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5
THE CELL: AN OVERVIEW
Chapter Outline
5.1 BASIC FEATURES OF CELL STRUCTURE AND FUNCTION
Cells are small and are visualized using a microscope
Cells have a DNA-containing central region that is surrounded by the cytoplasm
Cells occur in prokaryotic and eukaryotic forms, each with distinctive structures and organization
5.2 PROKARYOTIC CELLS
Prokaryotic cells have little or no internal membrane structure
5.3 EUKARYOTIC CELLS
Eukaryotic cells have a membrane-enclosed nucleus and cytoplasmic organelles
The eukaryotic nucleus contains much more DNA than the prokaryotic nucleoid
An endomembrane system divides the cytoplasm into functional and structural compartments
Mitochondria are the powerhouses of the cell
Microbodies carry out vital reactions that link metabolic pathways
The cytoskeleton supports and moves cell structures
Flagella propel cells, and cilia move materials over the cell surface
5.4 SPECIALIZED STRUCTURES OF PLANT CELLS
Chloroplasts are biochemical factories powered by sunlight
Central vacuoles have diverse roles in storage, structural support, and cell growth
Cell walls support and protect plant cells
5.6 THE ANIMAL CELL SURFACE
Cell adhesion molecules organize animal cells into tissues and organs
Cell junctions reinforce cell adhesions and provide avenues of communication
The extracellular matrix organizes the cell exterior
Learning Objectives
After reading the chapter, you should be able to:
1.
Understand the basic tenets of the cell theory.
2.
Understand the implications of how the surface-to-volume ratio constrains cell size.
3.
Compare and contrast the general features of prokaryotic and eukaryotic cells.
4.
Be able to distinguish the organelles and structures typical of eukaryotic plant and animal cells.
5.
Describe the nucleus of eukaryotes with respect to structure and function.
6.
Describe the organelles associated with the endomembrane system, tell the general function of each, and evaluate
the importance of the continuous nature of the endomembrane system.
7.
Contrast the structure and function of mitochondria and chloroplasts.
8.
List several surface structures of cells and describe how they help with cellular survival and function.
9.
Describe the cytoskeleton of eukaryotes and distinguish it from the endomembrane system.
10. Discuss the various mechanisms that enable a cell to move.
Key Terms
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Chapter Five
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cell theory
nuclear envelope
microscopy
nuclear pores
outer mitochondrial
membrane
thylakoids
inner mitochondrial
membrane
plastids
grana
microscope
nucleoplasm
light microscope
chromatin
electron microscopes
magnification
eukaryotic
chromosome
resolution
nucleoli
microbodies
cytoplasm
endomembrane system
peroxisomes
cytosol
endoplasmic reticulum
cytoskeleton
organelles
cisternae
microtubules
plasma membrane
ER lumen
intermediate filaments
prokaryotes
rough ER
microfilaments
nucleoid
smooth ER
cell center
cell adhesion
molecules
eukaryotes
golgi complex
centrosome
cell junctions
cell wall
secretory vesicles
centrioles
extracellular matrix
capsule
exocytosis
basal body
anchoring junctions
prokaryotic
chromosome
endocytosis
chloroplasts
desmosomes
endocytic vesicle
adherens junctions
ribosomes
lysosomes
outer boundary
membrane
flagella
phagocytosis
inner boundary
membrane
gap junctions
prokaryotic flagellum
mitochondria
stroma
cristae
mitochondrial matrix
amyloplasts
chromoplasts
central vacuoles
tonoplast
primary cell wall
secondary cell wall
middle lamella
plasmodesmata
tight junctions
Lecture Outline
A.
B.
C.
D.
Robert Hooke in the mid-1600s coined the term “cells”.
Anton van Leeuwenhoek made microscopes and described a variety of biological systems.
Robert Brown described the nucleus.
Many others contributed to the creation of the cell theory:
1. All organisms are composed of one or more cells.
2. The cell is the smallest unit that has the properties of life.
3. Cells arise only from the growth and division of preexisting cells.
5.1 Basic Features of Cell Structure and Function
A. Cells carry organized molecules and genetic material.
1. Cells use organic fuels for energy.
2. Some are unicellular (bacteria, archaea, and protozoan).
3. Multicellular organisms, both plants and animals, have specialized cells that perform specific
functions.
4. Viruses consist only of a nucleic acid molecule surrounded by a protein coat and cannot carry out all
the activities of life.
