Eukaryotic Cell Flashcards
With the biological focus of the new MCAT, an understanding of eukaryotic cells is especially vital. Use these cards to familiarize yourself with microtubules and microfilaments, the phases of mitosis, and the various types of membrane transport. For enhanced practice, think about how these concepts relate to real-life topics like cancer and human aging.
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 and 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?
Eukaryotic cells 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?
Prokaryotic cells 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.
Define:
cytosol
The cytosol is the fluid contained within a cell.
In contrast, the cytoplasm includes both the intracellular fluid and all of the extranuclear organelles.
Define:
cytoplasm
The 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
An organelle is 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?
The nucleus, mitochondria, Golgi apparatus, endoplasmic reticulum, peroxisomes, and lysosomes are membrane-bound. 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 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.
Which genetic processes take place in the nucleus?
The main processes that take place in the nucleus are replication and transcription.
In contrast, translation occurs at ribosomes outside the nucleus. These organelles can either be bound to the ER or located in the cytoplasm.
In what part of the cell is the nucleolus located, and what function does it serve?
The nucleolus 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?
Mitochondria contain 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.
What main cellular function is performed by the mitochondria?
Mitochondria 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.
Binary fission is most relevant to the production of which organelle?
Binary fission is the method of replication for mitochondria.
Just like prokaryotic asexual reproduction, which produces identical daughter cells, this method of division yields identical organelles.
What characteristic of mitochondrial inheritance deviates from Mendel’s laws?
Mitochondria are only passed down through the maternal line.
Though sperm contain paternal mitochondria, they are quickly destroyed by the egg after fertilization.
A woman has a muscle disease and passes it down to her two sons and three daughters. Her brother has the same disease, but none of his children do. Where is the gene for this condition likely located?
The gene is likely mitochondrial.
Unlike nuclear genes, mitochondrial genes are inherited only through the maternal line. A mother can pass the gene on to both sons and daughters.
Which organelle 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.
Which cell types are likely to contain an above-average number of mitochondria?
Muscle cells contain large numbers of mitochondria.
Specifically, red or “slow-twitch” muscle fibers are high in mitochondria due to their increased need to perform aerobic respiration. This produces the ATP needed as part of the contraction cycle.
What is the cellular role of lysosomes?
Lysosomes 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.
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?
The rough ER synthesizes proteins.
These can include enzymes and peptide hormones, among other examples.
What biological products are synthesized in the smooth endoplasmic reticulum?
The smooth ER synthesizes lipids.
These include steroid hormones and phospholipids, among other examples.
What is the cellular role of the Golgi apparatus?
The Golgi apparatus 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 are peroxisomes, and what cellular function do they perform?
Peroxisomes 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 two membrane-bound organelles are unique to plant cells?
Plant cells, unlike animal cells, contain chloroplasts and vacuoles.
Chloroplasts resemble mitochondria and perform the reactions of photosynthesis. Vacuoles are involved in storage.
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.
A cell taken from a multicellular eukaryote lacks chloroplasts but does contain a cell wall. Which type of cell is this?
This is a fungal cell.
Plants, animals, and fungi are all multicellular, but plants do contain chloroplasts while animals lack cell walls. This sample, then, must come from a fungus.
Define:
cytoskeleton
The cytoskeleton is 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?
The cytoskeleton mainly functions to provide shape to the cell, but also is 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.
The three components of the cytoskeleton are:
- microtubules
- intermediate filaments
- microfilaments
Describe the structure and role of microfilaments.
Microfilaments 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.
Intermediate filaments 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.
Microtubules 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.