DNA Structure and Nucleotides

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Questions and Answers

During which phase of the cell cycle is DNA typically found in the chromatin form?

  • Interphase (correct)
  • Anaphase
  • Mitosis
  • Telophase

Which type of bond connects the sugar and phosphate groups in the DNA backbone?

  • Ionic bond
  • Hydrogen bond
  • Phosphodiester bond (correct)
  • Peptide bond

In the structure of DNA, what forms the 'rungs' of the double helix 'ladder'?

  • Nitrogenous bases (correct)
  • Pentose sugars
  • Phosphodiester bonds
  • Phosphate groups

If a strand of DNA has the sequence 5'-GATTACA-3', what would be the sequence of its complementary strand?

<p>3'-CTAATGT-5' (B)</p> Signup and view all the answers

What is the significance of the Human Genome Project (HGP)?

<p>It sequenced the entire human genome. (B)</p> Signup and view all the answers

Why is DNA replication described as 'semi-conservative'?

<p>Because the new DNA molecule contains one original strand and one newly synthesized strand. (B)</p> Signup and view all the answers

Which of the following distinguishes RNA from DNA in terms of its nitrogenous base composition?

<p>RNA contains uracil, while DNA contains thymine. (B)</p> Signup and view all the answers

If a mutation occurs in a DNA sequence, what is directly affected?

<p>The nucleotide sequence of DNA. (C)</p> Signup and view all the answers

Which of the following statements accurately describes the base pairing rules in DNA?

<p>Adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C). (B)</p> Signup and view all the answers

How does the number of hydrogen bonds differ between the base pairs A-T and G-C in DNA?

<p>A-T has two hydrogen bonds, while G-C has three. (D)</p> Signup and view all the answers

What is the primary function of the pentose sugar within a nucleotide?

<p>To form part of the DNA backbone and link to the phosphate group. (A)</p> Signup and view all the answers

Considering the antiparallel nature of DNA, what does this imply about the two strands in the double helix?

<p>One strand runs 5' to 3', while the other runs 3' to 5'. (B)</p> Signup and view all the answers

Which component of a nucleotide accounts for the genetic variation among different DNA molecules?

<p>The nitrogenous base. (D)</p> Signup and view all the answers

Which of the following represents the correct order of events during DNA replication?

<p>Unwinding of DNA → Primer binding → Elongation → Termination (C)</p> Signup and view all the answers

In RNA, if a sequence of bases on one strand is AUCG, what would be the complementary sequence on the opposing strand?

<p>UAGC (B)</p> Signup and view all the answers

How would a mutation that changes a single nucleotide base in a gene's coding sequence most likely affect the resulting protein?

<p>It could change a single amino acid or introduce a premature stop codon. (C)</p> Signup and view all the answers

What structural feature contributes most to DNA's stability under varying environmental conditions?

<p>The specific pairing of nitrogenous bases and their hydrogen bonds (B)</p> Signup and view all the answers

What is the functional significance of the hydroxyl group difference between ribose and deoxyribose sugars?

<p>It impacts the stability and secondary structure formation of the nucleic acid. (A)</p> Signup and view all the answers

Flashcards

DNA Structure

DNA is composed of two molecules arranged in a double helix, resembling a ladder shape.

DNA Forms: Interphase vs. Mitosis

During interphase, DNA exists in a loosely packed form called chromatin, allowing for access during normal cell functions. As mitosis starts, DNA condenses into tightly packaged chromosomes for organized division.

Nucleotide

The building blocks of DNA; each contains a phosphate group, a pentose sugar, and a nitrogenous base.

Pentose Sugar

A five-carbon sugar molecule that is a component of a nucleotide. In DNA it is deoxyribose; in RNA, it is ribose.

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DNA Backbone

The structural framework of a DNA molecule, composed of alternating sugar and phosphate groups linked by phosphodiester bonds.

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Antiparallel DNA

The property of DNA strands running in opposite directions (5' to 3' and 3' to 5').

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Nitrogenous Bases

The four nitrogenous bases in DNA are Adenine (A), Guanine (G), Thymine (T), and Cytosine (C).

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Complementary Base Pairs

Specific pairing of nitrogenous bases in DNA: Adenine (A) pairs with Thymine (T), and Guanine (G) pairs with Cytosine (C).

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Mutation

A change in the nucleotide sequence of DNA, which can lead to variations in traits.

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Genome

The complete set of DNA sequences found within a cell or organism.

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Semiconservative Replication

The process by which DNA makes a copy of itself, resulting in two DNA molecules, each with one original and one new strand.

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Uracil (U)

In RNA Uracil (U) base pairs with Adenine (A).

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Study Notes

  • DNA consists of two molecules arranged in a double helix (ladder) shape.
  • During interphase, DNA exists in chromatin form.
  • As mitosis begins, DNA condenses into chromosome form.
  • A DNA molecule comprises millions of nucleotides.

Nucleotide Components

  • Phosphate group (circle)
  • Pentose sugar (pentagon)
  • Nitrogenous base (rectangle)

Pentose Sugar

  • Five-carbon sugars, numbered 1 through 5.
  • RNA contains ribose.
  • DNA contains deoxyribose, differing by the presence of a hydroxyl group.
  • Phosphate and sugar form the DNA molecule's backbone, with bases forming the rungs.
  • Sugars and phosphates are connected by phosphodiester bonds.
  • DNA strands are antiparallel.

Nucleotides

  • Adenine (A)
  • Guanine (G)
  • Thymine (T)
  • Cytosine (C)

Nitrogenous Base Pairing

  • Each base bonds with a specific complementary base pair.
  • Adenine (A) pairs with Thymine (T) via two hydrogen bonds.
  • Guanine (G) pairs with Cytosine (C) via three hydrogen bonds.
  • In RNA, Uracil (U) pairs with Adenine (A).

Mutations

  • Mutations are changes in the nucleotide sequence of DNA.

Genome

  • Genome is the complete DNA sequence in every cell of an organism.
  • The Human Genome Project (HGP) sequenced the human genome in 2003.

DNA Replication

  • Double helix unwinds, and each DNA strand serves as a template for a new strand.
  • Newly created double-stranded DNA contains one original and one new strand.
  • This replication method is called semi-conservative.

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