3: Biological Macromolecules Flashcards
Synthesis of Biological Macromolecules, Carbohydrates, Lipids, Proteins, Nucleic Acids (196 cards)
1
Q
What is a biological macromolecule?
A
A large molecule necessary for life that is built from smaller organic molecules.
2
Q
What is dehydration synthesis?
A
A reaction that links monomer molecules together, releasing a molecule of water for each bond formed. AKA condensation.
3
Q
What is hydrolysis?
A
A reaction that causes breakdown of larger molecules into smaller molecules with the utilization of water.
4
Q
What is a monomer?
A
The smallest unit of larger molecules called polymers.
5
Q
What is a polymer?
A
A chain of monomer residues that is linked by covalent bonds; polymerization is the process of polymer formation from monomers by condensation.
6
Q
What are the major classes of biological macromolecules?
A
Carbohydrates, lipids, proteins, and nucleic acids.
7
Q
How does a dehydration synthesis reaction occur?
A
The hydrogen of one monomer combines with the hydroxyl group of another monomer, releasing a molecule of water, while also sharing electrons and forming covalent bonds.
8
Q
What are some of the polymers formed by the glucose monomer?
A
Starch, glycogen, and cellulose.
9
Q
How does hydrolysis occur?
A
A polymer is broken into two components, where one part gains a hydrogen atom (H+) and the other gains a hydroxyl molecule (OH–).
10
Q
How are dehydration and hydrolysis reactions catalyzed?
A
They are catalyzed by specific enzymes; dehydration reactions involve the formation of new bonds, requiring energy, while hydrolysis reactions break bonds and release energy.
11
Q
What are some enzymes that break down carbohydrates?
A
Amylase, sucrase, lactase, maltase.
12
Q
What are some enzymes that break down proteins?
A
Pepsin, peptidase, and hydrochloric acid.
13
Q
What are some enzymes that break down lipids?
A
Lipases.
14
Q
What is a carbohydrate?
A
A biological macromolecule in which the ratio of carbon to hydrogen and to oxygen is 1:2:1; carbohydrates serve as energy sources and structural support in cells and form the cellular exoskeleton of arthropods.
15
Q
What is cellulose?
A
A polysaccharide that makes up the cell wall of plants; provides structural support to the cell.
16
Q
What is chitin?
A
A type of carbohydrate that forms the outer skeleton of all arthropods that include crustaceans and insects; it also forms the cell walls of fungi.
17
Q
What is a disaccharide?
A
Two sugar monomers that are linked together by a glycosidic bond.
18
Q
What is glycogen?
A
Storage carbohydrate in animals.
19
Q
What is a glycosidic bond?
A
A bond formed by a dehydration reaction between two monosaccharides with the elimination of a water molecule.
20
Q
What is a monosaccharide?
A
A single unit or monomer of carbohydrates.
21
Q
What is a polysaccharide?
A
A long chain of monosaccharides; may be branched or unbranched.
22
Q
How many carbons are usually found in monosaccharides?
A
Usually from three to seven.
23
Q
What are some ways in which monosaccharides are classified?
A
Most monosaccharide names end with the suffix -ose. If the sugar has an aldehyde group (the functional group with the structure R-CHO), it is known as an aldose, and if it has a ketone group (the functional group with the structure RC(=O)R’), it is known as a ketose. Depending on the number of carbons in the sugar, they also may be known as trioses (three carbons), pentoses (five carbons), or hexoses (six carbons).
24
Q
What is the chemical formula for glucose?
A
C6H12O6
25
How is glucose used by humans?
In humans, glucose is an important source of energy. During cellular respiration, energy is released from glucose, and that energy is used to help make adenosine triphosphate (ATP).
26
What is the source of glucose?
Plants synthesize glucose using carbon dioxide and water, and glucose in turn is used for energy requirements for the plant. Excess glucose is often stored as starch that is catabolized by humans and other animals that feed on plants.
27
What are some structural isomers of glucose?
Galactose (part of lactose, or milk sugar) and fructose (found in sucrose, in fruit).
28
How are glucose, galactose and fructose classified?
They are isomeric monosaccharides (hexoses). Glucose and galactose are aldoses and fructose is a ketose.
29
Are monosaccharides linear- or ring-shaped?
