chromosome – A discrete unit of the genome carrying many genes.
◦ Each chromosome consists of a very long molecule of duplex DNA and an approximately equal mass of proteins, and is visible as a morphological entity only during cell division.
structural gene – A gene that codes for any RNA or polypeptide product other than a regulator.
Bacterial transformation provided the first support that DNA is the genetic material of bacteria. During transformation, genetic properties can be transferred from one bacterial strain to another by extracting DNA from the first strain and adding it to the second strain.
The DNA of S-type bacteria can transform R-type bacteria into the same S-type
transforming principle –DNA that is taken up by a bacterium and whose expression then changes the properties of the recipient cell. Phage infection showed that DNA is the genetic material of viruses. When the DNA and protein components of bacteriophages are labeled with different radioactive isotopes, only the DNA is transmitted to the progeny phages produced by infecting bacteria.
DNA can be used to introduce new genetic traits into animal cells or whole animals. transfection – In eukaryotic cells, the acquisition of new genetic markers by incorporation of added DNA. In some viruses, the genetic material is RNA.
Eukaryotic cells can acquire a new phenotype as the result of transfection The genetic material of phage T2 is DNA
A nucleoside consists of apurine or pyrimidine base linked to the 1′ carbon of a pentose sugar. The difference between DNA and RNA is in the group at the 2′ position of the sugar.
◦ DNA has a deoxyribose sugar (2′–H); RNA has a ribose sugar (2′–OH).
A nucleotide consists of a nucleoside linked to a phosphate group on either the 5′ or 3′ carbon of the (deoxy)ribose. DNA contains the four bases adenine,guanine, cytosine, and thymine; RNA has uracil instead of thymine.
Successive (deoxy)ribose residues of a polynucleotide chain are joined by a phosphate group between the 3′ carbon of one sugar and the 5′ carbon of the next sugar. One end of the chain (conventionally written on the left) has a free 5′ end and the other end of the chain has a free 3′end.
A polynucleotide chain
Supercoiling occurs only in “closed” DNA with no free ends. supercoiling – The coiling of a closed duplex DNA in space so that it crosses over its own axis.
A supercoiled DNA has a twisted and condensed form
Closed DNA is either circular DNA or linear DNA in which the ends are anchored so that they are not free to rotate.
The B-form of DNAis a double helix consisting of two polynucleotide chains that run antiparallel.
A polynucleotide chain
The nitrogenous bases of each chain are flat purine or pyrimidine rings that face inward and pair with one another by hydrogen bonding to form only A-T or G-C pairs. complementary – Base pairs that match up in the pairing reactions in double helicalnucleic acids (A with T in DNA or with U in RNA, and C with G).
Flat base pairs lie perpendicular to the sugar-phosphate backbone
The diameter of the double helix is 20 Å, and there is a complete turn every 34 Å, with ten base pairs per turn (~10.4 base pairs per turn in solution). The double helix has a major (wide) groove and a minor (narrow) groove.
semiconservativereplication – DNA replication accomplished by separation of the strands of a parental duplex, each strand then acting as a template for synthesis of a complementary strand. The sequences of the daughter strands are determined by complementary base pairing with the separated parental strands.
Base pairing provides the mechanism for replicating DNA