Chapters 2 and 3 - The Cytoplasm and the Nucleus

Question 1

What is the cell membrane composed of?

Answer 1

1- Lipid molecules:
a- phospholipids
b- cholesterol
2- Protein molecules
3- Carbohydrate molecules

Question 2

Where is cholesterol located in the cell membrane?

Answer 2

It is incorporated within the tails of the phospholipids

Question 3

describe the structure of a phospholipid

Answer 3

1- One polar hydrophilic head
2- Two long non-polar hydrophobic tails (fatty acids)

Question 4

What is the function of phospholipids?

Answer 4

They create a semi-permeable bilayer that prevents the passage of water soluble substances and polar ions.

Question 5

What is the function of cholesterol?

Answer 5

1- Stabilizes the membrane (-> supports the structure)
2- Regulates membrane fluidity

Question 6

What are the membranous organelles?

Answer 6

1- Nucleus
2- Mitochondria
3- Endoplasmic reticulum
4- Lysosomes
5- Golgi apparatus
6- Endosomes
7- Peroxisomes

Question 7

What are the non-membranous organelles?

Answer 7

1- Ribosomes
2- Centrosomes

Question 8

describe the structure of a ribosome

Answer 8

It is composed of a large and small subunits made from ribosomal RNA (synthesized in the nucleus) and proteins (synthesized in the cytoplasm)

Question 9

Where are ribosomes present?

Answer 9

They are present in all cells, especially proteins synthesizing cells

Question 10

What is the general function of ribosomes?

Answer 10

protein synthesis

Question 11

What is the function of free solitary proteins?

Answer 11

They store proteins that are used in shortages (i.e. they act as reserves)

Question 12

What is the function of free aggregated ribosomes (polysomes)?

Answer 12

They synthesize cytosolic proteins

Question 13

What is the function of bound ribosomes?

Answer 13

They synthesize secretory proteins, lysosomal enzymes, and membrane proteins

Question 14

How are bound ribosomes seen under a microscope?

Answer 14

• They cannot be seen under a light microscope.
• Under an electron microscope, they appear as small electron dense particles attached to the rough ER.

Question 15

How are free aggregated ribosomes seen under a microscope?

Answer 15

• They cannot be seen under a light microscope.
• Under an electron microscope, they appear as ten or more ribosomes connected by a single mRNA strand.

Question 16

How are free solitary proteins seen under a microscope?

Answer 16

• Under a light microscope, they cannot be seen, but large amounts of them gives cytoplasmic basophilia.
• Under an electron microscope, they appear as small electron dense particles.

Question 17

What are the two types of ribosomes?

Answer 17

1- Bound ribosomes
2- Free ribosomes:
a- free solitary ribosomes
b- free aggregated ribosomes

Question 18

What is the function of the rough endoplasmic reticulum?

Answer 18

1- synthesis of secretory proteins, lysosomal enzymes, and membrane proteins.
2- post-translation modification of protein
3- transport of proteins to the Golgi apparatus in transport vesicles

Question 19

What is the function of the smooth endoplasmic reticulum?

Answer 19

1- lipid, cholesterol, steroid hormones, and glycogen synthesis.
2- detoxification of toxic substances
3- regulation of calcium ions during muscle contraction

Question 20

How is the rough endoplasmic reticulum seen under a microscope?

Answer 20

• Under the light microscope, they cannot be seen, but in large amounts, they can be seen as cytoplasmic basophilia
• Under the electron microscope, they resemble parallel, flattened, interconnected tubules that are studded with ribosomes

Question 21

In which cells is the rough endoplasmic reticulum most abundant?

Answer 21

in protein secreting cells, such as the liver and fibroblast

Question 22

How is the smooth endoplasmic reticulum seen under a microscope?

Answer 22

• Under a light microscope, they cannot be seen, but in large amounts, they can be seen as cytoplasmic acidophilia
• Under and electron microscope, they can be seen as interconnected branched tubules and vesicles.

Question 23

In which cells is the smooth endoplasmic reticulum most abundant?

Answer 23

in steroid secreting cells, such as the liver and muscles

Question 24

In which cells is the Golgi apparatus most abundant?

Answer 24

in protein synthesizing cells and secretory cells

Question 25

What is the function of a Golgi apparatus?

Answer 25

**1- modifying proteins 2- packing proteins into vesicles 3- sorting and targeting vesicles to the right destination:** a- formation of lysosomes b- formation of secretory granules for exocytosis c- membrane recycling

Question 26

In which cells are lysosomes most abundant?

