The Cell Flashcards
The ____________ occurs only in eukaryotic cells, and houses many different types of nucleic acids–the more famous ones being DNA and RNA.
Nucleus. A cell that contains a distinct nucleus is known as a eukaryotic cell, as opposed to a prokaryotic cell (no nucleus). RNA moves out into the cytoplasm ( what lies between the nucleus and the cell wall).
The __________ is an area of the nucleus where ribosomes are constructed.
Nucleolus. There are usually two nucleoli per nucleus.
The nuclear envelope is a double-membrane structure. Numerous pores occur in the envelope, allowing RNA and other chemicals to pass, but not allowing ______ to pass.
DNA. DNA is restricted to the nucleus.
The nucleus of the average human cell is only six micrometers (6 ´ 10-6 meter) in diameter, yet it contains about 1.8 meters of DNA. This is distributed among 46 _____________, each consisting of a single DNA molecule about 40 millimeters (1 1/2 inches) long.
Chromosomes. It’s an extraordinary packaging problem. If you enlarge this by a million times, a DNA molecule would still be a thin string two millimeters thick, and the average chromosome would contain 40 kilometers (25 miles) of DNA. At this magnification, with a diameter of only six meters, the nucleus would contain 1,800 kilometers of DNA.
DNA is not simply crammed into the nucleus; it is organized, by molecular interaction with specific nuclear proteins, into a precisely packaged structure, creating a dense, compact fiber called_____________.
Chromatin. An extreme example of the ordered folding and compaction that chromatin can undergo is seen during cell division, when the chromatin of each chromosome condenses and is divided between two daughter cells.
The _________ maintains the shape of the cell as well as anchoring organelles, moving the cell and controlling internal movement of structures.
Cytoskeleton. The cytoskeleton consists of fibrous proteins that occur in the cytoplasm. The cytoplasm was defined earlier as the material between the plasma membrane (cell membrane) and the nuclear envelope.
______________ are made up of globular proteins called tubulins. They play an important role in cell division (mitosis) and serve as a “temporary scaffolding” for other organelles.
Microtubules. They participate in the formation of spindle fibres during cell division (mitosis). They help give shape to many cells and are major components of cilia and flagella, the ‘limbs’ that enable cell movement.
________________ are single-membrane organelles located within the cell–a space within a cell that is empty of cytoplasm, lined with a membrane, and filled with fluid.
Vacuoles. Many organisms will use vacuoles as storage areas. “Vesicles” are much smaller than vacuoles and function in transport within and to the outside of the cell.
___________ are the sites of protein synthesis. It is inside them that the information carried in the genetic code is converted into protein molecules.
Ribosomes. Made up of 40% protein and 60% RNA, they are not membrane-bound and thus occur in both prokaryotes (no membrane bound organelles and no distinct membrane-bound nucleus) and eukaryotes (distinct, membrane-bound nucleus). Eukaryotic ribosomes are slightly larger than prokaryotic ones.
Often ribosomes cluster on the ____________ reticulum (ER), in which case they resemble a series of factories adjoining a railroad line.
Endoplasmic. The ER usually constitutes more than half of the membrane of the cell and is continuous with the outer membrane of the nuclear envelope.
___________ are the shipping containers within cells.
Vesicles. Vesicles are used to package liquids containing a wide variety of substances and carry these materials to other parts of the cell or to the outside of the cell. Vesicles also form around material (liquid or solid) that is brought into the cell.
_______ __________ are flattened stacks of membrane-bound sacs. They function as a packaging plant, modifying vesicles from the ER (Endoplasmic Reticulum).
Golgi Complexes. The function of the Golgi apparatus (another name for golgi complex) is two-fold: First, modification of lipids and proteins; Second, storage and packaging of materials that will be exported from the cell.
Lysosomes are relatively large vesicles formed by the Golgi. They contain hydrolytic ____________ that could destroy the cell were they not safely contained inside the vesicle.
Enzymes. Lysosomes are a special type of vesicle which contain these potent enzymes. These enzymes within the lysosomes are acid hydrolases, responsible for the cell’s digestion of macromolecules, old cell parts, and microorganisms.
When members of two different species enter into a living relationship, the arrangement is known as ___________.
Symbiosis. These are classified into mutualism, commensalism, and parasitism. Both positive (beneficial) and negative (unfavorable to harmful) associations are therefore included, and the members are called symbionts.
A long time ago (perhaps even a billion years), bacteria-like organisms are thought to have been incorporated into eukaryotic cells by some kind of symbiosis. Today, these organelles–the ___________– are known as the powerhouse of the cell.
Mitochondria. They contain their own DNA (termed mDNA) and function as the sites of energy release (following glycolysis in the cytoplasm) and respiration.
Remember: Mitochondria are the powerhouse of the cell.
During the 1980s, Lynn Margulis proposed the theory of ____________ to explain the origin of mitochondria and chloroplasts from permanent resident prokaryotes.
Endosymbiosis. According to this idea, a larger prokaryote (or perhaps early eukaryote) engulfed or surrounded a smaller prokaryote some 1.5 billion to 700 million years ago. Instead of digesting the smaller organisms, the large one and the smaller one entered into a type of symbiosis known as mutualism, wherein both organisms benefit and neither is harmed.
Chloroplasts are the sites of ______________ in eukaryotes. They contain many different types of accessory pigments, depending on the organism being observed.
Photosynthesis. The pigments are inside sacs called thylakoids which float in a fluid called stroma.
Obviously chloroplasts are only going to be found in autotrophs (organisms that create their own energy i.e. plants), as opposed to heterotrophs (organisms that obtain energy from another organism i.e. humans).
Like mitochondria, chloroplasts have their own ______. This is why chloroplasts of Green Algae (Protista) and Plants (descendants of some Green Algae) are thought to have originated by endosymbiosis of a prokaryotic alga similar to living Prochloron (Prochlorobacteria).
DNA. The DNA of chloroplasts are termed cpDNA.
Chloroplasts are one of the three types of _________. The other types are 1)Leukoplasts which store starch, and sometimes protein or oils, and 2) Chromoplasts which store pigments associated with the bright colors of flowers and/or fruits.
Plastids. Plastids are round, oval, or disk-shaped bodies which occur only in plants and photosynthetic eukaryotes.
Internal movements of organelles within a cell are governed by __________ filaments. Internal movement is known as cytoplasmic streaming.
Actin. These filaments make an area in which organelles such as chloroplasts can move.
External movement of cells is determined by special organelles for locomotion. __________ work as whips pulling or pushing the organism through the water.
Flagella. A shorter kind of whip is cilia. Cilia work like oars on a viking longship (Paramecium has 17,000 such oars covering its outer surface).
As you can see above, one of the cells uses whip-like flagella for movement, and the other one uses thousands of hair-like cilia to propel itself through the liquid.
Both cilia and flagella have the characteristic __________ arrangement of microtubules.
9 + 2. See figure below.
Microtubules are straight, hollow cylinders which participate in a wide variety of cell activities–most of which involve motion. Cilia and flagella are constructed from microtubules, and it is important to remember that it is called a 9+2 arrangement.