DNA

• DNA is a molecule of nucleic acid
• DNA stands for deoxyribonucleic acid
• DNA contains all of the chemical information (instructions) needed for determining one's traits
• A DNA molecule is made up of repeating subunits called nucleotides
• Each nucleotide is identified by a characteristic section known as a nitrogen base
• There are 4 different nitrogen bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G)
• The shape of DNA is described as a double helix
• The double helix is two strands that twist around each other, like a spiral staircase
• The two strands attach at the complementary nitrogen bases
• The double helix model was developed by Dr. James Watson and Dr. Francis Crick after interpreting an x-ray photo taken by Rosalind Franklin
• A DNA strand is constructed of repeating units of nucleotides
• Each nitrogen base has a complementary base
• Adenine binds to Thymine
• Cytosine binds to Guanine
• DNA makes up rod-shaped structures called chromosomes
• Chromosomes are composed of DNA and proteins
• Chromosomes are found in the nucleus of a cell
• Humans have 23 pairs of chromosomes (46 total) in the nucleus of each cell
• A gene is a specific section of DNA that codes for the production of a particular protein, which determines the presence or absence of a trait
• While genes are thousands of base pairs long, they are divided into triplet sets known as "codons"
• Each codon corresponds to a single amino acid, which, when assembled into a long chain, form a protein
• A change in the DNA sequence is known as a mutation
• This mistake can cause a cell to produce an incorrect protein
• The organism's trait will be different from what it might have been
• The effect of a mutation can result in:

  • No effect
  • Different protein made
  • Malfunction of protein
• Proteins are made when the body uses the information contained in genes
• Proteins are made in two stages:

  • Stage 1: The process by which a strand of "messenger" RNA is copied from the sequence of bases along a gene (a section of DNA)
  • Stage 2: The process by which amino acids are assigned to each codon to make a protein
• RNA is needed for the production of proteins
• Differences between RNA and DNA:

  • Sugar in DNA is deoxyribose; in RNA it is ribose
  • Bases in DNA are ATCG; in RNA they are AUCG
  • DNA is made of two strands; RNA is made of one strand
  • DNA is found in the nucleus; RNA is found in the nucleolus
• DNA tells the body which proteins to make, and the presence or absence of those proteins result in the appearance of an organism's traits
• During transcription, RNA copies the code from DNA
• mRNA carries the coded message out into the cytoplasm and arrives at an organelle called a ribosome, where it is "decoded"
• At the ribosome, every 3 bases of the mRNA sequence - every codon - is assigned a single amino acid that recognizes that specific sequence. Amino acids are assembled one by one into a long chain, ultimately forming a protein. This process is called translation
• DNA is referred to as the universal code, and the code is the same in all living things
• Transcription - DNA gene sequence is copied onto a strand of mRNA
• Translation - the mRNA is "decoded" by the ribosome by assigning amino acids in a specific order to create a protein
• Replication is the process by which DNA copies itself before a cell divides in half; this gives the new cell an exact copy of all the information contained in DNA
• Steps of Replication:

  • First, the DNA unzips, causing the two strands to separate
  • Next, free-floating nucleotides found in the nucleus align with their complementary bases along each original strand, resulting in two identical DNA molecules
  • The result is two identical DNA molecules, each possessing a strand of the original molecule and one strand newly constructed complementary strand