They can exist as a linear chain or as ring-shaped molecules; in aqueous solutions they are usually found in ring form.
30
What are the different arrangements of ring-form glucose?
Glucose in a ring form can have two different arrangements of the hydroxyl group (OH) around the anomeric carbon (carbon 1 that becomes asymmetric in the process of ring-formation). If the hydroxyl group is below carbon 1 in the sugar, it is said to be in the alpha (*α*) position, and if it is above the plane, it is said to be in the beta (*β*) position.
31
What are the types of glycosidic bonds?
Alpha and beta.
32
What are some common disaccharides?
Lactose, maltose, and sucrose. Lactose is a disaccharide consisting of the monomers glucose and galactose. It is found naturally in milk. Maltose, or malt sugar, is a disaccharide formed by a dehydration reaction between two glucose molecules. The most common disaccharide is sucrose, or table sugar, which is composed of the monomers glucose and fructose.
33
How large are polysaccharides?
The molecular weight may be 100,000 daltons or more depending on the number of monomers joined.
34
How is starch produced?
It is made up of a mixture of amylose and amylopectin (both polymers of glucose). Plants are able to synthesize glucose, and the excess glucose, beyond the plant's immediate needs, is stored as starch in different plant parts, including roots and seeds.
35
How is starch consumed?
The starch in seeds provides food for the embryo as it germinates and can also act as a source of food for humans and animals. The starch that is consumed by humans is broken down by enzymes, such as salivary amylases, into smaller molecules, such as maltose and glucose. The cells can then absorb the glucose.
36
How are starch monomers joined?
Starch is made up of glucose monomers that are joined by alpha 1-4 or alpha 1-6 glycosidic bonds, where the numbers refer to the carbon number of the two residues that have joined to form the bond.
37
How are amylose and amylopectin joined?
Amylose is starch formed by unbranched chains of glucose monomers (only alpha 1-4 linkages), whereas amylopectin is a branched polysaccharide (a 1-6 linkages at the branch points).
38
How is glycogen stored and used in animals?
Glycogen is highly branched and usually stored in liver and muscle cells. When blood glucose levels decrease, glycogen is broken down to release glucose in a process known as glycogenolysis.
39
What is the most abundant natural biopolymer?
Cellulose
40
How are cellulose monomers joined?
Cellulose is made up of glucose monomers that are linked by beta 1-4 glycosidic bonds.
41
Why does cellulose have high tensile strength?
Every other glucose monomer is flipped over, and the monomers are packed tightly as extended long chains. This gives cellulose its rigidity and high tensile strength, which is important to plant cells.
42
How is cellulose digested?
The beta 1-4 linkages cannot be broken down by human digestive enzymes, however herbivores such as cows, koalas, buffalos, and horses are able, with the help of specialized flora in their stomach, to digest plant material that is rich in cellulose. In these animals, certain species of bacteria and protists reside in the rumen (part of the digestive system of herbivores) and secrete the enzyme cellulase. The appendix of grazing animals also contains bacteria that digest cellulose. Cellulases can break down cellulose into glucose monomers that can be used as an energy source by the animal. Termites are also able to break down cellulose because of the presence of other organisms in their bodies that secrete cellulases.
43
What is chitin made of?
Repeating units of N-acetyl-*β*-d-glucosamine, a modified sugar.
44
Where do dietitians work?
Registered dietitians help plan nutrition programs for individuals in various settings. They often work with patients in health care facilities, designing nutrition plans to treat and prevent diseases. For example, dietitians may teach a patient with diabetes how to manage blood sugar levels by eating the correct types and amounts of carbohydrates. Dietitians may also work in nursing homes, schools, and private practices.
45
How can you become a dietitian?
You need to earn at least a bachelor's degree in dietetics, nutrition, food technology, or a related field. In addition, registered dietitians must complete a supervised internship program and pass a national exam. Those who pursue careers in dietetics take courses in nutrition, chemistry, biochemistry, biology, microbiology, and human physiology. Dietitians must become experts in the chemistry and physiology (biological functions) of food (proteins, carbohydrates, and fats).
46
How many calories are provided by carbohydrates versus fats?
Carbohydrate provides 4.3 Kcal/g compared to 9 Kcal/g in fats.
