CH.5

Chaperonins, a type of protein shields a newly forming protein from cytoplasmic influences while it is folding into its functional form.

A polypeptide chain of a given amino acid sequence can spontaneously arrange itself into a three-dimensional shape determined and maintained by the interactions responsible for secondary and tertiary structure. This folding normally occurs as the protein is being synthesized in the crowded environment within a cell, aided by other proteins. Crucial to the folding process are chaperonins (also called chaperone proteins), protein molecules that assist in the proper folding of other proteins. Chaperonins shield proteins from "bad influences" (interactions with other molecules in the cytoplasm) while they are folding into their functional forms.

Hydrophobic interaction

A type of interaction that contributes to tertiary structure. As a polypeptide folds into its functional shape, amino acids with hydrophobic (nonpolar) side chains usually end up in clusters at the core of the protein, out of contact with water. Thus, a "hydrophobic interaction" is actually caused by the exclusion of nonpolar substances by water molecules. Once nonpolar amino acid side chains are close together, van der Waals interactions help hold them together.

One characteristic shared by sucrose, lactose, and maltose is that they are all disaccharides.

Carbohydrates include both sugars and polymers of sugars. The simplest carbohydrates are the monosaccharides, or simple sugars; these are the monomers from which more complex carbohydrates are constructed. Carbohydrates also include macromolecules called polysaccharides, polymers composed of many sugar building blocks. Disaccharides, such as sucrose, maltose, and lactose, are double sugars, consisting of two monosaccharides joined by a glycosidic linkage. A polysaccharide is composed of many monosaccharide building blocks. A monosaccharide is a simple sugar containing three to seven carbons. All three of these molecules are digestible by humans.

Carbohydrates are used in our bodies mainly for energy storage and release.

Carbohydrates include both sugars and polymers of sugars. The simplest carbohydrates are the monosaccharides, or simple sugars; these are the monomers from which more complex carbohydrates are constructed. Carbohydrates also include macromolecules called polysaccharides, polymers composed of many sugar building blocks. Simple sugar molecules, stored in polysaccharides such as glycogen in animals and starch in plants, are a major energy source for cellular work. Membranes are composed primarily of lipids.

Sugars are molecules that have a 1:2:1 ratio of C:H:O and are called carbohydrates.

Carbohydrates include sugars and polymers of sugars. The simplest carbohydrates are the monosaccharides, or simple sugars; these are the monomers from which more complex carbohydrates are built. Monosaccharides (from the Greek monos, single, and sakchar, sugar) generally have molecular formulas that are some multiple of the unit CH2O. Glucose (C6H12O6), the most common monosaccharide, is of central importance in the chemistry of life. Disaccharides are double sugars consisting of two monosaccharides joined by a covalent bond. Carbohydrate macromolecules are polymers called polysaccharides, which are composed of many sugar building blocks.

Chitin is not found in humans.

Chitin is a structural polysaccharide found in the exoskeleton of arthropods.

In living organisms, DNA exists as a double helix with the strands running antiparallel.

DNA molecules have two polynucleotides, or "strands," that wind around an imaginary axis, forming a double helix. The two sugar-phosphate backbones run in opposite 5′ → 3′ directions from each other; this arrangement is referred to as antiparallel and is somewhat like a divided highway. The sugar-phosphate backbones are on the outside of the helix, and the nitrogenous bases are paired on the interior of the helix. The two strands are held together by hydrogen bonds between the paired bases. Most DNA molecules are very long, with thousands or even millions of base pairs. For example, the one long DNA double helix in a eukaryotic chromosome includes many genes, each one a particular segment of the molecule.

Disulfide bridges may further reinforce the shape of a protein.

Disulfide bridges form where two cysteine monomers, which have sulfhydryl groups (-SH) on their side chains, are brought close together by the folding of the protein. The sulfur of one cysteine bonds to the sulfur of the second, and the disulfide bridge (-S-S-) rivets parts of the protein together.

Protein molecules are polymers (chains) of amino acid molecules.

Diverse as proteins are, they are all unbranched polymers constructed from the same set of 20 amino acids. Polymers of amino acids are called polypeptides. A protein is a biologically functional molecule that consists of one or more polypeptides, each folded and coiled into a specific three-dimensional structure.

