Carbohydrates and Monosaccharides Quiz
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Questions and Answers

What is the primary function of glucose in the human body?

  • It serves as the main source of energy. (correct)
  • It acts as a building block for proteins.
  • It helps in blood clotting.
  • It aids in digestion.

    • Which of the following carbohydrates can be classified as a monosaccharide?

  • Cellulose
  • Maltose
  • Sucrose
  • Galactose (correct)

    • What type of bond forms between two monosaccharides to create a disaccharide?

  • Covalent bond (correct)
  • Ionic bond
  • Hydrogen bond
  • Van der Waals bond

    • Which disaccharide is composed of glucose and galactose?

    <p>Lactose</p> Signup and view all the answers

    Which carbohydrate is not a sweet-tasting substance?

    <p>Cellulose</p> Signup and view all the answers

    In which molecule does ribose play a critical role?

    <p>Ribonucleic acid (RNA)</p> Signup and view all the answers

    What is an example of a structural polysaccharide?

    <p>Cellulose</p> Signup and view all the answers

    Which of the following is an epimer of glucose?

    <p>Mannose</p> Signup and view all the answers

    Which carbohydrate class includes oligosaccharides?

    <p>Polysaccharides</p> Signup and view all the answers

    How is lactose primarily utilized in animals?

    <p>Source of energy</p> Signup and view all the answers

    What type of carbohydrate is chitin?

    <p>Structural polysaccharide</p> Signup and view all the answers

    Which functional group characterizes an aldose monosaccharide?

    <p>Aldehyde group</p> Signup and view all the answers

    What is the main difference between ribose and deoxyribose?

    <p>Deoxyribose has a hydrogen atom at position 2.</p> Signup and view all the answers

    Which carbohydrate serves as a major energy storage material in animals?

    <p>Glycogen</p> Signup and view all the answers

    What is the primary composition of lipids?

    <p>Glycerol and fatty acids</p> Signup and view all the answers

    Which of the following best describes saturated fatty acids?

    <p>Having all single bonds between carbon atoms</p> Signup and view all the answers

    What type of lipid is essential for maintaining membrane fluidity at different temperatures?

    <p>Steroids</p> Signup and view all the answers

    Which statement about phospholipids is incorrect?

    <p>They form a triple-layer structure in membranes.</p> Signup and view all the answers

    What is the function of glycolipids in cell membranes?

    <p>To contribute to cell recognition and communication</p> Signup and view all the answers

    How are trans-fatty acids primarily formed?

    <p>From the artificial hydrogenation of vegetable oils</p> Signup and view all the answers

    What is the primary structure of a protein?

    <p>The specific linear sequence of amino acids in a polypeptide chain.</p> Signup and view all the answers

    Which type of fatty acid is particularly beneficial for cardiovascular health?

    <p>Omega-3 fatty acids</p> Signup and view all the answers

    Which amino acids are classified as positively charged?

    <p>Lysine, Arginine, Histidine</p> Signup and view all the answers

    In the context of lipid classification, which of the following is categorized as a complex lipid?

    <p>Glycerophospholipids</p> Signup and view all the answers

    How does denaturation affect proteins?

    <p>It leads to a loss of secondary, tertiary, and quaternary structures.</p> Signup and view all the answers

    What process describes the breaking down of triglycerides into glycerol and fatty acids?

    <p>Hydrolysis</p> Signup and view all the answers

    What role do chaperone proteins play in the cell?

    <p>They assist in the folding of linear amino acid chains.</p> Signup and view all the answers

    Which of the following lipids is involved in cell signaling and acts as a second messenger?

    <p>Phospholipids</p> Signup and view all the answers

    Which of the following correctly describes a contractile protein?

    <p>Proteins that mediate contraction of muscle fibers.</p> Signup and view all the answers

    Which lipid component is NOT directly involved in cellular energy storage?

    <p>Phospholipids</p> Signup and view all the answers

    Which classification includes lipids obtained after hydrolysis of simple and complex lipids?

    <p>Derived lipids</p> Signup and view all the answers

    Which amino acid is a non-essential amino acid?

    <p>Glutamine</p> Signup and view all the answers

    Which fat type is associated with a higher risk of heart disease?

    <p>Trans fats</p> Signup and view all the answers

    What distinguishes fibrous proteins from globular proteins?

