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Chapter 14: Problem 6

What determines the sites at which DNA molecules will be cleaved by a restriction endonuclease?

Short Answer

Expert verified
Cleavage sites are determined by specific recognition sequences unique to each restriction enzyme.

Step by step solution

01

Understand Restriction Endonucleases

Restriction endonucleases are enzymes that cut DNA molecules at or near specific recognition nucleotide sequences, known as restriction sites. These enzymes are naturally found in bacteria and function to protect the bacteria from invaders like viruses by cleaving the DNA of the invaders.
02

Identify Restriction Sites

Restriction sites are specific sequences of nucleotides that are recognized by restriction endonucleases. These sequences are typically palindromic, meaning the sequence reads the same forwards and backwards, such as 5'-GAATTC-3'. Each type of restriction enzyme has its own specific recognition sequence.
03

How Recognition Sequences Determine Cleavage

When a restriction endonuclease encounters its specific recognition sequence in a DNA molecule, it binds to the DNA and cleaves the DNA at or near this site. The cleavage can result in blunt ends or sticky ends, depending on how the enzyme cuts the DNA.
04

Conclusion about Cleavage Sites

The sites at which DNA molecules will be cleaved by a restriction endonuclease are determined purely by the presence of its specific recognition sequence in the DNA. Different restriction enzymes will recognize and cut different sequences, thus influencing where the cleavage occurs.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Restriction Sites
Restriction sites are specific locations on a DNA molecule where restriction endonucleases bind to perform their cutting action. These sites are identified by unique sequences of nucleotides, which are specific to each type of restriction enzyme.

One of the key characteristics of many restriction sites is their palindromic nature. This means the sequence of nucleotides reads the same forwards and backwards on complementary strands. For example, the sequence 5'-GAATTC-3' complements with 3'-CTTAAG-5', creating a unique pattern.

  • Restriction sites are also known as recognition sites.
  • Each restriction enzyme has a specific restriction site it can identify and bind to.
  • Palindromic nature aids in consistent binding and cleavage by the enzymes.
Recognition Sequences
Recognition sequences are the specific DNA sequences identified by restriction endonucleases to execute the cutting process. These sequences are critical for the function of restriction enzymes because they determine precisely where the enzyme will bind and cleave the DNA.

Every restriction enzyme is tailored to recognize one or a few specific sequences. For instance, the enzyme EcoRI will specifically recognize the sequence 5'-GAATTC-3'. This specificity arises from the exact match between the enzyme's active site and the DNA sequence.

  • They enable restriction enzymes to locate and bind specific DNA regions.
  • Recognition sequences vary in length, but are generally between 4-8 base pairs.
  • Enzyme specificity ensures precise DNA modification.
DNA Cleavage
DNA cleavage refers to the cutting action performed by restriction endonucleases at the recognition sequences. Once bound to the DNA at the recognition sequence, the enzyme will cleave the DNA strand.

The way in which the DNA is cleaved can result in two types of ends:
  • **Blunt Ends:** The enzyme cuts straight through the DNA, leaving no overhanging nucleotides.
  • **Sticky Ends:** The cuts are staggered, leaving overhanging ends that can easily pair with complementary sequences.
These different types of ends are crucial for various applications in genetic engineering, such as cloning and recombinant DNA technology. By understanding where and how enzymes cut, scientists can strategically manipulate DNA for research and biotechnology.

  • The type of end generated depends on the specific restriction enzyme used.
  • Knowledge of DNA cleavage patterns aids in designing genetic experiments.

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Most popular questions from this chapter

Restriction endonucleases are invaluable tools for biologists. However, genes encoding restriction enzymes obviously did not evolve to provide tools for scientists. Of what possible value are restriction endonucleases to the microorganisms that produce them?

You are studying a circular plasmid DNA molecule of size 10.5 kilobase pairs (kb). When you digest this plasmid with restriction endonucleases \(B a m \mathrm{HI}, E_{\text {ro }} \mathrm{RI}\), and HindIII , singly and in all possible combinations, you obtain linear restriction fragments of the following sizes: $$\begin{array}{ll} \text { Enzymes } & \text { Fragment Sizes (in kb) } \\ \hline \text {BrmHI} & 7.3,3.2 \\ \text {EroRI} & 10.5 \\ \text {HindIII} & 5.1,3.4,2.0 \\ \text {BamHI }+\text {EcoRI} & 6.7,3.2,0.6 \\ \text {BamHI + HindIII} & 4.6,2.7,2.0,0.7,0.5 \\ \text {EcoRI + HindIII} & 4.0,3.4,2.0,1.1 \\ \text {BamHI }+\text {EcoRI }+\text {HindIII} & 4.0,2.7,2.0,0.7,0.6,0.5 \end{array}$$ Draw a restriction map for the plasmid that fits your data.

One of the procedures for cloning foreign DNA segments takes advantage of restriction endonucleases like HindIII (see Table 14.1 ) that produce complementary single-stranded ends. These enzymes produce identical complementary ends on cleaved foreign DNAs and on the vector DNAs into which the foreign DNAs are inserted. Assume that you have inserted your favorite gene into the HindIII site in the polycloning region of the Bluescript cloning vector with DNA ligase, have amplified the plasmid containing your gene in \(E\), coli, and have isolated a large quantity of gene/Bluescript DNA. How could you excise your favorite gene from the Bluescript vector?

(a) In what ways is the introduction of recombinant DNA molecules into host cells similar to mutation? (b) In what ways is it different?

If the sequence of base pairs along a DNA molecule occurs strictly at random, what is the expected frequency of a specific restriction enzyme recognition sequence of length (a) four and (b) six base pairs?
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