CHAPTER 10Highlights 221
Key Concepts
Study CHAPTER HIGHLIGHTS
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Key Terms
Section 1
ribonucleic acid (RNA) (208)
uracil (208)
transcription (208)
translation (208)
gene expression (208)
RNA polymerase (209)
messenger RNA (211)
codon (211)
genetic code (211)
transfer RNA (212)
anticodon (212)
ribosomal RNA (212)Section 2
operator (216)
operon (216)
lacoperon (216)
repressor (216)
intron (218)
exon (218)
point mutation (219)BIOLOGYBIOLOGY
Unit 6 —Gene Expression
Use Topics 3–6 in this unit to review the key
concepts and terms in this chapter.From Genes to Proteins
The instructions needed to make proteins are coded in
the nucleotides that make up a gene. The instructions
are transferred to an mRNA molecule during transcrip-
tion. The RNA is complementary to the gene, and the
RNA nucleotides are put together with the help of RNA
polymerase.
During translation, the mRNA molecule binds to a ribo-
some, and tRNAs carry amino acids to the ribosome
according to the codons on the mRNA. Each codon
specifies an amino acid. The amino acids are joined to
form a protein.
The genetic code (codons) used by most organisms to
translate mRNA is nearly universal.Gene Regulation and Structure
Prokaryotic and eukaryotic cells are able to control which
genes are expressed and which are not, depending on the
cell’s needs.
In prokaryotes, gene expression is regulated by operons.
Gene expression is switched off when repressor proteins
block RNA polymerase from transcribing a gene.
In eukaryotes, an enhancer must be activated for a eukary-
otic gene to be expressed. Transcription factors initiate tran-
scription by binding to enhancers and to RNA polymerases.
Many eukaryotic genes are interrupted by segments of
DNA that do not code for proteins; these segments are
called introns. The segments of DNA that are expressed are
called exons. After transcription, the introns are cut out,
and the exons are joined. The exons are then translated.
Mutations are changes in DNA. Gene alterations are muta-
tions that change a gene. These mutations can involve a
change in a single nucleotide or an entire gene.