DNA Transcription & Protein Translation

Today’s Objectives

Introduce Protein SynthesisCompare types of nucleic acid

RNA-ribonucleic acid

Uses the information from DNA to synthesis proteins.

3 Main Differences from DNA

1. RNA has one strand of nucleotides

2. RNA has ribose as it’s sugar

3. RNA has Uracil as a nitrogen base instead of thymine (U bonds with A)

Three Classes of RNA

Messenger RNA mRNA

Carries the “blueprint” for protein assembly to the ribosome

Ribosomal RNA

rRNA-combines proteins to form ribosomes upon which polypeptides are assembled

Transfer RNA

tRNA Brings the correct amino acid to the ribosome

and pairs up a mRNA code for that amino acid

Codon-A series of 3 bases that code for an amino acid Located on the mRNA strand

Anti-Codon-a triplet of nucleotides in transfer RNA that is complementary to the codon in messenger RNA which specifies the amino acid

Located on the tRNA molecule

DNA Transcription

DNA must be copied to messenger RNA (mRNA)

mRNA goes from nucleus to the ribosomes in cytoplasm

mRNA complements known as codons– Only 3 nucleotide “letters” long

Remember RNA has uracil (U) instead of thymine (T)!

Transcription – Step I

A C G T A T C G C G T A T G C A T A G C G C A T

Template DNA Strands

Transcription – Step II

A C G T A T C G C G T A U G C A U A G C G C A U

Template DNA is Matched Up with Complementary mRNA Sequences

Transcription Reminders

The template strand is the DNA strand being copied

The rRNA strand is the same as the DNA strand except Us have replaced Ts

Protein Translation

Modified genetic code is “translated” into proteins

Codon code is specific, but redundant!– 20 amino acids– 64 triplet (codon) combinations

Using the Codon Table

learn how to use a codon table to translate mRNA into its associated amino acids

Let’s Play Bingo!!

tRNA in cytoplasm has a codon attached to an amino acid

tRNA structure

3-base code (triplet) is an “anticodon” Protein molecule Attached amino acid that is carried from

cytoplasm to ribosomes

Protein Synthesis

Start: Ribosome binds to mRNA at start codon (AUG)

Elongation: – tRNA complexes bind to mRNA codon by forming

complementary base pairs with the tRNA anticodon– The ribosome moves from codon to codon along the

mRNA. – Amino acids are added one by one

Release: release factor binds to the stop codon

Transcription – Step III

mRNA leaves nucleus and goes to ribosomes

U G C A U A G C G C A U

A new complementary RNA strand is made (rRNA)

A C G U A U C G C G U A