Protein Synthesis PROTEIN SYNTHESIS n Protein synthesis involves

Protein Synthesis

PROTEIN SYNTHESIS

n Protein synthesis involves two types of nucleic acids: DNA (deoxyribonucleic acid) RNA (ribonucleic acid)

Differences Between DNA and RNA DNA double-stranded RNA single-stranded sugar = deoxyribose sugar = ribose bases = A, T, C, G bases = A, U, C, G (uracil takes the place of thymine)

RNA n RNA, like DNA, is a polymer formed by a sequence of nucleotides

Free Nucleotide

Protein Synthesis involves two processes: 1. Transcription: the copying of the genetic instructions (DNA) into a molecule of m. RNA 2. Translation: m. RNA is used to assemble an amino acid sequence into a polypeptide (protein)

Pathway to Making a Protein DNA Transcription m. RNA Translation Protein

Transcription n Process in which genetic instructions are transcribed (rewritten) to form an RNA molecule. n occurs in the nucleus of eukaryotic cells n Transcription occurs in 3 major steps:

Step 1: n RNA polymerase (enzyme) binds to the promoter. – Promoter – a specific nucleotide sequence of DNA that initiates transcription. (“START” sequence) n DNA strand unwinds and separates

Step 2: n RNA polymerase adds free RNA nucleotides that are complementary to the nucleotides on one of the DNA strands.

Complementary Pairings: EXAMPLE: DNA RNA A = U T = A C = G G = C A = U C = G

Step 3: n RNA polymerase reaches the “termination signal” sequence of nucleotides that marks the end of transcription. n RNA polymerase releases both the DNA strand the newly formed RNA strand.

n The RNA made during transcription can be any of the three types of RNA: 1. messenger RNA (m. RNA) 2. transfer RNA (t. RNA) 3. ribosomal RNA (r. RNA)

Transcription Animation

Translation (Protein Synthesis) RNA protein

Translation n occurs in the cytoplasm of the cell, at the ribosome n All RNAs needed in translation – m. RNA, t. RNA, and r. RNA

Messenger RNA (m. RNA) n Carries coded instructions for protein synthesis (translation) – From the DNA in the nucleus to the ribosome

The genetic code n Codons – instructions for making a protein, a series of three nucleotides on the m. RNA – Each codon signifies start, stop, or an amino acid

The genetic code

Transfer RNA (t. RNA) n Brings amino acids to the ribosome so it can build proteins n It has Anticodons – 3 nucleotide sequence complementary to the m. RNA codon

Ribosomal RNA (r. RNA) n Makes up ribosomes

Translation Step 1: n m. RNA from nucleus Through cytoplasm to the ribosome m. RNA start codon AUG signals beginning of protein

Translation Step 2: n t. RNA with the complementary anticodon carries amino acid (a. a. ) to bind to the codon

Translation Step 3: n Enzymes help form peptide bonds between amino acids Peptide bond

Translation Step 4: n This continues until a stop codon is reached n Protein is released into the cell

Translation Animation