Cell Structure Flashcards
What name is given to the basic functional and structural unit of all living organisms?
cell
For the AP Biology exam, you’ll want to be familiar with animal and plant cells, as well as the general structure of bacterial cells.
The cell theory, originally composed in 1838, includes three primary tenets. Name them.
- The cell is the basic unit of life.
- All living things are composed of cells, whether one or many.
- All cells arise from other cells.
All cells can be categorized into which two broad groups?
- Prokaryotic cells
- Eukaryotic cells
Prokaryotic cells are generally simpler and include bacterial species. Eukaryotes can range from single-celled organisms (like yeast) to complex animals (like humans).
What main features characterize eukaryotic cells?
They have membrane-bound organelles, including nuclei, and linear chromosomes. They are also larger than prokaryotic cells and differ in specific aspects like flagellum structure.
Eukaryotic cells can comprise either unicellular or multicellular organisms.
What main features characterize prokaryotic cells?
They lack membrane-bound organelles. They generally contain one circular chromosome within a nucleoid region, but can also possess circular plasmids outside the genome.
Prokaryotic cells always comprise unicellular organisms.
How do eukaryotic and prokaryotic cells differ with respect to organelles?
Unlike eukaryotes, prokaryotes lack a nucleus, as well as all membrane-bound organelles.
Note that membrane-bound organelles include mitochondria, lysosomes, the ER, and the Golgi apparatus, but not ribosomes. Prokaryotes do contain ribosomes, a fact that may appear on the AP Biology exam.
How do eukaryotic and prokaryotic organisms differ in their cellular organization?
Prokaryotes are always unicellular, while eukaryotes can be either unicellular or multicellular.
One common example of a unicellular eukaryote is yeast, a fungus. Most other single-celled eukaryotes are classified as protists.
Determine if an organism with the following traits is a prokaryote or a eukaryote:
- composed of a single cell
- linear DNA
- has mitochondria
eukaryote
Only a eukaryote would possess mitochondria, since prokaryotes lack membrane-bound organelles. Eukaryotes also have linear, not circular, chromosomes. Note that both eukaryotes and prokaryotes can be unicellular.
Define:
cytosol
The fluid contained within a cell.
In contrast, the cytoplasm includes both the intracellular fluid and all of the extranuclear organelles.
Define:
cytoplasm
Includes both the intracellular fluid, or cytosol, and the organelles.
The only organelle that is not included in the cytoplasm is the nucleus.
Define:
organelle
A separate, specialized structure within a cell.
Many organelles are enclosed by lipid bilayers, but some, including ribosomes, are not membrane-bound.
What is the cellular role of the plasma membrane?
Also called the cell membrane, it protects the interior of the cell from its environment. It also limits the movement of specific materials into and out of the cell.
Describe the composition of the plasma membrane.
It consists of a phospholipid bilayer, with polar heads on the exterior (pointing toward the extracellular fluid and cytoplasm) and nonpolar tails on the interior.
The membrane also contains cholesterol, associated large proteins, and sphingolipids, among other components.
Explain the fluid mosaic model.
This is used to describe the plasma membrane. It is composed of lipids with a “mosaic” of embedded proteins and other components, and its “fluidity” allows these macromolecule components to move laterally within the membrane.
In animal cells, which organelle serves as the location for DNA in the form of linear chromosomes?
The nucleus.
It is also the site of DNA replication and transcription.
While the mitochondria also include DNA, mitochondrial DNA is found in small circular chromosomes, not linear ones.
What structural features are present in the nucleus?
The nucleus is encased in a double membrane, known as the nuclear envelope. This membrane is marked by channels called nuclear pores. Inside, a fluid (the nucleoplasm) surrounds linear chromosomes.
In what part of the cell is the nucleolus located, and what function does it serve?
It is located within the nucleus. It serves as the site of ribosomal RNA transcription and synthesis of ribosomal subunits.
Which organelle has two subunits and serves as the location for protein synthesis?
The ribosome.
Ribosomes are small organelles found in both eukaryotic and prokaryotic cells. At these organelles, proteins are synthesized (translated). A typical ribosome includes a small and a large subunit, although the sizes of these subunits vary depending on the type of cell.
How do eukaryotic and prokaryotic organisms differ in the composition of their ribosomes?
- Eukaryotic ribosomes are slightly larger, with a 40S and a 60S subunit combining to yield 80S.
- Prokaryotic ribosomes have a 30S and a 50S subunit, which combine to form 70S.
The abbreviation “S” refers to the rate at which a molecule settles in a centrifuge.
Describe the structural characteristics of the endoplasmic reticulum (ER).
The ER is a folded membrane divided into two regions: rough ER and smooth ER.
Rough ER contains ribosomes bound to its surface, while the smooth ER does not.
Within the cell, what is the role of the endoplasmic reticulum (ER)?
The ER is involved in a variety of processes, with smooth ER and rough ER performing different functions. The smooth ER is involved in lipid anabolism and detoxification, while the rough ER, with its many ribosomes, is the site of protein translation.
Both types of ER help synthesize macromolecules and shuttle them to the Golgi apparatus to be secreted from the cell.
What biological products are synthesized in the rough endoplasmic reticulum?
proteins
These can include enzymes and peptide hormones, among other examples.
What biological products are synthesized in the smooth endoplasmic reticulum?
lipids
These include steroid hormones and phospholipids, among other examples.
What is the cellular role of the Golgi apparatus?
It modifies molecules that arrive from the ER. It has the ability to break off into vesicles and can thus facilitate the exocytosis of these modified products.
What main cellular function is performed by the mitochondria?
They are involved in cellular metabolism, specifically the production of energy via aerobic respiration.