47
What is the role of fiber in diet?
Fiber is the insoluble part of carbohydrates and promotes regular bowel movement by adding bulk and regulates the rate of consumption of blood glucose. It also helps to remove excess cholesterol from the body: fiber binds to the cholesterol in the small intestine, then attaches to the cholesterol and prevents the cholesterol particles from entering the bloodstream, and then the cholesterol exits the body via feces. Fiber-rich diets also have a protective role in reducing the occurrence of colon cancer.
48
Why should carbohydrates not be eliminated from diet?
Meals containing whole grains and vegetables gives a feeling of fullness. Glucose is broken down to produce ATP, which provides energy. A better way to lose weight is a low-calorie diet that is rich in whole grains, fruits, vegetables, and lean meat, together with exercise and water consumption.
49
What is starch?
Storage carbohydrate in plants.
50
What is a lipid?
A macromolecule that is nonpolar and insoluble in water.
51
What is an omega fat?
A type of polyunsaturated fat that is required by the body; the numbering of the carbon omega starts from the methyl end or the end that is farthest from the carboxylic end.
52
What is a phospholipid?
A major constituent of the membranes; composed of two fatty acids and a phosphate-containing group attached to a glycerol backbone.
53
What is a saturated fatty acid?
A long-chain of hydrocarbon with single covalent bonds in the carbon chain; the number of hydrogen atoms attached to the carbon skeleton is maximized.
54
What is a steroid?
A type of lipid composed of four fused hydrocarbon rings forming a planar structure.
55
What is a trans fat?
A fat formed artificially by hydrogenating oils, leading to a different arrangement of double bond(s) than those found in naturally occurring lipids.
56
What is a triglyceride / triacylglycerol?
A fat molecule; consists of three fatty acids linked to a glycerol molecule.
57
What is an unsaturated fatty acid?
A long-chain hydrocarbon that has one or more double bonds in the hydrocarbon chain.
58
What is a wax?
A lipid made of a long-chain fatty acid that is esterified to a long-chain alcohol; serves as a protective coating on some feathers, aquatic mammal fur, and leaves.
59
What are some uses of lipids?
Cells store energy for long-term use in the form of fats. Lipids also provide insulation from the environment for plants and animals. They help to keep aquatic birds and mammals dry when forming a protective layer over fur or feathers because of their water-repellant hydrophobic nature. They are also the building blocks of many hormones and are an important constituent of cellular membranes.
60
What are the different types of lipids?
Fats, oils, waxes, phospholipids, and steroids.
61
What are triglycerides made of?
Glycerol and fatty acids. The fatty acids are attached to each of the three carbons of the glycerol molecule with an ester bond through an oxygen atom. The three fatty acids in the triacylglycerol may be similar or dissimilar.
62
What is glycerol?
Glycerol is an organic compound (alcohol) with three carbons, five hydrogens, and three hydroxyl (OH) groups.
63
What is a fatty acid?
Fatty acids have a long chain of hydrocarbons to which a carboxyl group is attached, hence the name “fatty acid”. The number of carbons in the fatty acid may range from 4 to 36; most common are those containing 12 to 18 carbons.
64
What happens during the ester bond formation of triglycerides?
Three water molecules are released.
65
What are some examples of fatty acids?
Palmitic acid, a saturated fatty acid, is derived from the palm tree. Arachidic acid is derived from *Arachis hypogea*, the scientific name for groundnuts or peanuts.
66
What is an example of a saturated and unsaturated fatty acid?
Stearic acid is a saturated fatty acid, and oleic acid is an unsaturated fatty acid.
67
How are unsaturated fatty acids classified?
If there is one double bond, it is known as a monounsaturated fat, and if there is more than one, it is known as a polyunsaturated fat.
68
What is an example of a monounsaturated and a polyunsaturated fat?
Olive oil is monounsaturated, and canola oil is polyunsaturated.
69
What are some examples of food products containing saturated fats?
Animal fats with stearic acid and palmitic acid (common in meat) and the fat with butyric acid (common in butter).
70
Where are fats stored in plants and animals?
Mammals store fats in specialized cells called adipocytes, where globules of fat occupy most of the cell's volume. In plants, fat or oil is stored in many seeds and is used as a source of energy during seedling development.
