Chapter 4 The images on this CD have been lifted directly, without change or modification, from textbooks and image libraries owned by the publisher, especially from publications intended for college majors in the discipline. Consequently, they are often more richly labeled than required for our purposes. Further, dates for geological intervals may vary between images, and between images and the textbook. Such dates are regularly revised as better corroborated times are established. Your best source for current geological times is a current edition of
Transcript
Chapter 4
The images on this CD have been lifted directly, without change or modification, from textbooks and image libraries owned by the publisher, especially from publications intended for college majors in the discipline. Consequently, they are often more richly labeled than required for our purposes. Further, dates for geological intervals may vary between images, and between images and the textbook. Such dates are regularly revised as better corroborated times are established. Your best source for current geological times is a current edition of the textbook, whose dates should be used when differences arise.
Eukaryotic cell, generalized from an animal Note the plasma membrane containing various organelles, membrane-bound structures
within the cytoplasm, and the nuclear envelope bounding the nucleus, which holds DNA. Besides the mitochondria (production of energy molecules), the organelles include compartments and channels involved in manufacture, processing, and transport of synthesized products (rough endoplasmic reticulum, smooth endoplasmic reticulum, Golgi apparatus, and lysosomes). Often microvilli, small projections, occur on the cell surface.
Base-pairing DNA is composed of two specialized strands of nucleic acid wound in a spiral helix.
Between the double strands of DNA, the nitrogenous bases pair specifically and preferentially: adenine (A) with thymine (T), and guanine (G) with cytosine (C). In large part, this is the basis for coding of information within DNA, and later transcription to RNA. Each end of a DNA strand is polarized—one end is the 3’ end, the other the 5’ end. During DNA duplication, the new strand of DNA lengthens in the 5’ 3’ direction.
Information transfer—DNA to RNA to protein The organized sequence of bases in DNA is used in transcription to produce a
complementary, chemically matched, mRNA molecule. In turn, three bases each form a codon, which specifies a particular amino acid. Sequentially, codon by codon, the mRNA is a cipher program used in translation to produce a connected chain of particular amino acids, the protein molecule.
Transcription and translation in prokaryotes and eukaryotes (a) Bacterial genes are transcribed into mRNA, which is translated immediately into a
protein. (b) Eukaryotic genes typically contain long stretches of nucleotides, called introns, that do not code for proteins. Introns, whose function is poorly known, are removed from mRNA before mRNA directs the synthesis of the protein.
Cell metabolism Food is broken down during digestion, yielding end the products of carbohydrates, fats, and
proteins. These enter various metabolic pathways where energy is harvested and stored in ATP or temporarily in NADH. These metabolic pathways include glycolysis, the Krebs cycle, and the electron transport system, represented diagrammatically in the figure. Various chemical intermediates in these pathways are indicated (pyruvate, lactate, Acetyl-CoA). Oxygen (O2) is used up; carbon dioxide (CO2) is given off.
Photosynthesis Plant cells include numerous chloroplasts, such as the one shown here in this cut-away
view. In chloroplasts, energy from light is used eventually to produce energy storage molecules, ATP and NADP+. These fuel the Calvin cycle, which in turn produces PGAL, an intermediate on its way to becoming a sugar used in cellular respiration and manufacture of plant tissues. Note that water (H2O) is taken up and oxygen (O2) given off as a byproduct.
FIGURE 4.3 Life in Test Tubes, The Miller-Urey Experiment Heated water produced water vapor circulating through the closed system of glass chambers. Into the
upper chamber, Miller and Urey placed gases thought present in Earth’s early atmosphere, and applied a spark. Condensers cooled any gases, causing molecular products to collect in the water. From this water, samples were taken over the next week and analyzed. Among the organic molecules formed were amino acids, basic building blocks of protein. Subsequent follow-up trials, by many other biologists, using various combinations of “primitive atmospheres,” produced even more complex organic compounds.
FIGURE 4.10 Information Transfer-DNA to RNA to Protein The organized sequence of bases in DNA is used in transcription to produce a
complementary, chemically matched, mRNA molecule. In turn, three adjacent bases form a codon, which specifies a particular amino acid. Sequentially, codon by codon, the mRNA is a cipher program used in translation to produce a connected chain of particular amino acids, the protein molecule.
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