History

• Frederick Griffith (1928) – experimented with pneumonia – ability to cause disease was inherited by the transformed bacteria’s offspring, the transforming factor might be a gene

• Oswald Avery (et al.) (1944) – nucleic acid DNA stores and transmits the genetic information from one generation of an organism to the next (genes are composed of DNA)

Cont.

• Hershey-Chase (1952) – genetic material of the bacteriophage was DNA, not protein

• Watson-Crick – develop the double-helix model of the structure of DNA

• Gilbert-Maxam-Sanger (1977)-develop methods to read the DNA sequence

• Human Genome Project (2000) – sequence all human DNA

Function of DNA

• 1. genes have to carry information from one generation to the next

• 2. put information to work by determining the heritable characteristic of organisms

• 3. genes have to be easily copied

Components

• DNA – long molecule made up of units celled nucleotides

• Nucleotides:– 5-carbon sugar– Phosphate group– Nitrogenous base

Cont.

• Purines:

• Adenine and guanine

• Pyrimidines:

• Cytosine and thymine

• Form chains in A=T and G=C (Chargaff’s rules)

• Base pairing – hydrogen bonds form between certain bases

Cont.

• Chromatin – DNA and a protein (histones) called nucleosomes

• Nucleosomes can fold DNA into tiny space

Replication

• Each strand of DNA in the double helix has the exact information needed to copy itself

• Produces two new complementary strands following the rules of base pairing

• Each strand of the double helix of DNA serves as a template for the new strand

Cont.

• Replication – duplicates its DNA (replication forks)

• Enzymes “unzip” by breaking the hydrogen bond

• DNA polymerase is the enzyme used in replication and “proofreads” the DNA to maximize the perfect copy of DNA

RNA and Protein Synthesis

• RNA –long chain of nucleotides of sugar, phosphate and base

• Differences:– Ribose (sugar)– Generally single-stranded– Contains uracil in place of thymine

Cont.

• Three main types of RNA: mRNA, rRNA, and tRNA

• mRNA: carry copies of instructions for assembling amino acids into proteins; serve as a “messenger” for DNA to rest of the cell

• rRNA: proteins are assembled on ribosomes

Cont.

• tRNA: transfers each amino acid to the ribosome as it is specified by coded messages in mRNA

• Transcription: RNA polymerase binds to DNA and separates the DNA strand, RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of RNA

Cont.

• RNA polymerase enzyme will only bind to DNA regions where promoters are present, which have specific base sequences

• Introns are not involved in coding proteins, exons are the DNA sequences that code for proteins and are “expressed” in the synthesis of proteins

Cont.

• Introns are removed from the final RNA molecule and the exons are spliced together to from the mRNA

• Proteins form from long chains of amino acids called polypeptides – containing and or all of the 20 different amino acids

• mRNA’s “language” of instructions is called the genetic code

Cont.

• Bases on RNA – A, U, C, G read 3 letters at a time, each coded “word” is called a codon and will represent a specific amino acid or stop codons

• Translation - decoding or reading of codons takes place in ribosomes, and uses information from mRNA to produce proteins

Steps in RNA

• 1. mRNA transcribes from DNA in nucleus and released into cytoplasm

• 2. mRNA in cytoplasm attaches to ribosome and each codon of mRNA moves through the ribosome and specific amino acid is transferred to polypeptide chain ---tRNA has 3 unpaired bases called anticodon

Mutations

• Mutations – mistakes (harmful/beneficial)

• Changes in genetic material

• Point mutation happens at a single point in a base and includes: substitution, deletion, and insertion and are called frame shift mutations

• Causes can be dramatic as code has “shifted” from that point on

Cont

• Chromosomal mutations

• Deletion – loss of all or part of chromosome

• Duplication – extra copy is produced

• Inversion – reverses the direction of parts of chromosomes

• Translocation – chromosome breaks off and attached to another

Cont.

• Harmful – cause many genetic diseases (Down Syndrome, Turner’s syndrome, Fragile X syndrome and cancers)

• Beneficial – large crops, allows for variations in species

Progeria

22q11 deletions

Wolf-Hirschhorn

Neurofibromatosis

Proetus Syndrome

Regulation

• Operon – group of genes that operate together

• Eukaryotic genes are controlled individually and have regulatory sequences that are complex

• Differentiation – specialized structure and function

• Hox genes – control cells and tissues