Cells

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Cells

• Chapter 3

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• I. Overview
• Cell Membrane
• Cytoplasm
• Cytosol
• Organelles
• Nonmembranous Cytoskeleton, Microvilli,
  Centrioles, Cilia, Flagella, Ribosomes
• Membranous Mitochondria, Nucleus, Endoplasmic
  Reticulum, Golgi Apparatus, Lysosomes,
  Peroxisomes, Vesicles

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• II. Plasma Membrane (Cell Membrane)
• "Fluid Mosaic Model" - plasma membrane is
  composed of a double layer (bilayer) of    
  phospholipid molecules with proteins that
  float/move among the phospholipids, yet the    
  plasma membrane is stable.
• Proteins function....
• As cell markers for recognition by immune system
• As receptors (e.g for hormones)
• As catalysts
• Transportation

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• Proteins in the membrane...
• integral proteins (maintain selective transport)
• peripheral proteins (catalyst and mechanical
  function)
• The plasma membrane also contains a myriad of
  biological compounds such as glycoproteins,
  glycolipids, and proteoglycans (all referred to
  as glycocalyx) that extend outward from the
  plasma membrane

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• III. Cytoplasm
• Cytoplasm is the material found inside the cell
  and is divided into two subdivisions cytosol
      and organelles.
• Cytosol (intracellular fluid) contains dissolved
  nutrients, ions, soluble and insoluble    
  proteins, and waste products.
• Organelles are structures that perform specific
  functions within the cell and are classified as
      membranous and non-membranous.

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Mitochondria  Rod-like, double membrane, inner membrane folded into projections called cristae Site of ATP synthesis.
Ribosomes  Dense particles consisting of two subunits, each composed of ribosomal RNA and proteins can be free or it can be attached to ER site of protein synthesis
E. R. (rough)  Coiling membrane system with ribosomes attached proteins synthesized are packaged into vesicles for transport to the golgi apparatus
E. R. (smooth)  Coiling membrane system lacking ribosomes synthesizes lipids and carbohydrates
Golgi apparatus  Stack of smooth membrane sacs adjacent to the nucleus modifies synthesized proteins, then packages the proteins (e.g. lysosomes peroxisomes) in vesicles for transport around/out of cell
Lysosomes Membranous sacs containing hydrolytic enzymes used in cell digestion
Peroxisomes  Membranous sacs containing oxidative enzymes (e.g. peroxidase) that degrade toxic compounds such as hydrogen  peroxide
Vesicles  Membrane bound sac that transports cellular material
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Microfilaments Filaments containing the contractile protein actin part of the cytoskeleton and functions in intracellular movement
Intermediate filaments Protein fibers that provides strength, stabilize the position of organelles, and transport materials within the cytoplasm
Microtubules  Hollow tubes composed of the globular protein tubulin microtubules provide strength and rigidity and anchoring major organelles
Thick filaments    Large and long strands of myosin protein found in muscle cells that interact with thin actin filaments to produce muscle contraction
Centrioles   Cylindrical structure composed of nine triplets of microtubules centrioles direct the movement of DNA during cell division as well as form the bases of cilia and flagella
Microvilli   Small, finger-shaped projections of the cell membrane that actively absorb fluid and nutrients
Cilia Cell surface projections composed of microtubules cilia move to propel substance across the cell surface
Flagella  Larger and longer cilia that provides cellular locomotion (e.g. human sperm)
Nucleus  Structure housing genetic information and is surrounded by a membrane (nuclear envelope)
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Endoplasmic Reticulum
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• IV. Membrane Transport Processes
• Transportation of materials across the cell
  membrane is determined by the components in the
  membrane that impart permeability.
• Most cells have selective permeability, free
  passage of some materials and restricts the
  passage of others.
• Permeability may be based on size, electrical
  charge, molecular shape, solubility, etc...
  Passage across the membrane is classified as
  active (requiring energy) and passive (not
  requiring energy)

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• Membrane transport processes
• Passive
• Diffusion - net movement of particles from an
  area of higher concentration to an area of lower
  concentration.
• Osmosis - diffusion of water through a
  selectively permeable membrane
• Facilitated diffusion - diffusion of a substance
  with the aid of a membrane carrier.
• Filtration - movement of water and solutes
  through a semipermeable membrane from a region of
  higher hydrostatic pressure to a region of lower
  hydrostatic pressure

