Cell Structure and Function

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Chapter 4
Cell Structure and Function
Left Robert Hooke first observed cork cell
walls under microscope
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4.1 Basic aspects of cells

• All cells (eukaryotes and prokaryotes) contain
• Plasma membrane- maintains the cell structure,
  but allows for movement within
• Nucleus (membrane bound) or Nucleoid (region of
  cell)- houses DNA
• Cytoplasm- matrix that contains everything in cell

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4.1 (cont.)

• Above Right proteins embedded in
• membrane allow for diffusion via hormone
  receptor activation
• Lipid bilayer in cell membranes (see below)
  prevents free passage of particles in and out of
  cell
• The yolk of bird eggs is ONE cell. Why arent
  all cells big?
• Answer surface-to-volume relationship
• Volume increases faster than
• surface area

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4.2 Microscopes

• Light microscope (light travels through 2 or more
  lenses to magnify-see right)
• Electron microscope (TEM uses
• a magnetic field to focus electrons,SEM
• scans e- over metal sheet to create image)
• Far left TEM scan of cilia creates
  a thin section image, Right SEM produces
  a 3-D image

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4.3 Eukaryotic cells

• Organelle- membrane-bound compartment that
  carries out specific function
• Nucleus
• Endoplasmic Reticulum
• Golgi Body
• Mitochondria
• Various vesicles (vacuole, lysosomes)
• non-membrane-Ribosomes and Cytoskeleton

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4.4 The Nucleus

• Nuclear envelope- 2 membranes surround the
  nucleoplasm (nuclear fluid) pores allow for
  transport of materials
• Nucleolus- RNA and proteins combine to make
  ribosomal subunits
• Below TEM of nucleolus

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4.4 (cont.)

• Chromosome-one threadlike, condensed or
  duplicated DNA
• Chromatin- total collection of DNA and proteins
  in cell

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4.5 Endomembrane system

• Endoplasmic Reticulum (ER) (see below right)
• Rough ER exists as flattened sacs attached
  ribosomes synthesize polypeptide chains, making
  proteins
• Smooth ER is free of ribosomes exists as
  connecting pipes, assembles most lipids
• Golgi Bodies- looks like stack of flattened
  pancakes places finishing touches on proteins
  and lipids packages them inside vesicles for
  shipment (see above left)

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4.5 (cont.)

• Vesicles- membranous sacs that move
• Lysosomes- intracellular digestion (below right)
• Peroxisomes- break down
• fatty acids and amino acids
• abundant in liver (below left)
• and kidney cells

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4.6 Mitochondria

• Where aerobic respiration takes place
• C6H12O6 O2 ? H2O CO2 energy (ATP)
• Double membrane system
• allows for 1. Hydrogen ions to
• stockpile in the outer-layer,
• which then 2. flows to the inner
• compartment to drive the
• formation of ATP
• Possibly evolved from
• prokaryotic cell (pg. 66)

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4.7 Plant Organelles

• Plastids-organelles that specialize in
  photosynthesis
• Chloroplasts, Chromoplasts and Amyloplasts
• Chloroplasts- stroma (fluid) is enclosed
• in 2 membranes thylakoid membrane-
• inner holds granum stacks
• Chromoplasts- lack chlorophyll (reflect
• green light) have carotenoids (red-yellow)
• Amyloplasts- lack pigments, store starch
• Central Vacuole-stores carbs, amino
• acids, wastes etc.
• can take up to 90 of cell volume

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4.9 Cytoskeleton

• Microtubules- largest built from tubulin
  monomers in animals, grow out from centrosome
  (far left)
• Microfilament- thinnest actin monomers
  establishes cell cortex, which is responsible for
  cytoplasmic streaming (above)
• Myosin- and kinesis are motor proteins that bond
  with microtubules and filaments to aid in ATP
  formation (middle)
• Intermediate filaments- anchor organelles and
  maintain shape of cell (far right)

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4.10 Cell Movement

• Flagella- whip-like tail (below)
• Cilia- hairs (far right) most have a 92
  microtubule
• protein with spokes- centriole, also known as
  basal body
• Allows organism to bend and not slide
• Pseudopods- false feet microtubules allow for
  cytoplasmic
• Streaming to project amoeba forward (far right)

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4.11 Cell wall and junctions

• Cell Wall- protects and supports cell found in
  plants, some protists and fungi
• Primary wall- glue-like sugars, glycoproteins and
  cellulose cement
• adjacent cell together waxy cuticle is outermost
  layer in cells exposed to air
• Secondary wall- deposited as plant ages more
  rigid, aiding in structural support high content
  of cellulose and in woody plants, lignin
  (waterproofs the cell)
• (below, primary and secondary walls are seen in
  xylem)
• Cell Junctions- plasmodesma a channel connection
  two cell membranes
• Tight junctions- connect cells of most body
  tissues
• Adhering junctions- connect tissues that stretch
• ex) heart, skin
• Gap junctions- channels with neighboring cells

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4.12 Prokaryotic cells