Transcript Cell Structure chapt04

Cell Structure
Chapter 4
Cell Theory
• Cells were discovered in 1665 by Robert
Hooke.
• Early studies of cells were conducted by
• Mathias Schleiden (1838) - plant cells
•Theodor Schwann (1839) - animal cells
• Schleiden and Schwann proposed the Cell
Theory.
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Cell Theory
• Cell Theory
1. All organisms are composed of cells.
2. Cells are the smallest living things.
3. Cells arise only from pre-existing cells.
• All cells today represent a continuous line
of descent from the first living cells.
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Cell Theory
• Cell size is limited.
•
As cell size increases, it takes longer for
material to diffuse from the cell membrane to
the interior of the cell.
• Surface area-to-volume ratio: as a cell
increases in size, the volume increases 10x
faster than the surface area
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Cell Theory
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Cell Theory
• Microscopes are required to visualize cells.
• Light microscopes can resolve structures
that are 200nm apart.
• Electron microscopes can resolve
structures that are 0.2nm apart.
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Fig. 4.2
Cell Theory
• All cells have certain structures in common:
1. Genetic Material – in a nucleoid or nucleus
2. Cytoplasm – a semifluid matrix
3. Plasma Membrane – a phospholipid bilayer
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Phospholipids
• Chapter 3: Phospholipids are Amphiphilic molecules
Polar Head Group
Nonpolar Hydrocarbon Tail
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Two Cell Types
1. Prokaryotic Cells
2. Eukaryotic Cells
• Recall Three Domains (Ch. 1)
• Defined by cell type
1.Eukarya
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Plantae
Fungi
Animlia
Protista
2.Bacteria
3.Archaea
Eukaryotic
Prokaryotic
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1. Prokaryotic Cells
Prokaryotic Cells
• Origin: ‘pro’-before; ‘karyote’ - nut
• Lack a membrane-bound nucleus.
- genetic material is present in the nucleoid
• Two types of prokaryotes:
1. Archaea
2. Bacteria
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1. Prokaryotic Cells
• Prokaryotic Cell Characteristics:
• Simplest organisms - simple internal
organization
• Very small (1 to 10 microns across)
• Genetic material in the nucleoid
• No membrane-bound organelles
• Capsules
• Cytoplasm
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1. Prokaryotic Cells
• Prokaryotic and Eukaryotic Characteristics:
• DNA, RNA
• Ribosomes
• Plasma membrane
• Cell walls (bacteria, archaea)
• Flagella
• Pilli
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1. Prokaryotic Cell Structure
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Prokaryotic Cell Structure
• Prokaryotic cell walls
– Surround and protect cell and maintain cell shape
– Composed of polysaccharides (sugar coated)
• Bacterial cell walls composed of peptidoglycan
• Archaean cell walls lack peptidoglycan.
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Recall Ch. 3
Polysaccharides
b. Function
1. Structural Molecules
Cellulose - plant cell walls
Chitin – Fungi cell walls
Peptidoglycan - Bacterial cell walls
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Prokaryotic Cell Structure
Bacterial cell walls composed of peptidoglycan
• Two Types of Bacterial Cell Walls
1. Gram Positive
2. Gram Negative
• Gram Positive/Gram Negative type is
determined by cell cell wall structure and the
Gram Stain Reaction
• Gram Positive Bacteria Stain Purple
• Gram Negative Bacteria Stain Pink
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Gram + vs. Gram • Gram + Bacteria stain Purple
• Gram – Bacteria stain Pink
Courtesy: Dr. O’Steen
Prokaryotic Cell Structure
Flagella (singular, flagellum)
•
Whip-like proteins attached to cell wall used for
locomotion
•
Present in some prokaryotic cells
- one to several flagella on a single cell
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Rotary motion of flagellum propels the cell
through fluid environment
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Flagella powered by protein motors
- uses energy of a proton gradient
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Flagella Structure
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2. Eukaryotic Cells
•
Eukaryotic Cells
Origin: ‘eu’ - true, good; ‘karyote’ - nut
• Possess a membrane-bound nucleus.
