Biochemistry : DNA and RNA
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Example Questions
Example Question #21 : Dna And Rna
Which of the following statements about B DNA structure is incorrect?
It has a pitch of 10 base pairs per helical turn.
It is a right handed helix with a diameter of 20 A.
Its glycosidic bonds are in the syn conformation.
Its minor groove is narrow and deep.
Its glycosidic bonds are in the syn conformation.
The glycosidic bonds of B DNA are in the anti conformation. This means that the nucleotide and sugar are on opposite sides of the N-glycosidic bond.
Example Question #22 : Dna And Rna
Which of the following is not a feature of both DNA and RNA?
Guanine can pair with cytosine.
Uses a ribose sugar.
Uses adenine nitrogenous bases.
Read from the 5' to 3' direction.
Uses a ribose sugar.
DNA and RNA share many common characteristics, as they are both nucleic acids. One of the key differences is that DNA use a deoxyribose sugar while RNA uses a ribose sugar. It should be noted that while RNA is typically assumed to be single stranded, it can still exhibit complementary base pairing. As a result, the guanine and cytosine base pairing can still take place.
Example Question #23 : Dna And Rna
A histone is mutated so all lysine residues are changed to glutamate. What effect will this mutation have?
The histone will introduce more negative supercoils in the DNA.
The histone will be tagged with ubiquitin.
The histone will have an increased binding affinity for DNA.
The histone will have a reduced binding affinity for DNA.
The histone will have a reduced binding affinity for DNA.
DNA is negatively charged because of the sugar-phosphate backbone. Histones are rich in lysine residues because they are positively charged and are ideal for DNA to wrap around. If the lysines became glutamates, the histone would overall have a negative charge, causing the DNA to bind weakly to each histone. The function of introducing negative supercoils would be reduced, and ubiquitination would not be affected.
Example Question #24 : Dna And Rna
Primase is needed for which of the following?
Supplying a DNA primer with a free 5' end
Reliving supercoiling stress on DNA
Suppling a DNA primer with a free 3' end
Suppling and RNA primer with a free 3' end
Supplying an RNA primer with a free 5' end
Suppling and RNA primer with a free 3' end
Primase is an enzyme used in the replication of DNA. DNA polymerase synthesizes DNA in a 5' to 3' direction, so it needs a free 3' end to begin its replication from. The primase constructs an RNA substrate with a free 3' end, that binds complementary to the unwound and single-stranded DNA template that is about to be replicated.
Example Question #25 : Dna And Rna
Starting with the first start codon, what is the third codon in the following mRNA sequence?
5'AAUGUUAGCGUGCGCUA3'
UAC
AUG
CUA
CGC
GCG
GCG
A codon is a set of three nucleic acids on the messenger RNA that codes for an amino acid. The start codon is AUG. In this strand, AUG is the first codon, the second is UUA, and the third is GCG.
Example Question #25 : Dna And Rna
During bacterial DNA replication, what is required for sealing the Okazaki fragments of DNA together after the RNA primers have been replaced with DNA?
Primase and free nucleic acids
DNA polymerase 3
DNA polymerase 1
DNA ligase and AMP
DNA ligase and ATP
DNA ligase and ATP
After DNA Polymerase 1 replaces the RNA primers with DNA. DNA ligase then comes along and uses an ATP for energy as it connects the 3' and 5' ends of the DNA gap, completing the replication of the template strand.
Example Question #26 : Dna And Rna
Which of the following statements is true about the B and Z forms of the DNA helix?
I. Z-DNA is a left-handed helix; B-DNA is a right-handed helix.
II. Z-DNA has 12 base pairs per turn of the helix; B-DNA has 10 base pairs per turn of helix.
III. B-DNA is present in chromosomal DNA.
IV. Z-DNA can occur in sequences with many guanine (G), cytosine(C) residues (polyGC sequence).
II and III
I and IV
I and II
III and IV
I, II, III, and IV
I, II, III, and IV
There are 3 conformations of the DNA molecule. The B form is in chromosomal DNA, the A form is representative of DNA-RNA hybrids. The Z form of DNA appears in poly GC (poly guanine, cytosine) sequences.
Example Question #27 : Dna And Rna
How are base pairs positioned and what is the number of base pairs per complete helical turn in the B form of DNA helix (predicted by Watson and Crick)?
Base pairs are towards the inside of the helix; there are 10 base pairs per complete turn of the helix.
None of these
Base pairs are towards the inside of the helix; there are 8 base pairs per complete turn of the helix.
Base pairs are towards the outside of helix; there are 6 base pairs per complete turn of the helix.
Base pairs are towards the outside of the helix; there are 8 base pairs per complete turn of the helix.
Base pairs are towards the inside of the helix; there are 10 base pairs per complete turn of the helix.
The deoxyribose–phosphate backbone of DNA is on the outside (hydrophylic) of the helix while the hydrophobic bases are inside. The classical B form, found in chromosomal DNA, and predicted by Watson and Crick, is a right-handed helix with 10 bases per turn of helix. The number of bases is different in Z and A DNA helix conformations.
Example Question #28 : Dna And Rna
What is the name of a deoxynucleotide in which the base is thymine?
I. Deoxythymidine monophosphate
II. Deoxythymidine diphosphate
III. Deoxythymine monophosphate
IV. Deoxythymine diphosphate
I, II, III, and IV
II, III, and IV
I, II, and III
I and II
III and IV
I and II
Phosphate groups attach to the 5' carbon of the nucleosides forming nucleotides. Phosphodiester bonds of DNA form between the 3'-hydroxyl group of the deoxy pentose of one nucleotide and the 5'-hydroxyl group of the deoxy pentose of another nucleotide.Deoxythymidine is the deoxynucleotide with thymine as its base. It can be mono-, di, or tri- phosphorylated as deoxythymidine mono-, di- or triphosphate.
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