Protein Synthesis

PROTEIN SYNTHESIS

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

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

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

Free Nucleotide

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

Pathway to Making a Protein DNA mRNA Protein Transcription Translation

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

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

Step 2: 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

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

The RNA made during transcription can be any of the three types of RNA: messenger RNA (mRNA) transfer RNA (tRNA) ribosomal RNA (rRNA)

Transcription Animation

Translation (Protein Synthesis) RNA  protein

Translation occurs in the cytoplasm of the cell, at the ribosome All RNAs needed in translation mRNA, tRNA, and rRNA

Messenger RNA (mRNA) Carries coded instructions for protein synthesis (translation) From the DNA in the nucleus to the ribosome

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

The genetic code

Transfer RNA (tRNA) Brings amino acids to the ribosome so it can build proteins It has Anticodons 3 nucleotide sequence complementary to the mRNA codon

Ribosomal RNA (rRNA) Makes up ribosomes

Translation Step 1: mRNA from nucleus Through cytoplasm to the ribosome mRNA start codon AUG signals beginning of protein

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

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

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

Translation Animation