Transcription & Translation Objective 3.01 Analyze the molecular basis of heredity as it relates to Protein Synthesis
Transcription • Occurs in the nucleus • The process begins with the DNA unzipping. • Single-stranded messenger RNA (mRNA) is made by base pairing. The mRNA is a copy of the DNA (replacing T with U).
The mRNA then separates from the DNA and the DNA zips back up. • The mRNA leaves the nucleus and goes to a ribosome in the cytoplasm.
So Let’s Practice Transcription G -- ___ C -- ___ T -- ___ A -- ___ T -- ___ G -- ___ A -- ___ T -- ___ C -- ___ Original DNA Strand New mRNA Strand
Translation • Occurs at the ribosome • mRNA is read by the ribosome 3 bases at a time. • These 3 bases are called a codon. • Each codon on the mRNA CODES for an amino acid. • Translation begins when the ribosome finds the codon AUG (Start Codon)
“Hey, tRNA! I gotta code for an amino acid, here! Why don’t you go fetch it for me!” Amino Acid GGC Glycine • Transfer RNA (tRNA) brings amino acids to the ribosome. • Translation stops when the ribosome reads a STOP codon (there are 3 stop codons). • Amino acids at the ribosome link together by a peptide bond to form a protein! “Ref” Ribosome “Terrell” tRNA
Nucleus AminoAcid mRNA tRNA Ribosome mRNA Start codon
Growing polypeptide chain A.K.A. PROTEIN!!!! Ribosome tRNA Amino Acid tRNA mRNA mRNA Translation direction Ribosome
Protein Synthesis Animation • Protein Synthesis Animation
There is also Ribosomal RNA (rRNA), component that makes up about 50% of a ribosome. • It keeps the ribosome functioning and protects the RNA during the translation process. rRNA Ribosome
Check Point! • Why do cells have to replicate their DNA? Because before they do mitosis and divide into daughter cells, they need to copy all the DNA to give to the new cell! • When in the cell cycle does DNA replication occur? Remember 2 phases in the Cell Cycle: Interphase & Mitosis! Replication must occur BEFORE the cell divides, so it happens during interphase! • What kind of bond holds the nitrogen bases together? Why is this important? Hydrogen; because it’s a weak bond…remember, an enzyme is going to come along and “unzip” it anyway!