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. (88 cards)
1
Q
The cell theory, originally composed in 1838, includes three primary tenets. Name them.
A
- 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.
2
Q
All cells can be categorized into which two broad groups?
A
- 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).
3
Q
What main features characterize eukaryotic cells?
A
- 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.
4
Q
What main features characterize prokaryotic cells?
A
- 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.
5
Q
Define:
cytosol
A
It is the fluid contained within a cell.
In contrast, the cytoplasm includes both the intracellular fluid and all of the extranuclear organelles.
6
Q
Define:
cytoplasm
A
It includes both the intracellular fluid, or cytosol, and the organelles.
The only organelle that is not included in the cytoplasm is the nucleus.
7
Q
Define:
organelle
A
It is a separate, specialized structure within a cell.
Many organelles are enclosed by lipid bilayers, but some, including ribosomes, are not membrane-bound.
8
Q
Which organelles are membrane-bound?
A
- 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.
9
Q
Which organelles contain DNA?
A
The nucleus is the location of most genetic material, but the mitochondria also contain DNA.
In plants, chloroplasts have DNA as well.
10
Q
What structural features are present in the nucleus?
A
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.
11
Q
Which genetic processes take place in the nucleus?
A
- replication
- transcription
In contrast, translation occurs at ribosomes outside the nucleus. These organelles can either be bound to the ER or located in the cytoplasm.
12
Q
In what part of the cell is the nucleolus located, and what function does it serve?
A
within the nucleus
It serves as the site of ribosomal RNA transcription and synthesis of ribosomal subunits.
13
Q
What membranes and spaces are present in a mitochondrion?
A
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.
14
Q
What main cellular function is performed by the mitochondria?
A
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.
15
Q
Binary fission is most relevant to the production of which organelle?
A
mitochondria
Just like prokaryotic asexual reproduction, which produces identical daughter cells, this method of division yields identical organelles.
16
Q
What characteristic of mitochondrial inheritance deviates from Mendel’s laws?
A
Mitochondria are only passed down through the maternal line.
Though sperm contain paternal mitochondria, they are quickly destroyed by the egg after fertilization.
17
Q
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?
A
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.
18
Q
Which organelle may have arisen as a result of mutualism?
A
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.
19
Q
Which cell types are likely to contain an above-average number of mitochondria?
A
Muscle cells
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.
20
Q
What is the cellular role of lysosomes?
A
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.
21
Q
Describe the structural characteristics of the endoplasmic reticulum (ER).
A
It 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.
22
Q
Within the cell, what is the role of the endoplasmic reticulum (ER)?
A
- It 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.
23
Q
What biological products are synthesized in the rough endoplasmic reticulum?
A
proteins
These can include enzymes and peptide hormones, among other examples.
24
Q
What biological products are synthesized in the smooth endoplasmic reticulum?
A
lipids
These include steroid hormones and phospholipids, among other examples.
25
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.
26
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.
## Footnote
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.
27
Which two membrane-bound organelles are unique to plant cells?
Plant cells, unlike animal cells, contain **chloroplasts** and **vacuoles**.
## Footnote
Chloroplasts resemble mitochondria and perform the reactions of photosynthesis. Vacuoles are involved in storage.
28
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.
## Footnote
Fungal walls are made of chitin, plant walls are made of cellulose, and bacterial cell walls are composed of peptidoglycan.
29
A cell taken from a multicellular eukaryote lacks chloroplasts but does contain a cell wall. Which type of cell is this?
fungal
## Footnote
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.
30
# Define:
cytoskeleton
It is a structural web of protein that can change shape to perform a variety of cellular processes.
## Footnote
The prefix "cyto-" means "cell," so the cytoskeleton is the "cell's skeleton."
31
What main functions are executed by the **cytoskeleton**?
It 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.
## Footnote
Cytoskeletal proteins have the unusual ability to self-assemble into larger units, and can thus change shape based on the cell's needs.
32
Name the three primary, protein-based components of the cytoskeleton.
1. microtubules
2. intermediate filaments
3. microfilaments
33
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.
## Footnote
As actin polymers, microfilaments play a crucial role in muscle contraction and also facilitate cytokinesis.
34
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.
## Footnote
These fibers contribute to the rigidity of the cell and also form desmosomes, a type of cellular junction.
35
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.
## Footnote
Microtubules form the spindle apparatus, an essential component of cell division. They also comprise cilia and flagella and perform various other functions.
36
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.
37
Which type of cytoskeletal fiber is associated with **MTOCs**?
**Microtubules** are anchored at MTOCs, or microtubule-organizing centers. The fibers attach to the MTOC at one end and radiate toward other parts of the cell.
## Footnote
Centrosomes are a specific type of MTOC involved in cell division. Spindle fibers attach to the centrosomes, each of which is composed of two tubulin-based centrioles.
38
Label the following structures on the diagram below: centrosome, centriole, spindle fiber, aster.
