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d at a node with a start codon, binds directly to the ribosome P site, and links to a special methionine to begin a polypeptide chain X inactivation condensation of X chromosomes into Barr bodies during embryonic development in females to compensate for the double genetic dose X-linked gene present on the X, but not th... |
king are used: inductive reasoning and deductive reasoning. Inductive reasoning is a form of logical thinking that uses related observations to arrive at a general conclusion. This type of reasoning is common in descriptive science. A life scientist such as a biologist makes observations and records them. These data ca... |
oratory techniques that are now used to identify genetic diseases, pinpoint individuals who were at a crime scene, and determine paternity. Without basic science, it is unlikely that applied science would exist. Figure 1.22 Shows DNA replication and cell division by the process of mitosis. Note: diploid means each cell... |
gen as designated on a periodic table (credit: Science Activist/Flickr) b. The element of helium as designated on a periodic table (credit: Science Activist/Flickr) The four elements common to all living organisms are oxygen (O), carbon (C), hydrogen (H), and nitrogen (N). Some elements common to all living organisms a... |
he seeds destroys the vessels and directly kills the tumor cells in the vicinity of the treatment. Radioisotopes emit subatomic particles that can be detected and tracked by imaging technologies. One of the most advanced uses of radioisotopes in medicine is the positron emission tomography (PET) scanner. The procedure ... |
dioactive isotope: an isotope that spontaneously emits particles or energy to form a more stable element reactivity: the ability of elements to combine and chemically bond with each other valence shell: the outermost electron shell Access for free at https://openstax.org/ 37 2.2 Chemical Bonds Chemical Reactions and Mo... |
nds. (credit: Benjah-bmm27/Public Domain) In a polar covalent bond, the shared pair of electrons spend more time closer to one atom's nucleus than to the other atom's nucleus. Because of the unequal distribution of electrons between the different nuclei, a slightly positive (δ+) or slightly negative (δ–) charge develop... |
han many other liquids and substances. Temperature measures the motion of molecules. As the motion increases, energy is higher, and therefore the temperature is higher. Water can absorb a great deal of energy before its temperature rises due to a large number of hydrogen bonds that hold water Access for free at https:/... |
er to make sure the water in an outdoor swimming pool is treated correctly. In both cases, this pH test measures the amount of hydrogen ions that exist in a given solution. H2O(I)↔H+(aq)+OH−(aq) *(aq) means water is the solvent that dissolves the ions Hydrogen ions spontaneously generate in pure water by the dissociati... |
to be 4.6 billion years old, but for the first 2 billion years the atmosphere lacked oxygen. Without oxygen, the planet could not support life. One hypothesis about how life emerged on earth involves the concept of “primordial soup.” This hypothesis proposes that life began in a body of water when metals and gases from... |
sing water" (Figure 3.6a). Conversely, the covalent bonds that hold the polymer together can also be broken if need be. When a hydrolysis reaction occurs, a water molecule is used to break a chemical bond (Figure 3.6b). We will look more closely at each type of reaction below. Figure 3.6 (a) In dehydration synthesis, t... |
he potato plant. When animals consume potatoes, the starch is broken down through hydrolysis reactions into monomers of glucose. Cells can then absorb the glucose and use it to generate their form of energy, ATP. Figure 3.13 a. A potato represents the root of a plant that stores the plant's starch. b. Potato cells stai... |
peanut butter, and shortening are examples of artificially hydrogenated trans-fats. Recent studies have shown that an increase in trans-fats in the human diet may lead to increased levels of low-density lipoprotein (LDL), or “bad” cholesterol. High levels of LDL can lead to plaque formation in the blood vessels, resul... |
Keratin, another critical protein in mammals, is the major component of skin and hair. Hair provides physical protection from damaging UV rays and helps organisms maintain stable body temperatures. Access for free at https://openstax.org/ 87 Proteins play many additional roles that are important in sustaining life. Ta... |
