Lecture 5: Introduction to Nucleic Acids
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Questions and Answers

What type of RNA is primarily responsible for conveying genetic instructions from the nucleus to the cytoplasm?

  • Catalytic RNA (ribozyme)
  • Ribosomal RNA (rRNA)
  • Messenger RNA (mRNA) (correct)
  • Transfer RNA (tRNA)

Which of the following statements accurately describes a primary structure difference between RNA and DNA?

  • RNA has a higher molecular weight than DNA.
  • RNA includes uracil, whereas DNA contains thymine. (correct)
  • RNA contains deoxyribose while DNA contains ribose.
  • RNA is generally double-stranded compared to the single-stranded structure of DNA.

Which process is directly catalyzed by ribozymes?

  • Translation of mRNA into proteins.
  • Formation of peptide bonds between amino acids.
  • Replication of DNA.
  • Splicing of RNA sequences. (correct)

What structural feature distinguishes ribozymes from standard proteins?

<p>Ribozymes are known for their catalytic capacities. (C)</p> Signup and view all the answers

What form of RNA is most likely to be single-stranded and exhibit various conformation types?

<p>Messenger RNA (mRNA) (C)</p> Signup and view all the answers

In a eukaryotic cell, where is DNA primarily located?

<p>Nucleus (D)</p> Signup and view all the answers

What is formed by pairing of bases within approximately 5–10 nucleotides of each other in single-stranded RNA?

<p>Hairpin (D)</p> Signup and view all the answers

What is the correct flow of genetic information in cells?

<p>DNA → RNA → protein (D)</p> Signup and view all the answers

What was the main conclusion drawn from Griffith's experiment with Streptococcus pneumoniae?

<p>Harmless bacteria can become pathogenic through transformation. (C)</p> Signup and view all the answers

What does the term 'transforming principle' refer to in Griffith's research?

<p>The genetic material that enables transformation of bacteria. (D)</p> Signup and view all the answers

Which experiment provided the first strong evidence that genes are composed of DNA?

<p>Avery, MacLeod, and McCarty Experiment (D)</p> Signup and view all the answers

What was a significant limitation of using antibiotics during Griffith's time of experimentation?

<p>They were not discovered yet. (B)</p> Signup and view all the answers

What does transformation in the context of genetics mean?

<p>The genetic alteration of a cell through uptake of genetic material. (A)</p> Signup and view all the answers

In the Griffith experiment, what was the outcome when mice were injected with heat-killed pathogenic bacteria and live harmless bacteria?

<p>The mice died and their blood contained live pathogenic bacteria. (B)</p> Signup and view all the answers

What was the primary method used by Avery, MacLeod, and McCarty to identify DNA as the 'transforming principle'?

<p>Purifying extracts from pathogenic bacteria. (B)</p> Signup and view all the answers

Which of the following statements about DNA is true based on the experiments discussed?

<p>DNA serves as the hereditary material in all living organisms. (B)</p> Signup and view all the answers

What significant finding did Erwin Chargaff make in his analysis of DNA composition?

<p>The base composition varies significantly between different species. (C)</p> Signup and view all the answers

What was the main technique used by Rosalind Franklin and Maurice Wilkins to study DNA structure?

<p>X-ray crystallography (B)</p> Signup and view all the answers

Which statement accurately describes the pairing of nitrogenous bases in DNA?

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

What does it mean for DNA backbones to be described as 'antiparallel'?

<p>The sugar-phosphate backbones run in opposite directions. (B)</p> Signup and view all the answers

What inspired James Watson to conclude that DNA had a helical structure?

<p>Franklin's X-ray diffraction pattern indicating a helical arrangement. (A)</p> Signup and view all the answers

Which statement reflects the core concept of Chargaff's Rules?

<p>The number of adenines and thymines is equal within a single species. (D)</p> Signup and view all the answers

What role did Raymond Gosling play in the discovery of DNA's structure?

<p>He captured a crucial X-ray diffraction image known as 'Photo 51'. (A)</p> Signup and view all the answers

What was one of the conclusions drawn by Rosalind Franklin regarding the structure of DNA?

<p>DNA has two antiparallel sugar-phosphate backbones. (A)</p> Signup and view all the answers

What distinguishes purines from pyrimidines in terms of structure?

<p>Purines have a six-membered ring fused to a five-membered ring. (B)</p> Signup and view all the answers

What type of bond links the nucleotides within a single polynucleotide chain?

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

Which nitrogenous base forms a hydrogen bond with adenine in DNA?

<p>Thymine (A)</p> Signup and view all the answers

In how many directions do the two backbones of a DNA molecule run?

<p>Two antiparallel directions (A)</p> Signup and view all the answers

Which component is absent in RNA compared to DNA?

<p>Thymine (D)</p> Signup and view all the answers

What is the primary function of nucleic acids in organisms?

<p>Enable reproduction of complex components (D)</p> Signup and view all the answers

What term describes the part of a nucleotide that consists of a nitrogenous base and a sugar?

