Biology: Structure of DNA and RNA

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Questions and Answers

What are the three components of a nucleotide?

Phosphate group, hexose sugar, nitrogen base

Phosphate group, pentose sugar, nitrogen base (correct)

Phosphate group, ribose, amino acid

Pentose sugar, nitrogen base, ribosomal RNA

Which nitrogenous base is found in RNA but not in DNA?

Uracil (correct)

Adenine

Guanine

Thymine

What type of bond links nucleotides together in a polynucleotide chain?

Hydrogen bond

Peptide bond

Phosphodiester bond (correct)

Ionic bond

Which of the following is NOT a use of ATP in cells?

Digestion of carbohydrates Signup and view all the answers

How do the two strands of DNA orient relative to each other?

Antiparallel Signup and view all the answers

What is the primary function of ATP in cells?

To act as a universal energy currency Signup and view all the answers

During the formation of a polynucleotide, how are water molecules involved?

They are formed through condensation reactions. Signup and view all the answers

What structure is primarily formed by the links of deoxyribose and phosphate in DNA?

Sugar-phosphate backbone Signup and view all the answers

What role do hydrogen bonds play in the structure of DNA?

They hold the two polynucleotide strands together. Signup and view all the answers

Why is the semi-conservative replication of DNA significant?

Each original strand serves as a template for a new strand. Signup and view all the answers

What is the consequence of the degeneracy of the genetic code?

Some amino acids can be represented by multiple codons. Signup and view all the answers

Which statement correctly describes the structure of DNA?

The sugar phosphate backbone is linked by phosphodiester bonds. Signup and view all the answers

What is the main function of DNA helicase during DNA replication?

To break hydrogen bonds between base pairs. Signup and view all the answers

How do complementary base pairs contribute to DNA's accuracy in replication?

They ensure few mistakes during replication. Signup and view all the answers

What is the result of coiling DNA into a double helix?

It prevents enzymes from altering the DNA structure. Signup and view all the answers

What is a codon?

A sequence of three bases coding for an amino acid. Signup and view all the answers

What does the term 'sense strand' refer to in DNA?

The strand that carries the code for protein synthesis. Signup and view all the answers

What occurs during the S phase of the cell cycle?

DNA is replicated semi-conservatively. Signup and view all the answers

Study Notes

Structure of DNA and RNA

Nucleic acids consist of polynucleotides formed by linking nucleotides via phosphodiester bonds.
Nucleotides are composed of a phosphate group, a pentose sugar (deoxyribose in DNA, ribose in RNA), and a nitrogenous base.
Formation of a mononucleotide involves a condensation reaction resulting in the elimination of two water molecules.

Nitrogenous Bases

DNA contains five nitrogenous bases: adenine (A), thymine (T), guanine (G), and cytosine (C).
RNA replaces thymine with uracil (U), comprising adenine (A), uracil (U), guanine (G), and cytosine (C).
Adenosine triphosphate (ATP) is a phosphorylated mononucleotide made from ribose, adenine, and can have one to three phosphate groups (AMP, ADP, ATP).

ATP Significance

ATP is termed the universal energy currency for cells.
It is small and water-soluble, facilitating easy diffusion between cell organelles.
Acts as an immediate energy donor, easily hydrolyzed to ADP to release energy.

Uses of ATP

Vital for cell division, muscle contraction, and maintenance of body temperature.
Plays a role in anabolic reactions, such as protein synthesis and nerve impulse transmission.

Formation of Polynucleotide

Occurs during interphase through condensation reactions creating phosphodiester bonds.
Links the phosphate of one nucleotide to the 3' carbon of the sugar in another nucleotide, creating a sugar-phosphate backbone.

Structure of DNA Molecule

Comprises two polynucleotide strands of deoxyribose, phosphate, and nitrogenous bases.
Strands run in opposite directions (antiparallel).
Hydrogen bonds between nitrogenous bases connect the strands, adhering to complementary base pairing (A=T, G≡C).

Importance of Hydrogen Bonding in DNA

Hydrogen bonds hold the two polynucleotide strands together and contribute to the DNA's 3D structure.
Provide stability, allowing for easier separation during replication and transcription.
Specificity in base pairing reduces replication errors, ensuring faithful genetic replication.

Structural Features Contributing to DNA Stability

Complementary base pairing and numerous hydrogen bonds enhance structural integrity.
The sugar-phosphate backbone is reinforced with phosphodiester bonds.
The double helix configuration protects bases from chemical attacks.

Importance of DNA Stability

Prevents spontaneous changes in sequences, minimizing mutation risk and ensuring functional proteins.
Ensures the preservation of genetic information across generations, maintaining integrity in daughter cells.
Keeps DNA size manageable for storage within the nucleus.

Semi-Conservative Replication of DNA

Semi-conservative replication generates two identical DNA molecules, each containing one original and one new strand.
Occurs during the S phase of the cell cycle, using each old strand as a template for new complementary strand synthesis.

Steps of DNA Replication

The double helix unwinds, and hydrogen bonds between complementary bases break, facilitated by the enzyme DNA helicase.
Free activated nucleotides align along the separated strands, pairing with complementary bases (A=T, C≡G).
DNA polymerase adds new nucleotides sequentially, while DNA ligase forms phosphodiester bonds between adjacent nucleotides.

Sense and Anti-sense Strands

Sense strand encodes for protein manufacture, while anti-sense strand stabilizes the DNA and serves as a template for mRNA synthesis.
A triplet of bases (codon) in the template strand codes for one amino acid, forming the genetic code.

Genetic Code Characteristics

Each triplet of bases specifies one amino acid, resulting in 64 possible codons from four bases.
The genetic code is universal across living organisms, suggesting a common ancestry.
Degenerate nature allows multiple codons to code for the same amino acid, totaling 61 codons usable for amino acids and three stop codons.

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Description

This quiz explores the fundamental structure of DNA and RNA, focusing on the formation of nucleotides and the significance of ATP. It delves into the composition of nucleic acids, the nitrogenous bases involved, and the crucial role of ATP in cellular energy transfer.