4.1 cells as life’s fundamental unit
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4.1 Cells as Life’s Fundamental Unit. Cells as Life’s Fundamental Unit. With the possible exception of viruses, every form of life on Earth either is a cell or is composed of cells. Cells as Life’s Fundamental Unit. Cells come into existence only through the activity of other cells. - PowerPoint PPT PresentationTRANSCRIPT
A Guide to the Natural World
David Krogh
© 2011 Pearson Education, Inc.
Chapter 4 • Lecture OutlineLife’s Home: The Cell
Biology
Fifth Edition
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4.1 Cells as Life’s Fundamental Unit
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Cells as Life’s Fundamental Unit
• With the possible exception of viruses, every form of life on Earth either is a cell or
is composed of cells.
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Cells as Life’s Fundamental Unit
• Cells come into existence only through the activity of other cells.
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4.2 Prokaryotic and Eukaryotic Cells
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Prokaryotic and Eukaryotic Cells
• All cells can be classified as prokaryotic or eukaryotic.
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Prokaryotic and Eukaryotic Cells
• Prokaryotic cells either are bacteria or another single-celled life-form called archaea.
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Prokaryotic and Eukaryotic Cells
• Setting bacteria and archaea aside, all other cells are eukaryotic.
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Prokaryotic and Eukaryotic Cells
• Eukaryotic cells have most of their DNA contained in a membrane-lined compartment, called the cell nucleus, whereas prokaryotic cells do not have a nucleus.
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Prokaryotic and Eukaryotic Cells
• Eukaryotic cells tend to be much larger than prokaryotic cells. They have more of the specialized internal structures called organelles than do prokaryotic cells.
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Prokaryotic and Eukaryotic Cells
• Many eukaryotes are multicelled organisms, whereas all prokaryotes are single-celled.
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Prokaryotic cells Eukaryotic cells
within membrane-bound nucleusspread through much of cell
DNA
much smaller
Size
always single-celled
Organization
Organelles
only one type of organelle
much larger
often multicellular
many types of organelles
Figure 4.2
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4.3 The Eukaryotic Cell
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The Eukaryotic Cell
• There are five principal components to the eukaryotic cell: the nucleus, other organelles, the cytosol, the cytoskeleton, and the plasma membrane.
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The Eukaryotic Cell
• Organelles are “tiny organs” within the cell that carry out specialized functions, such as energy transfer and materials recycling.
© 2011 Pearson Education, Inc. Figure 4.4
The Animal CellThe nucleus contains the cell’s primary complement of DNA.
nuclear poresDNA
nuclear envelopenucleolus
Mitochondria are the powerplantorganelles that extract energyfrom food and put it into a formcells can use.
plasma membrane
The folds of the rough endoplasmicreticulum form a set of chambers within which proteins are processed.
All the cell’s structures outside the nucleus are immersed in a jelly-like fluid called the cytosol. Composed mostly of water, the cytosol is a location for countless chemical reactions carried out within the cell.
The smooth endoplasmic reticulumis the site of the production of lipidmolecules such as estrogen and testosterone.
free ribosomes
cytoskeleton
lysosome
transport vesicle
How are cell proteins sorted and shipped, so that they end up at the right location? Partly through the work of the Golgi complex.
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The Eukaryotic Cell
• The cytosol is the jelly-like fluid outside the nucleus in which these organelles are immersed.
• The cytosol should not be confused with the cytoplasm, which is the region of the cell inside the plasma membrane but outside the nucleus.
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The Eukaryotic Cell
• The cytoskeleton is a network of protein filaments.
• It functions in cell structure, cell movement, and the transport of materials within the cell.
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The Eukaryotic Cell
• The plasma membrane is the outer lining of the cell.
• A membrane can be defined as the flexible, chemically active outer lining of a cell or of its compartments.
© 2011 Pearson Education, Inc. Figure 4.3
The Eukaryotic Cell
Components of eukaryotic cells
nucleus other organelles cytosol cytoskeleton plasma membrane
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4.4 A Tour of the Animal Cell’s Protein Production Path
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Tour of the Animal Cell’s Protein Production Path
• Information for the construction of proteins is contained in the DNA located in the cell nucleus.
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The Protein Production Path
• This information is copied onto a length of messenger RNA (mRNA) that departs the cell nucleus through its nuclear pores and goes to the sites of protein synthesis, structures called ribosomes, which lie in the cytoplasm.
