Chapter 6 - The Cell FRQ and Notes

A Panoramic View of the Eukaryotic Cell

- A eukaryotic cell has internal membranes that partition the cell into organelles - Plant and animal cells have most of the same organelles

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

- A lysosome is a membranous sac of hydrolytic enzymes that can digest(hydrolyze) macromolecules - Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and nucleic acids

- All organisms are made of ______________________ - The ______________ is the simplest collection of matter that can live - _______________ structure is correlated to cellular function - All cells are related by their ____________________________

- All organisms are made of cells - The cell is the simplest collection of matter that can live - Cell structure is correlated to cellular function - All cells are related by their descent from earlier cells

Functions of Endoplasmic Reticulum

- Biosynthetic Factory - The endoplasmic reticulum (ER) accounts for more than half of the total membrane in many eukaryotic cells - The ER membrane is continuous with the nuclear envelope - There are two distinct regions of ER: -Smooth ER, which lacks ribosomes -Rough ER, with ribosomes studding its surface

Describe Cell fractionation

- Cell fractionation takes cells apart and separates the major organelles from one another - Ultracentrifuges fractionate cells into their component parts - Cell fractionation enables scientists to determine the functions of organelles - Biochemistry and cytology help correlate cell function with structure

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 - Chromosome movements in cell division - Organelle movements

Mitochondria: Chemical Energy Conversion

- Mitochondria are in nearly all eukaryotic cells -They have a smooth outer membrane and an inner membrane folded into cristae -The inner membrane creates two compartments: intermembrane space and mitochondrial matrix -Some metabolic steps of cellular respiration are catalyzed in the mitochondrial matrix -Cristae present a large surface area for enzymes that synthesize ATP

Which two domains consist of prokaryotic cells? Which domains consist of Eukaryotic cells?

- Only organisms of the domains Bacteria and Archaea consist of prokaryotic cells - Protists, fungi, animals, and plants all consist of eukaryotic cells

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

- Prokaryotic cells are characterized by having - No nucleus -DNA in an unbound region called the nucleoid -No membrane-bound organelles -Cytoplasm bound by the plasma membrane - Eukaryotic cells are characterized by having -DNA in a nucleus that is bounded by a membranous nuclear envelope -Membrane-bound organelles -Cytoplasm in the region between the plasma membrane and nucleus -Eukaryotic cells are generally much larger than prokaryotic cells

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

- Ribosomes are particles made of ribosomal RNA and protein - Ribosomes carry out protein synthesis in two locations: -In the cytosol (free ribosomes) -On the outside of the endoplasmic reticulum or the nuclear envelope (bound ribosomes)

Study the electron micrographs in your text. Describe the different types of images obtained from: scanning electron microscopy (SEM) transmission electron microscopy (TEM)

- Scanning electron microscopes (SEMs) focus a beam of electrons onto the surface of a specimen, providing images that look 3-D - Transmission electron microscopes (TEMs) focus a beam of electrons through a specimen. They are used mainly to study the internal structure of cells

List and describe three major functions of the smooth ER.

- Synthesis of lipids : Enzymes of the smooth ER are important in the synthesis of lipids, including oils, phospholipids, and steroids. -Metabolizes carbohydrates : breaks foods down into sugars, which are also called saccharides. These molecules begin digesting in the mouth and continue through the body to be used for anything from normal cell functioning to cell growth and repair -Detoxifies poison : Detoxification usually involves adding hydroxyl groups to drug molecules, making them more soluble and easier to flush from the body. -Stores calcium : In muscle cells , the smooth ER membrane pumps calcium ions from the cytosol into the ER lumen

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

- The cytoskeleton is a network of fibers that organizes structures and activities in the cell - The cytoskeleton is a network of fibers extending throughout the cytoplasm -It organizes the cell's structures and activities, anchoring many organelles -It is composed of three types of molecular structures: -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

- The logistics of carrying out cellular metabolism sets limits on the ______________ of cells - The ______________ to _______________ of a cell is critical - As the ______________________ increases by a factor of n2, the volume increases by a factor of n3 - Small cells have a __________________ surface area relative to volume

- The logistics of carrying out cellular metabolism sets limits on the size of cells - The surface area to volume ratio of a cell is critical - As the surface area increases by a factor of n2, the volume increases by a factor of n3 - Small cells have a greater surface area relative to volume

What is the nuclear lamina? Nuclear matrix?

