ANAPHY Chapter 3

• Ribosomes


  • May be attached to other organelles, such as the endoplasmic reticulum
  • Those that are not attached to any other organelle are called free ribosomes
• Rough endoplasmic reticulum (ER)


  • ER with ribosomes attached to it
  • Large amount of rough ER in a cell indicates that it is synthesizing large amount of protein for export from the cell
• Smooth endoplasmic reticulum (ER)


  • ER without ribosomes
  • A site for lipid synthesis and participates in detoxification of chemicals within cells
• Golgi apparatus


  • Also called the Golgi complex
  • Consists of closely packed stacks of curved, membrane-bound sacs
  • Collects, modifies, packages, and distributes protein and lipid manufactured by the ER
  • Present in large numbers and is most highly developed in cells that secrete protein
• Secretory vesicles


  • Vesicle – small, membrane-bound sac that transports or stores materials within cells
  • Pinch off from the Golgi Apparatus and move to the cell membrane
  • Membrane of a secretory vesicle then fuses with the cell, membrane, and the contents of the vesicles are released to the exterior of the cell
  • In many cells, secretory vesicles accumulate in the cytoplasm and are released to the exterior when the cell receives a signal
  • Secretory vesicles containing hormones remain in the cytoplasm of endocrine cells until signals stimulate their release
• Lysosomes


  • Membrane-bound vesicles formed from the Golgi Apparatus
  • Contain variety of enzymes that function as intracellular digestive systems
  • Enzymes within the lysosomes break down the materials in the endocytotic vesicle
  • Vesicles formed by endocytosis may fuse with lysosomes

  
• Peroxisomes


  • Small, membrane-bound vesicles containing enzymes that break down fatty acids, amino acids, and hydrogen peroxide (H202)
  • Hydrogen peroxide is a by-product of fatty acid and amino acid breakdown and can be toxic to a cell
  • Enzymes in peroxisomes break down hydrogen peroxide to water and O2
• Mitochondria


  • Small organelles with inner and outer membranes separated by a space
  • Outer membranes have a smooth contour, but the inner membranes have numerous folds called cristae, which project into the interior of the mitochondria
  • Material within the inner membrane is the mitochondrial matrix and contains enzymes and mitochondrial DNA (mtDNA)
  • Major sites of adenosine triphosphate (ATP) production within cells
  • Carry out aerobic respiration, require O2 to break down food molecules to produce ATP
  • ATP is the main energy source for most chemical reactions within the cell

  
• Cytoskeleton


  • Acts as the internal framework of the cell
  • Consist of protein structures that support the cell, hold organelles in place, and enable the cell to change shape
  • Protein structures are microtubules, microfilaments, and intermediate filaments
• Microtubules

  • Hollow structures formed from protein subunits
  • Perform variety of roles, includes helping to support the cytoplasm of cells, assisting in cell division, and forming essential components of certain organelles
• Microfilaments


  • Small fibrils formed from protein subunits that structurally support the cytoplasm, determining cell shape
  • Some are involved with cell movement
• Intermediate filaments


  • Fibrils formed from protein subunits that are smaller in diameter than microtubules but larger in diameter than microfilaments
  • Provide mechanical support to the cell
  • Example: Keratin – a protein associated with skin cells
• Centrioles


  • Small, cylindrical organelle composed of microtubules organized into nine triplets
  • Each triplet consists of three parallel microtubules joined together
• Centrosome


  • Specialized area of cytoplasm close to the nucleus where microtubule formation occurs
  • Contain two centrioles
• Cilia

  • Project from the surface of cells
  • Vary in number from none to thousands per cell; capable of moving
  • Cylindrical structures
  • Composed of microtubules, organized in a pattern similar to that of centrioles
  • Numerous on surface cells that line the respiratory tract
  • Transports mucus
• Flagella


  • Have a structure similar to that of cilia but are much longer
  • Only one per cell
  • Sperm cells have one flagellum, which propels the sperm cell
• Microvilli

  • Specialized extension of the cell membrane that are supported by microfilaments
  • Do not actively move
  • Numerous on cells that have them and they increase the surface are of those cells

