Biology Chapter 4: Protein and Carbohydrate Structures
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Questions and Answers

What primarily determines the tertiary structure of a protein?

  • The primary sequence alone
  • Hydrophobic and hydrophilic interactions among amino acids (correct)
  • Interaction of multiple polypeptide chains
  • Only covalent bonding of disulfide linkages

Which of the following correctly describes quaternary structure?

  • It involves the bonding of amino acids into a chain.
  • It relies solely on primary sequences of amino acids.
  • It is the overall three-dimensional shape of a single polypeptide.
  • It involves interactions between multiple subunits of a protein. (correct)

Which step occurs first in the process of protein synthesis?

  • Post-translational modifications
  • Translation
  • Amino acid synthesis
  • Transcription (correct)

How are amino acids obtained by the body?

<p>Synthesized by the body from precursors and also obtained through diet. (D)</p> Signup and view all the answers

What role does mRNA play during translation?

<p>It determines the order of amino acids in a polypeptide chain. (B)</p> Signup and view all the answers

Which carbohydrate contains only one sugar molecule?

<p>Galactose (A)</p> Signup and view all the answers

What is the primary characteristic of polysaccharides?

<p>They contain more than ten sugar molecules. (A)</p> Signup and view all the answers

Which of the following statements is true regarding disaccharides?

<p>They contain two sugar molecules and may have a glycoside bond. (D)</p> Signup and view all the answers

Which of the following is an example of a polysaccharide?

<p>Cellulose (B)</p> Signup and view all the answers

What distinguishes monosaccharides from other types of carbohydrates?

<p>They are always reducing sugars. (C)</p> Signup and view all the answers

What characterizes simple proteins?

<p>They consist only of amino acid residues. (A)</p> Signup and view all the answers

Which type of protein primarily includes fibrous proteins?

<p>Simple proteins (A)</p> Signup and view all the answers

What effect do physical agents like heat have on proteins?

<p>They can denature proteins, leading to coagulation. (A)</p> Signup and view all the answers

How are tertiary structures of proteins predominantly stabilized?

<p>By hydrogen bonds and hydrophobic interactions. (B)</p> Signup and view all the answers

What is the primary structure of a protein?

<p>The sequence of amino acids in the polypeptide chain. (D)</p> Signup and view all the answers

At which point does a protein not move in an electric field?

<p>At the isoelectric point (pI). (D)</p> Signup and view all the answers

What defines conjugated proteins?

<p>They contain non-protein moieties combined with protein components. (C)</p> Signup and view all the answers

Which of the following correctly describes secondary derived proteins?

<p>They are degraded products of simple and conjugated proteins. (A)</p> Signup and view all the answers

What role do carbohydrates play in living organisms?

<p>They are the primary energy source for living beings. (A)</p> Signup and view all the answers

Which carbohydrate is primarily used for energy storage in animals?

<p>Glycogen (C)</p> Signup and view all the answers

What type of carbohydrate cannot be broken down by hydrolysis?

<p>Monosaccharides (A)</p> Signup and view all the answers

Which of the following carbohydrates is classified as an oligosaccharide?

<p>Sucrose (A), Maltose (C)</p> Signup and view all the answers

Which carbohydrate serves as a structural component of the cell wall in plants?

<p>Cellulose (B)</p> Signup and view all the answers

During photosynthesis, what compounds are used for the formation of carbohydrates?

<p>Carbon dioxide and water (D)</p> Signup and view all the answers

Which of the following statements about carbohydrates is FALSE?

<p>All carbohydrates are energy sources. (C)</p> Signup and view all the answers

What is the energy yield of carbohydrates per gram?

<p>4 kcal/gram (C)</p> Signup and view all the answers

Which type of carbohydrate is defined by having an aldehyde as the most oxidized functional group?

<p>Aldose (C)</p> Signup and view all the answers

What distinguishes epimers from other isomers?

<p>They differ at only one specific carbon atom. (B)</p> Signup and view all the answers

Which of the following pairs are considered C-2 epimers?

<p>Glucose and mannose (C)</p> Signup and view all the answers

What suffix do ketoses typically have?

<p>-ulose (B)</p> Signup and view all the answers

Which configuration do most sugars found in humans belong to?

<p>D-sugars (D)</p> Signup and view all the answers

How are enantiomers defined in terms of their structural relationship?

<p>Structures that are mirror images of one another. (C)</p> Signup and view all the answers

At which carbon atom is the orientation of the -OH group used to determine D or L configuration?

