Module 2 - Mastering Activities: Tour of the cell

C. The nucleus contains most of a cell's DNA.

Choose the letter that indicates the organelle that contains most of a cell's DNA.

Plasma Membrane Why? The plasma membrane regulates the passage of material into and out of the cell.

The _____ is a selective barrier, regulating the passage of material into and out of the cell.

Microtubules Eukaryotic cilia and flagella are composed of microtubules.

The cilia and flagella of eukaryotic cells are composed of _____.

Desmosomes Why? The primary role of desmosomes (anchoring junctions) is to bind cells together.

The primary role of _____ is to bind animal cells together.

Only one of the two fusion proteins possesses a nuclear localization signal. The nuclear localization signal is only present in the fusion protein that enters the nucleus.

Nucleoplasmin is a nuclear protein. This protein was divided into two segments and linked to the same large cytoplasmic protein, generating two fusion proteins. After injecting these fusion proteins into a cell, one of the proteins was found in the nucleus and the other in the cytoplasm. Which of the following conclusions can be drawn from these results?

Exterior of the cell Black spots would appear on the exterior of the cell after 3 hours, indicating that the proteins had been secreted from the cell.

Pancreatic cells, which secrete a large amount of digestive enzymes, are labeled with radioactive leucine and then chased for several hours with nonradioactive leucine. Photographic emulsions are prepared at different times during the chase. Where would the black spots appear on an emulsion prepared 3 hours after the pulse?

D. Microfilaments are a component of the cytoskeleton.

Which of these provides the cell with structural support?

Gap (communicating) junctions Why? Gap junctions allow for the passage of material between cells, thus facilitating communication between these cells.

_____ aid in the coordination of the activities of adjacent animal cells.

Fimbriae Fimbriae bacterial cells to stick to a surface.

_____ are surface appendages that allow a bacterium to stick to a surface.

Ribosomes Why? Ribosomes are the site of protein synthesis.

_____ are the sites of protein synthesis.

Basal bodies Why? Basal bodies and centrioles have identical structures.

_____ is/are identical in structure to centrioles.

Plants and animals are made up of billions of cells. These cells are surrounded by extracellular components that facilitate their interactions and provide a suitable environment for the construction and protection of tissues. Comparing the extracellular environments of plants and animals The cellular organization and extracellular environments of plants and animals are very different. Drag the labels to their appropriate locations in the table below. Labels of Group 2 may be used more than once.

A primary distinction between plant cells and animal cells is the fact that plant cells are surrounded by cell walls. If it were not for plasmodesmata, the cell walls would essentially imprison the plant's cells, making intercellular communication and the distribution of nutrients nearly impossible. Animal cells have a variety of intercellular junctions, including tight junctions, desmosomes, and gap junctions. The gap junctions of animal cells are most similar to the plasmodesmata of plants. Gap junctions tend to be limited to tissues that require rapid and coordinated signal relay systems, such as heart muscle; they play no role in nutrient distribution.

Passive Transport A 25,000-dalton protein is small enough to diffuse through nuclear pores without any expenditure of energy.

A small protein (molecular weight = 25,000 daltons) is injected into a cell and observed in the nucleus a short time later. What type of transport has taken place?

-ER Protein -Insulin -Lysosome Enzyme Why? Most proteins that function in the cytosol (such as actin) or in the nucleus (such as DNA polymerase) are synthesized by free ribosomes. Proteins that function within the endomembrane system (such as lysosomal enzymes) or those that are destined for secretion from the cell (such as insulin) are synthesized by bound ribosomes. As a protein destined for the endomembrane system is being synthesized by a ribosome, the first amino acids in the growing polypeptide chain act as a signal sequence. That signal sequence ensures that the ribosome binds to the outer membrane of the ER and that the protein enters the ER lumen.

All proteins are synthesized by ribosomes in the cell. Some ribosomes float freely in the cytosol, while others are bound to the surface of the endoplasmic reticulum. Most proteins made by free ribosomes function in the cytosol. Proteins made by bound ribosomes either function within the endomembrane system or pass through it and are secreted from the cell. Which of the following proteins are synthesized by bound ribosomes?

transferring of information from DNA to messenger RNA Transcription is the first of the two main steps of protein synthesis.

