Chapter 7 a tour of the cell
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CHAPTER 7 A TOUR OF THE CELL. Section A: How We Study Cells 1. Microscopes provide windows to the world of the cell Cell biologists can isolate organelles to study their function. Objectives. Distinguish between prokaryotic and eukaryotic cells

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CHAPTER 7 A TOUR OF THE CELL

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Chapter 7 a tour of the cell

CHAPTER 7A TOUR OF THE CELL

Section A: How We Study Cells

1. Microscopes provide windows to the

world of the cell

Cell biologists can isolate organelles to study

their function


Objectives

Objectives

  • Distinguish between prokaryotic and eukaryotic cells

  • Explain why there are upper and lower limits to cell size

  • Explain the function of compartmentalization in eukaryotic cells


Chapter 7 a tour of the cell

  • Describe the structure and function of the nucleus

  • Describe the structure and function of the eukaryotic ribosome

  • List the components of the endomembrane system, describe their structures and functions and summarize the relationships among them

  • Describe the types of vacuoles and how their functions differ


Chapter 7 a tour of the cell

  • Explain the role of peroxisomes in eukaryotic cells

  • Describe the structure of a typical mitochondrion, detail its function and explain how compartmentaliztion in the mitochondrion is important to this function

  • Explain the structure and functioning of the chloroplast


Chapter 7 a tour of the cell

  • Describe the functions of the cytoskeleton and distinguish among microtubules, microfilaments and intermediate filaments

  • Describe the structure of flagella and cilia and briefly summarize the relationship between this structure and their functioning


1 microscopes provide windows to the world of the cell

1. Microscopes provide windows to the world of the cell

  • The discovery and early study of cells progressed with the invention and improvement of microscopes in the 17th century.

  • In a light microscope (LMs) visible lightpasses through the specimen and then through glass lenses.

    • The lenses refract light such that the image is magnified into the eye or a video screen.

    • A light microscope can be used to resolve individual cells


Chapter 7 a tour of the cell

  • Microscopes vary in magnification and resolving power.

  • Magnification is the ratio of an object’s image to its real size.

  • Resolving power is a measure of image clarity.

    • It is the minimum distance two points can be separated and still viewed as two separate points.

    • Resolution is limited by the shortest wavelength of the source, in this case light.


Chapter 7 a tour of the cell

  • The minimum resolution of a light microscope is about 2 microns, the size of a small bacterium

  • Light microscopes can magnify effectively to about 1,000 times the size of the actual specimen.

    • At higher magnifications, the image blurs.

Fig. 7.1


Chapter 7 a tour of the cell

  • A light microscope can resolve individual cells but it cannot resolve much of the internal anatomy, especially the organelles.

  • To resolve smaller structures we use an electron microscope (EM), which focuses a beam of electrons through the specimen or onto its surface.

    • the practical limit of a modern EM is about about 2 nm (the size of a single rhinovirus).


Chapter 7 a tour of the cell

  • Transmission electron microscopes (TEM) are used mainly to study the internal ultrastructure of cells.

    • A TEM aims an electron beam through a thin section of the specimen.

    • The image is focused and magnified by electromagnets.

    • To enhance contrast, the thin sections are stained with atoms of heavy metals.

Fig. 7.2a


Chapter 7 a tour of the cell

  • Scanning electron microscopes (SEM) are useful for studying surface structures.

    • The sample surface is covered with a thin film of gold.

    • The beam excites electrons on the surface.

    • These secondary electrons are collected and focused on a screen.

  • The SEM has great depth of field, resulting in an image that seems three-dimensional.

Fig. 7.2b


Chapter 7 a tour of the cell

  • Electron microscopes reveal organelles, but they can only be used on dead cells and they may introduce some artifacts.

  • Light microscopes do not have as high a resolution, but they can be used to study live cells.

  • Microscopes are a major tool in cytology, the study of cell structures.

  • Cytology + biochemistry = modern cell biology.


Cell theory

Cell Theory

  • All known living things are made up of cells.

  • The cell is structural & functional unit of all living things.

  • All cells come from pre-existing cells by division. (Spontaneous Generation does not occur).

    1838: Schleiden and Schwann proposed cell theory

    These first three are the very basic foundations of Cell Theory. All six

    of these components make up modern Cell Theory

  • Cells contains hereditary information which is passed from cell to cell during cell division.

  • All cells are basically the same in chemical composition.

  • All energy flow (metabolism & biochemistry) of life occurs within cells.    


2 cell biologists can isolate organelles to study their functions

2. Cell biologists can isolate organelles to study their functions

  • The goal of cell fractionation is to separate the major organelles of the cells so that their individual functions can be studied.


Chapter 7 a tour of the cell

  • Uses an ultracentrifuge, a machine that can spin at up to 130,000 revolutions per minute and apply forces more than 1 million times gravity (1,000,000 g).

