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Fatty acid biosynthesis

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Using your knowledge of fatty acid biosynthesis, provide an explanation for the following experimental observations:

(a) The addition of uniformly labeled [14C] acetyl-CoA to a soluble liver fraction yields palmitate uniformly labeled with 14C.

(b) However, the addition of a trace of uniformly labeled [14C]acetyl-CoA in the presence of an excess of unlabelled malonyl-CoA to a soluble liver fraction yields palmitate labeled with 14C only in C-15 and C-16.

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Solution Preview

How does fatty acid biosynthesis proceed?

Acetyl-CoA is used to form malonyl-CoA with the help of acetyl-CoA carboxylase and CO2. This is an important key in the process. Once malonyl-CoA is formed, the malonyl group is transferred to the fatty acid synthase as malonyl-ACP. Likewise, the acetyl group from acetyl-CoA is transferred to the enzyme as acetyl-ACP. These two activated groups react via the 3-ketoacyl synthase to form acetoacetyl-ACP. This acetoacetyl-ACP complex is reduced (forming the alcohol), then dehydrated (with the loss of H2O) forming the double bond, then reduced again forming the butyryl-ACP complex.

This cycle is now repeated and the chain grows by two carbons each round.

Now, where are the two carbons from the malonyl unit in the first condensation? The two carbons from malonyl unit are the two carbons nearest the ACP group. Or, ...

Solution Summary

This solution give detailed explanations for two given experimental observations, addressing soluble liver fractions yield and malonyl-CoA

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Synthesis/RNA/DNA

1.The basic differences between RNA and DNA are:
a.The organic bases only
b.Bases, ribose units, and the phosphodiester linkage
c.Bases, ribose units, and the glycosidic bond type
d.Bases and the ribose units only.

2.The solubility characteristics of the pyrimidine or purine bases and the corresponding nucleosides differ greatly. Which of the following statements is not true?
a.purine bases are quite soluble in water.
b.Nucleosides are much more soluble than the corresponding bases.
c.Nucleosides and nucleotides are quite soluble in water.
d.Ribose units are very soluble in water.

3.Adenosine and guanosine are found predominantly in which tautomeric forms, respectively?
a.Amino & keto, respectively
b.Imino & keto, respectively
c.Amino & enol, respectively
d.Imino & enol, respectively

4.The component(s) of DNA which is (are) responsible for the absorbance band at 250-270 nmis:
a.Bases, pentoses. and phosphates all contribute
b.Only bases
c.Only bases and pentoses
d.Only pentoses and phosphates

5.AMP has three relevant ionizable groups. NI of adenine has pKa 4.0 and the phosphomonoester has pKas at 1.0 and 6.0 the net charge on AMP at pH 7.0 is approximately:
a.-3
b.-2
c.-1
d. 0

6.The thermodynamically most favorable form for pyrimidine nucleotides is:
a.Syn conformation
b.Anti conformation
c.Both are equally favored
d.Cannot be predicted

7.Which molecule contains an acid anhydride bond?
a. DNA
b.ATP
c.AMP
d. CAMP

8.All the NTPs are essential for RNA synthesis but GTP is also essential in:
a.Protein biosynthesis
b.Glycogen biosynthesis
c.Phospholipid biosynthesis
d.Fatty acid biosynthesis

9.The oligonucleotide, AUGGp, has all these properties except
a.Composed of ribonucleotides
b.Contains a 3' phosphate
c.Has a net charge pf -2 at pH 8.5
d.Contains three phosphodiester bonds.

10.To what target sequence on DNA is the oligonucleotide pAATTCCGG complementary?
a.TIAAGGCC
b.CCGGAATT
c.UUAAGGCC
d.CCGGAAUU

11.Which of the following characterizes the DNA in human cells?
a.DNA is located at a mesosome.
b.DNA is complexed with nonhistone proteins to form a nucleosome.
c.DNA is complexed with histone proteins with the DNA residing in the interior of the nucleosome.
d.DNA is complexed with the basic histone proteins and winds around the exterior of the histone protein "core".

12.An individual heterogeneous nuclear RNA (hnRNA):
a.Contains intron sequences not found in the final mature mRNA.
b.Contains exon sequences which are removed prior to translation.
c.Encodes more than one protein.
d.Can be found in the cytoplasm.

13.The RNA molecules which are involved in processing the hnRNA are:
a.mRNA
b.tRNA
c.rRNA
d.snRNA

14.RNA is hydrolyzed in basic solution but DNA is not. This occurs because:
a.Thymine is found in DNA, but uracil is not.
b.DNA is double stranded. while RNA is single stranded.
c.DNA contains a 2'-deoxyribose, while RNA does not.
d.RNA has modified bases, while DNA does not

15. What statement is incorrect about the different RNA molecules?
a.tRNA contain numerous intramolecular hydrogen bonds between bases.
b.There are more distinct tRNA molecules than there are rRNA molecules.
c.rRNA are complexed to proteins in the ribosomes.
d.The most abundant RNA molecule in the cell is mRNA.

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