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Chapter 4 : Expression of Genetic Information

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Abstract:

This chapter focuses on how the information in DNA is translated into proteins and how changes in DNA and subsequent changes in proteins can affect their functions. The human genome consists of ~3 billion base pairs of DNA, and over 90% of it does not encode proteins. This noncoding DNA is often in the form of repeated sequences, sometimes in large clusters, which appears to be typical of eukaryotic genomes. Cellular enzymes synthesize a working copy of a gene to carry its genetic code to the ribosomes. This working copy is an RNA molecule called messenger RNA (mRNA), and the process of synthesizing it is called transcription. After transcription and processing are complete, the mRNA moves to the ribosome, the site of protein synthesis. The ribosome and the mRNA fit together so that the mRNA codons can be read correctly. The effect of a mutation on an organism depends on how the mutation affects the expression of genetic information and how the change in gene expression affects the organism within its environment. For example, a sequence change in a region of DNA that wasn’t part of a protein-coding sequence would probably not have any effect on the organism. Antibiotics treat bacterial infections by blocking essential bacterial processes, such as protein synthesis. Bacterial cells are prokaryotic, and their ribosomes are different enough from human ribosomes that antibiotics can interfere with bacterial protein synthesis without harming human protein synthesis.

Citation: Kreuzer H, Massey A. 2005. Expression of Genetic Information, p 71-88. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch4

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Bacterial Proteins
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Amino Acid Addition
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Figures

Image of Figure 4.1
Figure 4.1

The base sequence of DNA determines the amino acid sequences of proteins.

Citation: Kreuzer H, Massey A. 2005. Expression of Genetic Information, p 71-88. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch4
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Image of Figure 4.2
Figure 4.2

Transcription. Base pairing between incoming RNA nucleotides and the DNA template guides the formation of a complementary mRNA molecule. A single strand of the DNA molecule is used as a template. The DNA template closes behind the transcription site, releasing the RNA molecule and leaving the DNA template intact.

Citation: Kreuzer H, Massey A. 2005. Expression of Genetic Information, p 71-88. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch4
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Image of Figure 4.3
Figure 4.3

Splicing of an RNA transcript in eukaryotes.

Citation: Kreuzer H, Massey A. 2005. Expression of Genetic Information, p 71-88. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch4
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Image of Figure 4.4
Figure 4.4

A tRNA molecule. Complementary base pairing between different portions of the tRNA molecule maintains its shape. We show only the anticodon bases.

Citation: Kreuzer H, Massey A. 2005. Expression of Genetic Information, p 71-88. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch4
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Image of Figure 4.5
Figure 4.5

Translation. Complementary base pairing between the anticodons of incoming tRNA molecules and the codons of the mRNA guides the formation of the amino acid chain.

Citation: Kreuzer H, Massey A. 2005. Expression of Genetic Information, p 71-88. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch4
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Image of Figure 4.6
Figure 4.6

Major genetic traffic signals. Promoter, site where transcription begins; ribosome recognition element, bases recognized and bound by ribosome to hold RNA in place for translation; initiation codon, first codon in protein-coding sequence (ATG or AUG for methionine); stop codon, where translation stops; terminator, site where transcription ends.

Citation: Kreuzer H, Massey A. 2005. Expression of Genetic Information, p 71-88. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch4
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Image of Figure 4.7
Figure 4.7

Passage of a secreted protein through the cell's shipping department. The newly translated protein has a sequence of amino acids at one end that targets it to the ER. There, the protein is modified and shipped to the Golgi apparatus, where it is packaged into vesicles for secretion.

Citation: Kreuzer H, Massey A. 2005. Expression of Genetic Information, p 71-88. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch4
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Image of Figure 4.8
Figure 4.8

Hormone signaling in pigment production. In black or chocolate Labrador retrievers, binding of the hormone MSH-1 to its receptor gives the signal for melanin pigment production. In yellow Labs, the MSH-1 receptor is nonfunctional, so cells never receive the signal to produce melanin and the dogs are yellow instead of black or brown.

Citation: Kreuzer H, Massey A. 2005. Expression of Genetic Information, p 71-88. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch4
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Image of Figure 4.9
Figure 4.9

The coat color difference in the chocolate Lab and the yellow Lab puppies is caused by the puppies' lack of a functional receptor for MSH-1. (Photographs courtesy of Thomas A. Martin [top] and Donna Morgan [bottom].)

Citation: Kreuzer H, Massey A. 2005. Expression of Genetic Information, p 71-88. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch4
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Image of Figure 4.10
Figure 4.10

A single base change in the hemoglobin gene, highlighted in yellow, gives rise to the disease sickle-cell anemia.

Citation: Kreuzer H, Massey A. 2005. Expression of Genetic Information, p 71-88. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch4
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Image of Figure 4.11
Figure 4.11

Representation of sickle-cell hemoglobin aggregation. Normal hemoglobin molecules do not stick together. The hydrophobic patch on the surface of sickle-cell hemoglobin caused by the glutamate-to-valine substitution at position 6 fits neatly into a hydrophobic pocket on a second molecule. Thus, sickle-cell hemoglobin molecules can form chains in a head-to-tail arrangement.

Citation: Kreuzer H, Massey A. 2005. Expression of Genetic Information, p 71-88. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch4
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Image of Figure 4.12
Figure 4.12

Sickle-cell anemia. Normal red blood cell. Red blood cell in sickle-cell anemia. Chains of mutant hemoglobin molecules distort the shape of the cell, impairing circulation. (Photographs courtesy of Connie Noguchi, National Institute of Diabetes and Digestive and Kidney Diseases.)

Citation: Kreuzer H, Massey A. 2005. Expression of Genetic Information, p 71-88. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch4
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Image of Figure 4.13
Figure 4.13

Schematic representation of how the loss of 70 amino acids from one end of the erythropoetin receptor protein results in increased red blood cell (RBC) production.

Citation: Kreuzer H, Massey A. 2005. Expression of Genetic Information, p 71-88. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch4
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References

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Tables

Generic image for table
Table 4.1

The genetic code

Citation: Kreuzer H, Massey A. 2005. Expression of Genetic Information, p 71-88. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch4
Generic image for table
Table 4.2

DNA and RNA process terminology

Citation: Kreuzer H, Massey A. 2005. Expression of Genetic Information, p 71-88. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch4

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