Bioc lec 4 Flashcards
(178 cards)
1
Q
What are biological lipids?
A
structurally diverse group of molecules defined by their hydrophobicity
2
Q
What solvents are used to dissolve lipids?
A
Organic solvents are used to dissolve lipids.
3
Q
What are the biological functions of lipids?
A
- Energy storage: Example: Triacylglycerols (fats and oils).
2.Structural elements of membranes: Example: Phospholipids and sterols.
3.Signal transduction (cell-cell communication): Example: Steroid hormones, prostaglandins.
4.Enzyme cofactors: Example: Coenzyme Q in the mitochondrial electron transport chain.
5.Vitamins: Example: Vitamins A, D, E, K.
6.Light-absorbing pigments: Example: Carotene
4
Q
How can lipids occur covalently linked to other biomolecules?
A
Lipids can form:
-Glycolipids: Contain sugar and lipid portions (e.g., sphingolipids, gangliosides).
Example: Define human blood groups (O, A, B) through glycolipids on blood cells.
- Lipoproteins: Plasma lipoproteins (e.g., VLDL, LDL, HDL) linked to cardiovascular health.
5
Q
What are glycolipids, and why are they important?
A
Glycolipids contain both sugar and lipid portions, are found in cell membranes, and define human blood groups (O, A, B).
6
Q
What are lipoproteins, and what do they do?
A
Lipoproteins (e.g., VLDL, LDL, HDL) are plasma proteins that transport lipids and are associated with cardiovascular health and disease.
7
Q
What are the main types of lipids?
A
Fatty acids:
Building blocks of complex lipids.
Central intermediates in metabolism.
Simplest lipid but not found in free form.
Triacylglycerols:
Storage fats.
Phosphoglycerides:
Major membrane lipids.
8
Q
What are fatty acids?
A
Fatty acids are:
-Building blocks of many complex lipids.
-Central intermediates in metabolism.
-Simplest lipids but present in trace amounts and not found in free form.
9
Q
What are triacylglycerols?
A
Triacylglycerols are lipids used for energy storage and commonly known as fats and oils.
10
Q
What are phosphoglycerides?
A
Phosphoglycerides are major lipids in biological membranes.
11
Q
What is the structure of carboxylic acids in fatty acids?
A
Carboxylic acids in fatty acids have hydrocarbon chains ranging from 4 to 36 carbons.
12
Q
What are saturated fatty acids?
A
Saturated fatty acids have only single bonds and no double bonds between carbons in their chain.
13
Q
What are unsaturated fatty acids?
A
Unsaturated fatty acids have one or more double bonds in their hydrocarbon chain.
14
Q
What are monounsaturated fatty acids?
A
Monounsaturated fatty acids have 1 double bond in their chain.
15
Q
What are polyunsaturated fatty acids?
A
Polyunsaturated fatty acids have more than one double bond in their chain.
16
Q
How are carbons in fatty acids numbered?
A
C-1: Carbon of the carboxyl group.
α (alpha): Carbon next to the carboxyl group.
17
Q
How do you represent fatty acids with numbers?
A
-The first number represents the number of carbons in the chain.
-The second number represents the number of double bonds.
-These are separated by a colon (e.g., 18:2 for an 18-carbon chain with 2 double bonds).
18
Q
How do you indicate the positions of double bonds in fatty acids?
A
Use parentheses with a triangle (Δ) and list the double bond positions in superscript, starting from the carboxyl carbon.
Example: 18:2(Δ⁹,¹²)
19
Q
What is an alternative way to name polyunsaturated fatty acids?
A
Specify the position of the first double bond relative to the methyl carbon (ω).
Example: ω-3 fatty acids and ω-6 fatty acids.
20
Q
What are the key features of commonly occurring fatty acids?
A
Common fatty acids:
-Have an even number of carbon atoms.
-Are unbranched.
-Contain double bonds in the cis configuration.
21
Q
What is the pattern of double bonds in polyunsaturated fatty acids (PUFAs)?
