Chapter 4: Tour of the Cell
It is believed that meldonium works on which of the following?
mitochondria
Chromosomes/chromatin
Composed of DNA and proteins; found in the nucleus; tightly packed during cell division and dispersed during normal cell operations
Animal Cell Structures
Centriole
The primary role of _____ is to bind animal cells together.
desmosomes
Which of these organelles produces H2O2 as a by-product? 1) mitochondrion 2) nucleus 3) centrioles 4) flagellum 5) peroxisome
5
Where is most of cell's DNA?
nucleus
The diameter of a typical eukaryotic cell is approximately ten times the diameter of a typical prokaryote. What is the ratio of the volume of typical eukaryotic:prokaryotic cells?
1000:1
cellulose
A polysaccharide that is used to synthesize plant cell walls, which protect cells and help maintain their shape
_____ are surface appendages that allow a bacterium to stick to a surface
Fimbriae
_____ aid in the coordination of the activities of adjacent animal cells.
Gap (communicating) junctions
What scientific hypotheses can be tested by a pulse-chase experiment?
Movement of molecules through a cell over time
In which of the following countries would it likely be easiest to obtain meldonium?
Russia
The cilia and flagella of eukaryotic cells are composed of _____.
microfilaments
The NBA decides to look into the use of meldonium in the league following the same protocol as the WADA. Which of the following will be randomly tested?
urine
The only cytoskeletal fibers not associated with intracellular movement or whole cell locomotion are the ______________ .
intermediate filaments
tight junctions
Membrane proteins that create a watertight seal between animal cells to connect them and to keep fluid from crossing barriers
Which organelle plays a role in intracellular digestion?
lysomsome
demosomes
membrane protein complexes that strengthen adhesion between cells like rivets to protect against
Ribosomal subunits are manufactured by the _____.
nucleoulus
Endoplasmic Reticulum
The endomembrane system is critical for the synthesis, processing, and movement of proteins and lipids in the cell.
Identify the correct statement about differences between rough and smooth endoplasmic reticulum (ER). A. Rough ER consists of a network of membranous tubules and sacs called cisternae, whereas smooth ER is less complex. B. The outer surface of smooth ER lacks ribosomes, whereas the outer surface of rough ER has ribosomes. C. Smooth ER is part of the endomembrane system of the eukaryotic cell, and rough ER is not.
B
Which of the following are common traits of chloroplasts and mitochondria? A. Both are found in plant and animal cells. B. Both are surrounded by a single membrane. C. Both have their own DNA. D. Both reproduce by meiosis. E. Proteins for both are synthesized on ribosomes in the rough ER
C. Both have their own DNA. Mitochondria and chloroplasts contain their own DNA and ribosomes.
Which molecules do not normally cross the nuclear membrane?
DNA
In a bacterium, where are proteins synthesized?
ribosomes
Why would a professional athlete be interested in using meldonium?
enhance endurance
Which of these manufactures cellular membranes by adding membrane proteins and phospholipids to its own membrane? A. lysosomes B. ribosomes C. nucleolus D. Golgi apparatus E. rough endoplasmic reticulum
rough ER
Rough ER
site of secretory protein synthesis
Where is calcium stored?
smooth ER
What cell junctions form a barrier to the passage of materials?
tight junctions
Smooth ER
lipid synthesis and processing
During muscle contractions, myosin motor proteins move across tracks of ______________
microfilaments
1. In eukaryotic flagella, the fibers that slide past one another due to the activity of dynein proteins are __________ .
microtubules
Where is a bacterial cell's DNA found?
nucleoid region
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. A.) Smooth ER B.) Rough ER C.) Golgi Apparatus D.) Lysosomes 1. protein synthesis 2. cisternal maturation 3. lipid synthesis 4. calcium ion storage 5. protein modification and sorting 6. poison detoxification 7. macromolecule digestion 8. autophagy
A.) Smooth ER: lipid synthesis, calcium storage, poison detoxification B.) Rough ER: protein synthesis C.) Golgi apparatus: protein modification, sorting, cisternal maturation D) Lysosomes: macromolecule digestion, autophagy
What path does a protein in the secretory pathway take, starting from its site of synthesis?
Rough ER, Golgi apparatus, secretory vesicles, plasma membrane
What is the first step in a pulse-chase experiment?
Incubating cells with a labeled molecule
collagen
Long fibers of protein found in the extracellular matrix that provide structural support for animal cells
Select the correct statement describing the cellular structure or function: A. Plant and animal cells both carry out cellular respiration, producing ATP. B. Only plant cells contain chloroplasts, and only animal cells contain mitochondria. C. Mitochondria and chloroplasts are part of the endomembrane system of the eukaryotic cell.
