Biochem - Cellular (Cell Cycle, Cell Trafficking, & Select organelles)

Question 1

In general, what controls transitions between phases of cell cycle? What are 3 factors/substances that regulate this process?

Answer 1

Checkpoints control transitions between phases of cell cycle; This process is regulated by cyclins, cyclin-dependent kinases (CDKs), and tumor suppressors

Question 2

What is the shortest phase of the cell cycle? What is included in this phase?

Answer 2

Mitosis (shortest phase of cell cycle) includes prophase, metaphase, anaphase, and telphase

Question 3

Describe the duration of G1 and G0 cell cycle phases.

Answer 3

G1 and G0 are of variable duration

Question 4

What 2 words describe the normal functionality of CDKs?

Answer 4

Constitutive and inactive

Question 5

What are Cyclins, and how do they function?

Answer 5

Regulatory proteins that control cell cycle events; Phase specific; Activate CDKs

Question 6

What must happen to Cyclin-CDK complexes in order for cell cycle to progress?

Answer 6

Must be both activated and inactivated for cell cycle to progress

Question 7

What are 2 examples of tumor suppressors that function in the cell cycle? What function do they have?

Answer 7

p53 and hypophosphorylated Rb normally inhibit G1-to-S progression

Question 8

What results from mutations in tumor suppressor genes? Give an example.

Answer 8

Mutations in these genes result in unrestrained cell division (e.g., Li-Fraumeni syndrome)

Question 9

What defines the permanent cell type?

Answer 9

Remain in G0, regenerate from stem cells

Question 10

What are 4 examples of permanent cells?

Answer 10

(1) Neurons (2) skeletal and (3) cardiac muscle (4) RBCs

Question 11

What defines the stable (quiescent) cell type?

Answer 11

Enter G1 from G0, when stimulated

Question 12

What are 2 examples of stable (quiescent) cells?

Answer 12

(1) Hepatocytes (2) Lymphocytes

Question 13

What defines the labile cell type?

Answer 13

Never go to G0, divide rapidly with a short G1.

Question 14

What are 5 examples of labile cells?

Answer 14

(1) Bone marrow (2) Gut epithelium (3) Skin (4) Hair follicles (5) Germ cells

Question 15

Which cell type is most affected by chemotherapy?

Answer 15

Labile cell type

Question 16

What are 2 events that occur at/in the rough endoplasmic reticulum?

Answer 16

Site of synthesis of secretory (exported) proteins and of N-linked oligosaccharide addition to many proteins

Question 17

What are Nissl bodies? What function do they serve?

Answer 17

Nissl bodies (RER in neurons) - synthesize peptide neurotransmitters for secretion

Question 18

What defines free ribosomes? What function do they serve?

Answer 18

Free ribosomes - unattached to any membrane; site of synthesis of cytosolic and organellar proteins

Question 19

Give 2 examples of cells that are rich in RER.

Answer 19

Mucus-secreting goblet cells of the small intestine and antibody-secreting plasma cells are rich in RER

Question 20

What is the function of smooth endoplasmic reticulum?

Answer 20

Site of steroid synthesis and detoxification of drugs and poisons

Question 21

How does smooth endoplasmic reticulum differ from rough endoplasmic reticulum in its appearance?

Answer 21

Lacks surface ribosome

Question 22

Give 2 examples of cells that rich in SER.

Answer 22

Liver hepatocytes and steroid hormone-producing cells of the adrenal cortex and gonad are rich in SER.

Question 23

What function does the golgi serve?

Answer 23

Golgi is the distribution center for proteins and lipids from the ER to the vesicles and plasma membrane

Question 24

How does the golgi modify asparagine?

Answer 24

Modifies N-oligosaccharides on asparagine

Question 25

How does the golgi modify serine? What other amino acid is modified by the golgi in the same way?

Answer 25

Modifies O-oligosaccharides on serine and threonine

Question 26

How does the golgi modify certain proteins, and for what reason?

Answer 26

Adds mannose-6-phosphate to proteins for trafficking to lysosomes

Question 27

What are endosomes, and what function do they serve?

Answer 27

Endosomes are sorting centers for material from outside the cell or from the Golgi, sending it to lysosomes for destruction or back to the membrane/Golgi for further use

Question 28

What does the I in I-cell disease stand for? What kind of disorder is it?

Answer 28

I-cell disease (inclusion cell disease) - inherited lysosomal storage disorder

Question 29

What is the defect in I-cell disease, and what cellular effect(s) does it have?

Answer 29

Defect in phosphotransferase => Failure of the Golgi to phosphorylate mannose residues (i.e., decreased mannose-6-phosphate) on glycoproteins => Proteins are secreted extracellularly rather than delivered to lysosomes

Question 30

What are 4 signs/symptoms that result from I-cell disease?

Answer 30

Results in coarse facial features, clouded corneas, restricted joint movement, and high plasma levels of lysosomal enzymes

Question 31

What is often the prognosis/outcome of I-cell disease?

Answer 31

Often fatal in childhood

Question 32

What is SRP? What function does it serve?

Answer 32

Signal recognition peptide (SRP); Abundant, cytosolic ribonucleoprotein that traffics protein from the ribosome to the RER.

Question 33

What happens in the event of an absent or dysfunctional SRP?

Answer 33

Absent or dysfunctional SRP => proteins accumulate in the cytosol

Question 34

Name 3 vesicular trafficking proteins.

Answer 34

(1) COPI (2) COPII (3) Clathrin

Question 35

What is the function of COPI?

Answer 35

Vesicular trafficking protein; COPI: Golgi => Golgi (retrograde); Golgi => ER

Question 36

What is the function of COPII?

Answer 36

Vesicular trafficking protein; COPII: Golgi => Golgi (anterograde); ER => Golgi

Question 37

What is the function of Clathrin?

Answer 37

Vesicular trafficking protein; Clathrin: trans-Golgi => lysosomes; Plasma membrane => endosomes (receptor-mediated endocytosis) [e.g., LDL receptor activity]

Question 38

Which vesicular trafficking protein is involved in receptor-mediated endocytosis? Give an example of receptor-mediated endocytosis.

Answer 38

Clathrin: trans-Golgi => lysosomes; Plasma membrane => endosomes (receptor-mediated endocytosis) [e.g., LDL receptor activity]

Question 39

What is the peroxisome, and what function does it serve?

Answer 39

Membrane-enclosed organelle involved in catabolism of very-long-chain fatty acids, branched-chain fatty acids, and amino acids

Question 40

What is the proteasome, and what function does it serve?

Answer 40

Barrel-shaped protein complex that degrades damaged or ubiquitin-tagged proteins

Question 41

In what important disease have defects in ubiquitin-proteasome system been implicated?

Answer 41

Defects in the ubiquitin-proteasome system have been implicated in some cases of Parkinson’s disease