    <p>Fibrous proteins are long and narrow, while globular proteins are round and spherical.</p> Signup and view all the answers

    Which lipid is known to serve as a precursor for bioactive lipids, such as prostaglandins?

    <p>Phospholipids</p> Signup and view all the answers

    What happens during the formation of a peptide bond?

    <p>A dehydration-condensation reaction links amino acids together.</p> Signup and view all the answers

    What is the quaternary structure of a protein?

    <p>The arrangement of multiple polypeptide chains in a protein complex.</p> Signup and view all the answers

    Which factor does not contribute to the stabilization of tertiary structure in proteins?

    <p>Ionic strength of the solution</p> Signup and view all the answers

    Which protein class is responsible for transporting essential substances in the body?

    <p>Transport proteins</p> Signup and view all the answers

    Which type of amino acids are considered essential?

    <p>Those that must be obtained from the diet</p> Signup and view all the answers

    What is the effect of heat above 50°C on protein structures?

    <p>It induces denaturation of protein structures.</p> Signup and view all the answers

    What happens to proteins when they undergo misfolding?

    <p>They might cause diseases such as Alzheimer's.</p> Signup and view all the answers

    Agarose provides a supporting structure in the cell wall of marine ______.

    <p>algae</p> Signup and view all the answers

    Heparin acts as a natural ______ that prevents blood from clotting.

    <p>anticoagulant</p> Signup and view all the answers

    Chondroitin is an essential component of ______ that provides resistance against compression.

    <p>cartilage</p> Signup and view all the answers

    The primary structure of proteins is defined as the linear sequence of ______ linked together.

    <p>amino acids</p> Signup and view all the answers

    A peptide bond forms between the amine group of one amino acid and the ______ of another amino acid.

    <p>carboxylic acid</p> Signup and view all the answers

    The tertiary structure of proteins is stabilized by hydrogen bonds, electrostatic forces, disulfide linkages, and ______ forces.

    <p>Vander Waals</p> Signup and view all the answers

    Fibrous proteins are typically ______ in water, while globular proteins are usually soluble.

    <p>insoluble</p> Signup and view all the answers

    In amino acids, the R-group is the only unique feature, distinguishing one amino acid from ______.

    <p>another</p> Signup and view all the answers

    Denaturation of proteins can be caused by changes in ______, pH, or exposure to chemicals.

    <p>temperature</p> Signup and view all the answers

    Essential amino acids cannot be synthesized by the cell and must be obtained from the ______.

    <p>diet</p> Signup and view all the answers

    The quaternary structure refers to the arrangement of multiple folded protein ______.

    <p>subunits</p> Signup and view all the answers

    Proteins that catalyze biochemical reactions are known as ______.

    <p>enzymes</p> Signup and view all the answers

    Polar side-chain amino acids typically contain ______ groups that make them hydrophilic.

    <p>hydroxyl</p> Signup and view all the answers

    Amino acids with non-polar side chains are classified as ______.

    <p>hydrophobic</p> Signup and view all the answers

    Lipids are organic compounds primarily composed of glycerol and ______.

    <p>fatty acids</p> Signup and view all the answers

    Fatty acids can be classified as ______ or unsaturated based on their chemical structure.

    <p>saturated</p> Signup and view all the answers

    Phospholipids have a hydrophilic 'head' and two ______ 'tails'.

    <p>hydrophobic</p> Signup and view all the answers

    Triglycerides can be hydrolyzed to produce glycerol and three ______.

    <p>fatty acids</p> Signup and view all the answers

    A process that converts unsaturated fat into saturated fat by adding hydrogen is known as ______.

    <p>hydrogenation</p> Signup and view all the answers

    Lipid molecules with a fused ring structure are known as ______.

    <p>steroids</p> Signup and view all the answers

    Cis-fatty acids have hydrogen atoms on the ______ side of the double bond.

    <p>same</p> Signup and view all the answers

    The main lipid component of cell membranes is ______.

    <p>phospholipids</p> Signup and view all the answers

    Omega-3 fatty acids are known for their role in ______ health.

    <p>cardiovascular</p> Signup and view all the answers

    Unsaturated fatty acids can be either monounsaturated or ______.

