasm during mitotic or meiotic cell division
• mitosis is the process by which one parent cell divides into two daughter cells that are genetically identical to the original parent cell
• meiosis is the process by which one diploid (2n) parent cell divides twice to form four haploid (n) gamete cells
• Mitosis takes place in somatic of body cells
• Centromere - point that divides the chromosome into two sections
• DNA replication - happens during S phase
• synapsis - pairing of homologous chromosome
• tetrad - 4 sister chromatids of paired homologous chromosome
• crossing over - recombination of alleles in homologous chromosomes
• meiosis is a type of cell division where one parental cell produces four genetically different daughter cells.
• Four stages : Prophase, Metaphase, Anaphase, and Telophase
• cytokinesis - the division of cytoplasm
• most prokaryotes such as bacteria reproduce through binary fission
• the nucleus and the cytoplasm are the major cell parts involved in cell division.
• most eukaryotes, especially humans, began as a fertilized egg called zygote.