Transcription and Translation. What is Transcription? It is a process that produces a complementary...

Transcription and Translation

What is Transcription?• It is a process that produces a

complementary strand of RNA by copying a complementary strand of DNA

– DNA is copied to messenger RNA (mRNA)

– mRNA goes from nucleus to the ribosomes that are in the cytoplasm

• Remember: A=U and C=G

How does Transcription Work?

• It requires RNA polymerase which is an

enzyme that binds to DNA and separates the DNA strands.

• The Enzyme then uses one strand of DNA as a template in which nucleotides are assembled into a strand of mRNA

Transcription

• Template DNA is Matched Up with Complementary mRNA Sequences

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

mRNA

Where does Transcription take place?

RNADNA

RNApolymerase

Adenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)

In the Nucleus

The Genetic Code

It is the language of mRNA that codes for amino acids

• They are in a 3-nucleotide sequence on mRNA called a Codon. This 3 letter codon codes for a specific amino acid

The Genetic Code

–Codons code for amino acids using the genetic code

–There are 20 amino acids

–AUG codon is the start codon

Deciphering the Genetic Code:If the mRNA looks like:

UCGCACGGUThe codon sequence breaks down into:

UCG- CAC- GGU

Use the codon chart to find each amino acid as:

Serine- Histidine- Glycine (the amino acid sequence)

The Genetic Code

What isTranslation?• The decoding a mRNA message into proteins

– Also called protein synthesis (making proteins)

– Takes place on the ribosome

• tRNA structure: – Anticodon: group of 3 bases that are

anticodon

tRNA

What are the steps to Translation?

1. mRNA is transcribed from DNA in the nucleus and released into the cytoplasm

What are the steps to Translation?

2. mRNA in cytoplasm binds to ribosome at the start codon (AUG)

What are the steps to Translation?

3. tRNA binds to mRNA codon by forming complementary base pairs with the tRNA anticodon

The correct amino acid is brought to the ribosome by the tRNA

What are the steps to Translation?

4. The amino acid is transferred to the growing polypeptide chain

What are the steps to Translation?

5. The polypeptide chain continues to grow until the ribosome reaches a “stop” codon

What are the steps to Translation?

6. The polypeptide chain is released

A polypeptide chain is a protein

Translation

Translation cont.