<p>Nucleoside (A)</p> Signup and view all the answers

Which structures collectively form the double helix of DNA?

<p>Two polynucleotides spiraling around an axis (A)</p> Signup and view all the answers

Which sugar is found in DNA?

<p>Deoxyribose (A)</p> Signup and view all the answers

How do the nitrogenous bases pair in the DNA double helix?

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

What defines the antiparallel arrangement of DNA strands?

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

Which of the following is NOT a component of nucleotides?

<p>Amino acid (A)</p> Signup and view all the answers

During the formation of a DNA molecule, what role do hydrogen bonds play?

<p>Connect complementary base pairs between strands. (C)</p> Signup and view all the answers

Which of the following does NOT accurately describe ribonucleic acid (RNA)?

<p>Contains thymine as a nitrogenous base (D)</p> Signup and view all the answers

Flashcards

Chargaff's rule

DNA composition varies between species; within each species, A=T and G=C.

DNA composition

The specific proportions of the four bases (A, T, G, C) in DNA.

X-ray crystallography

A technique used to study molecular structures by analyzing X-ray diffraction patterns.

Photo 51

A famous X-ray diffraction image of DNA, crucial in understanding its structure.

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Antiparallel

Describes the opposite orientations of DNA strands (5' to 3' and 3' to 5').

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Base Pairing

The specific way nitrogenous bases connect (A with T, C with G).

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DNA Helix

The spiral shape of a DNA molecule.

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Molecular Diversity

The variation in the molecular composition of different species.

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Griffith Experiment

Experiment demonstrating that a factor in heat-killed bacteria can transform harmless bacteria into pathogenic ones, suggesting a "transforming principle" carrying genetic information

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Transforming Principle

The unknown substance in heat-killed bacteria that can transfer genetic information, ultimately shown to be DNA

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Avery, MacLeod, McCarty Experiment

Experiment that identified the transforming principle as DNA, providing crucial evidence that DNA carries genetic information

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DNA as genetic material

DNA is the molecule that carries the hereditary instructions for development and other traits in living organisms

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Transformation (Genetics)

The process where genetic material is directly taken up and incorporated from the surrounding environment into a cell, modifying its genetic make-up

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Streptococcus pneumoniae

A bacterium that can cause pneumonia, critical in experiments like Griffith's and Avery, MacLeod, and McCarty's research

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Hereditary Information

The information encoded in DNA and passed from generation to generation, controlling characteristics of an organism

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DNA Structure Discovery

The elucidation of the structure of DNA, primarily through X-ray diffraction analysis with crucial insights from Chargaff's rules, provided a framework for understanding how genetic information is stored and replicated.

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Nucleic Acids

Polymers called polynucleotides, enabling organisms to reproduce complex components.

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Polynucleotide

A polymer made of nucleotide monomers

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Nucleotide

Monomer of nucleic acids, consisting of a nitrogenous base, sugar, and phosphate group.

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Nucleoside

Nucleotide without the phosphate group; nitrogenous base + sugar.

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Nitrogenous Base

A molecule with nitrogen, crucial for base pairing.

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Pyrimidine

Single six-membered ring nitrogenous base (Cytosine, Thymine, Uracil).

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Purine

Double ring nitrogenous base (Adenine, Guanine).

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DNA

Deoxyribonucleic acid; double helix structure with A-T and G-C base pairs.

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RNA

Ribonucleic acid; different sugar and base composition than DNA.

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Deoxyribose

Sugar found in DNA.

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Ribose

Sugar found in RNA

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Double Helix

The spiral, two-stranded structure of DNA.

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Antiparallel

Opposite 5' to 3' directions of DNA strands.

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Base Pairing

A-T and G-C; specific hydrogen bonds.

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Phosphate Group

A part of a nucleotide that connects the nucleotides in a chain.

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DNA Replication Direction

DNA replicates in a specific direction, following a template with complementary base pairs.

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RNA Synthesis from DNA

DNA sequences direct the creation of messenger RNA (mRNA), which carries instructions.

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mRNA Function

mRNA carries genetic instructions from the nucleus to the cytoplasm for protein synthesis.

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RNA Structure Difference from DNA

RNA uses ribose sugar, which has an extra oxygen atom, and uracil instead of thymine.

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RNA Conformation

RNA molecules, unlike DNA, usually exist as single-stranded and have different shapes that help enable diverse functions.

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Ribozyme Definition

RNA molecules that possess catalytic activity (ability to speed up chemical reactions) in a cell.

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RNA Base Pairing

RNA bases pair (A-U, G-C) to allow the formation of temporary structures like hairpins and stem loops.

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Protein Synthesis Location

Protein synthesis occurs in the cytoplasm of a eukaryotic cell, with ribosomes as the sites.

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Study Notes

Introduction to Nucleic Acids

  • Nucleic acids, DNA and RNA, enable living organisms to reproduce their complex components.

