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.
ER Lumen / cisternal space
The internal compartment of the ER
-Is separated from the cytosol
Two regions of the ER
Smooth ER
Rough ER
Smooth ER is so named because…
Its outer surface lacks ribosomes.
Rough ER is so named because…
It is studded with ribosomes on the outer surface of the membrane and thus appears rough through the electron microscope.
Functions of smooth ER
Synthesis of lipids
Metabolism of carbohydrates
Detoxification of drugs and poisons
Storage of calcium ions
Steroids produced by smooth ER
Sex hormones
Steroid hormones secreted by the adrenal glands
Detoxification usually involves…
Adding hydroxyl groups to drug molecules, making them more soluble and easier to flush from the body.
Smooth ER helps detoxify drugs and poisons, especially in…
Liver cells
Smooth ER stores calcium, particularly in what cells?
Muscle cells
Glycoproteins
Proteins with carbohydrates covalently bonded to them.
-Secretory proteins
How are glycoproteins made?
Polypeptide chain is threaded into the ER lumen.
Secretory proteins are separated from proteins that will remain in the cytosol by the ER membrane.
True
Secretory proteins depart from the ER wrapped the membranes of _________ from a specialized region called _______
vesicles, transitional ER
Transport vesicles
Vesicles in transit from one part of the cell to another.
In addition to making secretory proteins, rough ER is a membrane factory for the cell.
True
After leaving the ER, many transport vesicles travel to the _______
Golgi apparatus
What happens in the Golgi apparatus?
Products of the ER, such as proteins, are modified and stored and then sent to other destinations.
The Golgi apparatus consists of…
Cisternae
Vesicles in the vicinity of the Golgi apparatus are enhanced in…
The transfer of material between parts of the Golgi and other structures.
The two sides of a Golgi stack
Cis face “on the same side”
Trans face “on the opposite side”
The cis face is usually located
Near the ER
The trans face gives rise to…
Vesicles that pinch off and travel to other sites.
Products of the ER are usually modified during their transit from the ________ to the _______ of the Golgi apparatus.
cis region, trans region
Golgi apparatus also manufactures some macromolecules
True
What does the cisternal maturation model state about the Golgi apparatus?
The cisternae of the Golgi actually progress forward from the cis to the trans face, carrying and modifying their cargo as they move.
A Golgi stack dispatches its products by budding vesicles from the trans face. Before this, it sorts these products and targets them for various parts of the cell using ________
Molecular identification tags, such as phosphate groups
Lysosome
Is a membranous sac of hydrolytic enzymes that many eukaryotic cells use to digest (hydrolyze) macromolecules.
Lysosomal enzymes work best in…
The acidic environment found in lysosomes.
Phagocytosis
A type of endocytosis in which large substances or small organisms are taken up by a cell.
How is a food vacuole made?
Through phagocytosis.
How does a food vacuole digest food?
The food vacuole fuses with a lysosome, whose enzymes digest the food.
Autophagy
A process where lysosomes use their hydrolytic enzymes to recycle the cell’s own organic material.
Vacuoles
Are large vesicles derived form the endoplasmic reticulum and Golgi apparatus.
Types of vacuoles
Food vacuoles
Contractile vacuoles
Central vacuole
Contractile vacuole
Pumps excess water out of the cell.
How does a central vacuole develop?
By the coalescence of smaller vacuoles.
Cell sap
Solution inside the central vacuole
Mitochondria
Are the sites of cellular respiration, the metabolic process that uses oxygen to drive the generation of ATP by extracting energy from sugars, fats, and other fuels.
Chloroplasts
Are the sites of photosynthesis. The process that converts solar energy to chemical energy by absorbing sunlight and using it to drive the synthesis of organic compounds such as sugars from carbon dioxide and water.
Endosymbiont
A cell living within another cell.
Endosymbiont theory
This theory states that an early ancestor of eukaryotic cells engulfed an oxygen-using non-photosynthetic prokaryotic cell. Eventually, the engulfed cell formed a relationship with the host cell in which it was enclosed, becoming an endosymbiont.
Cristae
Foldings in the inner membrane of the mitochondria.
Each of the two membranes enclosing a mitochondrion is a _________
Phospholipid bilayer
Intermembrane space
The narrow region between the inner and outer membrane
The inner membrane divides the mitochondrion into two internal compartments:
Intermembrane space
Mitochondrial matrix
Mitochondrial matrix
Is enclosed by the inner membrane. Contains many different enzymes as well as the mitochondrial DNA and ribosomes.
How long is a mitochondrion?
1-10 micrometers long
Mitochondria in a living cell form a branched tubular network
True
Length of chloroplast
3-6 micrometers
Thylakoids
Membranous system in the form of flattened, interconnected sacs
Granum (plural grana)
Stack of thylakoids
Stroma
Fluid outside the thylakoids. Contains the chloroplast DNA and ribosomes as well as many enzymes.
