Molecular Genetics: DNA and Genetic Code

Molecular Basis of Inheritance - Key Concepts

• Nucleotides in a DNA strand are linked by phosphodiester bonds.
• A nucleoside lacks a phosphate group when compared to a nucleotide.
• Deoxyribose and ribose are pentoses.
• Purine-pyrimidine base pairing in DNA double helix results in uniform width throughout DNA.
• DNA has a net negative electric charge and histones have a net positive charge.

Transcription and Genetic Code

• The promoter and terminator sites for transcription are located at the 5' (upstream) and 3' (downstream) ends respectively.
• Sickle cell anemia is a molecular disease.
• AUG codes for methionine and acts as an initiation codon in both prokaryotes and eukaryotes.
• DNA can be the first genetic material.
• Mature mRNA in eukaryotes contain exons but not introns.
• Human chromosome 1 has the highest and chromosome Y has the least number of genes.

DNA Structure and Function

• Rosalind Franklin did not contribute to the development of the double helix model of DNA.
• DNA nucleotides are linked by 3'-5' phosphodiester bonds; preventing polymerization can be achieved by removing/replacing the 3' OH group in deoxyribose.
• Discontinuous DNA synthesis occurs because DNA polymerase can only catalyse polymerisation in one direction (5' → 3').
• RNA polymerase catalyzes elongation during transcription.
• Gene expression in prokaryotes is controlled at the transcription level.
• Regulatory proteins in prokaryotes can act as activators and repressors in transcription.
• Chromosome 1 was the last human chromosome to be completely sequenced.
• RNA functions as a carrier of genetic information, carries amino acids to ribosomes and is a constituent component of ribosomes.

DNA Analysis and Genetic Processes

• Chargaff's rule can be used to conclude that the DNA in the sample is double stranded linear DNA.
• In some viruses, DNA is synthesised by using RNA as template, such a DNA is called cDNA.
• The RNA polymerase holoenzyme transcribes the promoter, structural gene, and the terminator region.
• The tRNA sequence pairing mRNA codon 5'-AUG-3' must be 5'-CAU-3'.
• Amino acids attach to the tRNA at its 3' end.
• mRNA first binds to the smaller ribosomal sub-unit to initiate translation.
• In E. coli, the lac operon is switched on when lactose is present and binds to the repressor.