DNA Structure and Discovery
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DNA Structure and Discovery

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Questions and Answers

Which components make up a DNA nucleotide?

  • Nitrogenous base, glucose, phosphate group
  • Nitrogenous base, deoxyribose sugar, phosphate group (correct)
  • Nitrogenous base, ribose sugar, phosphate group
  • Nitrogenous base, deoxyglycerol, sulfate group

    • What is the primary function of DNA in the cell?

  • To provide energy for cellular processes
  • To facilitate protein synthesis
  • To carry genetic information (correct)
  • To regulate enzymatic activity

    • Which nitrogenous bases are classified as purines?

  • Cytosine and Thymine
  • Adenine and Cytosine
  • Adenine and Guanine (correct)
  • Thymine and Uracil

    • What differentiates deoxyribose from ribose in the structure of nucleic acids?

    <p>Deoxyribose has one less oxygen atom than ribose</p> Signup and view all the answers

    What is the significance of the hydrolysis of DNA?

    <p>It breaks DNA into nucleotides and their components</p> Signup and view all the answers

    Which statement is true regarding the structure of pyrimidines?

    <p>Pyrimidines contain one C-N ring</p> Signup and view all the answers

    What charge is present in polynucleotides due to the phosphate groups?

    <p>Negative charge</p> Signup and view all the answers

    Who coined the term 'nucleic acid' in reference to the isolated material from nuclei?

    <p>Atlman</p> Signup and view all the answers

    What defines a polynucleotide?

    <p>It is a polymeric compound composed of repeating nucleotides.</p> Signup and view all the answers

    What role does the phosphate group play in nucleotide structure?

    <p>It connects the 5th Carbon of one sugar to the 3rd Carbon of the next.</p> Signup and view all the answers

    Which statement is true regarding the orientation of nucleotides in a polynucleotide?

    <p>The nucleotides are all orientated in the same direction.</p> Signup and view all the answers

    Which base pairs with adenine in DNA?

    <p>Thymine</p> Signup and view all the answers

    What structural feature characterizes the DNA double helix?

    <p>It has two strands organized in an antiparallel manner.</p> Signup and view all the answers

    What is the significance of the order of bases in a polynucleotide?

    <p>It determines the genetic information of the molecule.</p> Signup and view all the answers

    In what way does a dinucleotide differ from a mononucleotide?

    <p>It consists of two units of nucleotides.</p> Signup and view all the answers

    Which statement accurately describes the composition of a nucleotide?

    <p>It consists of a sugar, a nitrogenous base, and a phosphoric acid.</p> Signup and view all the answers

    What is the role of phosphodiester bonds in nucleic acids?

    <p>They connect nucleotides through covalent 3<code>-5</code> linkages.</p> Signup and view all the answers

    Which atoms are involved in the glycosidic bond linking the sugar to the base in nucleosides?

    <p>N-1 of pyrimidines or N-9 of purines.</p> Signup and view all the answers

    What distinguishes deoxyribonucleotides from ribonucleotides?

    <p>Deoxyribonucleotides lack an oxygen atom at the 2` position of the sugar.</p> Signup and view all the answers

    What defines the 5`-end of a DNA strand?

    <p>It contains a free phosphate group.</p> Signup and view all the answers

    How are nucleotides joined together within a nucleic acid chain?

    <p>By covalent 3<code>-5</code> phosphodiester linkages.</p> Signup and view all the answers

    Which base pairs with adenine in DNA?

    <p>Thymine</p> Signup and view all the answers

    What is the ratio of adenine to thymine in a DNA molecule according to Chargaff's Rule?

    <p>1:1</p> Signup and view all the answers

    Which of the following describes a characteristic of nucleosides?

    <p>They consist of a base linked to a sugar.</p> Signup and view all the answers

    Which part of a nucleotide attaches to the sugar at the C-5` position?

    <p>Phosphate group</p> Signup and view all the answers

    How many hydrogen bonds are formed between guanine and cytosine?

    <p>3</p> Signup and view all the answers

    What type of bond is formed between the carbon-1 on one sugar and carbon-4 on another in polysaccharides?

