Chapter 13 –RNA and Protein Synthesis Section 1 - RNA

RNA RNA stands for RiboNucleic Acid RNA is a nucleic acid; therefore, made of nucleotides RNA works with DNA to make proteins Proteins are made through a process called protein synthesis Review: Proteins are made of amino acids Review: Proteins are made by ribosomes

Phosphate Nitrogen Base Guanine Cytosine Adenine Thymine (only in DNA) Uracil (only in RNA) 5 – Carbon Sugar - Ribose (if RNA) - Deoxyribose (if DNA)

Differences between RNA and DNA Has the sugar deoxyribose Double stranded - double helix Has thymine RNA Has the sugar ribose Single stranded Has uracil

The Nucleotides of RNA

DNA has the 5-carbon sugar, deoxyribose. RNA has the 5-carbon sugar, ribose. DNA has thymine, adenine, cytosine and guanine. RNA has uracil, adenine, cytosine and guanine. DNA is a double stranded molecule. It has base-pairs with hydrogen bonds between the nitrogen bases. The molecule is anti-parallel. RNA is a single stranded molecule.

3 types of RNA There are 3 major types of RNA: Messenger RNA (mRNA) – carries the genetic code from DNA to the ribosome (site of protein synthesis) Ribosomal RNA (rRNA) – makes the two subunits of ribosomes Transfer RNA (tRNA) – transports amino acids (monomers of proteins) to the ribosomes

3 types of RNA Messenger RNA (mRNA) – carries code from DNA to ribosome for protein synthesis Ribosomal RNA (rRNA) – assembles amino acids brought by tRNA in a specific order from mRNA to make proteins; made of RNA by the nucleolus Transfer RNA (tRNA) – transports specific amino acid to ribosome for protein synthesis

Production of RNA RNA is made through a process called transcription “trans” – across “script” – to write DNA is split and one strand forms a template A sequence of DNA that codes for a protein is known as a gene There are portions of DNA that do not code for protein

Transcription DNA template is formed when it untwists and hydrogen bonds between nitrogen bases are broken RNA polymerase (an enzyme) binds complementary nucleotides to the template Places Cytosine with Guanine Places Adenine with Thymine Places Guanine with Cytosine . . . BUT Place URACIL with Adenine RNA DOES NOT HAVE THYMINE!!

Transcription

Transcription DNA “unzips” One side of DNA becomes a template Free nucleotides of RNA attach to open sites of the template by RNA Polymerase (not shown) Cytosine attaches to Guanine Uracil attaches to Adenine Guanine attaches to Cytosine Adenine attaches to Thymine Messenger RNA is produced and released mRNA is edited Introns removed Exons spliced together mRNA goes to ribosomes for protein synthesis

Another look at transcription . . .

Transcription (cont’d) Transcription starts at a location called the promoter Promoter is a specific sequence of DNA that starts transcription Pre-RNA is produced Introns are cut out and thrown out Exons are spliced together to form mRNA mRNA is sent to ribosomes to be decoded

Editing/Refining Introns and Exons are processed Introns are removed and exons are placed together Exons are expressed; introns disappear Purpose of introns are not known

A sequence of nitrogen bases on a segment of DNA of one of its strands that actually carries instructions for the order of amino acids in a protein is called a gene. When DNA separates, one side becomes the template. Which side is the template? The side that is a code for a protein! After transcription, a molecule of mRNA with codons is produced. During translation, each codon of mRNA is matched with an anti-codon on a tRNA molecule with the amino acid it carries.