A
The _____ is the bacterial structure that acts as a selective barrier, allowing nutrients to enter the cell and wastes to leave the cell.
plasma membrane
A biologist wants specifically to examine the surfaces of different types of cells in kidney tubules of small mammals. The cells in question can be distinguished by external shape, size, and 3-D characteristics. Which of the following would be the optimum method for her study?
scanning electron microscopy
Plant and Animal Cell Structures
Nucleus, Plasma membrane, Mitochondrion, Cytoskeleton, Endoplasmic reticulum, Golgi apparatus
plasmodesmatas
Small channels between cells that are otherwise surrounded by walls; enable movement of water and solutes between plant cells
gap junctions
Small channels that form across the plasma membranes of adjacent animal cells; especially important in intercellular communication; help coordinate activities of adjacent cells
In experiments to test whether a protein can enter the nucleus, why would proteins be labeled with fluorescent molecules?
To make the proteins easy to see
mitochondrion
an organelle in EUKARYOTIC CELLS where CELLULAR RESPIRATION occurs. Enclosed by two membranes, it is where most of the cell's ATP is made
What name is given to the rigid structure, found outside the plasma membrane, that surrounds and supports the bacterial cell?
cell wall
1 meter = _____ centimeters.
100
Which statement correctly describes an endomembrane function? A. Products of the ER are usually modified during their transit from the CIS to the TRANS region of the Golgi Apparatus. B. The lumen of the endoplasmic reticulum (ER) is continuous with the cell nucleus. C. Secretory proteins in transit from one part of the cell to another are carried in lysosomes.
A
Athletes can apply for an exception to use a banned substance if it is used for medical purposes. Which of the following athletes is most likely to be allowed to use meldonium if she or he is using it for its original intended purpose? 1.) An Olympic speedskater using it for chronic fatigue syndrome. 2.) A professional tennis player using it for chronic pain. 3.) A professional runner using it for a heart condition. 4.) An Olympic wrestler using it as a sleep aid.
A professional runner using it for a heart condition.
What is the path a secretory protein follows from synthesis to secretion?
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.
A cell has formed a food vacuole as it ingested a food particle. Which of the following events is associated with the breakdown of that food particle?
Digestion of the food particle occurs in a vesicle enclosed by a membrane that separates the digestion from the cytoplasm.
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
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? Proteins produced during the "chase" phase of a pulse-chase experiment are labeled with radioactive material
False, during the chase phase, cells are provided with a large amount of nonradioactive material, so they are not labeled.
_____ is/are identical in structure to centrioles. 1) Mitochondria 2) Nuclear envelopes 3) Chromatin 4) Microfilaments 5) Basal bodies
5
Which statement about extracellular structures (plant cell walls and the extracellular matrix of animal cells) is correct A. Extracellular structures store energy in the form of polysaccharides for subsequent metabolism by the cell. B. Proteins and lipids are common components of extracellular structures. C. All extracellular structures form barriers to separate adjacent cells. D. Information can be transmitted from these extracellular structures to the cytoplasm. E. Extracellular structures regulate the passage of water molecules across the cell membrane.
Information can be transmitted from these extracellular structures to the cytoplasm.
Which of the following functions is NOT associated with the cytoskeleton in eukaryotic cells? A. the contraction of muscle cells in animals B. maintaining the position of the nucleus in the cell C. the beating of cilia or flagella determining the shape of animal cells D. movement of RNA molecules from the nucleus to the cytoplasm
Movement of RNA molecules from the nucleus to the cytoplasm, RNA molecules exit the nucleus via nuclear pores.
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?
Only one of the two fusion proteins possesses a nuclear localization signal
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?
Passive transport, a 25,000-dalton protein is small enough to diffuse through nuclear pores without any expenditure of energy.
phatocytosis
Some cells ingest smaller particles
Gaucher disease is the most common of lipid storage diseases in humans. It is caused by a deficiency of an enzyme necessary for lipid metabolism. This leads to a collection of fatty material in organs of the body including the spleen, liver, kidneys, lungs, brain, and bone marrow. Using your knowledge of the structure of eukaryotic cells, identify the statement below that best explains how internal membranes and the organelles of cells would be involved in Gaucher disease.
The lysosomes lack sufficient amounts of enzymes necessary for the metabolism of lipids.
Which of the following statements about the nuclear envelope is false? 1.) Nuclear pores are made up of a group of proteins that are collectively called the nuclear pore complex. 2.) The nuclear envelope is continuous with the Golgi apparatus. 3.) The nuclear envelope is composed of two lipid bilayers. 4.) Molecules pass into and out of the nucleus through nuclear pores.
The nuclear envelope is continuous with the Golgi apparatus.
Which statement correctly describes the nuclear envelope of a eukaryotic cell? 1.) The nuclear envelope is a single membrane, consisting of a phospholipid bilayer. 2.) Plasmadesmosomes in the nuclear envelope permit the exchange of macromolecules between the nucleus and the cytoplasm. 3.) All of the proteins of the cell are synthesized on ribosomes bound on the nuclear envelope. 4.) The nuclear envelope is continuous with the endoplasmic reticulum. 5.) The outer layer of the nuclear envelope is coated with laminin.
