Chapter 6: A Tour of the Cell

Question 1

What is cell fractionation?

Answer 1

separating organelles by breaking components of cell apart (ex. grinding up or osmotic shock) then blend to homogenate, then centrifuge

Question 2

Three key differences between prokaryotes and eukaryotes

Answer 2

euks larger
prokaryotes have nucleoid, euks have nucleus
euks have distinct organelles

Question 3

Name the three reasons cells are small

Answer 3

need appropriate surface to volume ratio
rate of movement into cell
local concentration of cell contents is maintained

Question 4

large cells have a ___ surface to volume ratio than smaller cells

Answer 4

smaller

Question 5

The more cell surface area available, the more

Answer 5

nutrients you can absorb

Question 6

What is the endomembrane system?

Answer 6

consists of organelles that help regulate protein function

Question 7

The components in the endomembrane system are connected via transfer by

Answer 7

vesicles

Question 8

What are the two regions of the ER?

Answer 8

Rough and Smooth

Question 9

Describe characteristics of the smooth ER

Answer 9

lack ribosomes
contains enzymes in lipid based rxn
stores intercellular calcium

Question 10

Describe characteristics of rough ER?

Answer 10

Has membrane bound sacs and ribosomes
ribosomes generate polypeptides within endomembrane system

Question 11

What occurs in golgi apparatus?

Answer 11

where proteins are packaged and shipped

Question 12

What is a lysosome?

Answer 12

Membranous sac of hydrolytic enzymes that can digest large molecules, think of as recycle center

Question 13

What is the purpose of the proton pumps on surface of lysosomes?

Answer 13

Maintains pH

Question 14

What are vacuoles?

Answer 14

Plant cell lysosome
stores pigments, toxins

Question 15

Mitochondrial DNA are ___ chromosomes

Answer 15

linear

Question 16

Mitochondria and chloroplasts share some similarities with bacteria. What are they?

Answer 16

Enveloped by double membrane
free ribosomes and circular DNA
produced somewhat independently in cells

Question 17

What occurs on peroxisomes?

Answer 17

Reduction and oxygenation reactions

Question 18

What is the cytoskeleton?

Answer 18

Network of fibers that organizes structures and activities in cell

Question 19

cell crawling is made possible by ____

Answer 19

actin filaments

Question 20

The most abundant compoennt of the ECM in animal cells is

Answer 20

collagen

Question 21

True or False: the cell wall is considered an extracellular component

Answer 21

True

Question 22

What are tight junctions?

Answer 22

when a cell attachment is adjacent to proteins in another cell. Forms a tight seal that prevents fluid from leaking out

Question 23

What are desmosomes?

Answer 23

proteins found in membrane that form bridges between anchoring proteins and adjacent
intermediate filaments reinforce desmosomes by attaching to proteins

Question 24

What are gap junctions

Answer 24

provide a means of cell communication

channels in adjacent cells that allow small molecules from one cell to next
allow for rapid communication

Question 25

What are plasmodesmata?

Answer 25

cell junctions that occur in regions where there are holes in the cell wall

Question 26

Describe the molecular composition of nucleoli and explain their function.

Answer 26

Nucleoli consist of DNA and the ribosomal RNAs (rRNAs) made according to its genes in the DNA, as well as proteins imported from the cytoplasm. Together, the rRNAs and proteins are assembled into large and small ribosomal subunits. (These are exported through nuclear pores to the cytoplasm, where they will participate in polypeptide synthesis.)

Question 27

Describe the structural and functional distinctions between rough and smooth ER.

Answer 27

The primary distinction between rough and smooth ER is the presence of bound ribosomes on the rough ER. Both types of ER make phospholipids, but membrane proteins and secretory proteins are all produced by the ribosomes on the rough ER. The smooth ER also functions in detoxification, carbohydrate metabolism, and storage of calcium ions.

Question 28

Imagine a protein that functions in the ER but requires modification in the Golgi apparatus before it can achieve that function. Describe the protein’s path through the cell, starting with the mRNA molecule that specifies the protein.

