BIOL 67B SI Content Review

Which enzyme produced cAMP from ATP?

adenylyl cyclase

Do peptide hormones enter the target cell?

No, they act by binding membrane receptors

What is the main effect of protein kinase A activation in peptide hormone signaling?

phosphorylation of target proteins to alter their activity

What is the initial form of a peptide hormone when it is first synthesized?

Preprohormone

Name the two second messengers produced by phospholipase C.

IP3 (inositol triphosphate) and DAG (diacyglycerol)

What peptide is secreted alongside insulin and can be measured clinically?

C-peptide

How is the prohormone transported from the RER to the Golgi apparatus?

via transport vessicles

Which second messenger activates protein kinase A (PKA)?

cAMP

Peptide Hormones

• made in advance; stored in secretory vesicles

• exocytosis release from parent cell

• dissolved in plasma

• short half life

• receptor located in cell membrane

• activation of second messenger systems; induction of new protein synthesis

• modification of existing proteins and induction of new protein synthesis

• ex: insulin, parathyroid hormone

Steroid Hormones

• synthesized on demand from precursors

• simple diffusion release from parent cell

• bound to carrier proteins

• long half life

• receptor located on cytoplasm or nucleus; some have membrane receptors also

• activation of genes for transcription and translation; may habe nongenomic actions

• induction of new protein synthesis

• ex: estrogen, androgens, cortisol

Amine Hormones - Catecholamines

• made in advance; stored in secretory vesicles

• exocytosis

• dissolved in plasma

• short half life

• receptor located on cell membrane

• activation of second messenger systems

• modification of existing proteins

• ex: epinephrine, norepinephrine

Amine Hormones - Thyroid Hormones

• made in advance; precursor stored in secretory vesicles

• simple diffusion

• bound to carrier proteins

• long half life

• receptor located on nucleus

• activation of genes for transcription and translation

• induction of new protein synthesis

• ex: thyroxine (T4_

Tyrosine Kinases Receptor (Cell Surface Receptors)

• signal molecule/ligand binds to the receptor, which causes a conformational change in the receptor

• this change causes dimerization, where 2 receptor tyrosine kinase dimerizes

• dimerization activates the intercellular tyrosine kinase, which phosphorylates other enzymes (phosphorylation) to perform cellular response

GPCR

alpha and beta-gamma subunits

Alpha Subunit

1. Ligand binds to a receptor, and the G protein dissociates

2. Alpha subunit binds to adenylate cyclase

3. ATP is converted to cAMP and 2 Pi

4. cAMP activates protein kinase A

5. Activated protein kinase phosphorylates other enzymes

6. Phosphorylation either inhibits or increases enzyme activity

Beta-Gamma Subunit

1. Ligand binds to a receptor, and the G protein dissociates

2. Beta-gamma subunit binds to phospholipase C (PLC)

3. PLD splits the plasma membrane into IP3 and DAG

4. IP3 diffuses through the cytoplasm and binds to the ER receptors

5. Ca2+ channels open as a result of the binding between IP3 and ER receptors

6. Ca2+ binds to calmodulin, and it activates protein kinase C

7. PKC phosphorylates other enzymes

8. DAG activates PKC, which phosphorylates proteins

Steroid Hormone Synthesis and Processing

• Most steroid hormones are bound to a carrier protein to flow in the blood

• steroid hormones are lipophilic, so they can diffuse easily through plasma membranes without any cell membrane receptors; only unbound hormones can diffuse into target cell

• Steroid hormone receptors are in the cytoplasm or nucleus

• Steroid hormones bind to either cytoplasmic receptors or nuclear receptors to form hormone-receptor complexes; 2 of these complexes form dimers (dimerization)

• that dimerized receptor hormone complex binds to DNA and activate or represses one or more genes

• activated genes create new mRNA that moves back to the cytoplasm (transcription)

• translation produces new proteins for cell processes

A patient is prescribed levothyroxine (T4) for hypothyroidism. How does T4 work in the body?

A. Binds to a GPCR and increases cAMP

B. Acts through a nuclear receptor to regulate gene expression

C. Inhibits insulin receptors

D. Stimulates ion channels in the thyroid gland

B. Acts through a nuclear receptor to regulate gene expression

Hydrocortisone is given to treat inflammation. How does it work at the cellular level?

A) Binds intracellular glucocorticoid receptors to regulate anti-inflammatory genes

B) Activates GPCR to increase cAMP

C) Opens ion channels to reduce inflammation

D) Blocks receptor tyrosine kinase activity

A) Binds intracellular glucocorticoid receptors to regulate anti-inflammatory genes

A patient with hypogonadism is given testosterone therapy. How does testosterone exert its effect?

A) Activates GPCR on cell membrane to increase cAMP

B) Binds intracellular androgen receptors and regulates gene transcription

C) Activates receptor tyrosine kinase

D) Inhibits calcium channels

B) Binds intracellular androgen receptors and regulates gene transcription

Which organelle contains its own DNA and plays a central role in ATP production?

A. Nucleus

B. Golgi apparatus

C. Mitochondria

D. Lysosome

C. Mitochondria

A patient presents with muscle weakness. A biopsy shows impaired calcium storage within muscle cells. Which organelle is defective?

A. Smooth endoplasmic reticulum

B. Rough endoplasmic reticulum

C. Golgi apparatus

D. Mitochondria

A. Smooth endoplasmic reticulum

A patient presents with chronic muscle weakness. A biopsy reveals abnormal mitochondria with disrupted cristae. Which process is most impaired?

A. DNA replication

B. ATP production

C. Protein synthesis

D. Lipid digestion

B. ATP production

Which of the following is required for a target cell to respond to a signal?

A. High concentration of ligand in blood

B. Specific receptor protein for the signal

C. Absence of receptor proteins

D. Enzyme amplification only

B. Specific receptor protein for the signal