Critical temperature for liquid nitrogen is ?
True statement about vitamin K is?
Mechanism of cyanide poisoning is by inhibiting:
NEET-PG 2013 - Biochemistry NEET-PG Practice Questions and MCQs
Question 131: Critical temperature for liquid nitrogen is ?
- A. 36.5°C
- B. -20°C
- C. -147°C (Correct Answer)
- D. -242°C
Explanation: ***-147°C*** - The **critical temperature** is the temperature above which a gas cannot be liquefied, no matter how much pressure is applied. For **liquid nitrogen**, this value is approximately **-147°C**. - At temperatures above **-147°C**, nitrogen exists only in its gaseous phase. *36.5°C* - This temperature is close to **human body temperature** and is not relevant to the critical temperature of nitrogen. - Nitrogen would be in a gaseous state at this temperature and below its critical pressure. *-20°C* - While a low temperature, **-20°C** is still well above nitrogen's **critical temperature**. - At **-20°C**, nitrogen would be a gas unless subjected to very high pressures. *-242°C* - This temperature is below the **critical temperature** of nitrogen, but it is also below its **boiling point** of **-196°C**. - At **-242°C**, nitrogen would be a liquid, but this value is not its critical temperature.
Question 132: True statement about vitamin K is?
- A. Vitamin K is needed for action of clotting factor 8
- B. Vitamin K deficiency leads to DVT
- C. Vitamin K is water soluble
- D. Vitamin K affects bone health by activating proteins that bind calcium (Correct Answer)
Explanation: ***Vitamin K affects bone health by activating proteins that bind calcium*** - Vitamin K plays a crucial role in **osteocalcin activation**, a protein essential for integrating calcium into the bone matrix. - This activation process involves **gamma-carboxylation of glutamic acid residues** on osteocalcin, allowing it to bind calcium and strengthen bone. *Vitamin K is needed for action of clotting factor 8* - Vitamin K is essential for the activation of **clotting factors II, VII, IX, and X**, as well as proteins C and S, through gamma-carboxylation. - **Factor VIII** (antihemophilic factor A) is not directly dependent on vitamin K for its activation. *Vitamin K deficiency leads to DVT* - Vitamin K deficiency primarily leads to **impaired blood clotting** and an increased risk of bleeding, not DVT. - DVT (deep vein thrombosis) is typically associated with **hypercoagulable states**, venous stasis, or endothelial injury. *Vitamin K is water soluble* - Vitamin K is a **fat-soluble vitamin**, meaning it is absorbed with fats in the diet and stored in the body's fatty tissues and liver. - Water-soluble vitamins include **B vitamins and vitamin C**, which are not stored to the same extent and are excreted in urine.
Question 133: Mechanism of cyanide poisoning is by inhibiting:
- A. Mitochondrial DNA synthesis
- B. ATP production
- C. Electron transport chain
- D. Cytochrome oxidase (Correct Answer)
Explanation: ***Cytochrome oxidase*** - Cyanide poisoning works by **irreversibly binding** to the ferric ion (Fe3+) in **cytochrome c oxidase** (Complex IV) of the electron transport chain. - This binding prevents the enzyme from carrying electrons to oxygen, thereby **halting cellular respiration** and ATP production. *Mitochondrial DNA synthesis* - While mitochondria are affected, cyanide does not primarily disrupt **DNA synthesis** in these organelles. - Its main target is the process of energy generation, not genetic replication. *ATP production* - Although cyanide poisoning ultimately leads to a **cessation of ATP production**, this is the *consequence* of its action, not the primary mechanism. - The direct mechanism involves inhibiting a key enzyme in the electron transport chain. *Electron transport chain* - Cyanide does indeed inhibit the **electron transport chain**, but this option is too broad. - The most specific mechanism targets a particular complex within the chain, which is **cytochrome oxidase**.