A
In PUFAs, the double bonds are methylene-bridged, following a double bond, single bond, double bond, single bond pattern.
22
Q
Are double bonds in polyunsaturated fatty acids conjugated?
A
No, the double bonds in PUFAs are not conjugated because they are separated by a methylene (-CH₂) carbon.
23
Q
Common saturated fatty acids to know (LMPSA - let my pal stay around
A
- 12 carbons, Laurate, bay and laurel
- 14 carbons, myristate, myrtle and nutmeg
- 16 carbons, palmitate, palm
- 18 carbons, stearate, tallow
- 20 carbons, arachidate, peanut
24
Q
How are trans fatty acids formed?
A
Trans fatty acids are formed during the partial hydrogenation of unsaturated fatty acids, such as in margarine production, which isomerizes double bonds to create trans fats.
25
What is the effect of trans double bonds on fatty acid structure?
Trans double bonds allow fatty acids to adopt an extended conformation, similar to saturated fatty acids.
26
What are the health concerns of trans fats?
Synthetic trans fats are linked to serious negative effects on cardiovascular health.
27
What is the structure of saturated fatty acid chains?
Saturated fatty acid chains:
-Have extended conformations.
-Pack in an orderly way with many favorable van der Waals interactions due to tight packing.
28
How do chain length and saturation affect the melting point of fatty acids?
-As chain length increases, the melting point increases due to stronger collective interactions.
-Unsaturated fatty acids have a lower melting point because cis double bonds create kinks, preventing tight packing.
29
How does chain length affect fatty acid solubility?
As chain length increases, solubility decreases because tightly packed interactions resist separation by solvents or heat.
30
Why do unsaturated fatty acids have lower melting points?
-The kink from cis double bonds reduces tight packing.
-Fewer favorable interactions mean less thermal energy is required to disrupt packing, lowering the melting point.
31
How do double bonds affect membrane fluidity?
The lower melting temperature of unsaturated fatty acids contributes to greater fluidity in lipid membranes.
32
Why do trans fatty acids have higher melting points than cis forms?
The extended nature of trans fatty acids allows them to pack more regularly, resulting in higher melting points compared to cis forms.
Example:
18:1 (Cis) = 13.4°C
18:1 (Trans) = 45.0°C
33
What factors increase the melting temperature of fatty acids?
-Saturation: Saturated fatty acids have higher melting points because they lack double bonds and pack tightly.
-Chain length: Longer chains have higher melting temperatures due to stronger intermolecular forces.
34
What are triacylglycerols (TAGs)?
acid derivatives formed by linking three fatty acids to a glycerol molecule through ester linkages.
35
In what form are most fatty acids in biological systems found?
As
triacylglycerols (TAGs).
36
Why are TAGs highly hydrophobic?
TAGs are highly hydrophobic because the polar carboxylic acids of the fatty acids are tied up as less polar esters with glycerol.
37
What determines the melting point of TAGs?
The melting point of TAGs depends on:
-The length of their fatty acid chains.
-The degree of saturation in their fatty acid chains.
38
What are the types of TAGs?
-Simple TAGs: Have the same fatty acid at all three positions on glycerol.
-Mixed TAGs: Contain two or three different fatty acids attached to glycerol.
39
What are natural fats made of?
Most natural fats are complex mixtures of simple and mixed TAGs.
40
How does the composition of fatty acids affect the melting temperature of natural fats?
Fats with higher amounts of long-chain (C16 and C18) saturated fatty acids have higher melting temperatures.
41
What are examples of TAG-rich substances?
TAGs are major components of bulk fats and oils, including the human body’s depot fat.
42
Where are phosphate derivatives found?
in molecules such as phospholipids, DNA, RNA, and many proteins.
43
What is phosphoric acid (H₃PO₄)?
Phosphoric acid is a triprotic acid, meaning it can donate three H⁺ ions (protons).
At pH 7, it exists as an equilibrium mixture of H₂PO₄⁻ and HPO₄²⁻, collectively represented as Pi.
44
How does phosphorylation affect molecules?