at there are still more exciting details to be learned on the process of protein folding. CONCEPTS IN ACTION - For an additional perspective on proteins, view this animation called “Biomolecules: The Proteins.” Access for free at https://openstax.org/ 93 MICRO CONNECTIONS - Primary Structure, Dysfunctional Proteins, an... |
e RNA, which is necessary to synthesize protein. DNA dictates the structure of mRNA in a process called transcription, and RNA dictates the protein's structure in a process called translation. This is the Central Dogma of Life, which holds true for many organisms (Figure 3.39). However, exceptions to the rule occur wit... |
by Ed Uthman, MD; scale-bar data from Matt Russell / Biology 2E OpenStax) Answer: Compound light microscope 106 Return to Table of Contents Section Summary A cell is the smallest unit of life. Most cells are so small that they cannot be viewed with the naked eye. Therefore, scientists must use microscopes to study cel... |
ize b. is similar in size c. is larger in size d. can be smaller or larger in size 3. Describe the structures that are characteristic of a prokaryote cell. Answers 1. (d) 2. (a) 3. Prokaryotic cells are surrounded by a plasma membrane and have DNA, cytoplasm, and ribosomes. They have cell walls and may have a cell caps... |
h organelles include the endoplasmic reticulum, Golgi apparatus, chloroplasts, mitochondria, and others (Figure 4.18). The word “organelle” means “little organ” and organelles have specialized cellular functions just as your body's organs have specialized functions. 120 Return to Table of Contents Figure 4.18 These fig... |
s that break down and digest unneeded cellular components, such as a damaged organelle. A lysosome is like a wrecking crew that takes down old and unsound buildings in a neighborhood. Lysosomes are also important for breaking down food materials or foreign materials that may be dangerous to the cell. For example, when ... |
proteins. Despite their fundamental similarities, there are some striking differences amongst the different groups of cells that make up the eukaryotes. Those groups being Plantae, Protista, Animalia, and Fungi. We will briefly introduce the groups Protista and Fungi, before focusing our attention on the kingdoms Plant... |
to be transported from cell to cell (Figure 4.33). These junctions between neighboring cells always remain open, and therefore, materials are continuously being shared amongst cells. Figure 4.33 A plasmodesma is a channel between two adjacent plant cells' cell walls. (credit: Clark et al. / Biology 2E OpenStax). Tight ... |
structure and function, all living cells are surrounded by a plasma membrane. As the outer layer of your skin separates your body from its environment, the cell membrane, also known as the plasma membrane, separates the inner contents of a cell from its exterior environment. This cell membrane provides a protective ba... |
re? a. protein b. cholesterol c. carbohydrate d. phospholipid 2. The phospholipids tails of the plasma membrane are composed of _____ and are _______? a. phosphate groups; hydrophobic b. fatty acid groups; hydrophilic c. phosphate groups; hydrophilic d. fatty acid groups; hydrophobic 3. Why is it advantageous for the c... |
h a semipermeable membrane separating the two sides or halves (Figure 5.10). On both sides of the membrane, the amount of water molecules is the same, but there are different concentrations of a dissolved substance, or solute, on each side. For example, on one side of the beaker, there is a single teaspoon of sugar dis... |
tant commonality—the cell did not have to use energy, ATP, to move materials. During active transport energy is required to move a substance across a membrane, often with the help of integral proteins, and usually against its concentration gradient. If a material must be moved out of the cell against its concentration ... |
During photosynthesis, plants use energy from sunlight to convert carbon dioxide gas (CO2) and water (H2O) into sugar molecules like glucose (C6H12O6) and oxygen (Figure 5.18). This metabolic pathway is quite extensive and will be covered in chapter 7. For now, we will summarize this metabolic pathway in the following... |
entropy. As the food coloring molecules begin to slowly diffuse in a glass of water, the entropy increases (Figure 5.25). Figure 5.25 Entropy increases as molecules diffuse. (credit: Modified by Elizabeth O'Grady original work of Robby Remedi) Living organisms are highly ordered. Organisms require a constant input of e... |