    <p>polyunsaturated</p> Signup and view all the answers

    Lipids that possess characteristics of simple and complex lipids are called ______ lipids.

    <p>derived</p> Signup and view all the answers

    Glycolipids play several roles in cell recognition and ______ transduction.

    <p>signal</p> Signup and view all the answers

    One function of steroids is to act as ______ molecules.

    <p>signaling</p> Signup and view all the answers

    Glycolipids are found on the cell membranes of all ______ and some prokaryotic cells.

    <p>eukaryotic</p> Signup and view all the answers

    Carbohydrates consist of carbon (C), hydrogen (H), and oxygen (O) atoms, and are also called ______.

    <p>saccharides</p> Signup and view all the answers

    Monosaccharides are the simplest carbohydrates and are also known as ______.

    <p>simple sugars</p> Signup and view all the answers

    Glucose, mannose, and galactose are examples of ______.

    <p>monosaccharides</p> Signup and view all the answers

    The covalent bond formed between two monosaccharides is known as a ______ bond.

    <p>glycosidic</p> Signup and view all the answers

    Maltose consists of two units of ______.

    <p>glucose</p> Signup and view all the answers

    Ribose and deoxyribose are classified as ______.

    <p>aldopentoses</p> Signup and view all the answers

    Oligosaccharides yield ______ to 10 molecules of monosaccharides upon hydrolysis.

    <p>3</p> Signup and view all the answers

    A polysaccharide is a chain of more than ______ monosaccharides joined together.

    <p>10</p> Signup and view all the answers

    Starch, glycogen, and cellulose are examples of ______.

    <p>polysaccharides</p> Signup and view all the answers

    Cellulose is a structural polysaccharide found in the ______ wall of plants.

    <p>cell</p> Signup and view all the answers

    Fructose has a ______ group rather than an aldehyde group.

    <p>ketone</p> Signup and view all the answers

    Galactose can be obtained from milk sugar, known as ______.

    <p>lactose</p> Signup and view all the answers

    Epimers are carbohydrates that vary in one position for the placement of the ______ group.

    <p>-OH</p> Signup and view all the answers

    ______ is the main source of energy in humans, central to energy consumption.

    <p>Glucose</p> Signup and view all the answers

    Study Notes

    Carbohydrates

    • Biomolecules composed of carbon, hydrogen, and oxygen atoms with a hydrogen-oxygen ratio of 2:1 (empiric formula (CH2O)n or CnH2nOn)
    • Most abundant class of organic compounds in living organisms
    • Originate from photosynthesis, an endothermic reductive condensation of carbon dioxide requiring light energy and chlorophyll
    • Key source of metabolic energy for plants and animals
    • Classified into four categories: monosaccharides, disaccharides, oligosaccharides, and polysaccharides based on degree of polymerization

    Monosaccharides

    • Simplest carbohydrates, cannot be hydrolyzed into smaller carbohydrates
    • Building blocks for disaccharides and polysaccharides, known as simple sugars
    • Two types: Aldose (containing the aldehyde group) and Ketose (containing a ketone group)
    • Examples:
      • Glucose, mannose, and galactose (C6H12O6)
        • Isomers with the same molecular formula but different spatial arrangements
        • Stereoisomers with the same structure but different spatial arrangements of atoms
        • Epimers differ in the position of the -OH group (Glucose is the C-2 epimer of mannose and the C-4 epimer of galactose)
      • Fructose (C6H12O6)
        • Structural isomer of glucose, mannose, and galactose
        • Has a ketone group instead of an aldehyde group
      • Ribose (C5H10O5) and deoxyribose (C5H10O4)
        • Aldopentose (monosaccharide with five carbon atoms and an aldehyde functional group)
        • Ribose has a hydroxyl (OH) group at position 2, while deoxyribose has a hydrogen (H) atom at position 2
    • Functions:
      • Glucose: Main source of energy in humans
      • Galactose: Essential for cellular metabolism, obtained from lactose (milk sugar)
      • Mannose: Constituent of mucoproteins and glycoproteins
      • Fructose: Found in fruits and honey, metabolized by the liver to produce mainly glucose
      • Ribose: Component of ribonucleotides (building blocks of RNA), essential for gene coding, decoding, regulation, and expression
      • Deoxyribose: Along with phosphate, forms the sugar-phosphate backbone of DNA (genetic material)

