90 Questions
What is the length of the human mitochondrial genome?
16,569 base pairs
What percentage of all the RNAs and proteins needed by the mitochondrion does the human mitochondrial genome encode?
5%
What is the approximate length of circular DNA molecules in chloroplasts?
120,000 bp
Where are the chromosomes localized and replicated within the eukaryotic cell?
Nucleus
What is the function of nuclear pores?
Provide direct contact between the cytosol and the nucleoplasm
What is the size limit for small particles to freely move through nuclear pores via simple diffusion?
10 nm in diameter
What enables the active transport of large proteins across the nuclear membrane?
Nuclear localization signals (NLS)
What is the nuclear matrix?
An insoluble fibrous network that helps maintain the shape of the nucleus
Where are ribosomal subunits assembled within the nucleus?
Nucleolus
What do fibrils in the nucleolus contain?
DNA being transcribed into ribosomal RNA (rRNA)
Which protein stabilizes DNA loops 50,000–100,000 bp in length in chromatin packing?
Cohesin protein
What is the function of histone deacetylase (HDAC) in chromatin packing?
Removal of acetyl groups from histone side chains
How are cells able to regulate the portions of chromatin that are active or inactive?
Through altering histones and histone code
What is the structure in which the 30-nm fiber seems to be packed together?
An irregular, three-dimensional zigzag structure
What can serve as a signal for activation or repression of transcription, depending on the lysine involved?
Methylation of lysine via histone methyltransferase
What is the opposite function of histone acetyltransferase (HAT)?
Catalyzed by histone deacetylase (HDAC)
What is the length of the DNA loops stabilized by cohesin protein?
50,000–100,000 bp
What can alter chromatin packing and regulate the portions of chromatin that are active or inactive?
Changes in histones and chromatin remodeling proteins
What can create a histone code?
Various combinations of tags like methyl, acetyl, phosphate, or other groups
What is the function of histone acetyltransferases (HATs) in chromatin packing?
Acetylation of histone side chains
What is the function of centromeres during cell division?
Maintain sister chromatid cohesion
What is the difference between facultative heterochromatin and constitutive heterochromatin?
Facultative heterochromatin can convert to euchromatin, while constitutive heterochromatin remains permanently compacted
What is the composition of telomeres?
Highly repetitive DNA sequences
What are euchromatin and heterochromatin based on their packing?
Euchromatin is more loosely packed, and heterochromatin is highly compacted
What happens to all chromatin in preparation for cell division?
It becomes highly compacted
What is the role of repeated DNA sequences in eukaryotic chromosomes?
Constitute a large portion of the genome
What is the function of tandemly repeated DNA in a typical mammalian genome?
Accounts for 10–15% of the genome
What is the role of interspersed repeated DNAs in mammalian genomes?
Account for 25–50% of the genome
What did Roy Britten and David Kohne discover about eukaryotic chromosomes in the 1960s?
They contain large amounts of repeated DNA sequences
What is the purpose of Giemsa staining in identifying chromosomes?
Reveals unique banding patterns on chromosomes
What can alter chromatin packing and regulate the portions of chromatin that are active or inactive?
Histones and chromatin remodeling proteins
What is the function of cohesin protein in chromatin packing?
Stabilizing DNA loops 50,000–100,000 bp in length
Which tagging reaction can serve as a signal for activation or repression of transcription?
Methylation of lysine via histone methyltransferase
What is the opposite function of histone acetyltransferase (HAT) in chromatin packing?
Histone deacetylase (HDAC)
What is the structure in which the 30-nm fiber seems to be packed together?
Irregular, three-dimensional zigzag structure
What is the length of DNA loops stabilized by cohesin protein in chromatin packing?
50,000–100,000 bp
What are the protruding tails of histones tagged by to create a histone code?
Methyl, acetyl, phosphate, or other groups
Where are the DNA loops stabilized by cohesin protein spatially arranged through attachment to?
Nonhistone proteins forming a chromosomal scaffold
What can serve as a signal for activation or repression of transcription, depending on the lysine involved?
Histone methylation
What enables cells to tightly regulate the portions of chromatin that are active or inactive?
Altering histones and chromatin remodeling proteins
What is the approximate length of the human mitochondrial genome?
16,569 base pairs
What is the approximate length of circular DNA molecules in chloroplasts?
120,000 base pairs
What is the function of nuclear pores?
Provide direct contact between the cytosol and the nucleoplasm
What is the size limit for small particles to freely move through nuclear pores via simple diffusion?
Less than 10 nm in diameter
What enables the active transport of large proteins across the nuclear membrane?