In the mitochondria, the Krebs cycle produces electron carriers, while the electron transport chain facilitates the formation of a proton gradient. This gradient is used to produce ATP.
What membranes and spaces are present in a mitochondrion?
It contains both an outer and an inner membrane. The intermembrane space is located between the two, while the mitochondrial matrix is the innermost space, bounded by the inner membrane.
Both membranes are phospholipid bilayers.
Binary fission is most relevant to the production of which organelle?
mitochondria
Just like prokaryotic asexual reproduction, which produces identical daughter cells, this method of division yields identical organelles.
Which organelle found in animal cells may have arisen as a result of mutualism?
Mitochondria may have evolved from a symbiotic relationship between small bacteria and larger cells. This is known as the endosymbiotic theory.
Like all instances of mutualism, this situation is thought to have provided benefits to both organisms. The smaller bacterium was given a livable environment while providing energy for the larger host.
What is the cellular role of lysosomes?
They break down engulfed pathogens, nutrient molecules, and components of the cell itself that are no longer functional.
Like the stomach, a lysosome contains enzymes and an acidic interior.
Describe the structural role of microtubules.
They are thick, hollow tubulin polymers. Specifically, units of alpha- and beta-tubulin dimerize, and many of these dimers come together to form a microtubule.
Microtubules form the spindle apparatus, an essential component of cell division. They also comprise cilia and flagella and perform various other functions.
Describe the structure and role of microfilaments.
They are linear, thin filaments composed of many actin monomers. Microfilaments are thinner than either microtubules or intermediate filaments.
As actin polymers, microfilaments play a crucial role in muscle contraction and also facilitate cytokinesis.
Describe the structure and role of intermediate filaments.
They are fibers composed of various cell-specific proteins; many are composed of keratin. Intermediate filaments are thicker than microfilaments but thinner than microtubules.
These fibers contribute to the rigidity of the cell and also form desmosomes, a type of cellular junction.
What term refers to the tubular structure used for locomotion in some bacteria?
flagellum
What structural and functional differences exist between cilia and flagella?
- Cilia are short, found in large numbers, and beat rhythmically in a back-and-forth pattern.
- Flagella are longer, with only a few found per cell at the most, and beat more slowly but powerfully to propel the cell in a certain direction.
In eukaryotes, both cilia and flagella have a 9+2 method of organization. This consists of 9 microtubule pairs arranged in a circle surrounding 2 single microtubules.
Which two membrane-bound organelles are unique to plant cells?
- chloroplasts
- vacuoles
Chloroplasts resemble mitochondria and perform the reactions of photosynthesis. Vacuoles are involved in storage.
In animal cells, where is most cholesterol found?
plasma membrane
Specifically, cholesterol (shown here) is a lipid that confers rigidity to the membrane. Cholesterol can either be acquired through the diet or synthesized by cells.
What is a concentration gradient, and what is its biological significance?
It is a difference in the amount of solute molecules per unit volume between one region and another.
Molecules are prone to moving down their concentration gradient. For example, if the outside of a cell contains a much higher concentration of glucose than the inside, glucose will tend to move into the cell (if possible). If the membrane is impermeable to glucose, water will tend to move out instead.
What is facilitated diffusion, and is it an active or passive process?
- It is the movement of a substance down its concentration gradient with the help of transmembrane protein channels.
- Since facilitated diffusion does not require energy, it is a form of passive transport.
If a normal human cell is placed in a container of pure water, what will result?
The cell will swell, possibly to the point of lysing (rupturing).
Since pure water contains no solute, it is hypotonic in comparison to the cell. Water will travel down its concentration gradient from the exterior of the cell to the interior.
What will happen to a human cell when it is placed in a hypertonic solution?
Water will exit the cell, causing it to shrivel.
A hypertonic solution is one that contains a comparatively high amount of solute (salt). Due to osmosis, water will flow from a low-solute to a high-solute environment in an attempt to equalize the solute concentrations.
Define:
endocytosis
It is a form of transport in which a material is engulfed by the cell membrane, then enters the cell in a vesicle. Endocytosis requires the expenditure of energy.
Phagocytosis and pinocytosis are both subtypes of endocytosis.
Define:
exocytosis
It is a form of transport in which a material is packaged into a vesicle which then fuses with the cell membrane. This process, which requires energy, allows the material to be exported from the cell.
Waste products and secreted hormones often leave a cell via exocytosis.
Define:
pinocytosis
It is a type of endocytosis. In this process, the cell membrane engulfs the extracellular fluid, as well as the small particles it contains, in a vesicle.
Other types of endocytosis include phagocytosis and receptor-mediated endocytosis.
What term is given to the separation of molecules based on their differing abilities to diffuse through a semipermeable membrane?
Dialysis
In a dialysis procedure, large particles are unable to diffuse through the dialysis membrane, so small particles are left to diffuse in an attempt to reduce the overall concentration gradient between the compartments. This technique is often used to remove toxins from the blood in cases of kidney failure.
What features characterize tight junctions?
They are composed of multiple proteins, including claudins, and form an impermeable seal between adjacent cells. This prevents fluid and solutes from going “around” the cell to enter a cavity.
Tight junctions are found between cells in the same epithelial layer.
What features characterize gap junctions?
They are small channels formed from connexin proteins. They allow small solutes and fluid to pass from one cell to another.
While gap junctions are found between most cells, they are generally associated with cells that must communicate or function together, like neurons.
What features characterize desmosomes?
They are composed of intermediate filaments and are found at localized regions throughout a cell’s membrane. They generally attach one epithelial or cell layer to another.
Desmosomes are found in epithelial and muscle tissue.