    Disaccharides

    • Consist of two sugar units linked by a glycosidic bond
    • Can be hydrolyzed into two monosaccharides
    • Examples:
      • Maltose (glucose + glucose)
      • Cellobiose (glucose + glucose)
      • Sucrose (glucose + fructose)
      • Lactose (glucose + galactose)
    • Sources:
      • Maltose: Found in fruits like apples, oranges, peaches, etc.
      • Cellobiose: Basic component of cellulose
      • Sucrose: Found in sugarcane, sugar beets, dates
      • Lactose: Found in milk
    • Functions:
      • Maltose: Important intermediate in starch and glycogen digestion
      • Cellobiose: Product of cellulose breakdown, utilized by certain organisms
      • Sucrose: Product of photosynthesis, provides carbon and energy for plants
      • Lactose: Energy source for animals, primarily found in milk

    Oligosaccharides

    • Contain 3 to 10 monosaccharide molecules linked through N- or O-glycosidic bonds
    • N-linked oligosaccharides attach to asparagine
    • O-linked oligosaccharides attach to threonine or serine
    • Functions:
      • Glycoproteins: Carbohydrates attached to proteins; function as cell-surface receptors, cell-adhesion molecules, immunoglobulins, and tumor antigens
      • Glycolipids: Carbohydrates attached to lipids; important for cell recognition and modulate membrane proteins as receptors

    Polysaccharides

    • Chains of more than 10 monosaccharides linked by glycosidic bonds, also known as glycans
    • Generally not sweet and not soluble in water
    • Examples:
      • Starch (energy storage in plants)
      • Glycogen (energy storage in animals)
      • Cellulose (structural polysaccharide in plant cell walls)
    • Functions:
      • Starch: Digestible for humans, providing energy
      • Glycogen: Stored in the liver for energy
      • Cellulose: Indigestible for humans, acts as digestive fiber
    • Other polysaccharides:
      • Chitin: Provides structural stability to fungal cell walls
      • Peptidoglycan: Essential component of bacterial cell walls

    Carbohydrates

    • Monosaccharides are composed of one sugar molecule
    • Disaccharides are composed of two sugar molecules
    • Oligosaccharides are composed of 3-10 sugar molecules
    • Polysaccharides are composed of more than 10 sugar molecules

    Amino Acids

    • Amino acids are organic compounds composed mainly of carbon, hydrogen, and nitrogen
    • The structure of an amino acid consists of a hydrogen atom, a carboxyl group, an amino group, and an R-group or side chain
    • Glycine is the only amino acid that does not have a D configuration
    • There are 20 different amino acids that are utilized as building blocks for proteins

    Essential Amino Acids

    • Essential amino acids cannot be synthesized by the cell and must be obtained from the diet
    • Essential amino acids help the body repair muscle tissue and form neurotransmitter precursors

    Non-Essential Amino Acids

    • Non-essential amino acids can be produced by the cell
    • Non-essential amino acids are involved in proper brain function, the production of red and white blood cells, and waste removal from the body

    Classification of Amino Acids

    • There are 9 non-polar amino acid side chains that are hydrophobic: alanine (A), valine (V), leucine (L), glycine (G), isoleucine (I), methionine (M), tryptophan (W), phenylalanine (F), and proline (P)
    • There are 6 uncharged polar amino acid side chains: serine (S), threonine (T), cysteine (C), tyrosine (Y), asparagine (N) and glutamine (Q)
    • There are 3 positively charged amino acids: lysine (K), arginine (R), and histidine (H)
    • There are 2 negatively charged amino acids: aspartic acid (D) and glutamic acid (E)

    Proteins

    • Proteins are large biological molecules made up of one or more amino acid chains linked together by peptide bonds
    • Peptide bonds form through dehydration-condensation reaction, forming an amide group (CO-NH)
    • Peptide bonds are catalyzed by ribosomes
    • Polypeptide: A long, continuous, unbranched peptide chain

    Protein Structure

    • Primary structure is the sequence of amino acids linked together to form a polypeptide chain
    • Secondary structure arises from interactions between amino acids close to each other, forming local patterns such as α-helix and β-strands
    • Tertiary structure is the overall 3D folding of the polypeptide chain which is stabilized by hydrogen bonds, electrostatic forces, disulfide linkages, and van der Waals forces.
    • Quaternary structure is the spatial arrangement of two or more tertiary structures which form a multi-subunit complex
    • Tertiary structures can be fibrous or globular.