71
What is the source of unsaturated fats or oils?
They are usually of plant origin and contain *cis* unsaturated fatty acids.
72
What is the difference between *cis* and *trans* fats?
*Cis* and *trans* indicate the configuration of the molecule around the double bond. If hydrogens are present in the same plane, it is referred to as a cis fat; if the hydrogen atoms are on two different planes, it is referred to as a trans fat. The *cis* double bond causes a bend or a “kink” that prevents the fatty acids from packing tightly, keeping them liquid at room temperature.
73
What are some examples of unsaturated fats?
Olive oil, corn oil, canola oil, and cod liver oil.
74
What is the impact of fat consumption in human diet?
Unsaturated fats help to lower blood cholesterol levels whereas saturated fats contribute to plaque formation in the arteries.
75
How are oils artificially hydrogenated in the food industry?
Artificial hydrogenation makes oils semi-solid and of a consistency desirable for many processed food products. Hydrogen gas is bubbled through the oils to solidify them. During this hydrogenation process, double bonds of the *cis*-conformation in the hydrocarbon chain may be converted to double bonds in the *trans*-conformation.
76
What are some food products that may contain artificially hydrogenated trans fats?
Margarine, some types of peanut butter, and shortening.
77
What is the impact of trans fats in human diet?
An increase in trans fats in the human diet may lead to an increase in levels of low-density lipoproteins (LDL), or “bad” cholesterol, which in turn may lead to plaque deposition in the arteries, resulting in heart disease.
78
What are essential fatty acids?
Fatty acids that are required but not synthesized by the human body and must be supplemented through diet.
79
What are the essential fatty acids for humans?
Omega-3 and omega-6 fatty acids.
80
What are some examples of omega-3 fatty acids?
Alpha-linoleic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), all of which are polyunsaturated.
81
What are some sources of omega-3 fatty acids?
Salmon, trout, and tuna.
82
What are some benefits of omega-3 fatty acids?
Research indicates that they reduce the risk of sudden death from heart attacks, reduce triglycerides in the blood, lower blood pressure, and prevent thrombosis by inhibiting blood clotting. They also reduce inflammation, and may help reduce the risk of some cancers in animals.
83
What are some benefits of fats in human diet?
Many vitamins are fat soluble, and fats serve as a long-term storage form of fatty acids: a source of energy. They also provide insulation for the body.
84
How do phospholipids differ from triglycerides?
Like fats, they are composed of fatty acid chains attached to a glycerol or sphingosine backbone, but instead of three fatty acids, there are two fatty acids forming diacylglycerol, and the third carbon of the glycerol backbone is occupied by a modified phosphate group.
85
What is phosphatidate?
A phosphate group alone attached to a diacylglycerol, AKA diacylglycerol 3-phosphate, and is the precursor of phospholipids. The phosphate group is modified by an alcohol.
86
What are some examples of phospholipids found in plasma membranes?
Phosphatidylcholine and phosphatidylserine.
87
Are phospholipids hydrophilic or hydrophobic?
They are amphiphilic, where the fatty acid chains (the tail) are hydrophobic and the phosphate-containing group (the head) is hydrophilic.
88
How do phospholipids compose plasma membranes?
A bilayer is formed, with the fatty acid tails facing inward and the phosphate head facing the outward.
89
What is a micelle?
A structure formed spontaneously in aqueous solutions by phospholipids with the phosphate heads facing outward and the fatty acid tails facing inward.
90
What is the structure of steroids?
All steroids have four linked carbon rings and several of them, like cholesterol, have a short tail. Many steroids also have the -OH functional group, which puts them in the alcohol classification (sterols).
91
Why are steroids considered lipids?
Because they are hydrophobic and insoluble in water.
92
What is cholesterol?
The most common steroid. Cholesterol is mainly synthesized in the liver and is the precursor to many steroid hormones such as testosterone and estradiol, which are secreted by the gonads and endocrine glands. It is also the precursor to vitamin D. Cholesterol is also the precursor of bile salts, which help in the emulsification of fats and their subsequent absorption by cells.
93
What role does cholesterol play in the body?
