Chapter 7: A View of the Cell

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Chapter 7 A View of the Cell

• 7.1. The Discovery of Cells

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The Cell Theory (History)

• The microscope was invented by Anton van
  Leeuwenhoek.
• The first person to see a cell (in cork) was
  Robert Hooke.
• Matthias Schleiden concluded that all plants have
  cells
• Theodore Schwann observed that animals were also
  composed of cells

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The Cell Theory

• 3 main ideas
• All living things are composed of one or more
  cells
• The Cell is the basic unit of organization of
  organisms
• All cells come from cells

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The Light Microscope

• Uses light and lenses
• The Simple light Microscope used one lens and
  natural light (Leeuwenhoek)
• The Compound light microscope Uses multiple
  lenses
• Magnifies up to 1500 times

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The Electron Microscope

• Invented in the 1940s
• Uses a beam of electrons
• Magnifies up to 500,000 times
• Two Kinds
• Scanning electron microscope (SEM) Scans the
  surface of cells.
• Transmission electron microscope (TEM) Allows
  for study of structures inside cells.

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The Electron Microscope
SEM
TEM
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Two Basic Cell Types

• Prokaryotes Cells lacking internal
  membrane-bound structures
• Eukaryotes Cells containing internal
  membrane-bound structures
• The membrane-bound structures are called
  organelles
• Contains a nucleus organelle that manages
  cellular function. First observed by Robert
  Brown. Rudolf Virchow concluded that it was
  responsible for cell division.

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Chapter 7 A View of the Cell

• 7.2 The Plasma Membrane

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Maintaining a Balance

• The Plasma membrane is the boundary between the
  cell and its environment
• Needs to let the good stuff (e.g. nutrients) in
  and the bad stuff (waste) out
• The plasma membrane maintains homeostasis.

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Plasma Membrane
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The Plasma Membrane

• Maintains Homeostasis regulates internal
  environment Good in (but not too much), Bad Out
• Selective permeability Allows some molecules
  into the cell and keeps some out.
• Some molecules can cross the plasma membrane
  (i.e. water). Others must go through channels
  (i.e. Na, Ca, etc)

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Structure of the Plasma Membrane

• Composed of a phospholipid bilayer.
• A Lipid with a phosphate group attached
• Has only 2 fatty acid tails
• Forms a sandwich
• The phosphate group forms the polar head
• The fatty acid tails form the nonpolar tail

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Fluid Mosaic Model

• The membrane is fluid It is flexible and
  phospholipids can move in the membrane like water
  in a lake.
• The membrane is mosaic There are proteins
  embedded in the membrane that also move (like
  boats in the lake)

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Other components

• Cholesterol Helps stabilize the plasma membrane,
  and prevents the phospholipids from sticking
  together.
• Transport Proteins Proteins that span the entire
  membrane and form channels for specific molecules
  to enter and leave (like a door).
• Other Proteins and carbohydrates on the external
  surface Helps with identification.
• Proteins on internal surface Provides
  flexibility by attaching the plasma membrane to
  the cells internal structure.

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Chapter 7 A View of The Cell

• 7.3 Eukaryotic Cell Structure

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Cellular Boundaries

• Plasma membrane surrounds the cell
• In plants, fungi, most bacteria and some
  protists, the cell wall surrounds the plasma
  membrane
• Fairly rigid
• Provides support and protection
• Made up of the carbohydrate cellulose
• Has pores to allow molecules through

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Nucleus and cell control

• The Nucleus is the leader of the cells
• Gives directions for the making of proteins
• The master set of directions is in chromatin
• During cell division, chromatin condenses to form
  chromosomes.

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Nucleus and Cell Control

• Inside the nucleus there is also the nucleolus
• Makes ribosomes
• Ribosomes are sites where proteins and other
  enzymes are made, according to instructions from
  DNA
• Ribosomes leave the nucleus, into the cytoplasm
  in order to make proteins
• Cytoplasm The fluid inside the cell

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Nucleus and cell control

• The Nuclear envelope is a double membrane that
  surrounds the nucleus.
• Made up of 2 phospholipid bilayers
• Contains small nuclear pores

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Assembly and Transport

• The endoplasmic reticulum A series of highly
  folded membranes
• Where cellular chemical reactions take place
• Like a large workspace
• Some parts have ribosomes attached (rough
  endoplasmic reticulum - RER)
• Others dont (smooth endoplasmic reticulum SER)

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Assembly and Transport

• RER Proteins made in the RER may
• form part of the plasma membrane
• be released from the cell
• transported to other organelles
• SER involved in production and storage of lipids.

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Assembly and Transport

• The Golgi apparatus flattened system of tubular
  membranes and vessicles
• Modifies proteins
• Sorts and packages proteins
• Its kind of like the post office Sorts the mail
  and sends it to the right place

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Assembly and Transport

• RER

Golgi apparartus
vessicles
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Vacuoles

• A vacuole is a sac surrounded by membrane
• Used for temporary storage of
• Food
• Enzymes
• Waste
• Plant cells usually have one large vacuole,
  animal cells have many smaller ones

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Lysosomes and recycling

• Lysosomes are organelles that contain digestive
  enzymes
• They digest food particles, organelles and
  engulfed viruses or bacteria
• Can fuse with vacuoles and digest the contents.
• Can also digest cells that contain them.
• i.e. tadpoles tail

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Energy Transformers

• For all the cellular processes to happen, energy
  is needed
• Two organelles provide that energy
• Choloroplasts (in plants)
• Mitochondria (in animals and plants)

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Chloroplasts

• Chloroplasts are organelles that captures light
  energy and produces food to store for later
• Has a double membrane (like the nucleus)
• The inner membrane folds in to form stacks of
  membranous sacs called grana/thylakoids.

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Chloroplasts

• In the thylakoid membrane there is the green
  pigment called Chlorophyll
• Traps light energy
• Gives leaves and stems their green color

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Mitochondria

• Mitochondria produces energy in a form that can
  be used by the cell when necessary.
• Has an outer membrane and a highly folded inner
  membrane.
• Provides large surface area.

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Structures for Support and Locomotion

• Cytoskeleton forms the framework of the cell
• Maintains shape
• Composed of
• Microtubules thin hollow cylinders made of
  protein
• Microfilaments thin, solid protein fibers

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Structures for Support and Locomotion

• Cilia and flagella Structures that aid in
  locomotion and feeding.
• Composed of pairs of microtubules, with a central
  pair surrounded by 9 additional pairs.
• Cilia are short, numerous, hair-like projections
  that move in a wavelike motion
• Flagella are longer projections, move in a
  whip-like motion.

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