Cell Structure and Function

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Cell Structure and Function
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Cell Theory

• Developed from a series of observations made by
  Matthais Schleiden, Robert Brown, Theodor Schwann
  in the 1800s
• All organisms are composed of cells
• Cells are basic structural units
• Cells come from other cells

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Why are cells so small?
4 cm
1 cm
Surface-to-volume ratio about 1.51
Surface-to-volume ratio about 61
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Major Types of Cells

• Prokaryotes
• Do not have membrane-bound organelles
• Smaller than eukaryotes
• Cell envelope consisting of three parts
• Smaller quantity of DNA (Chromosome) loosely
  organized (no nucleus)
• Accessory DNA in the form of plastids

• Eukaryotes
• Have many different membrane-bound organelles
• Larger than prokaryotes
• Cell membrane
• Large quantity of DNA housed in a nucleus

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A Typical Prokaryotic Cell or a jelly bean?
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Prokaryotic Cell Structure

• Cell envelop
• Plasma membrane
• Cell wall
• Glycocalyx (Capsule or Slime coating)

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Prokaryotic Cell Structure

• Other Features
• Nucleoid and plasmid
• Ribosomes
• Inclusion bodies

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Eukaryotic Cell Structure

• Complex tasks are performed by organelles
• Cellular specialization dictated by types of
  organelles and other cell structures

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Origins of Organelles

• Organelles are thought to have resulted from
  symbiotic relationships
• Mitochondria and chloroplasts support this
  hypothesis
• Similarity of size between bacteria,
  mitochondria, chlropolasts
• They have circular DNA
• Divide by binary fission like bacteria

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Animal Cells
Often depicted as spherical, but they may exist
in other forms
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Epithelial cells for example, have three
different shapes
Flattened (Squamous) epithelium
Cuboidal epithelium
Columnar epithelium
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Light vs. Electron Microscopy
Nuclei only
Many other organelles visible
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Animal Cell Organelles

• Nucleus
• Smooth and rough endoplasmic reticulum
• Golgi apparatus
• Vesicle
• Mitochondria
• Lysosome
• Peroxisome
• Centriole

Generalized animal cell
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Nucleus

• Houses DNA
• DNA molecules essentially represent blue prints
  for various purposes
• DNA is transcribed into RNA and RNA leaves
  nucleus through nuclear pores
• RNA is translated by ribosomes which manufacture
  proteins

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Mitochondria

• Typically kidney bean-shaped
• Cell membrane (cristae) folded inward producing
  high surface area
• Cellular respiration
• Energy production

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ER and Golgi
Vesicles merging with cell membrane Exocytosis

• DNA transcribed (transcription) by ribosomes into
  RNA
• RNA translated (translation) into proteins
• Proteins manufactured by rER are packaged into
  vesicles
• Proteins could be enzymes, hormones,
  neurotransmitters, etc
• Vesicles transport proteins elsewhere

Smooth ER
Ribosomes
Rough ER
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Transcription, and Translation
Protein is folded into a specific shape inside
the endoplasmic reticulum Proteins usually have
an complex or intricate structure
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Lysosomes and Peroxisomes

• Spherical organelles
• Lysosomes digest internalizes substances,
  cellular organelles or other structures

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Cilia and Flagella

• Cilia and flagella operate via microtubules
• Microtubules are composed of proteins arranged in
  a helix
• ATP causes dynein proteins to flex microtubules

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Plant Cells

• Vacuoles represent storage compartments of plant
  cells

Vacuole
Chloroplast

• Chloroplasts trap light energy during
  photosynthesis
• Cell wall made of a rigid polysaccharide called
  cellulose

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Leaf cross section
Should see nucleus and chloroplasts
Vascular bundle
Epidermis
Palisade mesophyll
Spongy mesophyll
Stomata with guard cells