    <p>Glycosidic bond.</p> Signup and view all the answers

    What is the major groove in the DNA double helix?

    <p>An area where bases are more accessible for protein binding.</p> Signup and view all the answers

    Which of the following is NOT part of DNA's backbone structure?

    <p>Ribose</p> Signup and view all the answers

    What characterizes the minor groove in DNA?

    <p>Less than 180º from glycosidic bond to bond.</p> Signup and view all the answers

    What is the significance of the grooves in DNA?

    <p>They facilitate interactions with DNA binding proteins.</p> Signup and view all the answers

    Which type of bond connects the sugar and bases in DNA?

    <p>Glycosidic bond</p> Signup and view all the answers

    What is the most common conformation of DNA?

    <p>B-DNA</p> Signup and view all the answers

    How many base pairs are present in one complete turn of B-DNA?

    <p>10.4</p> Signup and view all the answers

    What is the diameter of the double helix structure of B-DNA?

    <p>2.37nm</p> Signup and view all the answers

    Under which conditions is Z-DNA typically formed?

    <p>High salt concentrations</p> Signup and view all the answers

    How does the pitch of the helix in A-DNA compare to that of B-DNA?

    <p>A-DNA has a smaller pitch</p> Signup and view all the answers

    Which type of organisms typically have DNA that is present as a single circular molecule?

    <p>Prokaryotic organisms</p> Signup and view all the answers

    Which of the following correctly describes the major groove of Z-DNA?

    <p>No longer a groove, but a convex surface</p> Signup and view all the answers

    Which statement accurately describes prokaryotic DNA?

    <p>It is naked, lacking associated histone proteins</p> Signup and view all the answers

    Study Notes

    DNA Structure

    • DNA is a polymer of deoxyribonucleotides found in chromosomes, mitochondria, and chloroplasts.
    • Nuclear DNA is bound to basic proteins called histones.
    • DNA carries genetic information.

    History of DNA Discovery

    • Meischer isolated a phosphorous-rich substance called "nuclein" from white blood cell nuclei in 1868, which was later discovered to be nucleic acid + protein (nucleoprotein).
    • Altman isolated a protein-free preparation of nuclei in 1898 and coined the term “Nucleic acid”.
    • Deoxyribonucleic acid (DNA) is the specific nucleic acid found in the nucleus.

    Components of DNA

    • DNA hydrolysis produces nitrogenous bases, deoxypentose sugar, and phosphate groups.
    • Sugar: Deoxyribose
    • Nitrogenous Bases:
      • Purines: Adenine (A) and Guanine (G)
      • Pyrimidines: Cytosine (C) and Thymine (T)
    • Phosphate
    • Nucleotide: Sugar + Base + Phosphate

    DNA Sugar Structure

    • Ribose is the sugar found in RNA.
    • Deoxyribose is the sugar found in DNA.
    • Both ribose and deoxyribose are sugars present in the ring form.
    • In RNA, both 2' and 3' positions have OH groups attached to the sugar.
    • In DNA, OH group is attached at the 3' position of the sugar.

    Nitrogenous Bases

    • Nitrogenous bases have C-N ring structures, giving them their name.
    • Purines: Adenine and Guanine have two joined C-N rings with different side chains.
    • Pyrimidines: Thymine and Cytosine have one C-N ring with different side chains.

    Phosphate Group

    • Phosphates attached to DNA are rigid units with no internal flexibility.
    • Four oxygen atoms occupy a tetrahedral arrangement around the phosphorus center.
    • Negative charge at the phosphate group contributes to the acidity of nucleic acids.

    Nucleosides

    • Base + 5-carbon sugar (ribose/deoxyribose) = Nucleoside
    • Ribose + Base = Ribonucleosides
    • Deoxyribose + Base = Deoxyribonucleosides
    • Glycosidic bonds link the C-1' of the sugar to either N-1 (pyrimidines) or N-9 (purines) of the base.

