Chapter 6 - The Cell

Question 1

What is a light microscope?

Answer 1

Visible light is passed through the specimen and then through glass lenses. This magnifies the image.

Question 2

What are 3 important parameters in microscopy?

Answer 2

Magnification - the ratio of an object’s image size to its real size.

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

Contrast - the difference in brightness between the light and dark areas of an image.

Question 3

How much can LMs magnify an image?

Answer 3

To about 1,000 times the size of the actual specimen.

Question 4

What is an organelle?

Answer 4

The membrane enclosed structures within eukaryotic cells that have specialized functions.

Question 5

What is an electron microscope?

Answer 5

The EM focuses a beam of electrons through the specimen or onto its surface in order to study subcellular structures.

Question 6

What are the two different kinds of electron microscopes? How do they function?

Answer 6

Scanning electron microscope (SEM) - useful for the detailed study of the topography of a specimen. The electron beam scans the surface of the sample, which is usually coated with a thin film of gold, showing a 3D image of the surface.

Transmission electron microscope (TEM) - useful for studying the internal structures of cells. The thin specimen is usually stained with atoms of heavy metals, which attach to certain cellular structures, thus enhancing the electron density of some parts of the cell more than others, making that portion more visible.

Question 7

What is cytology?

Answer 7

The study of cell structure.

Question 8

What is biochemistry?

Answer 8

The study of the chemical processes (metabolism) of cells.

Question 9

What is cell fractionation?

Answer 9

Takes cells apart and separates major orangelles and other subcellular structures from one another. Ultracentrifuges fractionate cells into their component parts. This enables scientists to study and determine the functions of organelles.

Question 10

What basic features do all cells share?

Answer 10

1. Bounded by a selective barrier called the plasma membrane
2. Inside all cells is a semifluid, jellylike substance called cytosol
3. Contain chromosomes, which carry genes in the form of DNA
4. Contain ribosomes, which synthesize proteins

Question 11

What is cytosol?

Answer 11

A jellylike substance inside all cells, in which subcellular components are suspended.

Question 12

What is a eukaryotic cell?

Answer 12

Cells that have internal membrane bound organelles that compartmentalize their functions. Contains a double membrane bounded nucleus with DNA. The cytoplasm is in the region between the plasma membrane and the nucleus. Includes protists, fungi, plants, and animals. Generally much larger than prokaryotic cells.

Question 13

What is a prokaryotic cell?

Answer 13

Organisms of the domains bacteria and archaea. Contains no nucleus. The DNA is contained in an unbounded region called the nucleoid. Contains no membrane enclosed organelles. The cytoplasm is bound by the plasma membrane.

Question 14

What is a nucleoid?

Answer 14

A non membrane enclosed area of a prokaryotic cell where its chromosome (DNA) is located.

Question 15

What is the cytoplasm?

Answer 15

The interior of either type of cell. Refers only to the region between the nucleus and the plasma membrane.

Question 16

What are the smallest cells known?

Answer 16

Bacteria called mycoplasmas.

Question 17

What is the plasma membrane?

Answer 17

Functions as a selective barrier that allows passage of enough oxygen, nutrients, and wastes to service the entire cell.

Question 18

What is the general structure of a biological membrane?

Answer 18

A double layer of phospholipids.

Question 19

Explain the surface area to volume ratio and its importance in cellular metabolism.

Answer 19

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 a high surface-to-volume ratio facilitates the exchange of materials between a cell and its environment. As the surface area increases by a factor of n^2, the volume increases by a factor of n^3. Therefore, as a cell increases in size, the surface area grows proportionately less than its volume.

Question 20

Explain the organelles in eukaryotic cells.

Answer 20

The eukaryotic cell has extensive, elaborately arranged internal membranes that divide the cell into compartments, which provide different local environments that support specific metabolic functions.

Question 21

What is the nucleus?

Answer 21

Contains most of the cells genes and is usually the most conspicuous organelle.

Question 22

What is the nuclear envelope?

Answer 22

A double membrane. Each membrane is a lipid bilayer with associated proteins. The nuclear envelope encloses the nucleus, separating its contents from the cytoplasm.

