Biochemistry : Biochemistry
Study concepts, example questions & explanations for Biochemistry
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Example Questions
Example Question #26 : 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.
Base pairs are towards the outside of the helix; there are 8 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 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 #27 : 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, and III
III and IV
I, II, III, and IV
I and II
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.
Example Question #1 : Nucleic Acid Derivatives
What is the purpose of the pentose phosphate pathway (also known as the hexose monophosphate shunt or HMS)?
Production of 
Production of pentose phosphate for chemical signaling between cells
Regulation of gluconeogenesis
Detoxification of hepatic cells
Production of
The pentose phosphate pathway (also known as the hexose monophosphate shunt or HMS), mainly serves to produce 
Example Question #154 : Biochemistry
Which of the following is an example of a nucleoside?
Adenine
Adenosine
Guanosine monophosphate
Cytosine
Adenosine
A nucleoside is composed of both a nitrogenous base as well as a sugar. Cytosine and adenine are just nitrogenous bases. Guanosine monophosphate (or GMP) is also composed of a phosphate group, which designates it as a nucleotide. The only nucleoside is adenosine.
Example Question #1 : Modifications And Epigenetics
Which statement concerning DNA methylation in mammals is false?
CpG sites are mutation hot spots
Deamination of methylated cytosine gives thymine
None of the other answers is false
Deamination of unmethylated cytosine gives uracil
DNA methyltransferase adds a methyl group to cytosines of the dinucleotide CpG
None of the other answers is false
Unmethylated cytosine spontaneously deaminates to uracil. Over time, methylated cytosine is spontaneously deaminated to thymine. Random deamination of methylcytosines causes mutation, creating hot spots. The vast majority of DNA methylations in mammals occurs at CpG (cytosine-phospate-guanine) sites.
Example Question #2 : Modifications And Epigenetics
Which of the following describes a mutation in which a segment of DNA detaches from a chromosome and reattaches to another chromosome?
Point mutation
Translocation
Deletion
Null mutation
Inversion
Translocation
A null mutation is one that deactivates a gene entirely. Point mutations are those that occur within a single, small site in a gene. Inversion involves the reversal of orientation of a DNA segment. Deletion occurs when a whole part of a chromosome is removed, joining two ends that were far apart. Translocation involves the exchange of genetic material from two chromosomes that are not homologous.
Example Question #3 : Modifications And Epigenetics
Generally, silencing of a gene is accomplished by __________?
Acetylation
Decarboxylation
Ligation
Phosphorylation
Methylation
Methylation
The silencing of a gene is most often accomplished via methylation of the DNA. The methyl groups are added to the gene's promoter region and thus, the DNA is not read by transcriptional enzymes.
Example Question #4 : Modifications And Epigenetics
How does methylation cause the silencing of a gene?
Methyl groups are added to the coding sequence in the DNA
Methyl groups are removed from the coding sequence in the DNA
Methyl groups are transferred from the coding sequence of the DNA to the promoter region
Methyl groups are removed from the promoter region of the DNA
Methyl groups are added to the promoter region of the DNA
Methyl groups are added to the promoter region of the DNA
In order to silence a gene by methylation, methyl groups are added to the promoter region of DNA. This area is upstream of the coding sequence and is responsible for initiation of transcription. Thus, methylating the promoter region inhibits further transcription of the gene.
Example Question #153 : Biochemistry
Which of the following DNA bases can be methylated in the promoter region to silence a gene?
Thymine
Guanine and thymine
Cytosine and adenine
Cytosine
Guanine and adenine
Cytosine and adenine
The only two bases that can be methylated are cytosine and adenine.
Example Question #5 : Modifications And Epigenetics
Formation of thymine dimers in DNA can lead to conditions such as melanoma when unrepaired. This DNA mutation is primarily caused by __________.
alkylating agents such as nitrogen mustard
UV irradiation
defects in DNA topoisomerase
UV irradiation
Alkylating agents and 
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