- The nuclear lamina is the net like array of protein filaments that maintains the shape of the nucleus by mechanically supporting the nuclear envelope - The nuclear matrix is a framework of protein fibers extending throughout the nuclear interior. - The nuclear matrix and lamina both help organize the genetic material so it functions efficiently. -In the nucleus, DNA and proteins form genetic material called chromatin -Chromatin condenses to form discrete chromosomes -The nucleolus is located within the nucleus and is the site of ribosomal RNA (rRNA) synthesis

Plasma Membrane

- The plasma membrane is a selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell - The general structure of a biological membrane is a double layer of phospholipids

Structure of Mitochondria and chloroplasts

-Are not part of the endomembrane system -Have a double membrane -Have proteins made by free ribosomes -Contain their own DNA

List all the structures of the endomembrane system.

-Components of the endomembrane system: -Nuclear envelope -Endoplasmic reticulum -Golgi apparatus -Lysosomes -Vacuoles -Plasma membrane -These components are either continuous or connected via transfer by vesicles

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

-Has bound ribosomes, which secrete glycoproteins (proteins covalently bonded to carbohydrates) -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. -Is a membrane factory for the cell

Centrosomes and Centrioles In many cells, microtubules grow out from a _______________ near the nucleus The centrosome is a __________________________ In animal cells, the centrosome has a pair of _____________________, each with nine triplets of microtubules arranged in a ring

-In many cells, microtubules grow out from a centrosome near the nucleus -The centrosome is a "microtubule-organizing center" -In animal cells, the centrosome has a pair of centrioles, each with nine triplets of microtubules arranged in a ring

Cilia and flagella are also composed of microtubules. The arrangement of microtubules is said to be "9 + 2." Make a sketch of a cross section here.

-Microtubules control the beating of cilia and flagella, locomotor appendages of some cells

The Golgi Apparatus: Shipping and Receiving Center

-The Golgi apparatus consists of flattened membranous sacs called cisternae -Functions of the Golgi apparatus: -Modifies products of the ER -Manufactures certain macromolecules -Sorts and packages materials into transport vesicles

Chloroplasts: Capture of Light Energy

-The chloroplast is a member of a family of organelles called plastids -Chloroplasts contain the green pigment chlorophyll, as well as enzymes and other molecules that function in photosynthesis -Chloroplasts are found in leaves and other green organs of plants and in algae -Chloroplast structure includes: -Thylakoids, membranous sacs, stacked to form a granum -Stroma, the internal fluid

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

-The nucleus contains most of the cell's genes and is usually the most conspicuous organelle -The nuclear envelope encloses the nucleus, separating it from the cytoplasm -The nuclear membrane is a double membrane; each membrane consists of a lipid bilayer -Pores regulate the entry and exit of molecules from the nucleus -The shape of the nucleus is maintained by the nuclear lamina, which is composed of protein

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?

After 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 transitional ER

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

Amoebas and many other protists cell can eat by engulf ing another cell by phagocytosis; this forms a food vacuole. This food vacuole formed fuses with a lysosome whose enzymes digest the food. Digestion products including simple sugars, amino acids, and other monomers, pass into the cytosol and become nutrients for the cell. Some of the human cells that carry out phagocytosis are macrophages, a type of white blood cell that helps defining the body by engulfing and destroying bacteria and other invaders. Lysosomes also use enzymes to recycle the cell's own organelles and macromolecules, a process called autophag

What is an endosymbiont?

An endosymbiont is a cell living with another cell

Animal cells have a centrosome that contains a pair of centrioles. Plant cells do not have centrioles. What is another name for centrosomes? 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

Recall the relationship of structure to function. Why is the inner membrane of the mitochondria highly folded? What role do all the individual thylakoid membranes serve? (Same answer for both questions.) Chloroplasts and mitochondria both have ribosomes and their own DNA. You will learn later about their evolution, but for now hold onto these facts. They are semiautonomous organelles that grow and reproduce within the cell. And you're lucky today— there is not a question here!