Beginning within the nucleus, the first step leading to the synthesis of a polypeptide is _____.

Proteins that are secreted from a eukaryotic cell must first travel through the endomembrane system.

Drag the labels onto the diagram to identify the path a secretory protein follows from synthesis to secretion. Why? As they are being synthesized, secretory proteins enter the lumen of the endoplasmic reticulum. From the ER, vesicles transport these proteins to the Golgi, where they are sequentially modified and concentrated in a cis-to-trans direction. Secretory vesicles bud from the Golgi and move along cytoskeletal filaments to eventually fuse with the plasma membrane, secreting their protein cargo. Each of these transport steps requires specialized proteins to ensure that the cargo is sent to the proper location and is able to fuse with the target membrane.

The final destination of the proteins was the lysosome. This conclusion can be drawn from the results, since the radioactive spots were last detected at the lysosome, which is not a secretory vesicle.

During a pulse-chase experiment, photographic emulsions were prepared at different times during the chase, and radioactive spots were detected at the following times and locations: 5 minutes: rough ER; 10 minutes: Golgi apparatus; 40 minutes: endosomes; 70 minutes: lysosomes; 140 minutes: lysosomes. Which of the following conclusions can be drawn from these results?

Plant organelle functions Drag the correct description under each cell structure to identify the role it plays in the plant cell.

Each organelle in a plant cell carries out a specific function. Mitochondria and the Golgi apparatus serve the same functions in both plant cells and animal cells.

Nucleolus Why? Ribosomes are manufactured by the nucleolus.

Ribosomal subunits are manufactured by the _____.

D The nucleoid region contains DNA.

The DNA-containing region of this bacterial cell is indicated by the letter _____.

chromatin Why? Chromatin is composed of DNA and protein.

The _____ is composed of DNA and protein.

Plasma Membrane The plasma membrane is selectively permeable.

The _____ is the bacterial structure that acts as a selective barrier, allowing nutrients to enter the cell and wastes to leave the cell.

The various parts of the endomembrane system serve different functions in the cell. In this activity, you will identify the roles of each part of the endomembrane system.

The endomembrane system is critical for the synthesis, processing, and movement of proteins and lipids in the cell. The smooth ER functions mainly in lipid synthesis and processing. The rough ER is the site of secretory protein synthesis. These proteins are processed further in the Golgi apparatus, from where they are dispatched in vesicles to the plasma membrane. Lysosomes, whose enzymes and membranes are made and processed by the rough ER and Golgi apparatus, function in the hydrolysis of macromolecules, such as in phagocytosis and autophagy.

C The plasma membrane is selectively permeable.

The structure that regulates the passage of material into and out of this bacterial cell is indicated by the letter _____.

The eukaryotic cell has well-defined structures that serve discrete functional roles. An organism's ability to perform essential functions such as metabolism, reproduction, and maintaining homeostasis depends on the proper functioning of structures at the cellular level. Although these structures are present in all animal cells, their number or activity level may vary depending on the cell type. For example, cells in the pancreas that produce the hormone insulin have extensive rough endoplasmic reticula, while muscle cells contain numerous mitochondria.

To understand how cells function as the fundamental unit of life, you must first become familiar with the individual roles of the cellular structures and organelles. Drag the labels on the left onto the diagram of the animal cell to correctly identify the function performed by each cellular structure.

False During the chase phase, cells are provided with a large amount of nonradioactive material, so they are not labeled.

True or false? Proteins produced during the "chase" phase of a pulse-chase experiment are labeled with radioactive material.

Ribosomes Ribosomes are involved in the manufacture of polypeptides (proteins).

In a bacterium, where are proteins synthesized?

To make the proteins easy to see. Fluorescent tags make the location of the proteins easy to visualize.

In experiments to test whether a protein can enter the nucleus, why would proteins be labeled with fluorescent molecules?