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• b) Osmosis movement of a solvent (water)
  through a semi- permeable membrane down a
  concentration gradient (higher to lower)
• Solutions
• Isotonic
• Hypertonic
• Hypotonic

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• A human red blood cell is composed of 0.9 salt
  and 99.1 water. If this cell is placed in a
  solution of 0.9 salt and 99.1 water (saline)
  the solution is isotonic and the blood cell will
  remain unchanged

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Isotonic
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• The same RBC is placed in a beaker of distilled
  water (100 H2O and 0 salt), water will enter
  the cell and cause it to burst (lysis). Water
  goes from higher conc. to lower conc. This
  solution is hypotonic (hypoless salt in
  solution).

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Hypotonic
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• The same RBC is placed in a beaker of 50 salt
  water (50 H2O and 50 salt), water will leave
  the cell and cause it to shrink (crenation).
  Water goes from higher conc. to lower conc. This
  solution is hypertonic (hypermore salt in
  solution).

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Hypertonic
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• Active
• Active transport - movement of a substance (with
  the aid of a membrane carrier) through a membrane
  against its concentration gradient.
• Exocytosis - substances enclosed in a vesicle
  fuses with the plasma membrane, the vesicle then
  ruptures, releasing the substances outside the
  cell.
• Endocytosis (types)
• Phagocytosis - the cell membrane extends outward
  and encloses large particles which are then
  transported into the cell.
• Pinocytosis - particles attach to the cell
  membranes which collapses, causing particles to
  be taken into the cell.
• Receptor-mediated - pinocytotic movement
  initiated by protein receptors on the plasma
  membrane.

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• Movement of particle may be....
• Symport - movement of two or more different kinds
  of material in the same direction across the cell
  membrane.
• Uniport - movement of one type of material in one
  direction across the cell membrane.
• Antiport - moving two types of material across
  the cell membrane in opposite directions.

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• V. Cell Division (Cell Life Cycle)
• Multicellular organisms develop from a zygote,
  which is formed by the fusion of a sperm and an
  egg (gametes). Each gamete has half the
  compliment of chromosomes (haploid number) and
  when combined gives rise to a zygote with a
  complete set (diploid number) of chromosomes. In
  order for the zygote to develop into a
  multicellular organism, it must repeatedly
  undergo cellular divisions. The series of events
  a cell (or zygote) undergoes that ultimately
  produces a new cell is called the cell cycle.

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• Nucleus
• - located in the center of the cell
• - controls all functions of organelles
• - cell reproduction/division takes place
• - DNA (Deoxyribonucleic Acid) is housed
• - blueprint of heredity
• - as cell divides the DNA coil tightly, called
  chromatin, to form chromosomes (46)
• - bound by nuclear envelope double layered
  membrane enclosing nucleoplasm
• Nucleoli are darkly stained areas within the
  nucleus that indicate rapid RNA synthesis.

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• Cell Growth and reproduction produces two
  identical daughter cells from one parent cell
• - cell life cycle has two major sections
• Interphase (cell growth not dividing)
• G1 phase growth
• S phase growth and DNA synthesis
• G2 phase growth and final preparation for
  cell division

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• Mitotic phase (M) dividing phase
• Prophase
• Metaphase
• Anaphase
• Telophase
• IPMAT

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• Interphase G1 , S and G2 phases. (90 of
  its time)
• G1 (gap 1) cell grows vigorously and
  metabolically very active.
• - depending on cell type, this phase may
  last minutes to years.
• - centrioles begin replicating
• S DNA replicates itself chromatin condenses.
  Ensures daughter cells receive identical genetic
  information.

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DNA replication (S phase)
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• G2 phase is very brief.
• - centriole replication is complete
• - ready to divide

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• Mitotic phase (M)
• Prophase Chromosomes are visible.
• - early prophase longest phase of mitosis.
• - chromatin condenses to form chromosomes.
• - centriole pairs start to separate/nuclear
  membrane breaks down.
• - mitotic spindles (microtubules) start to
  develop

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• late prophase
• - centrioles migrate away from each to opposite
  poles of cell.

