chapter 7

Question 1

describe the relationship between the nucleus and ribosomes

Answer 1

the nucleus synthesized RNA (from the genes of DNA). proteins imported from the cytoplasm are assembled with rRNA into lage and small subunits of ribosomes. these subunits then exit the nucleus through the nuclear pores to the cytoplasm, where a large and a small subunit can assemble into a ribosome. ribosomes translate the mRNA’s genetic mesage into a primary structure of specific polypeptide

Question 2

Describe the key role played by transport vesicles in the endomembrane system.

Answer 2

transport vessicles are vesicles in transit from one part of the cell to another part of the cell. enzymes build in the rough ER assemble phospolipids (made by the rough ER) from precursors in the cytosol. The ER membrane expands, and portions of it are transferred in the form of transport vesticles to other components of the endomembrane system.

Question 3

What does the endosymbiont theory propose as the orgin for mitchondria and chloroplasts. explain ?

Answer 3

this theory states that an early ancestor of eukaryotic cells (a host cell) engulfed an oxygenusing nonphotosynthetic prokaryotic cell. eventually the engulfed cel formed a relationship with a host cell in which it was enclosed becoming an endosymbiont (a cell living inanotcher cell) indeed over the course over the evolution, the host cell and its endosymbiont merged into a single organisme, a eukaryotic cell with the endosymbiont having become a mitochondrion. at least one of these cells may have taken up a photosynthetic prokaryote, becoming the ancestor of eukarytic cells that contain chloroplast.

Question 4

what is the geometric relationship between surface area and volume?

Answer 4

as a cell increases in size, its surface area grows proportional to the linear demension. thus a smaller cell has a greater reatio of surface area to volume. a sufficiently high ratio of surface area to volume is especially importand in cells that exchange a lot of material with their suroundings.

Question 5

endoplasmic reticulum (ER) (figure 7,8)

Answer 5

network of membranous sacs and tubes: active in membrane synthetic and metabolic processes; has rough (ribosome-studded) and smooth regions.

Question 6

centrosome (figure 7,8)

Answer 6

regions where the cell’s microtubules are initiated; contains a pair of centrioles

Question 7

cytoskeleton (figure 7,8)

Answer 7

reinforces cell’s shape: functions in cell movement; components are made of protein. includes : microfilaments. intermediate filaments and microtubules.

Question 8

microvilli (figure 7,8)

Answer 8

membrane projections that increase the cell’s surface area

Question 9

what does the nucleus (figure 7,8) exists of

Answer 9

nuclear envelope, nucleolus and chromatin

Question 10

nuclear envelope

Answer 10

double membrane enclosing the nucleus perforated by pores, continuous with ER.

Question 11

nucleolus

Answer 11

nonmembranous structure involved in produciton of ribosomes; a nucleus has one or more nicleoli

Question 12

chromatin

Answer 12

material consisting of DNA and proteins; visibale in a dividing cell as individual condenced chromosomes

Question 13

ribosomes

Answer 13

(small brown dots) complexes that make proteins; free in cytosol or bound to rough ER or nuclear envelope

Question 14

golgi apparatus

Answer 14

organelle active in synhesis, modification, sorting and secreting of cell products.

Question 15

lysosomes

Answer 15

digestive organelle where macromolecules are hydrolyzed

Question 16

mitochondrion

Answer 16

organelle where cellular respiration occurs and most ATP is generated. the number of mitochondria correlates with the cell’s level of metabolic acitivity.