Biochemistry Chapter 4 Quiz

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Questions and Answers

What type of bond is involved in the nucleoside triphosphates that provide chemical energy?

Peptide bonds

Ionic bonds

Phosphoanhydride bonds (correct)

Hydrogen bonds

What is the primary reason ATP is considered an unstable molecule?

It has a very strong covalent bond.

It holds too many phosphate groups.

It readily loses its phosphate group. (correct)

It is a double-stranded molecule.

Which product is formed when a phosphate group from ATP is transferred to glucose?

AMP

Sucrose

Phosphorylated glucose (correct)

Fructose

Why is the reaction involving glucose-P and fructose energetically favorable?

Glucose-P is relatively unstable. Signup and view all the answers

Which nucleoside triphosphate is NOT listed as providing chemical energy?

Thymidine triphosphate (TTP) Signup and view all the answers

What role do tRNA molecules play in protein synthesis?

They deliver amino acids to the ribosome. Signup and view all the answers

What type of reaction do aldonic acids undergo to form lactones?

Intramolecular esterification Signup and view all the answers

Which type of nucleotide is found in RNA?

Ribonucleotide Signup and view all the answers

What type of bond connects the nucleotides in a nucleic acid polymer?

Phosphodiester bond Signup and view all the answers

What results from the oxidation of the carbonyl (C1) group of an aldose?

Aldonic acid Signup and view all the answers

Which of the following statements about alditols is true?

They generate the same caloric intake as monosaccharides. Signup and view all the answers

What is the role of the 3' oxygen in the formation of a new nucleotide bond during DNA synthesis?

It acts as a nucleophile to form a bond with phosphorus. Signup and view all the answers

Ascorbic acid is classified as which type of compound?

γ-lactone of a hexonic acid Signup and view all the answers

Which of these nitrogen bases is NOT found in DNA?

Uracil Signup and view all the answers

Which of the following best describes the oxidation process in organic chemistry?

Loss of hydrogens or gain of oxygens Signup and view all the answers

What is the significance of complementary base pairing in DNA?

It ensures the accurate replication and transcription of genetic information. Signup and view all the answers

What characteristic do both aldonic and uronic acids share?

Both can form 5 or 6-membered lactones. Signup and view all the answers

How do singular nucleotides contribute to cellular functions beyond being building blocks?

They play roles in cellular energy storage and provision. Signup and view all the answers

Which reaction type can produce alditols from aldoses and ketoses?

Reduction reactions Signup and view all the answers

What sequence structure is read by the cell to produce proteins?

Groups of three bases Signup and view all the answers

What is the result of the oxidation of both the last alcohol group and the aldehyde group in an aldose?

Aldaric acid Signup and view all the answers

What is a characteristic of D(-)-sorbitol?

It has a sweetening power of 70% of sucrose. Signup and view all the answers

Which statement about xylitol is true?

It provides the same caloric intake as sucrose. Signup and view all the answers

What defines a glycosidic bond?

The bond connecting the anomeric carbon with an alcoholic oxygen. Signup and view all the answers

Under what conditions can glycosides be hydrolyzed?

In an acidic environment. Signup and view all the answers

What is a common industrial use of D(-)-sorbitol?

In jams due to its hygroscopicity. Signup and view all the answers

How are glycosides often referred to when considering their pharmacological applications?

Pro-drugs Signup and view all the answers

What is a feature of xylitol regarding dental health?

It is not cariogenic. Signup and view all the answers

What distinguishes the components of glycosides?

They include a glyconic component and an aglyconic component. Signup and view all the answers

What is the simplest aldose that exhibits optical activity?

D-glyceraldehyde Signup and view all the answers

Which classification describes monosaccharides with the same molecular formula but different configurations at one carbon atom?

Epimers Signup and view all the answers

How many possible stereoisomers are there for a monosaccharide with 'n' chiral centers in the aldose form?

2n-2 Signup and view all the answers

Where is the hydroxyl group located in the D series of monosaccharides?

On the right side of the asymmetrical carbon Signup and view all the answers

What type of cyclic structure does a monosaccharide with six carbon atoms form?

Pyranose Signup and view all the answers

What is the optical rotation of a D-glucose solution at room temperature?

+52.7° Signup and view all the answers

Which monosaccharide possesses a sweetening power of 140% compared to sucrose?