It is a component of the plasma membrane of animal cells and is found within the phospholipid bilayer. Being the outermost structure in animal cells, the plasma membrane is responsible for the transport of materials and cellular recognition and it is involved in cell-to-cell communication.
94
What is an alpha-helix structure?
A type of secondary structure of proteins formed by folding of the polypeptide into a helix shape with hydrogen bonds stabilizing the structure.
95
What is an amino acid?
A monomer of a protein; has a central carbon or alpha carbon to which an amino group (NH2), a carboxyl group (COOH), a hydrogen, and an R group or side chain is attached; the R group is different for all 20 amino acids.
96
What is a beta-pleated sheet?
A secondary structure found in proteins in which "pleats" are formed by hydrogen bonding between atoms on the backbone of the polypeptide chain.
97
What is a chaperone?
A protein that helps nascent proteins in the folding process. AKA chaperonin.
98
What is denaturation?
Loss of shape in a protein as a result of changes in temperature, pH, or exposure to chemicals.
99
What is an enzyme?
A catalyst in a biochemical reaction that is usually a complex or conjugated protein.
100
What is a hormone?
A chemical signaling molecule, usually protein or steroid, secreted by endocrine cells that act to control or regulate specific physiological processes.
101
What is a peptide bond?
A bond formed between two amino acids by a dehydration reaction.
102
What is a polypeptide?
A long chain of amino acids linked by peptide bonds.
103
What is the primary structure?
The linear sequence of amino acids in a protein.
104
What is a protein?
A biological macromolecule composed of one or more chains of amino acids.
105
What is the quaternary structure?
The association of discrete polypeptide subunits in a protein.
106
What is the secondary structure?
The regular structure formed by proteins by intramolecular hydrogen bonding between the oxygen atom of one amino acid residue and the hydrogen attached to the nitrogen atom of another amino acid residue.
107
What is the tertiary structure?
The three-dimensional conformation of a protein, including interactions between secondary structural elements; formed from interactions between amino acid side chains.
108
What roles do proteins play?
Proteins may be structural, regulatory, contractile, or protective; they may serve in transport, storage, or membranes; or they may be toxins or enzymes. Each cell in a living system may contain thousands of proteins, each with a unique function.
109
How are enzymes classified?
* Catabolic enzymes break down their substrates
* Anabolic enzymes build more complex molecules from their substrates
* Catalytic enzymes increase the rate of reaction
Note that all enzymes increase the rate of reaction and are therefore considered to be organic catalysts.
110
What is an example of an enzyme?
Salivary amylase, which hydrolyzes its substrate amylose, a component of starch.
111
What is an example of a hormone?
Insulin is a protein hormone that helps to regulate the blood glucose level.
112
What do digestive enzymes do?
Help in digestion of food by catabolizing nutrients into monomeric units.
113
What do transport proteins do?
Carry substances in the blood or lymph throughout the body.
114
What do structural proteins do?
Construct different structures, like the cytoskeleton.
115
What do hormones do?
Coordinate the activity of different body systems.
116
What do defense proteins do?
Protect the body from foreign pathogens.
117
What do contractile proteins do?
Effect muscle contraction.
118
What do storage proteins do?
Provide nourishment in early development of the embryo and the seedling.
119
What are some examples of digestive enzymes?
Amylase, lipase, pepsin, trypsin.
120
What are some examples of transport proteins?
Hemoglobin, albumin.
121
What are some examples of structural proteins?
Actin, tubulin, keratin.
122
What are some examples of hormones?
Insulin, thyroxine.
123
What are some examples of defense proteins?
Immunoglobulins.
124
What are some examples of contractile proteins?
Actin, myosin.
125
What are some examples of storage proteins?
Legume storage proteins, egg white (albumin).
126
What general shapes do proteins take?
Some proteins are globular whereas others are fibrous.
127
What is an example of a globular and a fibrous protein?
Hemoglobin is a globular protein, but collagen, found in our skin, is a fibrous protein.
128
Why are amino acids so-named?
They contain both an amino group and a carboxyl acid group in their basic structure.
129
What are essential amino acids?
10 of the 20 amino acids present in proteins are considered essential in humans because they cannot be biologically synthesized and must be provided through diet.
130
How are peptide bonds formed?
The carboxyl group of one amino acid and the amino group of the incoming amino acid combine and release a molecule of water.