sses that require energy. In Figure 5.34, this sodium-potassium pump drives sodium out of the cell and potassium into the cell against its concentration gradient. For the pump to work, it requires energy in the form of ATP. When ATP hydrolyzes, its phosphate does not simply float away but is transferred onto the pump p... |
(credit: Clark et al. / Biology 2E OpenStax) Non-competitive inhibition In non-competitive inhibition, an inhibitor molecule binds to the enzyme in a location other than the active site, often called an allosteric site. The inhibitor still prevents the substrate from binding to the active site; however, it does so by c... |
in the form of heat. Aerobic cellular respiration can be summarized by the equation below: Figure 6.2 shows the reaction for aerobic cellular respiration. Note that this process consists of several chemical reactions, as indicated by the multiple arrows. (credit: Jason Cashmore) Breaking down sugar molecules occurs th... |
cose is oxidized to produce small amounts of ATP. Figure 6.10 Cellular respiration oxidizes glucose molecules through glycolysis, Krebs cycle (citric acid cycle), and oxidative phosphorylation to produce ATP. (credit: Betts et al. / Anatomy and Physiology OpenStax) Access for free at https://openstax.org/ 201 Glycolysi... |
valent), 6 NADH molecules, and 2 FADH2 molecules. Exercises 1. What do the electrons added to NAD+ do? a. They become part of glycolysis b. They go on to the electron transport chain. c. They energize the entry of the acetyl group into the citric acid cycle. d. They are converted into NADP. 2. In eukaryotic cells, wher... |
ppens to NADH when it arrives at the electron transport chain? a. It is reduced to NAD+ b. It is oxidized to NAD+ c. It is reduced to FAD d. It is oxidized to FAD 3. Chemiosmosis in eukaryotic cells involves: a. the movement of electrons across the cell membrane b. the movement of hydrogen atoms across the outer cell m... |
ntermediates and produce the same amount of ATP molecules as glucose. 220 Return to Table of Contents Connections of Proteins to Glucose Metabolism In cells, proteins are broken down by a variety of enzymes called proteases. Most of the time, amino acids are recycled into new proteins. If there are excess amino acids o... |
oids are stacked, disc-shaped structures found within the chloroplasts. Thylakoids are made up of membranes embedded with proteins and chlorophyll. Chlorophyll is a pigment molecule necessary to absorb light. The thylakoid membrane encloses an internal space called the thylakoid lumen. As shown in Figure 7.8, a stack o... |
y each type of pigment. Not all photosynthetic organisms have full access to sunlight. Some organisms grow underwater, where the light intensity decreases with depth, and the water absorbs certain wavelengths. Other organisms grow in places where they must compete for light. For example, plants on the rainforest floor ... |
ht-dependent reactions harness energy from the sun to produce ATP and NADPH. These energy-carrying molecules travel into the stroma where the Calvin cycle reactions take place. (credit: Fowler et al. / Concepts of Biology OpenStax) The Calvin cycle reactions (Figure 7.21) can be organized into three basic stages: carbo... |
ically identical cells. All multicellular organisms use cell division for growth, maintenance, and cell repair. Single-celled organisms, such as bacteria or yeast, must also reproduce; however, they do so on their own, asexually. At the end of asexual reproduction, the new daughter cells should be identical to the pare... |
e 8.9 (a) A centrosome is composed of two centrioles positioned at right angles to each other. (b) In animal cells, the centrosomes (arrows) serve as microtubule-organizing centers of the mitotic spindle during mitosis. (credit: Parker et al. / Microbiology OpenStax) G2 Phase In the G2 phase, or gap 2, the cell repleni... |
anchored to spindle fibers arising from opposite poles of the cell. 260 Return to Table of Contents CONCEPTS IN ACTION- Watch what occurs at the G1, G2, and M checkpoints by visiting this animation of the cell cycle. CANCER CONNECTION: The Implication of an Out of Control Cell Cycle Cancer is a collective name used to ... |
e cell elongates, and the duplicated chromosomes separate and move to opposite poles of the cell. Finally, the cell begins cytokinesis. Cytokinesis is directed by proteins that result in the formation of a septum. The septum consists of the bacterial cell wall and outer cell membranes. Once the septum is complete, the ... |
osome pairs one through twenty-two and do not determine a person’s biological sex (Figure 8.22). The twenty-third pair of chromosomes are referred to as the allosomes (Figure 8.22). Humans contain the allosomes X and Y. Some resources use the term “sex chromosomes” instead of allosomes. “Sex chromosome” is misleading. ... |