    Fibrous vs. Globular Protein

    • Fibrous Proteins are long and narrow. They have a repetitive amino acid sequence and are less sensitive to changes in pH or temperature. Generally insoluble in water. Examples: Collagen, myosin, fibrin, actin, keratin, elastin.
    • Globular Proteins are round/spherical. They have an irregular amino acid sequence and are more sensitive to changes in pH or temperature. Generally soluble in water. Examples: Haemoglobin, myoglobin, immunoglobin, insulin, enzymes.

    Protein Denaturation

    • Denaturation is the loss of the quaternary, tertiary, and secondary structure of a protein
    • Denaturation can be caused by changes in temperature, pH, or exposure to chemicals
    • Denaturation can be reversible or irreversible.

    Protein Folding

    • Protein folding is the process by which a linear chain of amino acids (the polypeptide) acquires its functional 3D structure.
    • The correct folding of a protein is necessary for its function.
    • Protein misfolding can lead to disorders and diseases.

    Protein Folding Assistance

    • Chaperones are functionally related proteins that assist in protein folding.
    • The ubiquitin–proteasome (UPS) system degrades short-lived proteins and those containing structural abnormalities.
    • Autophagy is a process that removes unnecessary or dysfunctional cell components through a lysosome-dependent regulated mechanism.

    Protein Function

    • Structural proteins provide structural components of the body. Examples: Collagen, Keratin
    • Contractile proteins mediate contraction of cardiac and skeletal muscle. Examples: Myosin and Actin.
    • Transport proteins carry substances throughout the body. Examples: Haemoglobin (oxygen), Lipoproteins (lipids)
    • Storage proteins function in the storage of nutrients. Examples: Casein (protein in milk), Ferritin (iron)
    • Hormonal proteins regulate body metabolism and the nervous system. Examples: Insulin (regulates blood glucose), Growth hormone (regulates body growth)
    • Enzymatic proteins catalyze biochemical reactions in the cell. Examples: Trypsin (digests proteins), Amylase (digests starches)
    • Protective proteins recognize and destroy foreign substances. Examples: immunoglobulins (stimulate immune responses)

    Protein Summary

    • The building blocks of proteins are amino acids.
    • Amino acids are bonded together using peptide bonds to form polypeptides.
    • Polypeptide chains fold to form primary, secondary, tertiary, and quaternary structures.

    Introduction to lipids

    • Lipids are organic compounds containing hydrogen, carbon, and oxygen atoms.
    • They are essential for the structure and function of living cells.

    Structure

    • Lipids are primarily composed of glycerol and fatty acids.
    • Glycerol contains three carbon atoms, a hydroxyl group, and hydrogen atoms.
    • Fatty acids have an acid group at one end and a hydrocarbon chain (denoted by 'R').
    • Fatty acids can be saturated or unsaturated.

    Physical properties

    • Lipids are soluble in non-polar solvents (acetone, chloroform, alcohol).
    • Insoluble in water (hydrophobic).
    • Energy-rich.
    • Can be liquid or solid at room temperature.
    • Greasy texture.
    • Devoid of ionic charges.
    • Exist in saturated or unsaturated forms.
    • Stored in adipose tissues.

    Chemical properties

    • Hydrolysis of triglycerides: Triglycerides break down into glycerol and three fatty acids.
    • Saponification: Triglycerides react with a strong base to form fatty acid metal salts (soap-making).
    • Hydrogenation: Unsaturated fats are converted to saturated fats by adding hydrogen.
    • Halogenation: Unsaturated fatty acids bind to halogens (Cl2, Br2, I2), causing decolorization.
    • Rancidity: Oxidation and hydrolysis of fats and oils lead to a disagreeable odor.

    Classification

    • Simple lipids:
      • Fats and oils: Esters of fatty acids with glycerol.
      • Waxes: Esters of fatty acids with long-chain alcohols.
    • Complex lipids:
      • Phospholipids: Glycerol backbone with a phosphate group and two fatty acid tails.
      • Glycolipids: Lipids with a carbohydrate attached.
    • Derived lipids:
      • Products of simple and complex lipid hydrolysis.
      • Examples: steroids, fatty acids, glycerol, ketone bodies, vitamins, hormones.