D-fructose Signup and view all the answers

Which of the following processes leads to the formation of hemiacetals and hemiketals in monosaccharides?

Reaction of alcohols with carbonyl groups Signup and view all the answers

What defines an anomer in the context of monosaccharides?

They are cyclic structures differing at the anomeric carbon Signup and view all the answers

Which category do monosaccharides fall into based on their functional groups?

Aldoses and ketones Signup and view all the answers

What describes amylose in terms of its structure?

It consists of a linear chain of glucose linked by α-(1→4) bonds. Signup and view all the answers

Which of the following statements about starch is true?

Starch contains two main components: amylose and amylopectin. Signup and view all the answers

What is the significance of polymerizing glucose in starch?

To prevent an increase in osmotic pressure. Signup and view all the answers

Which of the following disaccharides consists of a glucose and a fructose unit?

Sucrose Signup and view all the answers

In polysaccharides, how are the homopolysaccharides characterized?

They consist of a single type of monosaccharide. Signup and view all the answers

Which bond is primarily found in both amylose and amylopectin?

α-(1→4) glycosidic bond Signup and view all the answers

What type of end does amylopectin have at the non-reducing end?

A hydroxyl group Signup and view all the answers

What distinguishes trehalose from sucrose?

Sucrose contains a glucose and a fructose unit. Signup and view all the answers

Study Notes

Plane Electromagnetic Waves

Electromagnetic waves consist of oscillating electric and magnetic fields.
These fields radiate outwards at the speed of light.

Polarization of Light Waves

Normal light has electric fields oscillating in all directions.
A polarizing filter allows only light oscillating in a single plane to pass through.
Plane-polarized light is light that oscillates in a single direction.
Chiral molecules rotate the plane of polarization of plane-polarized light.
Jean-Baptiste Biot discovered this effect in 1815.
Naturally occurring organic substances, like camphor, can rotate the plane of polarization.
The rotation direction (clockwise or counterclockwise) depends on the chirality of the substance.

Molecules That Rotate Plane-Polarized Light

Dextrorotatory molecules rotate plane-polarized light clockwise.
Levorotatory molecules rotate plane-polarized light counterclockwise.
Enantiomers rotate light by the same amount but in opposite directions.

Amino Acids, Proteins, Enzymes, and Receptors

Amino acids are chiral.
Proteins are chiral.
Enzymes and receptors are chiral.
Enzymes and receptors form a chiral environment in the human body that distinguishes between R and S enantiomers.

Carbohydrates

Monosaccharides are simple sugars.
They cannot be hydrolyzed into simpler carbohydrate molecules.
Monosaccharides are analogous to amino acids.
Polysaccharides are analogous to proteins.
Nucleotides are analogous to nucleic acids.

Carbohydrates: Transformations of Light Energy

Carbohydrates are largely produced by photosynthesis.
They are the most abundant class of biological molecules.
They form the essential components of all living organisms.
They account for more than 90% of dry matter in plants.
They contribute to 55-70% of the caloric intake in humans.

The Building Blocks

Chiral tetrahedral carbon atoms are covalently linked to a hydroxyl group, a carbonyl group, and the rest of the chain.
They are often aldehydes or ketones of aliphatic polyhydroxy alcohols.
The number of carbon atoms in these molecules ranges from 3 to 7.
These molecules display several chiral centers.
D stereoisomerism predominates in nature.

Glyceraldehyde

Glyceraldehyde is the simplest aldose.
It displays optical activity (C2 asymmetric).
The two enantiomers are indicated by D(+) and L(-).
Glyceraldehyde stereoisomers are used to classify all monosaccharides.

Monosaccharides

These are aldehydes or ketones of polyhydroxy alcohols.
The number of carbon atoms range from 3 to 7.
In D-series monosaccharides, the hydroxyl group bound to the asymmetric carbon furthest from the carbonyl group is positioned right.

Classification of Monosaccharides

Monosaccharides are categorized according to the type of carbonyl group (aldehyde or ketone) and the number of carbon atoms.
The trioses are the three-carbon monosaccharides (e.g., glyceraldehyde and dihydroxyacetone).
The hexoses are the six-carbon monosaccharides (e.g., glucose and fructose).