- genetic material is highly organized within
double-layer nuclear envelope
- DNA never leaves the nuclear envelope
• Types of eukaryotes divided into 4
kingdoms:
1. Plantae 2. Fungi
3. Animalia 4. Protista
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2. Eukaryotic Cells
• Eukaryotic Cell Characteristics:
• More complex organisms
• highly organized structure (compartmentalization)
known as endomembrane system
• Typically larger than prokaryote (10-100 microns)
• Genetic material in the membrane-bound nucleus
• Many membrane-bound organelles
• Cytoplasm
• Cytoskeleton
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2. Eukaryotic Cells
• Eukaryotic and Prokaryotic Characteristics:
• DNA, RNA
• Ribosomes
• Plasma membrane
• Cytoplasm
• Cell walls (plantae, fungi, protista, not present in
animal cells)
• Flagella
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Eukaryotic Cells
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Eukaryotic Cells
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Eukaryotic Cells
Nucleus
• Largest most definitive organelle in the
cytoplasm
• Surrounded by a nuclear envelope
composed of 2 phospholipid bilayers
• Stores the genetic material of the cell as
long separate chains of DNA known as
chromosomes
• Cell DNA is organized with proteins to
form chromatin
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Eukaryotic Cells
Nucleus
• Cell DNA is organized with proteins to
form chromatin
- Chromosomes are tightly packed
(condensed) with proteins inside the nucleus
into nucleosomes
- DNA is wound around histone proteins to
resembles beads on a string
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Fig. 4.9
Eukaryotic Cells
Nucleolus (plural, nucleoli)
• Dark staining zone within the nucleus
• Composed of RNA
• Synthesis of ribosomal RNA (rRNA)
occurs here
- rRNA is involved in the translation of DNA into
protein
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Eukaryotic Cells
Nuclear Envelope
• Composed of an inner and outer
phospholipid bilayer
- the outer layer is continuous with the
membrane of the endoplasmic reticulum - an
organelle for protein synthesis
• Nuclear pores provide passage for
proteins and rRNA into and out of the
nucleus
- DNA never leaves the nucleus
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Eukaryotic Cells
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Eukaryotic Cells
Ribosomes
• Present in prokaryotic and eukaryotic
cells
• Composed of ribosomal RNA and
proteins
• Found in the cytoplasm and attached to
internal membranes of the endoplasmic
reticulum
• Important protein function in protein
synthesis in the cell
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Eukaryotic Cells
Ribosomes
• Composed of 2 subunits of ribosomal
RNA (rRNA) and protein
• The two subunits associate to form
complete Ribosomes
• Other types of RNA assist with protein
synthesis:
- mRNA
- tRNA
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Fig. 4.10
Endomembrane System
Endomembrane system
• A series of membranes throughout the
eukaryotic cytoplasm
• Divides cell into compartments where
different cellular functions occur:
1. Endoplasmic Reticulum
2. Golgi Apparatus
3. Lysosomes
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Endomembrane System
1. Endoplasmic Reticulum (ER)
• Membranes that create a network of
channels throughout the cytoplasm
• Membrane continuous with the outer
membrane of the nuclear envelope
• Location for protein synthesis
• Two Sections of the ER
1. Rough Endoplasmic Reticulum
2. Smooth Endoplasmic Reticulum
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Endomembrane System
1. Rough Endoplasmic Reticulum (RER)
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•
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System of cytoplasmic membranes that
create a network of channels throughout the
cytoplasm
Ribosomes are attached to the outside of the
RER membrane giving it a rough appearance
under the microscope
Synthesis of proteins to be secreted out of
the cell, or packaged and sent to lysosomes
or plasma membrane
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Proteins are synthesized into the RER
channels (cisternal space)
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Endomembrane System
2. Smooth Endoplasmic Reticulum (SER)
• Relatively few associated ribosomes
• Functions:
- Synthesis of membrane lipids
- Calcium storage
- Detoxification of foreign substances
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Endomembrane System
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Endomembrane System
Golgi Apparatus
• Flattened stacks of interconnected
membranes folds (cisternae) known
individually as Golgi bodies
• Located peripheral to the nucleus and ER
• Function in packaging and distribution of
materials to different parts of the cell
• Synthesis of cell wall components
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Fig. 4.12
• Cis face of
Golgi faces
and receives
products from
the ER
• Trans face of
Golgi releases
secretory
vesicles
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Endomembrane System
Lysosomes
• Membrane bound vesicles containing
digestive enzymes to break down
macromolecules
• Packaged and secreted by Golgi
apparatus
• Function to destroy cells or foreign matter
that the cell has engulfed by phagocytosis
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Endomembrane System
Microbodies
• Membrane bound vesicles that do not
originate from the endomembrane system
• Contain enzymes:
- Glyoxysomes in plants contain enzymes for
converting fats to carbohydrates
- Peroxisomes contain oxidative enzymes
such as H2O2 and catalase
