Biochemistry Questions 1. Which of the following is an enzyme that removes a fat
ID: 53732 • Letter: B
Question
Biochemistry Questions
1. Which of the following is an enzyme that removes a fatty acyl group from a phospholipid?
A: protein phosphatase A
B: protein kinase A
C: phophorylase kinase A
D: phospholipase A
2: in the double helix model of DNA
A: a purine in one strand always hydrogen bonds with a purine in the other strand
B: A-T pairs share two hydrogen bonds
C: at each end of th ehelix there are either two 3' ends or two 5' ends
D: the 5' ends of both strands are at one end of the helix
E: the bases point towards the outside of the helix
3: a DNA chain elongation reaction directly involves
A: deoxynucleoside monophosphates and the free 5' end of the growing strand
B: deoxynucleoside triphosphates and the free 5' end of the growing strand
C: deoxynucleoside monophosphates and the free 3' end of the growing strand
D: deoxynucleoside triphosphates and the free 3' end of the growing strand
4. Which of the following lipids contain fatty acid?
A: Plasmalogen
B: Prostaglandins
C: Sphingolipids
D: Glycerophospholipids
E: All of the Above
5: In the formation of a nucleotide from a ribose, a phosphate, and a nitrogenous base
A: A water molecule is formed
B: Two water molecules are formed
C: Three water molecules are formed
D: One water molecule is formed but it is used immediately to complete the nucleotide so zero water
6: What is TRUE about double bonds in fatty acids
A: Most organisms produe about equal proportion of cis- and trans- fatty acids
B: trans-fatty acids have a lower melting point than cis-fatty acids
C: cis-fatty acids pack more densly in a biological membrane
D: trans fatty acids are mostly associated with industrial processes
E: All of the above.
Explanation / Answer
Answer1: Phospholipase A (option 4) removes fatty acyl group from phospholipids.
There are 2 types of phospholipase A (PLA): A1 and A2. PLA1 hydrolysis SN-1 acyl chain while PLA2 hydrolysis SN-2 acyl chain. PLA2 releases arachidonic acid from the membrane phospholipids, which serves as a precursor for formation of prostaglandins (known for their role in inflammation).
Answer 2: The correct answer is option B (A-T share two hydrogen bonds).
In a double helix model of DNA, there are 2 strands of polynucleotides that are antiparallel i.e. one strand runs from 5’ to 3’ direction while other runs in 3’ to 5’ direction. 3’ refers to 3’ OH of the sugar while 5’ means 5’ phosphate attached to C5 of sugar. Purines namely adenine (A), guanine (G) pairs with pyrimidine i.e. thymine (T) and cytosine (C) by means of 2 and 3 hydrogen bonds respectively. To form a stable DNA molecule, all the bases form the core (point inward) stabilized by base stacking and hydrogen bond pairing.
Answer 3: In the DNA elongation reaction directly involves deoxynucleoside triphosphate and free 3’ end of the growing strand (Option D).
During the DNA/ chain elongation process, DNA polymerase added DNA nucleotides (dATP, dCTP, dGTP, and dTTP) to the 3’ end of the newly synthesized DNA strand. The nucleotides added are always complementary to the parent strand i.e. if parent strand has A, DNA polymerase adds T to new strand. The DNA synthesis always proceeds from 5’to 3’ end.
Answer 4: All of the above mentioned lipids contain fatty acid (Option E).
Plasmalogens are phospholipids that contain fatty alcohol at SN-1 and fatty acids at SN-2 position (details of SN-1 and SN-2 in answer 1). Prostaglandins are derived from fatty acid. They are the lipids composed of 20 carbon atoms including five-carbon ring and COOH.
Sphingolipids contains sphingosine and fatty acid (one molecule). Glycerophospholipids contain glycerol backbone, which is linked with three molecules of fatty acids.
Answer 5: In the formation of a nucleotide from a ribose, a phosphate, and a nitrogenous base, two water molecules are formed (Option B).
In first step, base (A/T/G/C) condenses with C1 (carbon 1) of deoxyribose to lose one water. In this formed molecule, phosphoric acid attacks 5’ OH of deoxyribose to form a nucleoside and release of a water molecule. So, in total 2 water molecules are released as a result of formation of nucleoside.
Answer 6: Trans fatty acids are mostly associated with industrial process (Option D).
Cis fatty acids are commonly occurring fatty acids in food but trans fatty acids are reported in food like meat, dairy products and processed foods. Cis fatty acids contains same groups on one side so that it produces a kink and hence the packing of cis fatty acids is not dense. They have low melting point in comparison to trans fatty acids. Trans fatty acids are produced by hydrogenation of cis fatty acids.
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