Biochemistry Chapter 4: DNA Manipulation Techniques
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Questions and Answers

An enzyme with a longer recognition sequence, such as ______, cuts at an eight-nucleotide sequence.

NotI

______ would be expected to cut a DNA molecule once every 62 nucleotides.

NotI

During conventional gel electrophoresis, DNA molecules travel a distance based on their ______.

size

Poor resolution of DNA is observed above a certain ______ size in gel electrophoresis.

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

The conventional gel electrophoresis technique differs from ______ field alternation gel electrophoresis (OFAGE).

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

A tetranucleotide sequence occurs once every ______ nucleotides.

<p>256</p> Signup and view all the answers

The production of ______ ends does not create overhangs.

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

EcoRI is a restriction enzyme known for producing ______ ends.

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

Different restriction endonucleases can produce the same ______ ends.

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

The 'N' in the sequences represents any of the four nucleotides, which are A, G, C, or ______.

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

The calculations about nucleotide occurrences assume a ______ arrangement of the nucleotides.

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

In practice, the assumption of equal proportions of nucleotides implies a GC content of ______%.

<p>50</p> Signup and view all the answers

Most restriction endonucleases function adequately at pH ______.

<p>7.4</p> Signup and view all the answers

Restriction endonucleases usually require ______ strength for their function.

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

All type II restriction endonucleases require ______ in order to function.

<p>Mg2+</p> Signup and view all the answers

Adding a reducing agent like ______ stabilizes the enzyme.

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

Incorrect NaCl or Mg2+ concentrations might cause changes in the ______ of the enzyme.

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

A suitable buffer for BglII contains ______ mM of MgCl2.

<p>100</p> Signup and view all the answers

Most restriction endonucleases work best at ______°C.

<p>37</p> Signup and view all the answers

TaqI is a restriction enzyme from ______ aquaticus.

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

The enzyme ______ is derived from Escherichia coli.

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

______ is known for producing the sticky end sequence GAATTC.

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

BamHI is an enzyme from the organism ______.

<p>Bacillus amyloliquefaciens</p> Signup and view all the answers

The sequence recognized by BglII is ______.

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

______ produces a blunt end when cut at CAGCTG.

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

The enzyme HindIII cuts DNA at the sticky end sequence ______.

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

The organism Staphylococcus aureus is associated with the enzyme ______.

<p>Sau3A</p> Signup and view all the answers

The sequence GCGGCCGC is recognized by the enzyme ______.

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

Restriction endonucleases are enzymes responsible for ______ DNA.

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

Ligases are enzymes that ______ nucleic acid molecules together.

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

Nucleases are enzymes that ______, shorten, or degrade nucleic acid molecules.

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

Polymerases are enzymes that make ______ of DNA molecules.

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

Exonucleases remove nucleotides one at a time from the ______ of a DNA molecule.

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

Endonucleases break internal ______ bonds within a DNA molecule.

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

DNA manipulative enzymes can be grouped into four broad classes based on the type of ______ they catalyze.

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

Some enzymes act on RNA, but this discussion will generally focus on those that act on ______.

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

To obtain gene B, digest with ______.

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

To obtain gene D, digest with ______ + Sall.

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

A series of restriction digests must be performed to construct a ______.

<p>restriction map</p> Signup and view all the answers

The sizes of the fragments produced by each restriction endonuclease must be determined by ______.

<p>gel electrophoresis</p> Signup and view all the answers

Double digestions involve cutting the DNA with two restriction ______ at once.

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

Adjusting the reaction mixture is necessary if the two digestions have different requirements for ______.

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

Size markers are used to compare the sizes of the ______ produced.

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

Information from single digestions must be supplemented by data from ______ digestions.

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

Flashcards

Nucleases

Enzymes that break down nucleic acid molecules by breaking the phosphodiester bonds linking nucleotides.

Exonucleases

Nucleases that remove nucleotides one by one from the end of a DNA molecule.

Endonucleases

Nucleases that break internal phosphodiester bonds within a DNA molecule.

Ligases

Enzymes that join two nucleic acid molecules together by forming a phosphodiester bond.

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Polymerases

Enzymes that make copies of nucleic acid molecules.