es decondense and the nuclear envelopes reform in telophase I. In other organisms, such as some protists, cytokinesis occurs without the reformation of the nuclei. 278 Return to Table of Contents Figure 8.27 demonstrates independent assortment in metaphase I. (credit: Clark et al./ Biology 2E OpenStax) Cytokinesis I In... |
ting cells are haploid meiosis II: the second round of meiotic cell division following meiosis I; sister chromatids are separated from each other, and the result is four unique haploid cells sperm: the male gamete; a haploid cell somatic cell: all the cells of a multicellular organism except the gamete-forming cells te... |
ppens in animal cells. a. True b. False 4. Explain what a karyotype is and why a karyogram helps identify different genetic conditions. Answers 1. (b) 2. (a) 3. (b) 4. A karyotype is the number and appearance of an individual’s chromosomes, including their length, banding pattern, and centromere position. Abnormalities... |
hypothesis because of what is commonly referred to as continuous variation. Continuous variation occurs when a character, such as height in humans, is influenced by several different genes. Mendel worked with traits that show discontinuous variation. Discontinuous variation is when each individual exhibits one of two e... |
offspring have an equal likelihood of inheriting either gene. Recall that in meiosis, homologous chromosomes are separated into different haploid gametes arbitrarily (Figure 9.5). An individual’s characteristics are a result of the genes carried on chromosomes. When a haploid gamete from one parent fertilizes a haploi... |
an genetic characteristics (Figure 9.10). A pedigree is chart used to study inheritance patterns of genetic characteristics. How can a pedigree be used to study inheritance patterns? Let’s look at an example of a recessive disorder, alkaptonuria, in which two amino acids, phenylalanine and tyrosine, are not properly me... |
nant and one recessive, could exist for a given gene. For example, violet or white flowers and yellow or green seeds. We know now that this is an oversimplification in most cases. Many genes have more than just two different alleles. Human blood type is an example of a character that is determined by three different al... |
s led to the Chromosomal Theory of Inheritance. The Chromosomal Theory of Inheritance states that genes are found at specific locations on chromosomes and that it is the chromosomes that independently assort and segregate during metaphase I and anaphase I of meiosis I (Figure 9.17). Figure 9.17: Shows how chromosomes a... |
ong individuals as the: a. variant b. wild type c. dosage d. none of the above 3. When two genes are located in close proximity on the same chromosome, they are considered linked, and their alleles tend to be passed through meiosis together. a. TRUE b. FALSE Answers 1. (1) During meiosis, homologous chromosome pairs mi... |
. Figure 9.23 X-Linked Recessive Inheritance Given two parents in which the father is normal, and the mother is a carrier of an X-linked recessive disorder, a son would have a 50 percent probability of being affected with the disorder. In contrast, daughters would either be carriers or entirely unaffected. (credit: U.S... |
ents learned about nucleic acids, one of the four different biologically important molecules found in all living cells. Recall that there are two important polymers of nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Although both DNA and RNA are made up of nucleotides, they function differently w... |
how the replication took place. There were three models suggested (Figure 10.11): conservative, semi-conservative, and dispersive. Access for free at https://openstax.org/ 343 In conservative replication, the “old” parental DNA strands remains together, and the newly formed DNA strands come together to form the second... |
mpared to the multiple linear chromosomes found in eukaryotic cells. We will only briefly discuss prokaryotic replication in this chapter, but students that take microbiology will have the opportunity to look more closely at this process. DNA replication has been extremely well-studied in prokaryotes, primarily because... |
fragments together DNA polymerase: an enzyme that synthesizes a new strand of DNA complementary to a template strand helicase: an enzyme that helps to open up the DNA helix during DNA replication by breaking the hydrogen bonds lagging strand: during replication of the 3' to 5' strand, the strand that is replicated in ... |