B. Cells are small and are visualized using a microscope.
1. Humans cannot see objects smaller than about 0.1 mm without a microscope.
2. Units of measure used in biology can be found in Figure 5.3.
C. Two types of microscopes are used in biology: light and electron.
1. Magnification is the ratio of the object as viewed to its real size.
2. Resolution is the minimum distance two points can be separated and seen as two points.
D. Surface-to-volume ratio limits the size of cells.
E. Flattening or extending their membranes increases the cell’s ability to exchange materials.
F. Cells have DNA surrounded by cytoplasm.
1. DNA codes for genetic traits.
2. Cytoplasm has ions and organic molecules in an aqueous solution.
3. Eukaryotic cells have membrane-bound organelles.
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4. The plasma membrane surrounds the cell and is made of a lipid bilayer.
G. Cells occur in prokaryotic and eukaryotic forms, each with distinctive structures and organization.
1. Prokaryotes (before the nucleus) have no membrane-bound nucleus.
2. Eukaryotes (after the nucleus) have membrane-bound DNA and other organelles.
5.2 Prokaryotic Cells
A. Prokaryotes have little or no internal membrane structure.
1. They have a rigid cell wall surrounded by a slime capsule.
2. Cytoplasm is the location of most metabolic activity.
3. DNA makes RNA, which makes protein.
B. Prokaryotes divide into Bacteria and Archaea.
1. Bacteria and Archaea share some biochemical features.
2. Archaea has some characteristics in common with eukaryotes.
5.3 Eukaryotic Cells
A. Eukaryotic cells have a membrane-bound nucleus and internal organelles.
B. Eukaryotes are divided into protists, fungi, animals, and plants.
C. Eukaryotic cells contain more DNA than prokaryotic cells.
1. The nuclear envelope has nuclear pores that open between both layers.
2. The nucleus contains chromatin, a mixture of DNA and protein.
3. A chromosome is one complete DNA molecule and associated proteins.
4. Eukaryotes have one or more nuclei.
D. The endomembrane system separates functional and structural compartments.
1. Functions to synthesize proteins
2. Acts as a packaging and transport system
3. Sequestration of toxic chemicals
E. Endoplasmic reticulum
1. Cisternae membrane surrounding a space called a lumen
2. Rough ER (rER) contains many ribosomes for protein synthesis.
3. Proteins formed are chemically modified in the lumen.
4. Smooth ER (sER) produces lipids and breaks down toxins.
5. rER and sER are often continuous systems.
F. Golgi complex
1. Membranous sacs without attached ribosomes
2. Chemical modification and packaging occurs in the Golgi complex (GC).
3. It regulates movement and placement of many proteins.
4. The GC is involved in endocytosis of external substances.
G. Lysosomes
1. Membrane vessicle that contains hydrolytic enzymes for digestion and protection
2. Acidic pH found in lysosomes
3. Important to phagocytosis
H. Mitochondria are the powerhouses of the cell.
1. Cellular respiration or the breakdown of organic molecules to produce energy occurs in mitochondria.
2. This process requires oxygen.
3. Folds of the inner membrane form cristae.
I. Microbodies link vital metabolic pathways.
1. Small simple membrane structures
2. NOT produced by ER or GC
3. Often-preparatory step to metabolic processes
J. Cytoskeleton supports and moves cell structures.
1. Fibers and tubes provide structure.
2. Microtubules (Figure 5.19a), intermediate filaments, and microfilaments are all made of assembled
proteins.
3. A eukaryotic cell moves by “motor” proteins that push or pull against the cytoskeleton.
K. Flagella and cilia are eukaryotic propellers.
1. The structure extends to the tip of cilia and flagella.
2. 9 + 2 complex allows movement.
5.4 Specialized Structures of Plant Cells
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A. Chloroplasts are biochemical factories powered by sunlight.
1. Membranes surround stroma and thylakoids.
2. Chlorophyll is the primary pigment that makes carbohydrates from carbon dioxide and water.
3. Amyloplasts are structures that store starch.
B. Central vacuoles function for storage, structure, and growth.
1. Tonoplasts are transport membranes of the central vacuole.
2. Central vacuoles store salts, sugars, enzymes, and other proteins.
C. Cell walls support and protect.
1. Cell walls are made of cellulose.
2. The primary cell wall is soft and flexible.
3. The secondary cell wall is reinforced with lignin and becomes tough and rigid.
4. Adjacent cells are held together by the lamella.
5. Plasmadesmata are perforations that connect adjacent cells.
6. Fungal cells use chitin instead of cellulose.
5.5 The Animal Cell Surface
A. Cells are held together by cell adhesion molecules.
B. Cell or gap junctions connect adjacent cells.
C. Cell adhesion molecules organize tissues and organs.
1. Cancer cells lose adhesion molecules.
2. Bacteria and viruses target these adhesion molecules.
D. Cell junctions reinforce cell adhesions.
1. Desmosomes use microfilaments.
2. Tight junctions seal the space between two cells.
3. Gap junctions open channels between cells for ion transport.
E. The extracellular matrix organizes the cells exterior.
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