Chapter 6: A Tour of the Cell

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. What are four functions of microtubules?

- Maintenance of cell shape - cell motility (as in cilia or flagella); - chromosome movements in cell division (forming structures called centrosomes made of 2 centrioles in animal cells); - organelle movements

There are three main types of fibers that make up the cytoskeleton. Name them.

-Microtubules are the thickest of the three components of the cytoskeleton - Microfilaments, also called actin filaments, are the thinnest components - Intermediate filaments are fibers with diameters in a middle range

List and describe three major functions of the smooth ER.

-Synthesizes lipids -Metabolizes carbohydrates -Detoxifies drugs and poisons -Stores calcium ions

What are the three roles of the cytoskeleton?

-The cytoskeleton helps to support the cell and maintain its shape -It interacts with motor proteins to produce cell motility -Inside the cell, vesicles can travel along tracks provided by the cytoskeleton

What are the intercellular junctions between plant cells? What can pass through them?

Plasmodesmata are channels that perforate plant cell walls. Through plasmodesmata, water and small solutes (and sometimes proteins and RNA) can pass from cell to cell.

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

Primary cell wall

What is a lysosome? What do they contain? What is their pH?

A lysosome is a membranous sac of hydrolytic enzymes that can digest and break down macromolecules. Lysosomal enzymes work best in the acidic environment inside the lysosome.

Which two domains consist of prokaryotic cells?

Bacteria and Archaea

What is the function of the chloroplasts?

Chloroplasts, found in plants and algae, are the sites of photosynthesis. Chloroplasts contain the green pigment chlorophyll, as well as enzymes and other molecules that function in photosynthesis.

Compare and contrast cilia and flagella. How are they different?

Cilia and flagella differ in their beating patterns, length and number per cell: - Flagellum is longer than cilium - Cilia occurs in large numbers on the cell surface while flagella are limited to one or few per cell - Cilia have alternating power and recovery stroke, while flagellum has an undulating motion like the tail of a fish.

Compare and contrast cilia and flagella. How are they similar?

Cilia and flagella share a common structure: - A group of microtubules sheathed by an extension of the plasma membrane - A basal body that anchors the cilium or flagellum - A motor protein called dynein, which drives the bending movements of a cilium or flagellum

#32. How do motor proteins called dyneins cause movement of cilia? What is the role of ATP in this movement? This figure might help you explain.

Dynein has two "feet" that "walk" along microtubules. One foot maintains contact, while the other releases and reattaches one step farther along. Movements of the feet cause the microtubules to bend, rather than slide, because the microtubules are held in place. ATP is needed for the movement of motor proteins.

There are many types of vacuoles. Briefly describe:

Food vacuoles: are formed by phagocytosis Contractile vacuoles: found in many freshwater protists, pump excess water out of cells Central vacuoles in plants found in many mature plant cells, hold organic compounds and water

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.

Free Ribosomes: Located in cytosol, produces free proteins in the cystol Bound Ribosomes: Located on the outside of the endoplasmic reticulum or the nuclear envelope, produces proteins inserted in the membrane, or needed in some organelles, or secreted from the cell

A major difference between prokaryotic and eukaryotic cells is the location of their DNA. Describe this difference.

In prokaryotic cells, DNA is in a region called the nucleoid. This region is not membrane bound. In eukaryotic cells, DNA is in a nucleus that is bounded by a double membrane.

A second function of lysosomes is to recycle cellular components in a process called autophagy. Describe this process.

Lysosomes also use enzymes to recycle the cell's own organelles and macromolecules, a process called autophagy. Lysosomes fuse with a vesicle containing damaged organelles and digest the molecules. The resulting small organic compounds are released to the cytosol for reuse.

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 an oak tree. His contemporary, Anton van Leeuwenhoek, crafted lenses; and with the improvements in optical aids, a new world was opened. Magnification and resolving power limit what can be seen. Explain the difference.