131
What are the terms for the ends of a polypeptide?
The amino (N) terminal and the carboxyl (C) terminal.
132
What are the differences between polypeptides and proteins?
A polypeptide is a polymer of amino acids, whereas a protein is a polypeptide or joined polypeptides, often have bound non-peptide prosthetic groups, have a distinct shape, and have a unique function.
133
What are some examples of post-translational modifications?
Proteins may undergo cleavage, phosphorylation, or may require the addition of other chemical groups.
134
What is the role of cytochrome c?
Cytochrome c is an important component of the electron transport chain, a part of cellular respiration, and it is normally found in mitochondria. This protein has a heme prosthetic group, and the central ion of the heme gets alternatively reduced and oxidized during electron transfer. Cytochrome c plays an essential role in producing cellular energy.
135
How has cytochrome c evolved over time?
It has changed very little over millions of years. Protein sequencing has shown that there is a considerable amount of cytochrome c amino acid sequence homology among different species.
136
How many amino acids are found in human cytochrome c?
104
137
How many sequence differences in cytochrome c are there between humans and chimpanzees?
None.
138
How many sequence differences in cytochrome c are there between humans and rhesus monkeys?
One.
139
At what position is there a difference in sequence in cytochrome c between humans and yeast?
A difference occurs at the 44th position.
140
What is an enzyme's active site?
The site where an enzyme can bind a specific substrate. If the active site is altered because of local changes in overall protein structure, the enzyme may be unable to bind to the substrate.
141
What are the levels of protein structure?
Primary, secondary, tertiary, quaternary.
142
What are some features of the primary structure of insulin?
The pancreatic hormone insulin has two polypeptide chains, A and B, and they are linked together by two disulfide bonds. The N terminal amino acid of the A chain is glycine, whereas the C terminal amino acid is asparagine. The A chain is 21 amino acids long, and the B chain is 30 amino acids long. The sequences of amino acids in the A and B chains are unique to insulin.
143
How is the sequence of amino acids in a protein determined?
By the gene encoding the protein. A change in nucleotide sequence of the gene's coding region may lead to a different amino acid being added to the growing polypeptide chain, causing a change in protein structure and function.
144
What is the cause of sickle cell anemia?
The hemoglobin *β* chain has an amino acid substitution of glutamic acid by valine at position 7.
145
What is the structure of hemoglobin?
Hemoglobin is made up of two alpha chains and two beta chains that each consist of about 150 amino acids.
146
How large is the difference between normal and sickle cell hemoglobin?
One amino acid (1 of 600), caused by a single point mutation (1 in 1800).
147
What are the effects of sickle cell anemia?
Because of the amino acid substitution, hemoglobin molecules form fibers that distort the biconcave, or disc-shaped, red blood cells and assume a crescent or “sickle” shape, which clogs arteries. This can lead to myriad health problems such as breathlessness, dizziness, headaches, and abdominal pain. Sickle cell anemia dramatically decreases life expectancy.
148
What are the most common types of secondary structure in proteins?
The alpha-helix and the beta-pleated sheet.
149
How is the alpha-helix secondary structure formed?
Hydrogen bonds form between the oxygen atom in the carbonyl group in one amino acid and another amino acid that is four amino acids farther along the chain. Every helical turn in an alpha helix has 3.6 amino acid residues. The R groups of the polypeptide protrude out from the alpha-helix chain.
150
How is the beta-pleated sheet secondary structure formed?
It is formed from hydrogen bonding between atoms on the backbone of the polypeptide chain. The R groups are attached to the carbons and extend above and below the folds of the pleat. The pleated segments align parallel or antiparallel to each other, and hydrogen bonds form between the partially positive nitrogen atom in the amino group and the partially negative oxygen atom in the carbonyl group of the peptide backbone.
151
How is a protein's tertiary structure formed?
It is due to chemical interactions among the R groups of the protein, where those with like charges are repelled by each other and those with unlike charges are attracted to each other, forming ionic bonds. During protein folding, non-polar hydrophobic R groups will tend toward the interior, and polar hydrophilic R groups will tend toward the exterior. Interactions between cysteine side chains forms disulfide linkages in the presence of oxygen, the only covalent bond forming during protein folding.