Stereoisomerism

Monosaccharides have numerous chiral centers.
The number of possible stereoisomers is 2^n-2 (n=number of chiral centers) for aldoses and 2^n-3 for ketoses.
Stereoisomers that differ only in the configuration of a carbon atom are called epimers.

Epimers

Epimers are stereoisomers.
They differ in the position of a hydroxyl group (OH) on a single carbon atom (e.g., glucose and mannose).

Cyclic Conformations

The hydroxyl and carbonyl groups in 5 and 6-carbon monosaccharides spontaneously react intramolecularly to form cyclic hemiacetals and hemiketals.

Haworth Projections

A monosaccharide with a 6-carbon ring is called a pyranose.
A monosaccharide with a 5-carbon ring is called a furanose.

D(+)-glucose

It is a reducing sugar, with 70% of the sweetening power of sucrose.
It exhibits a specific optical rotation (+52.7°) at room temperature.
It readily reacts with amino acids and is involved in Maillard reactions.
It dissolves easily in water.

D(-)-fructose

It was initially known as levulose.
It has 140% sweetening power compared to sucrose.
Displays a specific optical rotation (-92.4°) at room temperature.

Glucose Cyclization

The cyclization of a monosaccharide induces asymmetry in the carbonyl carbon.
This leads to the formation of two diastereomers called anomers.
The anomer 'a' has the anomeric hydroxyl in the opposite direction to the CH2OH (glucose C6) bound to the chiral center (glucose C5).
The other anomer is called 'b'.

Mutarotation

D-glucose anomers have different specific optical rotations.
At room temperature, a solution of D-glucose has a specific optical rotation.
The two anomers interconvert rapidly.
The open-chain form of glucose in solution is present at very low concentrations in equilibrium.

The Conformation of Monosaccharides

The stability of pyranose and furanose rings depends on stereochemical interactions between the ring substituents.

Derivatives of Monosaccharides

Deoxysugars—one or more hydroxyl groups are substituted by an H.
Aminosugars—one or more hydroxyl groups are substituted by amino groups (often acetylated).

Glucose Family

The relationship between monosaccharides is similar to the relationship between side chains and amino acids.

Redox Reactions

Carbohydrates display typical reactivity of aldehydes and ketones.
Mild oxidation of the carbonyl group (C1) in an aldose generates an aldonic acid.
Oxidation of the last alcohol group (C6) gives rise to an uronic acid.
Oxidation of both the last alcohol group and the aldehyde group creates an aldaric acid.

Lactonization

Aldonic and uronic acids tend to undergo intramolecular esterification.
This results in the formation of 5- or 6-membered lactones.

Ascorbic Acid

Vitamin C is a y-lactone of a hexonic acid.
It has an enediol structure at carbon atoms 2 and 3.

Reduction Reactions

Aldoses and ketoses can be reduced to alditols under mild conditions.
Alditols do not possess a carbonyl group.
They are commonly found in nature.
They provide the same caloric intake as their corresponding monosaccharides but are absorbed more slowly.

D(-)-sorbitol

Sorbitol results from the reduction of glucose.
It is a prevalent component in plants.
It is slowly metabolized in humans.
It provides the same caloric intake as glucose without increasing blood sugar.
It is not fermented by yeasts.
It has high hygroscopicity, thermostability, and crystallisation retardation properties.
It is used industrially, particularly in jams.

Xylitol

Xylitol is present in small amounts in fruits and vegetables.
Structurally similar to sucrose.
Provides the same sweetening and caloric value as sucrose.
It is not cariogenic.
In humans, it is partially converted to glucose.
Used in diabetic foods.

Glycosidic Bond

The derivative formed by the reaction between a monosaccharide and an alcohol is a glycoside.
Glycosides are stable in alkaline and oxidant conditions.

Glycosides

Glycosides are derivatives of monosaccharides.
The products are stable under alkaline and oxidant conditions.
These products can be hydrolyzed in acidic environments.
They are commonly found in nature.

Glycosides (Hetero/pro-drugs)

Glycosides, also known as heterosides, are pro-drugs.
They undergo enzymatic hydrolysis to separate the sugar component from the aglycone to yield the pharmacologically active moiety.
The sugar part, however, helps modulate some properties of the molecule (e.g., toxicity or solubility).