Phosphorylation adds negative charges to molecules, increasing their water solubility.
Example: Phospholipids, DNA, RNA, and many proteins.
45
What types of reactions can phosphoric acid undergo?
Reaction with alcohols: Forms phosphate esters.
Hydroxyl group reacts with phosphorus, releasing water to form a phosphate ester.
Reaction with acids: Forms phosphoanhydrides.
46
What are glycerophospholipids (phosphoglycerides)?
Glycerophospholipids, also known as phosphoglycerides, are the primary components of biological membranes.
47
What is the structure of glycerophospholipids? (mention bonding)
1. Carbon 1 and 2 of glycerol are ester-bonded to two fatty acids (the hydrophobic tail).
-One fatty acid is saturated, and one is unsaturated.
2. A highly polar or charged head group (X) is attached to carbon 3 through a phosphodiester bond.
48
Why are glycerophospholipids amphipathic?
Glycerophospholipids are amphipathic because they have:
-A hydrophilic head (polar or charged group).
-A hydrophobic tail (fatty acids).
49
What is the biological importance of glycerophospholipids?
They are a major structural component of biological membranes, contributing to their properties and function.
50
What is phosphatidylcholine (lecithin)?
Phosphatidylcholine (lecithin) represents a class of lipids, not just a single molecule.
51
What distinguishes different phosphatidylcholine molecules?
The class of phosphatidylcholine lipids varies due to different combinations of fatty acids at positions R1 and R2 on the glycerol backbone.
52
What happens when lipids are dispersed in water?
Lipids aggregate spontaneously to form complexes due to their amphipathic nature.
53
What structures do fatty acids form in water?
Fatty acids group together to form spherical micelles, with diameters ranging from 3 nm to hundreds of nm.
54
Why don't phospholipids form micelles?
The hydrophobic tails of phospholipids are too bulky to pack tightly into micelles, so they form bilayers instead.
55
What structures do lipid bilayers form?
Lipid bilayers fold onto themselves to form liposomes or vesicles, with diameters as large as 1 micron or more.
56
What is the fundamental structure of the cell membrane?
The lipid bilayer is the fundamental structure of the cell membrane.
57
How are lipids analyzed and separated?
Lipids can be separated based on polarity using silica gel columns or thin-layer chromatography (TLC).
58
How are polar lipids separated in column chromatography?
In a silica gel column, polar lipids elute as solvents of increasing polarity are passed through the column.
59
How do lipids behave on a TLC plate?
On a TLC plate:
-Less polar lipids move farther.
-More polar lipids remain closer to the starting point.
60
What is the most abundant biomolecule on Earth?
Sugar (carbohydrates) is the most abundant biomolecule on Earth.
61
How do proteins and sugars differ in terms of building blocks?
Proteins are built from a limited number of building blocks.
Sugars have a huge variety of molecules.
62
Why are sugars important?
-Crucial in energy metabolism.
-Essential components of nucleic acids.
63
What are sugars also called?
Sugars are also known as saccharides.
64
What are the types of saccharides?
1. Monosaccharides: Single sugar unit (e.g., glucose).
2. Disaccharides: Two sugar units (e.g., sucrose).
3. Oligosaccharides: Short chains of monosaccharides.
4. Polysaccharides: Polymers of 20 or more sugar units (e.g., glycogen, cellulose).
65
What are the chemical properties of monosaccharides?
1. Very water-soluble.
2. Poorly soluble or insoluble in organic solvents (e.g., ether, hexane).
3. Colorless.
4. Most are sweet.
5. Approximate formula: (CH₂O)ₙ.
66
What functional groups do monosaccharides contain?
-A carbonyl (C=O) group, either as an aldehyde or ketone.
-At least two hydroxyl (-C-OH) groups.
67
What is the simplest monosaccharide?
The simplest monosaccharide is a triose, which contains three carbon atoms.
68
What are the two types of trioses?
Aldotriose: Contains an aldehyde group.
Ketotriose: Contains a ketone group.