<p>Carbon 5 (D)</p> Signup and view all the answers

Which statement about isomers is correct?

<p>Isomers can include sugars with the same formula but different structures. (A)</p> Signup and view all the answers

What characterizes a reducing sugar?

<p>It has a free aldose or ketose group at the anomeric carbon. (D)</p> Signup and view all the answers

Which of the following sugars is classified as a non-reducing sugar?

<p>Sucrose (D)</p> Signup and view all the answers

What is the role of the anomeric carbon in a reducing sugar?

<p>It is necessary for the sugar to reduce chromogenic reagents. (B)</p> Signup and view all the answers

Which of the following statements is true about non-reducing sugars?

<p>They do not have a free aldehyde or ketone group. (A)</p> Signup and view all the answers

What happens to the anomeric carbon of a reducing sugar when it acts as a reducing agent?

<p>It gets oxidized. (C)</p> Signup and view all the answers

Which disaccharide is correctly identified as a reducing sugar?

<p>Cellobiose (A), Maltose (C)</p> Signup and view all the answers

The reaction of reducing sugars with Benedict's reagent results in what outcome?

<p>Reduction of cupric ions to form a colored cuprous ion. (A)</p> Signup and view all the answers

Which of the following best represents the structure of sucrose?

<p>O-α-D-Glucopyranosyl-(1→2)-β-D-fructofuranoside (C)</p> Signup and view all the answers

What type of glucose monomer is found in cellulose?

<p>β-glucose (C)</p> Signup and view all the answers

What bond type is primarily found in the structure of glycogen?

<p>α(1→4) and α(1→6) glycosidic bonds (C)</p> Signup and view all the answers

Which of the following describes the physical structure of starch?

<p>Coiled unbranched and long branched chains (D)</p> Signup and view all the answers

What type of bond links monosaccharides in glycosidic bonds?

<p>Covalent bonds (A)</p> Signup and view all the answers

Which type of polysaccharide is composed of identical monosaccharide units?

<p>Homopolysaccharide (C)</p> Signup and view all the answers

Which of the following tests can indicate the presence of reducing sugars?

<p>Benedict's test (B)</p> Signup and view all the answers

What are the two forms of starch, and how do they differ in structure?

<p>Amylose and amylopectin; one is linear and the other is branched. (B)</p> Signup and view all the answers

What is the predominant form of glucose in solution?

<p>Pyranose form (A)</p> Signup and view all the answers

Which structure is formed from the reaction between the aldehyde group and an alcohol group in monosaccharides?

<p>Cyclic structure (B)</p> Signup and view all the answers

What represents the anomeric carbon in a cyclic aldose structure?

<p>Carbon 1 (C)</p> Signup and view all the answers

What term describes the ability of α and β anomers to interconvert in solution?

<p>Mutarotation (D)</p> Signup and view all the answers

Which statement correctly describes the OH group on the anomeric carbon of α-D-glucose in a Haworth projection?

<p>It is trans to the CHâ‚‚OH group. (C)</p> Signup and view all the answers

Flashcards

Simple Proteins

Proteins composed only of amino acid residues. Hydrolysis yields only amino acids.

Conjugated Proteins

Proteins composed of amino acid chains with additional non-protein components.

Derived Proteins

Degraded products of simple and conjugated proteins.

Primary Structure

The sequence of amino acids in a polypeptide chain, held together by peptide bonds.

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Secondary Structure

Local conformations of a polypeptide chain, like alpha-helices and beta-sheets, stabilized by hydrogen bonds between backbone atoms.

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Tertiary Structure

The overall three-dimensional shape of a protein, determined by interactions between amino acid residues.

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Quaternary Structure

The arrangement of multiple polypeptide chains (subunits) in a protein, stabilized by interactions similar to those in the tertiary structure.

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Isoelectric Point (pI)

The pH at which a protein has no net charge and does not migrate in an electric field.

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Transcription

The process of converting DNA into messenger RNA (mRNA). This occurs in the cell nucleus and involves enzymes called RNA polymerases.

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Translation

The process of using the information encoded in mRNA to build a polypeptide chain. Ribosomes read the mRNA sequence and link together amino acids in a specific order determined by the genetic code.

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Post-translational Modifications

The final steps in protein synthesis that occur after the polypeptide chain has been formed. These steps include modifying the protein, such as folding, cleavage, and adding chemical modifications. These changes allow the protein to become fully functional.

