Cell 4

Question 1

Where are calcium ions stored and released from in contractile cells such as skeletal and cardiac muscle cells?

Answer 1

ER

Question 2

What is the smooth ER called in muscle cells?

Answer 2

sarcoplasmic reticulum (calcium is released when stimulated)

Question 3

What deleterious effects do elevated calcium levels have?

Answer 3

• membrane damage
• nuclear damage
• ATP

Question 4

How are phospholipids in the sER and rER synthesized?

Answer 4

they are synthesized on the cytosolic side as a monolayer. an enzyme called scramblase then flips some of the phospholipids to the lumen side so there are an even number on both sides

Question 5

What occurs when the mitochondrial membrane needs to expand?

Answer 5

A phospholipid exchange protein will shuttle the ER phospholipid over to the mitochondrial membrane

Question 6

What is Atlastin?

Answer 6

GTPase involved in constructing and shaping the ER

Question 7

What does an abundance of atlastin leads to?

Answer 7

increased ER membrane fusion and normal Golgi is absent (excessive amounts of scaffolding protein can affect Golgi)

Question 8

What is hereditary spastic paraplegia?

Answer 8

linked to atlastin deficiency leading to ER fragmentation. (symptoms: leg stiffness, gait disturbances such as tripping and stumbling)

Question 9

What are proteasomes?

Answer 9

large molecular complexes located in the cytoplasm and nucleus that degrade proteins marked by ubiquitin (ie protein misfolding). ATP-dependent process

Question 10

What is the role of proteasomes in the cell cycle?

Answer 10

control mitotic factors by eliminating them at various stages for progression of the cell cycle

Question 11

It is thought that defective ubiquination plays a role in which disease?

Answer 11

Alzheimer’s

Question 12

Abnormal prion proteins inhibit what structure?

Answer 12

proteasomes

Question 13

Defective ubiquination of proteins is implicated in what disease?

Answer 13

Parkinson’s

Question 14

If a protein is slow to fold into its proper form, what happens to it, as in the case of cystic fibrosis?

Answer 14

it is marked by ubiquitin and is degraded by proteasomes, such as the functional CFTR ABC transport protein that is slow to fold in cystic fibrosis

Question 15

The inhibition of proteasomes by bortezomib is effective against multiple myeloma, why?

Answer 15

it decreases the degradation of pro-apoptotic factors, which are factors that promote cells to undergo apoptosis

Question 16

What is the function of the Golgi apparatus?

Answer 16

sorting of proteins by the linear sequence of amino acids or by the carbohydrates that are attached to them. the proteins are then modified and packed into secretory vesicles or sorted to lysosomes or endosomes

Question 17

Where are enzymes that are destined to function in the sER synthesized? How does it work?

Answer 17

rER. a signal sequence is recognized on the protein being synthesized and it will be moved to the translocon located on the membrane. the protein is then released into the membrane.

Question 18

How does the sER increase size/volume in response to detoxification needs?

Answer 18

by integrating proteins into the ER membrane via translocation

Question 19

What is the function of ATP7B (copper transporter)?

Answer 19

It is embedded in both the Golgi and vesicles and allows the intake of copper by both.

Question 20

What happens to vesicles containing copper?

Answer 20

the copper is transported to be secreted into bile

Question 21

What is ceruloplasmin?

Answer 21

copper + copper-binding protein

Question 22

What is defective in Wilson’s disease?

Answer 22

copper transporter

Question 23

What happens to the serum level of ceruloplasmin in Wilson’s disease?

Answer 23

decrease due to defect in copper transporter

Question 24

The formation of Kayser-Fleischer ring in the cornea is indicative of what?

Answer 24

copper deposition due to Wilson’s disease and its inability to be properly handled (ie excreted to bile) Note that not every patient with Wilson’s disease will develop this condition

Question 25

What are microperforations?

Answer 25

occurs when muscles undergo physical activity (normal)

Question 26

What should be done about microperforations? Why?

Answer 26

they need to be patched, otherwise it will cause calcium ions to leak into the muscle cells (damaging effects)

Question 27

What is dysferlin?

Answer 27

protein packaged and dispatched by the Golgi in response to microperforations in contractile cells to initiate patching mechanism

Question 28

What are the three types of muscular dystrophy found in dysferlin gene mutations?

Answer 28

• Miyoshi myopathy
• limb-girdle muscular dystrophy type 2b
• distal myopathy tibialis anterior muscle onset
  Note that patching mechanism has been compromised and will lead to injury, atrophy and even necrosis

Question 29

Describe the synthesis and packaging of insulin.

Answer 29

preproinsulin is synthesized by the ER and packaged to be sent to the Golgi. The preprolnsulin is converted to proinsulin in the Golgi and is packaged into a secretory vesicle along with a prohormone converting enzyme (cleaves proinsulin to insulin upon signal)

Question 30

What occurs in proinsulinemia?

Answer 30

proinsulin is mutated and the sorting mechanism by the Golgi gets messed up. The proinsulin is being sorted to the constitutive pathway but the prohormone converting enzyme is still being packaged into vesicles (regulative pathway). This leads to accumulation of proinsulin without a way to be cleaved into its active form.

Question 31

What occurs at the cis face of Golgi?

Answer 31

receives material from ER

Question 32

What occurs at the trans face of Golgi?

Answer 32

product is packaged and destined for secretion

Question 33

When the nucleus appears light in color and the nucleolus is clearly visible and there are large volume of rER and secretory vesicles, what could be occurring inside the cell?

Answer 33

the cell is actively transcribing and there’s a high rate of protein synthesis

Question 34

What is the pH of early endosome, late endosome and finally lysosome?

Answer 34

early endosome: 6
late endosome: 5.5
lysosome: 4.7

Question 35

How do endosomes and lysosomes get acidic?

Answer 35

they contain hydrogen ion transporters

Question 36

Describe the role of recycling endosomes and glucose transporters in response to insulin.

Answer 36

recycling endosomes contain glucose transporters. upon insulin signalling, the endosomes relocate to the plasma membrane and release their contents (glucose transporters) thus increasing glucose uptake

Question 37

What are the four fates of endocytosed receptors and ligands?

Answer 37

1) receptor is recycled and ligand is degraded
2) receptor and ligand are both recycled
3) receptor and ligand are both degraded
4) receptor and ligand are transported across the cell and secreted (transcytosis)

Question 38

Explain how in Acondroplasia where the receptor is not degraded.

Answer 38

FGFR2 is the the growth factor receptor responsible for bone growth. This receptor is normally degraded and stops proliferation (important for proper development). In achondroplasia, the receptor is not degraded and is recycled back to the plasma membrane instead. This leads to overstimulation of the growth factor, leading to faster maturation of long bones, leading to short stature (dwarfism)

Question 39

How do IgA get secreted?

Answer 39

via transcytosis