Chapter 5: Cell Structure and Function

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Chapter 5Cell Structure and Function
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The Cell Theory

• The microscopic analyses of cells led to three
  generalizations that constitute the Cell Theory
• 1. Every organism is composed of one or more
  cells.
• 2. The smallest living organisms are single
  cells and cells are the functional units of
  multicellular organisms.
• 3. All cells arise from preexisting cells.

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Cell Size

• Most cells are too tiny to see with the naked
  eye.
• Cell size is governed by the physical
  relationship called the Surface-To-Volume Ratio.
• According to this relationship, an objects volume
  increases with the cube of the diameter, but the
  surface area increases only with the square of
  the diameter. Therefore, volume increases faster
  than surface area.

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Cell Size
Volume increases 64 times (43) Surface area
increases 16 times (42)
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r
r
r
distance to center (r)
1.0
3.0
1.0
surface area (4pr2)
12.6
339.4
113.1
volume (4/3 pr3)
4.2
113.1
113.1
area/volume
3.0
3.0
1.0
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All Cells are Similar

• All cells share a few common features.
• They all contain a Plasma Membrane
• The plasma membrane is responsible for
  maintaining the cell as a distinct entity.
• They all contain a region of DNA
• The region of DNA can be contained in a membrane
  bound sac (nucleus) or simply occupy a region of
  the cell interior (nucleoid).
• They all contain a region of Cytoplasm
• The cytoplasm is everything between the plasma
  membrane and the region of DNA.
• All cells obtain energy and nutrients from their
  environment

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All Cells are Similar
Plasma Membrane
Region of DNA
Region of Cytoplasm
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Two Main Types of Cells

• There are two main types of cells.
• 1. Prokaryotic cells (eubacteria and
  archaebacteria)
• Do Not contain a true nucleus, only a nucleoid
  region of DNA
• Do Not contain membrane bound Organelles
• 2. Eukaryotic cells (plants, animals, and fungi)
• Contain a true membrane bound nucleus
• Contain other membrane bound Organelles in
  addition to the Nucleus

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Two Main Types of Cells
Typical Prokaryotic Cell
Typical Eukaryotic Cell
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chromosome (nucleoid region)
pili
ribosomes
food granule
prokaryotic flagellum
capsule or slime layer
cell wall
plasma membrane
plasmid (DNA)
cytoplasm
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The Cell Wall

• A semi-rigid structure that helps the cell
  maintain its shape and resist rupturing.
• Composed of peptidoglycan molecules
• The cell wall is often enclosed by a glycocalyx
  or a sticky mesh composed of polypeptides,
  polysaccharides, or both. It helps the cell
  attach to surfaces such as teeth and mucous
  membranes and protect against phagocytosis.
• When highly organized and firmly attached it
  forms a capsule
• When less organized and loosely attached it forms
  a slime layer.

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Eukaryotic Cells

• Eukaryotic cells have internal membrane bound
  compartments called Organelles.
• Organelles perform one or more specialized
  functions within the cell.
• Organelles make it possible to carry out various
  activities simultaneously in a very limited
  space.
• They also allow for compatible and interconnected
  reactions to proceed at different times.

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Organelles

• Nucleus
• Endomembrane System
• Vesicles
• Mitochondria
• Plastids
• Central Vacuole
• Cytoskeleton
• All Eukaryotic cells do not contain all of the
  organelles listed above.

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nuclear pore
chromatin (DNA)
nucleus
nucleolus
centriole
nuclear envelope
flagellum
intermediate filaments
cytoplasm
rough endoplasmic reticulum
plasma membrane
ribosome
lysosome
Golgi complex
vesicle
microtubules
Smooth endoplasmic reticulum
free ribosome
mitochondrion
vesicle
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plastid
mitochondrion
Microtubules (part of cytoskeleton)
chloroplast
central vacuole
Golgi complex
smooth endoplasmic reticulum
plasmodesma
vesicle
cell wall
rough endoplasmic reticulum
plasma membrane
nucleolus
nuclear pore
nucleus
chromatin
nuclear envelope
intermediate filaments
ribosomes
free ribosome
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The Nucleus

• The Nucleus is a membrane bound compartment that
  contains chromatin (DNA associated with protein),
  nucleoplasm, and the Nucleolus.
• The Nucleolus is an aggregation of RNA and
  proteins.
• The nuclear membrane (nuclear envelope) is a
  double bilayer that contains tiny membrane lined
  channels called nuclear pores.
• The outer membrane is studded with ribosomes and
  is continuous with membranes of the rough
  endoplasmic reticulum.

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nuclear envelope
nucleolus
nuclear pores
chromatin
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The Nuclear Envelope
Nuclear pore
bilayer facing cytoplasm
Nuclear envelope
bilayer facing nucleoplasm
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The Endomembrane System

• The Endomembrane System is a series of
  functionally connected organelles including the
  Rough and Smooth Endoplasmic Reticuli, Golgi
  bodies, and sorting vesicles.
• The Endomembrane System is the site of membrane
  and secretory protein synthesis and modification.
  It is also the site of lipid assembly.

