Molecular Cell Biology - Problem Drill 06: Genes and Chromosomes

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1 Molecular Cell Biology - Problem Drill 06: Genes and Chromosomes Question No. 1 of Which of the following statements about genes is correct? Question #1 (A) Genes carry the information for protein and DNA synthesis. (B) Genes carry the information for protein and RNA synthesis. (C) A gene is a region of RNA that controls a hereditary characteristic. (D) Genes are arranged on chromosomes in a circular fashion. Genes carry the information for protein and RNA synthesis. B. Correct! Genes carry the information for protein and RNA synthesis. A gene is a region of DNA that controls a hereditary characteristic. Genes are arranged on chromosomes linearly. A gene is a region of DNA that controls a hereditary characteristic. It carries the information for protein and RNA synthesis. Genes are arranged on chromosomes linearly.

2 Question No. 2 of Which of the following statements about eukaryotic chromosomes is correct? Question #2 (A) Eukaryotic cells are haploid they have a single copy of genes. (B) Eukaryotic cells are diploid they have two non-paired homologous chromosomes. (C) Eukaryotic chromosomes have linear DNA molecules. (D) Eukaryotic chromosomes have circular DNA molecules. Eukaryotic cells are diploid they have two paired homologous chromosomes. Eukaryotic cells are diploid they have two paired homologous chromosomes. C. Correct! Eukaryotic chromosomes have linear DNA molecules. Eukaryotic chromosomes have linear DNA molecules. Chromosomes are classified into eukaryotic chromosomes and prokaryotic chromosomes. Prokaryotic chromosomes are usually circular, one cell contains one single chromosome, and the DNA is naked, which means there is no histone proteins are complexed with DNA. The prokaryotic cells are normally haploid, meaning they contain a single copy of each gene. Eukaryotic chromosomes have linear DNA molecules, the cells contain multiple chromosomes, and DNA forms highly organized structure and wrapped with histones. The eukaryotic cells are diploid they have two paired homologous chromosomes.

3 Question No. 3 of Which of the following statements about viral chromosomes is correct? Question #3 (A) The viral genome has DNA packaged into its chromosomes. (B) The DNA on viral chromosomes can be single stranded or double stranded. (C) The DNA or RNA on viral chromosomes can be single stranded or double stranded. (D) The DNA or RNA on viral chromosomes is single stranded. The viral genome can be either DNA or RNA. The DNA or RNA on viral chromosomes can be single stranded or double stranded. C. Correct! The DNA or RNA on viral chromosomes can be single stranded or double stranded. The DNA or RNA on viral chromosomes can be single stranded or double stranded. Viruses have various chromosomes. The viral genome can be either DNA or RNA, therefore they are divided into DNA virus or RNA virus. These DNA or RNA can be single stranded or double stranded. One viral genome can contain single molecule or multiple molecules; the DNA or RNA can be circular or linear. In total, viral genome are the most diversified in terms of composition.

4 Question No. 4 of Which of the following statements about the bacteria phage chromosome is correct? Question #4 (A) It has linear double stranded DNA, the ends of the DNA is sticky, meaning that the two ends can complement each other and fold back to form a circular molecule. (B) It has linear single stranded DNA, the ends of the DNA is sticky, meaning that the two ends can complement each other and fold back to form a circular molecule. (C) The whole genome can be integrated into its host SV40 virus for replication. (D) Select portions of the genome can be integrated into its host E. coli chromosome for replication. A. Correct! It has linear double stranded DNA, the ends of the DNA is sticky, meaning that the two ends can complement each other and fold back to form a circular molecule. It has linear double stranded DNA, the ends of the DNA is sticky, meaning that the two ends can complement each other and fold back to form a circular molecule. The whole genome can be integrated into its host E. coli chromosome for replication. The whole genome can be integrated into its host E. coli chromosome for replication. Bacterial lambda phage is one example of viral genome. It has a linear double strand DNA, the ends of the DNA is sticky, meaning that the two ends can complement each other and fold back to form a circular molecule. The whole genome can be integrated into its host E. coli chromosome for replication.

5 Question No. 5 of Which of the following statements about mitochondrial DNA is correct? Question #5 (A) The mitochondria are the only organelle in a eukaryotic cell to have its own genome. (B) The chloroplast is the only organelle in a eukaryotic cell to have its own genome. (C) The mitochondrial genome encodes some of the mitochondrial proteins, and the genomes vary from about 10 kb to nearly 200 kb in size, depending on different organisms. (D) The mitochondrial genome encodes all of the mitochondrial proteins, and the genomes vary from about 10 kb to nearly 200 kb in size, depending on different organisms. The mitochondria and the chloroplast are the only organelles in eukaryotic cells to have their own genome. The mitochondria and the chloroplast are the only organelles in eukaryotic cells to have their own genome. C. Correct! The mitochondrial genome encodes some of the mitochondrial proteins, and the genomes vary from about 10 kb to nearly 200 kb in size, depending on different organisms. The mitochondrial genome encodes some of the mitochondrial proteins, and the genomes vary from about 10 kb to nearly 200 kb in size, depending on different organisms. Two organelles of eukaryotic cells have their own genome, these are mitochondrial and chloroplast. Mitochondrial genome encodes some of the mitochondrial proteins, and the genomes vary from about 10 kb to nearly 200 kb in size, depending on different organisms. The number of circular DNA also varies from one copy to multiple copies. The figure shown here is a human mitochondrial genome.

