5.3 Internal Organization of Cells

Question 1

Describe the internal organization of cells.

Answer 1

in addition to the plasma membrane, many cells contain membrane-bound regions within which specific functions are carried out

• such cell can be compared to a large factory, each department has a specific function and internal organization that contribute to the work of the factory

Question 2

What do all cells have?

Answer 2

plasma membrane

genetic material

Question 3

What are the two classes have cells and what are they based on?

Answer 3

prokaryotes and eukaryotes, based on the absence or presence of a nucleus

Question 4

What are prokaryotes?

Answer 4

organisms, including bacteria and archaeons, that lack a nucleus

*figure 5.16 textbook

Question 5

What are eukaryotes?

Answer 5

organisms, including animals, plants, fungi, and protists that have a nucleus

*figure 5.16 textbook

Question 6

What does the presence of a nucleus in eukaryotes allow?

Answer 6

for processes of transcription and translation to be separated in time and space

this separation allows for more complex ways to regulate gene expression than are possible in prokaryotes

Question 7

What are other differences between prokaryotes and eukaryotes?

Answer 7

• transcription and translation differ
• the types of lipids that make up their cell membranes (mammals have cholesterol)
• in eukaryotes other than mammals, diverse sterols are synthesized and present in cell membranes, most prokaryotes do not but some synthesize compounds called hopanoids

Question 8

What is cholesterol?

Answer 8

belongs to a group of chemical compounds known as sterols, which are molecules containing a hydroxyl group attached to a four-ringed structure

Question 9

What are hopanoids?

Answer 9

five-ringed structures that are thought to serve a function similar to that of cholesterol in mammalian cell membranes

Question 10

From an evolutionary perspective, how are the three domains of life related?

Answer 10

archaeons and eukaryotes are more closely related to each other than either are to bacteria

ie. archaeons share with eukaryotes many genes involved in transcription and translation, and DNA is packaged with histones in both groups

Question 11

What do prokaryotic cells lack?

Answer 11

• nucleus

- extensive internal compartmentalization

Question 12

What do prokaryotes have instead of a nucleus?

Answer 12

nucleoid: a structure with multiple loops formed from supercoils of DNA

DNA is concentrated in this discrete region of the cell interior

Question 13

What are plasmids?

Answer 13

in bacteria, a small circular molecules of DNA carrying a small number of genes that replicate independently of the DNA in the bacterium’s circular chromosome

Question 14

What are plasmids commonly transferred between and how?

Answer 14

bacteria through the action of threadlike structures known as pili, which extend from one cell to another

ie. genes for antibiotic resistance are commonly transferred this way, which accounts for the quick spread of antibiotic resistance among bacterial populations

Question 15

Describe the size of prokaryotes.

Answer 15

• small, typically 1-2 micrometers in diameter or smaller
• this means they have a relatively high ration of SA to V, which makes sense for an organisms that absorbs nutrients from the environment
• in other words, a large amount of membrane SA is available for absorption relative to the volume of the cell that it serves

Question 16

Describe the size of eukaryotes.

Answer 16

larger, on the order of 10 times larger in diameter than prokaryotes, and 1000 times larger in volume

Question 17

What do eukaryotes have?

Answer 17

• nucleus

- specialized internal structures

Question 18

What is the nucleus?

Answer 18

physical barrier separating genetical material from the rest of the cell, houses most of the cell’s DNA

Question 19

What does the nuclear membrane do?

Answer 19

allows for more complex regulation of gene expression than is possible in prokaryotic cells

Question 20

Describe the steps that eukaryotes take to instruct the synthesis of proteins.

Answer 20

DNA is transcribed to RNA inside the nucleus, but the RNA molecules carrying the genetic message travel from inside to outside the nucleus, where they instruct the synthesis of proteins

Question 21

What are organelles?

Answer 21

any one of several compartments in eukaryotes that divide the cell contents into smaller spaces specialized for different functions

*figure 5.17 textbook

Question 22

What does the internal array of membranes define?

Answer 22

compartments called organelles

Question 23

What do plant cells have that animal cells don’t?

Answer 23

• cell wall outside the plasma membrane
• vacuoles specialized for water uptake
• chloroplasts that convert energy of sunlight into chemical energy
• intercellular connections called plasmodesmata

Question 24

What is chloroplast?

Answer 24

an organelle in photosynthetic eukaryotes that converts energy of sunlight into chemical energy by synthesizing simple sugars

Question 25

What are plasmodesmata?

Answer 25

channels that allow the passage of large molecules such as mRNA and proteins between neighbouring cells

Question 26

What is cytoplasm?

Answer 26

the entire contents of a cell other than the nucleus

Question 27

What is cytosol?

Answer 27

the jelly-like internal environment of the cell that surrounds the organelles inside the plasma membrane