Protein Synthesis Jan 2006

The Link Between Genes and Proteins Slide # 2 The Link Between Genes and Proteins 1. Gene: portion of DNA that codes for a protein that controls a trait. 2. Two types of proteins Structural proteins: determine how we look EX: Hair & skin color; ear lobe shape Enzymes: determine how we function Control every chemical reaction in the body EX: Sucrase breaks down sucrose (table sugar) 3. DNA (gene)  Protein Trait Detached ear lobes Attached ear lobes Jan 2006

Overview of RNA and Protein Synthesis Slide # 3 Sequence (order) of nitrogen bases of a gene determines the genetic instructions or “genetic code” of an organism. DNA NEVER leaves the nucleus, but the code (gene) must be read so that proteins can be made. RNA makes a copy of DNA code of a gene. One strand of the DNA code is copied by RNA RNA carries the copied code out of the nucleus to the ribosome. The ribosome “reads” the code & makes the protein. DNA code Jan 2006

Comparison of DNA and RNA Nucleotides Slide # 4 Comparison of DNA and RNA Nucleotides Structure of DNA Nucleotide Structure of RNA Nucleotide Nitrogen Bases: adenine, thymine, guanine, & cytosine Nitrogen Bases: adenine, uracil, guanine, & cytosine Jan 2006

Comparison of DNA and RNA Slide # 5 3 Main differences between DNA & RNA Sugar: DNA: Deoxyribose RNA: Ribose Nitrogen Bases: DNA: A, T, C, G RNA: A, U, C, G U = uracil Number of strands that make up the molecule: DNA: two strands RNA: one strand DNA RNA Jan 2006

Types of RNA Messenger RNA = mRNA Slide # 6 Messenger RNA = mRNA Copies instructions from DNA code; carries code out of nucleus to ribosome 2. Ribosomal RNA = rRNA Ribosomes are made of protein and RNA 3. Transfer RNA = tRNA Carries and transfers a specific amino acid to the amino acid chain assembled by the ribosome T-shape mRNA rRNA tRNA Jan 2006

How Proteins are Made: Protein Synthesis Slide # 7 How Proteins are Made: Protein Synthesis Step 1: Transcription Transcription: a single strand of mRNA is copied from DNA in the nucleus DNA unwinds – sides of ladder separate An enzyme (RNA polymerase) “reads” DNA bases and makes the RNA strand If DNA is TACCAGTTT mRNA will be c. mRNA is removed and DNA strands will re-join & re-coil back into the spiral AUGGUCAAA Jan 2006

How Proteins are Made: Protein Synthesis Slide # 8 Step 2: mRNA editing mRNA editing: cutting and splicing mRNA before it leaves the nucleus Introns- (intruders--“junk DNA” ) are cut out Exons- “good DNA” are left Exons are “sewn” together to create an edited version of mRNA Edited mRNA is sent out of nucleus to ribosome Introns are removed and exons are spliced together. This is the message that is translated. Jan 2006

How Proteins are Made: Protein Synthesis Slide # 9 Step 3: Translation How the code is read: Every 3 bases on mRNA represents a code for an amino acid (building block of protein) Every 3 bases on mRNA is called a codon. Amino acids are abbreviated most times by using the first 3 letters of the amino acid’s name. Met = methonine Leu = leucine Jan 2006

Reading the Codon Chart Slide # 10 Reading the Codon Chart Examples: AUG = Methionine CAU = Histidine UAG = Stop (Column) First Position (row) Third Position (line) Try these: GCU: UAC: CUG: UUA: Answers: Alanine Tyrosine Leucine This chart only works for mRNA codons. Jan 2006

How Proteins are Made: Protein Synthesis Slide # 11 How Proteins are Made: Protein Synthesis Step 3: Translation Edited mRNA is sent out of nucleus to ribosome Ribosome reads the codons on mRNA Codon on mRNA specifies which tRNA brings in the designated amino acid Notice the anticodon on tRNA Anticodon “reads” the codon on mRNA Ribosome joins the amino acids together with chemical bonds called peptide bonds to build an amino acid chain called a “polypeptide” DNA (gene) RNA  Protein Trait Jan 2006

Translation Nucleus mRNA  t RNA  Anticodon Ribosome mRNA  Slide # 12  Translation Nucleus mRNA  Lysine Phenylalanine t RNA Methionine  Anticodon Ribosome mRNA  Start codon Go to Section: Jan 2006

Translation Growing polypeptide chain The Polypeptide “Assembly Line” Slide # 13 Translation Growing polypeptide chain The Polypeptide “Assembly Line” Ribosome tRNA Lysine tRNA mRNA Completing the Polypeptide mRNA Translation direction Ribosome Go to Section: Jan 2006