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The Protein Production Path
• Many ribosomes that receive mRNA chains process only a short stretch of them before migrating to, and then embedding in, one of a series of sacs in a membrane network called the rough endoplasmic reticulum (RER).
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The Protein Production Path
• The polypeptide chains produced by the ribosomal “reading” of the mRNA sequences are dropped from ribosomes into the internal spaces of the RER.
• There, the polypeptide chains fold up, thus becoming proteins, and undergo editing.
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Tour of an Animal Cell
Suggested Media Enhancement:
Tour of an Animal Cell
• To access this animation go to folder C_Animations_and_Video_Filesand open the BioFlix folder.
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The Protein Production Path
• Some ribosomes are not embedded in the RER but instead remain free-standing in the cytosol.
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The Protein Production Path
• Materials move from one structure to another in the cell via the endomembrane system.
• Here a piece of membrane, with proteins or other materials inside, can bud off from one organelle, move through the cell, and then fuse with another membrane-lined structure.
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The Protein Production Path
• Membrane-lined structures that carry cellular materials are called transport vesicles.
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The Protein Production Path
• Once protein processing is finished in the rough ER, proteins undergoing processing move, via transport vesicles, to the Golgi complex.
• They are processed further and marked for shipment to appropriate cellular locations.
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The Golgi Complex
Figure 4.9
Golgi complex
1. Transport vesicle from RER fuses with Golgi
2. Protein undergoes more processing in Golgi
cisternae
cisternalspace
vesicle
to cytosol
to plasma membrane
for exportout of cell
3. Proteins are sorted and shipped…
Side chains are edited (sugars may be trimmed, phosphate groups added).
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4.5 Cell Structures Outside the Protein Production Path
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Cell Structures Outside the Protein Production Path
• The smooth endoplasmic reticulum is a network of membranes that functions to synthesize lipids and to detoxify potentially harmful substances.
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Lysosomes and Cellular Recycling
• Lysosomes are organelles that break down worn-out cellular structures or foreign materials that come into the cell.
• Once this digestion is completed, the lysosomes return the molecular components of these materials to the cytoplasm for further use.
© 2011 Pearson Education, Inc. Figure 4.10
lysosome
worn-outorganelle
digestiveenzymes
1. Lysosome fuses with worn-out organelle.
2. Organelle broken down.
3. Small molecules returned to cytosol.
4. Waste molecules expelled from cell.
5. Usable molecules recycled to make new organelles.
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Mitochondria and Energy
• Mitochondria are organelles that function to extract energy from food and to transform this energy into a chemical form the cell can use, the molecule ATP.
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outermembrane
innermembrane
watercarbon dioxideATP
foodoxygen
Mitochondrion
Figure 4.11
Mitochondria and Energy
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4.6 The Cytoskeleton: Internal Scaffolding
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The Cytoskeleton: Internal Scaffolding
• Cells have within them a web of protein strands, called a cytoskeleton.
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The Cytoskeleton: Internal Scaffolding
• The cytoskeleton provides the cell with structure, facilitates the movement of materials inside the cell, and facilitates cell movement.
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The Cytoskeleton: Internal Scaffolding
• There are three principal types of cytoskeleton elements.
• Ordered by size, going from smallest to largest in diameter, they are microfilaments, intermediate filaments, and microtubules.
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(a) Microfilaments (in red) (b) Intermediate filaments (c) Microtubules
7 nmMain function: changes in cell shape
10 nm 25 nmMain function: maintenance of cell shape Main functions: maintenance
of cell shape, movement of organelles, cell mobility (cilia and flagella)
Figure 4.12
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Microfilaments
• Microfilaments are made of the protein actin.
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Microfilaments
• They help the cell move and capture prey by forming rapidly in the direction of movement and decomposing rapidly at their other end.
© 2011 Pearson Education, Inc. Figure 4.13
Microfilaments
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Intermediate Filaments
• Intermediate filaments provide support and structure to the cell.
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Microtubules
• Microtubules play a structural role in cells and facilitate the movement of materials inside the cell by serving as transport “rails.”
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Microtubules
• Cilia and flagella are extensions of cells composed of microtubules.
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Cilia
• Cilia extend from cells in great numbers, serving to move the cell or to move material around the cell.
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Flagella
• By contrast, one—or at most a few—flagella extend from cells that have them.
