PROTEIN SYNTHESIS

Protein Synthesis The production of polypeptide chains (proteins) Two phases: Transcription & Translation

DNA  RNA  Protein Eukaryotic Cell DNA Pre-mRNA mRNA Ribosome Protein Nuclear membrane Transcription RNA Processing Translation DNA Pre-mRNA mRNA Ribosome Protein Eukaryotic Cell

Structure of RNA Like DNA, RNA is a polymer of nucleotides. In an RNA nucleotide, the sugar ribose is attached to a phosphate molecule and to a base, either G, U, A, or C. Notice that in RNA, the base uracil replaces thymine as one of the pyrimidine bases. RNA is single-stranded, whereas DNA is double-stranded.

Genes & Proteins Proteins are made of amino acids 20 total amino acids Amino acids chains are called polypeptides

Two Parts of Protein Synthesis Transcription: DNA makes a copy of mRNA Translation: mRNA makes a chain of amino acids (protein)

Genetic Code Each three-letter unit on mRNA is called a codon The fact that the genetic code is about universal in living things suggests that the code dates back to the first organisms on earth and that all living things are related.

Notice that in this chart, each of the codons (white rectangles) is composed of three letters representing the first base, second base, and third base. For example, find the rectangle where C for the first base and A for the second base intersect. You will see that U, C, A, or G can be the third base. CAU and CAC are codons for histidine; CAA and CAG are codons for glutamine.

Transcription Translation Transcription occurs when DNA acts as a template for mRNA synthesis. Translation occurs when the sequence of the mRNA codons determines the sequence of amino acids in a protein. Translation

Transcription (DNA RNA) During transcription in the nucleus, a segment of DNA unwinds and unzips RNA polymerase joins the RNA nucleotides so that the codons in mRNA are complementary to the DNA

During transcription, complementary RNA is made from a DNA template During transcription, complementary RNA is made from a DNA template. A portion of DNA unwinds and unzips at the point of attachment of RNA polymerase. A strand of mRNA is produced when complementary bases join in the order dictated by the sequence of bases in DNA. Transcription occurs in the nucleus, and the mRNA passes out of the nucleus to enter the cytoplasm.

RNA Processing in the nucleus Pre-mRNA has introns (garbage) & exons (code) Cut introns out intron exon exon intron splicesome exon

Messenger RNA (mRNA) Primary structure of a protein A U G C aa1 aa2 start codon codon 2 codon 3 codon 4 codon 5 codon 6 codon 7 codon 1 methionine glycine serine isoleucine alanine stop codon protein Primary structure of a protein aa1 aa2 aa3 aa4 aa5 aa6

Transfer RNA (tRNA) Transports amino acids to the mRNA Have anticodons that are complementary to mRNA codons

Ribosomes Large subunit P Site A Site mRNA A U G C Small subunit

Translation (RNA Protein) Happens in the ribosome Three steps: 1. initiation: start codon (AUG) 2. elongation: amino acids linked 3. termination: stop codon Let’s Make a Protein !