Cell biology - Chapter 5

chichi's version from 2015-07-27 21:06


Question Answer
DNA molecules, like proteins, consist of a single, long polymeric chain that is assembled from small monomeric subunits.False, DNA is double-stranded. It actually made of two polymers that are complementary in sequence
The polarity of a DNA strand results from the polarity of the nucleotide subunits.True
There are five different nucleotides that become incorporated into a DNA strand.False, There are four different nucleotides that are used to make a DNA polymer: adenine, thymine, guanine, and cytosine. A fifth nucleotide, uracil, is found exclusively in RNA molecules, replacing thymine nucleotides in the DNA sequence.
Hydrogen bonds between each nucleotide hold individual DNA strands together.False, Nucleotides are linked covalently through phosphodiester bonds. Hydrogen-bonding between nucleotides from opposite strands holds the DNA molecule together
Which of the following chemical groups is not used to construct a DNA molecule?six-carbon sugar


Question Answer
The human genome has enough DNA to stretch more than 2 m. However, this DNA is not contained in a single molecule; it is divided into linear segments and packaged into structures called chromosomes. What is the total number of chromosomes found in each of the somatic cells in your body?46
DNA replication is considered semiconservative becauseeach daughter DNA molecule consists of one strand from the parent DNA molecule and one new strand
A molecule of bacterial DNA introduced into a yeast cell is imported into the nucleus but fails to replicate the yeast DNA. Where do you think the block to replication arises? Choose the protein or protein complex below that is most probably responsible for the failure to replicate bacterial DNAInitiator Proteins
Even though DNA polymerase has a proofreading function, it still introduces errors in the newly synthesized strand at a rate of 1 per 107 nucleotides. To what degree does the mismatch repair system decrease the error rate arising from DNA replication?100-fold
The repair of mismatched base pairs or damaged nucleotides in a DNA strand requires a multistep process. Which choice below describes the known sequence of events in this process?DNA damage is recognized, the newly synthesized strand is identified by an existing nick in the backbone, a segment of the new strand is removed by repair proteins, the gap is filled by DNA polymerase, and the strand is sealed by DNA ligase.


Question Answer
RNA in cells differs from DNA in that is single-stranded and can fold up into a variety of structures
Transcription is similar to DNA replication in that ___________________.nucleotide polymerization occurs only in the 5′-to-3′ direction
Which of the following statements is false?Unlike DNA, RNA uses a uracil base and a deoxyribose sugar.
Transcription in bacteria differs from transcription in a eucaryotic cell because __________________________.RNA polymerase (along with its sigma subunit) can initiate transcription on its own
Which of the following does not occur before a eucaryotic mRNA is exported from the nucleus?The ribosome binds to the mRNA.


Question Answer
Which of the following statements about RNA splicing is false?For a gene to function properly, every exon must be removed from the primary transcript in the same fashion on every mRNA molecule produced from the same gene.
Which of the following statements about the genetic code is correct?The genetic code is redundant.
Ribozymes catalyze which of the following reactions?RNA splicing
Each strand of DNA contains all the information needed to create a new double-stranded DNA molecule with the same sequence information.True
All functional DNA sequences inside a cell code for protein products.False, Some sequences encode only RNA molecules. some bind to specific regulatory proteins, and others are sites where specific chromosomal protein structures are built (for example, centromeric and telomeric DNA.)


Question Answer
Gene expression is the process of duplicating genes during DNAFalse, Gene expression is the process of going from gene sequence to RNA sequence, to protein sequence
Gene sequences correspond exactly to the respective protein sequences produced from themFalse, This statement is false for two reasons. First, genes often contain intron sequences. Second, genes always contain nucleotides flanking the protein-coding sequences that are required for the regulation of transcription and translation
Comparing the relative number of chromosome pairs is a good way to determine whether two species are closely relatedFalse, Same number of genes different number of chromosomes
Chromosomes exist at different levels of condensation, depending on the stage of the cell cycleTrue
Eukaryotic chromosomes contain many different sites where DNA replication can be initiated.True


Question Answer
The telomere is a specialized DNA sequence where microtubules from the mitotic spindle attach to the chromosome so that duplicate copies move to opposite ends of the dividing cell.True
When DNA is being replicated inside a cell, local heating occurs, allowing the two strands to separateFalse, The two strands do need to separate for replication to occur, but this is accomplished by the binding of initiator proteins at the origin of replication
DNA replication origins are typically rich in G-C base pairsFalse, DNA replication origins are typically rich in A-T base pairs, which are held together by only two hydrogen bonds (instead of three for C‐G base pairs), making it easier to separate the strands at these sites.
Meselson and Stahl ruled out the dispersive model for DNA replicationTrue
DNA replication is a bidirectional process that is initiated at multiple locations along chromosomes in eukaryotic cells.True


Question Answer
Primase is needed to initiate DNA replication on both the leading strand and the lagging strandTrue
The sliding clamp is loaded once on each DNA strand, where it remains associated until replication is complete.False. Although the sliding clamp is only loaded once on the leading strand, the lagging strand needs to unload the clamp once the polymerase reaches the RNA primer from the previous segment and then reload it where a new primer has been synthesized.
Telomerase is a DNA polymerase that carries its own RNA molecule to use as a primer at the end of the lagging strand.True
Primase requires a proofreading function that ensures there are no errors in the RNA primers used for DNA replication.False – the RNA primers are removed during replication and replaced by DNA via DNA polymerase II, therefore primase needs no proof-reading abilities

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