The cell

Question 1

What is a light microscope (LM)?

Answer 1

• visible light is passed through the specimen and then through glass lenses.
• The lenses refract (bend) the light in such a way that the image of the specimen is magnified as it is projected into the eye or into a camera

Question 2

What are 3 important parameters in microscopy?

Answer 2

1. magnification
2. resolution
3. contrast.

Question 3

What is magnification?

Answer 3

• the ratio of an object’s image size to its real size.
• LM can magnify effectively to about 1,000 times the actual size of the specimen;
• at greater magnifications, additional details cannot be seen clearly.

Question 4

What is Resolution?

Answer 4

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

Question 5

What is contrast?

Answer 5

• the difference in brightness between the light and dark areas of an image.
• Methods for enhancing contrast include staining or labeling cell components to stand out visually.

Question 6

What are organelles?

Answer 6

the membrane-enclosed structures within eukaryotic cells.

Question 7

What is the electron microscope (EM)?

Answer 7

• a beam of electrons through the specimen or onto its surface.
• Resolution is inversely related to the wavelength of the light (or electrons) a microscope uses for imaging, and electron beams have much shorter wavelengths than visible light.

Question 8

What is transmission electron microscope (TEM) used to study?

Answer 8

• is used to study the internal structure of cells

Question 9

What is cytology?

Answer 9

the study of cell structure

Question 10

What is cell fractionation?

Answer 10

• used to separate (fractionate) cell components based on size and density.
• Cell fractionation enables researchers to prepare specific cell components in bulk and identify their functions, a task not usually possible with intact cells.

**More info**

The piece of equipment that is used for this task is the centrifuge, which spins test tubes holding mixtures of disrupted cells at a series of increasing speeds.

At each speed, the resulting force causes a subset of the cell components to settle to the bottom of the tube, forming a pellet.

At lower speeds, the pellet consists of larger components, and higher speeds result in a pellet with smaller components.

Question 11

What do all cells have in common?

Answer 11

1. They are all bounded by a selective barrier, called the plasma membrane (also referred to as the cell membrane).
2. Inside all cells is a semifluid, jellylike substance called cytosol, in which subcellular components are suspended.
3. All cells contain chromosomes, which carry genes in the form of DNA.
4. All cells have ribosomes, tiny complexes that make proteins according to instructions from the genes.

Question 12

State a major difference between prokaryotic and eukaryotic cells

Answer 12

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

• eukaryotic cell, most of the DNA is in an organelle called the nucleus, which is bounded by a double membrane.
• In a prokaryotic cell, the DNA is concentrated in a region that is not membrane-enclosed, called the nucleoid

Question 13

All cells share certain basic features: Name them!

Answer 13

1. Plasma membrane (also referred to as the cell membrane).
2. Cytosol
3. Contain chromosomes, which carry genes in the form of DNA.
4. Ribosomes, tiny complexes that make proteins according to instructions from the genes

Question 14

What is cytosol?

Answer 14

• Inside all cells is a semifluid, jellylike substance in which subcellular components are suspended.

Question 15

Where is the DNA in a Eukaryote cell? In a prokaryote cell?

Answer 15

• Eukaryote cell: most of the DNA is in an organelle called the nucleus, which is bounded by a double membrane
• Prokaryotic cell: the DNA is concentrated in a region that is not membrane-enclosed, called the nucleoid

Question 16

What does plasma membrane do?

Answer 16

• functions as a selective barrier that allows passage of enough oxygen, nutrients, and wastes to service the entire cell
• Only a limited amount of a particular substance can cross per second, so the ratio of surface area to volume is critical.

Question 17

What is the cytoplasm?

Answer 17

The interior of either type of cell

• Eukaryotic cells, this term refers only to the region between the nucleus and the plasma membrane.
  
  • Within the cytoplasm - suspended in cytosol, are a variety of organelles
• prokaryotic cytoplasm is not a formless soup.

Question 18

What is the nucleus in a EC?

Answer 18

The contains most of the genes in the eukaryotic cell.

Question 19

What is the nuclear envelope?

Answer 19

• encloses the nucleus separating its contents from the cytoplasm.
• is a double membrane, each a lipid bilayer with associated proteins
• 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

Question 20

What is chromatin?

Answer 20

• The complex of DNA and proteins making up chromosomes
• When a cell is not dividing, the chromosomes cannot be distinguished from one another, even though discrete chromosomes are present.
• cell prepares to divide, the chromosomes coil (condense) further, becoming thick enough to be distinguished under a microscope as separate structures.

Question 21

What is the nucleolus?

