Assignment 4: Chapter 6 Tour of the Cell PDF

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Assignment 4, Chapter 6: Tour of the cell....

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Assignment 4 Chapter 6: A Tour of the Cell

Identify how common techniques of microscopy and biochemistry are used in cell biology. 1.The study of cells has been limited by their small size, and so they were not seen and described until 1665, when Robert Hooke first looked at dead cells from the bark of an oak tree. His contemporary, Antoni van Leeuwenhoek, crafted lenses and opened a new world with the improvements in optical aids. Magnification and resolving power limit what can be seen. Explain the difference. The difference was in the magnification, the ration of the objects image size to its real size, as well as resolving power which is the ability of the microscope to show detail. 2.The development of electron microscopes has further opened our window on the cell and its organelles. What is considered a major disadvantage of the electron microscope? The methods used from the electron microscope which are used in order to prepare the specimen end up killing the cells. 3.

Study the electron micrographs in your text. Describe the different types of images obtained from: scanning electron microscopy (SEM)- This type of microscopy shows the surface of a cell from a trachea cover with cell projections. transmission electron microscopy (TEM)- This type of microscopy profiles a thin section of a specimen, which results in various views of the cells prepared.

4.

Which two domains consist of prokaryotic cells? ____Bacteria and Archaea______________________ 5. On the figure of a prokaryotic cell, label each of these features and give its function or description. cell wall: Rigid structure outside of the plasma membrane. plasma membrane: cytoplasm.

Membrane

enclosing

the

bacterial chromosome: Carries genes in the form of DNA. nucleoid: The region at which the cell’s DNA is located. ribosomes: Is a micro-machine for making proteins. flagella: Locomotion organelles of some bacteria.

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Surface area-to-volume ratio is an important concept as it determines the ability of a cell to exchange materials with the environment. It is important that you be able to both calculate this ratio and also understand its significance. 6.

Why are cells so small? Explain the relationship of surface area to volume. Cells are small due to the fact that there is a high surface area to volume ratio, which facilitates the exchange of materials between a cell and its environment. As a cell increases in its size, its volume grows proportionally more than the surface area. Therefore, smaller objects will have a greater ratio of surface area to volume.

7.

Exchange of materials across the plasma membrane requires a high surface-to-volume ratio. How do the microvilli of intestinal cells facilitate this? They increase the surface area without increasing the volume.

Describe the structure of the nucleus, chromosomes, and ribosomes, and explain their functions. 8.

Describe the nuclear envelope. How many layers does it consist of? What connects the layers? How do molecules such as mRNA pass through the envelope? The nuclear envelope encloses the nucleus, which separates its contents from the cytoplasm. It contains a double membrane, where there are two lipid bilayers. The layers are able to connect by the lamina, a netlike array of protein filaments.

9.

Found within the nucleus are the chromosomes. They are made of chromatin. What are the two components of chromatin? When do the thin chromatin fibers condense to become distinct chromosomes? The two components of chromatin are proteins and DNA. Chromatin fibers condense to become a distinct chromosomes as a cell prepares to divide.

10.

When are the nucleoli visible? What organelles are assembled here? The nucleoli are visible in a nondividing nucleus and in cells active in protein synthesis. Large and small subunits of ribosomes are assembled at the nucleoli by proteins imported from the cytoplasm with rNA.

11.

What is the function of ribosomes? What are their two components? Ribosomes are cellular components that carry out protein synthesis. The two components are large and small subunit.

12.

Ribosomes in any type of organism are all the same, but we distinguish between two types of ribosomes based on where they are found, and the destination of the protein product made. Complete this chart to demonstrate this concept. Type of Ribosome

Location

Product -2-

Free ribosomes

Suspended in cytosol.

Proteins which function within cytosol.

Bound ribosomes

Attached to the outside of endoplasmic reticulum or the nuclear envelope.

Proteins for insertion into membranes.

Identify the parts of the endomembrane system and describe their roles in the cell. 13.