39
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.
## Footnote
A large surface area gives the cell a greater ability to obtain nutrients and eliminate waste through its cell membrane.
40
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.
41
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.
## Footnote
The membrane also contains cholesterol, glycoproteins, and sphingolipids, among other components. Large proteins are associated with it, both integral (embedded within the membrane) and peripheral (bound to the outside of the membrane).
42
A certain plasma membrane protein is high in valine, isoleucine, and glycine, and contains very few aspartate or lysine residues. What type of protein is this likely to be?
membrane-embedded protein
## Footnote
Peripheral proteins are located on the exterior of the membrane and are likely to be hydrophilic / charged, while membrane-embedded proteins are positioned inside the bilayer and are generally hydrophobic / uncharged. Valine, isoleucine, and glycine are nonpolar (hydrophobic) amino acids.
43
Explain the **fluid mosaic model**.
It 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.
44
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.
## Footnote
Large molecules and ions must enter cells through special protein channels or via endocytosis.
45
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.
## Footnote
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.
46
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.
47
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.
## Footnote
Since facilitated diffusion does not require energy, it is a form of passive transport.
48
What traits distinguish molecules that require membrane channels to enter a cell?
Substances that require membrane channels include large molecules, polar molecules, and ions.
## Footnote
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.
49
Which type of hormone requires membrane receptors to act on a target cell?
**Peptide hormones**, as well as the catecholamines **epinephrine** and **norepinephrine**
## Footnote
As polar molecules, these hormones cannot pass through the hydrophobic cell membrane.
50
What term describes the passive movement of water or another solvent down its concentration gradient?
osmosis
## Footnote
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.
51
What is the meaning of the term “isotonic?”
It is one with the same solute concentration as a solution to which it is compared.
## Footnote
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.
52
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.
## Footnote
For example, say that a certain compartment contains 0.2 M NaCl. A solution of 0.1 M NaCl would be hypotonic, while a solution of 0.5 M NaCl would be hypertonic.
53
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).
## Footnote
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.
54
The hammerhead shark lives in a tropical ocean environment. Are its cells likely to be hypertonic or hypotonic compared to human cells?
hypertonic
## Footnote
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.
55
What will happen to a human cell when it is placed in a hypertonic solution?
Water will exit the cell, causing it to **shrivel**.
## Footnote
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.
56
# Define:
endocytosis
Itis 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.
## Footnote
Phagocytosis and pinocytosis are both subtypes of endocytosis.
57
# 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.
## Footnote
Waste products and secreted hormones often leave a cell via exocytosis.
58
# 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.
## Footnote
Other types of endocytosis include phagocytosis and receptor-mediated endocytosis.
59
Name the three distinct junctions that separate the cells of vertebrates.
1. tight junctions
2. desmosomes
3. gap junctions
60
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.
## Footnote
Tight junctions are found between cells in the same epithelial layer.
61
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.
## Footnote
Desmosomes are found in epithelial and muscle tissue.
62
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.
## Footnote
While gap junctions are found between most cells, they are generally associated with cells that must communicate or function together, like neurons.
63
Which type of junction is especially important in the heart?
Gap junctions
## Footnote
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.
64
Name the four phases of the cell cycle.
1. G1
2. S (synthesis)
3. G2
4. M (mitosis)
## Footnote
An additional phase is G0, in which the cell is not immediately preparing for cell division. G0 can be either temporary or permanent.
65
Which phases of the cell cycle are part of interphase?
* G1
* S
* G2
## Footnote
In these phases, the cell grows, replicates its DNA, and prepares for mitosis.
The M phase (mitosis itself) is not a part of interphase. G0 is generally thought to be distinct when it is permanent (as in neurons, which do not divide), but that is unlikely to be tested on the MCAT.
66
What is the significance of the **G0 phase**?
It is a stage of prolonged inactivity. In this phase, the cell is not preparing for mitosis.
## Footnote
Mature neurons and cardiac muscle are in a permanent G0 phase, since they do not undergo mitosis.
67
During which phase of the cell cycle would DNA helicase be especially active?
DNA helicase, as well as the other enzymes involved in DNA replication, would be most active during the **S phase**.
## Footnote
In the S (synthesis) phase, DNA is replicated to prepare for cell division.
68
What does the cell assess at the G1 checkpoint?
The **G1 checkpoint**, also known as the G1/S checkpoint or the restriction checkpoint, assesses the DNA to ensure that it is in proper condition to be replicated.
## Footnote
Passage through this checkpoint is required to enter the S phase of the cell cycle.
69
What does the cell assess at the G2 checkpoint?
The **G2 checkpoint**, also known as the G2/M checkpoint, makes sure that sufficient cell growth has occurred and that the DNA was replicated properly.
## Footnote
Passage through this checkpoint is required to enter the M phase of the cell cycle.
70
What is the **difference** between germ cells and somatic cells?
