Biochemistry 🧪

Question 1

what is the importance of intracellular communication?

Answer 1

Intracellular communication is very important to cell adaptation to the change in their internal or external environment

Question 2

what are the types of intracellular communication?

Answer 2

direct & indirect

Question 3

compare between Direct intracellular communication & Indirect intracellular communication

Answer 3

Question 4

compare between endocrine system and nervous system according to:

• Types of chemical messenger
• Distance of action
• Speed of response
• Duration of action
• Major function

Answer 4

Question 5

what is the definition of hormones?

Answer 5

are natural organic substances, secreted (released) from the ductless glands into the blood and alter the metabolism of target cell (act as chemical messengers)

Question 6

what are target cells?

Answer 6

It is the cell that contains the specific receptors of the hormone.

Question 7

in what manner does the hormone fit in its receptor?

Answer 7

hormone fits receptor on target cell like a lock and a key (Lock and key system)

Question 8

what is the definition of hormone receptors?

Answer 8

They are cell-associated recognition molecules.

Question 9

what is the nature of hormone receptors?

Answer 9

They are protein in nature.

Question 10

what are the parts (functional sites) of hormone receptors?

Answer 10

Each receptor has two functional sites:

1) Recognition site: it binds the hormone specifically.
2) Signaling site:it couples hormone binding to intracellular effect.

Question 11

what is the cellular location of hormone receptors?

Answer 11

Intracellular receptors: Located inside the cell either in the:
* In the cytosol: eg Steroid hormones.
* In the nucleus. eg. Thyroid hormones

Cell-membrane receptors: Located in the plasma membrane of the cell.
- Proteins, peptides, catecholamines.

Question 12

what are hormones classified according to?

Answer 12

• Chemical Nature
• Solubility

Question 13

what are types of hormones according to chemical nature?

Answer 13

1. Steroid hormones
2. Non steroid

Question 14

what are steroid hormones derived from?

Answer 14

They are derived from cholesterol.

Question 15

what are examples of steroid hormones?

Answer 15

• Glucocorticoids
• Mineralocorticoids.
• Sex hormones: Testosterone, Estrogen, and progesterone

Question 16

what are types of non-steroid hormones?

Answer 16

Protein Hormones & Amino Acid Derived Hormones

Question 17

what are examples of protein hormones?

Answer 17

Large polypeptides:
- Growth hormone, Insulin & Glucagon, parathyroid hormone , Prolactin.

Small polypeptides: (small number of amino acids)
- ADH (9 a.a.),
- oxytocin (9 a.a.)
- TRH (3 a.a.).

Glycoprotein hormone:
- FSH
- LH
- TSH
- HCG

Question 18

what are examples of amino-acid derived hormones?

Answer 18

• Thyroid hormones, adrenalin, noradrenalin from Tyrosine AA
• Melatonin from Tryptophan AA

Question 19

compare between lipophilic hormones & Hydrophilic hormones according to:

• solubility
• transport in plasma
• penetraton of plasma membrane
• receptor
• mechanism of action
• response
• mediator

Answer 19

Question 20

give an example of lipophilic hormones & hydrophilic hormones

Answer 20

Lipophilic: Steroid and thyroid hormones

Hydrophilic: Proteins, peptide hormones & catecholamines

Question 21

what is the mechansim of action hormones which act via intracellular receptors (modify gene expression)

Answer 21

• Lipophilic hormone (Steroid hormones. Thyroid hormones, Calcitriol, Retinoids)
• These hormones are transport in blood bonded to plasma proteins
• Being fat soluble, so it penetrate the phospholipid bilayer of the cell membrane→The binds to a receptor in the nucleus or cytoplasm that carries it into the nucleus
• Then the hormone–receptor complex binds to DNA → RNA polymerase to bind to specific gene → Catalyzes the transcription of DNA into messenger RNA (mRNA)→ mRNA leaves the nucleus→ attaches to a ribosome in cytoplasm → directs the synthesis of a specific protein product (translation)

Question 22

what is the mechanism of action of hormones which act via extracellular receptors (2nd messenger)?