Answer 21

• plural, nucleoli
• Here a type of RNA called ribosomal RNA (rRNA) is synthesized from instructions in the DNA.
• Proteins imported from the cytoplasm are assembled with rRNA into large and small subunits of ribosomes.
• As we saw in Figure 5.22, the nucleus directs protein synthesis by synthesizing messenger RNA (mRNA) according to instructions provided by the DNA.

Question 22

1. What are Ribosomes?
2. Name the two types
   
   • Name function of each type

Answer 22

• carry out protein synthesis
• (Note that ribosomes are not membrane bounded and thus are not considered organelles.)
• Bound and free ribosomes are structurally identical, and ribosomes can play either role at different times.

1. Free ribosomes are suspended in the cytosol -
   
   • Most of the proteins made on free ribosomes function within the cytosol
2. Bound ribosomes are attached to the outside of the endoplasmic reticulum or nuclear envelope.
   
   • generally make proteins that are destined for insertion into membranes, for packaging within certain organelles such as lysosomes

Question 23

What is the endomembrane system?

Answer 23

• includes the nuclear envelope, the endoplasmic reticulum, the Golgi apparatus, lysosomes, various kinds of vesicles and vacuoles, and the plasma membrane.
• 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.
• Related either through direct physical continuity or by the transfer of membrane segments as tiny vesicles (sacs made of membrane).

Question 24

What are vesicles?

Answer 24

Sacs made of membrane

Question 25

What is the endoplasmic reticulum (ER)?

Answer 25

• Accounts for more than half the total membrane in many eukaryotic cells.
• Consists of a network of membranous tubules and sacs called cisternae
• Separates the ER lumen (cavity) from the cytosol.
• ER membrane is continuous with the nuclear envelope, the space between the two membranes of the envelope is continuous with the lumen of the ER

Question 26

What is the Smooth ER?

Answer 26

• Outer surface lacks ribosomes.
• Involved in diverse metabolic processes:
  • synthesis of lipids, metabolism of carbohydrates, detoxification of drugs and poisons, and storage of calcium ions.
• Other enzymes of the smooth ER help detoxify drugs and poisons, especially in liver cells.
  
  • Detoxification usually involves adding hydroxyl groups to drug molecules, making them more soluble and easier to flush from the body.
  • Alcohol, and many other drugs induce the proliferation of smooth ER and its associated detoxification enzymes, thus increasing the rate of detoxification which increases tolerance to the drugs, meaning that higher doses are required to achieve a particular effect, such as sedation
• Also stores calcium ions - in muscle cells

Question 27

What is the rough ER and it’s function(s)?

Answer 27

• Many cells secrete proteins that are produced by ribosomes attached to rough ER.
  
  • Polypeptide chain grows from a bound ribosome, the chain is threaded into the ER lumen through a pore formed by a protein complex in the ER membrane.
  • The new polypeptide folds into its functional shape as it enters the ER lumen.

Question 28

What are glycoproteins?

Answer 28

• Most secretory proteins are glycoproteins proteins with carbohydrates covalently bonded to them.
• The carbohydrates are attached to the proteins in the ER lumen by enzymes built into the ER membrane.

Question 29

What are transport vesicles?

Answer 29

Vesicles in transit from one part of the cell to another

Question 30

1. What is the Golgi apparatus?
2. Structure?
3. Function?

Answer 30

Function

• Think of the Golgi as a warehouse for receiving, sorting, shipping, and even some manufacturing - Products of the ER, are modified and stored and then sent to other destinations.
• Golgi apparatus is especially extensive in cells specialized for secretion.

Structure:

• Consists of a group of associated, flattened membranous sacs—cisternae
  
  • Membrane of each cisterna in a stack separates its internal space from the cytosol.
  • Distinct structural directionality two sides of a Golgi stack
    
    • are referred to as the cis face - receiving. Term cis means “on the same side,” usually located near the ER.
    • and the trans face; shipping
      
      • Transport vesicles move material from the ER to the Golgi

Process to movie through Golgi

1. Vesicles move from ER to Golgi.
2. Vesicles coalesce to form new cis Golgi cisternae.
3. Cisternal maturation: Golgi cisternae move in a cisto-trans direction.
4. Vesicles form and leave Golgi, carrying specific products to other locations or to the plasma membrane for secretion.
5. Vesicles transport some proteins backward to less mature Golgi cisternae, where they function.
6. Vesicles transport some proteins backward to less mature Golgi cisternae, where they function.

Question 31

What is a lysosome?

