Lecture 5: Chromosome Structure

Week 1

What is the primary goal of DNA replication?

A) To copy instructions for protein synthesis
B) To copy a cell’s genome for partitioning to daughter cells
C) To produce mRNA molecules
D) To build proteins from amino acids

B) To copy a cell’s genome for partitioning to daughter cells

During replication, DNA polymerase synthesizes the new strand in the 5’→3’ direction by reading the template strand in which direction?

A) 5’→3’
B) 3’→5’
C) 5’→5’
D) 3’→3’

B) 3’→5’

Which of the following best explains why DNA is tightly compacted within the bacterial nucleoid?

A) To facilitate gene expression by opening chromatin
B) To fit the ~1.6 mm circular DNA into a 2 µm long cell
C) To protect DNA from damage by RNA polymerase
D) To promote DNA methylation

B) To fit the ~1.6 mm circular DNA into a 2 µm long cell

Which histone modification is associated with transcriptional repression and promotes chromatin condensation?

A) Acetylation of lysine residues
B) Methylation of histone tails
C) Phosphorylation of serine residues
D) Ubiquitination of lysines

B) Methylation of histone tails

What is the role of “pioneer” transcription factors in chromatin remodeling?

A) To degrade nucleosomes
B) To bind enhancers and recruit chromatin-modifying enzymes that open chromatin
C) To methylate DNA sequences at promoters
D) To initiate replication at origins

B) To bind enhancers and recruit chromatin-modifying enzymes that open chromatin

Why is telomerase necessary during DNA replication in eukaryotes?

A) To replicate centromeric DNA sequences
B) To add DNA methylation marks at telomeres
C) To extend the 3’ ends of linear chromosomes and prevent telomere shortening
D) To remove histones from chromatin

C) To extend the 3’ ends of linear chromosomes and prevent telomere shortening

The nucleosome core particle consists of how many histone proteins and how are they arranged?

A) 10 histones arranged as two pentamers
B) 8 histones arranged as a histone octamer: 2 each of H2A, H2B, H3, and H4
C) 5 histones including H1
D) 4 histones arranged as tetramers

B) 8 histones arranged as a histone octamer: 2 each of H2A, H2B, H3, and H4

What is the role of histones in chromatin?

A) To degrade DNA
B) To tightly bind and compact DNA
C) To transcribe DNA
D) To replicate DNA

B) To tightly bind and compact DNA

Which histone is NOT part of the nucleosome core?

A) H2A
B) H2B
C) H3
D) H1

D) H1

What is the approximate length of DNA wrapped around a nucleosome?

A) 50 bp
B) 146 bp
C) 1000 bp
D) 10,000 bp

B) 146 bp

Euchromatin is characterized by:

A) Tightly compacted DNA
B) Active gene expression and loose compaction
C) Lack of genes
D) Constitutive heterochromatin

B) Active gene expression and loose compaction

Heterochromatin is generally:

A) Transcriptionally active
B) Found only in bacteria
C) Tightly compacted and mostly transcriptionally inactive
D) Found only in euchromatin

Heterochromatin is generally:

A) Transcriptionally active
B) Found only in bacteria
C) Tightly compacted and mostly transcriptionally inactive
D) Found only in euchromatin

What is the primary difference between facultative and constitutive heterochromatin?

A) Constitutive heterochromatin contains mostly actively transcribed genes
B) Constitutive heterochromatin is always compacted; facultative can be decondensed depending on cell type or developmental stage
C) Facultative heterochromatin is found only at centromeres
D) Facultative heterochromatin contains repetitive sequences only

B) Constitutive heterochromatin is always compacted; facultative can be decondensed depending on cell type or developmental stage

How do histone acetylation and methylation typically affect the charge of histone tails and their interaction with DNA?

A) Both acetylation and methylation increase positive charge, tightening DNA binding
B) Acetylation reduces positive charge, loosening DNA binding; methylation generally maintains or enhances compaction
C) Both acetylation and methylation neutralize DNA charge
D) Acetylation increases positive charge, methylation decreases it

B) Acetylation reduces positive charge, loosening DNA binding; methylation generally maintains or enhances compaction

Which sequence features characterize telomeres in eukaryotic chromosomes?

A) Unique protein-coding regions at chromosome ends
B) Repetitive sequences found only in centromeres
C) Tandem repeats of short G-rich sequences (e.g., TTAGGG) that protect chromosome ends
D) Non-repetitive sequences enriched with histone genes

B) Acetylation reduces positive charge, loosening DNA binding; methylation generally maintains or enhances compaction

During transcription, RNA polymerase reads the template DNA strand in the 3’→5’ direction. Which strand serves as the coding strand?

A) The template strand
B) The non-template (coding) strand, which is complementary to the template strand
C) The strand complementary to mRNA
D) Both strands serve equally as templates

B) The non-template (coding) strand, which is complementary to the template strand

What distinguishes the p and q arms of a chromosome?

A) p arm is the longer arm; q arm is the shorter
B) p arm is the short arm (petite); q arm is the long arm
C) Both arms are the same length but differ in sequence
D) p arm contains only heterochromatin; q arm contains only euchromatin

B) p arm is the short arm (petite); q arm is the long arm

Which of the following statements about centromeres is FALSE?

A) Centromeres consist of repetitive DNA sequences
B) Centromeric chromatin is highly condensed heterochromatin
C) Centromeres are the sites where DNA replication initiates
D) Kinetochore proteins bind to centromeres during mitosis

C) Centromeres are the sites where DNA replication initiates

In eukaryotic cells, what percentage of the chromosome proteins are histones?

A) 10%
B) About 50%
C) 75%
D) 100%

B) About 50%

What is the functional significance of the positively charged amino acids lysine and arginine in histone proteins?

A) They repel the negatively charged DNA backbone
B) They facilitate tight binding to negatively charged DNA phosphate groups
C) They catalyze DNA replication
D) They are targets for DNA methylation

B) They facilitate tight binding to negatively charged DNA phosphate groups

Which of the following is TRUE about the poly-A tail in eukaryotic mRNAs?

A) It is encoded within the gene sequence
B) It is found in the 3’-UTR of the gene
C) It is not part of the gene but added post-transcriptionally
D) It is removed during mRNA splicing

C) It is not part of the gene but added post-transcriptionally

What is the main difference between chromatin compaction and condensation?

A) Compaction only occurs in prokaryotes
B) Condensation refers to the high-level packaging during mitosis, while compaction can be more general throughout the cell cycle
C) Condensation loosens chromatin
D) They are unrelated processes

B) Condensation refers to the high-level packaging during mitosis, while compaction can be more general throughout the cell cycle

Which enzyme charges tRNAs with their appropriate amino acids during translation?

A) DNA polymerase
B) RNA polymerase
C) Aminoacyl-tRNA synthetase
D) Ribosome

C) Aminoacyl-tRNA synthetase

Which of the following correctly matches the polymerase with its function?

A) DNA polymerase – synthesizes mRNA
B) RNA polymerase – synthesizes DNA
C) RNA polymerase – synthesizes RNA from a DNA template
D) Telomerase – synthesizes proteins

C) RNA polymerase – synthesizes RNA from a DNA template

What is the role of histone H1 in chromatin?

A) It forms the nucleosome core
B) It binds DNA at origins of replication
C) It helps package nucleosomes into higher-order chromatin structures
D) It is involved in DNA repair

C) It helps package nucleosomes into higher-order chromatin structures