MCM_Final_TBL11

Question 1

Post-Translational Modification: Phosphorylation

Answer 1

• adds a phosphate, serine, threonine or tyrosine

Question 2

Post-Translational Modification: Glycosylation

Answer 2

• attaches SUGAR
• usually at an “N” or “O” in an amino side chain

Question 3

Post-Translational Modification: Ubiquitination

Answer 3

• adds ubiquitin to lysine residue of a target protein for DEGRADATION

Question 4

Post-Translational Modification: SUMOylation

Answer 4

• adds a small protein SUMO (small ubiquitin-like modifier) to a target protein

Question 5

Post-Translational Modification: Disulfide Bond

Answer 5

• covalently links the “S” atoms of two different CYSTEINE residues

Question 6

Post-Translational Modification: Acetylation

Answer 6

• adds an acetyl group to an N-terminus of a protein or Lysine group

Question 7

Post-Translational Modification: Lipidation

Answer 7

• attaches a lipid such as an (fatty acid) to a PROTEIN CHAIN

Question 8

Post-Translational Modification: Methylation

Answer 8

• adds a methyl group at Lysine or Argenine residues

Question 9

Post-Translational Modification: Hydroxylation

Answer 9

• attaches a hydroxyl OH group to a side chain of protein

Question 10

Process of Protein Excretion

Answer 10

1. membrane bound/excreted proteins are made** in the ribosomes located on the **membranes of the RER
   
   • these proteins have a 1-36 N-Terminal signal peptide domain
2. the signal peptide is recognized by a protein comlex called the SIGNAL RECOGNITION PARTICAL (SRP)
3. once the peptide moves past the ER membrane, the signal peptide is removed
   
   • signal peptidase removes the signal peptide
4. Proteins containing a signal peptide are called pre-proteins

Question 11

Glycosylation

Answer 11

• glycans add sugar to molecules
  
  • can add monosaccharides (i.e transcription factors) OR complex branched polysacharides (i.e cell receptors)
• use activated donors like UDP-sugar OR GDP-sugar
• attached at:
  
  • asparagine-linked (N-linked) oligosaccharides OR
    
    • N-glycosylation occrs in RER
  • serine/threonine (O-linked) oligosaccharides
    
    • O-glycosylation occrs in GOlgi
• ex) Viral Spike Protein (Covid) binds ACE2 to gain entry into human hosts

Question 12

Methylation

Answer 12

• can be added to either nitrogen** or **oxygen AA side chains
  
  • mediated by methyltransferases & requires S-adenosyl methionine (SAM)
• uses:
  
  1. methylation = ↑ hydroPHOBicity
  2. TRImethylation = permanant charge shift
  3. epigenetic regulation
     
     • (ex) histone methylation: makes DNA unaccesible for transcription

Question 13

SAM & Nutrition Connection

Answer 13

• SAM = methionine + ATP
• With the ACTIVATION of Vit. B12 (cobalamin), ATP donates adenosine
• after the transfer of methyl, SAM becomes S-adonosyhomocysteine (SAH)
  
  • then hydrolyzed to form homocysteine and adenosine

Question 14

N-Acetylation

Answer 14

• transfer of acetyl to lysine (REDUCES CHARGE)
• N-Acetylation is REVERSIBLE
  
  • ​(methylation tends to be irreversible)

Question 15

N-Terminal Acetylation

Answer 15

• initial Met is cleaved and
• N-acetyltransferases (NAT) enzymes use acetyl-coA to neutralize the N-terminal AA

Question 16

Lysine Acetylation

Answer 16

• occurs on the side chain instead of the N-terminal
• ex) histone lysine acetylation ↓ charge = ↑ access of promotors, which allows transcription factors (TF) to COUNTERACT histone METHYLATION
  
  • 2 enzymes:
    
    • histone acetyltransferases (HAT)
    • histone deacetylases (HDAC)

Question 17

MyeloDysplastic Syndromes (MDS) and Acute Myeloid Leukaemia (AML)

Answer 17

• MDS & AML = man, immature BC = blood cancer
• caused by hypermethylation of β-catenin promoter
• Two Treatments:
  
  1. Azacytinide: stops doxy-Cysteine methylation
  2. Vorinostate: histone deacetylase (HDAC) inhibitor

Question 18

Hydroxylation

Answer 18

• addition of OH to proline and others

Question 19

Hydroxylation Disorder

Answer 19

• collagen = 25% of all protein in body
  
  • collogen hydroxylation is done by prolyl-hydroxylase using Vit. C as a cofactor
  • this rxn occurs at every 3rd AA in collagen to stabilize it’s triple helical structure
• therefore, LACK of Vit C = Scurvy (defective collagen formaton)…
• symptoms of Scurvy:
  
  • subcutaneous hemorrhage (bruising)
  • aching bones/joints/muscles
  • rigid position and pain
    ​
• recommended Vit C intake is 75-90 mg

Question 20

Protein Lipidation

Answer 20

• attachment of lipid to proteins
• used to anchor proteins to membranes:
  
  1. ​​organelle membranes (ER, Golgi, Mito)
  2. vesicle membranes (endosomes, lysosomes)
  3. plasma membranes

Question 21

Major Types of Lipidation (4)