152
How is a protein's quaternary structure formed?
Some proteins are formed from several polypeptides, also known as subunits, and the interaction between these subunits forms the quaternary structure. Weak interactions between the subunits help to stabilize the overall structure.
153
What are some characteristics of insulin's quaternary structure?
Insulin, a globular protein, has a combination of hydrogen bonds and disulfide bonds that cause it to be mostly clumped into a ball shape. Insulin starts out as a single polypeptide and loses some internal sequences in the presence of post-translational modification after the formation of the disulfide linkages that hold the remaining chains together.
154
What are some characteristics of the quaternary structure of silk?
Silk, a fibrous protein, has a beta-pleated sheet structure that is the result of hydrogen bonding between different chains.
155
How can protein denaturation be reversible?
Denaturation is often reversible because the primary structure of the polypeptide is conserved in the process if the denaturing agent is removed, allowing the protein to resume its function.
156
What is an example of irreversible protein denaturation?
When an egg is fried. The albumin protein in the liquid egg white is denatured when placed in a hot pan.
157
What are some examples of proteins that are not denatured under extreme conditions?
Bacteria that survive in hot springs have proteins that function at temperatures close to boiling. The stomach is also very acidic and denatures proteins as part of the digestive process, however the digestive enzymes of the stomach retain their activity under these conditions.
158
How do chaperones work?
They act by preventing aggregation of polypeptides that make up the complete protein structure, and they disassociate from the protein once the target protein is folded.
159
What is deoxyribonucleic acid (DNA)?
A double-helical molecule that carries the hereditary information of the cell.
160
What is messenger RNA (mRNA)?
RNA that carries information from DNA to ribosomes during protein synthesis.
161
What is a nucleic acid?
A biological macromolecule that carries the genetic blueprint of a cell and carries instructions for the functioning of the cell.
162
What is a nucleotide?
A monomer of nucleic acids; contains a pentose sugar, one or more phosphate groups, and a nitrogenous base.
163
What is a phosphodiester?
A covalent chemical bond that holds together the polynucleotide chains with a phosphate group linking two pentose sugars of neighboring nucleotides.
164
What is a polynucleotide?
A long chain of nucleotides.
165
What is a purine?
A type of nitrogenous base in DNA and RNA; adenine and guanine are purines.
166
What is a pyrimidine?
A type of nitrogenous base in DNA and RNA; cytosine, thymine, and uracil are pyrimidines.
167
What is ribonucleic acid (RNA)?
A single-stranded, often internally base-paired, molecule that is involved in protein synthesis.
168
What is ribosomal RNA (rRNA)?
RNA that ensures the proper alignment of the mRNA and the ribosomes during protein synthesis and catalyzes the formation of the peptide linkage.
169
What is transcription?
The process through which messenger RNA forms on a template of DNA.
170
What is transfer RNA (tRNA)?
RNA that carries activated amino acids to the site of protein synthesis on the ribosome.
171
What is translation?
The process through which RNA directs the formation of protein.
172
Where is DNA found?
It is found in the nucleus of eukaryotes and in the organelles, chloroplasts and mitochondria. In prokaryotes, the DNA is not enclosed in a membranous envelope.
173
What shape does DNA take?
The entire genetic content of a cell is known as its genome. In eukaryotic cells but not in prokaryotes, DNA forms a complex with histone proteins to form chromatin, the substance of eukaryotic chromosomes. A chromosome may contain tens of thousands of genes. Many genes contain the information to make protein products; other genes code for RNA products. DNA controls all of the cellular activities by turning the genes “on” or “off”.
174
What is the role of RNA?
RNA is mostly involved in protein synthesis. The DNA molecules never leave the nucleus but instead use mRNA to communicate with the rest of the cell. Other types of RNA—like rRNA, tRNA, and microRNA—are involved in protein synthesis and its regulation.
175
How are nucleotides structured?
Each nitrogenous base in a nucleotide is attached to a sugar molecule, which is attached to one or more phosphate groups.
176
How are the carbons in a nucleotide notated?
Carbon residues in the pentose are number 1' through 5' (the prime distinguishes these residues from those in the base, which are numbered without using a prime notation).
177
At which positions are the nitrogenous base and phosphate attached to the sugar?
