ch 12 g

What is transfection?

Introduction of viral DNA alone into bacterial cells; a type of transformation.

What is the difference between transfection and transduction?

Transfection introduces viral DNA alone, while transduction uses bacteriophages to transfer DNA between bacteria.

What is reverse transcriptase?

An RNA-dependent DNA polymerase that synthesizes complementary DNA from an RNA template.

What is a nucleic acid?

A polymer of nucleotides, such as DNA or RNA.

What is a nucleotide?

A nitrogenous base, pentose sugar, and phosphate group.

What is a nucleoside?

A nitrogenous base and pentose sugar without a phosphate group.

What is melting temperature (Tm)?

The temperature at which 50% of DNA is melted or denatured.

What is a C0t curve?

A graph showing DNA renaturation based on initial DNA concentration and time.

What does complementary mean in DNA?

The bases on opposite strands pair specifically: A with T and G with C.

What three properties must genetic material have?

Storage and expression of information, replication, and variation through mutation.

What did Griffith's experiment demonstrate?

—demonstrating that a living, harmless strain of bacteria (the R-strain) could absorb an unknown "transforming principle" from a dead, virulent strain (the S-strain) and permanently transform into a lethal, disease-causing form

A substance from heat-killed virulent bacteria could transform living avirulent bacteria into virulent bacteria.

What bacteria did Griffith use?

Streptococcus pneumoniae.

What is the difference between smooth and rough bacterial strains?

Smooth (S) strains are virulent; rough (R) strains are avirulent.

What happened when Griffith mixed living rough bacteria with heat-killed smooth bacteria?

The mouse died, and living smooth bacteria were recovered.

What did Avery, MacLeod, and McCarty demonstrate?

DNA is the transforming material responsible for bacterial transformation.

Which enzyme prevented transformation in the Avery experiment?

DNase, because it destroys DNA.

What happened when RNA or proteins were destroyed in the Avery experiment?

Transformation still occurred, showing RNA and proteins were not the transforming material.

What is transformation?

Introduction of free DNA into bacterial cells, resulting in a genetic change.

What did Hershey and Chase demonstrate?

DNA, not protein, is the genetic material in bacteriophages.

What radioactive isotope did Hershey and Chase use to label DNA?

32P (radioactive phosphorus).

What radioactive isotope did Hershey and Chase use to label protein?

35S (radioactive sulfur).

What were the results of the Hershey and Chase experiment?

32P-labeled DNA entered bacteria and appeared in progeny phages, while 35S-labeled protein remained outside.

How did transgenic experiments provide evidence that DNA is genetic material?

Eukaryotic genes inserted into bacteria produced their corresponding gene products.

Can RNA serve as genetic material?

Yes, RNA is the genetic material in some viruses, such as tobacco mosaic virus.

How do retroviruses replicate their genetic material?

Reverse transcriptase makes complementary DNA from viral RNA, which can integrate into the host genome.

What are the three components of a DNA nucleotide?

A phosphate group, deoxyribose sugar, and nitrogenous base.

What is the difference between DNA and RNA?

DNA contains deoxyribose and thymine and is usually double-stranded; RNA contains ribose and uracil and is usually single-stranded.

What is the difference between ribose and deoxyribose?

Ribose has an OH group at the 2' carbon; deoxyribose has H at the 2' carbon.

What are the purines?

Adenine (A) and guanine (G); double-ring bases.

What are the pyrimidines?

Cytosine (C), thymine (T), and uracil (U); single-ring bases.

What is DNA polarity?

DNA has a 5' end and a 3' end, giving each strand direction.

What is a phosphodiester bond?

A bond linking nucleotides between the 3' OH of one sugar and the 5' phosphate of another.

In what direction is DNA synthesized?

5' to 3'.

What are Chargaff's rules?

A = T and G = C; total purines equal total pyrimidines in double-stranded DNA.

What did Rosalind Franklin's X-ray diffraction studies reveal?

Evidence that DNA has a helical structure.

What is the Watson-Crick model of DNA?

A right-handed double helix with two antiparallel strands held together by complementary base pairing.

What does antiparallel mean?

One DNA strand runs 5' to 3', while the other runs 3' to 5'.

How many base pairs are in one turn of the DNA double helix?

10 base pairs per turn, approximately 3.4 nm.

How many hydrogen bonds form between A-T and G-C?

A-T forms 2 hydrogen bonds; G-C forms 3 hydrogen bonds.

What is GC content?

The percentage of DNA bases that are guanine or cytosine.

How does GC content affect DNA density?

Higher GC content increases DNA density.

How does GC content affect melting temperature?

Higher GC content increases Tm because G-C pairs have three hydrogen bonds compared with two in A-T pairs.

What is DNA denaturation?

Separation of complementary DNA strands by heating or high pH.

What is DNA renaturation?

Complementary single DNA strands rejoin through base pairing when conditions become favorable.

How does UV absorbance change when DNA melts?

UV absorbance at approximately 260 nm increases (hyperchromic shift).

How does genome size affect DNA renaturation on a C0t curve?

More complex genomes generally renature more slowly and appear farther to the right on the C0t curve.

What is molecular hybridization?

The binding of complementary nucleic acid strands through base pairing after denaturation.

How do molecular hybridization techniques detect specific DNA sequences?

A labeled nucleic acid probe binds to a complementary target sequence, allowing it to be detected.

What is the difference between Southern and Northern blotting?

Southern blotting detects specific DNA sequences; Northern blotting detects specific RNA sequences.