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Chapter 2: Cells and Cell Division. By the completion of this chapter, you should have an understanding of: The structure and organization of cells in higher organisms Chromosomes as cellular structures that carry genetic information The parts of the cell cycle The stages of mitosis

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Chapter 2: Cells and Cell Division

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chapter 2 cells and cell division

Chapter 2: Cells and Cell Division

By the completion of this chapter, you should have an understanding of:

The structure and organization of cells in higher organisms

Chromosomes as cellular structures that carry genetic information

The parts of the cell cycle

The stages of mitosis

The significance of mitosis and the genetic control of the cell cycle

The process of meiosis and it’s involvement in the formation of gametes

2 1 cell structure reflects function
2.1 Cell Structure Reflects Function
  • Cells vary widely in size, shape, function, and life cycle
  • All ours have a plasma membrane, cytoplasm, membrane-bound organelles, and a membrane-bound nucleus
  • Many genetic disorders alter cellular structure or function
plasma membrane
Plasma Membrane
  • Double-layered plasma membrane separates the cell from external environment
  • Controls what enters and exits the cell
  • Small molecules, gases, and water can pass easily through; larger molecules require energy
  • Molecules on the surface of the P.M. give the cell identity
  • Jelly-like mixture that contains specialized structures called organelles
  • In eukaryotes (contain a nucleus), organelles divide the cell into function compartments
endoplasmic reticulum
Endoplasmic Reticulum
  • Network of membranes that form channels in the cytoplasm
  • The space inside the ER is called the lumen – proteins are folded, modified, and readied for transport to other location.. Or are tagged for export from the cell
endoplasmic reticulum cont
Endoplasmic Reticulum, cont’
  • The outside of the ER is often covered with RIBOSOMES
    • Ribosomes are the most numerous cellular structures and can also be found in the cytoplasm
    • Ribosomes are the site of protein synthesis
golgi apparatus golgi body
Golgi Apparatus (Golgi Body)
  • Flattened membrane sacs
  • Receives proteins from the ER and distributes them to their destinations inside and outside cell
  • Sorts, modifies, and packages proteins
  • Membrane-enclosed vesicles that contain digestive enzymes
  • Enzymes are made in the ER, transported to Golgi, packaged into vesicles that bud off the Golgi and become lysosomes
  • Proteins, fats, carbs, and viruses that are brought into the cell are broken down and recycled, or exported for disposal in lysosomes
  • Energy transformation (food  energy)
  • Carries own genetic information in form of a circular DNA molecule
  • Largest organelle
  • Enclosed by a double membrane called nuclear envelope with pores that allow direct communication between nucleus and cytoplasm
  • Inside: Nucleolus (Nucleoli plural) makes ribosomes, and Chromatin (dark strands of DNA) eventually condense to form chromosomes
chromosome review
Chromosome Review
  • DNA + Proteins = Chromosomes
  • In humans, chromosomes exist in pairs
  • Body cells (somatic) carry 23 pairs, or 46 total chromosomes
  • Egg and sperm (gametes) carry only 23 UNPAIRED chromosomes
  • Sex chromosomes – X and Y – males have one of each; females have 2 X’s
  • All other 22 pairs of chromosomes are called AUTOSOMES
2 2 the cell cycle
2.2 The Cell Cycle
  • Two stages – Division and Non-division
  • Cell Cycle: the sequence of events from division to division
    • 3 parts= Interphase, Mitosis, Cytokinesis
    • Interphase = time between division
    • Mitosis = division of chromosomes
    • Cytokinesis = division of cytoplasm
  • 3 stages:
    • G1 (Gap 1) = cytoplasmic components are constructed; cell size doubles
    • S (Synthesis) = each chromatid is copied; chromosomes become double stranded
    • G2 (Gap 2) = a smaller period of cell growth
  • Division and distribution of chromosomes
  • End result = 2 identical daughter cells with 46 chromosomes each
  • 4 phases: Prophase, Metaphase, Anaphase, Telophase
  • Chromatin coils to become shorter, thicker chromosomes
  • At the end of prophase, chromosomes appear to be 2 strands of identical chromatids
  • Chromatids are held together by centromere
  • Two chromatids held together by a centromere are called SISTER CHROMATIDS
  • Near the end of Pro., nuclear membrane breaks down and spindle fibers form
  • Chromosomes are free in cytoplasm
  • Spindle fibers attach to centromeres and pull chromosomes to equator of cell
  • Centromeres divide
  • Sister chromatids become singular chromosomes
  • Chromosomes move to opposite ends of the cell
telophase and cytokinesis
Telophase and Cytokinesis
  • Chromosomes uncoil, spindle fibers break down, nuclear membrane reforms
  • Cleavage furrow down equator of cell causes constriction and eventually the cell divides in two (Cytokinesis)
2 3 mitosis is essential for growth and cell replacement
2.3 Mitosis is Essential for Growth and Cell Replacement
  • Bone Marrow – continuously producing 2 million red blood cells each second
  • Skin Cells – divide to replace dead cells
  • Many muscle cells – enter a state of G0 and do not divide (spinal cord cells do same)
  • Occasionally cells escape control of cell cycle = CANCER



Spindle Fiber


Nuclear Membrane




Cell Membrane








2 4 cell division by meiosis
2.4 Cell Division by Meiosis
  • Cells with 2 copies of each chromosome are called DIPLOID (2n) = body cells
    • 2n = 46 in humans
  • In meiosis, pairs of chromosomes separate so each cell receives only 1 of each chromosome
    • This is called HAPLOID (n)
    • In humans, egg and sperm are haploid
    • n= 23
  • n (sperm) + n (egg) = 2n (baby)
meiosis 1
Meiosis 1
  • Meiosis 1: Chromosome # Reduced
    • Interphase = same as interphase in mitosis
    • Prophase 1 = chromosomes find their matches (homologous chromosomes) and form a tetrad
    • Metaphase 1 = hom. chrom. line up together in middle of cell
    • Anaphase 1 = hom. chrom. separate
    • Telophase 1 = cell divides into 2 containing 1 of each chromosome
meiosis 2
Meiosis 2
  • Prophase 2 = spindle forms
  • Metaphase 2 = sister chromatids line up on equator attached @ centromere
  • Anaphase 2 = sister chromatids separate at centromere and move to opposite ends of cell
  • Telophase 2 = chromosomes uncoil, nuclear membrane reforms, cells divide into 4 cells total with half the number of original chromosomes
summary of meiosis
Summary of Meiosis

Comparing Mitosis and Meiosis

meiosis produces variation
Meiosis Produces Variation
  • Random Assortment of Chromosomes:
    • eggs/sperm can get combination of maternal and paternal chromosomes
  • Crossing Over:
    • genes on maternal chromosome can switch with genes on paternal chromosome during Prophase 1.