  • Fractionation begins with homogenization, gently disrupting the cell.

  • Then, the mixture is spun in a centrifuge to separate heavier pieces into the pellet while lighter particles remain in the solution.

    • As the process is repeated at higher speeds and longer durations, smaller and smaller organelles can be collected in subsequent pellets.


Chapter 7 a tour of the cell

  • Cell fractionation prepares quantities of specific cell components.

  • The functions of these organelles to be isolated, especially by the reactions or processes catalyzed by their proteins.

    • For example, one cellular fraction is enriched in enzymes that function in cellular respiration.

    • Electron microscopy reveals that this fraction is rich in the organelles called mitochondria.

  • Cytology and biochemistry complement each other in connecting cellular structure and function.


Section b a panoramic view of the cell

Section B: A Panoramic View of the Cell

1.Prokaryotic and eukaryotic cells differ in size and complexity

2.Internal membranes compartmentalize the functions of a eukaryotic cell


1 prokaryotic and eukaryotic cells differ in size and complexity

1. Prokaryotic and eukaryotic cells differ in size and complexity

  • All cells are surrounded by a plasma membrane. (What is this made of?)

  • The “liquid” inside the membrane is the cytosol, which contains the organelles.

  • All cells contain chromosomes which have genes in the form of DNA.

  • All cells also have ribosomes, organelles that make proteins using the instructions contained in genes.


Chapter 7 a tour of the cell

  • A major difference between prokaryotic and eukaryotic cells is the location of chromosomes.

  • In an eukaryotic cell, chromosomes are contained in a membrane-enclosed organelle, the nucleus.

  • In a prokaryotic cell, the DNA is concentrated in the nucleoid without a membrane separating it from the rest of the cell.


Chapter 7 a tour of the cell

Fig. 7.4 The prokaryotic cell is much simpler in structure, lacking a nucleus and the other membrane-enclosed organelles of the eukaryotic cell.


Cd rom activity 7 1

CD-Rom Activity 7.1

  • This activity will help you to review and gain an understanding of the structures and functions of prokaryotic cells.


Chapter 7 a tour of the cell

  • In eukaryote cells, the chromosomes are contained within a membranous nuclear envelope.

  • The region between the nucleus and the plasma membrane is the cytoplasm. (Sarah, this is for you.)

    • All the material within the plasma membrane of a prokaryotic cell is cytoplasm. (This includes the organelles.)

  • Within the cytoplasm of a eukaryotic cell is a variety of membrane-bounded organelles of specialized form and function.

    • These membrane-bounded organelles are absent in prokaryotes.


Chapter 7 a tour of the cell

  • Eukaryotic cells are generally much bigger than prokaryotic cells.

  • The logistics of carrying out metabolism set limits on cell size.

    • At the lower limit, the smallest bacteria, mycoplasmas, are between 0.1 to 1.0 micron.

    • Most bacteria are 1-10 microns in diameter.

    • Eukaryotic cells are typically 10-100 microns in diameter.


Chapter 7 a tour of the cell

  • Metabolic requirements also set an upper limit to the size of a single cell.

  • As a cell increases in size its volume increases faster than its surface area.

    • Smaller objects have a greater ratio of surface area to volume.

Fig. 7.5


Chapter 7 a tour of the cell

  • The plasma membrane functions as a selective barrier that allows passage of oxygen, nutrients, and wastes for the whole volume of the cell.

Fig. 7.6


Chapter 7 a tour of the cell

  • The volume of cytoplasm determines the need for this exchange.

  • Rates of chemical exchange may be inadequate to maintain a cell with a very large cytoplasm.

  • The need for a large surface to accommodate the volume explains the microscopic size of most cells.

  • Larger organisms do not generally have larger cells than smaller organisms - simply more cells.


2 internal membranes compartmentalize the functions of a eukaryotic cell

2. Internal membranes compartmentalize the functions of a eukaryotic cell

  • A eukaryotic cell has extensive and elaborate internal membranes, which partition the cell into compartments.

  • These membranes also participate in metabolism as many enzymes are built into membranes.

  • The barriers created by membranes provide different local environments that facilitate specific metabolic functions.


Chapter 7 a tour of the cell

  • The general structure of a biological membrane is a double layerof phospholipids with other lipids and diverse proteins.

  • Each type of membrane has a unique combination of lipids and proteins for its specific functions.

    • For example, those in the membranes of mitochondria function in cellular respiration.


Chapter 7 a tour of the cell

Fig. 7.7


Cd rom activity 7 2

CD-Rom Activity 7.2

  • This activity will help you to review and gain an understanding of the structures and functions of animal cells.


Chapter 7 a tour of the cell

Fig. 7.8


Cd rom activity 7 3

CD-Rom Activity 7.3

  • This activity will help you to review and gain an understanding of the structures and functions of plant cells.


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