typical prokaryotic mRNA lasts no more than five seconds. The mRNA transcript is first coated in RNA-stabilizing proteins to prevent it from degrading while it is processed and exported out of the nucleus. This occurs while the mRNA transcript is still being synthesized and involves adding a special nucleotide “cap” to... |
RNA is generated using the nitrogenous bases adenine, cytosine, guanine, and uracil. During translation the mRNA nucleotide sequence is used to generate a protein. Proteins can be made up of as many as 20 different amino acids. Each amino acid is defined by a threenucleotide sequence called the triplet codon. The relat... |
is extremely complex and will only be covered briefly. To understand how gene expression is regulated, we must first understand how a gene codes for a functional protein in a cell. The process occurs in both prokaryotic and eukaryotic cells, just in slightly different manners. Prokaryotic Gene Expression Because proka... |
pecies change overtime. Darwin not only explained the mechanism of how genetic change occurred (natural selection), but also provided data that supported that change. The view that species were static and unchanging was based on the writings of Plato. Other ancient Greeks at the time of Plato did not agree and expresse... |
s can and often do change. For example, finches with large bills were benefited in one climate, while finches with small bills were at a disadvantage. In a different climate, the relationship may be reversed. Patterns of Evolution The evolution of species has resulted in enormous variation in form and function. When tw... |
different traits. The advantageous traits will be passed on to offspring in greater proportion. Thus, the trait will have higher representation in the next and subsequent generations leading to genetic change in the population. The modern synthesis of evolutionary theory grew out of the understanding of Darwin’s, Walla... |
likely to remove all copies of an allele (Figure 11.9). 390 Return to Table of Contents Figure 11.9 Genetic drift has less of an impact on a large population vs. a small population. (credit: Elizabeth O’Grady) Genetic drift can also be magnified by natural or human-caused events, such as a disaster that randomly kills ... |
. Scientists call these synonymous parts homologous structures. Some structures exist in organisms that have no apparent function at all and appear to be residual “leftovers” from a past ancestor. For example, some snakes have pelvic bones despite having no legs. This can be explained by understanding that snakes desce... |
theory in science has survived significant efforts to discredit it. It is a culmination of the work done by many different scientists and the conclusions drawn have been verified and repeated numerous times. While theories can sometimes be overturned or revised, this does not lessen their weight but simply reflects the... |
the RNA transcript amino acid: a monomer of a protein anabolic: describes the pathway that requires a net energy input to synthesize complex molecules from simpler ones anaerobic cellular respiration: the use of an electron acceptor other than oxygen to complete metabolism anaerobic: process in which organisms do not r... |
carbon sugar molecule with a hydrogen atom rather than a hydroxyl group in the 2' position; the sugar component of DNA nucleotides dependent variable: the variable that will change when the independent variable is altered; this is what the researcher will measure or observe during the experiment desmosome: a linkage be... |
different alleles for a given gene on the homologous chromosomes homeostasis: the ability of an organism to maintain constant internal conditions homologous chromosomes: the randomness of how the homologous chromosome pairs align at the metaphase plate during metaphase I of meiosis I homologous structure: a structure ... |
equally between atoms, resulting in no regions with partial charges as in polar covalent bonds nuclear envelope: the double-membrane structure that constitutes the outermost portion of the nucleus nuclear pores: control the passage of ions, molecules, and RNA between the nucleus and the cytoplasm nucleic acid: a biolo... |
vations or phenomena second law of thermodynamics: states that every energy transfer or transformation increases the universe's entropy secondary structure: structure that proteins form by hydrogen bonding between the oxygen atom of one amino acid, and the hydrogen attached to the nitrogen atom of another amino acid se... |
credit c: modification of work by Michael Arrighi; credit d: modification of work by Frank Vassen Concepts of Biology OpenStax Creative Commons Attribution License v4.0 https://openstax.org/books/concepts-biology/pages/1-1themes-and-concepts-of-biology#fig-ch01_01_09 Figure1.15 Eric Gaba Figure1.16 Mario Modesto Conce... |
