Nucleic acids

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Questions and Answers

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?

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?

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?

It provides a mechanism for environmental effects to be genetically imprinted. Signup and view all the answers

What is a potential consequence of changes in chromatin structure due to epigenetic modifications?

Alteration in the activity of transcription factors and co-activators. Signup and view all the answers

What is the primary role of nucleotides in DNA polymers?

They serve as the building blocks of DNA. Signup and view all the answers

Which statement accurately describes the structure of RNA compared to DNA?

RNA is usually single-stranded, while DNA is double-stranded. Signup and view all the answers

What is a key feature of the process of DNA replication?

It requires a template strand for the synthesis of new DNA. Signup and view all the answers

Which technique is primarily used for amplifying DNA segments?

Polymerase chain reaction (PCR) Signup and view all the answers

Why is base-pairing important in nucleic acids?

It enables accurate replication and transcription of genetic information. Signup and view all the answers

Which nucleotide base is only present in RNA?

Uracil Signup and view all the answers

What type of sugar is found in DNA nucleotides?

Deoxyribose Signup and view all the answers

Which of the following base pairs is correctly matched?

C-G Signup and view all the answers

Which component of a nucleotide acts as a bridge between adjacent sugar molecules?

Phosphate group Signup and view all the answers

How are nucleotides linked to form DNA?

By phosphodiester bonds Signup and view all the answers

What type of bond holds the nitrogenous bases together in a DNA double helix?

Hydrogen bonds Signup and view all the answers

What is the structure of ATP classified as?

Nucleotide triphosphate Signup and view all the answers

In which process does A-U pairing occur?

Gene transcription Signup and view all the answers

What characterizes the base pairing in DNA?

C with G and T with A Signup and view all the answers

Which of the following correctly describes a purine?

A nitrogenous base with two rings Signup and view all the answers

Study Notes

DNA Replication

The fundamental building block of DNA and RNA is called a nucleotide.
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
ATP is a nucleotide triphosphate and a fundamental energy source in cells.
Nucleotides link together via phosphodiester bonds to form single-stranded RNA or double-stranded DNA.
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.
G-C base pairing is stronger than A-T base pairing.
New nucleotides are always added to the 3’-end of a polynucleotide chain.
DNA replication takes place during the S phase of interphase in the cell cycle.
DNA replication is critical for cell growth, repair, and reproduction.
DNA replication is semi-conservative, meaning each daughter DNA molecule consists of one old strand and one new strand.
DNA replication takes place in a bi-directional manner, with two replication forks moving in opposite directions.
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.
DNA helicase unwinds the double-stranded DNA to form a replication fork.
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.
DNA replication does not occur just from one site per chromosome; multiple origins of replication exist along each chromosome, speeding up the process.
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.