Nuclear localization signals (NLS)
What is the nuclear matrix?
An insoluble fibrous network that helps maintain the shape of the nucleus
Where are ribosomal subunits assembled within the nucleus?
Nucleolus
What do fibrils in the nucleolus contain?
DNA being transcribed into ribosomal RNA (rRNA)
What is the function of histone acetyltransferases (HATs) in chromatin packing?
Add acetyl groups to histones, leading to chromatin relaxation
What is the composition of telomeres?
Repetitive DNA sequences
What is the composition of telomeres?
Highly repetitive DNA sequences
What is the function of centromeres during cell division?
Maintain sister chromatid cohesion
What is the role of interspersed repeated DNAs in mammalian genomes?
Account for 25–50% of mammalian genomes and can move around the genome
What is the difference between facultative heterochromatin and constitutive heterochromatin?
Facultative heterochromatin can convert to euchromatin and vice versa, while constitutive heterochromatin remains permanently compacted
What is the size limit for small particles to freely move through nuclear pores via simple diffusion?
9 nm
What is the function of Giemsa staining in identifying chromosomes?
Create unique banding patterns for identifying chromosomes
What is the function of tandemly repeated DNA in a typical mammalian genome?
Account for 10–15% of a typical mammalian genome
What is the role of repeated DNA sequences in eukaryotic chromosomes?
Constitute a large portion of the genome and can move around the genome
What is the function of histone deacetylase (HDAC) in chromatin packing?
Remove acetyl groups from histones, leading to chromatin condensation
What is the function of nuclear pores?
Regulate the movement of molecules into and out of the nucleus
What is the approximate percentage of mammalian genomes accounted for by interspersed repeated DNAs, including transposable elements like LINEs and SINEs?
20-25%
What is the composition of telomeres, which are found at chromosome ends?
Highly repetitive DNA sequences
What is the function of Giemsa staining in identifying chromosomes?
Revealing unique banding patterns
What is the approximate percentage of a typical mammalian genome accounted for by tandemly repeated DNA?
5-10%
What is the role of constitutive heterochromatin in eukaryotic chromosomes?
Permanently compacted, serving structural functions
What are the two types of chromatin, based on their packing?
Euchromatin and heterochromatin
What is the function of centromeres on chromosomes?
Maintain sister chromatid cohesion during mitosis and meiosis
What is the approximate percentage of mammalian genomes accounted for by interspersed repeated DNAs, including transposable elements like LINEs and SINEs?
20-25%
What is the composition of telomeres, which are found at chromosome ends?
Highly repetitive DNA sequences
What is the function of Giemsa staining in identifying chromosomes?
Revealing unique banding patterns
What is the approximate length of the human mitochondrial genome?
16,569 base pairs
What is the approximate length of circular DNA molecules in chloroplasts?
120,000 base pairs
What is the size limit for small particles to freely move through nuclear pores via simple diffusion?
10 nm in diameter
What enables the active transport of large proteins across the nuclear membrane?
Nuclear localization signals (NLS)
What is the nuclear matrix (nucleoskeleton)?
An insoluble fibrous network that helps maintain the shape of the nucleus
Where are ribosomal subunits assembled within the nucleus?
Nucleolus
What do fibrils in the nucleolus contain?
DNA that is being transcribed into ribosomal RNA (rRNA)
What is the function of the nuclear lamina?
To maintain the shape of the nucleus
What is the function of the nuclear envelope?
To contain the nucleus with an inner and an outer membrane
What is the function of the nucleolus?
To assemble ribosomal subunits
What is the function of histone acetyltransferases (HATs) in chromatin packing?
Adding acetyl groups to histone tails, leading to a looser chromatin structure
What is the opposite function of histone deacetylase (HDAC) in chromatin packing?
Removing acetyl groups from histone tails, leading to a tighter chromatin structure
What is the approximate length of DNA loops stabilized by cohesin protein?
50,000–100,000 bp
What can serve as a signal for activation or repression of transcription, depending on the lysine involved?
Methylation of histone lysine
Where are the 30-nm fibers packed together in an irregular, three-dimensional zigzag structure?
Chromosomal scaffold
What enables cells to tightly regulate the portions of chromatin that are active or inactive?
Alteration of histone composition
What is the role of cohesin protein in chromatin packing?
Stabilizing DNA loops of specific lengths
What do histone tails have that can be tagged by the addition of methyl, acetyl, phosphate, or other groups?
Protruding tails
What is the function of nuclear pores?
Enabling the active transport of large proteins across the nuclear membrane
What is the function of the 30-nm fiber structure in chromatin packing?