tomy-andphysiology/pages/2-4-inorganic-compounds-essential-tohuman-functioning#fig-ch02_04_01 Figure 3.6 Betts et al. Figure 3.7 Clark et al. Figure 3.8 Clark et al. Figure 3.9 Fowler et al. Anatomy and Physiology OpenStax Creative Commons Attribution License v4.0 Biology 2E OpenStax Biology 2E OpenStax Creative Common... |
tion License v4.0 https://openstax.org/books/concepts-biology/pages/3-3eukaryotic-cells#fig-ch03_03_05 Figure 4.21 Clark et al. / credit b: modification of work by NIH; scale-bar data from Matt Russell Biology 2E OpenStax Creative Commons Attribution License v4.0 https://openstax.org/books/biology-2e/pages/4-3-eukaryot... |
izabeth O’Grady original work by Robby Remedi "dam": modification of work by "Pascal"/Flickr; "waterfall": modification of work by Frank Gualtieri Concepts of Biology OpenStax Creative Commons Attribution License v4.0 https://openstax.org/books/concepts-biology/pages/4-1energy-and-metabolism#fig-ch04_01_02 Anatomy and ... |
omain Creative Commons CC0 1.0 Universal Public Domain https://en.wikipedia.org/wiki/File:Catha_edulis.jpg https://en.wikipedia.org/wiki/File:The_Sun_by_the_Atmosp heric_Imaging_Assembly_of_NASA%27s_Solar_Dynamics _Observatory_-_20100819.jpg Figure 7.5 Fowler et al. Figure 7.6 Jason Cashmore Concepts of Biology OpenSta... |
openstax.org/books/biology-2e/pages/11-1-theprocess-of-meiosis#fig-ch11-01-03 https://openstax.org/books/biology-2e/pages/11-1-theprocess-of-meiosis#fig-ch11-01-04 https://openstax.org/books/biology-2e/pages/11-1-theprocess-of-meiosis#fig-ch11-01-06 https://openstax.org/books/biology-2e/pages/13-2chromosomal-basis-of-i... |
ve Commons Attribution License v4.0 https://openstax.org/resources/1dfbdea58671106a14e26fcc0 735627299c23dfa Figure 10.22 Betts et al. Anatomy and Physiology OpenStax Creative Commons Attribution License v4.0 https://openstax.org/resources/55d9345e34df0de9e0aa8c8e7 5e487835a900ff0 XXXIV Return to Table of Contents Figu... |
in did not actually discuss this idea in his book, but it followed directly from the principles he outlined. In a subsequent book, The Descent of Man, Darwin presented the argument directly, building a powerful case that humans and living apes have common ancestors. Although people had long accepted that humans closely... |
ciples of biology, introduced through a levels-oforganization framework (see figure 1.2). At the molecular, organellar, and cellular levels of organization, you will be introduced to cell biology. You will learn how cells are constructed and how they grow, divide, and communicate. At the organismal level, you will lear... |
make 1 gram! A proton weighs approximately 1 dalton (actually 1.009 daltons), as does a neutron (1.007 daltons). In contrast, electrons weigh only 1 1840 of a dalton, so their contribution to the overall mass of an atom is negligible. Within the nucleus, the cluster of protons and neutrons is held together by a force t... |
lectron is called oxidation, and the gain of an electron is called reduction (figure 2.6). It is important to realize that when an electron is transferred in this way, it keeps its energy of position. In organisms, chemical energy is stored in high-energy electrons that are transferred from one atom to another in react... |
icular ions in the compound; rather, they exist between an ion and all of the oppositely charged ions in its immediate vicinity. Na Cl Sodium atom Chlorine atom Na+ Cl Cl Na Cl Na Cl Na Cl Na Cl + (a) Sodium ion – Chloride ion (b) NaCl crystal FIGURE 2.9 The formation of ionic bonds by sodium chloride. (a) When a sodiu... |
2.13 Structure of a hydrogen bond. charges are much less than the unit charges of ions, however.) Molecules that exhibit charge separation are called polar molecules because of their magnet-like poles, and water is one of the most polar molecules known. The polarity of water underlies its chemistry and the chemistry o... |
an be induced in just this way. Water molecules, which are very polar, cling to one another, so that it takes considerable energy to separate them. Water also clings to other polar molecules, causing them to be soluble in water solution, but water tends to exclude nonpolar molecules. Chapter 2 The Nature of Molecules 3... |
toms. This charge separation makes water a polar molecule. • A hydrogen bond is formed between the partial positive charge of a hydrogen atom in one molecule and the partial negative charge of another atom, either in another molecule or in a different portion of the same molecule. • Water is cohesive and adhesive, has ... |
