BIOL 211 - Chapter 6

Given the extra cellular function, name the structure and if it's in a plant or animal. 1. Membrane protein complexes that strengthen the adhesion between adjacent cells, like rivets, to protect against pulling forces. 2. Small channels that form across the plasma membranes of adjacent cells; especially important in intercellular communication. 3. Membrane proteins that create a watertight seal between cells. 4. Small channels between cells that are otherwise surrounded by walls; enable movement of water and solutes between cells. 5. A polysaccharide that is used to synthesize cell walls and help maintain their shape. 6. Long fibers of protein found in the extracellular matrix that provide structural support for cells.

1. desmosomes-animal 2. gap junctions-animal 3. tight junctions-animal 4. plasmodesmata-plant 5. cellulose-plant 6. collagen-animal 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.

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. 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. microtubules 2. intermediate filaments 3. microtubules 4. microfilaments 5. intermediate filaments 6. 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.

_____ is/are identical in structure to centrioles.

Basal bodies

Which of the following are common traits of chloroplasts and mitochondria?

Both have their own DNA and ribosomes.

Which molecules do not normally cross the nuclear membrane?

DNA All processes involving DNA take place in the nucleus.

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.

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

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

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?

Lysosomal enzyme, insulin, and ER protein. 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.

Which of these provides the cell with structural support?

Microfilaments are a component of the cytoskeleton. Be able to locate.

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. The nuclear localization signal is only present in the fusion protein that enters the nucleus.

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.

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.

Plant cell only: cellulose cell wall, central vacuole, and chloroplast. Animal cell only: centriole. Both: mitochondrion, endoplasmic reticulum, golgi apparatus, cytoskeleton, nucleus, plasma membrane. 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.

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

Plant cell wall: strong, protective structure made from cellulose fibrils. Central vacuole: regulates cytoplasm composition, creates internal pressure, and stores cell compounds. Chloroplast: makes sugar by converting light energy into chemical energy. Mitochondrion: produces chemical energy (ATP) that can power the cell. Golgi apparatus: modifies and packages proteins. 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.

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: flagella, ribosomes, plasma membrane 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.

_____ are the sites of protein synthesis.

Ribosomes

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.

Smooth ER: lipid synthesis; calcium ion storage; poison detoxification. Rough ER: protein synthesis. Golgi Apparatus: protein modification and sorting; cisternal maturation. Lysosomes: macromolecule digestion; autophagy. 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.

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

The Golgi apparatus modifies, stores, and packages products of the ER. Be able to locate.

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. Be able to locate the structures that do the following: Drag the labels on the left onto the diagram of the animal cell to correctly identify the function performed by each cellular structure. a. synthesize lipids b. assembles ribosomes c. defines cell shape d. produces secretory proteins e. modifies and sorts proteins f. digest 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.

Which of the following statements about the nuclear envelope is false? a. The nuclear envelope is continuous with the Golgi apparatus. b. Nuclear pores are made up of a group of proteins that are collectively called the nuclear pore complex. c. Molecules pass into and out of the nucleus through nuclear pores. d. The nuclear envelope is composed of two lipid bilayers.

The nuclear envelope is continuous with the Golgi apparatus.

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

The nucleus contains most of a cell's DNA. Be able to locate.

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

This is the nuclear envelope. Be able to locate.

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

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. a. Their inner membrane has infoldings called cristae. b. They are the sites of reactions that convert solar energy into chemical energy. c. They contain the green pigment chlorophyll. d. They are the sites of reactions that convert chemical energy from food molecules to ATP. e. Their matrix contains enzymes that function in cellular respiration. f. They have membranous sacs called thylakoids that are surrounded by a fluid called stroma.

b. They are the sites of reactions that convert solar energy into chemical energy. c. They contain the green pigment chlorophyll. f. They have membranous sacs called thylakoids that are surrounded by a fluid called stroma. 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.

Which of the following choices correctly matches a tool and its proper application?

cell fractionation to study the function of specific organelles Cell fractionation can be used to separate different organelles to study their function separate from the rest of the cell.

The _____ is composed of DNA and protein.

chromatin

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

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

Which organelle plays a role in intracellular digestion? a. Golgi apparatus b. chloroplast c. lysosome d. plasmodesma e. ribosome

lysosome The prefix "lyso-" means decomposition.

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

microtubules

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

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

Which of these organelles carries out cellular respiration?

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

Ribosomal subunits are manufactured by the _____.

nucleolus

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

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

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

plasma membrane The plasma membrane regulates the passage of material into and out of the cell.

Which of the following clues would tell you if a cell is prokaryotic or eukaryotic?

whether or not the cell is partitioned by internal membranes Prokaryotic cells lack any internal membranous compartmentalization.

Proteins that are secreted from a eukaryotic cell must first travel through the endomembrane system. Identify the path a secretory protein follows from synthesis to secretion.

protein synthesis -> endoplasmic reticulum -> cis Golgi cisternae -> medial Golgi cisternae -> trans Golgi cisternae -> plasma membrane -> extracellular space 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.

Which of these manufactures cellular membranes by adding membrane proteins and phospholipids to its own membrane?

rough endoplasmic reticulum As membrane proteins grow from ribosomes on rough ER, the proteins are embedded into the rough ER membrane.

Where is calcium stored?

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

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

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

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

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