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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