To summarize – DNA is

• a double stranded helix
• “rungs” joined together by H bonds
• phospodiester linkages between 5’ & 3’ ends of nucleotides; 5’ 3’ direction
• contains deoxyribose sugar
• contains A, T, C, G nucleotides
• found in the nucleus of cells; some is found in the mitochondria

RNA is –

• primarily a single stranded molecule
• linked by the same type of phosphodiester bonds that join DNA together; 5’ 3’ direction
• contains ribose sugar
• contains A, U, C, G nucleotides
• 3 types of RNA – messenger, ribosomal & transfer (mRNA, rRNA, tRNA)
• found in the cytoplasm; however it is manufactured in the nucleus, so some is found there

A gene is a sequence of nucleotides that codes for a protein – so a protein is the product of hereditary information.  The human chromosomes -- 22 pairs of autosomal chromosomes and 1 pair of sex chromosomes -- contain almost 6 billion nucleotides – this is called the human genome.  Within these 6 billion nucleotides, there are about 30,000 - 40,000 protein-coding genes. This is a much smaller number than once predicted and is only twice as many as in the worm or fly – which are much smaller organisms than humans!  The gene coding regions in the human actually make up less than 5% of the 6 billion nucleotides.  Some chromosomes have a higher density of genes than others.  The function of the remaining 95% of the DNA is not clear.  Some genes are always expressed, while others are activated when they are needed.