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• Metaphase (meta middle)
• - chromosomes cluster toward the center of
  cell.
• - centromeres align along the equator of the
  spindle
• - enzyme separase will separate the chromatid.

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• Anaphase (apart) shortest phase.
• - centromeres of the chromosomes split
• - each chromatid becomes its own chromosome
• - Each chromosome is pulled to opposite pole

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• Telophase begins when chromosomal movement
  stops.
• - chromosomes uncoil goes back to fine threads
  of chromatin.
• - new nuclear envelope forms
• - cytoplasm pinches inward forming a cleavage
  furrow (cytokinesis)

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• Somatic (body) cells contain a diploid number of
  chromosomes.
• Human cells contain two sets of chromosomes (one
  member from each pair is inherited from each
  parent) homologous chromosomes
• 2n (n of different chromosomes). n23 in
  humans
• 2(23) 46
• 22 pairs are called autosomes while the last pair
  determines the sex of the individual sex
  chromosomes (X and Y)
• Mapping of chromosomes is called a karyotype

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• What can cause abnormal cell division?
• - radiation UV light, x-ray
• - viruses
• - organic chemicals pesticide, nicotine
• Teratogens substances that can cause severe
  congenital abnormalities.
• Carcinogens chemical or environmental agent that
  produces cancer

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• Cancer
•   - The p53 gene prevents these mutations from
  causing problems.
• - p53 is present in all DNA
• - p53 is responsible for cell division to stop
  so that mutated DNA can be repaired.
• - If DNA cannot be repaired the cell undergoes
  apoptosis in which the cell is programmed to
  die.
• - Defective or missing p53 can result in the
  cell mutating uncontrollably causing a tumor.
• - Normal cells will divide on average about 50
  times then the cell dies. While tumors divide
  without stopping.

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• Benign tumors are cell masses that do not
  fragment or spread beyond its original area of
  growth.
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• Malignant tumors are cell masses that break
  apart and spread or invade other parts of the
  body.  This movement is metastasis.            
                                           
• Cancer is the term used to refer to any tumor
  that has the potential to become malignant.

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• VI. Protein Synthesis
• Ribonucleic acid (RNA) links DNA's genetic
  instructions for making proteins to the process
  of protein synthesis
• It copies or transcribes the message from DNA and
  then translates that message into a protein.
• RNA, like DNA, is a nucleic acid or polymer of
  nucleotides
• RNA structure differs from DNA in the following
  ways
• The five carbon sugar in RNA nucleotides is
  ribose rather than deoxyribose
• The nitrogenous base uracil is found in place of
  thymine

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PROTEIN SYNTHESIS
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• The linear sequence of nucleotides in DNA
  ultimately determines the linear sequence of
  amino acids in a protein.
• Nucleic acids are made of four types of
  nucleotides which differ in their nitrogenous
  bases
• Hundreds or thousands of nucleotides long, each
  gene has a specific linear sequence of the four
  possible bases.
• Proteins are made of twenty types of amino acids
  linked in a particular linear sequence (the
  protein's primary structure).
• Information flows from gene to protein through
  two major processes, transcription and
  translation.

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• Transcription - the synthesis of RNA using DNA as
  a template
• A gene's unique nucleotide sequence is
  transcribed from DNA to a complimentary
  nucleotide sequence in messenger RNA (mRNA).
• The resulting mRNA caries this transcript of
  protein-building instructions to the cell's
  protein-synthesizing machinery.

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• Translation - synthesis of a polypeptide, which
  occurs under the direction of messenger RNA
  (mRNA)
• During this process, the linear sequence of bases
  in mRNA is translated into the linear sequence of
  amino acids in a polypeptide.
• Translation occurs on ribosomes, complex
  particles composed of ribosomal RNA (rRNA) and
  protein that facilitate the orderly linking of
  amino acids into polypeptide chains.
• Signals are contained in the RNA to start and
  stop translation.

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SUMMARY OF PROTEIN SYNTHESIS
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GENETIC CODE
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Translation