Facilitating the attachment of nonhistone proteins
Study Notes
Chromosomal DNA Structure and Composition
- Euchromatin and heterochromatin are two types of chromatin, with heterochromatin being highly compacted and euchromatin being more loosely packed.
- Active cells have euchromatic chromatin, but all chromatin becomes highly compacted in preparation for cell division.
- Each chromosome is composed of two identical chromatids after replication.
- Facultative heterochromatin can convert to euchromatin and vice versa, while constitutive heterochromatin remains permanently compacted, serving structural functions.
- Centromeres appear as constrictions on chromosomes and maintain sister chromatid cohesion during mitosis and meiosis.
- Centromeres are characterized by highly repetitive DNA sequences (CEN sequences) and vary across eukaryotic organisms.
- Telomeres, found at chromosome ends, contain highly repetitive DNA sequences and protect chromosome ends from degradation during DNA replication.
- Chromosomes can be identified by unique banding patterns and staining techniques, such as Giemsa staining.
- Eukaryotic chromosomes contain large amounts of repeated DNA sequences, as discovered by Roy Britten and David Kohne in the 1960s.
- Calf DNA consists of two classes of sequences that renature at different rates, with about 40% renaturing more rapidly than bacterial DNA.
- Repeated DNA sequences include tandemly repeated DNA, which accounts for 10–15% of a typical mammalian genome.
- Interspersed repeated DNAs, including transposable elements like LINEs and SINEs, account for 25–50% of mammalian genomes and can move around the genome.
Chromosomal DNA Structure and Composition
- Euchromatin and heterochromatin are two types of chromatin, with heterochromatin being highly compacted and euchromatin being more loosely packed.
- Active cells have euchromatic chromatin, but all chromatin becomes highly compacted in preparation for cell division.
- Each chromosome is composed of two identical chromatids after replication.
- Facultative heterochromatin can convert to euchromatin and vice versa, while constitutive heterochromatin remains permanently compacted, serving structural functions.
- Centromeres appear as constrictions on chromosomes and maintain sister chromatid cohesion during mitosis and meiosis.
- Centromeres are characterized by highly repetitive DNA sequences (CEN sequences) and vary across eukaryotic organisms.
- Telomeres, found at chromosome ends, contain highly repetitive DNA sequences and protect chromosome ends from degradation during DNA replication.
- Chromosomes can be identified by unique banding patterns and staining techniques, such as Giemsa staining.
- Eukaryotic chromosomes contain large amounts of repeated DNA sequences, as discovered by Roy Britten and David Kohne in the 1960s.
- Calf DNA consists of two classes of sequences that renature at different rates, with about 40% renaturing more rapidly than bacterial DNA.
- Repeated DNA sequences include tandemly repeated DNA, which accounts for 10–15% of a typical mammalian genome.
- Interspersed repeated DNAs, including transposable elements like LINEs and SINEs, account for 25–50% of mammalian genomes and can move around the genome.
Chromosomal DNA Structure and Composition
- Euchromatin and heterochromatin are two types of chromatin, with heterochromatin being highly compacted and euchromatin being more loosely packed.
- Active cells have euchromatic chromatin, but all chromatin becomes highly compacted in preparation for cell division.
- Each chromosome is composed of two identical chromatids after replication.
- Facultative heterochromatin can convert to euchromatin and vice versa, while constitutive heterochromatin remains permanently compacted, serving structural functions.
- Centromeres appear as constrictions on chromosomes and maintain sister chromatid cohesion during mitosis and meiosis.
- Centromeres are characterized by highly repetitive DNA sequences (CEN sequences) and vary across eukaryotic organisms.
- Telomeres, found at chromosome ends, contain highly repetitive DNA sequences and protect chromosome ends from degradation during DNA replication.
- Chromosomes can be identified by unique banding patterns and staining techniques, such as Giemsa staining.
- Eukaryotic chromosomes contain large amounts of repeated DNA sequences, as discovered by Roy Britten and David Kohne in the 1960s.
- Calf DNA consists of two classes of sequences that renature at different rates, with about 40% renaturing more rapidly than bacterial DNA.
- Repeated DNA sequences include tandemly repeated DNA, which accounts for 10–15% of a typical mammalian genome.
- Interspersed repeated DNAs, including transposable elements like LINEs and SINEs, account for 25–50% of mammalian genomes and can move around the genome.
Test your knowledge of chromosomal DNA structure and composition with this quiz. Explore the differences between euchromatin and heterochromatin, the role of centromeres and telomeres, and the presence of repeated DNA sequences on eukaryotic chromosomes.
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