Amygdalin/Laetrile

It is the most important cyanogenic glycoside.
It is found in the seeds of various Rosaceae plants.
It releases hydrogen cyanide (HCN).

Streptomycin

Streptomycin is an antibiotic.

Ouabain

Ouabain is a poison.
It inhibits Na+/K+ pump activity.

Reducing Sugars

Reducing sugars can reduce other chemical compounds. They have a free aldehyde or ketone group.
The carbonyl group of a reducing sugar can be oxidized.
When the anomeric carbon is part of a glycosidic bond the oxidation reaction can't occur.

Reducing Ends/Non-reducing ends/Branches

The non-reducing end of a polysaccharide is the end with an available anomeric carbon that is not involved in a glycosidic bond.
The reducing end is the end that can be oxidized.
Branching points exist in certain polysaccharides.

Disaccharides

Disaccharides are composed of two monosaccharides.
They can be either homo- or hetero-dimers (composed of the same or different monosaccharide units).
Common examples include lactose, sucrose, and trehalose.

Polysaccharides

Polysaccharides can be homo- or hetero-polymers (composed of the same or different monosaccharide units).
Polysaccharides are categorized based on their structure (linear or branched).

The Main Polysaccharides

Examples to consider: cellulose, starch (amylose and amylopectin), and glycogen.
Characteristics: source, subunit, bonds, branching, and shape.

Reserve Polysaccharides: Starch

Starch is the glucose reserve in plants and a major food for humans.
Glucose is stored as a polymer that avoid osmotic pressure.
In plants, starch is stored in granules.
Starch is a mixture of amylose and amylopectin.

Starch

Amylose consists of α(1→4)-linked glucose molecules.
Amylose takes on a helical conformation.
Amylopectin consists of linear chains of α (1-4)-linked glucose.
It contains α (1-6) branch points.

Starch structure

The stability of amylose and amylopectin depends on the stereochemical interactions between the substituents of the ring.

Starch Granules

Starch granules display a concentric lamellar structure with alternating crystalline and amorphous phases.
Those crystalline phases occur due to the regular packing of terminal amylopectin chains

Starch Gelatinization

Starch can be scarcely hydrated and is not easily attacked by hydrolytic enzymes.
Heating starch in water causes the disintegration of the crystalline phase, triggering granule hydration.

Starch Retrogradation

Upon cooling, linear portions of amylose molecules align.
This forms inter-chain H bonds between amylose and amylopectin molecules.
This process is known as retrogradation.

Cellulose

Cellulose is a structural polysaccharide.
It is composed of linear chains of ẞ(1→4)-linked glucose molecules.
Cellulose is insoluble in water due to extensive hydrogen bonding.

Chitin

Chitin is a linear polymer of N-acetyl-D-glucosamine.
It is linked by a β(1→4) glycosidic bond.
Chitin is a structural component of exoskeletons and cell walls.

Nucleosides and Nucleotides (Aglyconic and Sugar Moieties)

Nucleosides are glycosyl amines composed of a five-carbon sugar (ribose or deoxyribose) and a nitrogenous base(purine or pyrimidine).
Nucleotide is a nucleoside combined with one or more phosphate groups.
The nitrogenous bases are adenine, cytosine, guanine, thymine/uracil.

Nucleotides: DNA and RNA Building Blocks

Nucleotides are the building blocks of DNA and RNA.
They each have a five-carbon sugar, a nitrogenous base, and one or more phosphate groups.
Ribonucleotides are RNA molecules.
Deoxyribonucleotides are DNA molecules.
The sugar is phosphorylated at carbon 5'

Phosphodiester Bond

Phosphodiesters are bonds that link nucleotides together in DNA and RNA.
Nucleophilic substitution occurs at the 3' oxygen.

Complementary Base Pairing

Adenine always pairs with thymine/uracil (2 hydrogen bonds).
Guanine always pairs with cytosine (3 hydrogen bonds).

DNA Structure

DNA structure is analogous to side chain and amino acids.
The specific genetic code is determined by the sequence of bases in a DNA molecule.
The sequence of bases provides the instructions for producing molecules in a living organism.

Nucleotides and Energy: Phosphoanhydride Bonds

Nucleotides such as ATP, GTP, CTP and UTP are important for energy storage and transfer in cells.
They have multiple phosphate groups attached which are linked together through phosphoanhydride bonds.