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What are Monosaccharides?

Carbohydrates made of a single sugar molecule. Examples include glucose, fructose, and galactose.

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What are Disaccharides?

Carbohydrates consisting of two sugar molecules linked together. Examples include sucrose, lactose, and maltose.

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What are Polysaccharides?

Carbohydrates containing more than ten sugar molecules linked together. Examples include starch, glycogen, and cellulose.

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What is a Glycoside Bond?

The bond that connects sugar molecules in disaccharides and polysaccharides.

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What is the difference between trioses, tetroses, pentoses, hexoses, and heptoses?

The number of carbon atoms forming the backbone of a monosaccharide.

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What are carbohydrates?

Carbohydrates are polyfunctional compounds containing two types of functional groups: aldehydes or ketones and hydroxyl groups.

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What is the main function of carbohydrates in living organisms?

They are the most abundant dietary source of energy for all living beings (4 kcal/gram).

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How are carbohydrates formed in nature?

Plants create carbohydrates through photosynthesis, using sunlight, carbon dioxide, and water to produce glucose and oxygen.

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How are carbohydrates classified?

Carbohydrates are classified based on the number of monosaccharide units they contain.

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What are oligosaccharides?

Contain 2-9 monosaccharides. Examples: sucrose, maltose. They are formed by combining two monosaccharides with the release of water.

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What is starch?

The storage form of carbohydrates in plants.

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What is glycogen?

The storage form of carbohydrates in animals.

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Reducing Sugar

A sugar that can act as a reducing agent because its anomeric carbon has a free aldehyde or ketone group.

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Non-reducing Sugar

A sugar that cannot act as a reducing agent because its anomeric carbon is involved in a glycosidic bond.

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Anomeric Carbon

The carbon atom that's part of the carbonyl group in a sugar molecule, it's the one that can be either an aldehyde or a ketone.

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Glycosidic Bond

A bond formed between two sugars, where the anomeric carbon of one sugar is linked to a hydroxyl group on the other.

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Maltose

Type of reducing sugar: O-α-D-Glucopyranosyl-(1→4)-α-D-glucopyranose. This sugar is made of two glucose units.

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Lactose

Type of reducing sugar: O-β-D-Galactopyranosyl-(1→4)-β-D-glucopyranose. This sugar is made of galactose and glucose.

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Sucrose

Type of non-reducing sugar: O-α-D-Glucopyranosyl-(1→2)-β-D-fructofuranoside. This sugar is made of glucose and fructose.

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Reducing Ability

The ability of a sugar to reduce cupric ions in Benedict's or Fehling's solution, causing a color change. This is a test for reducing sugars.

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Aldoses

Carbohydrates that have an aldehyde as their most oxidized functional group.

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Ketoses

Carbohydrates that have a keto group as their most oxidized functional group.

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Isomers

Compounds with the same chemical formula, but different structures.

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Epimers

Two monosaccharides that differ in configuration around only one specific carbon atom (excluding the carbonyl carbon).

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Enantiomers

Pairs of structures that are mirror images of each other.

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D-Sugars vs L-Sugars

Sugars in humans are predominantly D-sugars. Enzymes are specific to the D-configuration.

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Determining D or L

The orientation of the -H and -OH groups around the carbon atom adjacent to the terminal primary alcohol carbon (carbon 5 in glucose) determines D or L configuration.

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Glucose is Dextrorotatory

Glucose is dextrorotatory (hence the alternative name dextrose).

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Homopolysaccharide

A type of polysaccharide where all the monosaccharide units are the same.

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Heteropolysaccharide

A type of polysaccharide where different types of monosaccharides are linked together.

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Glycogen

Highly branched polysaccharide of glucose, serving as energy storage in animals.

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Asymmetric Carbon

A carbon atom bonded to four different groups, making it chiral and capable of rotating plane-polarized light. This property gives rise to optical isomers or enantiomers.

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Cyclic Monosaccharide

The form of a monosaccharide where its aldehyde or ketone group reacts with an alcohol group on the same sugar, forming a ring structure.

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Pyranose

The six-membered ring structure of a monosaccharide, resembling pyran, containing 5 carbons and 1 oxygen.

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Furanose

The five-membered ring structure of a monosaccharide, resembling furan, containing 4 carbons and 1 oxygen.

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Haworth Projection

A representation of cyclic monosaccharides in which the ring is depicted as flat, with the substituents on the ring shown in their approximate positions above or below the plane of the ring.

