multiple choice questions - lecture 2
Here are some detailed multiple-choice revision questions based on the sources provided:
DNA Packaging
How is the DNA molecule, which is significantly longer than the cell itself, able to fit inside a bacterial cell such as E. coli?
The DNA molecule is fragmented into smaller pieces that are distributed throughout the cell.
The DNA molecule adopts a linear configuration, allowing it to be tightly packed within the cell.
The DNA molecule undergoes supercoiling, a process where the double helix twists upon itself to form a more compact structure.
The DNA molecule binds to specific proteins that condense and package it into a smaller volume.
Explanation: The sources describe how the DNA molecule in prokaryotes like E. coli is compacted through supercoiling. This process allows the long DNA strand to fit within the relatively small confines of the bacterial cell.
In eukaryotic cells, DNA is packaged into a complex structure called chromatin. What is the fundamental unit of chromatin?
A nucleosome, consisting of DNA wrapped around a core of histone proteins.
A chromosome, a highly condensed structure visible during cell division.
A gene, a segment of DNA that codes for a specific protein or functional RNA molecule.
An intron, a non-coding sequence within a gene that is removed during RNA processing.
Explanation: The sources explain that the basic unit of chromatin in eukaryotes is the nucleosome. DNA wraps around histone protein complexes to form nucleosomes, which further coil and condense to create the chromatin structure.
Eukaryotic chromatin exists in different states of condensation. Which of the following statements accurately describes euchromatin and heterochromatin, two major forms of chromatin?
Euchromatin is highly condensed and transcriptionally inactive, while heterochromatin is less condensed and transcriptionally active.
Euchromatin is less condensed and gene-rich, while heterochromatin is highly condensed and contains fewer genes.
Euchromatin is found primarily in the cytoplasm, while heterochromatin is located within the nucleus.
Euchromatin is replicated early in the cell cycle, while heterochromatin is replicated later.
Explanation: The sources indicate that euchromatin is the less condensed form of chromatin and is associated with active gene expression. Heterochromatin, on the other hand, is highly condensed and contains fewer actively transcribed genes.
Gene Structure and Organisation
Which statement accurately reflects a key difference in gene organisation between prokaryotes and eukaryotes?
Prokaryotic genes are typically much larger than eukaryotic genes, containing significantly more base pairs.
Prokaryotic genes are often organised into operons, where multiple genes are transcribed together under the control of a single promoter, whereas eukaryotic genes typically have their own individual promoters.
Prokaryotic genes contain introns, non-coding sequences that are removed during RNA processing, while eukaryotic genes lack introns.
Prokaryotic genes are primarily located on plasmids, extrachromosomal DNA molecules, whereas eukaryotic genes are found exclusively on chromosomes.
Explanation: The sources highlight that operons, clusters of genes under the control of a shared promoter, are a common feature of prokaryotic genomes. In contrast, eukaryotic genes usually have their own promoters.
What is the functional significance of introns in eukaryotic genes?
Introns serve as binding sites for regulatory proteins that control gene expression.
Introns allow for alternative splicing, where different combinations of exons can be joined together to produce multiple protein isoforms from a single gene.
Introns act as spacers between genes, preventing transcriptional interference between adjacent genes.
Introns provide structural stability to the DNA molecule, protecting it from damage.
Explanation: The sources explain that introns, the non-coding sequences within eukaryotic genes, play a role in alternative splicing. This process allows for the generation of different protein variants from the same gene by selectively including or excluding specific exons during RNA splicing.
Chromosome Organisation
Prokaryotic and eukaryotic chromosomes differ in their structure and organisation. Which of the following statements accurately contrasts these differences?
Prokaryotic chromosomes are linear and enclosed within a membrane-bound nucleus, while eukaryotic chromosomes are circular and located in the cytoplasm.
Prokaryotic chromosomes are typically circular and reside in a region called the nucleoid, while eukaryotic chromosomes are linear and found within the nucleus.
Prokaryotic chromosomes are composed primarily of RNA, while eukaryotic chromosomes are composed of DNA.
Prokaryotic chromosomes are much larger and more complex than eukaryotic chromosomes, containing significantly more genes.
Explanation: The sources state that prokaryotic chromosomes are generally circular and lack a membrane-bound nucleus. They are located in a region known as the nucleoid. Eukaryotic chromosomes, on the other hand, are linear and housed within the nucleus.
During interphase, the period between cell divisions, how are eukaryotic chromosomes organised within the nucleus?
They are randomly distributed throughout the nucleus.
They are clustered around the nucleolus, the site of ribosome synthesis.
They occupy distinct regions called chromosome territories.
They are linearly arranged along the inner surface of the nuclear membrane.
Explanation: The sources indicate that eukaryotic chromosomes are not randomly distributed during interphase but instead occupy defined territories within the nucleus.
Genome Organisation
What percentage of the human genome, the complete set of genetic information in a human cell, actually codes for proteins?
Approximately 98%.
Less than 2%.
Around 50%.
Close to 20%.
Explanation: The sources reveal that the protein-coding portion of the human genome is surprisingly small, accounting for less than 2% of the total DNA sequence.
Comparative genomics involves comparing the genomes of different species. What insights can be gained from comparative genomic studies?
Determining the precise number of genes present in each species.
Identifying the specific functions of all genes within a genome.
Understanding evolutionary relationships between species and how genomes have changed over time.
Predicting the susceptibility of different species to various diseases.
Explanation: The sources mention that comparative genomics allows researchers to compare the genomes of different species, shedding light on evolutionary relationships and the processes that have shaped genomes over evolutionary history.