Human Genetics: Concepts and Applications (Lewis), 9th Edition

Chapter 10: Gene Action: From DNA to Protein

Chapter Outline

CHAPTER OVERVIEW

1. DNA, the genetic material, contains information the cell requires to synthesize proteins and replicate itself.
2. Genes are segments of DNA containing the information to specify a sequence of amino acids in a protein.
3. Most of our DNA is not protein encoding. Rather, it is involved in controlling gene expression.
4. Transcription and translation are the two aspects of gene expression.
5. In a cell, transcription is the process that copies the information stored in DNA into RNA.
6. Translation uses the RNA's information to construct amino acid chains that comprise proteins.

1. The directional flow of genetic information from DNA to RNA to protein is known as the central dogma of molecular biology.
2. Gene regulation controls the pattern of gene expression and cellular differentiation.
3. RNA is copied from one strand of the double helix called the template strand.

1. RNA differs from DNA in that it is generally single-stranded, has uracil instead of thymine, and has ribose instead of deoxyribose.
2. Messenger RNA (mRNA) carries the information that specifies a particular amino acid sequence of a protein product. Each three mRNA bases in a row form a codon.
3. Ribosomal RNA (rRNA) joins certain proteins to form ribosomes. Ribosomes physically support the other structures involved in protein synthesis, and some rRNA catalyzes formation of peptide bonds.
4. Transfer RNA (tRNA) has a folded cloverleaf-shape. It caries a specific amino acid to each mRNA codon.

1. Bacterial genes are organized into operons and coordinately regulated.
2. Most eukaryotic genes are controlled by a complex set of transcription factors.
3. A few human diseases are due to defects in transcriptional factors.

1. Transcription factors and RNA polymerase recognize sequences in the DNA near a gene. This region is called a promoter.
2. The binding of transcription factors to the promoter attracts and binds RNA polymerase, which begins transcription.
3. Transcription proceeds as RNA polymerase inserts complementary RNA bases opposite the template strand of the DNA double helix.
4. A specific sequence in the DNA causes transcription to terminate.

1. In prokaryotes, RNA is translated as soon as it is transcribed.
2. In eukaryotes, RNA is often altered (or modified) before it is active.
3. Messenger RNA gains a modified nucleotide cap and a poly A tail.
4. Many genes have intervening sequences or introns which are transcribed and then cut from the mRNA. The protein encoding sequences in mRNA, termed exons, are then reattached.
5. Ribozymes are small RNAs with catalytic activity that can splice introns. They join proteins to form snurps (snRNPs), which associate to form spliceosomes.
6. Alternate RNA processing may produce different sized protein products in different cell types.
7. After being processed, the RNA must be exported from the nucleus before it is translated.

1. Crick and coworkers confirmed the triplet nature of the genetic code.
2. The reading frame of a gene is the particular sequence of amino acids in a protein that is encoded from a certain point in a gene. Adding or subtracting 1 or 2 DNA bases to a gene disrupts the reading frame. Adding or deleting 3 contiguous bases, adds or deletes one amino acid to the protein product but does not disrupt the reading frame.
3. The genetic code is nonoverlapping, continuous, virtually universal, and degenerate.
4. Crick hypothesized the existence of an adaptor molecule necessary for translation. This was later discovered and called transfer RNA (tRNA).

1. As translation begins, mRNA, tRNA with bound amino acids, ribosomes, energy molecules, and protein factors assemble.
2. To initiate translation, the mRNA leader sequence binds to rRNA in the small subunit of a ribosome, and the first codon attracts a tRNA to form the initiation complex.
3. In elongation, the large ribosomal subunit attaches to the initiation complex. Peptide bonds form between the amino acids attached to the aligned tRNAs, building a polypeptide.
4. Protein synthesis halts when a stop codon is reached.
5. Translation is efficient and economical, as RNA, ribosomes, enzymes, and key proteins are recycled.

1. The protein folds as translation proceeds, with enzymes and chaperone proteins assisting the amino acid chain in assuming its final functional (three-dimensional) shape.
2. In addition to folding properly, certain proteins must be modified before they are functional.
3. Misfolded and excess proteins are degraded by proteosomes
4. Errors in protein folding are the basis of some diseases.