Tour of the Eukaryotic Cell

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Tour of the Eukaryotic Cell

• All organisms are made of cells
• The cell, as a microcosm, illustrates the
  following principles

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1. Life at the cellular level arises from
   interactions among cellular components.
2. Ordered cellular processes (e.g., protein
   synthesis, respiration, photosynthesis, cell-cell
   recognition, cellular movement, membrane
   production and secretion) are based upon ordered
   structures.

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1. Cells are excitable, responding to environmental
   stimuli. In addition, cells are open systems that
   exchange materials and energy with their
   environment.
2. Evolutionary adaptations are the basis for the
   correlation between structure and function.

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Cell Size

• Size ranges of cells
• Cell Type
  Diameter
• Arechaea 0.1 - 1.0 µm
• Most bacteria 1.0 -
  10.0 µm
• Most eukaryotic cells 10.0 - 100.0
  µm

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Cell Size
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Range of cell size is limited by metabolic
requirements.

• The lower limits are probably determined by the
  smallest size with enough
• DNA to program metabolism.
• ribosomes, enzymes and cellular components to
  sustain life and reproduce.
• The upper limits of size are imposed by the
  surface area to volume ratio.
• As a cell increases in size, its volume grows
  proportionately more than its surface area.

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SA/Volume

• The surface area of the plasma membrane must be
  large enough for the cell volume, in order to
  provide an adequate exchange surface for oxygen,
  nutrients and wastes.

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Internal membranes compartmentalize the functions
of a eukaryotic cell

• The average eukaryotic cell has a thousand times
  the volume of the average prokaryotic cell, but
  only a hundred times the surface area.
• Eukaryotic cells compensate for the small surface
  area to volume ratio by having internal membranes
  which
• Partition the cell into compartments.
• Have unique lipid and protein compositions
  depending upon their specific functions.
• May participate in metabolic reactions with
  enzymes incorporated
• directly into the membrane.
• Sequester reactions, so they may occur without
  interference from incompatible metabolic
  processes elsewhere in the cell.

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The Nucleus and Ribosomes

• The nucleus contains a eukaryotic cell's genetic
  library
• Enclosed by a nuclear envelope.

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Nuclear envelope

• A double membrane
• Two lipid bilayers separated 20 to 40 nm. Each
  lipid bilayer has unique set of proteins.
• Attached to proteins on the nuclear side (inner
  side) is a network of protein filaments, the
  nuclear lamina, which stabilizes nuclear shape.
• Is perforated by pores
• The envelope's inner and outer membranes are
  fused at the lip of each pore.
• Pore complex regulates molecular traffic into and
  out of the nucleus.

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Nuclear Envelope
www.ncbi.nlm.nih.gov/bookshelf/.
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DNA

• The nucleus contains most of the cell's DNA which
  is organized with proteins into a complex called
  chromatin.
• Chromatin Complex of DNA and proteins, which
  makes up chromosomes
• Chromosomes Long threadlike association of genes

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Nucleolus

• The most visible structure within the nondividing
  nucleus
• Roughly spherical region which consists
• of nucleolar organizers ( genes for ribosomal
  RNA synthesis) (thus the nucleolus contains DNA)
• ribosomes in various stages of production
• Packages of ribosomal subunits
• Ribosomal subunits pass through nuclear pores to
  the cytoplasm,where their assembly is completed.

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Ribosomes

• Is the site for protein synthesis in the
  cytoplasm.
• Are complexes of RNA (ribo nucleic acid) and
  protein
• Constructed in the nucleolus

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RNA and Protein
www.pbs.org/wgbh/nova/photo51/pict-06.html
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Free and Bound Ribosomes

• Bound and free ribosomes are structurally
  identical and interchangeable.
• Free ribosomes are suspended in the cytosol
• Most proteins made by free ribosomes will
  function in the cytosol.
• Bound ribosomes are attached to the outside of
  the endoplasmic reticulum.
• Generally make proteins that are destined for
  membrane inclusion

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Task 1

• Draw a model of a nucleus. Include the following
  details
• Lipid bilayers
• inner and outer layer and inter-membrane space
• Nuclear pores
• Nuclear lamina
• Chromatin
• Nucleolus
• Nucleoplasm
• Smooth and rough ER

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Task 2Arrange the following from largest to
smallestPlace them on scale from .1 ?m to 200
µm

• Virus
• Atom
• Eubacteria
• Electron
• Neutron
• Archaean cell
• Proton
• Animal cell
• Small molecule
• Plant cell
• Lipid
• Protein
• Use the diagram given last week and your notes