List all the structures of the endomembrane system. -Nuclear envelope -Endoplasmic reticulum -Golgi apparatus -Lysosomes -Vesicles -Vacuoles -Plasma membrane

14.

The endoplasmic reticulum (ER) makes up more than half the total membrane system in many eukaryotic cells. Use this sketch to label and explain the lumen, transport vesicles, and the difference between smooth and rough ER. Smooth ER Rough ER

Lumen

Transport Vehicles

Lumen: The cavity or cisternal space. The space between the two membranes of the envelope is continuous with the limen of the ER. Transport vesicles: They bud off of a region of the rough ER called the transitional ER and travel to the golgi apparatus and other destinations. Smooth ER: Outer surface lacks ribosomes. Rough ER: Studded with ribosomes on the outer surface of the membrane and thus appears rough through the electron microscope. 15.

List and describe three major functions of the smooth ER.

-Synthesis of lipids: Smooth ER enzymes are important in synthesis of lipids. -Detoxification of drugs and poisons: Detoxification involves the adding of hydroxyl groups to drug molecules, which makes them more soluble and easier to flush from the body.

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-Storage of calcium ions: In muscle cells, the smooth ER membrane pumps calcium ions from the cytosol into the ER lumen. 16.

Why does alcohol abuse increase tolerance to other drugs such as barbiturates? Alcohol and barbiturates induce the proliferation of the smooth ER and its associated detoxification enzymes, which increases the rate of detoxification. Therefore, increasing the tolerance to drugs, where higher doses are required in order to achieves effects such as sedation.

17.

The rough ER is studded with ribosomes. As proteins are synthesized, they are threaded into the lumen of the rough ER. Some of these proteins have carbohydrates attached to them in the ER to form glycoproteins . What does the ER then do with these secretory proteins? As secretory proteins are formed, the ER membrane keeps them separate from proteins that are produced by free ribosomes and that will remain in the cytosol. Secretory proteins depart from the ER wrapped in the membranes of vesicles that bud like bubbles from a specialized region called the transitional ER.

18.

What is another major function of the rough ER? The rough ER grows membrane proteins and phospholipids for the cell by adding them to its own membrane. The ER membrane expands, and portions of it are transferred in the form of transport vesicles to other components of the endomembrane system.

19. The transport vesicles formed from the rough ER fuse with the Golgi apparatus. Use this sketch to label the cisterna of the Golgi apparatus, and its cis and trans faces. Describe all that can happen to a transport Cisternae

vesicland its contents after it arrives in the Golgi apparatus. Vesicles coalesce to form new cis Glogi cisternae. Golgi cisternae also move in a cis-to-trans direction. The vesicles then leave the Golgi and carry products to other locations or to the plasma membrane for secretion. They also transport proteins backward to less mature Golgi, or back to the ER, their site of function. 20.

What is a lysosome? What does it contain? What is the pH range inside a lysosome? A lysosome is a membranous sac of hydrolytic enzymes that an animal cell uses in order to digest macromolecules. The pH range inside of a lysosome is acidic.

21.

One function of lysosomes is intracellular digestion of particles engulfed by phagocytosis. Describe this process of digestion. Which human cells carry out phagocytosis? Amoebas and other protists eat through engulfing smaller organisms or food particles. The food vacuole fuses with a lysosome whose enzymes digest the food. Digestion products pass into the cytosol and become nutrients for the cell. -4-

Human cells that carry out phagocytosis are macrophages, type of white blood cell that defends the body by engulfing and destroying bacteria and other invaders. 22.

There are many types of vacuoles. Briefly describe each type of vacuole below. food vacuoles: Formed by phagocytosis contractile vacuoles: They pump excess water out of the cell, which allows it to maintain a suitable concentration of ions and molecules inside of the cell. central vacuoles in plants: Develop by the coalescence of smaller vacuoles, contained in mature plant cells. Solution inside the central vacuole, called cell sap, is the plant cell’s main repository of inorganic ions, including potassium and chloride. The central vacuole plays a major role in the growth of plant cells, which enlarges as the vacuole absorbs water, enabling the cell to become larger with a minimal investment in new cytoplasm.