Nitrogenous bases are classified as either purines or pyrimidines. Examples of purines are adenine and guanine.

Each nitrogenous base has one or two rings that include nitrogen atoms. (They are called nitrogenous bases because the nitrogen atoms tend to take up H++ from solution, thus acting as bases.) There are two families of nitrogenous bases: pyrimidines and purines. A pyrimidine has one six-membered ring of carbon and nitrogen atoms. The members of the pyrimidine family are cytosine (C), thymine (T), and uracil (U). Purines are larger, with a six-membered ring fused to a five-membered ring. The purines are adenine (A) and guanine (G). The specific pyrimidines and purines differ in the chemical groups attached to the rings. Adenine, guanine, and cytosine are found in both DNA and RNA; thymine is found only in DNA and uracil only in RNA.

Enzymes

Enzymes are proteins that act as biological catalysts.

A polysaccharide that is used for storing energy in human muscle and liver cells is glycogen.

Humans and other vertebrates store glucose as a polysaccharide called glycogen in their liver and muscles.

In a dehydration synthesis reaction, water is always formed as a by-product of the reaction.

In cells, these processes are facilitated by enzymes, specialized macromolecules that speed up chemical reactions. Monomers are connected by a reaction in which two molecules are covalently bonded to each other, with the loss of a water molecule; this is known as a dehydration reaction. When a bond forms between two monomers, each monomer contributes part of the water molecule that is released during the reaction: One monomer provides a hydroxyl group (-OH), while the other provides a hydrogen group (-H). This reaction is repeated as monomers are added to the chain one by one, making a polymer.

Cellulose is a carbohydrate.

It consists of carbon, oxygen, and hydrogen. It is a structural polysaccharide found in plant cell walls. It is a polymer.

The type of bond that forms to join monomers (such as sugars and amino acids) into polymers (such as starch and proteins) is a covalent bond.

Monomers are joined together by a dehydration reaction in which two molecules are covalently bonded to each other through the loss of a water molecule. A hydrogen bond is a relatively weak bond between polar molecules. An ionic bond cannot form because sugars are not ions. A peptide bond is a specific type of covalent bond not found in polysaccharides. Van der Waals interactions do not link monomers together. They play a role in the tertiary structure of proteins.

Sugars have a carbonyl (-C=O) group that interacts with a hydroxyl (-OH) group that forms ring structures when the dry molecule is placed in water.

Monosaccharides (from the Greek monos, single, and sakchar, sugar) generally have molecular formulas that are some multiple of the unit CH2O. Glucose (C6H12O6), the most common monosaccharide, is of central importance in the chemistry of life. In the structure of glucose, we can see the trademarks of a sugar: The molecule has a carbonyl group (CO) and multiple hydroxyl groups (-OH). Depending on the location of the carbonyl group, a sugar is either an aldose (aldehyde sugar) or a ketose (ketone sugar). Glucose, for example, is an aldose; fructose, an isomer of glucose, is a ketose. (Most names for sugars end in the suffix -ose.) Another criterion for classifying sugars is the size of the carbon skeleton, which ranges from three to seven carbon molecules long. Glucose, fructose, and other sugars that have six carbon molecules are called hexoses. Trioses (three-carbon sugars) and pentoses (five-carbon sugars) are also common.

The secondary structure of a peptide backbone is stabilized by hydrogen bonds forming either an α helix or a β pleated sheet.

Most proteins have segments of their polypeptide chains repeatedly coiled or folded in patterns that contribute to the protein's overall shape. These coils and folds, collectively referred to as secondary structure, are the result of hydrogen bonds between the repeating constituents of the polypeptide backbone (not the amino acid side chains). Within the backbone, the oxygen atoms have a partial negative charge, and the hydrogen atoms attached to the nitrogen atoms have a partial positive charge; therefore, hydrogen bonds can form between these atoms. Individually, these hydrogen bonds are weak, but because there are so many of them over a relatively long region of the polypeptide chain, they can support a particular shape for that part of the protein. One such secondary structure is the α helix, a delicate coil held together by hydrogen bonding between every fourth amino acid, as shown below. Although each transthyretin polypeptide has only one α helix, other globular proteins have multiple stretches of α helix separated by nonhelical regions. Some fibrous proteins, such as α-keratin, the structural protein of hair, have the α helix structure over most of their length. The other main type of secondary structure is the β pleated sheet. As shown below, in this structure two or more segments of the polypeptide chain lying side by side (called β strands) are connected by hydrogen bonds between parts of the two parallel segments of the polypeptide backbone.

