After today’s lesson you will be able to transcribe a DNA fragment into an RNA fragment and translate the RNA into a

polypeptide.

From Gene to Protein

Three Important Points to Remember:

Chromosomes are made of DNA Segments of DNA, called genes, code for

specific proteins Proteins in turn relate to a trait

Eye color, enzymes, hair type

PROBLEM!

DNA holds the instructions for proteins. Proteins are built in the cytoplasm at the

ribosomes. DNA CANNOT leave the nucleus!

How do the plans for each protein get to the site of protein synthesis??

From Gene to Protein

How are proteins synthesized from DNA?

DNA is transcribed into messenger RNA (mRNA) mRNA leaves the nucleus and travels to the

cytoplasm Ribosomes in the cytoplasm use the code on mRNA

to translate it into amino acids with the help of transfer RNA (tRNA)

Amino acids form a polypeptide chain – a protein!!

From Gene to ProteinSounds simple huh?

Well, you’re not getting off that easy, now we will break down each step of the process…

Question??

What does it mean to transcribe something?

The definition of transcribe is to make an exact copy of (a document, text, etc.).

During transcription we make a copy of a gene out of RNA which is able to leave the nucleus.

Ribonucleic Acid (RNA) RNA is very similar to DNA

with the following exceptions:

1. It is a single strand

2. It uses the base uracil instead of thymine

3. It has the sugar ribose, instead of deoxyribose

4. It CAN leave the nucleus

Transcription

Transcription takes place when DNA is unwound and the enzyme RNA polymerase reads the gene and builds a messenger RNA strand to carry the instructions for a protein out to the ribosome.

Question??

Why do you think it is so important that DNA does not leave the nucleus?

The base-pair rule is followed during transcription, except, instead of pairing thymine with adenine, when creating an RNA strand, uracil is used.

DNA Strand: T G C A T C A G A

RNA Strand:

Transcription

A UG U A CG UC

Transcription

No w you try…

Complete the two practice problems on your worksheet.

Now let’s see transcription in action.

Codon Chart

Translation

Messenger RNA travels out of the nucleus to the cytoplasm and finds a ribosome. This is where translation begins.

The ribosome begins to read the mRNA three bases at a time, we call these three bases a codon.

Translation

Each codon codes for one amino acid. We know that amino acids are strung together to make a protein.

See the chart in your handout.

Amino acids exist freely in the cytoplasm, many of them you acquire from your diet.

Translation

As the ribosome reads the code. It has help from another type of RNA called transfer RNA, which goes out into the cytoplasm and gets the amino acids.

Transfer RNA (tRNA) has an anticodon at one end and an amino acid at the other, it binds to the complimentary codon on the messenger RNA.

Another tRNA reads the next codon, the amino acid attached to it binds with the amino acid on the previous tRNA using a peptide bond. The first tRNA falls off.

Translation

This process continues until the “Stop” codon is reached.

Using your chart, determine what the three possible stop codons are?

Translation

The amino acid chain folds into a 3 dimensional structure, now a protein.

That protein can be an enzyme, a hormone, or any other structure in the body that gives it traits and functionality.

Protein Synthesis