23.

Label and use this figure to explain how the elements of the endomembrane system function together to secrete a protein and to digest a cellular component. Nucleus

Nuclear envelope

Rough ER

Smooth ER

Cis Golgi

Trans Golgi

This figure above demonstrates the endosymbiont theory, which details that an early ancestor of eukaryotic cells engulfed an oxygen using non-photosynthetic prokaryotic cell. Then later on the engulfed cell will form a relationship with the host cell, allowing it to become a cell living within another cell. Compare and contrast the structures and functions of mitochondria and chloroplasts. 24.

What is the endosymbiont theory? Summarize three lines of evidence that support the model of endosymbiosis. This theory states that an early ancestor of eukaryotic cells engulfed an oxygen using nonphotosynthetic prokaryotic cell, and over the course of evolution, the host cell and its endosymbiont merged into a single organism, a eukaryotic cell with a mitochondrion. At least one of the cells has taken up a photosynthetic prokaryote, becoming the ancestor of eukaryotic cells that contain chloroplasts. 1.Like organelles of the endomembrane system, mitochondria and typical chloroplasts have two membranes surrounding them. 2. Like Prokaryotes, mitochondria and chloroplasts contain ribosomes, as well as circular DNA molecules attached to their inner membranes. 3. Also consistent with their probable evolutionary origins as cells, mitochondria and chloroplasts are autonomous organelles that grow and reproduce within cells.

25.

Mitochondria and chloroplasts are not considered part of the endomembrane system, although they are enclosed by membranes. Sketch a mitochondrion here and label its outer membrane, inner membrane, inner membrane space, cristae, matrix, and ribosomes. -5-

Outer membrane Inner membrane

Ribosomes

Cristae

Matrix

26.

Now sketch a chloroplast and label its outer membrane, inner membrane, inner membrane space, thylakoids , granum, and stroma. Notice that the mitochondrion has two membrane compartments, whereas the chloroplast has three compartments. Ribosomes

Stroma

Outer membrane

Inner membrane

Granum

Thylakoid Inner membrane space

27.

What is the function of the mitochondria? Mitochondria are the sites of cellular respiration, the metabolic process that uses oxygen to generate ATP by extracting energy from sugars, fats, and other fuels.

28.

What is the function of the chloroplasts? Chloroplasts are sites of photosynthesis. These organelles convert solar energy to chemical energy by absorbing sunlight and using it to drive synthesis or organic compounds such as sugars from carbon dioxide and water.

29.

Explain the important roles played by peroxisomes. Peroxisomes contain enzymes that remove hydrogen atoms from various substances and transfer them to oxygen, thus producing hydrogen peroxide as a by-product.

30.

Use peroxisomes as an example to explain the value of compartmentalization in cells. Cell compartmentalization is the way in which organelles in eukaryotic cells live and work in separate areas in order to produce more efficient work. Peroxisomes similarly contain these enzymes in order to more effectively remove hydrogen atoms and transfer them to oxygen.

Describe the subunits and structures of the three types of cytoskeletal fibers and list their functions. -6-

31.

What is cytoskeleton? There are three main types of fibers that make up the cytoskeleton. Name them A cytoskeleton is a network of fibers extending throughout the cytoplasm. 1. Microtubules 2. Microfilaments 3. Intermediate filaments

32.

What are three functions of the cytoskeleton? 1. Maintenance of cell shape 2. Mechanical support 3. Cell motility

33.

Microtubules are hollow rods made of a globular protein called tubulin. Each tubulin protein is a dimer made of two subunits. These are easily assembled and disassembled. Describe several functions of microtubules. 1. Maintenance of cell shape 2. Cell motility 3. Chromosome movement in cell division 4. Organelle movement

34.

Animal cells have a centrosome that contains a pair of centrioles. Plant cells do not have centrioles. What is believed to be the role of centrioles? Another name for centrosome is “microtubule-organizing center”. The centrioles function as compression-resisting girders of the cytoskeleton.

