PROTEIN SYNTHESIS

Chapter 11

RNA • Genes are coded DNA instructions that control protein production

• First, DNA must be copied to RNA• RNA structure: identical to DNA except:

• Sugar = Ribose (not deoxyribose)• N base = C, G, A, and Uracil (U) (replaces thymine)• Single-stranded

Types of RNA

•Main function RNA: to assemble amino acids into proteins

•3 Types:• Messenger RNA (mRNA): carry copies of instructions to make proteins from DNA in nucleus → cytoplasm (ribosomes)

• Ribosomal RNA (rRNA): help make ribosomes

• Transfer RNA (tRNA): transfers amino acids to ribosomes for protein assembly

Transcription• Transcription: process by which portion of DNA is copied to complementary RNA sequence inside nucleus

• Requires RNA polymerase (an enzyme)• Binds to DNA and separates

strands• Uses DNA strand as template

to make RNA complement

The Genetic Code

• “Language” of mRNA instructions

• Read 3 letters at a time, called a codon, that specify a single amino acid

• 64 total possible codons → 20 amino acids

• Example:• UCGCAG = UCG + CAG• Serine + Glutamine… →

Protein (polypeptide)

Translation• Translation: the decoding of an mRNA sequence into amino acids on ribosomes• Begins at AUG (“start” codon)

• Codons of mRNA match up with Anticodons of complementary tRNA

• Translation continues until a “stop” codon is read (UAA, UAG, UGA)

• Result is chain of new proteins!!

Protein Assembly

• Amino acids connect with peptide bonds to form proteins (“polypeptides”)

• Proper synthesis of proteins is essential to organism survival• Proteins are enzymes – control most chemical reactions • i.e.: photosynthesis, cellular respiration, etc.

• “By coding for proteins, DNA holds the key to life”• Protein Synthesis