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Cyclization

The process by which an open-chain monosaccharide converts into a cyclic form.

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Mutarotation

The interconversion of α and β anomers of a monosaccharide in solution, driven by the equilibrium between the open-chain form and the cyclic forms.

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What is cellulose?

Cellulose is a long, straight-chain carbohydrate polymer made up of β-glucose monomers. It's a major component of plant cell walls and provides structural support. Humans cannot digest cellulose, but it's crucial for our digestive health.

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What are amylose and amylopectin?

Amylose and Amylopectin are two forms of starch. Amylose is a linear chain of α-glucose monomers linked by α(1→4) glycosidic bonds, while Amylopectin is a branched chain of α-glucose monomers linked by both α(1→4) and α(1→6) glycosidic bonds.

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What is dextran?

Dextran is a storage polysaccharide produced by yeast and bacteria. It consists mainly of α-1-6 linkages of D-glucose, with branched chains formed by 1-2, 1-3, or 1-4 linkages. It is a key component of dental plaque.

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What is the difference between α(1→4) and α(1→6) glycosidic bonds?

The α(1→4) glycosidic bond links glucose monomers in a straight chain, while the α(1→6) glycosidic bond creates branches in the chain.

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How are starch, glycogen, and cellulose different?

Starch, glycogen, and cellulose are all polysaccharides made of glucose monomers. However, they differ in the type of glucose (α or β) and the types of glycosidic bonds (α(1→4) or β(1→4)).

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Study Notes

Protein Classification

  • Proteins are classified based on their chemical nature, structure, shape, and solubility.

  • Simple proteins: Composed of only amino acid residues. On hydrolysis, these proteins yield only constituent amino acids. Further divided into:

    • Fibrous protein
      • Examples: Keratin, Elastin, Globulin, Collagen, Histones
    • Globular protein
      • Examples: Albumin, Globulin

  • Conjugated proteins: Combined with non-protein moiety. Example: Nucleoprotein, Phosphoprotein, Lipoprotein, Metalloprotein, etc.

  • Derived proteins: Derivatives or degraded products of simple and conjugated proteins.

    • Primary derived proteins: Proteans, Metaproteins, Coagulated proteins
    • Secondary derived proteins: Proteoses, peptones, peptides, albumoses

General Protein Features

  • Physical agents: Heat, radiation, pH

  • Chemical agents: Urea solution which forms new hydrogen bonds in the protein, organic solvents, detergents.

  • Coagulation: When proteins are denatured by heat, they form insoluble aggregates known as coagulation. All proteins are not heat coagulable, only a few like albumins, globulins.

  • Isoelectric point (pI): The pH at which the number of positive charges equals the number of negative charges, and the overall charge on the amino acid is zero. At this point, when subjected to an electric field, the proteins do not move either towards anode or cathode, hence this property is used to isolate proteins.

Protein Structure

  • Proteins are divided into four levels of organization:

1. Primary Structure

  • The primary structure of a protein consists of the amino acid sequence along the polypeptide chain.
  • Amino acids are joined by peptide bonds.
  • The sequence is determined by the genetic code.
  • The primary structure determines the further levels of organization.

2. Secondary Structure

  • Includes various types of local conformations in which the atoms of the side chains are not involved.
  • Secondary structures are formed by a regularly repeating pattern of hydrogen bond formation between backbone atoms.
  • Examples: α-helices, β-sheets, and other types of folding patterns.

3. Tertiary Structure

  • Refers to the protein's overall three-dimensional conformation.
  • Types of interactions:
    • Hydrophobic interactions
    • Electrostatic interactions
    • Hydrogen bonds
    • Covalent disulfide bonds
  • Produced by interactions between amino acid residues that may be located at a considerable distance from each other in the primary sequence of the polypeptide chain.
  • Hydrophobic amino acid residues tend to collect in the interior of globular proteins, where they interact with exclude water, whereas hydrophilic residues are usually found on the surface.

4. Quaternary Structure

  • Refers to the interaction of one or more subunits to form a functional protein.
  • The spatial arrangement of subunits in a protein that consists of more than one polypeptide chain.
  • Stabilized by the same forces that stabilize the tertiary structure.

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Test your knowledge on the structure and synthesis of proteins, as well as the different types of carbohydrates. This quiz covers key concepts including protein tertiary and quaternary structures, amino acid acquisition, and characteristics of sugars. Challenge yourself to see how well you understand these essential biomolecules.

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