69
What are the names of sugars based on carbon count?
Trioses: 3 carbon atoms.
Tetroses: 4 carbon atoms.
Pentoses: 5 carbon atoms.
Hexoses: 6 carbon atoms.
Heptoses: 7 carbon atoms.
70
Which monosaccharides are most common in nature?
The most common monosaccharides in nature are hexoses, such as D-glucose and D-fructose.
71
Why do we use special representations for sugar structures?
Special representations, such as Fischer projections and perspective formulas, depict the 3-D structure of sugars on a 2-D plane.
72
Do monosaccharides contain asymmetric carbon atoms?
Yes, all monosaccharides (except dihydroxyacetone) contain one or more chiral carbon atoms.
73
What is a chiral carbon atom?
A chiral carbon atom is a carbon atom with four different groups attached to it.
74
What is the significance of chiral carbons in monosaccharides?
Chiral carbons give rise to optically active isomeric forms, which are a type of stereoisomer.
75
What are D- and L-glyceraldehyde to eachother?
D- and L-glyceraldehyde are enantiomers, meaning they are mirror images of each other.
76
What are enantiomers?
Enantiomers are mirror images that differ in configuration at every chiral carbon atom. They are commonly referred to as left-handed and right-handed forms of molecules.
77
Do enantiomers have identical chemical properties? Where do they differ??
Yes, enantiomers have identical chemical properties, such as melting point and solubility, but differ in optical activity.
78
How do enantiomers differ in optical activity?
Enantiomers bend the plane of polarized light in opposite directions when passing through solutions. Light reflects differently after passing through each enantiomer's solution.
79
How do enantiomers differ in structure?
In enantiomers, the OH and H groups on chiral carbons swap sides when comparing the two forms.
80
What are diastereomers?
Diastereomers are stereoisomers of monosaccharides with more than one chiral carbon. They differ in the orientation around some chiral carbons but not all.
81
Do diastereomers have identical chemical properties?
No, diastereomers do not have identical chemical properties because the spatial relationships of the atoms in the molecule are different.
82
What is the D and L designation for sugars?
The D and L designation describes the configuration of the chiral carbon furthest from the carbonyl group in a sugar.
83
What configuration do amino acids and naturall sugars occur in?
Most amino acids occur in the L configuration.
Most naturally occurring sugars are in the D configuration.
84
When is a sugar called a "D" sugar?
A sugar is a "D" sugar if the chiral carbon furthest from the carbonyl group has the same configuration as D-glyceraldehyde.
85
When is a sugar called an "L" sugar?
A sugar is an "L" sugar if the chiral carbon furthest from the carbonyl group has the same configuration as L-glyceraldehyde.
86
What are epimers?
Epimers are a pair of sugars that are identical except for their configuration at one carbon.
87
How are epimers related to diastereomers?
Epimers are a special case of diastereomers, differing in configuration at only one carbon.
88
How do you determine the number of stereoisomers a sugar has?
A sugar with n chiral centers has 2^n stereoisomers.
89
How many stereoisomers does glyceraldehyde have? ( it has 1 chiral carbon)
Glyceraldehyde has 1 chiral carbon, so it has 2^1=2 stereoisomers.
90
How many stereoisomers does an aldose with 5 carbons have?
An aldose with 5 carbons has 3 chiral carbons, so it has 2^3 = 8 stereoisomers.
91
How are stereoisomers of sugars divided between D and L forms?
Half of the stereoisomers of a sugar are D sugars, and the other half are L sugars.
92
What do aldehydes and ketones react with to form hemiacetals and hemiketals?
Aldehydes and ketones react with alcohols to produce hemiacetals and hemiketals.
93
What happens to the carbonyl carbon when hemiacetals and hemiketals are formed?
The original carbonyl carbon becomes chiral upon forming hemiacetals or hemiketals.
94
What functional groups allow sugars to cyclize?
Sugars contain alcohol and aldehyde or ketone functional groups, enabling cyclization.
95
What is the nature of hemiacetal and hemiketal formation in sugars?