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Fig. 4.15
Endomembrane System
Vacuoles
• ‘Blank spaces’
• Membrane-bound structures with a variety
of functions depending on the cell type
• There are different types of vacuoles:
- Central Vacuole in plant cells
- Contractile Vacuole of some protists
- Storage Vacuoles
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Fig. 4.16
Mitochondria
Mitochondria
• ‘Power house of the cell”
• Present in all types of eukaryotic cells
• Contain oxidative metabolism enzymes
for the chemical reactions of cellular
respiration
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the transferring of energy within
macromolecules to ATP
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Mitochondria Structure
• Surrounded by 2 membranes:
1. Smooth outer membrane
2. Folded inner membrane with layers (cristae)
intermembrane space is located between the
two membranes
- matrix within the inner membrane
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• Similar in structure and function to
chloroplasts of photosynthesis
• Contain their own DNA (Mitochondrial DNA)
- Produce some essential proteins
- Mitochondria undergo their own division51
Mitochondria
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Chloroplasts
• Organelles present in cells of plants and
some other eukaryotes (Kingdom Protista)
• Contain chlorophyll for photosynthesis
• Surrounded by 2 membranes
- Inner membrane forms sacs known as
thylakoids
- Stacks of thylakoids are known as Grana
• Mitochondria, chloroplasts and similar DNA
containing organelles known collectively as
plastids
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Chloroplasts
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Mitochondria & Chloroplasts
Endosymbiosis
• Proposal that eukaryotic organelles
evolved through a symbiotic relationship
• One prokaryotic cell engulfed a second
prokaryotic cell and a symbiotic
relationship developed
• Mitochondria and chloroplasts are thought
to have evolved this way
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Mitochondria & Chloroplasts
• Evidence supports this endosymbiosis
theory:
• Mitochondria and chloroplasts:
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have 2 membranes
possess DNA and ribosomes
are about the size of a prokaryotic cell
divide by process of simple fission similar to
bacteria
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Mitochondria & Chloroplasts
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Cytoskeleton
Cytoskeleton
• Network of protein fibers found in all
eukaryotic cells
• Supports the shape of the cell
• Keeps organelles in fixed locations
• Helps move materials within the cell
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Cytoskeleton
• Three Fiber Types of Cytoskeleton:
1. Actin Filaments – responsible for cellular
contractions, crawling, “pinching”
- Composed of actin protein subunits
2. Microtubules – provide organization to the
cell and move materials within the cell
- Composed of tubulin protein subunits
3. Intermediate Filaments – provide structural
stability
- Composed of vimentin protein subunits
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Cytoskeleton
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Fig. 4.20a
Cytoskeleton
Centrosomes
• Organelles that organize microtubule
function within the cell
- Cell division
• Composed of two perpendicular
centrioles
- bundles of microtubules organized in 9 triplets
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Fig. 4.21
Cell Movement
• Cell movement takes different forms:
• Crawling is accomplished via actin filaments
and the protein myosin
• Molecular motor proteins such as kinesin and
dyein use ATP energy to move organelles in
the cytoplasm along microtubule tracks
• Flagella undulate to move a cell
• Cilia can be arranged in rows on the surface
of a eukaryotic cell to propel a cell forward64
Fig. 4.22
Cell Movement
• The cilia and flagella of eukaryotic cells
have a similar structure:
• 9-2 structure: 9 pairs of microtubules
surrounded by a 2 central microtubules
• dynein protein motors slide the microtubules
across each other causing them to undulate
• Flagella attached to cell body at basal
body
• Cilia are usually more numerous than
flagella on a cell
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Cell Movement
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Fig. 4.24b
Fig. 4.24a
Extracellular Structures
• Extracellular structures:
• Cell Walls:
• plants
• fungi
• some protists
• Extracellular Matrix
• surrounding animal cells
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Extracellular Structures
Cell Walls
• Present surrounding the cells of plants,
fungi, and some protists
• Composed of carbohydrates
-Type of carbohydrate present in the cell wall
vary depending on the cell type:
- plant and protist cell walls composed of cellulose
- fungal cell walls composed of chitin
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Fig. 4.25
Extracellular Structures
Extracellular matrix (ECM)
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Surrounds animal cells
- animal cells lack cell walls
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Composed of glycoproteins and fibrous
proteins such as collagen and elastin
- provide a protective layer over the cell
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Connected to plasma membrane via
fibronectins
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Connected to the cytoplasm via integrin
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proteins present in the plasma membrane
Extracellular Structures
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