Post on 21-Dec-2015
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
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
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
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
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