Magnification is the ratio of an object's image size to its real size. Light microscope magnifies effectively 1000 times the actual size of the specimen. Resolution is the measure of the clarity of an image. It is the minimum distance two points can be separated and still be distinguished as distinct points.

Intermediate filaments are bigger than microfilaments but smaller than microtubules. They are more permanent fixtures of cells. Give two functions of intermediate filaments.

Maintenance of cell shape (tension-bearing elements); anchorage of nucleus and certain other organelles; formation of nuclear lamina

Microfilaments are solid, and they are built from a double chain of actin. What are four functions of microfilaments? What are the motor proteins that move the microfilaments?

Maintenance of cell shape (tension-bearing elements); changes in cell shape; muscle contraction; cell motility (as in unicellular organisms' movement); division of animal cells. Myosins are the motor proteins that move microfilaments.

What is the middle lamella? Where is it found?

Middle lamella is a thin layer rich in sticky polysaccharides found between primary walls of adjacent cells.

What is the function of the mitochondria?

Mitochondria are the sites of cellular respiration, a metabolic process that uses oxygen to generate ATP. Some metabolic steps of cellular respiration are catalyzed in the mitochondrial matrix.

What is the composition of the cell wall?

Plant cell walls are made of cellulose fibers embedded in other polysaccharides and protein.

#17. 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 what happens to a transport vesicle and its contents when it arrives at the Golgi.

Products of ER are modified during their transit from cis face of Golgi to trans face of Golgi where they are secreted in transport vesicles to reach their final destination.

What is the function of ribosomes? What are their two components?

Ribosomes carry out protein synthesis. Ribosomes are complexes made of ribosomal RNA and proteins.

Besides packaging secretory proteins into transport vesicles, what is another major function of the rough ER?

Rough ER is a membrane factory to the cell. It grows in place by adding membrane proteins and phospholipids to its own membrane.

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?

Rough ER packages secretory proteins into membrane bound vesicles called transport vesicles. These vesicles travel to Golgi after leaving ER. From Golgi, these proteins are shipped along the cytoskeleton to reach the and fuse with the plasma membrane.

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

Smooth ER lacks ribosomes while rough ER has ribosomes bound to its membrane

One function of lysosomes is intracellular digestion of particles engulfed by phagocytosis. Describe this process of digestion. What human cells carry out phagocytosis?

Some types of cell, like macrophages - a type of white blood cells, can engulf another cell by phagocytosis; this forms a food vacuole. A lysosome fuses with the food vacuole and digests the molecules. Digestion products, including amino acids, simple sugars and other monomers, pass into the cytosol and become nutrients for the cell.

What are three functions of the cell wall?

The cell wall protects the plant cell, maintains its shape, and prevents excessive uptake of water.

What is the cytoskeleton?

The cytoskeleton is a network of fibers extending throughout the cytoplasm.

Describe the nuclear envelope. How many layers is it? What connects the layers?

The nuclear envelope is a double membrane; each membrane consists of a lipid bilayer. Pores, formed by proteins, regulate the entry and exit of molecules from the nucleus and connect the layers.

What is the nuclear lamina?

The nuclear side of the envelope is lined by the nuclear lamina, which is composed of proteins (intermediate filaments) and maintains the shape of the nucleus.

9. What are assembled in the nucleoli?

The nucleolus is located within the nucleus and is the site of ribosomal RNA (rRNA) synthesis.

Study the electron micrographs in your text. Describe the different types of images obtained from:

scanning electron microscopy (SEM) focus a beam of electrons onto the surface of a specimen, providing images that look 3-D transmission electron microscopy (TEM) focus a beam of electrons through a specimen. TEMs are used mainly to study the internal structure of cells.

List all the structures of the endomembrane system.

§ Nuclear envelope § Endoplasmic reticulum § Golgi apparatus § Lysosomes § Vacuoles § Plasma membrane