* **Germ cells**, including sperm and ova, are haploid and participate in reproduction. They are formed via meiosis.
* **Somatic cells** are diploid and include the rest of the cells in the body. Somatic cells only undergo mitosis.
71
Name the two types of eukaryotic cell division.
* mitosis
* meiosis
## Footnote
Mitosis produces somatic cells that are identical to the parent, while meiosis produces germ cells with only half of the parental genetic material.
72
Explain the **difference** between a haploid and a diploid cell.
* **Haploid cells** have only one full set of chromosomes. In humans, the only haploid cells are germ cells (sperm and eggs) produced by meiosis.
* **Diploid cells** have two distinct sets of chromosomes. In humans, all somatic cells are diploid and are produced by mitosis.
73
List the four phases of mitosis in the order that they occur in a dividing cell.
1. prophase
2. metaphase
3. anaphase
4. telophase and cytokinesis
74
What **features** distinguish homologous chromosomes from sister chromatids?
* **Homologous chromosomes** are genetically different; each homologous chromosome has the same locus, but different genes, compared to its partner. Homologous chromosomes separate during meiosis I.
* **Sister chromatids** are genetically identical, as they result from the replication of a single chromosome. Sister chromatids separate during meiosis II and mitosis.
75
Describe the role of the **centrioles** during cell division.
They are cylinder-shaped microtubular structures, generally found in pairs as part of the centrosome. Centrioles act to organize the spindle apparatus along which the chromosomes align.
76
Describe the role of the **centromere** during cell division.
At the **centromere**, sister chromatids attach in pairs. This region also contains the kinetochore, which binds to a spindle fiber and allows the chromatids to be pulled to opposite poles of the cell.
## Footnote
The centromere is the location on the chromosome that appears "pinched."
77
Describe the role of the **kinetochore** during cell division.
It is a complex arrangement of various proteins that forms on the centromere. Here, spindle fibers bind, allowing sister chromatids to be separated to opposite poles of the cell.
78
Name the microtubule-based structure that separates chromosomes during cell division.
The spindle apparatus
## Footnote
Spindle fibers radiate from the centrosome, which contains centrioles, and bind at the kinetochore region of the centromere.
79
What cellular events characterize **prophase**?
* Loose chromatin condenses into visible chromosomes.
* The nuclear membrane disintegrates.
* The nucleolus disappears.
* The centrioles and spindle apparatus form.
80
What cellular events characterize **metaphase**?
* At this point, spindle fibers are bound to the kinetochore of each chromosome.
* The chromosomes line up along the center of the cell, a region called the metaphase plate.
81
What cellular events characterize **anaphase**?
* Sister chromatids are cleaved apart.
* Spindle fibers shorten, causing each sister chromatid to move to the opposite pole as its partner.
82
What cellular events characterize **telophase**?
* The cell elongates.
* Each daughter nucleus forms a new nuclear membrane and nucleolus.
* The chromosomes start to become less condensed.
83
# Define:
cytokinesis
It is the actual formation of two distinct cells, characterized by the distribution of cytosol and organelles and the pinching of the cell membrane between the two nuclei.
## Footnote
Cytokinesis happens simultaneously with the later phases of mitosis and meiosis, but is often grouped with telophase.
84
An individual develops a condition where certain cells undergo mitosis rapidly, with interphase dramatically shortened. What name is commonly used for this condition?
Cancer
## Footnote
Cancer can be promoted by many factors, including carcinogens, DNA damage, failure of tumor suppressor genes, and failure of apoptosis, or a combination of these events.
85
Name **four broad differences** between mitosis and meiosis.
* Mitosis involves a single division, while meiosis involves two.
* Mitosis produces two identical diploid cells, while meiosis produces four haploid cells that are not identical.
* Mitosis is used to form somatic cells, while meiosis produces germ cells (gametes).
* Crossing over occurs in meiosis, but does not happen in mitosis.
86
Mitosis is broadly similar, but not identical, to meiosis I. Name three differences between the two processes.
* Mitosis involves the separation of sister chromatids, while meiosis I involves the separation of homologous chromosomes.
* Mitosis produces diploid cells, while the products of meiosis I are haploid.
* Crossing over occurs in prophase of meiosis I, but does not occur at all during mitosis.
87
During which stage of meiosis do daughter cells become haploid?
meiosis I
## Footnote
Meiosis I is known as "reductional division," since homologous chromosomes separate during this stage. This leaves two daughter cells, each with a single chromosome from each pair and its replicated copy. Meiosis II, or "equational division," separates these copies.
88
Which two processes ensure that none of the four daughter cells produced during meiosis are genetically identical?
* Crossing over
* Independent assortment
## Footnote
Crossing over is a method of genetic recombination that occurs during prophase I of meiosis. In this process, homologous chromosomes exchange genetic material, increasing total variation.
The principle of independent assortment, or Mendel's second law, states that genes for different traits separate into gametes independently of each other (as long as those traits are not linked).