As highly folded surfaces, the cristae give the inner mitochondrial membrane a large surface area, thus enhancing the productivity of cellular respiration. As in mitochondria, thylakoid membranes serve to increase the surface area and thus the function of the chloroplasts

Why are cells so small? Explain the relationship of surface area to volume.

Cells are so small because if a cell grows beyond a certain limit, not enough material will be able to cross the cell membrane. As a cell increases in size the volume grows proportionately more than its surface area. (Area is proportional to a linear dimension squared, whereas volume is proportional to the linear dimension cubed)

What is the function of the chloroplasts?

Chloroplasts, found in plants and algae, are the sites of photosynthesis. These organelles convert solar energy to chemical energy by absorbing sunlight and using it to drive synthesis of organic compounds such as sugars from carbon dioxide and water.

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?

Chromatin is composed of proteins and DNA. Chromatin fibers condense to become distinct chromosomes as a cell prepares to divide

Compare and contrast cilia and flagella. (This is a specific instruction that means you are to tell how they are alike—compare—and tell how they are different—contrast. Remember this hint when you see a similar phrase on an exam.)

Cilia and flagella share a common ultrastructure: -A core of microtubules sheathed by 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 Differences : -Cilia and flagella differ in their beating patterns -A flagellum has an undulating motion that generates force in the same direction as the flagellum's axis, like the tail of a fish. In contrast, ciia works more like ours, with alternating power and recovery strokes generating force in a direction perpendicular to the cilium's axis.

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

During autophagy, a damaged organelle or small amount of cytosol becomes surrounded by a double membrane , and a lysosome fuses with the outer membrane of this vesicle. The lysosomal enzymes dismantle the enclosed material, and the organic monomers are returned to the cytosol for reuse. With the help of the lysosomes, the cell community renews itself. A human liver cell for example, recycles half of its macromolecules every week.

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

Nuclear envelope is connected to Rough ER, which is also continuous with smooth ER. Membranes and proteins produced by the ER flow in the form of transport vesicles to the Golgi apparatus. Golgi apparatus pinches off transport vesicles and other vesicles that give rise to lysosomes, other types of specialized vesicles and vacuoles. Lysosome is available for fusion with another vesicle for digestion. Transport vesicle carries proteins to plasma membrane for secretion. Plasma membrane expands by fusion of vesicles; proteins are secreted from cell.

When are the nucleoli visible? What are assembled here?

Nucleoli are visible in a nondividing nucleus and in cells active in protein synthesis. Within the nucleoli, proteins imported from the cytoplasm are assembled with rRNA into large and small subunits of ribosomes.

Explain the important role played by peroxisomes.

Peroxisomes are oxidative organelles -Peroxisomes are specialized metabolic compartments bounded by a single membrane -Peroxisomes produce hydrogen peroxide and convert it to water -Oxygen is used to break down different types of molecules

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.

The ER Lumen - is the cavity, or cisternal space. Because the ER membrane is continuous within the nuclear envelope, the space between the two membranes of the envelope is continuous with the lumen of the ER Transport Vesicles - bud off from a region of the rough ER called transitional ER and travel to the Golgi apparatus and other destinations. Smooth ER - is so named because its outer surface lacks Ribosomes Rough ER - is studded with ribosomes on the outer surface of the membrane and thus appears rough through the electron microscope

There are many types of vacuoles. Briefly describe: food vacuoles contractile vacuoles central vacuoles in plants (give at least three functions/materials stored here)

Vacuoles are Diverse Maintenance Compartments - Food vacuoles are formed by phagocytosis - Contractile vacuoles, found in many freshwater protists, pump excess water out of cells, there by maintaining a suitable concentration of ions and molecules inside the cell. - Central vacuoles, found in many mature plant cells, hold organic compounds and water. 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 enlarge as the vacuole absorbs water, enabling the cell to become larger with a minimal investment in new cytoplasam

In the figure, label the nuclear envelope, nuclear pores, and pore complex.

see slide 20

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.

the vesicle adds its membrane and contents to the cis face, it is enveloped by the golgi. the golgi then modifies the product as needed. Then a new vesicle is formed from the trans face and the vesicle leaves the golgi.