The nuclear envelope is continuous with the endoplasmic reticulum.
Pulse-chase Experiment
The pulse-chase experiment is similar to fitting newly synthesized proteins with identification collars, much as one would do in the field to track animals. By using a chase, this cohort of newly synthesized proteins can be tracked as they move to different regions of the cell, without any subsequently synthesized proteins complicating the results. By tracking these proteins over time, the target region where the protein's function can be identified based on the concentration of radioactivity.
A newspaper ad for a local toy store indicates that a very inexpensive microscope available for a small child is able to magnify specimens nearly as much as the much more costly microscope available in your college lab. What is the primary reason for the price difference?
The toy microscope magnifies a good deal, but has low resolution and therefore poor-quality images.
Which statements are true for chloroplasts? Select the three that apply. They are the sites of reactions that convert solar energy into chemical energy. Their inner membrane has infoldings called cristae. Their matrix contains enzymes that function in cellular respiration. 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 chemical energy to ATP.
They are the sites of reactions that convert solar energy into chemical energy. They contain the green pigment chlorophyll. They have membranous sacs called thylakoids that are surrounded by a fluid called stroma.
Which of the following choices correctly matches a tool and its proper application? 1.) cell fractionation to study the function of specific organelles 2.) transmission electron microscopy (TEM) to study the surfaces of preserved cells 3.) light microscopy to study the internal structure of cilia 4.) scanning electron microscopy (SEM) to study the detailed movements of living cells 5.) transmission electron microscopy (TEM) to study the movement of organelles within a living cell
cell fractionation to study the function of specific organelles
Which of the following correctly matches an organelle with its function? 1.) ribosome-manufacture of lipids 2.) central vacuole-storage 3.) mitochondrion-photosynthesis 4.) nucleus-cellular respiration 5.) lysosome-movement
central vacuole-storage
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?
exterior of cell
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?
The final destination of the proteins was the lysosome.
Both the volume and the surface area for three different cells were measured. These values are listed in the following table: Volume Surface Area Cell 1 9.3 μm3 26.5 μm2 Cell 2 12.2 μm3 37.1 μm2 Cell 3 17.6 μm3 40.6 μm2 Using data from the table above, select the best explanation for why that cell will be able to eliminate waste most efficiently?
Cell 2 since it has the highest surface area-to-volume ratio which facilitates the exchange of materials between a cell and its environment.
Plant cell structures
Cellulose cell wall, Chloroplast, Central vacuole
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 proteins are synthesized by bound ribosomes?
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.
Part B - Comparing eukaryotic and prokaryotic cells 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.
Prokaryotic only: nucleoid Eukaryotic only: Lysosome, Mitochondria, Nucleolus Both: Ribosomes, Plasma membrane, Flagella 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.
Choose the best description of the cell cytoskeleton. A. The cell cytoskeleton is a dynamic network of fibers that can be quickly dismantled and reassembled to change cell shape and the position of cell components. B. The cell cytoskeleton serves as permanent scaffolding to anchor cell components into position within the cell cytoplasm. C. The cell cytoskeleton is similar to an animal skeleton in providing rigid internal support and structure to the cell.
The cell cytoskeleton is a dynamic network of fibers that can be quickly dismantled and reassembled to change cell shape and the position of cell components.
Pulse-chase experiments and protein location 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? secretion phagocytosis detoxification muscle contraction
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.
Part A - Animal cell structures and functions 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.
a. synthesizes lipids b. assembles ribosomes c. defines cell shape d. produces secretory proteins e. modifies and sorts proteins f. digests proteins g. generates ATP 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.
A biologist ground up some plant leaf cells and then centrifuged the mixture to fractionate the organelles. Organelles in one of the heavier fractions could produce ATP in the light, whereas organelles in the lighter fraction could produce ATP in the dark. The heavier and lighter fractions are most likely to contain, respectively,
chloroplasts and mitochondria
Many cell organelles, most notably the nucleus, are anchored by ___________ which are assembled from a diverse class of proteins.
intermediate filaments
The extension of pseudopodia in amoeba is due to the regulated assembly and destruction of ______________.
microfilaments
Centrosomes are sites where protein dimers assemble into __________
microtubules
Which of these are hollow rods that shape and support the cell? A) plasma membrane B) microtubules C) chloroplasts D) microfilaments E) peroxisomes
microtubules
Mitochondria are found in _____.
plant and animal cells
What is the function of a bacterium's capsule?
protection
ribosomes
site for protein synthesis
Which of the following clues would tell you if a cell is prokaryotic or eukaryotic? 1.) The presence or absence of a rigid cell wall. 2.) The presence or absence of ribosomes. 3.) Whether or not the cell contains DNA. 4.) Whether or not the cell carries out cellular respiration. 5.) Whether or not the cell is partitioned by internal membranes.
whether or not the cell is partitioned by internal membranes