6 Question No. 6 of Which of the following statements about the karyotype is correct? Question #6 (A) It is similar for all species and can be used for genetic diagnosis. (B) It is similar for most species and can be used for genetic diagnosis. (C) The karyotype means a complete set of all metaphase chromosomes in a cell. (D) The karyotype means a group of 10 metaphase chromosomes in a cell. It is species-specific and can be used for genetic diagnosis. It is species-specific and can be used for genetic diagnosis. C. Correct! The karyotype means a complete set of all metaphase chromosomes in a cell. The karyotype means a complete set of all metaphase chromosomes in a cell. The karyotype means a complete set of all metaphase chromosomes in a cell. It is species-specific and can be used for genetic diagnosis (change in number and deletion/fusion of arms).

7 Question No. 7 of Which of the following statements about DNA packaging into chromosomes is correct? Question #7 (A) The DNA double helix forms a nucleosome and then: chromatin fibers, and finally becomes a chromosome body. (B) The DNA double helix forms a nucleosome and then: chromatin fibers, extended chromatin, condensed chromatin and finally becomes a chromosome body. (C) A replicated metaphase chromosome measures about 1400nm and is smaller than a chromatin fiber. (D) A replicated metaphase chromosome measures about 1400nm and is smaller than a nucleosome. The DNA double helix forms a nucleosome and then: chromatin fibers, extended chromatin, condensed chromatin and finally becomes a chromosome body. B. Correct! The DNA double helix forms a nucleosome and then: chromatin fibers, extended chromatin, condensed chromatin and finally becomes a chromosome body. A replicated metaphase chromosome measures about 1400nm and is the largest form of packaged DNA. A replicated metaphase chromosome measures about 1400nm and is the largest form of packaged DNA. In eukaryotic cells, double helix DNA is highly packed, the packing ratio can reach about 7000 fold in humans. DNA fiber (width 2nm) is first packed into nucleosome, nucleosome then coil up to form chromatin fibers which is about 30 nm, the chromatin fiber further form 300nm coils and loops which upon condensation, becomes 700nm chromosome body. A replicated metaphase chromosome measures about 1400nm.

8 Question No. 8 of Which of the following statements about a nucleosome is correct? Question #8 (A) A DNA fiber (width 2nm) is first packed into nucleosome, nucleosomes then coil up to form chromatin fibers which is about 30 nm. (B) A DNA fiber (width 2nm) is first packed into condensed chromatin then coiled up to form a nucleosome. (C) The DNA between two nucleosomes is called an exon and it is associated with histone H1 which is called linker histone. (D) The DNA between two nucleosomes is called linker DNA and it is associated with RNA. A. Correct! A DNA fiber (width 2nm) is first packed into nucleosome, nucleosomes then coil up to form chromatin fibers which is about 30 nm. A DNA fiber (width 2nm) is first packed into nucleosome, nucleosomes then coil up to form chromatin fibers which is about 30 nm. The DNA between two nucleosomes is called linker DNA and it is associated with histone H1 which is called linker histone. The DNA between two nucleosomes is called linker DNA and it is associated with histone H1 which is called linker histone. The first step of packing is double helix DNA wraps two turns around a core histone structure which is made up of 2 subunits of each histone H2A, H2B, H3 and H4. Such a bead shape structure is called a nucleosome. The DNA between two nucleosomes is called linker DNA and it is associated with histone H1 which is called linker histone. In general on a nucleosome the wrapped DNA is 140bp, if the linker is accounted, then it is 200bp.

9 Question No. 9 of Which of the following statements about euchromatin is correct? Question #9 (A) Euchromatin is lightly packed and available for transcription. (B) Euchromatin is tightly packed and available for transcription. (C) Euchromatin stains heavily and is available for transcription. (D) Euchromatin stains lightly and is not available for transcription. A. Correct! Euchromatin is lightly packed and available for transcription. Euchromatin is lightly packed and available for transcription. Euchromatin stains lightly and is available for transcription. Euchromatin stains lightly and is available for transcription. When a cell is at interphase (not in DNA replication or mitosis), the chromatin is relatively loose and available for transcription. When an interphase nucleus is stained with a dye, regions of heavily stained and lightly stained can be visualized. The lightly stained region is called euchromatin, they are available for transcription. The heavily stained region is called heterochromatin. They are more tightly packed and therefore less available for transcription. The figure shows a human cell with heterochromatin and euchromatin regions in the nucleus.

10 Question No. 10 of Which of the following statements about telomeres is correct? Question #10 (A) Telomeres are in the middle of each chromosome and consist of repeats of a simple-sequence and play a critical role in replication of this region on DNA molecules. (B) Two telomeres are at the ends of each chromosome and consist of repeats of a simple-sequence and play a critical role in replication of the ends of linear DNA molecules. (C) Ensure precise combination of the duplicated chromatids. (D) Play no role in the segregation of the duplicated chromatids. Two telomeres are at the ends of each chromosome and consist of repeats of a simple-sequence and play a critical role in replication of the ends of linear DNA molecules. B. Correct! Two telomeres are at the ends of each chromosome and consist of repeats of a simple-sequence and play a critical role in replication of the ends of linear DNA molecules. Ensure precise segregation of the duplicated chromatids. Ensure precise segregation of the duplicated chromatids. A chromosome contains two telomeres at the ends of the chromosome, and a centromere in the middle. Centromere consists of specific DNA sequences and ensures precise segregation of the duplicated chromatids. Telomere consisting of repeats of a simple-sequence and play a critical role in replication of the ends of linear DNA molecules. Genes are arranged on the chromosome in a linear pattern. This shows amplified region of a chromosome, many genes are found. For each gene, there is a regulatory element, some exons which are the coding sequence and some introns which intersperse the exons and are non-coding sequence.