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Chapter 7 Cell Structure Lecture Notes Text-2

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Chapter 7

Inside the Cell

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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

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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

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A Prokaryotic Cell

Ribosomes

Plasmids

Flagellum

Cell wall

Plasma membrane

Chromosome

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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

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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.

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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

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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

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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

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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

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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

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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

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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

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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.

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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,

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A Motor Protein Moves Vesicles along Microtubules

Structure of kinesin

Tail

Stalk

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A Motor Protein Moves Vesicles along Microtubules

Kinesin “walks” along a microtubule track.

Microtubule

Kinesin Transport vesicle

 end  end

Every step

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