- They contain the green pigment chlorophyll. - They have membranous sacs called thylakoids that are surrounded by a fluid called stroma. - They are the sites of reactions that convert solar energy into chemical energy. Why? The chloroplast and the chemical reactions associated with it are extremely important for all living things. The photosynthetic reactions are responsible for converting solar energy into chemical energy that is used not only by the cells in which photosynthesis occurs but also by other organisms. For example, all of the foods you eat can be traced back to a plant or other photosynthetic organism. Furthermore, the chloroplast and its reactions have had a profound influence on the constitution of Earth's atmosphere due to the fact that oxygen is a byproduct of photosynthesis.

The structure of a chloroplast is closely tied to its function as the site of photosynthesis. Some of the following statements are true for chloroplasts; others are true for mitochondria. Which statements are true for chloroplasts? Select the three that apply.

False. Cytoplasmic proteins called importins bind to large proteins containing an NLS and mediate their transport across the nuclear membrane through an active transport (energy-requiring) process.

True or false? Large proteins containing a nuclear localization signal (NLS) bind to the nuclear pore and enter the nucleus without any expenditure of energy.

mitochondrion Why? Mitochondria convert the chemical energy of organic molecules to chemical energy in the form of ATP.

Which of these organelles carries out cellular respiration?

Protection A bacterium's capsule has a protective role.

What is a function of a bacterium's capsule?

PLANT CELL ONLY: - Chloroplast - Cellulose Cell Wall - Central Vacuole ANIMAL CELL ONLY: - Centriole BOTH: - Nucleus - Mitochondrion - Cytoskeleton - Golgi Apparatus - Endoplasmic Retciulum - Plasma Membrane Why? Plant cells and animal cells have more in common than they have differences. Nevertheless, plant cells' unique structures play important roles. Photosynthesis occurs in plant cells' chloroplasts. The plant cell's central vacuole takes up most of the space within the cell and serves a variety of functions, including storage and hydrolysis of organic compounds. Plant cell walls, which are composed primarily of cellulose, protect the cells from damage and maintain their shape. Cellulose is the most abundant organic compound on the planet.

Plant cells and animal cells share many of the same structures, but each type of cell also has unique structures. In this activity, you will indicate which cell structures are found only in plant cells, only in animal cells, or in both plant and animal cells. Drag each cell structure to the appropriate bin. If a structure is found in both plant cells and animal cells, drag it to the "both" bin.

phagocytosis The cells in this experiment were macrophages. These immune system cells have many lysosomes for the destruction of bacteria and other invaders brought into the cell via phagocytosis. The enzymes (hydrolases) that carry out this catabolic activity are synthesized in the endoplasmic reticulum, modified in the Golgi, and transported to the lysosomes.

Scientists can track the movement of proteins through the endomembrane system using an approach known as a pulse-chase experiment. This experiment involves the "pulse" phase: Cells are exposed to a high concentration of a radioactively labeled amino acid for a short period to tag proteins that are being synthesized. the "chase" phase: Any unincorporated radioactively labeled amino acids are washed away and large amounts of the same, but unlabeled, amino acid are added. Only those proteins synthesized during the brief pulse phase are radioactively tagged. These tagged proteins can be tracked through the chase period to determine their location in the cell. The data below were obtained from a pulse-chase experiment in which cells were examined at different times during the chase period. The numbers represent the radioactivity (measured in counts per minute) recorded at each of the indicated sites. The higher the number, the greater the radioactivity. Based on these data, what is the most likely function of the cells in this experiment?

1. In eukaryotic flagella, the fibers that slide past one another due to the activity of dynein proteins are _________. 2. Many cell organelles, most notably the nucleus, are anchored by _______ which are assembled from a diverse class of proteins. 3. Centrosomes are sites where protein dimers assemble into _______. 4. The extension of pseudopodia in amoeba is due to the regulated assembly and destruction of _________. 5. The only cytoskeletal fibers not associated with intracellular movement or whole cell locomotion are the ________. 6. During muscle contractions, myosin motor proteins move across tracks of _________. 1. Intermediate Filaments 2.Microtubules 3. Microfilaments 4. Intermediate Filaments 5. Microfilaments The eukaryotic cytoskeleton is appropriately named because, at the cellular level, these fibers and their associated motor proteins perform similar roles as an animal's musculoskeletal system. Microfilaments are responsible for cell locomotion and the cell's structural characteristics. Microtubules serve as intracellular highways for transporting vesicles and organelles; they are also required for cellular locomotion via flagella and cilia. Intermediate filaments are rope-like structures that anchor organelles and intercellular junctions called desmosomes. They are specialized for bearing tension.