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ribosomes
vesicles
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vesicles from ER
vesicles leaving Golgi complex
Golgi complex
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phagocytosis
exocytosis
plasma membrane
lysosome fused with food vacuole
food vacuole
Golgi complex
smooth endoplasmic reticulum
rough endoplasmic reticulum
nuclear envelope
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Specialized Vesicles

• Vesicles are tiny membranous sacs that move
  through the cytoplasm or take up positions in it.
• Assorting vesicles carry and sort membrane and
  secretory proteins.
• Lysosomes carries out intracellular digestion.
• Peroxisomes breaks down fatty acids and amino
  acids.

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Vacuoles

• Vacuoles are fluid filled sacs surrounded by a
  single membrane.
• Vacuoles serve many functions, including water
  regulation, support, and storage.
• Food vacuoles form during phagocytosis
• Freshwater microorganisms have contractile
  vacuoles
• Plant cells have central vacuoles

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contractile vacuole
collecting ducts
central reservoir
pore
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The Central Vacuole

• The Central Vacuole is a fluid filled organelle
  that stores amino acids, sugars, ions, and toxic
  wastes and helps the cell grow.
• The vacuole expands during growth as fluid
  pressure builds up. It can take up as much as 50
  to 90 of the cells interior.

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central vacuole
plasma membrane
cell wall
cytoplasm
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Mitochondria

• The Mitochondria are the site of cellular energy
  production in the form of ATP molecules.
• The mitochondrion has a double membrane system
• Contains its own DNA and some Ribosomes
• Thought to have evolved from an ancient
  prokaryote through a symbiotic relationship.

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outer membrane
inner membrane
intermembrane compartment
matrix
cristae
0.2 micrometer
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Specialized Plant Organelles

• Many plant cells contain specialized organelles
  called Plastids.
• Plastids are a general category of organelles
  that specialize in photosynthesis and storage.
• There are 3 types of plastids
• Chloroplast contain chlorophyll and use
  sunlight energy to make sugars and other organic
  compounds.
• Chromoplasts contains carotenoids
• Amyloplasts lack pigments and store starch
  grains

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outer membrane
inner membrane
stroma
thylakoid
channel interconnecting thylakoids
granum (stack of thylakoids)
1 micrometer
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plastid
starch globules
0.5 micrometer
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The Cytoskeleton

• The Cytoskeleton is a system of structural
  components that reinforce, organize, and move
  internal cell parts and often function in cell
  motility.
• There are 3 major Cytoskeletal components
• Microtubules composed of tubulin monomers
  (largest)
• Microfilaments composed of twisted chains of
  actin monomers (thinnest)
• Intermediate filaments there are 6 known groups
  of intermediate filaments (most stable)

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The Cytoskeleton
tubulin subunit
one polypeptide chain
Intermediate Filament
actin subunit
Microtubule
Microfilament
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plasma membrane
microfilaments
mitochondrion
intermediate filaments
ribosomes
endoplasmic reticulum
microtubule
vesicle
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microtubules (red)
nucleus
microfilaments (blue)
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Intracellular Movement

• Microtubules and Microfilaments are involved in
  cell movement.
• They are used as tracks and motor proteins are
  used as engines to move cell components.
• The two motor proteins kinesin and dyneins move
  along microtubules while the motor protein myosin
  moves along microfilaments.

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item to be moved binds here
end that binds cell component
Dynein
Kinesin
ATP binding head
ATP binding head
minus end
plus end
microtubule
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Whole Cell Movement

• Many cells move their body or parts of it through
  the environment by using either Flagella or
  Cilia.
• Flagella are usually longer and less numerous
  than Cilia. Sperm cells use Flagella as whiplike
  tails to swim.
• Cilia are used to stir fluid or air to direct
  movement.
• Both Cilia and Flagella have an internal array of
  nine microtubules and a pair of central
  microtubules. (the 9 2 array)
• Some cells move through the environment by using
  pseudopods (false feet) instead of Cilia or
  Flagella.

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central unfused pair of microtubules
Protein "arms"
fused pair of microtubules
x-section of cilium (92 arrangement)
0.1 micrometer
cilium
Paramecium
plasma membrane
basal body
x-section of basal body (90 arrangement)
0.1 micrometer
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one of the outer rings pairs of
microtubules (doublets)
dynein arm
two central microtubules
central sheath
plasma membrane
base of flagellum or cilium
plasma membrane
basal body
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Cilium
cilia lining trachea
Propulsion of fluid
power stroke
return stroke
plasma membrane
Flagellum
direction of locomotion
propulsion of fluid
flagellum of human sperm
continuous propulsion
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Cilium
propulsion of fluid
power stroke
return stroke
plasma membrane
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Flagellum
direction of locomotion
propulsion of fluid
continuous propulsion
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Key Points

• The Cell Theory
• Two cell types
• Organelles and their functions.