Cell Biology Flashcards
What name is given to the basic functional and structural unit of all living organisms?
cell
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.
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.
Define:
organelle
A separate, specialized structure within a cell.
Many organelles are enclosed by lipid bilayers, but some, including ribosomes, are not membrane-bound.
Which organelles are membrane-bound?
- nucleus
- mitochondria
- Golgi apparatus
- endoplasmic reticulum
- peroxisomes
- lysosomes
In plants, chloroplasts and vacuoles fall into this category as well.
Ribosomes, on the other hand, are not membrane-bound; while some are attached to the ER, they are not surrounded by membranes of their own.
Which organelles contain DNA?
The nucleus is the location of most genetic material, but the mitochondria also contain DNA.
In plants, chloroplasts have DNA as well.
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.
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.
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 are peroxisomes, and what cellular function do they perform?
They are small membrane-bound organelles that contain enzymes. They function in fatty acid breakdown, detoxification, and facilitation of the pentose phosphate pathway.
Peroxisomes are named for hydrogen peroxide (H2O2), which can be both formed and broken down within the organelle. This is important because H2O2 is a poisonous radical initiator.
Which eukaryotic cell types are encased in a cell wall?
Fungal and plant cells include cell walls, while animal cells do not. Bacterial cells, though not eukaryotic, also have cell walls.
Fungal walls are made of chitin, plant walls are made of cellulose, and bacterial cell walls are composed of peptidoglycan.
Define:
cytoskeleton
A structural web of protein that can change shape to perform a variety of cellular processes.
The prefix “cyto-“ means “cell,” so the cytoskeleton is the “cell’s skeleton.”
What main functions are executed by the cytoskeleton?
- Mainly functions to provide shape to the cell.
- Also involved in cell movement, endocytosis, and the formation of the spindle apparatus during cell division.
Cytoskeletal proteins have the unusual ability to self-assemble into larger units, and can thus change shape based on the cell’s needs.
Name the three primary, protein-based components of the cytoskeleton.
- microtubules
- intermediate filaments
- microfilaments
What factor plays the biggest role in limiting the size of a cell?
The cell must have a sufficiently large surface area-to-volume ratio. As the cell becomes larger, volume increases faster than surface area, causing this ratio to decrease.
A large surface area gives the cell a greater ability to obtain nutrients and eliminate waste through its cell membrane.
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.
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.
What traits distinguish molecules that can easily pass through the plasma membrane?
Molecules can easily travel through the membrane if they are small and nonpolar. To move passively, they also must be traveling down their concentration gradient.
Large molecules and ions must enter cells through special protein channels or via endocytosis.
What is the difference between passive and active transport?
- Passive transport involves the movement of a substance down its concentration gradient without the use of energy.
- Active transport requires energy, usually in the form of ATP, and moves a substance against its gradient.
What term describes the passive movement of water or another solvent down its concentration gradient?
osmosis
Water will always move from areas of low solute to areas with a higher solute concentration.
Osmosis is generally tested in cases where two compartments are separated by a semipermeable membrane. The membrane allows water, but not solute, to pass through; osmosis is thus required to promote similar solute concentrations on both sides.
What is the meaning of the term “isotonic?”
Itis one with the same solute concentration as a solution to which it is compared.
For example, fluids that are administered in an IV should be isotonic with human cells. In other words, they should have the same osmolality, or solute concentration.
What is the difference between a hypertonic and a hypotonic solution?
In comparison to a reference solution, a hypertonic solution has a greater solute concentration, while a hypotonic solution has a smaller solute concentration.
For example, say that a certain compartment contains 4 grams of NaCl per liter of solution. A solution of 2 g NaCl per L solution would be hypotonic, while a solution of 8 g NaCl per L solution would be hypertonic.
The hammerhead shark lives in a tropical ocean environment. Are its cells likely to be hypertonic or hypotonic compared to human cells?
Shark cells are likely hypertonic to human cells.
To avoid excessive water loss or gain, shark cells must be specialized to be isotonic, or at least close, to their surroundings. Since the ocean is composed of salt water, shark cells likely contain more solute than the cells of land-dwelling species.
What traits distinguish molecules that require membrane channels to enter a cell?
Substances that require membrane channels include large molecules, polar molecules, and ions.
When these materials move down their concentration gradient, the process is known as facilitated diffusion. Small, nonpolar molecules do not require membrane channels and can travel via simple diffusion.
Name the three distinct junctions that separate the cells of vertebrates.
- tight junctions
- desmosomes
- gap junctions
Which type of junction is especially important in the heart?
Gap junctions
The electrical impulse that triggers contraction must travel throughout the entire heart muscle, beginning at the SA node. Gap junctions facilitate the movement of ions, allowing the cells to act together as one unit.
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.
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).
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.
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.
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.
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 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.
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.
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.
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.
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.