The cytoskeleton of a eukaryotic cell plays a major role in organizing the structures and activities of the cell. The cytoskeleton consists of three main types of fibers: microfilaments, intermediate filaments, and microtubules. The three types of fiber differ in size, composition, and the functions they perform in the cell. Drag the terms on the left to the appropriate blanks in the sentences on the right. Terms can be used once, more than once, or not at all.

Only bacteria and archaea have prokaryotic cells, which lack a nucleus and other membrane-enclosed organelles. Prokaryotic cells are smaller and, at the level of the individual cell, are generally less versatile than eukaryotic cells, which compartmentalize many of their metabolic pathways into organelles. Nevertheless, prokaryotes are indispensable in every known ecosystem, and certain species are capable of surviving in some of the harshest and most nutrient-limiting environments on Earth. Prokaryotic Only: Nucleiod Eukaryotic Only: Nucleolus, Lysosome, & Mitochondria Both: Ribosomes, Plasma Membrane, & Flagella

Two fundamental types of cells are known to exist in nature: prokaryotic cells and eukaryotic cells (like the one shown in the Tour of an Animal Cell animation). Both prokaryotic and eukaryotic cells carry out all of the processes necessary for life, but they differ in some important ways. In this activity, you will identify which cell structures are found only in prokaryotic cells, only in eukaryotic cells, or in both types of cells. Drag each cell structure to the appropriate bin.

Incubating cells with a labeled molecule Cells are first "pulsed" with a large amount of labeled material for a short time.

What is the first step in a pulse-chase experiment?

Cell Wall The cell wall is a rigid supporting structure.

What name is given to the rigid structure, found outside the plasma membrane, that surrounds and supports the bacterial cell?

Rough ER, Golgi apparatus, secretory vesicles, plasma membrane Proteins are synthesized in the rough ER, modified in the Golgi apparatus, and carried in secretory vesicles to the plasma membrane, where they are secreted.

What path does a protein in the secretory pathway take, starting from its site of synthesis?

Movement of molecules through a cell over time Pulse-chase experiments allow for the tracking of molecules in a cell over time.

What scientific hypotheses can be tested by a pulse-chase experiment?

Nucleic Region Bacteria lack a nucleus; their DNA is found in the nucleoid region.

Where is a bacterial cell's DNA found?

smooth endoplasmic reticulum Why? In addition to storing calcium, the smooth ER also plays a role in detoxification and lipid synthesis.

Where is calcium stored?

DNA All processes involving DNA take place in the nucleus.

Which molecules do not normally cross the nuclear membrane?

The nuclear envelope is continuous with the Golgi apparatus. This statement is false; the nuclear envelope is continuous with the endoplasmic reticulum.

Which of the following statements about the nuclear envelope is false?

Microtubules Why? Microtubules are rods that also play a role in organelle movement.

Which of these are hollow rods that shape and support the cell?

tight junctions Why? Tight junctions form a barrier that prevents fluids from moving between cells.

Which of these cell junctions form a barrier to the passage of materials?

E. This is the nuclear envelope.

Which of these is the double membrane that encloses the nucleus?

Rough Endoplasmic Reticulum Why? The ribosomes associated with the rough ER synthesize secretory proteins bound for the exterior of the cell. Further processing and packaging occurs in the Golgi apparatus.

Which of these organelles manufactures proteins bound for secretion out of the cell?

peroxisome Why? Peroxisomes produce hydrogen peroxide as a by-product of their metabolic processes.

Which of these organelles produces H2O2 as a by-product?

A. Why? The Golgi apparatus modifies, stores, and packages products of the ER.

Which of these structures stores, modifies, and packages products?

Lysosome The prefix "lyso-" means decomposition.

Which organelle plays a role in intracellular digestion?