Pintar - Cell Structure II

Question 1

integral membrane protein

peripheral membrane protein

Answer 1

integral - transverse the entire width of the cell membrane. Have 3 domains - cytoplasmic, membrane-spanning, external

peripheral - attached to the cytoplasmic/extracellular side by non-covalent interactions.

Question 2

why is it that when you split a membrane there on more proteins found on the cytoplasmic side of the membrane?

Answer 2

The proteins are stabilized by the cytoskeleton on the inside of the cell. In the RBC, the cytoskeletal proteins are called actin and spectrin.

Question 3

Hereditary spherocytosis

Answer 3

In the absence of spectrin the RBCs will become more spherical and be more likely to become phagocytized. This is because spectrin is involved in the upkeep of the structure/stability of the cell. It becomes more sensitive to osmolarity.

Question 4

Functions of membrane proteins

Answer 4

1) can be linker/anchor molecules that such as those that interact with cytoskeletal proteins (spectrin)
2) transporter molecules
3) receptors
4) enzymes

Question 5

Brush Border

Answer 5

Plasma Membranes can have modifications to them. One such example is the brush border in which there are microvilli on the end of the apical surfaces of enterocytes. This increases the surface area for absorption. On t he edge of the microvilli is glycocalyx. On the lateral borders of these cells are junctional complexes that allows for the cells to adhere to each other.

Question 6

glycocalyx

Answer 6

oligosaccharide side chains attached to things on the PM. So, we have proteoglycans, glycolipids, and glycoproteins.

Question 7

microvilli

Answer 7

As was mentioned earlier, microvilli are on the surface of many cells PM. Microvilli are made up of bundles of actin filaments. These filaments are surrounded by the PM and have a glycocalyx coat on their tips. The bottom of the actin filaments congregate in what is called the Terminal Web. Myosin is also involved, which acts as a motor to move things up and down the actin. Actin is also involved in the cytoskeleton.

Question 8

Different junctional complexes

Answer 8

tight/occluding junctions (zonuda occludens)
belt desmosomes (zonuda adherens)
spot desmosomes (macula adherens)
communicating (gap junctions)

Question 9

microtubules

Answer 9

Are made up of a protein called tubulin. Is found in cilia, centrioles, and mitotic spindles.

Question 10

smooth ER

Answer 10

Site of lipid synthesis, Ca2+ storage, detoxification, metabolism of drugs and steroid synthesis. In a cell that is heavily involved in making steroids, you will see a lot of SER. There are no ribosomes. Site of many heme-linked proteins.

Question 11

Rough ER

Answer 11

Ribosome studded. Is essentially connected to the nucleus. Is able to translate all of the mRNA that is excreted from the cell. Once the proteins have been synthesized, they will go to the golgi where they are sorted and packaged. Cells with a lot of RER are indicative of having proteins entering the secretory pathway. The rRNA will bind positively charged dyes and create “basophilia.”

Question 12

Golgi apparatus

Answer 12

flattened membranes where proteins enter at the cis face and leave from the trans face. Cis face is right near the RER whereas the trans fce is near the PM. There is a medial face in between. Once vesicles are ready to leave, they depart from the trans face in a place called the “trans golgi network (TGN).”

Question 13

constitutive vs. regulated secretion

Answer 13

C - there is little if any secretory granules sitting around because they are always being secreted. This would be like in plasma cells where they constantly secrete antibodies.
R - large numbers of vesicles/granules accumulate in some secretory cells. An external stimulus will then tell the cell when to excrete it’s contents.

Question 14

endocytosis

Answer 14

a ligand binds to an external receptor thus causing the membrane to pinch in and form a vesicle. The invagination is initiated by coat proteins, one type is called clathrins. The vesicle and coat proteins form what is called a coated pit in order to detach from the PM. It is then called a coated vesicle. The coated vesicle can then form with an early endosome. Endosomes are where things that just entered the cell are sorted.

Question 15

Differences in mito depending on cell?

Answer 15

of cristae changes depending on the energy needs of the cell. The more cristae the more energy. Shape of mito can change as well (morphology).

Question 16

Lysosomes

Answer 16

Site of intracellular digestion. It can degrade antigens or things from the outside as well as old worn out cells. Generally they are stained blue. In eosinophils, the lysosomes might look like hamburgers due to the inclusion of crystalline inclusions.

Question 17

peroxisomes

Answer 17

membrane bound organelles involved in hydrogen peroxide metabolism. Can’t really see unless you section them and look at through an EM.

Question 18

amphipathic

Answer 18

Polar head groups and NP aliphatic carbon chains on the interior of the membrane.