Answer 28

The mRNA is synthesized in the nucleus and then passes out through a nuclear pore to the cytoplasm, where it is translated on a bound ribosome, attached to the rough ER. The protein is synthesized into the lumen of the ER and may be modified there. A transport vesicle carries the protein to the Golgi apparatus. After further modification in the Golgi, another transport vesicle carries it back to the ER, where it will perform its cellular function

Question 29

A classmate proposes that mitochondria and chloroplasts should be classified in the endomembrane system. Argue against the proposal

Answer 29

Mitochondria and chloroplasts are not derived from the ER, nor are they connected physically or via transport vesicles to organelles of the endomembrane system. Mitochondria and chloroplasts are structurally quite different from vesicles derived from the ER, which are bounded by a single membrane

Question 30

Do plant cells have mitochondria? Explain

Answer 30

Yes. Plant cells are able to make their own sugar by photosynthesis, but mitochondria in plant cells are the organelles that are able to generate ATP molecules to be used for energy generation from sugars, a function required in all cells

Question 31

In what way are the cells of plants and animals structurally different from single-celled eukaryotes?

Answer 31

The most obvious difference is the presence of direct cytoplasmic connections between cells of plants (plasmodesmata) and animals (gap junctions). These connections result in the cytoplasm being continuous between adjacent cells.

Question 32

If the plant cell wall or the animal extracellular matrix were impermeable, what effect would this have on cell function?

Answer 32

The cell would not be able to function properly and would probably soon die, as the cell wall or ECM must be permeable to allow the exchange of matter between the cell and its external environment.

Question 33

_____ guide vesicles from the ER to the Golgi apparatus and from the Golgi to the plasma membrane.____ are also involved in the separation of chromosomes during cell division,

Answer 33

microtubules

Question 33

In animal cells, microtu- bules grow out from a_____ a region that is often located near the nucleus. These microtubules function as compression-resisting girders of the cytoskeleton

Answer 33

centrosome

Question 33

True or False: Like microtubules, microfilaments seem to be present in all eukaryotic cells

Answer 33

True

Question 33

Within the centrosome is a pair of _____,each composed of nine sets of triplet microtubules arranged in a ring

Answer 33

centrioles

Question 34

the structural role of microfilaments in the cytoskeleton is to

Answer 34

bear tension

Question 35

Describe the role of myosin and microfilaments in muscle motility

Answer 35

The ”walking” of myosin projections (the so-called heads) drives the parallel myosin and actin filaments past each other so that the actin filaments approach each other in the middle (red arrows). This shortens the muscle cell. Muscle contraction involves the shortening of many muscle cells at the same time (TEM)

Question 36

True or False: intermediate filaments are found in other cells with the same frequency as microfilaments

Answer 36

false they are only found in some animals

Question 37

Compare intermediate filaments to microfilaments and microtubules

Answer 37

Intermediate filaments are more permanent fixtures of cells than are microfilaments and microtubules, which are often disassembled and reassembled in various parts of a cell.

Question 38

Describe tight junctions

Answer 38

tight junctions, the plasma membranes of neighboring cells are very tightly pressed against each other, bound together by specific proteins. Forming continuous seals around the cells, tight junctions establish a barrier that prevents leakage of extracellular fluid across a layer of epithelial cells (see red dashed arrow). For example, tight junctions between skin cells make us watertight.

Question 39

Describe desmosomes

Answer 39

Desmosomes (one type of anchor- ing junction) function like rivets, fastening cells together into strong sheets. Intermediate filaments made of sturdy keratin proteins an- chor desmosomes in the cytoplasm. Desmosomes attach muscle cells to each other in a muscle. Some “muscle tears” involve the rupture of desmosomes.

Question 40

Describe gap junctions

Answer 40

Gap junctions (also called com- municating junctions) provide cytoplasmic channels from one cell to an adjacent cell and in this way are similar in their function to the plasmodesmata in plants. Gap junctions consist of membrane pro- teins extending from the mem- branes of the two cells. These proteins create pores through which ions, sugars, amino acids, and other small molecules may pass. Gap junctions are necessary for communication between cells in many types of tissues, such as heart muscle, and in animal embryos