Transcription & TranslationBiology 6(C)

Learning Objectives• Describe how DNA is used to make protein• Explain process of transcription• Explain process of translation

Transcription and Translation

DNA (deoxyribonucleic acid)• Stores genetic code• Made of nucleotides

Nucleotides – building blocks of DNA• Phosphate group• Deoxyribose sugar• Nitrogenous base

DNA – Our Genetic Code

DNA is the genetic material of organisms• Master blueprint for all protein synthesis– Order of bases affects protein made

• What do proteins do?– Enzymes– Cell signaling– Structural

Purpose of DNA

How does a molecule create a protein?1. Copy of DNA made (transcription)2. Copy modified and leaves nucleus 3. Copy used to create amino acid chain

(translation)4. Amino acid chain folds into protein

From DNA to Protein

DNA• Stored in nucleus• Deoxyribose sugar• Double-stranded• Four bases– Adenine –

Thymine– Cytosine –

Guanine

RNA• Used in cytoplasm• Ribose sugar• Single-stranded• Four bases– Adenine – Uracil– Cytosine –

Guanine

DNA and RNA

Transcription – process by which a portion of DNA nucleotide sequence is used to produce a complementary mRNA (messenger RNA) strand

RNA polymerase – protein that initiates and operates transcription1. Binds to promoter section of DNA2. Separates DNA strands3. Builds mRNA strand using one DNA strand

as a template4. Releases mRNA strand at stop signal

Transcription

Transcription

RNAPolymerase

Non-template

DNA strand

TemplateDNA strand

RNAnucleotides

mRNA strand

A portion of DNA is shown below. What is the correct sequence of the resulting mRNA transcript if the top DNA strand is used as the template in transcription?

Writing mRNA Sequences

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

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

template DNAnon-template DNA

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

You can find the mRNA sequence using the steps below

Writing mRNA Sequences

Before leaving nucleus, mRNA must be processed

• Introns removed

• Exons spliced together

• Cap and tail added

• mRNA leaves nucleus

Processing and Exit

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

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

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

(cap) A U G G A C G U G A C G U G A (tail)

Proteins• Complex macromolecule• Polymer, made of amino acid chains– 20 different amino acids

• Order of amino acid specified in mRNACodons – three consecutive nucleotides in mRNA• Each codon specifics an amino acid

Decoding the Genetic Code

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

Each codon specifies one of 20 amino acids

Decoding the Genetic Code

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

First nucleotide

Second nucleotide

Thirdnucleotide

Translation – process by which information in mRNA strand is used to create amino acid chain (polypeptide chain)

Ribosome – protein complex where translation occurs

tRNA – transfer RNA, bring amino acids to the ribosome• Each has a specific anticodon and amino

acid

Translation

Translation

mRNAstrand

amino acid

anticodon

polypeptidechain

tRNA

codon

Ribosome

peptide bond

What polypeptide chain will be produced during translation if the mRNA strand below is used?

Writing mRNA Sequences

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

First nucleotide

Second nucleotide

Thirdnucleotide

Met Ser Ser Val Thr stop

You can translate the mRNA sequence using the steps below

Translating mRNA Sequences

Transcription• “Copying”• DNA to mRNA• Occurs in nucleus• RNA involved– mRNA

Translation• “Decoding”• mRNA to

polypeptide• Occurs in

cytoplasm• RNA involved– mRNA– tRNA– rRNA

Transcription and Translation

How does a polypeptide chain become a protein?• Edited– Sections cut out by enzymes

• Folds– Amino acids bond together

Editing & Folding

How does a molecule create a protein?1. Transcription– mRNA strand made from DNA template

2. mRNA modified and leaves nucleus– Introns removed, cap and tail added

3. Translation – Polypeptide chain made at ribosome using

mRNA

4. Polypeptide chain into protein – Edited & folded

From DNA to Protein

Learning Objectives• Describe how DNA is used to make protein• Explain process of transcription– DNA to mRNA

• Explain process of translation– mRNA to polypeptide chain

Transcription and Translation