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Ch 8-4
Flow of Genetic Information
• The flow of genetic information can be symbolized as
DNA
RNA
protein
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RNA Structure and Function
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RNA has the sugar ribose instead of deoxyribose
RNA has uracil (U) in place of thymine (T)
RNA is single stranded
RNA is shorter than DNA
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Types of RNA
– Cells have three major
types of RNA:
1. messenger RNA
(mRNA)
2. ribosomal RNA
(rRNA)
3. transfer RNA
(tRNA)
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Types of RNA
1. mRNA carries the genetic “message” from the
nucleus to the cytosol
2. rRNA is the major component of ribosomes
3. tRNA carries specific amino acids, helping to form
polypeptides (proteins)
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Transcription
• Making RNA from DNA
• DNA acts as a template
1. RNA polymerase binds to promoter site
2. 2 strands of DNA unwind
3. Complementary RNA nucleotides are added
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Transcription
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Ch 8-5
Genetic Code
• identifies the specific amino acids coded for by each
three-nucleotide mRNA codon
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Translation
– Making Proteins from RNA
– amino acids are assembled from information
encoded in mRNA
1. mRNA codons move through the ribosome
2. tRNAs add specific amino acids to the growing
polypeptide chain
3. Process continues until a stop codon is reached
4. Newly made protein is released
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Translation: Assembling Proteins
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Translation: Assembling Proteins, continued
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The Human Genome
• The entire gene sequence of the human genome is
now known
• To learn where and when human cells use each of the
proteins coded for in the approximately 30,000 genes
in the human genome will take much more analysis
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