Answer 22

• For Hydrophilic hormones (Proteins and peptide hormones, catecholamines)
• These hormones are water soluble → so, circulate mainly dissolved in the plasma→ reach to the target cells → but cannot penetrate the membrane as it is not fatsoluble → so, it binds to receptor proteins in the cell membrane.
• This hormone–receptor binding → activates an enzyme that catalyzes the synthesis of a second messenger (It is the signal produced because of hormone binding to its cell membrane receptor.
• This 2nd messenger activates other enzymes that catalyze a specific reaction in the cell to mediate the hormone action

Question 23

what is a (second messenger)?

Answer 23

It is the signal produced as a result of hormone binding to its cell membrane receptor.

Question 24

what is considered the first messenger?

Answer 24

The hormone itself is considered to be the first messenger

Question 25

what may the second messenger be?

Answer 25

The second messenger may be: 1) Cyclic Adenosine Monophosphate (cAMP). 2) Cyclic Guanosine Monophosphate (cGMP). 3) Calcium or phosphatidyl inositides (PIs) or both. 4) Protein kinase cascade.

Question 26

what is the function of the second messenger?

Answer 26

It mediates the effects of the hydrophilic hormones

Question 27

what is the mechanism of action of CAMP as a second messenger?

Answer 27

- Some hormones like catecholamines, glucagon utilize cAMP as 2nd messenger. - Binding of the hormone (ligand) to cell membrane receptor→ activates a regulatory G protein→ activates adenylate cyclase enzyme→ catalyzes the formation of cAMP from ATP. - Then cAMP: a) Activates protein kinase A →Phosphorylation of certain enzymes b) Or Bind to CREB protein→ Gene Expression. - The action of cAMP is terminated by phosphodiesterase enzyme (PDE) hydrolyses it to AMP

Question 28

do all hormones act via **activation** of adenyl cyclase?

Answer 28

No, Some hormones acts via inhibition (not activation) of adenyl cyclase.

Question 29

what are G-regulatory proteins?

Answer 29

regulatory proteins, consists of 3 polypeptide subunits: a. alpha-subunit. b. β subunit. c. γ subunit.

Question 30

what is the importance of G regulatory proteins?

Answer 30

- Binding of the hormone to its receptor activates G protein - The active α subunit affects the activity of the next reaction according to the type of G protein.

Question 31

what are the types of G proteins?

Answer 31

There are several types of G proteins: - Gs: Stimulates adenylate cyclase. - Gi: Inhibits adenylate cyclase. - Gq: Stimulates phospholipase C. - Other types affect Ca channels and K channels.

Question 32

what is the mechanism of action of CGMP as a second messenger?

Answer 32

- It is the 2nd messenger of Atrial natriuretic factor (ANF) that produced in cardiac atrial tissues. - The hormone binds to its specific G protein coupled receptor→ activates the membrane bound form of guanylate cyclase → catalyzes the transformation of GTP to cGMP→ cGMP activates protein kinase G→protein phosphorylation→ mediate the effects of ANF ( smooth muscle relaxation, vasodilatation) - After mediating its effects, cGMP is hydrolyzed by cGMP dependent phosphodiesterase enzyme 5’ GMP.

Question 33

what is the mechanism of action calcium or phosphatidyl inositol as a second messenger?

Answer 33

1. Some hormones like: GnRH, TRH, ADH utilize this 2nd messenger. 2. Binding of the hormone (ligand) to its specific receptor →activates G protein (Gq) →activates the enzyme phospholipase C (PLC)→ The active PLC hydrolyses phosphatidyl inositol bi biphosphate (PIP2) to: - Diacyl glycerol (DAG)→It activates protein kinase C→ phosphorylates of enzymes/protein → mediate the effects of the hormone. - Inositol Triphosphate (IP3)→ couple Ca Channel→releases Ca2+ from intracellular storage sites (ER , Mitochondria) → Ca2+ binds to Ca binding protein (calmodulin) to form Ca2+/ calmodulin complex→phosphorylation of enzymes → mediate the effects of the hormone.

Question 34

what is tyrosine kinase?

Answer 34

- are group of enzymes, which phosphorylate their substrates on tyrosine residues. - Tyrosine kinases may be: a) Intrinsic part of the receptor like Insulin b) Intracellular associated with the receptor but not an intrinsic part of it like GH