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Modifying Enzymes

Enzymes that add or remove chemical groups from nucleic acid molecules.

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DNA Polymerase with Degradative Activity

A specific type of polymerase that can both synthesize new DNA and break down existing DNA.

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RNA Manipulative Enzymes

A class of enzymes that act on RNA molecules.

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Restriction site

A specific sequence of DNA recognized and cut by a restriction endonuclease.

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Restriction endonuclease

An enzyme that cuts DNA at a specific sequence.

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Sticky end

A type of restriction endonuclease cut that leaves single-stranded overhangs at the ends of the DNA fragments.

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Blunt end

A type of restriction endonuclease cut that produces blunt ends, with no overhangs on the DNA fragments.

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EcoRI

A restriction endonuclease that recognizes and cuts the DNA sequence GAATTC.

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BamHI

A restriction endonuclease that recognizes and cuts the DNA sequence GGATCC.

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Restriction endonuclease name

A specific restriction endonuclease that recognizes and cuts a specific DNA sequence.

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Restriction endonuclease source organism

The source organism from which a restriction endonuclease was isolated.

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Recognition Site

The specific nucleotide sequence that a restriction endonuclease recognizes and cuts.

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Optimal pH

The ideal pH (7.4) at which most restriction endonucleases function optimally.

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Ionic Strength

The concentration of salts (like NaCl) needed for the restriction endonuclease to function properly.

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Magnesium Requirement

A crucial mineral (Mg 2+ ) required by all restriction endonucleases for their activity.

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Reducing Agent

A chemical stabilizer (like DTT) added to protect the enzyme from inactivation.

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Unit of Enzyme Activity

The standard unit for measuring enzyme activity. 1 unit cuts 1 fg of DNA in 1 hour.

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Optimal Incubation Temperature

The temperature at which the restriction endonuclease works optimally. Most work best at 37°C, but some have different requirements.

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Tetranucleotide Sequence

A specific sequence of four DNA nucleotides (A, T, C, G) that is repeated throughout a DNA molecule. Its frequency is expected to occur once every 256 nucleotides if all bases occur with equal probability.

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Hexanucleotide Sequence

A specific sequence of six DNA nucleotides that is repeated throughout a DNA molecule. Its frequency is expected to occur once every 4096 nucleotides if all bases occur with equal probability.

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GC Content

The percentage of guanine and cytosine bases in a DNA sequence. It impacts the frequency of restriction enzyme recognition sites.

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Equal Base Probability

The assumption that all four DNA bases (A, T, C, G) occur with equal probability in a sequence. This is not always true in real life.

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Non-Random Base Distribution

The distribution of restriction enzyme recognition sites is influenced by the actual order and frequency of bases in a real DNA sequence. This contrasts with the theoretical calculations that assume equal base probabilities.

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Gel Electrophoresis

A method of separating DNA molecules based on their size by applying an electric field through a gel matrix. Smaller molecules migrate faster than larger molecules, resulting in a gradient of DNA fragments based on size.

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Orthogonal Field Alternation Gel Electrophoresis (OFAGE)

A type of gel electrophoresis that improves separation of larger DNA molecules by applying alternating electric fields. This technique increases resolution for larger fragments making it suitable for analyzing larger genomes.

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Restriction Enzyme Cutting Frequency

The frequency of a specific restriction enzyme cutting a DNA molecule. This is determined by the length of the recognition sequence and the random distribution of the sequence within the DNA.

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Effect of Recognition Sequence Length

Longer recognition sequences for restriction enzymes lead to less frequent cutting. Consequently, fewer cuts occur, resulting in larger fragments.

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What does a restriction enzyme do?

A restriction enzyme cuts DNA at a specific sequence.

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Restriction Map

A diagram showing the locations of restriction enzyme cut sites within a DNA molecule.

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Restriction Digestion

The technique of using restriction enzymes to cut DNA into specific fragments.

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Genetic Map

A genetic map that indicates the order and relative distances of genes on a chromosome, often determined by the frequency of recombination.

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Double Digestion

A type of DNA digestion where two restriction enzymes are used simultaneously to cut DNA at two different sites.

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Size Markers

The process of comparing DNA fragment sizes with known standards to determine their exact length.