Answer 26

in phagocytic cells

Question 27

How are lysosomes seen under a microscope?

Answer 27

- Under light microscopes, they cannot be recognized by histochemical methods - Under electron microscopes, they are heterogeneous in shape and appearance of their interior. Some lysosomes are electron dense while others are lucent.

Question 28

What is the function of a lysosome?

Answer 28

intracellular digestion of different materials

Question 29

How are lysosomes synthesized?

Answer 29

by the fusion of clathrin-coated vesicles coming from the Golgi apparatus with late endosomes

Question 30

How is a cell protected from being digested by its own lysosomal enzymes?

Answer 30

1- a **phospholipid membrane** surrounds a lysosome, which prevents leaking 2- if leaking still happened, the released enzymes would be inactive because of **the neutral environment of a cell**

Question 31

How is the mitochondria seen under a microscope?

Answer 31

- Under a light microscope, it cannot be seen when stained with H&E (but might appear as cytoplasmic acidophilia in large amounts). It can be stained brown by special stains. - Under and electron microscope, it has: 1- a double membrane (the outer layer is smooth while the inner layer is folded in cristae) 2- two spaces: one inter-membranous and the other a matrix space

Question 32

In which cells can a mitochondria be found?

Answer 32

all body cells **except RBCs and keratinocytes**

Question 33

What is the function of a mitochondria?

Answer 33

production of energy stored in the form of ATP

Question 34

# True or False A mitochondria has its own genetic material.

Answer 34

True

Question 35

How is a peroxisome seen under the microscope?

Answer 35

- Under light microscopes, it cannot be seen. - Under electron microscopes, it is seen as a single membrane enclosed by fine granular contents (-> oxidative enzymes)

Question 36

Where can peroxisomes be found?

Answer 36

in many cells, especially liver cells

Question 37

What are the functions of peroxisomes?

Answer 37

1- produce energy in the form of heat 2- produce hydrogen peroxide 3- convert excess hydrogen peroxide to water 4- detoxify toxic substances

Question 38

What are the cytoskeletal components

Answer 38

1- microfilaments 2- intermediate filaments 3- microtubules

Question 39

How are the cytoskeletal components seen under a light microscope?

Answer 39

They can only be seen by means of immunochemistry

Question 40

How are microfilaments seen under an electron microscope?

Answer 40

thin electron dense filaments

Question 41

describe the structure of microfilaments

Answer 41

- They are the thinnest cytoskeletal component - They are dynamic structures - They are formed by polymers of G-actin called F-actin

Question 42

What are the functions of microfilaments?

Answer 42

1- muscle contraction 2- contractile ring in cell division 3- pseudopodia in migration 4- cytoplasmic streaming 5- microvilli 6- cell shape maintenance

Question 43

How are intermediate filaments seen under an electron microscope?

Answer 43

thick electron dense filaments

Question 44

What is the function of an intermediate filament?

Answer 44

structural support

Question 45

How are microtubules seen under an electron microscope?

Answer 45

They are seen as fine tubules

Question 46

What is the structure of a microtubule?

Answer 46

- They are the thickest microtubules - They are dynamic structures - They are formed by 13 protofilaments (-> polymers of tubulin dimers)

Question 48

What are the functions of microtubules?

Answer 48

1- transport of organelles and vesicles 2- formation of centrioles, cilia, and flagella

Question 49

What are inclusions?

Answer 49

They are intracellular non-living substances

Question 50

How is glycogen seen under a microscope?

Answer 50

- Under a light microscope, they cannot be seen with H&E, but they are magenta red in color when stained by PAS - Under an electron microscopes, they appear as dense granules that are larger than ribosomes (they also have rosette-shaped aggregates in hepatocytes)

Question 51

In which cells are glycogen most abundant?

Answer 51

liver and muscle cells

Question 52

What is the function of glycogen?

Answer 52

Glycogen act as a source of energy

Question 53

How are lipids seen under a microscope?

Answer 53

- Under a light microscope, they cannot be seen with H&E, but they are black in color when stained by osmium tetroxide and/or Sudan black - Under an electron microscope, they appear as either grey small droplets or large globules

Question 54

Where are lipids stored?

Answer 54

1- adipocytes 2- other cells, such as: a- suprarenal glands b- testes c- ovaries

Question 55

What are the functions of lipids?

Answer 55

1- source of energy 2- synthesis of steroid hormones and membranes