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Example Questions
Example Question #121 : Macromolecule Structures And Functions
Which of the the following DNA motifs is held together by hydrophobic interactions along the length of an amino acid side chain, to form a coiled-coil?
Zinc finger
Helix-turn-helix
Two-stranded beta sheet
Helix-loop-helix
Leucine zipper
Leucine zipper
The helix-turn-helix motif has two helices at a particular angle, with one of them, the recognition helix, fitting into a major groove. Zinc fingers have sheets and helices held together via zinc complexes. Beta sheets have hydrogen bonds along their strand backbones. The helix-loop-helix motif has one helix folded and packed against another. In the leucine zipper, two helices are coiled up to where they are "unzipped" to form a Y.
Example Question #23 : Nucleic Acid Structures
The backbone of a strand of DNA is comprised of which of these?
Sugars only
Nucleotides only
Nucleotides and phosphates
Sugars and nucleotides
Sugars and phosphates
Sugars and phosphates
The backbone of DNA is made up of alternating phosphate groups and sugar groups, linked together via phosphodiester bonds. The nitrogenous bases jut off of the backbone and form bonds with nitrogenous bases on other strands of DNA to become double stranded. A nucleotide consists of a sugar, nitrogenous base, and one or more phosphate groups.
Example Question #24 : Nucleic Acid Structures
What is the anticodon?
The region of tRNA that recognizes DNA
The region of a tRNA that recognizes mRNA
The region of mRNA that recognizes tRNA
The region of mRNA that recognizes DNA
The region of DNA that recognizes mRNA
The region of a tRNA that recognizes mRNA
The anticodon is a part of tRNA that is capable of finding its complementary codon on mRNA. This allows the tRNA to carry its specific amino acid to a ribosome when necessary in the production of proteins.
Example Question #15 : Dna And Rna
What types of bonds hold together a tRNA molecule?
Disulfide bonds
Ionic bonds
Hydrogen bonds
Covalent bonds
The tRNA molecule is not held together by bonds
Hydrogen bonds
The clover-like structure of tRNA is held together by hydrogen bonds between nitrogenous bases of the molecule. Without them, this tertiary structure would not be possible.
Example Question #25 : Nucleic Acid Structures
In RNA, which base pairs with adenine?
Adenine
Guanine
Cytosine
Uracil
Thymine
Uracil
In RNA the four bases are: adenine, uracil, guanine, and cytosine. The bases in DNA are similar, except uracil is replaced with thymine. In RNA, adenine will always pair with uracil, and guanine will always pair with cytosine. Remember, a purine (adenine, guanine) will always pair with a pyrimidine (cytosine, uracil or thymine).
Example Question #16 : Dna And Rna
Suppose that a portion of the coding strand in a given gene reads as follows:
What would the mRNA encoded by this gene read?
This question presents us with a portion of the coding strand of a gene, and asks us to determine the corresponding sequence of nucleotides in the mRNA that would be transcribed from this gene.
To begin, it is very important to recognize that the sequence given to us in the question stem is the coding strand. This is to distinguish it from the template strand.
For any given gene, there is a template strand and a coding strand. These two strands are complementary to one another and run in opposite directions. The template strand is the one that is transcribed to give rise to a complementary mRNA molecule that will go on to be translated into a polypeptide. Hence, it is called the template strand because it provides the template for the production of mRNA, and subsequently a protein.
The coding strand, on the other hand, is not transcribed. Instead, the coding strand gets its name because its sequence is identical to the sequence of the pre-mRNA (before introns are removed). The exception to this is that the coding strand contains thymine nucleotides, whereas the pre-mRNA contains uracil in place of thymine. The reason why these two have the same sequence is because both of them are complementary to the template strand. Sometimes, the template strand is also referred to as the antisense strand, while the coding strand is referred to as the sense strand.
It is important to realize this distinction because, without it, one might arrive at the incorrect answer. Because this is the coding strand (sense strand), the mRNA product will have an identical sequence, with the exception of uracil in place of thymine.
Coding strand:
mRNA strand:
Example Question #11 : Dna And Rna
The role of small nuclear RNA (snRNA) is to __________.
bind to complementary mRNA molecules to inhibit translation
bind to mRNA to facilitate its degradation
function as the template for protein synthesis
participate in the splicing of RNA exons
carry amino acids to the ribosome for translation
participate in the splicing of RNA exons
The function of snRNA is to participate in the splicing of RNA exons. Micro RNA binds to complementary mRNA to inhibit translation. Small interfering RNA binds to mRNA to facilitate its degradation. mRNA functions as a template for protein synthesis. Transfer RNA (tRNA) carries amino acids to the ribosome during translation.
Example Question #12 : Dna And Rna
What is the role of microRNA?
Binds to complementary mRNA strand to inhibit translation
Binds to mRNA to facilitate its degradation
Participates in the splicing of RNA exons
Functions as a template for protein synthesis
Carries amino acids to the ribosome during translation
Binds to complementary mRNA strand to inhibit translation
The function of snRNA is to participate in the splicing of RNA exons. Micro RNA binds to complementary mRNA to inhibit translation. Small interfering RNA binds to mRNA to facilitate its degradation. mRNA functions as a template for protein synthesis. Transfer RNA (tRNA) carries amino acids to the ribosome during translation.
Example Question #121 : Macromolecule Structures And Functions
In eukaryotes, the TATA box and/or Hogness box found on DNA are __________.
promoter sites
degradation sites
DNA replication origin sites
primer sites
transcription stop sites
promoter sites
The TATA box and/or the Hogness box are regions on DNA that function as promoter sites. RNA polymerase scans DNA for these regions and when it sees one, it recognizes that it should begin transcription of the following gene.
Example Question #122 : Macromolecule Structures And Functions
Which of the following statements about B DNA structure is incorrect?
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.
It has a pitch of 10 base pairs per helical turn.
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.
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