Hemiacetal and hemiketal formation in sugars is intramolecular, as the alcohol and aldehyde/ketone are part of the same molecule.
96
what does hemiacetal and hemiketal formation do to sugars?
Hemiacetal and hemiketal formation converts sugars into ring structures.
97
How does glucose cyclize?
The OH group at C-5 reacts with the carbon of the aldehyde group to form a stable six-membered ring.
98
What happens to C-1 during the cyclization of glucose?
C-1 becomes asymmetric, resulting in the formation of two stereoisomers: α-glucose and β-glucose.
99
What are anomers?
Anomers are two forms of the same sugar that differ in the position of the -OH group on the first carbon (anomeric carbon) in the ring form.
Alpha (α): The -OH is opposite the CH₂OH group.
Beta (β): The -OH is on the same side as the CH₂OH group.
100
What type of reaction occurs during glucose cyclization?
The reaction is similar to a hemiacetal formation, where an alcohol reacts with an aldehyde.
101
How does the cyclization of a ketose occur?
The reaction is similar to a hemiacetal formation, involving the reaction of a carbonyl carbon with the O of an OH group.
102
What distinguishes ketose cyclization from glucose cyclization?
In ketose cyclization, the reaction occurs at C-2, the carbonyl carbon of the ketose.
103
What does ketose cyclization produce?
Ketose cyclization produces α-fructose and β-fructose, two anomeric forms.
104
What type of reaction occurs in ketose cyclization?
The electrophilic carbonyl carbon reacts with the nucleophilic oxygen of an OH group, forming a cyclic structure.
105
What is mutarotation?
Mutarotation is the process where the α and β forms (anomers) of a sugar interconvert in aqueous solution, changing the optical rotation of the solution until equilibrium is reached.
106
What forms of glucose are present in the equilibrium during mutarotation?
The equilibrium mixture includes the α-form, β-form, and linear form of glucose.
107
What happens to solid glucose in water during mutarotation?
Solid glucose, initially in either α or β form, slowly interconverts into all forms in equilibrium.
108
What happens to α-D-glucose and β-D-glucose in solution over time?
They form identical equilibrium mixtures with identical optical properties.
109
What is the approximate composition of the equilibrium mixture for glucose?
The equilibrium mixture consists of:
⅓ α-D-glucose
⅔ β-D-glucose
Trace amounts of the linear form.
110
Why do α-D-glucose and β-D-glucose form equilibrium mixtures?
Due to mutarotation, where the α and β forms interconvert in solution until equilibrium is reached.
111
What are the two types of ring forms sugars can form during cyclization?
Pyranose – a 6-membered ring
Furanose – a 5-membered ring
112
What determines the size of the ring formed by a sugar during cyclization?
The size of the ring depends on the relative thermodynamic stabilities of the possible ring structures, which are influenced by the geometry of the molecule.
113
Which ring forms are common for glucose and fructose?
Glucose commonly forms a pyranose ring.
Fructose commonly forms a furanose ring.
114
How are Haworth projections formed for D-sugars?
The O of carbon 5 tracks the carbonyl carbon (C-1) to form the ring structure
115
What happens to OH groups from Fischer to Haworth projections?
OH groups on the left in Fischer are above the ring in Haworth projections.
Apply the rule: "Left Above, Beta Above".
116
Where is the anomeric OH located in Haworth projections?
β-form: The anomeric OH is above the ring.
α-form: The anomeric OH is below the ring.
117
What determines the type of ring formed during sugar cyclization?
The type of ring (pyranose or furanose) depends on which OH group acts as the nucleophile.
118
How does fructose form a pyranose ring?
If the OH of carbon 6 acts as the nucleophile, fructose forms a 6-membered pyranose ring
119
How do you complete the structure of a drawn ring?
Apply the rule: "Left Above, Beta Above" to position the groups correctly.
120
What defines a reducing sugar?
