Molecular Genetics

• Each gene codes for a specific protein

• Gene expression is the conversion of a gene into a specific trait

• Transcription occurs in the nucleus

• Translation occurs in the cytoplasm

Rna:

• Contains sugar ribose

• Single stranded

• Uracil (U) pairs with A

• Messenger RNA, Transfer RNA, ribosomal RNA

Transcription continued

• RNA Polymerase binds to open the double helix at the beginning of a gene

• Initiation: Recognizes the promoter sequence and begins to transcribe the DNA into an mRNA strand. Promoter indicates which DNA strand should be transcribed/where it should start.

• Elongation: RNA Polymerase builds an mRNA strand in 5’ to 3’ direction using the DNA as a template

• Termination: RNA polymerase passes the end of a gene and comes to a stop. mRNA is released

Translation (mRNA to protein)

• mRNA → chain of amino acids (polypeptides)

• mRNA leaves the nucleus and joins to a ribosome in cytoplasm

• 20 amino acids each coded for by a triplet of RNA nucleotides called a codon

• 64 possible codon codes

Ribosome binds to the mRNA and translation begins at the start codon (AUG). As ribosome moves, it reads 3 bases at a time.

• tRNA molecules in the cytoplasm carry a specific amino acid

• tRNA has an anticodon sequence of 3 complementary bases that connects to the mRNA. Drops off amino acid.

Ribosome shifts over to next codon on the mRNA and next corresponding tRNA attaches with the amino acid. Two tRNAs can attach at one time as the ribosome has 3 binding sites.

• Introns are sections of non-coding DNA that interrupt the codon sections (exons) of the gene

• Must be spliced out by spliceosome before the mRNA is translated.