DNA Transcription & Protein Translation

DNA Transcription

DNA must be copied to messenger RNA (mRNA) in the nucleus

mRNA travels from nucleus to the ribosomes in cytoplasm

Every set of three bases on mRNA is called a codon

Remember RNA has uracil (U) instead of thymine (T), it has one strand and it contains the sugar ribose, not deoxyribose!

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

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

One side of the DNA is Matched Up with a Complementary mRNA strand

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 for the other side of the DNA

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

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

tRNA matches the codons (set of 3 bases on the mRNA) with its own set of three bases (anticodon)

Each piece of tRNA brings in an amino acid– 20 amino acids

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