DNA: the Molecule of Heredity

DNA DNA is a long molecule made of repeating subunits called nucleotides Nucleotides have three parts sugar phosphate and a nitrogenous base. The sugar and phosphates make up the back bone of the DNA and the nitrogen base are in the middle.

The 4 nitrogenous bases

How do the nitrogenous bases link together in the double helix of DNA? Adenine (A) always links with Thymine (T) Cytosine always links with Guanine (G) This specific pairing of nitrogenous bases is known as BASE PAIRING

The importance of Nucleotide Sequence The sequence of nucleotides forms the unique genetic information of an organism Everyone’s sequence is unique!! This is why DNA can be used in forensic science.

DNA and genes The sequence of nucleotides in DNA contain information. This information is put to work through the production of proteins which create key structures of the organism. This protein production occurs in two steps. First transcription and then translation

Transcription Enzymes in the cell “unzip” a portion of the double helix of DNA. mRNA uses the DNA’s nucleotide sequence to form a an corresponding mRNA strand (as seen on figure on the right) The base pairing is the same for mRNA and it is for DNA except for instead of Thymine, Adenine is paired with a nitrogenous base called uracil

Translation mRNA formed during transcription detaches from the DNA and goes to a Ribosome. The ribosome “reads” the mRNA sequence with the help of tRNA. As the mRNA strand is “read” amino acids bind together to create proteins.

Translation

Mutations Mutation: as change in DNA sequence is called a mutation Mutations can be caused by errors in the following: –Replication –Transcription –Cell division –or external agents (ie: sun creates cancer) Any agent that can cause a change in DNA is called mutagen Skin cancer tumor

Affects of mutation Could have little or no harmful effect or it could be debilitating to the organism or even fatal

Types of Mutation Point mutation Frame shit mutation Chromosomal mutations

Point Mutation A point mutation is a change in a single base pair in DNA. Can cause the mRNA to be read wrong in the ribosome during translation.

Frameshift mutation Frameshift mutation: is when a single base is added or deleted from DNA. This causes the entire sequence to “shift” when being read by the ribosome therefore completely changing the structure of the protein These tend to affect an organism much more Than a point mutation

Chromosomal Mutation Chromosomal mutation: structural changes in the chromosome These changes could happen when: –When parts are broken off and lost during mitosis and meiosis. –When chromosome break and rejoin incorrectly. Typically fatal