Deoxyguanosine triphosphate dGTP. Thymidine triphosphate TTP. Click the button below to examine the structure of deoxyadenine monosphosphate dAMP.
Notice the angle of the sugar and phosphate groups in relation to the planar nitrogenous base. In double-stranded DNA, two long molecules twist around one another in a double helix. These molecules are d eoxy n ucleic a cids DNA : polymers made up of nucleotides In a DNA double helix, the phosphate and sugar groups make up the outer 'backbones,' and the flat nitrogenous bases are pointed toward the middle of the helix.
Click the buttons below to examine a segment of a DNA double helix from many angles. The first button has colored the backbone sugar and phosphate groups purple to simplify the image. One key point to notice in the DNA double helix structure is that the planar nitrogenous bases from the two strands are pointing toward each other, in the middle of the helix. Pairs of nitrogenous bases are set in the same plane, and interact with each other via hydrogen bonding.
These pairs are often referred to as base pairs , abbreviated 'bp. Recall that electronegativity values generally increase toward the top and right of the periodic table, as illustrated in the image below. Oxygen and nitrogen are electronegative atoms found in nitrogenous bases. They are represented in models by the color conventions: red for oxygen , and blue for nitrogen.
Electronegative O and N atoms with free lone pairs are potential hydrogen bond acceptors. Hydrogen atoms attached to very electronegative atoms like O and N have strong partial positive charge and are potential hydrogen bond donors.
Its conformation is essential to its function. The overall structure of the protein includes both alpha helices green and beta sheets red. The primary structure of a protein — its amino acid sequence — drives the folding and intramolecular bonding of the linear amino acid chain, which ultimately determines the protein's unique three-dimensional shape.
Hydrogen bonding between amino groups and carboxyl groups in neighboring regions of the protein chain sometimes causes certain patterns of folding to occur. Known as alpha helices and beta sheets , these stable folding patterns make up the secondary structure of a protein.
Most proteins contain multiple helices and sheets, in addition to other less common patterns Figure 2. The ensemble of formations and folds in a single linear chain of amino acids — sometimes called a polypeptide — constitutes the tertiary structure of a protein.
Finally, the quaternary structure of a protein refers to those macromolecules with multiple polypeptide chains or subunits. The final shape adopted by a newly synthesized protein is typically the most energetically favorable one.
As proteins fold, they test a variety of conformations before reaching their final form, which is unique and compact. Folded proteins are stabilized by thousands of noncovalent bonds between amino acids. In addition, chemical forces between a protein and its immediate environment contribute to protein shape and stability. For example, the proteins that are dissolved in the cell cytoplasm have hydrophilic water-loving chemical groups on their surfaces, whereas their hydrophobic water-averse elements tend to be tucked inside.
In contrast, the proteins that are inserted into the cell membranes display some hydrophobic chemical groups on their surface, specifically in those regions where the protein surface is exposed to membrane lipids. It is important to note, however, that fully folded proteins are not frozen into shape. Rather, the atoms within these proteins remain capable of making small movements.
Even though proteins are considered macromolecules, they are too small to visualize, even with a microscope. So, scientists must use indirect methods to figure out what they look like and how they are folded. The most common method used to study protein structures is X-ray crystallography. With this method, solid crystals of purified protein are placed in an X-ray beam, and the pattern of deflected X rays is used to predict the positions of the thousands of atoms within the protein crystal.
In theory, once their constituent amino acids are strung together, proteins attain their final shapes without any energy input. In reality, however, the cytoplasm is a crowded place, filled with many other macromolecules capable of interacting with a partially folded protein.
Inappropriate associations with nearby proteins can interfere with proper folding and cause large aggregates of proteins to form in cells. Cells therefore rely on so-called chaperone proteins to prevent these inappropriate associations with unintended folding partners. Chaperone proteins surround a protein during the folding process, sequestering the protein until folding is complete.
For example, in bacteria, multiple molecules of the chaperone GroEL form a hollow chamber around proteins that are in the process of folding. Molecules of a second chaperone, GroES, then form a lid over the chamber. Note that there are two strands: one shown in blue, one in yellow. Other examples of a helix include yarn, a phone cord, or a spiral staircase. Each chain of the double helix is made up of repeating units called nucleotides.
A single nucleotide is composed of three functional groups: a sugar , a triphosphate, and a nitrogenous nitrogen-containing base , as shown below.
Note that in the figures drawn in this unit, each unlabeled vertex of a structure represents a carbon atom. The sugar found in DNA is a variant of the five-carbon sugar called ribose. The structure of ribose is drawn below. Each carbon of ribose is numbered as shown. Correct answer: A nitrogenous base and a ribose or deoxyribose sugar.
Explanation : This question is mostly about the differentiations between a nucleoside and a nucleotide. Possible Answers: A covalent bond is formed. Correct answer: Maximized number of hydrogen bonds. Explanation : Cytosine and guanine, when base paired, have three hydrogen bonds between them. Chargaff is credited with which of the following discoveries about DNA base pairs?
Possible Answers: The ratio of adenine to guanine is close to and the ratio of cytosine to thymine is close to. Correct answer: The ratio of adenine to thymine is close to and the ratio of guanine to cytosine is close to.
Explanation : Due to DNA's double-helical structure, the nucleotide bases are paired. Copyright Notice. View AP Biology Tutors. Rachel Certified Tutor. University of Colorado Denver, Masters, Social Alyssa Certified Tutor. Reanna Certified Tutor. Report an issue with this question If you've found an issue with this question, please let us know. Do not fill in this field. Louis, MO Or fill out the form below:.
Company name. Copyright holder you represent if other than yourself. I am the owner, or an agent authorized to act on behalf of the owner of an exclusive right that is allegedly infringed.
I have a good faith belief that the use of the material in the manner complained of is not authorized by the copyright owner, its agent, or the law. This notification is accurate. I acknowledge that there may be adverse legal consequences for making false or bad faith allegations of copyright infringement by using this process. Find the Best Tutors Do not fill in this field. Your Full Name. Phone Number. Zip Code.
0コメント