Question 23

What is a pore complex?

Answer 23

The nuclear envelope is perforated by pore structures. At the lip of each pore, the inner and outer membranes of the nuclear envelope are continuous. An intricate protein structure called a pore complex lines each pore and plays an important role in the cell by regulating the entry and exit of proteins and RNAs, as well as large complexes of macromolecules.

Question 24

What is the nuclear lamina?

Answer 24

A netlike array of protein filaments that maintains the shape of the nucleus by mechanically supporting the nuclear envelope. Lines the inner surface of the nuclear envelope and may help organize the genetic material so it functions efficiently.

Question 25

What are chromosomes?

Answer 25

Within the nucleus, DNA is organized into discrete units called chromosomes. These are structures that carry the genetic information. Each chromosome contains one long DNA molecule associated with many proteins. Condensed chromatin.

Question 26

What is chromatin?

Answer 26

DNA and proteins form genetic material called chromatin.

Question 27

What is the nucleolus?

Answer 27

Located within the nucleus and is the site of ribosomal RNA synthesis.

Question 28

What are ribosomes?

Answer 28

Complexes made of ribosomal RNA and protein. The cellular components that carry out protein synthesis. Not membrane bound and thus not considered organelles.

Question 29

Where do ribosomes carry out protein synthesis? What are they called?

Answer 29

1. Free ribosomes - carry out synthesis in the cytosol - example; synthesize enzymes that catalyze sugar breakdown
2. Bound ribosomes - carry out synthesis in the nuclear envelope as they are attached to the outside of the ER - example; synthesize proteins that are destined for insertion into membranes, for packaging within certain organelles such as lysosomes or for export from the cell

Question 30

What is the endomembrane system?

Answer 30

The endomembrane system contains many different membranes in the cell;

1. Nuclear envelope
2. Endoplasmic riticulum
3. Golgi apparatus
4. Lysosomes
5. Vacoules and vesicles
6. Plasma membrane

This system of membranes regulates protein traffic and performs metabolic functions in the cell. This system carries out a variety of tasks in the cell, including synthesis of proteins, transport of proteins into membranes and organelles or out of the cell, metabolism and movement of lipids, and detoxification of poisons. The different components of this system are related either through direct physical continuity or by the transfer of membrane segments as tiny vesicles (sacs made of membrane).

Question 31

What are vesicles?

Answer 31

Tiny sacs made of membrane in the endomembrane system.

Question 32

What is the endoplasmic reticulum?

Answer 32

An extensive network of membranes. It accounts for more than half the total membrane in many eukaryotic cells. The ER consists of a network of membranous tubules and sacs called cisternae. The ER membrane separates the internal compartment of the ER (cavity) from the cytosol. The ER membrane is continuous with the nuclear envelope.

Question 33

What are the two different types of ER?

Answer 33

1. Smooth ER - lacks ribosomes

2. Rough ER - studded with ribosomes on the outer surface of the membrane

Question 34

What are the functions of smooth ER?

Answer 34

1. Synthesizes lipids, including oils, steroids, and new membrane phospholipids
2. Metabolizes carbohydrates
3. Detoxification of poison and drugs
4. Stores calcium ions

Question 35

What are the functions of rough ER?

Answer 35

1. Has bound ribosomes, which secrete glycoprotein (proteins covalently bonded with carbohydrates)
2. Distributes transport vesicles; transports the secretory proteins wrapped in membranes from the transitional ER
3. Membrane factory for the cell - it grows in place by adding membrane proteins and phospholipids to its own membrane

Question 36

What is the Golgi apparatus?

Answer 36

Consists of flattened membrane sacs called cisternae. Which we can think of as a warehouse for receiving, sorting, shipping, and even some manufacturing. In the Golgi apparatus, products of the ER, such as proteins, are modified and stored and then sent to other destinations.

Question 37

What are some functions of the Golgi apparatus?

Answer 37

1. Modifies products of the ER
2. Manufactures certain macromolecules
3. Sorts and packages materials into transport vesicles

Question 38

What are the two sides of the Golgi stack referred to as?

Answer 38

1. Cis face - the receiving side

2. Trans face - the shipping side