roup to the other, breaking a specific covalent bond in the macromolecule. Hydrolytic reactions release the energy that was stored in the bonds that were broken. FIGURE 3.3 Making and breaking macromolecules. (a) Biological macromolecules are polymers formed by linking subunits together. The covalent bond between the s... |
— OH — —— H O H2N — C — C — OH — ——— H O Alanine (Ala) Valine (Val) Leucine (Leu) Isoleucine (Ile) Phenylalanine (Phe) Tryptophan (Trp) Polar uncharged H — OH — CH2 — CH3 — H — C — OH — O NH2 C — CH2 — O NH2 C — CH2 — CH2 — OH — — CH2 — H2N — C — C — OH —— — H O H2N — C — C — OH —— — H O H2N — C — C — OH —— — H O H2N ... |
ly folded protein How does a protein fold into a specific shape? Nonpolar amino acids play a key role. Until recently, investigators thought that newly made proteins fold spontaneously as hydrophobic interactions with water shove nonpolar amino acids into the protein interior. We now know this is too simple a view. Pro... |
ied a million times! The molecule is so slender that it would take 50,000 of them to equal the diameter of a human hair. FIGURE 3.12 A scanning tunneling micrograph of DNA (false color; 2,000,000×). The micrograph shows approximately three turns of the DNA double helix (see figure 3.15). The Structure of Nucleic Acids ... |
gate together in water. This kind of aggregation by phospholipids forms biological membranes. Hydrophobic "tails" Hydrophilic "heads" (a) Hydrophilic region Hydrophobic region Hydrophilic region (b) Oil Water Water Water FIGURE 3.18 Phospholipids. (a) At an oil-water interface, phospholipid molecules will orient so tha... |
after another in long chains. Cellulose is a polysaccharide that serves as a structural building material in plants. It too consists entirely of glucose molecules linked together into chains, and special enzymes are required to break the links. Sugar Isomers Glucose is not the only sugar with the formula C6H12O6. Other... |
al for cells. Cellulose H H O (a) HO OH OH (b) H 4 H 1 H OH CH2OH α form of glucose For two glucose molecules to link together, the glucose subunits must be the same form. Glucose can form a ring in two ways, with the hydroxyl group attached to the carbon where the ring closes being locked into place either below or ab... |
. Most animals move about (figure 4.2), but movement from one place to another in itself is not diagnostic of life. Most plants and even some animals do not move about, while numerous nonliving objects, such as clouds, do move. The criterion of movement is thus neither necessary (possessed by all life) nor sufficient (... |
e 4.5), and then we will consider how those molecules might have become organized into living cells. Panspermia and spontaneous origin are the only testable hypotheses of life’s origin currently available. Scientists Disagree about Where Life Started While most researchers agree that life first appeared as the primitiv... |
that simple proteins are easier to synthesize from abiotic components than nucleotides, both can form in the laboratory under the right conditions. Deciding which came first is a chicken-and-egg paradox. In an effort to shed light on this problem, Julius Rebek and a number of Water Nitrogen Ammonia Carbon dioxide Carbo... |
ingle-stranded. Little is known about how the first cells originated. Current hypotheses involve chemical evolution within bubbles, but there is no general agreement about their composition, or about how the process occurred. Chapter 4 The Origin and Early History of Life 67 The Earliest Cells What do we know about the... |
by examining rocks containing particular kinds of fossils; the fossils are dated by determining the degree of spontaneous decay of radioactive isotopes locked within rock when it was formed. 70 Part I The Origin of Living Things Infolding of the plasma membrane DNA Cell wall Endoplasmic reticulum (ER) Nuclear envelope... |
ite photos taken in 1999 suggest that a few miles under the ice lies a liquid ocean of water larger than earth’s, warmed by the push and pull of the gravitational attraction of Jupiter’s many large satellite moons. The conditions on Europa now are far less hostile to life than the conditions that existed in the oceans ... |
ation at the low speeds used in these experiments does not disrupt the integrity or shape of the protoplasts. The protoplasts were immobilized for centrifugation by embedding them in an agar medium supported in a mold. The embedded protoplasts were spun in a centrifuge at 450 rpm for 15 minutes. Following centrifugatio... |
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