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Flagella
• The function of flagella is cell movement.
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(a) Transport monorails
transportvesicle
motorproteins
microtubule
(c) Flagellum(b) Cilia
Figure 4.14
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4.7 The Plant Cell
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Tour of a Plant Cell
Suggested Media Enhancement:
Tour of a Plant Cell
• To access this animation go to folder C_Animations_and_Video_Filesand open the BioFlix folder.
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The Plant Cell
• Plant cells have most of the structures found in animal cells—ribosomes, a cell nucleus, a rough ER, and so forth—although plant cells do not have the lysosomes found in animal cells.
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The Plant Cell
• Plant cells have three structures not found in animal cells: • a cell wall• a large central vacuole• the organelles called chloroplasts
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cell wall
chloroplast
central vacuole
cytoskeleton
Plant cells have a cell wall, chloroplasts, and a central vacuole, while animal cells do not.
nuclear envelopenuclear poresDNAnucleolus
nucleus
rough endoplasmicreticulum
smooth endoplasmicreticulum
free ribosomes
Golgi complexcytosol
plasma membrane
mitochondrion
Figure 4.17
The Plant Cell
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The Central Vacuole
• The central vacuole stores nutrients and degrades waste products.
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The Cell Wall
• The cell wall gives the plant structural strength and helps regulate the intake and retention of water.
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Chloroplasts
• Chloroplasts are the sites of photosynthesis.
© 2011 Pearson Education, Inc. Figure 4.19
Chloroplasts
watercarbon dioxide
minerals
outer membrane
inner membrane
sugar (food)oxygen
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Animation 4.1: The Structure of Cells
The Structure of Cells
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4.8 Cell-to-Cell Communication
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Cell-to-Cell Communication
• Cells are able to communicate with each other through special structures.
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Communication Among Plant Cells
• Plant cells have channels, called plasmodesmata, that are always open and hence have the effect of making the cytoplasm of one plant cell continuous with that of another.
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Communication Among Animal Cells
• Adjacent animal cells have channels, called gap junctions, that are composed of protein assemblages that open only as necessary.
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Communication Among Animal Cells
• These gap junctions allow the movement of small molecules and electrical signals between cells.
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Plant tissues
Animal tissues gap junction
plasmamembranes
cytoplasm
cytoplasm
plasmamembranecell walls
plasmodesmata
(a) Plasmodesmata
In plants, a series of tiny pores between plant cells, the plasmodesmata, allow for the movement of materials amongcells. Thanks to the plasmodesmata channels, the cytoplasm of one cell iscontinuous with the cytoplasm of the next; the plant as a wholecan be thought of as having a single complement of continuous cytoplasm.
(b) Gap junctions
In animals, protein assemblies come into alignment with one another, forming communication channels between cells. A cluster of many suchassemblies—perhaps severalhundred—is called a gapjunction.
Figure 4.20
© 2011 Pearson Education, Inc. Table 4.1
Table 4.1
Structures in Plant and Animal Cells
Name Function and Location Name Function and Location
NucleusSite of most of the cell’s DNALocation: Inside nuclear envelope
Synthesis of ribosomal RNALocation: Nucleus
Sites of protein synthesisLocation: Rough ER, Free-standing incytoplasm
Maintains cell shape, facilitates cellmovement and movement of materialswithin cellLocation: Cytoplasm
Protein-rich fluid in which organelles andcytoskeleton are immersedLocation: Cytoplasm
Processing, sorting of proteinsLocation: Cytoplasm
Digestion of imported materials and cell’sown used materialsLocation: Cytoplasm
Mitochondria
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
Vesicles
Central vacuole (in plant cells only)
Chloroplasts (in plant cells only)
Cell walls(in plant cells only)
Transform energy from foodLocation: Cytoplasm
Protein processingLocation: Cytoplasm
Lipid synthesis, storage; detoxification ofharmful substancesLocation: Cytoplasm
Transport of proteins and other cellularmaterialsLocation: Cytoplasm
Nutrient storage, cell pressuremaintenance, pH balanceLocation: Cytoplasm
PhotosynthesisLocation: Cytoplasm
Limit water uptake; maintain cellmembrane shape, protect from outsideinfluencesLocation: Outside plasma membrane
Nucleolus
Ribosomes
Cytoskeleton
Cytosol
Golgi complex
Lysosomes (in animal cells only)