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Compatible Restriction Enzymes

The ability of two different restriction enzymes to cut at their respective sites within a DNA molecule.

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Adjusting Reaction Conditions

Changing the reaction conditions (pH, Mg2+ levels, etc.) to accommodate two restriction enzymes in a single digestion.

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Study Notes

Chapter 4: Manipulation of Purified DNA

  • DNA manipulation techniques are crucial for gene cloning, DNA biochemistry, gene structure, and gene expression studies. These techniques involve cutting, joining, modifying, and copying DNA.
  • Purified enzymes are essential in most DNA manipulation techniques, as they perform essential cellular functions like DNA replication, transcription, and recombination in artificial conditions.
  • Nucleases: Enzymes that cut, shorten, or degrade nucleic acids.
    • Exonucleases: Remove nucleotides from the end of a DNA molecule.
    • Endonucleases: Break phosphodiester bonds within a DNA molecule, either at the ends of a strand, or internally.
  • Ligases: Join nucleic acid molecules together.
  • Polymerases: Make copies of molecules.
  • Modifying enzymes: Remove or add chemical groups. Some polymerases also possess nuclease activity (i.e., degrade DNA). There are corresponding RNA versions of these enzymes.

Restriction Endonucleases

  • Crucial for precise and reproducible DNA cutting in gene cloning.
  • Type II Restriction Endonucleases cut DNA at specific recognition sites.
  • Recognition sequences: Each enzyme recognizes a specific DNA sequence to cut the double-stranded DNA. Cutting locations can be blunt or sticky ends.
    • Blunt ends: A single strand cut precisely at the same point on the double-helix strand.
    • Sticky ends: Staggered double-helix cuts, resulting in short, complementary single-stranded overhangs. Sticky ends from different enzymes can ligate together if they are complementary.
  • Recognition sequences vary in length (4 to 8 base pairs), and frequency within a DNA.
  • Discovery: The discovery of restriction enzymes is a breakthrough in genetic engineering.

Ligation: Joining DNA Molecules

  • Joining together DNA pieces (e.g., vector and DNA to be cloned).
  • DNA ligase: The enzyme that catalyzes this reaction. Different ligases can handle different DNA ends (e.g., blunt or sticky).
    • Sticky ends ligation: More efficient: Complementary sticky ends can form temporary base-pairs aiding alignment for ligation.
    • Blunt ends ligation: Less efficient, requires higher DNA concentration to increase the probability of successful ligation.

DNA Polymerases

  • Enzymes that synthesize new DNA strands complementary to existing DNA or RNA templates.
  • Various different DNA polymerases have specific applications in the lab.
  • T4 DNA Polymerase: Fills in gaps and repairs nicks in DNA.
  • Klenow Fragment: Used in DNA sequencing and filling gaps, lacking the degradation feature of DNA Polymerase I
  • Taq polymerase: Thermostable polymerase commonly used in polymerase chain reaction (PCR).

DNA Modifying Enzymes

  • Adding, removing chemical groups from DNA.
  • Alkaline Phosphatase: Removes 5' phosphate groups.
  • Polynucleotide kinase: Adds phosphate groups to 5' termini.
  • Terminal deoxynucleotidyl transferase: Adds deoxyribonucleotides to 3' termini.

Restriction Digests

  • Methodology for the use and characterization of restriction enzymes in the lab.
  • Factors affecting restriction endonuclease activity: Temperature, pH, Mg2+ concentration.
  • Methods for analyzing restriction digests: Gel electrophoresis.

Gel Electrophoresis

  • Separates DNA fragments based on size.
  • Important for identifying and analyzing DNA fragments cut by restriction enzymes.
  • Visualization of DNA Fragments using EtBr, and other stains for visualization under UV light.
  • Estimating DNA fragment sizes: Comparison with known markers, which offer an estimate of fragment lengths.
  • OFAGE (Orthogonal Field Alternating Gel Electrophoresis): Improves resolution and analysis of larger DNA fragments than traditional methods.

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Explore Chapter 4, focusing on the manipulation of purified DNA. This quiz covers essential DNA manipulation techniques used in gene cloning and biochemistry, including the roles of various enzymes like nucleases, ligases, and polymerases. Test your understanding of how these enzymes interact in DNA replication and modification.

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