Answer 21

1. C-terminal Glycosyl PhosphatidylInositol (GPI) anchors:
2. N-terminal myristoylation, S-myristoylation (C14, Gly)
3. S-palmitoylation (C16, Cys)
4. S-prenylation (C15/C20, Cys)

Question 22

GPI Anchors

Answer 22

• anchor cell surface proteins to plasma membrane
• due to the ER signal sequence, glycolipid is added to newly made protein
• they will be reversibly localized to cholesterol and sphingolipid rafts in plasma membrane for signaling platforms
• ex) when GCPR signaling anchor released from Phosphlipase C

Question 23

N-myristoylation

Answer 23

• 14 C fatty acid on terminus
• selective, reversible localization signal that binds only some proteins to membranes
  
  • ex) Src-family kinases (i.e tyrosine kinases signals that regulate cell proliferation, differentiation, apoptosis, migration, and metabolism)
• enzyme: N-myristoyltransferases

Question 24

S-palmitoylation

Answer 24

• description: C16 added to thiol of cysetine
• enzyme: palmitoyl acyltransferases
• function:
  
  1. permanant anchor of membrane proteins
  2. on/off switch: to regulate membrane localization
     
     1. thioesterases can cleave Cys and the anchor
  3. strengthens other types of lipidation (i.e myristoylation OR farnesylation)

Question 25

S-prenylation

Answer 25

* description: **covalently** adds **C15 or C20** to **Cys** located **within 5 AA from C-terminus** * enzyme: **farnesyl transferases** (C15) or **geranylgeranyl transferases** (C20) * function: 1. \*\***HYDROLYTICALLY STABLE**\*\* (no rxn with H2O) 2. **keep** proteins **bound** to membranes * 2% of all proteins are prenylated * **Ras Superfamily** (*small GTP-ases)*

Question 26

Proteosomes

Answer 26

* RECYLES proteins * ***_initiated_*** by **ubiquitonation**

Question 27

Ubiquitin-Proteasome System

Answer 27

1. **protein** is **_inactivated_** by attaching a **ubiquitin** (*small 60 AA tag*) * specific ***ligases*** ***attach*** **ubiquitin** 2. initial ubiquitin event triggers **formation of ubiquitin POLYMER** 3. ubiquitin polymer **recognized by 26S preteosome** 4. 26S **proteosome** will **DEGRADE** ubiquitined **protein** and **RECYLE** **ubiquitin**

Question 28

Protein Quality Control

Answer 28

* **protein half-life = structural stability** * during stressful events, more proteins damaged/unfolded * (Outcome 1) = ↓ stress = ↑ protein acvity = ↑ protein recyling * (Outcome 2) = ↑ stress = ↑ UB-proteins = ↑ cell death * mechanism for **cancer treatment (chemo)**

Question 29

Classes of Signaling Machines (4)

Answer 29

1. GPCR (secondary cascading) 2. Hormone signaling (i.e glucocorticoid.. secondary +TF) 3. Nuclear signaling receptors (i.e transcription factors) 4. **Receptor Kinases** * use P to block or help target protein activity * **(ex) isocritrate dehydrogenase**

Question 30

3 Major Kinds of Receptors Kinases

Answer 30

1. **Tyrosine kinase receptor** 2. JAK-STAT receptors 3. Serine-Threonine kinase receptors

Question 32

Somatotropin Growth Hormone

Answer 32

**Tyrosine Kinase Receptor Example** * origin: pituitary * effect: growth * target cells: bones/muscles * type: peptide Actions: 1. Increase muscle mass 1. protein synthesis 2. lypolysis 2. Increase bone density 1. Ca 2+ retention

Question 33

Receptor Kinase Example: GH Totally Off

Answer 33

* typically a **receptor monomer** that extends into the extracellar portion * inactive kinases (**pseudokinase + kiase)** on the inside of the cell (**cystollic** side)

Question 34

Receptor Kinase Example: GH Phase 1

Answer 34

* **resting phase** * the **cystolic** side **kinase** is **not** **active** and the two are **inhibiting each other** * **Pseudokinase**: inhibits partner kinase * Kinase

Question 35

Receptor Kinase Example: GH Phase 2

Answer 35

* **growth hormone binds** leading to a structural change * conformation change = the **two cystolic kinases** (inside the cell) will **auto-phosphorylate** * = **moving** the **activation** **loop** and **activating the kinase**

Question 36

Receptor Kinase Example: GH Phase 3

Answer 36

* **Ras exchanges GDP → GTP** * *ACTIVATES Raf*

Question 37

Receptor Kinase Example: GH Phase 4

Answer 37

* **Raf** = secondary messenger = **many phosphorylation phase** * two cascading pathways (MEK → ERK & MAP paths) = **Gaq**

Question 38

Receptor Kinase Example: GH Phase 5

Answer 38

* **result: more** cells created & they are **bigger** cells * how? the pathway... 1. **expedited** the cell **cycle** 2. **activated more transcription factors** to make new cell material

Question 39

**Integration** Pathways: **Insulin**

Answer 39

* **insulin receptor = receptor kinases** * lots of **cross** **signaling** * **metabolism** is ***interwoven*** to bes utilize carbon and energy as needed Insulin v Adrenalin * **insulin** = **FED** state = **store** excess **energy** * **adrenaline** = **stress** = **use all** energy NOW Therefore, **insulin pathway STOPS adrenal signaling**