35.

Compare and contrast cilia and flagella. For both, select a human cell that has this feature, and describe the role for that cell. Cilia and flagella are both microtubule-containing extensions that project from some cells. Cilia and flagella share a common structure, each having a group of microtubules sheathed in an extension of the plasma membrane. Flagella and cilia differ in their beating patterns. A flagella has an undulating motion that generates force in the same direction as the flagellum’s axis, like the tail of a fish. In contrast, cilia works more like oars, with alternating power and recovery strokes generation force in a direction perpendicular to the cilium’s axis.

36.

How do motor proteins called dyneins cause movement of cilia? What is the role of ATP in this movement? Dyneins are primarily responsible for the bending and movements of the organelle. A dynein molecule performs a complex cycle of movements caused by changes in the shape of the protein, with ATP -7-

providing the energy for these changes. 37.

Microfilaments are solid, and they are built from a double chain of actin. Study Figure 6.26 in your text and explain three examples of movements that involve microfilaments. 1. Myosin motors in muscle cell contraction, myosin projections drive the parallel myosin and actin filaments past each other so that the actin filaments approach each other in the middle, which shortens the muscle cell. Muscle contraction involves the shortening of many muscle cells at the same time. 2. Amoeboid movement, Interaction of actin filaments with myosin causes contraction of the cell, pulling the cell’s trailing end forward. 3. Cytoplasmic streaming in plant cells, a layer of cytoplasm cycles around the cell, moving over a carpet of parallel actin filaments. Myosin motors attached to organelles in the fluid cytosol may drive the streaming by interacting with the actin.

38.

What are the motor proteins that move the microfilaments? Myosin.

39.

Intermediate filaments are bigger than microfilaments but smaller than microtubules. They are more permanent fixtures of cells. Give two functions of intermediate filaments. 1. Maintenance of cell shape 2. Anchorage of nucleus and certain other organelles 3. Formation of nuclear lamina

Compare and contrast (1) the extracellular components of plant and animal cells and (2) the cell junctions of plant and animal cells. 40.

What are three functions of the cell wall? 1. Protects the plant cell 2. Maintains its shape 3. Prevents excessive uptake of water

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41.

What is the composition of the cell wall? Microfibrils made up of the polysaccharide cellulose are synthesized by an enzyme called cellulose synthase and secreted to the extracellular space, where they become embedded in a matrix of other polysaccharides and proteins.

42.

What is the relatively thin and flexible wall secreted first by a plant cell? Primary cell wall.

43.

What is the middle lamella? Where is it found? What material is it made of? It is a thin layer of sticky polysaccharides called pectins, which is located between the primary walls of the adjacent cells.

44.

Animal cells do not have cell walls, but they do have an extracellular matrix (ECM). On this figure, label the elements indicated, and give the role of each. Also label the extracellular fluid and cytoplasm. Collagen: Fibers embedded in web of proteoglycan complexes.

Extracellular fluid Proteoglycan complex: Proteoglycan molecules attached noncovalently to polysaccharide molecule.

Fibronectin: ECM protein that attaches ECM to integrins. Integrins: Transmit signals between the cell’s external environment and its interior and can result in changes in cell behavior.

Plasma membrane

Cytoplasm Microfilaments

45.

What are the intercellular junctions between plant cells? What can pass through them? Plasmodesmata are intercellular junctions between plant cells. Cytosol passes through the plasmodesmata and joins the internal chemical environments of adjacent cells.

46.

Animal cells do not have plasmodesmata. This figure shows the three types of intercellular junctions seen in animal cells. Label each type and summarize its role.

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Tight junction

Desmosome

Intermediate filaments

Gap junction

ions

Plasma membranes

Extracellular matrix Space between cells

. Tight junctions: Seals neighboring cells together into an epithelial sheet in order to prevent leakage of molecules between them. Desmosomes: Joins the intermediate filaments into one cell to those in neighbor. Gap junctions: Allows the passage of small water-soluble ions and molecules.

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