Chapter 6 Flashcards
What year were microscopes invented?
1590 and further refined during the 1600s
Cell walls were first seen by…
Robert Hook in 1665
-They were from the bark of an oak tree
Light Microscope (LM)
In a LM, visible light is passed through the specimen and then through glass lenses.
Three important parameters in microscopy:
Magnification
Resolution
Contrast
Magnification
Is the ratio of an object’s image size to its real size.
Light microscopes can magnify effectively to about _____ times the actual size of the specimen
1,000
Resolution
-Is a measure of the clarity of the image
- It is the minimum distance two points can be separated and still be distinguished as separate points.
The light microscope cannot resolve detail finer than about _____________ or ___________
0.2 micrometer, 200 nanometers
Contrast
Is the difference in brightness between the light and dark areas of an image.
Methods for enhancing contrast
Staining or labeling cell components to stand out visually.
Organelles
The membrane-enclosed structures within eukaryotic cells.
When was the electron microscope introduced to biology?
1950s
Electron microscope (EM)
The EM focuses a beam of electrons through the specimen or onto its surface.
Resolution is inversely related to…
The wavelength of the light (or electrons) a microscope uses for imaging.
Electron beams have much shorter wave lengths than visible light.
True
Modern electron microscopes can theoretically achieve a resolution of about _____
0.002 nm (nanometers)
The scanning electron microscope (SEM) is especially useful for…
Detailed study of the topography of a specimen.
How does a SEM work?
-The electron beam scans the surface of the sample, usually coated with a thin film of gold.
- The beam excites the electrons on the surface.
- The patterns of electrons are translated into an electronic signal sent to a video screen
- An image of the specimen’s surface appears in 3-dimensions.
The transmission electron microscope (TEM) is used to…
Study the internal structure of cells.
How does a TEM work?
-The specimen is stained with heavy metals, which attach to certain cellular structures, thus enhancing the electron density of some parts of the cell.
- The electron beam is scattered in the denser regions.
- The image displays the pattern of transmitted electrons.
Instead of using glass lenses, the SEM and TEM use…
Electromagnets
Disadvantage of electron microscopy
The methods used to prepare the specimen kill the cells.
Super-resolution microscopy
Technique that allows LM to break the limit of resolution.
Cytology
The study of cell structure.
Biochemistry
The study of chemical processes (metabolism) of cells.
Cell fractionation
Takes cells apart and separates major organelles and other subcellular structures from one another.
Centrifuge
-Used for cell fractionation
-Spins test tubes holding mixtures of cells at a series of increasing speeds.
A pellet
Subset of cell components at the bottom of the tube in a centrifuge.
At lower speeds, the pellet consists of …
Larger components
At higher speeds, the pellet consists of …
Smaller components
All cells share certain basic features:
-Are all bounded by a selective barrier, the plasma membrane
-Inside all cells is a semifluid substance, the cytosol
-All contain chromosomes
-All have ribosomes
Where is the DNA of a eukaryotic cell?
In the nucleus.
Where is the DNA of a prokaryotic cell?
In a region called the nucleoid.
Cytoplasm in eukaryotic cells
The region between the nucleus and the plasma membrane.
-Is suspended in cytosol
Mycoplasmas
Bacteria with diameters between 0.1 and 1.0 micrometers
Eukaryotic cells are typically _____________ in diameter.
10-100 micrometers
Prokaryotic cytoplasm appears to be organized into different regions.
True
Plasma membrane
Functions as a selective barrier that allows passage of enough oxygen, nutrients, and wastes to service the entire cell.
Why is the ratio of surface area to volume critical?
Because for each square micrometer of membrane, only a limited amount of a particular substance can cross per second.
As a cell increases in size,…
It’s surface area grows proportionately less than its volume.
A smaller object has a greater ratio of surface area to volume.
True
Total surface area =
Sum of the surface areas of all box sides X number of boxes
Surface area =
Height X Width
Total volume =
Height X Width X Length X Number of boxes
Microvilli
Projections that increase surface area without an appreciable increase in volume.
Nucleus
Contains most of the genes in the eukaryotic cell.
Average diameter of a nucleus
About 5 micrometers
Nuclear envelope
Encloses the nucleus, separating its contents from the cytoplasm.
The nuclear envelope is a double membrane
True
The two membranes of a nuclear envelope are separated by a space of…
20-40 nm (nanometers)
Pore structures in the nuclear envelope have a diameter of…
100 nm
Pore complex
A protein structure that lines each pore and plays an important role in the cell by regulating the entry and exit of proteins and RNAs, as well as large complexes of macromolecules.
Nuclear lamina
A netlike array of protein filaments that maintains the shape of the nucleus by mechanically supporting the nuclear envelope.
(Does not affect pores)
Nuclear matrix
A framework of protein fibers extending throughout the nuclear interior.
Chromatin
The complex of DNA and proteins making up chromosomes.
Nucleolus
A prominent structure within the non dividing nucleus.
Where is ribosomal RNA (rRNA) synthesized?
In the nucleolus from instruction in the DNA.
How are ribosomes formed?
In the nucleolus, proteins imported from the cytoplasm are assembled with rRNA into a large and a small subunit of ribosomes.
- The large and small subunits layer assemble into a ribosome after they exit through the nuclear pores to the cytoplasm.
Ribosomes
Are the cellular complexes that carry out protein synthesis.
-Not membrane bound, thus not considered organelles.
Free ribosomes
Are suspended in the cytosol.
Bound ribosomes
Are attached to the outside of the endoplasmic reticulum or nuclear envelope.
Ribosomes can alternate between free and bound
True
Bound ribosomes generally make proteins that are destined for…
Insertion into membranes, for packaging within certain organelles such as lysosomes, or for export from the cell (secretion).
Endomembrane system includes:
Nuclear Envelope
Endoplasmic Reticulum
Golgi apparatus
Lysosomes
Various kinds of vesicles and vacuoles
Plasma membrane
Endomembrane system functions
Synthesis of proteins
Transport of proteins
Metabolism and movement of lipids
Detoxification of poisons
Vesicles
Sacs made of membrane
How are the organelles in the Endomembrane system related?
Through direct physical continuity or by the transfer of membrane segments as tiny vesicles.
The endoplasmic reticulum is such an extensive network of membranes that it accounts for more than half the total membranes in many eukaryotic cells.
True
Cisternae
A network of membranous tubules and sacs.