  
• Cell's characteristics are ultimately determined by the types of protein it produces
• DNA

  • Contains the information that directs protein synthesis
  • Influences the structural an functional characteristics of the entire organism because it directs protein synthesis
  • Molecule consists of nucleotides joined together to form two nucleotide strands
  • Resembles a ladder that is twisted around

  
• Gene

  • Sequence of nucleotides that provides a chemical set of instructions for making a specific protein
  • Nucleotide sequence of a gene determines the amino acid sequence of a specific protein
• Gene expression


  1. Transcription

  2. Translation
• Transcription


  • First step in gene expression
  • Takes place in the nucleus of the cell
  • DNA determines the structure of mRNA through transcription
  • Double strands of a DNA segment separate, and DNA nucleotides of the gene pair with RNA nucleotides that form the mRNA
  • Each nucleotide of DNA contains one of the following organic bases: thymine, adenine, cytosine, or guanine
  • Each nucleotide of mRNA contains uracil, adenine, cytosine, or guanine
  • DNA nucleotides pair only with specific RNA nucleotides
  • After pair up, an enzyme catalyzes reaction that form chemical bonds between the RNA nucleotides to form a long mRNA segment
  • Information in mRNA is carried in groups of three nucleotides called codons

  
• Translation

  • Synthesis of proteins based on the information in mRNA
  • Occurs at ribosomes
  • mRNA molecules produced by transcription pass through the nuclear pores to the ribosomes
  • Ribosomes consist of small and large subunits, which combine with mRNA during translation
  • Process of translation requires two other types of RNA – tRNA and ribosomal RNA (rRNA)
  • Ribosome binds to an mRNA and aligns the mRNA with tRNA molecules so that the anticodons of tRNA can pair with the appropriate codons on the mRNA
  • An enzyme associated with the ribosome causes the formation of a peptide bond between the amino acids bound to the tRNAs
  • Ribosome moves down the mRNA one codon at a time, releasing one of the tRNA and allowing the next tRNA to move into position
  • Translation ends when the ribosome reaches the stop codon on the mRNA
  • Polypeptide chain is released and becomes folded to form the three-dimensional structure of the protein molecule

  
• Cell cycle

  • Includes two major phases: Interphase (non-dividing phase) and Cell division
  • During interphase, DNA (located in chromosomes in the cell's nucleus) is replicated
  • Two strands of DNA separate and each strand serves as a template for the production of a new strand of DNA
  • At the end of interphase, a cell has two complete sets of genetic material
  • DNA is dispersed throughout the nucleus as thin threads called chromatin
  • Cell division is the formation of daughter cells from a single parent cell
  • New cells necessary for growth and tissue repair are formed through mitosis
  • Sex cells formed in meiosis
  • Human body has 46 chromosomes
  • Sex cells have half the number of chromosomes as other cells
  • 46 chromosomes are the diploid number of chromosomes and are organized to form 23 pairs of chromosomes
  • 1 pair is the sex chromosomes (two X chromosomes – female, X chromosome and Y chromosome – male)
  • Remaining 22 pairs are called autosomes

  
• Mitosis

  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase

  
• Differentiation

  • Process by which cells develop with specialized structures and function
  • Some portions of DNA are active and some are inactive
  • Active and inactive section of DNA differ with each cell type

  
• Apoptosis

  • Programmed cell death
  • Cell numbers within various tissues are adjusted and controlled
  • In developing fetus, apoptosis removes extra tissue
  • In some adult tissues, apoptosis eliminates excess cell to maintain constant number of cells within the tissue
• Cellular aspects of aging

  • Cellular clock – after a certain passage of time or certain number of cell divisions, results in the death of a given cell line
  • Death genes – causing cells to deteriorate and die
  • DNA damage – through time, DNA is damaged, resulting in cell degeneration and death
  • Free radicals – atoms or molecules with an unpaired electron
  • Mitochondrial damage – more sensitive to free-radical damage; result in loss of proteins critical to mitochondrial function