Cell Structure

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Cell Structure
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Cytoplasm

• All of the cellular contents between the plasma
  membrane and the nucleus

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Cytosol

• Fluid portion of the cytoplasm
• 55 of the cells volume
• 75-90 water
• Contains dissolved/suspended solutes
• Ions, glucose, ATP, lipids, proteins, amino
  acids, waste
• Site of most of the chemical reactions in the cell

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Organelles

• Specialized structures inside cells that have
  characteristic shapes and specific functions

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Cytoskeleton

• Network of protein filaments
• Microfilaments, intermediate filaments,
  microtubules

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Microfilaments

• Thinnest
• On the periphery of the cell
• Contribute to shape and strength
• Help generate movement
• Support microvilli

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Intermediate Filaments

• Thicker than microfilaments, thinner than
  microtubules
• Found in cells subject to tension
• Help to hold organelles in place

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Microtubules

• Largest
• Help determine shape
• Function in movement of organelles
• Function in movement of cilia and flagella

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Centrosome

• Near the nucleus
• Pair of centrioles
• Cylindrical structures composed of clusters of
  microtubules arranged in a circular pattern
• Pericentriolar Material
• Tubulins organizing center for the growth of
  mitotic spindles

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Cilia and Flagella

• Motile projections on the cell surface
• Cilia numerous short hair-like projections on
  the cell surface.
• Propel fluids across the surface of the cell
• Flagella longer than cilia, propel the entire
  cell.
• Only example in the human is sperm cell

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Ribosomes

• Site of protein synthesis
• High content of RNA
• 2 sub-units
• Large and small
• Made in the nucleolus and assembled in the
  cytosol
• Attached to ER or free in cytosol

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Endoplasmic Reticulum

• Network of folded membranes that extends through
  the cytoplasm
• Rough ER extends from nuclear envelope has
  ribosomes attached processes and sorts proteins
  that will be incorporated into the membranes
• Smooth ER extends from rough ER no ribosomes
  attached fatty acids and steroids are
  synthesized.

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Golgi Complex (Body Apparatus)

• Packages and transports materials
• Cisterns flattened membranous sacs with bulging
  edges that make up the Golgi Body

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Transport of Proteins by the Golgi Body

• Protein is surrounded by ER membrane and buds of
  to form a transport vesicle
• Transport vesicle moves toward Golgi Body
• Vesicle fuses with Golgi Body and proteins enter
• Proteins move from one cistern to another by
  transfer vesicles
• In last cistern proteins are sorted and packaged
• Proteins leave Golgi Body in secretory vesicles,
  other membrane vesicles or transport vesicles

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Lysosomes

• Membrane enclosed vesicles that contain digestive
  enzymes
• Help to recycle cellular components
• Autophagy worn out organelles are digested
• Autolysis enzymes destroy its own cell

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Tay-Sachs Disease

• An inherited condition in which one lysosomal
  enzyme is absent.
• Normally breaks down a membrane glycolipid found
  in nerve cells. It is not broken down, it
  accumulates which makes the nerve cell function
  less efficiently
• Seizure, muscle rigidity, blindness, dementia,
  uncooridated. Usually die before age 5

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Peroxisomes

• Similar to lysosomes but smaller
• Contain oxides
• Enzymes that can oxidize various organic
  substances
• Abundant in liver where there are a lot of toxic
  substances
• Contain catalase

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Proteasomes

• Contain enzyme called protease
• Continuously destroys unneeded, damaged or faulty
  proteins
• Recycles amino acids

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Mitochondria

• Site of cellular respiration (makes ATP)
• Active cells have a larger number
• Double Membrane
• Outer smooth
• Inner folded
• Cristae folds
• Enzymes that catalyze a series of reactions are
  found in the matrix

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Check Point Questions

• What is the difference between cytoplasm and
  cytosol?
• What is an organelle?
• Describe the structure of a ribosome, the Golgi
  Body and a mitochondrion.