THE GENETIC CODE OF GENES AND GENOMES

Paran, Lariza Mhay D.Valente, Marielle Julia F.

DNA: Molecule of Heredity

Inherited traits are affected by genes that are transmitted from parents to offspring in reproduction

Genes are composed of the chemical deoxyribonucleic acid = DNA

DNA: Molecule of Heredity

DNA was discovered by Friedrich Miescher in 1869

In 1920s microscopic studies with special stains showed that DNA is present in chromosomes

In 1944 Avery, McLeod and McCarty provided the first evidence that DNA is the genetic material

Griffith's experiment demonstrating bacterial transformation

Avery, McLeod and McCarty identified DNA as the chemical substance responsible for changing rough, nonvirulent cells of

S pneumoniae (R) into smooth encapsulated infectious cells (S)

DNA Structure: Double Helix

In 1953 Watson and Crick proposed the three dimensional structure of DNA

Molecular structure of DNA is a double-stranded helix comprised of a linear sequence of paired subunits = nucleotides

Each nucleotide contains any one of four bases =

adenine, thymine, guanine and cytosine

Pairing between nucleotides of the double helix is complementary: adenine pairs with thymine guanine pairs with cytosine

DNA Structure: Double Helix

DNA backbone forms right-handed helix

Each DNA strand has polarity = directionality

The paired strands are oriented in opposite directions = antiparallel

Central Dogma

Mutations

Mutation refers to any heritable change in a gene

The change may be: substitution of one base pair in DNA for a different base pair; deletion or addition of base pairs

Any mutation that causes the insertion of an incorrect amino acid in a protein can impair its function

NORMAL, WILD TYPEMUTATION INACTIVATES

ENZYME

DNA STRUCTURE, REPLICATION, AND

MANIPULATION

GENOME SIZE

•The genetic complement of a cell or virus constitutes its genome•In eukaryotes, this term is commonly used to refer to one complete haploid set of chromosomes, such as that found in a sperm or egg•The C-value = the DNA content of the haploid genome

DNA:Chemical Composition

DNA is a linear polymer of four deoxyribonucleotides

Nucleotides composed of 2'- deoxyribose (a five-carbon sugar), phosphoric acid, and the four nitrogen-containing bases denoted A, T, G and C

DNA: Chemical Composition

Two of the bases, A and G, have a double-ring structure; these are called purines

The other two bases, T and C, have a single-ring structure; these are called pyrimidines

DNA Sructure

The duplex molecule of DNA consists of two polynucleotide chains twisted around one another to form a right-handed helix in which the bases form hydrogen bondsAdenine pairs with thymine; guanine with cytosine.A hydrogen bond is a weak bond . The stacking of the base pairs on top of one another also contribute to holding the strands together. The paired bases are planar, parallel to one another, and perpendicular to the long axis of the double helix.

• The backbone of each polynucleotide strand consists of deoxyribose sugars alternating with phosphate groups that link 5 ' carbon of one sugar to the 3' carbon of the next sugar in line• The two polynucleotide strands of the double helix run in opposite directions • The paired strands are said to be antiparallel

DNA Replication

Watson-Crick model of DNA replication:

Hydrogen bonds between DNA bases break to allow strand separationEach DNA strand is a template for the synthesis of a new strandTemplate (parental) strand determines the sequence of bases in the new strand (daughter)= complementary base pairing rules

Replication of Linear DNA

The linear DNA duplex in a eukaryotic chromosome also replicates bidirectionally

Replication is initiated at many sites along the DNA

Multiple initiation is a means of reducing the total replication time

DNA Synthesis

One strand of the newly made DNA is synthesized continuously = leading strand

The other, lagging strand is made in small precursor fragments = Okazaki fragments

The size of Okazaki fragments is 1000–2000 base pairs in prokaryotic cells and 100–200 base pairs in eukaryotic cells.

Nucleic Acid Hybridization

DNA denaturation: Two DNA strands can be separated by heat without breaking phosphodiester bonds

DNA renaturation = hybridization: Two single strands that are complementary or nearly complementary in sequence can come together to form a different double helix

Single strands of DNA can also hybridize complementary sequences of RNA