The base is attached to the 1' position of the sugar, and the phosphate is attached to the 5' position.
178
How are nucleotides joined in a polynucleotide?
When a polynucleotide is formed, the 5' phosphate of the incoming nucleotide attaches to the 3' hydroxyl group at the end of the growing chain.
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What are the types of pentoses found in nucleotides?
Two types of pentose are found in nucleotides, deoxyribose (found in DNA) and ribose (found in RNA). Deoxyribose is similar in structure to ribose, but it has an H instead of an OH at the 2' position.
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What are the types of nitrogenous bases found in nucleotides?
Bases can be divided into two categories: purines and pyrimidines. Purines have a double ring structure, and pyrimidines have a single ring.
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Why are nitrogenous bases considered bases?
Because they contain an amino group that has the potential of binding an extra hydrogen, and thus, decreases the hydrogen ion concentration in its environment, make it more basic.
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Which nitrogenous bases are found in DNA and in RNA?
DNA contains A, T, G, and C, and RNA contains A, U, G, and C.
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At which positions is the phosphodiester linkage formed?
The phosphate residue is attached to the hydroxyl group of the 5' carbon of one sugar and the hydroxyl group of the 3' carbon of the sugar of the next nucleotide, which forms a 5'–3' phosphodiester linkage.
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How are phosphodiester linkages formed?
They are not formed by simple dehydration reactions, but rather the removal of two phosphate groups.
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How is the DNA double-helix structured?
The sugar and phosphate lie on the outside of the helix, forming the backbone of the DNA. The nitrogenous bases are stacked in the interior in pairs which are bound to each other by hydrogen bonds. Every base pair in the double helix is separated from the next base pair by 0.34 nm. The two strands of the helix run in opposite directions, meaning that the 5' carbon end of one strand will face the 3' carbon end of its matching strand, referred to as antiparallel orientation and is important to DNA replication and in many nucleic acid interactions.
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What is the base complementary rule?
Base pairing that occurs strictly between A and T or U, and G and C.
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What happens during DNA replication?
Each strand is copied, resulting in a daughter DNA double helix containing one parental DNA strand and a newly synthesized strand.
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What are the major types of RNA?
Messenger RNA (mRNA), ribosomal RNA (rRNA), transfer RNA (tRNA) and microRNA (miRNA).
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What is the role of mRNA?
mRNA carries messages from DNA, which controls all of the cellular activities in a cell. If a cell requires a certain protein to be synthesized, the gene for this product is turned “on” and the messenger RNA is synthesized in the nucleus. In the cytoplasm, the mRNA interacts with ribosomes and other cellular machinery.
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How does a ribosome interact with mRNA and tRNA?
A ribosome has two parts: a large subunit and a small subunit. The mRNA sits between the two subunits. A tRNA molecule recognizes a codon on the mRNA, binds to it by complementary base pairing, and adds the correct amino acid to the growing peptide chain.
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What is a codon?
mRNA is read in sets of three bases known as codons. Each codon codes for a single amino acid. In this way, the mRNA is read and the protein product is made.
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What is the role of rRNA?
Ribosomal RNA (rRNA) is a major constituent of ribosomes on which the mRNA binds. The rRNA ensures the proper alignment of the mRNA and the ribosomes. The rRNA of the ribosome also has an enzymatic activity (peptidyl transferase) and catalyzes the formation of the peptide bonds between two aligned amino acids.
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What is the role of tRNA?
Transfer RNA (tRNA) is one of the smallest of the four types of RNA, usually 70-90 nucleotides long. It carries the correct amino acid to the site of protein synthesis. It is the base pairing between the tRNA and mRNA that allows for the correct amino acid to be inserted into the polypeptide chain.
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What is the role of microRNAs?
microRNAs are the smallest RNA molecules and their role involves the regulation of gene expression by interfering with the expression of certain mRNA messages.
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How does base pairing occur in RNA?
Even though RNA is single-stranded, most RNA types show extensive intramolecular base pairing between complementary sequences, creating predictable three-dimensional structure essential for their function.
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What is the Central Dogma of Life?
DNA dictates the structure of mRNA in a process known as transcription, and RNA dictates the structure of protein in a process known as translation.
