WHAT IS A CELL

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WHAT IS A CELL?

• Lecture 2
• June 27th, 2008

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I. What is a cell?

• Eukaryotic cell Prokaryotic cell

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The Domains of Life

• Bacteria
• Archaea
• Eukarya

prokaryotic
prokaryotic
eukaryotic
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All cells have in common.

• Plasma membrane
• Semifluid cytosol (cytoplasm)
• Chromosomes
• Ribosomes

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Prokaryotic cell

• Single-celled organisms
• No membrane-bound organelles
• DNA is condensed into nucleoid, and is circular
• 1-10 um in diameter

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Eukaryotic cell (animal)

• Single-celled or multicellular organisms
• Nucleus fully bounded by membrane called a
  nuclear envelope
• Membrane-bound specialized organelles
• 10-100um in diameter

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ENDOPLASMIC RETICULUM
NUCLEUS
RIBOSOMES
GOLGI APPARATUS
PLASMA MEMBRANE
MITOCHONDRION
LYSOSOME
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Eukaryotic cell (plant)

• Thick cell wall outside plasma membrane,
  perforated by channels called plasmodesmata
• Plastids (chloroplasts)
• Central vacuole

No lysosomes
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II. Organelles Activity

• You will be assigned a group (of 2 or 3) and
  given an organelle
• Read the workbook section about that organelle
• Designate one scribe and one speaker
• Each speaker needs to give an overview of what
  the organelle does ( 5 minutes)

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Activiy Groups

• Nucleus Brenda, Yariza, Jasmin
• Ribosomes Juana, Erica
• ER Joanna, Justine, Sabrina
• Golgi apparatus Jamese, Lily, Blanca
• Lysosomes Sonia, Juan, Abel
• Vacuoles Tim, Valerie
• Mitochondria Sulamita, Johnny, Adam
• Chloroplasts Elaine, Emily

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Activity Guidelines

• What is the shape of the organelle? Describe its
  overall structure.
• What does the organelle do? How many functions
  does it have, and are these functions unique to
  this organelle?
• What kinds of cells have need for this particular
  organelle? Why?

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II. Organelles Nucleus

• Typically the largest organelle
• Contains most of the genes
• Directs protein synthesis

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II. Organelles Ribosomes

• Carries out protein synthesis
• Composed of two parts (subunits)
• Free ribosomes make proteins for cell bound
  ribosomes make secretory proteins

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II. Organelles Endoplasmic reticulum
Smooth ER

• Enzymes help in
• the synthesis of lipids and steroids
• metabolism of carbohydrates
• the detoxification of drugs

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II. Organelles Endoplasmic reticulum
Rough ER

• Site of protein synthesis
• Membrane factory

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II. Organelles Golgi apparatus

• Modifies ER products
• Manufactures its own macromolecules
• Sorts and ships products

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II. Organelles Lysosomes

• Membrane bound
• Contain hydrolytic enzymes
• Digests food particles and its own organic
  material

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II. Organelles Vacuoles

• Mature plant cells usually have a large central
  vacuole enclosed by tonoplast
• Storage site for ions, by-products of metabolism,
  pigments, poisons

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Endomembrane system
Plasma membrane Nuclear envelope Endoplasmic
reticulum Golgi apparatus Lysosomes Vacuoles
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II. Organelles Mitochondria

• Site for cellular respiration (generates ATP)
• Contains its own DNA

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II. Organelles Chloroplast

• Contains green pigment chlorophyll
• Converts energy of sunlight into chemical energy
  stored in sugar molecules
• Contains its own DNA

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Discussion Question

• Why dont plant cells have lysosomes?

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Discussion Question

• Single-celled eukaryotic organisms evolved from
  prokaryotic organisms. How do you think this
  might have happened?

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III. Inside the cell the cytoskeleton

• Provides support for the organelles
• Enables the cell to move
• Made up of microtubules, microfilaments, and
  intermediate filaments

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III. Outside the cell
intercellular junctions
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III. Outside the cell
intercellular junctions

• Tight Junctions Make seals between adjacent
  cells
• Desmosomes Anchoring connections that rivet
  cells together in strong sheets
• Gap Junctions Communicating junctions that
  provide channels between cells for molecules to
  pass
• Plasmodesmata Like gap junctions, but in plants

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IV. Cell diversity
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IV. Cell diversity
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IV. Cell diversity

• Human pancreas has a high rate of protein
  synthesis
• Ovaries and testes produce steroids
• Secretory cells

? ribosomes
? smooth er
? Golgi apparatus