A reducing sugar undergoes a redox reaction where the carbonyl carbon of the sugar reacts with Cu²⁺ under alkaline conditions, oxidizing to a carboxylic acid while reducing Cu²⁺ to Cu⁺, forming a red precipitate.
121
Why do only linear forms of sugars react in redox reactions?
The redox reaction occurs only in the linear form of sugars, which contains a carbonyl group (aldehyde or ketone). The cyclic forms exist in equilibrium with the linear form but do not participate in the redox reaction.
In conclusion, needs a carbonyl group
122
How can you identify a reducing sugar by examining the anomeric
If the anomeric carbon of a ring form is free with an OH group on either side, it is a reducing sugar.
123
What is a glycoside?
A glycoside is formed when the anomeric carbon of a sugar reacts with a nucleophilic alcohol (-OH) or amine (-NH) group through condensation. The bond formed is either a glycosidic (C-O) or glycosyl (C-N) bond.
124
What are common examples of glycosides?
Common glycosides include polysaccharides, nucleosides, and the cardiac drug dioxin.
125
What happens when the anomeric carbon is involved in a glycosidic
When the anomeric carbon is involved in a glycosidic bond, the sugar becomes a non-reducing sugar, as the anomeric carbon can no longer open up to form the linear (reducing) form.
126
Why do non-reducing sugars not undergo oxidation by cupric ions?
Non-reducing sugars cannot undergo oxidation by cupric ions because their anomeric carbon is involved in a glycosidic bond, preventing the sugar from opening up into its linear form, which is necessary for the oxidation reaction.
127
How can you tell if a sugar is reducing or non-reducing?
If the anomeric carbon has a free hydroxyl group, the sugar is a reducing sugar and can open up into the linear form. If the anomeric carbon is involved in a glycosidic bond, the sugar is a non-reducing sugar.
128
What is a disaccharide?
A disaccharide is formed when two monosaccharides are linked by a glycosidic bond. The reaction occurs between the electrophilic anomeric carbon of one sugar and the nucleophilic hydroxyl group of the other.
129
What is an example of a disaccharide and how is it formed?
Lactose is a disaccharide formed by the condensation of glucose and galactose through a glycosidic bond.
130
What type of bond is formed in lactose?
A glycosidic bond
131
How is the glycosidic bond in lactose formed?
By the anomeric carbon of galactose in the beta (β) configuration reacting with the hydroxyl group on carbon 4 of glucose.
132
How is the glycosidic bond in lactose described?
As β(1→4), indicating the bond goes from carbon-1 of galactose in the β configuration to carbon-4 of glucose
133
Why is the anomeric carbon of galactose in lactose unable to undergo mutarotation?
Because it is involved in a glycosidic bond and cannot revert to the linear form, making it non-reducing.
134
Why is lactose considered a reducing sugar?
The anomeric carbon of glucose is free, allowing it to undergo mutarotation and exist in alpha (α-lactose), beta (β-lactose), or linear forms.
135
What is the term for the end of a disaccharide or polysaccharide chain with a free anomeric carbon?
The reducing end.
136
Which atom in a sugar is the electrophilic atom involved in glycosidic bond formation?
The anomeric carbon.
137
What acts as the nucleophile in the formation of a glycosidic bond?
The hydroxyl (OH) group.
138
Where can the nucleophilic OH group be located in glycosidic bond formation?
On the anomeric carbon of a second sugar or any other hydroxyl group in the sugar.
139
What are structural isomers of lactose?
Other disaccharides formed from galactose and glucose with different glycosidic bond arrangements.
140
Why is sucrose a non-reducing sugar
Both anomeric carbons of glucose and fructose are involved in the glycosidic bond, preventing mutarotation and the formation of a linear form.
141
What are most carbohydrates in nature classified as?
Polysaccharides, which are polymers of monosaccharide units.
142
Why are polysaccharides often highly branched?
Sugars have several hydroxyl (OH) groups, each capable of acting as a nucleophile to form glycosidic bonds, bonding a single subunit to two or more others.
143
How do polysaccharides differ from one another?
