History and Structure of DNA

Study Notes

Gregor Mendel is known as the "Father of Genetics" for his experiments with plants in 1857.
DNA was first observed by Frederich Miescher in 1869.
James Watson and Francis Crick determined the structure of DNA in 1953, based on the work of Rosalind Franklin.

Nucleic acids are large biomolecules made from monomers known as nucleotides.
There are two types of nucleic acids: Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA).

DNA is a long polymer made of repeating units called nucleotides.
The base pairs that join the two strands of DNA are in a spiral staircase formation in the molecule's interior.
Hydrogen bonds hold the two strands together.
The B form of DNA is right-handed and contains 10 base pairs per turn.
The A form is similar to the B form but more compact.
The Z form is left-handed and has bases positioned toward the helix's periphery.
The DNA strands run in opposite directions, known as antiparallel, from 5' to 3'.
Covalent bonds connect the sugar and phosphates of two nucleotides, forming phosphodiester bonds.
Hydrogen bonds connect complementary nitrogenous bases. This is known as Chargaff's Rule: Adenine pairs with Thymine (A-T) and Guanine pairs with Cytosine (G-C).
DNA is the genetic material, found in the nucleus of non-dividing cells as chromatin.
Chromatin is a complex of protein and DNA.
Chromosomes are formed during cell division.

DNA is found in the nucleus, while RNA is found in the cytoplasm.
DNA contains deoxyribose sugar, while RNA contains ribose sugar.
DNA contains the bases Adenine, Thymine, Guanine, and Cytosine, while RNA contains Adenine, Uracil, Guanine, and Cytosine.
DNA is a double helix, while RNA is a single helix.
There is only one type of DNA, while there are several types of RNA: mRNA, tRNA, and rRNA.
DNA is synthesized through replication, while RNA is synthesized through transcription.
DNA functions as storage and transfer of genetic information, while RNA functions in protein synthesis through translation.

mRNAs (Messenger RNAs) code for proteins.
rRNAs (Ribosomal RNAs) form the basic structure of the ribosome and are essential for protein synthesis.
tRNAs (Transfer RNAs) adapt between mRNA and amino acids, playing a central role in protein synthesis.
snRNAs (Small nuclear RNAs) function in a variety of nuclear processes, including pre-mRNA splicing.
snoRNAs (Small nucleolar RNAs) process and chemically modify rRNAs.
miRNAs (MicroRNAs) regulate gene expression by blocking translation of specific mRNAs and causing their degradation.
siRNAs (Small interfering RNAs) turn off gene expression by directing the degradation of selective mRNAs and regulating chromatin structure.
piRNAs (Piwi-interacting RNAs) bind to piwi proteins, protecting the germ line from transposable elements.
lncRNAs (Long noncoding RNAs) act as scaffolds and regulate various cell processes, including X-chromosome inactivation.

Denaturation occurs when alkali or heat causes DNA strands to separate but doesn't break phosphodiester bonds.
Renaturation happens when separated DNA strands are brought back together through slow temperature decrease, allowing base pairs to reform.
Hybridization occurs when a single strand of DNA or RNA forms base pairs with a complementary sequence on another strand of DNA or RNA.

Mitochondrial DNA is a circular double-stranded molecule found within the mitochondrial matrix.
The mitochondrial genetic code slightly differs from genomic DNA.
Mitochondrial DNA codes for 13 protein subunits of the electron transport chain, large and small ribosomal RNA (rRNA), and 22 transfer RNAs (tRNAs).
Mitochondrial DNA is inherited maternally with mitochondria from the egg contributing entirely to the zygote.
Mitochondrial DNA has a higher mutation rate than the nuclear genome.