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Chapter 14 Gene Expression: From Gene to Protein
 Gene expression: the process by which DNA directs the synthesis of proteins
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Translation: the synthesis of
a polypeptide using the
information of DNA 
ribosome: sites of
translation – complex
molecules that facilitate the
orderly linking of amino
acids into polypeptide chains
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 Reading frame: the correct groupings 

 DNA controls metabolism by directing cells to make specific enzymes and other proteins, via the
process of gene expression
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Gene code for polypeptide chains or specify RNA molecules
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 Translation is the synthesis of a polypeptide whose
amino acid sequence is specified by the nucleotide sequence in mRNA; this informational transfer involves
a change of language, from that of nucleotides to that of amino acids 
 Genetic Information is encoded as a sequence of codons
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Codons must be read
in the correct reading frame
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2 Transcription is the DNA-directed synthesis of RNA: a closer look
 RNA Synthesis is catalyzed by RNA polymerase, which links together RNA nucleotides complementary
to a DNA template strand
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Three stages of transcription:
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Elongation
o Only one of the unwound DNA acts as a template for the RNA synthesis
o RNA polymerase can only add nucleotides to the 3’ end of the strand so like DNA, RNA
must be synthesized in the 5’ to 3’ direction
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o As RNA polymerase advances, the process continues
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o Transcription stops and mRNA polymerase and the new mRNA transcript are released
from DNA
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o The termination sequence usually consists of a series of adjacent adenines preceded by a
nucleotide palindrome
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o This configuration stops RNA polymerase from transcribing any further
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Transcription factors help eukaryotic RNA polymerase recognize promoter sequences, forming a

transcription initiation complex
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 Most eukaryotic genes are split into segments
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In RNA splicing introns are removed and exons joined
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 The catalytic
ability of some RNA molecules, called ribozymes derived from the properties of RNA
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After being bound to a
specific amino acid by an aminoacyl-tRNA synthetase, a tRNA lines up via its anticodon at the
complementary codon on mRNA
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Ribosomes coordinate the three stages of translation: initiation, elongation, and termination
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After translocation, modifications to proteins can affect their shape
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A gene can be transcribed by multiple RNA polymerases simultaneously
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In bacteria, these processes
are coupled, but in eukaryotes they are separated in time and space by the nuclear membrane
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5 Mutation of one or a few nucleotides can affect protein structure and function
 Mutagens: physical and chemical agents that cause mutations
 insertion/ deletions: are additions or losses of nucleotide pairs
in a gene
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 Nucleotide-pair substitutions can cause
missense or nonsense mutations
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 Spontaneous mutations can occur during DNA replication,
recombination, or repair
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