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What is the primary function of histones in DNA packaging?
Histone acetylation leads to DNA remaining compact and restricting gene expression.
False
What role do acetyl groups play in DNA packaging?
They allow DNA to open up for gene expression.
The first level of DNA packaging is called a ______.
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Match the following levels of DNA packaging with their descriptions:
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What is the primary direction of synthesis for the leading strand during DNA replication?
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Okazaki fragments are longer than 2000 nucleotides in length.
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What is the function of RNA primers in DNA replication?
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The ends of chromosomes, known as ______, are protected by repetitive DNA sequences.
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Match each component of DNA replication with its function:
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What is a key difference between RNA and DNA?
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RNA does not contain ribose sugar.
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What carries genetic information from DNA to the ribosome?
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The enzyme that unwinds the DNA double helix during replication is called ______.
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Which of the following enzymes synthesizes the leading strand in DNA replication?
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Match the type of RNA with its function:
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The lagging strand is synthesized continuously during DNA replication.
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Name the two replication forks formed during DNA replication.
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Study Notes
DNA Packaging Overview
- DNA packaging condenses long DNA (approximately 2 meters in animal cells) into the small nucleus (5-10 microns in diameter).
Levels of DNA Packaging
- Histones: Proteins that organize DNA into nucleosomes, the fundamental unit of DNA packaging.
- Nucleosomes: The structure formed by histones with DNA wrapped around them, acting as the first level of organization.
- Solenoids: Higher-order structures created by the coiling of nucleosomes, further compaction of DNA.
Control Mechanisms
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Acetylation of Histones: A key regulatory mechanism allowing the cell to control DNA condensation.
- Addition of acetyl groups to lysine residues in the histone tails neutralizes their positive charge.
- Neutralization facilitates DNA unwinding, making it more accessible for transcription factors and gene expression.
Effects of Histone Acetylation
- With Acetyl Groups: DNA becomes relaxed and accessible, promoting gene expression.
- Without Acetyl Groups: DNA remains tightly packed, limiting gene expression.
RNA Structure
- RNA stands for ribonucleic acid and is integral to gene expression.
- Composed of ribose sugar, which has a hydroxyl group at the 2' carbon, while DNA contains a hydrogen atom.
- Contains uracil (U) instead of thymine (T) present in DNA.
- Has a phosphodiester backbone giving it a net negative charge.
RNA Pairing
- Adenine (A) pairs with uracil (U) in RNA, while it pairs with thymine (T) in DNA.
- Guanine (G) pairs with cytosine (C) in both RNA and DNA.
Types of RNA
- mRNA (messenger RNA): Carries genetic information from DNA to the ribosome for protein synthesis.
- tRNA (transfer RNA): Delivers amino acids to the ribosome during protein synthesis.
- rRNA (ribosomal RNA): A major component of ribosomes, facilitating protein synthesis.
DNA Replication
- Occurs in three stages: initiation, elongation, and termination.
Initiation
- Involves specific sequences on DNA known as the origin of replication.
- ORC (Origin of Replication Complex) recruits enzymes for replication.
- MCM (Mini-Chromosome Maintenance) unwinds DNA.
Elongation
- Helicase unwinds the DNA double helix.
- DNA polymerase synthesizes new DNA strands.
- Leading strand is synthesized continuously; lagging strand is synthesized in short segments.
Termination
- The replication fork is the area where DNA is replicated, with two forks moving in opposite directions.
Enzymes Involved in DNA Replication
- Helicase: Unwinds the DNA double helix.
- DNA polymerase epsilon: Synthesizes the leading strand.
- DNA polymerase alpha and delta: Synthesize the lagging strand.
Topoisomerase and Torsional Stress
- Topoisomerase alleviates torsional stress during replication by cutting one DNA strand, allowing unwinding.
Leading and Lagging Strands
- Leading strand synthesized continuously in the 5' to 3' direction.
- Lagging strand synthesized in short, discontinuous fragments (Okazaki fragments) in the 3' to 5' direction.
Okazaki Fragments
- Short segments of DNA on the lagging strand, typically 1000-2000 nucleotides long, synthesized in the 5' to 3' direction.
RNA Primers
- Short RNA molecules provide a 3' hydroxyl group for DNA polymerase extension, crucial for lagging strand synthesis.
DNA Polymerase
- Synthesizes new DNA strands by adding nucleotides to a template strand, requiring a 3' hydroxyl group.
PCNA (Proliferating Cell Nuclear Antigen)
- Functions as a sliding clamp that holds DNA polymerase onto the DNA template, enhancing its processivity.
Termination of Replication
- Occurs when the replication machinery reaches the chromosome's end, with the leading strand synthesized continuously and lagging fragments joined later.
Telomeres and Telomerase
- Telomeres are protective repetitive DNA sequences at chromosome ends.
- Telomerase extends the lagging strand of the telomere, allowing proper replication.
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Description
This quiz explores the process of DNA packaging, focusing on how DNA is condensed into the nucleus of a cell. Learn about the different levels of DNA packaging, including histones and nucleosomes, and their significance in cellular biology.