They differ in the identity of sugar units,
chain length,
type of bonds linking the units,
degree of branching.
144
What are homopolysaccharides?
Polysaccharides made from a single type of sugar monomer.
145
What are heteropolysaccharides?
Polysaccharides made from two or more kinds of sugar subunits.
146
What are glucans? Name examples.
Glucose homopolymers. Examples include starch (plants), glycogen (animals), cellulose, and chitin.
147
What are mannans?
Mannose homopolymers.
148
What is the primary function of nucleic acids?
To encode genetic information.
149
What is the primary structure of nucleic acids?
Linear polymers made by connecting nucleotides with phosphodiester bonds.
150
What is the repeating unit of nucleic acids?
The nucleotide, consisting of a sugar, a base, and a phosphate group.
151
What forms the backbone of nucleic acids?
The sugar-phosphate backbone, formed by linking sugars with phosphate groups.
152
What type of sugar does RNA contain?
D-ribose.
153
What type of sugar does DNA contain?
D-2-deoxyribose, where the -OH group on carbon 2 is replaced by -H.
154
In what form do the pentose sugars in nucleic acids occur?
β-furanose form.
155
What are the two types of bases in nucleic acids?
Purines and pyrimidines.
156
157
What are pyrimidines? Name examples.
Pyrimidines are nitrogenous bases with a single ring structure. Examples include:
Cytosine (C): Found in both DNA and RNA.
Thymine (T): Found only in DNA.
Uracil (U): Found only in RNA.
158
What are heterocycles?
Aromatic rings containing atoms such as nitrogen (N), oxygen (O), or sulfur (S), with nucleic acid bases only containing nitrogen.
159
What are tautomeric forms?
Isomers that differ by the shift of a hydrogen atom and a double bond.
160
What type of tautomerism does the hydroxyl (-OH) group undergo in cytosine?
Keto/enol tautomerism.
161
What type of tautomerism does the amino (-NH2) group undergo in cytosine?
Amino/imino tautomerism.
162
Which tautomeric form of cytosine predominates?
The amino + keto form.
163
What is the structure of a purine ring?
A fused, two-ring heterocyclic structure.
164
Name the two purine bases found in both RNA and DNA.
Adenine (A) and Guanine (G).
165
How is a nucleoside formed?
By joining a base to a sugar through a glycosidic bond.
166
What type of molecule is a nucleoside?
A special type of glycoside found in nucleic acids.
167
What is another name for the glycosidic bond in nucleosides?
Glycosylic bond, to designate the C-N linkage.
168
Which atom of purines links to the anomeric carbon of ribose or deoxyribose?
The nitrogen atom (NH) at position 9.
169
Which atom of pyrimidines links to the anomeric carbon of ribose or deoxyribose?
The nitrogen atom (NH) at position 1.
170
How is a nucleotide formed?
By combining a base, a sugar, and a phosphate group.
171
What are nucleotides chemically?
Phosphorylated nucleosides.
172
How are nucleotide units in DNA and RNA linked?
Through phosphodiester linkages.
173
What does the phosphate group bridge in a phosphodiester linkage?
The 5' hydroxyl (OH) of one nucleotide unit and the 3' hydroxyl (OH) of another.
174
Is the phosphodiester linkage pattern the same in DNA and RNA?
Yes, it is the same for both.
175
What is the structure of a linear nucleic acid strand?
-It has a specific 5' end, which lacks a nucleotide at the 5' position.
-It has a specific 3' end, which lacks a nucleotide at the 3' position.
176
What is the charge of phosphate groups at pH 7?
Completely ionized and negatively charged.
177
In what direction are nucleotide sequences written?
From 5' to 3'.
178
Net charge on the RNA oligonucleotide 5’ UGCUAC 3’ (bearing -OH groups at the 5’ and 3’ ends, at neutral pH, and ignoring any counter ions will be:
-5
For a sequence of six nucleotides like UGCUAC, there are five phosphate groups linking the nucleotides together (one between each pair of nucleotides).
Each of these phosphate groups carries a -1 charge