The components of nucleic acids are a nitrogenous base, a pentose sugar, and a phosphate.

Nucleic acids are macromolecules that exist as polymers called polynucleotides. As indicated by the name, each polynucleotide consists of monomers called nucleotides. A nucleotide, in general, is composed of three parts: a five-carbon sugar (a pentose), a nitrogen-containing (nitrogenous) base, and one or more phosphate groups. In a polynucleotide, each monomer has only one phosphate group. The portion of a nucleotide without any phosphate group is called a nucleoside.

A shortage of phosphorus in the soil would make it especially difficult for a plant to manufacture DNA.

Nucleic acids are macromolecules that exist as polymers called polynucleotides. DNA (deoxyribonucleic acid) is an example of a nucleic acid. As indicated by the name, each polynucleotide consists of monomers called nucleotides. A nucleotide, in general, is composed of three parts: a nitrogen-containing (nitrogenous) base, a five-carbon sugar (a pentose), and one or more phosphate groups. In a polynucleotide, each monomer has only one phosphate group. The backbone of a nucleic acid consists of alternating sugar and phosphate groups. Proteins are made up of amino acids, and none of the amino acids used by living organisms contains phosphorus.

Things peptide bonds are not:

Peptide bonds are not weak interactions, such as hydrogen bonds. Peptide bonds do not link simple sugars together. A peptide bond is not a hydrogen bond, and it does not join nucleotides together. Nucleotides are joined together by phosphodiester linkages, not peptide bonds.

Water is always involved in hydrolysis reactions.

Polymers are disassembled to monomers by hydrolysis, a process that is essentially the reverse of the dehydration reaction. Hydrolysis means "water breakage" (from the Greek hydro, water, and lysis, break). The bond between monomers is broken by the addition of a water molecule, with a hydrogen group from water attaching to one monomer and the hydroxyl group attaching to the other monomer.

At a conference, the speaker's grand finale was sautéing mealworms (insect larvae) in butter and serving them to the audience. They were crunchy (like popcorn hulls) because their exoskeletons contain the polysaccharide chitin.

Polysaccharides are macromolecules, polymers with a few hundred to a few thousand monosaccharides joined by glycosidic linkages. Some polysaccharides serve as storage material, hydrolyzed as needed to provide sugar for cells. Other polysaccharides serve as building material for structures that protect the cell or the whole organism. Chitin is the structural polysaccharide found in arthropod exoskeletons.

Fatty acids have long carbon skeletons with a carbonyl group at one end.

They do not contain phosphorus.

tertiary structure is the result of

R group interactions.

The molecule with four fused rings that is found in animal membranes and is the precursor of vertebrate sex hormones is cholesterol.

Steroids are lipids characterized by a carbon skeleton consisting of four fused rings. Different steroids are distinguished by the particular chemical groups attached to this ensemble of rings. Cholesterol, a type of steroid, is a crucial molecule in animals. It is a common component of animal cell membranes and is also the precursor from which other steroids, such as the vertebrate sex hormones, are synthesized. In vertebrates, cholesterol is synthesized in the liver and is also obtained from the diet. A high level of cholesterol in the blood may contribute to atherosclerosis. In fact, both saturated fats and trans fats exert their negative impact on health by affecting cholesterol levels.

The sex hormones estrogen, progesterone, and testosterone belong to lipids.

Steroids, such as estrogen, progesterone, and testosterone, are lipids based on their insolubility in water. The molecules are characterized by a carbon skeleton consisting of four fused rings of carbon atoms. Different steroids, such as cholesterol and the vertebrate sex hormones, are distinguished by the particular chemical groups attached to this ensemble of rings. Sex hormones are not proteins, amino acids, carbohydrates, or nucleic acids.

The tertiary structure of a protein includes all of the following interactions except peptide bonds.

Superimposed on the patterns of secondary structure is a protein's tertiary structure. While secondary structure involves interactions between backbone constituents, tertiary structure is the overall shape of a polypeptide resulting from interactions between the side chains (R groups) of the various amino acids.

