Chapter 12: Protein Synthesis What is DNA? What is DNA?
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Transcript of Chapter 12: Protein Synthesis What is DNA? What is DNA?
Chapter 12: Protein SynthesisWhat is DNA?
– The DNA of the gene is transcribed into RNA• Which is translated into protein
• The flow of genetic information from DNA to RNA to Protein is called the CENTRAL DOGMA
DNA
Transcription
RNA
Protein
Translation
Chapter 13 Protein Synthesis - Overview
Central Dogma - FLOW IS FROM DNA TO RNA TO PROTEIN
Chapter 12 Protein Synthesis (Overview)
FLOW IS FROM DNA TO RNA TO PROTEIN
• Genes on DNA are expressed through proteins, which provide the molecular basis for inherited traits
• A particular gene, is a linear sequence of many nucleotides
– Specifies a polypeptide (long protein made of amino acids)
Chapter 13 Protein Synthesis (Overview)
Genes - discrete units of hereditary information comprised of a nucleotide sequence found in a DNA molecule.
Chapter 12 Protein Synthesis (Overview)
12.1 RNAThree Types of RNA
• Messenger RNA (mRNA) – carries copies of genes (DNA) to the rest of the cell.
• Ribosomal RNA (rRNA) – make up the ribosomes.
• Transfer RNA (tRNA) – transfers the amino acids to the ribosomes as specified by the mRNA
12-1 Messenger (mRNA)
1. Three main differences between mRNA and DNA
• Ribose instead of deoxyribose• mRNA is single stranded• mRNA has uracil in place of thymine (U
instead of T)
12.1 TRANSCRIPTION: The process of making mRNA from DNA
– Why do you need this process?• Location of DNA?
Nucleus
• Location of Ribosome? Cytoplasm
– mRNA takes code from DNA in the nucleus to the cytoplasm
T A C T T C A A A A T C
A T G A A G T T T T A G
A U G A A G U U U U A G
Transcription
Translation
RNA
DNA
Met Lys PhePolypeptide
Startcondon
Stopcondon
Strand to be transcribed
Transcription produces genetic messages in the form of mRNA12.1 In the nucleus, the DNA helix unzips
• And RNA polymerase lines up nucleotides along one strand of the DNA, following the base pairing rules
– As the single-stranded messenger RNA (mRNA) peels away from the gene
• The DNA strands rejoinRNApolymerase
RNA nucleotides
Direction of transcription
Template Strand of DNA
Newly made RNA
TC
A T C C A A TT
GG
CC
AATTGGAT
G
U
C A U C C AA
U
12.1 Eukaryotic mRNA is processed before leaving the nucleus
– Noncoding segments called introns are spliced out leaving only the coding exons
• A 5’ cap and a poly A tail are added to the ends of mRNA
• Cap and tail protect mRNA
Exon Intron Exon Intron Exon
DNA
Cap TranscriptionAddition of cap and tail
RNAtranscript with capand tail
Introns removedTail
Exons spliced together
mRNA
Coding sequence Nucleus
Cytoplasm
5’ 3’
Direction of transcription
T
C
AT C C A A T
T
GG
C
CA
ATTGGAT
G
U
C A U C C AA
U
12-3 Protein Synthesis - Translation
• Translation is defined as going from mRNA to protein– tRNA which have amino acids attached are
going to the ribosome in the cytoplasm.• What are amino acids? monomers of proteins
• Does the order of amino acids matter? Yes, they must be in order for the protein to fold correctly.
Amino acid attachment site
– How does the correct tRNA (with amino acid attached) bind to the mRNA? The tRNA contains an anticodon which matches up with the mRNA sequence (codon).
Amino acid attachment site
Hydrogen bond
RNA polynucleotide chain
AnticodonAnticodon
Amino acid attachment site
Transfer RNA (tRNA) molecules serve as interpreters during translation
Ribosomes build polypeptides (proteins)– A ribosome consists of two subunits
• Each made up of proteins and a kind of RNA called ribosomal RNA
• Translation at RibosometRNAmolecules
mRNA Small subunit
Growingpolypeptide
Largesubunit
12.3 Translation
– The subunits of a ribosome• Hold the tRNA and mRNA close together during
translation
12.3 Translation
Met Met
Initiator tRNA
1 2mRNA Small ribosomal
subunit
Startcodon
Large ribosomalsubunit
A siteU A CAU C
A U G A U G
P site
Elongation adds amino acids to the polypeptide chain until a stop codon terminates translation
– Once initiation is complete amino acids are added one by one to the first amino acid
– The mRNA moves a codon at a time• A tRNA with a complementary anticodon pairs with
each codon, adding its amino acid to the peptide chain
Animation
1. Take the DNA and transcribe it into mRNAExample: TAC ATA CTA GCG ACT
mRNA:
2. Take the mRNA sequence and decode it using the codon chart.
AUG UAUGAU CGC UGA
AUG = METUAU = TYRGAU = ASPCGC = ARG
Figure out the exact sequence of amino acids needed