2.Cells and Organelles

Question 1

explain structure and major functions of plasma membrane. what does it look like on the TEM? 
thickness? 
hydrophilic portion?
hydrophobic portion?
why is the glycocalyx important?
integral vs peripheral proteins?

Answer 1

outermost part of the cell
selective transport and barrier
*important role: keeps ion content constant in cytoplasm

7.5-10nm thick

contains proteins that are integral and peripheral

hydrophilic portion: basic phopholipid group
hydrophobic portion: cholesterol and fatty acid chains

glycocalyx important for cell-cell recognition and adsorption

integral proteins span the length of the membrane and are amphipathic while the peripheral are just on one side and can be removed with salt solutions

Question 2

recognize the microscopic images of plasma membrane and ER

Answer 2

in the microscopic image of the plasma membrane:

• using TEM: TRILAMINAR membrane:
• 2 dark linked enclosing a clear band
• dark layers correspond to reduced osmium deposited on the hydrophilic phosphate groups
• fuzzy material on outer surface is the attached oligosaccharides to the phsopholipids and proteins = gllycocalyx (cell recognition)

Question 3

200 different cell types derived from teh___

Answer 3

zygote

Question 4

what color does the nucleus stain and why

Answer 4

dark blue or black bc lots of basophilic rRNA

Question 5

experiment demonstrating fluidity of membrane proteins

Answer 5

2 cells fused together- one had fluorescene and the other didn’t. after fusion, they both had it all over

Question 6

describe the structure and function of the cytosol

Answer 6

viscous fluid with dissolved ions

provides support for organelles and medium for diffusion

Question 7

proteins synthesized on the free ribosome are destined for :

proteins synthesized on the rough endoplasmic reticulum are destined for?

Answer 7

free ribosome: stay in the cytoplasm
-think membrane bound organelles 
-mitochondria
-peroxisomes
-nucleus
and cytoskeleton

RER:
eventually extruded from the cell or sent to lysosomes
-

Question 8

size of ribosomes
where are they synthesized
what is their charge? why?
what do they stain?

Answer 8

20x30nm in size

• synthesized in the nucleus (components made in cytoplasm but then go to nucleus for assembly)
• charge is basophilic due to lots of phosphate groups on the rRNA, making it a polyanion

Simplistically, ACID pH stains (positive charge) are attracted to the base pH tissue(negative charge), so they are called basophilic stains

therefore these stain blue

Question 9

why would a erythroblast stain blue?

why would nissl bodies stain blue?

Answer 9

Image of neuronal cell bodies from the dorsal root ganglion. Hematoxylin reacts with the ribosomal RNA and appears as basophilic patches in the cytoplasm (only called nissl bodies in neurons)

erythroblast:
The cytoplasm is intensely basophilic as a result of a large population of free polyribosomes.

Question 10

what are the major functions of the SER?

how does the TEM of SER differ from RER

Answer 10

functions:

• detox
• making fats
• sequestraiton of calcium

TEM:
SER is more tubular (will look like white circles) while RER is flattened sacs
**note glycogen inclusion around SER as only SER is involved in glycogen metabolism

The lining of the smooth endoplasmic reticulum is smooth, has no ribosomes, and has branched tubules

Question 11

what are the principle functions of the RER

structure?

Answer 11

• synthesis of proteins destined to leave the plasma membrane or go to lysosomes
• assemble multichain proteins
• modify proteins to form glycoproteins and other post translational modifications
• structure:
• ER lacks bound polyribosomes

Question 12

protein synthesis on RER

Answer 12

• translated polypeptide has 15-40 hydrophobic aa signal that a SRP (signal recognition particle) binds to and knows that it is to be sent to ribosome
• so SRP takes it and binds it to the SRP receptor on the ER
• large ribosomal subunit is bound to the ER, hydrophobic signal peptide is translocated through protein pore in the ER membrane and the SRP is freed for reuse
• signal peptide removed from the growing peptide by a peptidase and translocation continues until completely segregated into the ER cistern or embedded in the ER membrane

Question 13

proteosomes degrade misfolded and denatured proteins

how are they different than lysosomes

Answer 13

misfolded proteins are conjugated to ubiquitin and targeted for proteasomal degradation

proteasomes are about the size of ribosomes

lysosomes digest bulk material introduced into the cell or whole organelles and vesicles
-proteasomes only degrade ubiquitin marked proteins and break proteins down into aa or reuse antigens

Question 14

protein aggregates interfere with..

Answer 14

Prions or other protein aggregates can interfere with proteosome function leading to or exacerbarating diseases, eg. neurodegeneration in Alzheimer’s disease.

Question 15

what can you tell about the function of a cell by the number of ribosomes it has

1) cells with extensive RER and Golgi apparatus show…

Answer 15

ribosomes and lots of RER and Golig apparatus= cell makes lots of proteins
*** the ultrastructure and many general histological aspects of a cell are determined by the nature of the most prominent proteins the cell is making

show few secretory granules bc proteins undergo exoctyosis right after golgi processing is complete

Question 16

what color does golgi stain?

Answer 16

it doesn’t

Question 17

what does polarity tell you?

Answer 17

epithelial cells specialized for secretion have distance polarity:
RER abundant at their basal ends and
mature secretory granules at the apical poles under exocytosis

Question 18

what structures can be seen with H&E and light microscope?

which cannot?

Answer 18

cytoplasm
golgi
ribosmes in nissl bodies
large bundles of collagen  in EM
large (over 0.2 miromeers) 

cannot:
water bc size is less than 0.2 micron
SER

*plasma membrane is sometimes too thick to see in light microscope