Podcast
Questions and Answers
What is the primary role of epigenetic modifications in gene expression?
What is the primary role of epigenetic modifications in gene expression?
- They eliminate the need for transcription factors.
- They enhance the synthesis of DNA.
- They change the DNA sequence directly.
- They alter chromatin structure to control gene accessibility. (correct)
Which of the following is NOT an example of an epigenetic modification?
Which of the following is NOT an example of an epigenetic modification?
- Acetylation of lysine residues
- Substitution of thymine for adenine in DNA (correct)
- Methylation of cytosine bases
- Methylation of lysine and arginine residues
How can environmental stimuli influence epigenetic marks?
How can environmental stimuli influence epigenetic marks?
- By promoting RNA transcription only.
- By causing changes in histone modifications and DNA methylation. (correct)
- By deleting portions of the DNA.
- By adding new genes to the DNA sequence.
Which of the following statements about epigenetics is true?
Which of the following statements about epigenetics is true?
What is a potential consequence of changes in chromatin structure due to epigenetic modifications?
What is a potential consequence of changes in chromatin structure due to epigenetic modifications?
What is the primary role of nucleotides in DNA polymers?
What is the primary role of nucleotides in DNA polymers?
Which statement accurately describes the structure of RNA compared to DNA?
Which statement accurately describes the structure of RNA compared to DNA?
What is a key feature of the process of DNA replication?
What is a key feature of the process of DNA replication?
Which technique is primarily used for amplifying DNA segments?
Which technique is primarily used for amplifying DNA segments?
Why is base-pairing important in nucleic acids?
Why is base-pairing important in nucleic acids?
Which nucleotide base is only present in RNA?
Which nucleotide base is only present in RNA?
What type of sugar is found in DNA nucleotides?
What type of sugar is found in DNA nucleotides?
Which of the following base pairs is correctly matched?
Which of the following base pairs is correctly matched?
Which component of a nucleotide acts as a bridge between adjacent sugar molecules?
Which component of a nucleotide acts as a bridge between adjacent sugar molecules?
How are nucleotides linked to form DNA?
How are nucleotides linked to form DNA?
What type of bond holds the nitrogenous bases together in a DNA double helix?
What type of bond holds the nitrogenous bases together in a DNA double helix?
What is the structure of ATP classified as?
What is the structure of ATP classified as?
In which process does A-U pairing occur?
In which process does A-U pairing occur?
What characterizes the base pairing in DNA?
What characterizes the base pairing in DNA?
Which of the following correctly describes a purine?
Which of the following correctly describes a purine?
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Study Notes
DNA Replication
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The fundamental building block of DNA and RNA is called a nucleotide.
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Nucleotides are composed of three components:
- A nitrogenous base: Pyrimidine (C, T, U - T in DNA, U in RNA) or Purine (G, A)
- A pentose sugar: deoxyribose in DNA, ribose in RNA
- A phosphate group: acts as a bridge between adjacent ribose/deoxyribose groups
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ATP is a nucleotide triphosphate and a fundamental energy source in cells.
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Nucleotides link together via phosphodiester bonds to form single-stranded RNA or double-stranded DNA.
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The DNA double helix is held together by hydrogen bonds between complementary bases.
- C (pyrimidine) always pairs with G (purine).
- T (pyrimidine) always pairs with A (purine).
- A-U bonding occurs during gene transcription.
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G-C base pairing is stronger than A-T base pairing.
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New nucleotides are always added to the 3’-end of a polynucleotide chain.
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DNA replication takes place during the S phase of interphase in the cell cycle.
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DNA replication is critical for cell growth, repair, and reproduction.
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DNA replication is semi-conservative, meaning each daughter DNA molecule consists of one old strand and one new strand.
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DNA replication takes place in a bi-directional manner, with two replication forks moving in opposite directions.
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Each strand at the replication fork is replicated by a different process to handle the directionality:
- Leading strand: Oriented 3’ to 5’ and replicated continuously.
- Lagging strand: Oriented 5’ to 3’ and replicated discontinuously.
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DNA helicase unwinds the double-stranded DNA to form a replication fork.
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RNA primers are short segments of RNA that bind to the 3’ end of the strand and serve as a starting point for DNA synthesis.
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DNA replication does not occur just from one site per chromosome; multiple origins of replication exist along each chromosome, speeding up the process.
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New chromosomes are formed from old chromosomes, which separate as sister chromatids after replication.
Epigenetic Inheritance
- Epigenetics refers to heritable changes in gene expression caused by factors other than changes in the DNA base sequence.
- Epigenetic modifications can alter chromatin structure by affecting the accessibility of transcription factors to activate or deactivate genes.
- Histone modifications, such as acetylation and methylation, and DNA modifications, such as methylation of cytosine, contribute to epigenetic inheritance.
- Environmental stimuli can alter epigenetic marks, providing a mechanism for environmental factors to be imprinted genetically.
- Histone inheritance is a complex process. Some histones remain intact during replication, while others are replaced.
- The process of histone replication ensures that epigenetic modifications are passed on to daughter cells.
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