DNA → RNA→ Protein Sec. 12.3, DNA, RNA, and Protein Main Idea—DNA codes for RNA, which guides protein synthesis. The central dogma of biology: DNA codes for RNA, which guides the making of proteins (which determines the traits!). DNA → RNA→ Protein

RNA (Ribonucleic Acid) There are 3 main differences between DNA and RNA: RNA is single stranded RNA has ribose sugar RNA has uracil instead of thymine

3 Types of RNA Messenger RNA (mRNA)—formed complementary to 1 strand of DNA Travels from the nucleus to the ribosome to “direct” the making of protein.

Ribosomal RNA (rRNA)—associates with ribosomes to “read” the messenger RNA

Transfer RNA (tRNA)—small segments that transport amino acids to the ribosome Amino acids are the subunits (smaller parts) that make up proteins.

Transcription Transcription—mRNA is made from DNA mRNA is made in the nucleus but can leave through the nuclear pores. mRNA has U instead of T.

The Code DNA is used to make mRNA, and mRNA codes for amino acids that make up proteins. There are 20 amino acids that are used to make proteins.

Amino Acids Amino acids are coded for by 3-base sequences called codons. Example—GCG (codon) codes for alanine (amino acid)

Since there are 4 bases, there are 64 codons. (43 = 64). So, most amino acids have more than 1 codon.

There are special codons to signal “start” and “stop.” AUG is the start codon (it also codes for methionine). UAA, UGA, and UAG are stop codons.

Translation Translation—the mRNA code is read and translated to make protein tRNA carries amino acids to the mRNA/ribosome unit to join the protein. tRNA has an anticodon that allows it to temporarily join with mRNA during this process.