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 arms alternately grab, move, and release the outer microtubules -Performs a complex cycle Protein of movements caused by changes in the shape of the protein, with ATP providing energy for these changes -Protein cross-links limit sliding -Forces exerted by dynein arms cause doublets to curve, bending the cilium or flagellum

Describe how many neurons and intestinal cells each have greatly increased surface area.

A sufficiently high ratio of surface area to volume is especially important in cells that exchange a lot of material with their surroundings.

Why does alcohol abuse increase tolerance to other drugs such as barbiturates?

Barbiturates, alcohol, and many other drugs induce the proliferation of smooth ER and its associated detoxification enzymes , thus increasing the rate of detoxification. This in turn increases the tolerance to drugs, meaning that higher doses are required to achieve a particular effect, such as sedation.

Comparing Prokaryotic and Eukaryotic Cells

Basic features of all cells: -Plasma membrane -Semifluid substance called cytosol -Chromosomes (carry genes) -Ribosomes (make proteins)

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?

Functions of Microfilaments -Microfilaments are solid rods about 7 nm in diameter, built as a twisted double chain of actin subunits -The structural role of microfilaments is to bear tension, resisting pulling forces within the cell -They form a 3-D network called the cortex just inside the plasma membrane to help support the cell's shape -Bundles of microfilaments make up the core of microvilli of intestinal cells Motor proteins that move the microfilaments: -Myosin motors in muscle cell contraction : The "walking" of Myosin projections (the so called heads) drives the parallel myosin and actin filaments past each other so that the actin filaments approach each other in the middle. This shortens the muscle cell Muscle contraction involves shortening of many muscle cells at the same time. -Amoeboid movement : Interaction of actin filaments with myosin causes contraction of the cell, pulling the cell's trailing end forward -Cytoplasmic streaming in plant cells: A layer of cytoplasm 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.

What happens in Tay-Sachs disease? Explain the role of the lysosomes in Tay-Sachs.

In Tay-Sachs disease, a lipid-digesting enzyme is missing or inactive, and the brain becomes impaired by an accumulation of lipids in the cells. The lysosomes lack a functioning hydrolytic enzyme normally present.

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. Resolution is a measure of the clarity of the image; it is the minimum distance two points can be separated and still be distinguished as two points.

What is microvilli? How do these structures relate to the function of intestinal cells?

Microvilli are long, thin projections from the cell surface area without an appreciable increase in volume. A sufficiently high ratio of surface area to volume is especially important in cells that exchange a lot of materials with their surroundings, such as intestinal cells.

What is the function of the mitochondria?

Mitochondria are the sites of cellular respiration, a metabolic process that uses oxygen to generate ATP by extracting energy from sugars, fats and other fuels

In cell fractionation, whole cells are broken up in a blender, and this slurry is centrifuged several times. Each time, smaller and smaller cell parts are isolated. This will isolate different organelles and allow study of their biochemical activities. Which organelles are the smallest ones isolated in this procedure?

Ribosomes

What are the three roles of the cytoskeleton?

Roles of the Cytoskeleton: Support, Motility, and Regulation -The cytoskeleton helps to support the cell and maintain its shape -It interacts with motor proteins to produce motility -Inside the cell, vesicles can travel along "monorails" provided by the cytoskeleton -Recent evidence suggests that the cytoskeleton may help regulate biochemical activities

What is the endosymbiont theory? Summarize three lines of evidence that support the model of endosymbiosis

The endosymbiont theory states that an early ancestor of eukaryotic cells engulfed an oxygen using non photosynthetic 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 these cells may have taken up a photosynthetic prokaryote, becoming the ancestor of eukaryotic cells that contain chloroplasts Three lines of evidence that support the model of endosymbiosis: 1. Rather than being bound by single membrane, 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.

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 microscopes?

The methods used to prepare the specimen kill the cells.

Describe the organization of microtubules in a centriole. Make a sketch here that shows this arrangement in cross section.

The two centrioles are at right angles to each other, and each is made up of nine sets of three microtubules.