12-3 RNA AND PROTEIN SYNTHESIS

1. THE STRUCTURE OF RNA

RNA is made of: long chains of nucleotides Ribose Single-stranded Has Uracil instead of thymine

An RNA molecule is a working copy of a single gene Genes- coded DNA instructions that control the making of proteins w/i the cell

DISCUSS: What is a protein? List the protein you ate today and/or yesterday What role do proteins play in your body functions ?

2. TYPES OF RNA

There are 3 main types of RNA: Messenger RNA (mRNA)– carry copies instructions from genes for putting together amino acids into proteins. Carry “messages” from DNA to the rest of the cell.

Ribosomal RNA (rRNA)- makes up a major part of the ribosome (proteins are put together here)

Transfer RNA (tRNA)- transfers each amino acid to the ribosome as it is specified by coded messages in mRNA.

3. TRANSCRIPTION

Transcription happens when:  RNA polymerase connects to DNA & separates the DNA strands.  RNA polymerase (an enzyme) then uses one strand of DNA as a template (model) to put together nucleotides into a strand of RNA.  Transcription- RNA molecules are made by copying a part of the nucleotides from a DNA sequence

RNA Polymerase- an enzyme that binds to DNA & separates the DNA strands during transcription Promoters- An area of DNA nucleotide sequences where RNA begins transcription

TRANSCRIPTION

RESULTS OF TRANSCRIPTION: DNA strand: AATGCTGCGGATC mRNA strand: UUACGACGCCUAG

2. RNA EDITING

Introns- DNA sequences of nucleotides that do not code for a protein Exons- sequences that does code for a protein The introns are cut out of RNA molecules. The exons are then spliced together to form mRNA.

3. THE GENETIC CODE

Is universal in all organisms Proteins are made by putting together a lot of polypeptides. Polypeptides are a combination of any or all 20 different amino acids. The order of the amino acid determines the property of the protein mRNA’s language is called the genetic code which is 3 “letters” transcribed from DNA. The code is written using four “letters” (the bases: A, U, C, and G

Codon -three nucleotides that are next to each other on mRNA that specify a particular amino acid

THE GENETIC CODE

3. TRANSLATION

Takes place on the ribosomes Translation- the decoding of an mRNA message into a polypeptide chain (protein) 1.Translation begins when an mRNA molecule attaches to a ribosome. 2.As each codon of the mRNA molecule moves through the ribosome, the proper amino acid is brought into the ribosome by tRNA. 3.In the ribosome, the amino acid is transferred to the growing polypeptide chain.

In the process anticodons are formed Anticodon- 3 unpaired bases of tRNA that are complementary to mRNA

4. GENES & PROTIENS

THE RIBOSOME BINDS NEW TRNA MOLECULES AND AMINO ACIDS AS IT MOVES ALONG THE MRNA Start codonmRNA

PROTEIN SYNTHESIS

THE PROCESS CONTINUES UNTIL THE RIBOSOME REACHES A STOP CODON.

The sequence of bases in DNA is used as a template for mRNA. The codons of mRNA specify the sequence of amino acids in a protein.