  • DNA stores hereditary information, which is encoded in the chemical language of DNA.

  • This information is reproduced in every cell.

  • The DNA program directs the development of traits.

How is the DNA structure discovered?

  • By the 1920s, scientists agreed genes reside on chromosomes, composed of both DNA and proteins.
  • The question arose: which is the hereditary molecule?
  • Griffith Experiment (1928):
    • Fred Griffith studied Streptococcus pneumoniae (pneumococcus), a pneumonia-causing bacterium.
    • The bacterium exists in two forms:
      • Pathogenic: causes lethal infections.
      • Harmless: easily conquered by the immune system.
    • Griffith injected mice with different combinations of S. pneumoniae:
      • Experiment 1: Live pathogenic strain = death.
      • Experiment 2: Live harmless strain = survival.
      • Experiment 3: Heat-killed pathogenic strain = survival.
      • Experiment 4: Live harmless strain + Heat-killed pathogenic strain = death. The mice's blood contained live pathogenic bacteria
  • This unexpected result indicated a "transforming principle" that causes this change.
  • Avery, MacLeod, and McCarty (1944):
    • Followed Griffith's work.
    • Identified the transforming principle as DNA, not proteins or other molecules.
  • They purified the transforming principle.
  • This demonstrated that DNA was the transforming principle and hence the hereditary molecule.

Transformation

  • Transformation: genetic alteration of a cell from the direct uptake and incorporation of exogenous genetic material from its surroundings.

Erwin Chargaff

  • (1947): Erwin Chargaff analyzed DNA base composition from various organisms.
  • DNA composition varies between species.
  • Number of adenines (A) nearly equals number of thymines (T).
  • Number of guanines (G) nearly equals number of cytosines (C).
  • This supports the idea that DNA carries the hereditary information.

Rosalind Franklin & X-ray Crystallography

  • Maurice Wilkins & Rosalind Franklin used X-ray crystallography to study DNA structure.
  • Franklin's graduate student, Raymond Gosling, took a key X-ray diffraction image—"Photo 51."
  • This image provided essential clues about DNA structure.

Determining the DNA Structure

  • Watson and Crick (1953) used Franklin's photo and Chargaff's data to propose the double-helical structure of DNA.
  • DNA is a double helix.
  • Two antiparallel sugar-phosphate backbones.
  • Nitrogenous bases are paired in the molecule's interior: - Adenine with Thymine - Cytosine with Guanine

Components of Nucleic Acids

  • Nucleic acids are polymers called polynucleotides.
  • Each polynucleotide is made of monomers called nucleotides.
  • Each nucleotide consists of:
    • A nitrogenous base
    • A pentose sugar
    • A phosphate group

Nucleotide Monomers

  • Nucleoside = nitrogenous base + sugar.
  • Two families of nitrogenous bases:
    • Pyrimidines (single six-membered ring): Cytosine, Thymine, Uracil
    • Purines (six-membered ring fused to a five-membered ring): Adenine, Guanine.
  • In DNA, sugar is deoxyribose; in RNA, sugar is ribose.
  • Nucleotide = nucleoside + phosphate group

The DNA Double Helix

  • A DNA molecule has two polynucleotides spiraling around an imaginary axis, forming a double helix.
  • The two backbones run in opposite 5' → 3' directions, an arrangement referred to as antiparallel.
  • The nitrogenous bases in DNA pair up and form hydrogen bonds:
    • Adenine (A) always pairs with Thymine (T)
    • Guanine (G) always pairs with Cytosine (C)

RNA

  • Unlike DNA, most cellular RNAs are single-stranded and exhibit various conformations.
  • The simplest secondary structures in single-stranded RNAs are formed by pairing of complementary bases.
    • Hairpins
    • Stem-loops.
  • These simple folds can cooperate to form more complicated tertiary structures, such as pseudoknots.
  • The folded domains of RNA molecules may have catalytic capacities. Such catalytic RNAs are called ribozymes.

RNA World Hypothesis

  • The RNA world is a hypothetical stage in the evolutionary history of life on Earth.
  • Self-replicating RNA molecules proliferated before the evolution of DNA and proteins.

Types of RNA

  • The vast majority of genes specify the amino acid sequences of proteins.
  • Some genes code for RNA molecules.
  • Important RNAs for transcription:
    • mRNA: encodes proteins.
    • tRNA: acts as an adaptor between mRNA and amino acids during protein synthesis.
    • rRNA: forms the core of the ribosome's structure and catalyzes protein synthesis.
  • Other noncoding RNAs have various functions, including RNA splicing, gene regulation, telomere maintenance, and other processes.

DNA vs RNA

  • DNA

    • of strands: Two (double)

    • Sugar: Deoxyribose
    • Bases: A, T, C, G
    • Location: Nucleus
  • RNA

    • of strands: One (single)

    • Sugar: Ribose
    • Bases: A, U, C, G
    • Location: Nucleus & cytoplasm

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