Answer 31

• A membranous sac of hydrolytic enzymes that many eukaryotic cells use to digest (hydrolyze) macromolecules.
• Lysosomes carry out intracellular digestion in a variety of circumstances. Lysosomal enzymes work best in the acidic environment found in lysosomes.
• If a lysosome breaks open or leaks its contents, the released enzymes are not very active because the cytosol has a near-neutral pH. Excessive leakage from a large number of lysosomes can destroy a cell by self-digestion.
• Tay-Sachs disease, for example, a lipid-digesting enzyme is missing or inactive, and the brain becomes impaired by an accumulation of lipids in the cells.

Question 32

What is phagocytosis?

Answer 32

Amoebas and many other unicellular eukaryotes eat by engulfing smaller organisms or food particles

Question 33

What is autophagy? Think lysosome

Answer 33

• lysosome use their hydrolytic enzymes to recycle the cell’s own organic material,
• During autophagy, a damaged organelle or small amount of cytosol becomes surrounded by a double membrane (of unknown origin), and a lysosome fuses with the outer membrane of this vesicle
• The lysosomal enzymes dismantle the inner membrane with the enclosed material, and the resulting small organic compounds are released to the cytosol for reuse.
• With the help of lysosomes, the cell continually renews itself.

Question 34

What are Vacuoles?

Answer 34

• large vesicles derived from the endoplasmic reticulum and Golgi apparatus.
• integral part of a cell’s endomembrane system.
• vacuolar membrane is selective in transporting solutes; as a result, the solution inside a vacuole differs in composition from the cytosol.
• Types:
  
  • Food vacuoles, formed by phagocytosis
  • Many unicellular eukaryotes living in fresh water have contractile vacuoles that pump excess water out of the cell, thereby maintaining a suitable concentration of ions and molecules inside the cell
  • In plants and fungi, certain vacuoles carry out enzymatic hydrolysis, a function shared by lysosomes in animal cells.

Question 35

What is a central vacuole?

Answer 35

• In plant cells and develops by the coalescence of smaller vacuoles.
• Solution inside the central vacuole, (sap) is the plant cell’s main repository of inorganic ions, including potassium and chloride.
• 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 cytoplasm.
• Because cytosol often occupies only a thin layer between the central vacuole and the plasma membrane, so the ratio of plasma membrane surface to cytosolic volume is sufficient, even for a large plant cell.

Question 36

Review relationships among organelles of the endomembrane system.

Answer 36

1. The nuclear envelope is connected to the rough ER, which is also continuous with the smooth ER.
2. Membranes and proteins produced by the ER move via transport vesicles to the Golgi.
3. The Golgi pinches off transport vesicles and other vesicles that give rise to lysosomes, other types of specialized vesicles, and vacuoles.
4. The lysosome is available for fusion with another vesicle for digestion.
5. A transport vesicle carries proteins to the plasma membrane for secretion.
6. The plasma membrane expands by fusion of vesicles; proteins are secreted from the cell.

Question 37

What are Mitochondria?

Answer 37

• (singular, mitochondrion) are the sites of cellular respiration, the metabolic process that uses oxygen to drive the generation of ATP by extracting energy from sugars, fats, and other fuels.
• found in nearly all eukaryotic cells, including those of plants, animals, fungi, and most unicellular eukaryotes.
• the number correlates with the cell’s level of metabolic activity.
• two membranes enclosing the mitochondrion is a phospholipid bilayer with a unique collection of embedded proteins (Figure 6.17).
  
  • The outer membrane is smooth
  • Inner membrane is convoluted, with infoldings called cristae, a large surface area, thus enhancing the productivity of cellular respiration. Example of structure fitting function.
  • The inner membrane divides the mitochondrion into two internal compartments.
    
    • First: intermembrane space, the narrow region between the inner and outer membranes.
    • Second: the mitochondrial matrix, is enclosed by the inner membrane. The matrix contains many different enzymes as well as the mitochondrial DNA and ribosomes.
      • Enzymes in the matrix catalyze some of the steps of cellular respiration. Other proteins that function in respiration, including the enzyme that makes ATP, are built into the inner membrane

Question 38

What are Chloroplasts?

Answer 38

• Found in plants and algae, are the sites of photosynthesis.
  
  • Used in photosythesis

Question 39

What is th endosymbiont theory of the origins of mitochondria and chloroplasts in eukaryotic cells.

Answer 39

• States that an early ancestor of eukaryotic cells engulfed an oxygen-using nonphotosynthetic prokaryotic cell.
• Eventually, the engulfed cell formed a relationship with the host cell in which it was enclosed, becoming an endosymbiont (a cell living within another cell).
• 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 then taken up a photosynthetic prokaryote, becoming the ancestor of eukaryotic cells that contain chloroplasts.