The subunits (monomers) in cellulose are linked together by glycosidic linkages.

The glucose monomers of cellulose are linked together by a specific type of covalent bond known as a glycosidic linkage. Polysaccharides are macromolecules, polymers with a few hundred to a few thousand monosaccharides joined by covalent bonds.

Generally, animals cannot digest (hydrolyze) the glycosidic linkages between the glucose molecules in cellulose. Cows get enough nutrients from eating grass because microorganisms in their digestive tracts hydrolyze the cellulose to individual glucose units.

The polysaccharide called cellulose is a major component of the tough walls that enclose plant cells. Like starch, cellulose is a polymer of glucose, but the glycosidic linkages in these two polymers differ. In starch, all the glucose monomers are in the α configuration. In contrast, the glucose monomers of cellulose are all in the β configuration, making every glucose monomer "upside down" with respect to its neighbors. Enzymes that digest starch by hydrolyzing its α linkages are unable to hydrolyze the β linkages of cellulose because of the distinctly different shapes of these two molecules. In fact, few organisms possess enzymes that can digest cellulose. Cows have digestive chambers populated by microorganisms that can produce certain hydrolytic enzymes that cows cannot. The enzymes hydrolyze (digest) the cellulose polymer into glucose monomers.

When comparing saturated and naturally occurring unsaturated fats, the unsaturated fats have cis double bonds and are liquids at room temperature.

The terms saturated fats and unsaturated fats are commonly used in the context of nutrition. These terms refer to the structure of the hydrocarbon chains of the fatty acids. If there are no double bonds between carbon atoms composing a chain, then as many hydrogen atoms as possible are bonded to the carbon skeleton. Such a structure is said to be saturated with hydrogen, and the resulting fatty acid is therefore called a saturated fatty acid. An unsaturated fatty acid has one or more double bonds, with one fewer hydrogen atom on each double-bonded carbon. Nearly all double bonds in naturally occurring fatty acids are cis double bonds, which cause a kink in the hydrocarbon chain wherever they occur.

The peptide bond is a covalent bond joining amino acids together to form a polypeptide.

When two amino acids are positioned so that the carboxyl group of one is adjacent to the amino group of the other, they can become joined by a dehydration reaction, with the removal of a water molecule. The resulting covalent bond is called a peptide bond. Repeated over and over, this process yields a polypeptide, a polymer of many amino acids linked by peptide bonds.

Starch is:

a storage polysaccharide found especially in certain plant tissues.

Thymine and cytosine

are both pyrimidines.

Hair and fingernails

are composed primarily of protein.

Receptor proteins

bind signaling molecules such as endorphins that may change the behavior of a cell.

Macromolecules, the molecules of life, include

carbohydrates, proteins, nucleic acids.

Estrogen and testosterone: they are derived from

cholesterol and are sex hormones, not components of animal membranes.

A phospholipid is

found in animal membranes, it is not a four-ring structure called a steroid.

Antibodies

have a specific form that allows them to bind to foreign materials in the body.

Fatty acids are:

joined to glycerol by ester linkages.

Nucleotides are:

joined together by phosphodiester linkages

secondary structure is the result of

hydrogen bond formation.

Collagen

is a structural protein found in tendons and ligaments (among other places).

Genetic material

is composed of nucleic acids, and enzymatic proteins catalyze its construction.

Sucrose is a disaccharide sugar

it does not contain phosphorus.

Carbohydrate monomers are:

not ions linked by ionic bonds.

Sickle-cell anemia is a disease that is caused by a single amino acid change in the primary structure of the protein.

sickle-cell disease, an inherited blood disorder, is caused by the substitution of one amino acid (valine) for the normal one (glutamic acid) at a particular position in the primary structure of hemoglobin, the protein that carries oxygen in red blood cells. Normal red blood cells are disk-shaped, but in sickle-cell disease, the abnormal hemoglobin molecules tend to aggregate into chains, deforming some of the cells into a sickle shape. A person with the disease has periodic "sickle-cell crises" when the angular cells clog tiny blood vessels, impeding blood flow.

The sequence of amino acids in a protein is called

the primary structure of the protein.

Glycerol is a

three-carbon straight-chain lipid.

quaternary structure is the result of

two or more peptides interacting with each other.

Fibrous proteins

usually function as structural proteins.