Chapter 7
Inside the Cell
What’s Inside the Cell?
• Looking at cell structure, there are two broad groupings of life:
1. Prokaryotes, which lack a membrane-bound nucleus.
2. Eukaryotes, which have such a nucleus.
• Looking into groupings by evolutionary history, there are two
Prokaryotic Cells
• The prokaryotic plasma membrane surrounds the cytoplasm, a
term that includes all the contents of the cell. Prokaryotic cells generally have few or no substructures separated from the rest of the cell by internal membranes.
• Prokaryotes have a tough cell wall that protects the cells and
A Prokaryotic Cell
Ribosomes
Plasmids
Flagellum
Cell wall
Plasma membrane
Chromosome
Prokaryotic Cells
• Most prokaryotic species have one supercoiled circular
chromosome containing DNA that is found in the nucleoid
region of the cell.
• All prokaryotic cells contain ribosomes for protein synthesis.
Ribosomes have a large and a small subunit and contain both RNA and protein molecules.
• The inside of prokaryotic cells is supported by a cytoskeleton of
protein filaments.
• Some prokaryotes have tail-like flagella on the cell surface that
Eukaryotes and Prokaryotes Compared
• Major differences between typical eukaryotes and prokaryotes are
as follows:
(1) Eukaryotic chromosomes are found inside a
membrane- bound compartment called a nucleus.
(2) Eukaryotic cells are often much larger.
(3) Eukaryotic cells contain extensive amounts of internal membrane.
Eukaryotic Cells
• The relatively large size of the eukaryotic cell makes it difficult
for molecules to diffuse across the entire cell. This problem is
partially solved by breaking up the large cell volume into several
smaller membrane-bound organelles.
• The compartmentalization of eukaryotic cells increases chemical
Animal and Plant Cells
Generalized animal cell
Generalized plant cell
Centrioles Cell wall Chloroplast Cytoskeletal element Plasma membrane Mitochondrion Peroxisome Vacuole (lysosome) Golgi apparatus Smooth endoplasmic reticulum Ribosomes Rough endoplasmic reticulum Chromosomes Nucleolus Nucleus Nuclear envelope Nuclear envelope Nucleolus Nucleus Chromosomes Rough endoplasmic reticulum Ribosomes Smooth endoplasmic reticulum Golgi apparatus Peroxisome Mitochondrion Plasma membrane Cytoskeletal element Lysosome Structures that occur in animal cells but not plant cells
Structures that occur in plant cells but not animal cells
Animal and Plant Cells
Generalized animal cell
Centrioles
Nuclear envelope
Nucleolus
Chromosomes
Nucleus
Rough endoplasmic reticulum
Ribosomes
Peroxisome
Smooth endoplasmic reticulum
Golgi apparatus
Lysosome
Mitochondrion
Cytoskeletal element
Plasma membrane
Animal and Plant Cells
Generalized plant cell
Cell wall Chloroplast Cytoskeletal element Plasma membrane Mitochondrion Peroxisome Vacuole (lysosome) Golgi apparatus Smooth endoplasmic reticulum Ribosomes Rough endoplasmic reticulum Chromosomes Nucleolus Nuclear envelope Nucleus Structures that occur in plant cells but not animal cells
The Endomembrane System
• Ions, ATP, amino acids, and other small molecules diffuse
randomly throughout the cell, but the movement of proteins and other large molecules is energy demanding and tightly regulated.
• In the endomembrane system, proteins that are synthesized in the
The Secretory Pathway Hypothesis
THE SECRETORY PATHWAY: A MODEL
RNA Rough ER
Golgi apparatus
cis face of
Golgi apparatus
trans face of Golgi apparatus
Plasma membrane
1. Protein enters ER while being synthesized by ribosome.
2. Protein exits ER, travels to cis face of Golgi apparatus.
3. Protein enters Golgi apparatus and is processed as the cisternum moves toward the trans face.
4. Protein exits Golgi apparatus at trans face and moves to plasma membrane.
5. Protein is
How Are Products Shipped from the Golgi?
• Each protein that comes out of the Golgi apparatus has a
molecular tag that places it in a particular type of transport
vesicle. Each type of transport vesicle also has a tag that allows it to be transported to the correct destination.
• Figure 7.30 illustrates the current model for how proteins are
sorted into distinct vesicles in the Golgi and then targeted to their correct destination.
• Some proteins are sent to the cell surface in vesicles that fuse with
the plasma membrane, releasing their contents to the exterior of
The Golgi Apparatus: Proteins Are Sorted into Vesicles
PROTEIN SORTING AND VESICLE TRANSPORT
Lumen of Golgi apparatus Cytosol “Tags” Receptors Transport vesicles
Return to the ER To plasma membrane
for secretion
Lysosome
1. In the endomembrane system, proteins bound for lysosomes or rough ER are given different carbohydrate “tags.” Proteins bound for secretion have built-in export signal.
2. Proteins are sorted in the Golgi when they bind to different
receptors.
3. Transport vesicles bud off the trans face of the Golgi and travel to their destinations.
4. Proteins on vesicle surface interact with receptors at destination.
The Dynamic Cytoskeleton
• The cytoskeleton is a complex network of fibers that helps
maintain cell shape by providing structural support. The
cytoskeleton is dynamic; it changes to alter the cell’s shape, to transport materials in the cell, or to move the cell itself.
• The three types of cytoskeletal elements are actin filaments,
A Motor Protein Moves Vesicles along Microtubules
Structure of kinesin
Tail
Stalk
A Motor Protein Moves Vesicles along Microtubules
Kinesin “walks” along a microtubule track.
Microtubule
Kinesin Transport vesicle
end end
Every step