Phosphoric Anhydrides (Energy Storage)

High-energy phosphate bonds are formed by phosphoanhydride linkages.
ATP is a common nucleotide used for energy storage.

Reaction Coupling

Coupled reactions allow energetically unfavorable reactions to take place.
An energetically favorable reaction drives an unfavorable one, resulting in the overall release of energy and reaction spontaneity.

Glycogen and Glucose Regulation

Glycogen is the storage form of carbohydrates in animals.
Found primarily in muscle tissue and liver.
Glycogen is a branched polymer of glucose.
Insulin and glucagon regulate blood glucose levels, respectively, promoting glycogen synthesis and degradation.

Glycogen Synthase vs Glycogen Phosphorylase

Glycogen synthase catalyzes glycogen synthesis.
Glycogen phosphorylase catalyzes glycogen degradation.
Their activities are regulated by glucose and allostery.

Glucose Transformations Before Glycogen Synthesis

Glycolysis, before glycogen synthesis occurs, involves a series of enzymatic transformations to form glucose-6-phosphate.
Then, glucose-6-phosphate will be converted into UDP-glucose.

Glycogenesis

The formation of glycogen from glucose is a process called glycogenesis.
A series of enzymatic reactions, catalyzed by key enzymes such as glucokinase and glycogen synthase, convert glucose into UDP-glucose, and then incorporate the UDP-glucose into the growing glycogen polymer.

Glycogen Synthesis Strategy

The substrate for glycogen synthase reaction is UDP-glucose, not glucose-1-phosphate.
The OH group of glucose is not directly reactive; it requires enzymatic activation.

Conversion of Glucose-1-Phosphate into UDP-Glucose

The conversion of glucose-1-phosphate to UDP-glucose is necessary due to the reactive nature of UDP-glucose and its ability to form glycosidic bonds in the elongating glycogen chain.

Glycogen Synthesis

Synthesis of glycogen is catalyzed by glycogen synthase.
UDP-glucose is used as a substrate for the synthesis reaction.
The first glucose residue is added to a pre-existing glycogen molecule, which is often formed on a protein called glycogenin.

Glycogen «de novo» Synthesis

A process that builds a glycogen chain from the beginning starting with glycogenin. The reaction starts by using UDP-glucose and a unique protein called glycogenin.

Glycogen Synthase Mechanism

The actual reaction mechanism of glycogen synthase catalyzed the addition of UDP-glucose to the non-reducing ends of the polymer chain.

Regulation of Glycogen Synthesis

Glycogen Synthase is a homotetrameric enzyme
Its activity is regulated by phosphorylation/dephosphorylation, primarily by protein kinase A(PKA) and mediated by allosteric effectors such as AMP, ATP, glucose-6-phosphate.

Regulation of Glycogen Hydrolysis

Glycogen hydrolysis involves the use of glycogen phosphorylase.
This enzyme uses inorganic phosphate to give glucose-1-phosphate.
Glycogen phosphorylase is modulated by phosphorylation.

Starch Synthesis

Starch is synthesized from sucrose.
Sucrose is hydrolyzed into glucose and fructose.
Fructose is then converted to glucose.
Glucose is transformed into UDP-glucose which is then converted into glucose-1-phosphate (G-1-P).
G-1-P is transformed into glucose-6-phosphate (G-6-P)
G-6-P is the substrate for enzymes involved in amylose and amylopectin synthesis.

Structural Polysaccharides: Cellulose

Cellulose is a linear polymer composed of beta-1,4-linked glucose units.
Cellulose is a structural component in plant cell walls.
It has a distinctive linear structure and extensive hydrogen bonding.

Structural Polysaccharides: Amylose and Cellulose (Differences)

Both amylose and cellulose are polymers of glucose, but cellulose has beta linkages while amylose has alpha linkages.
This difference influences the structure of the polymers (helical vs. linear).
The specific glycosidic bonds influence the properties and function in the organisms.

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Description

Test your knowledge of nucleotides, ATP, and protein synthesis in this biochemistry quiz. Cover topics such as energy transfer mechanisms, nucleoside triphosphates, and RNA structure. Challenge yourself and see how well you understand these essential biochemical concepts.