The membranes of the chloroplast divide the chloroplast space into three compartments:
The Intermembrane space
The stroma
The thylakoid space
The chloroplast is a specialized member of a family of closely related plant organelles called______
Plastids
Examples of plastids
Chloroplast
Amyloplast
Chromoplast
Peroxisome
Is a specialized metabolic compartment bounded by a single membrane.
What does a peroxisome do?
Peroxisomes contain enzymes that remove hydrogen atoms from various substrates and transfer them to oxygen (O2), producing hydrogen peroxide (H2O2) as a by-product (from which the organelle derives its name).
Functions of peroxisomes
Break down fatty acids
Detoxify alcohol / other harmful compounds
Glyoxysomes
Specialized peroxisomes found in fat-storing tissues of plant seeds
Cytoskeleton
A network of fibers extending throughout the cytoplasm.
The eukaryotic cytoskeleton is composed of three types of molecular structures:
Microtubules
Microfilaments
Intermediate filaments
Primary function of the cytoskeleton
Give mechanical support to the cell and maintain its shape.
The cytoskeleton can be quickly dismantled in one part of the cell and reassembled in a new location, changing the shape of the cell
True
All eukaryotic cells have microtubules
True
Microtubules
Hollow rods constructed from a globular protein called tubilin.
What is a dimer?
A molecule made up of two subunits.
Microtubules grow in length by adding ______
Tubulin dimers
Two types of tubulin dimers
Alpha tubulin
Beta tubulin
The two ends of a microtubule are slightly different
True
“Plus end”
The end of the microtubule that can accumulate or release tubulin dimers rapidly
Function of microtubules
Shape and support the cell
-Serve as tracts where organelles with motor proteins can move
-Guide vesicles from the ER to the Golgi apparatus
-Involved in cell division
Centrosomes
The region where Microtubules grow out of in animal cells.
-Located near the nucleus
Centrioles
Within the centrosome is a pair of centrioles, each composed of nine sets of triplet microtubules arranged in a ring.
Primary cilium
Cilium that act as a signal-receiving “antenna” for the cell.
Specialized arrangement of Microtubules responsible for movement (beating)
Flagella
Cilia
Common structure between motile cilia and flagella
The “9+2” pattern
Nine doublets of microtubules are arranged in a ring, with two single microtubules in its center.
Nonmotile primary cilia have a “9+0” pattern
True
The microtubule assembly of a cilium or flagellum is anchored in the cell by a _________
Basal body
The basal body is structurally very similar to a centriole
True
Bending involves large motor proteins called _________
Dyneins
Microfilaments
Are thin solid rods. Is a twisted double chain of actin subunits.
AKA actin filaments.
-Present in all eukaryotic cells.
Structural role of microfilaments
To bear tension (pulling forces).
Cortex
The outer cytoplasmic layer of a cell.
Cortical microfilaments
Helps support the cell’s shape and gives the cortex the semisolid consistency of a gel.
The cell crawls along a surface by extending cellular extensions called _________
Pseudopodia
Cytoplasmic streaming
A circular flow of cytoplasm within cells.
Intermediate filaments are named for their…
Diameter, which is larger than the diameter of Microfilaments but smaller than that of microtubules.
Intermediate filaments are only found in the cells of some animals, including vertebrates.
True
Intermediate filaments are specialized for…
Bearing tension (like Microfilaments)
Even after cells die, intermediate filament networks often persist.
True
Cell wall
Protects the plant cell, maintains its shape, and prevents excessive uptake of water.
Plant cell wall thickness
0.1 micrometers to several micrometers
Structure of cell wall
Microfibrils made of cellulose embedded in a matrix of other polysaccharides and proteins.
Primary cell wall
A relatively thin and flexible wall. Secreted by young plant cells.
Middle lamella
A thin layer rich in sticky polysaccharides called pectins. The middle lamella glues adjacent cells together.
Secondary cell wall
A wall between the plasma membrane and the primary wall.
-Offers protection and support to the cell.
Ingredients of an animal cell’s extracellular matrix (ECM)
Glycoproteins and other carbohydrate-containing molecules secreted by the cells.
Most abundant glycoprotein in the ECM
Collagen, which forms strong fibers outside the cells.
Proteoglycans
A proteoglycan molecule consists of a small core protein with many carbohydrate chains covalently attached, so that it may be up to 95% carbohydrate.
Integrins
Are cell-surface receptor proteins that are built into the plasma membrane
Plasmodesmata
Channels that connect cells.
Three main types of cell junctions
Tight junctions
Desmosomes
Gap junctions
Tight junctions
Establish a barrier that prevents leakage of extracellular fluid across a layer of epithelial cells.
Desmosomes
Fasten cells together into strong sheets. For example, some “muscle tears” involve the rupture of Desmosomes.
Gap junctions (communicating junctions)
Provide cytoplasmic channels from one cell to an adjacent cell.
