Flow of Genetic Information
• Flow of genetic information from DNA to RNA to protein
• The DNA genetic code (genotype) is expressed as proteins which provide the physical traits (phenotype) of an organism
GCTGCTAACGTCAGCTAGCTCGTAGC GCTAGCGCTTGCGTAGCTAAAGTCGAGCTCGCTTGCGTAGCTAAAGTCGAGCTGCTGCTAACGTCAGCTAGCTCGTAG AGCGCTTGCGTAGCTAAAGTCGAGCT AGCGCTTGCGTAGCTAAAGTCGAGCT GCTGCTAACGTCAGCTAGCTCGTAGC AGCGCTTGCGTAGCTAAAGTCGAGCT AGCGCTTGCGTAGCTAAAGTCGAGCT GCTGCTAACGTCAGCTAGCTCGTAGC AGCGCTTGCGTAGCTAAAGTCGAGCT AGCGCTTGCGTAGCTAAAGTCGAGCT GCTGCTAACGTCAGCTAGCTCGTAGC AGCGCTTGCGTAGCTAAAGTCGAGCT GCTGCTAACGTCAGCTAGCTCGTAGC AGCGCTTGCGTAGCTAAAGTCGAGC, cont.
RNA Proteins
GCTGTAATTACGTAACTAGCTCGTAGCCTAGCGCTTGCGTAGCTAAAGTCGAGCTCGGCTGTAATTACGTAAGTCGAGCTGCTGCTAACGTCAGCTAGCTCGTAGGCTGTAATTACGTAAAGCGCTTGCGTAGCTAAAGTCGAGCTGCTGTAATTACGTAAAGCGCTTGCGTAGCTAAAGTCGAGCTGCTGCTAACGTCAGCTAGCTCGTAGCGCTGTAATTACGTAAAGCGCTTGCGTAGCTAAAGTCGAGCTGCTGTAATTACGTAAAGCGCTTGCGTAGCTAAAGTCGAGCTGCTGTAATTACGTAA GCTGCTAACGTCAGCTAGCTCGTAGCGCTGTAATTACGTAAGCTGTAATTACGTAAGCTGTAATTACGTAAGCTGTAATTACGTAAGCTGTAATTACGTAAGCTGTAATTACGTAAGCTGTAATTACGTAAGCTGTAATTACGTAA, cont.
RNA Proteins
Different DNA Sequence….
Protein Synthesis
• TranscriptionProcess in which a
molecule of DNA is copied into a complementary strand of RNA
• TranslationProcess in which the
message in RNA is made into a protein
Forms of RNA
3 Main Types of RNA1) mRNA (messenger RNA) – RNA that decodes
DNA in nucleusbrings DNA message out of nucleus to the cytoplasmEach 3 bases on mRNA is a “codon”
2) tRNA (transfer RNA) – RNA that has the “anticodon” for mRNA’s codon The anticodon matches with the codon from mRNA to determine which amino acid joins the protein chain
3) rRNA (ribosomal RNA) – make up the ribosomes—RNA that lines up tRNA molecules with mRNA molecules
Transcription produces genetic messages in the form of RNA
Figure 10.9A
RNApolymerase
RNA nucleotide
Direction oftranscription
Newly made RNA
Templatestrand of DNA
Copyright © 2003 Pearson Education, Inc. publishing Benjamin Cummings
Transcription1. Initiation:
• RNA polymerase (enzyme) attaches to DNA at the promoter and “unzips” the two strands of DNA
2. Elongation:• RNA polymerase then “reads”
the bases of DNA and builds a single strand of complementary RNA called messenger RNA (mRNA)
3. Termination:• When the enzyme reaches the
terminator sequence, the RNA polymerase detaches from the RNA molecule and the gene
Transcription
The code on DNA tells how mRNA is put together.
Example: DNAACCGTAACG
mRNAUGGCAUUGC
• Each set of 3 bases is called a triplet or codon (in mRNA)
UGG CAU UGC
• Noncoding segments called introns are spliced out
• Coding segments called exons are bonded together
• A 5’cap and a 3’ poly-A tail are added to the ends
Eukaryotic RNA is processed before leaving the nucleus
Figure 10.10
DNA
RNAtranscriptwith capand tail
mRNA
Exon Intron IntronExon Exon
TranscriptionAddition of cap and tail
Introns removed
Exons spliced together
Coding sequence
NUCLEUS
CYTOPLASM
Tail
Cap
Copyright © 2003 Pearson Education, Inc. publishing Benjamin Cummings
• In the cytoplasm, a ribosome attaches to the mRNA and translates its message into a polypeptide
• The process is aided by tRNAs
Transfer RNA molecules serve as interpreters during translation
Figure 10.11A
Hydrogen bond
Amino acid attachment site
RNA polynucleotide chain
Anticodon
Copyright © 2003 Pearson Education, Inc. publishing Benjamin Cummings
• The mRNA moves a codon at a time relative to the ribosome– A tRNA pairs with each codon, adding an amino acid
to the growing polypeptide
Elongation adds amino acids to the polypeptide chain until a stop codon terminates translation
Translation1. Initiation:– mRNA molecule binds to the small ribosomal subunit – Initiator tRNA binds to the start codon (AUG—
Methionine) in the P-site of the ribosome– The large ribosomal subunit binds to the small one so
that the initiator tRNA is in the P-site to create a functional ribosome
Translation2. Elongation:– Codon recognition: anticodon
of incoming tRNA molecule, carrying its amino acid, pairs with the mRNA codon in the A-site of the ribosome
– Peptide formation: polypeptide separates from the tRNA in the P site and attaches by a peptide bond to the amino acid carried by the tRNA in the A site
– Translocation: the tRNA in the P-site now leaves the ribosome, and the ribosome moves along the mRNA so that the tRNA in the A-site, carrying the growing polypeptide, is now in the P-site. Another tRNA is brought into the A-site
Translation
3. Termination:– Elongation continues until a
stop codon is reached—UAA, UAG, or UGA
– The completed polypeptide is released, the ribosome splits into its subunits
Mutations
• Mutagenesis—creation of mutations• Can result from Spontaneous Mutations
• Errors in DNA replication or recombination• Mutagens—physical or chemical agents
– High-energy radiation (X-rays, UV light)
Types of Mutations• Mutations within a gene
– Can be divided into two general categories.• Base substitution• Base deletion (or insertion)
– Can result in changes in the amino acids in proteins.
Normal hemoglobin DNA
mRNA
Normal hemoglobin
Glu
Mutant hemoglobin DNA
mRNA
Sickle-cell hemoglobin
Val
Normal hemoglobin DNA
mRNA
Normal hemoglobin
Glu
Mutant hemoglobin DNA
mRNA
Sickle-cell hemoglobin
Val
Sickle-CellDisease
Substitution Mutations
• Missense mutation: altered codon still codes for an amino acid, although maybe not the right one
• Nonsense mutation: altered codon is a stop codon and translation is terminated prematurely– Leads to nonfunctional
proteins
Insertions and Deletions
• Frameshift mutation: addition or loss of one or more nucleotide pairs in a gene shifts the reading frame for translation and incorrect protein is made
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