    Nucleotides

    • Base + Sugar + Phosphate = Nucleotide
    • Phosphate is linked to a free hydroxyl group of the sugar, either at C-3' or C-5' of ribose.
    • Deoxyribose containing nucleotides are called deoxyribonucleotides.
    • Ribose containing nucleotides are called ribonucleotides.
    • Deoxyribonucleotides are the building blocks of DNA.
    • Ribonucleotides are the building blocks of RNA.
    • Phosphodiester bonds join nucleotides together in nucleic acids.

    DNA Strand Formation

    • Covalent 3'-5' phosphodiester linkages bind nucleotides in each strand of the DNA double helix.
    • Each phosphodiester bond involves a phosphate residue linking the 3'-OH group of one nucleotide with the 5'-OH group of the next nucleotide.
    • This bonding generates a linear polydeoxyribonucleotide strand with two free ends.
    • The 5' end bears a free 5' phosphate group.
    • The 3' end bears a free 3' hydroxyl or 3' phosphate group.

    Nucleic Acid Classification

    • Mononucleotide: Single nucleotide consisting of one base, one sugar, and one phosphate group.
    • Dinucleotide: Consists of two units, each containing a base, a sugar, and a phosphate group.
    • Polynucleotide: A polymer composed of many nucleotides.

    DNA Double Helix

    • The 3D structure of DNA was deciphered in 1953 by Watson and Crick, based on X-ray diffraction photographs by Franklin and Wilkins.
    • DNA comprises two strands twisted around each other to form a double helix, with the bases inside and the sugar-phosphate backbones on the outside.
    • The two DNA strands are antiparallel, meaning one strand is oriented 5' to 3' and the other 3' to 5'.
    • Bases form hydrogen bonds with each other, A with T and G with C, known as complementary base pairing.

    Chargaff's Rule

    • Adenine always pairs with Thymine (A-T).
    • Guanine always pairs with Cytosine (G-C).
    • The amounts of A and T, and G and C in a DNA molecule are equal (1:1).
    • There are two hydrogen bonds between A and T, and three hydrogen bonds between G and C.

    DNA Grooves

    • The glycosidic bonds between sugar and bases are not directly opposite each other in DNA, resulting in two grooves of unequal width around the double helix.
    • Major groove: Wider than 180 degrees from glycosidic bond to glycosidic bond.
    • Minor groove: Narrower than 180 degrees from glycosidic bond to glycosidic bond.

    Protein Interaction with DNA

    • Proteins bind to DNA to alter its structure or regulate transcription and replication.
    • The major groove is more accessible to DNA-binding proteins due to its width and lack of backbone obstruction.
    • The edges of bases are more exposed in the major groove.

    DNA Conformations

    • DNA can exist in various conformations depending on base composition and physical conditions.
    • These conformations do not alter the information content of DNA.
    • B-DNA: The most common DNA conformation, right-handed helix, one complete turn every 10.4 base pairs, pitch is 3.4nm, 0.33nm length increase per base pair, diameter is 2.37nm, narrow minor groove, wide major groove.
    • A-DNA: Right-handed helix, wider and flatter than B-DNA, short and stubby, occurs in dehydrated conditions or low salt concentrations, pitch is 2.46nm, 11 base pairs per turn, deep major groove, shallow minor groove.
    • Z-DNA: Left-handed helix, found under high salt concentrations, longer and thinner than B-DNA, 12 base pairs per turn, pitch is 4.56nm, diameter is 1.84nm, major groove is a convex surface, minor groove is a deep cleft.

    Prokaryotic vs. Eukaryotic DNA

    • Prokaryotic DNA: Found in bacteria and archaea, lacks a membrane-bound nucleus, circular DNA molecule called a bacterial chromosome, DNA is naked without associated histone proteins.
    • Eukaryotic DNA: Found in complex multicellular organisms (plants, animals, fungi) and some single-celled organisms (amoeba, yeast), has a membrane-bound nucleus, DNA is bound to histone proteins.

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    DNA Final Presentation PDF

    Description

    This quiz covers the essential components and structure of DNA, including its historical discovery and the roles of various nucleotides. Understand the significance of deoxyribonucleic acid and its foundational role in genetics. Test your knowledge on the parts that make up DNA and the scientists who contributed to its discovery.

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