Module 1: DNA and Gene Structure

• DNA is vital for all living things and holds the instructions for an organism's development, survival and reproduction.
• DNA is very stable and serves as a long-term storage of information.
• DNA is a polymer with nucleotides as its monomers.
• Each nucleotide has three parts: sugar (2' deoxyribose), phosphate groups, and base.
• There are four bases in DNA: adenine and guanine are purines, cytosine and thymine are pyrimidines.
• The four bases are attached to sugar with a β-N-glycosidic bond.
• Chargaff's Rule states that the total number of purines in a DNA molecule is equal to the total number of pyrimidines.
• The names of the four nucleotides are 2' -deoxy--- 5' -triphosphate, insert the bases ---: adenosine, guanine, cytidine and thymidine

  *joined by 5'-P terminus (a phosphodiester bond) to 3'-OH terminus (5-3 direction)
• DNA has a direction, for example, 5'  3'.
• Nucleotides are joined together to form the DNA polymer by phosphate-deoxyribosyl linkage.
• Z-DNA is found naturally with B-DNA but only in certain regions.
• B-DNA has a function in biology but the function of Z-DNA is still not clear.
• The amount of G + C nucleotides in an organism’s DNA is called its GC content.
• The bonding between the two strands of the DNA double helix is called complementary base-pairing, where A pairs with T, G pairs with C.
• The two strands of the DNA double helix are held together by base-pairing and hydrogen bonds.
• In living cells, DNA is a double helix made up of two polynucleotide strands.
• A-DNA is rare and only forms when there is not enough water around – dehydrating conditions.
• Important features of the DNA double helix include the two strands being antiparallel, there being a major and a minor groove, and the DNA helix can exist in different forms.
• Chargaff's Rule states that the total number of purines in a DNA molecule is equal to the total number of pyrimidines.
• Human DNA has a GC content of 40.3%.
• Plasmodium falciparum, which causes malaria, has a GC content of 19.0%.
• There are three types of DNA double helix: B-DNA, A-DNA, and Z-DNA.
• Streptomyces griseolus, a soil bacteria, has a GC content of 72.4%.
• B-DNA is the most common and predominant form of DNA.
• Genes are the functional units of the genome and code for the proteins and RNAs that are required for cell function.
• Gene families play a role in the evolution and diversity of multicellular organisms.
• A gene is a segment of a DNA molecule and the DNA sequence within this segment contains biological information.
• The unit of length of a DNA molecule is the base pair (bp).
• 1 kilobase pair (kb) equals 1 megabase pair (Mb) in the human genome.
• The shortest genes are about 100 bp, for example, tRNAs, and the longest genes are about 2,400,000 bp, for example, human muscle protein dystrophin.
• Many genes are discontinuous and are split into exons which contain information to make a protein and introns which contain information not needed to make a protein.
• In many genes, the introns can make up almost 90% of the total length.
• The average human gene contains 8 introns and 9 exons.
• The mean intron length is 3365 bp and the mean exon length is 145 bp.
• The information carried by a gene is the nucleotide sequence.
• The information is read by the process called gene expression.
• Proteins and RNAs are the functional end products of gene expression.
• In a complex multigene family, the genes are not identical but have similar DNA sequences.
• These are ones where the gene product is needed in large amounts, examples are the ribosomal RNA genes.
• The genes in a multigene family arise by gene duplication.