    Phospholipids

    • Glycerophospholipids: Phospholipids with a glycerol backbone.
    • Sphingolipids: Phospholipids with a sphingosine backbone.
    • Main component of cell membranes: Responsible for semi-permeability.
    • Phospholipid bilayer: Two layers of phospholipids with hydrophobic tails facing inwards and hydrophilic heads facing outwards.

    Glycolipids

    • Glycoglycerolipids: Glycerol, fatty acids, and carbohydrates, found mostly in plants.
    • Glycosphingolipids: Sphingosine, fatty acids, and carbohydrates, prevalent in animals.
    • Located on cell membranes: Extend into the extracellular environment.
    • Functions: Cell recognition, cell-cell communication, and signal transduction.

    Functions of phospholipids and glycolipids

    • Phospholipids:
      • Membrane structure (barrier between inside and outside of the cell).
      • Membrane fluidity (allow movement of proteins and lipids).
      • Cell signaling (act as second messengers).
      • Energy storage (fatty acid tails can be cleaved for energy).
      • Precursors for bioactive lipids (e.g., prostaglandins).
      • Membrane protein function (control protein activity and location).
      • Cellular trafficking and membrane remodeling (vesicle production, exocytosis, endocytosis).
    • Glycolipids:
      • Membrane stability (contribute to structural integrity).
      • Cell proliferation (interact with growth factor receptors).
      • Calcium signaling (role in neuronal function).
      • Cell recognition (act as cell markers).
      • Immune response (carbohydrate binds to leukocytes and endothelial cells).
      • Surface receptors (carbohydrate part binds to specific receptors).

    Steroids

    • Lipids with a fused ring structure.
    • Alter membrane fluidity.
    • Act as signaling molecules.
    • Examples: cholesterol, sex hormones (estradiol, testosterone).

    Cholesterol

    • Principal sterol in animals.
    • Structural component of cell membranes.
    • Regulates membrane fluidity (increases melting point at high temperatures, prevents aggregation at low temperatures).
    • Building block for steroid hormones (vitamin D, bile acids).

    Fatty acids

    • Carboxylic acids with an aliphatic chain.
    • Saturated or unsaturated.
    • Dietary fuel source.
    • Structural components of cells.

    Saturated fatty acids

    • No double bonds in the hydrocarbon chain.
    • Associated with high cholesterol and increased risk of heart disease.
    • Found in butter fat, meat fat, tropical oils.

    Unsaturated fatty acids

    • One or more double bonds in the hydrocarbon chain.
    • Monounsaturated: One double bond.
    • Polyunsaturated: More than one double bond.
    • Found in avocado, fish oil.
    • Neuro-protective, antioxidant, anti-inflammatory effects, and cardiovascular health.

    Polyunsaturated fatty acids (PUFAs)

    • Omega-3 fatty acids:
      • Double bond at the third carbon from the omega end.
      • Important for animal lipid metabolism.
      • Examples: ALA, EPA, DHA.
      • Found in algae, fish, and plants.
      • Lower risk of cardiovascular disease.
    • Omega-6 fatty acids:
      • Double bond at the sixth carbon from the omega end.
      • Promote skin and hair growth, bone health, metabolism regulation, and reproductive system function.
      • Found in nuts, seeds, eggs, vegetable oils.

    Cis- and Trans-fatty acids

    • Cis-fatty acids: Hydrogen atoms on the same side of the double bond.
    • Trans-fatty acids: Hydrogen atoms on opposite sides of the double bond.
    • Trans-fatty acids:
      • Found in fried and bakery products.
      • Disrupt metabolism of essential fatty acids.
      • Increase risk of heart disease.

    Functions of lipids

    • Energy storage.
    • Membrane structure.
    • Metabolic regulators (steroid hormones).
    • Surfactants, detergents, emulsifying agents.
    • Electrical insulators in neurons.
    • Insulation against temperature changes.
    • Protection of internal organs.
    • Absorption of fat-soluble vitamins.
    • Second messengers in hormone action.

    Carbohydrates

    • Carbohydrates are biomolecules consisting of carbon (C), hydrogen (H) and oxygen (O) atoms with a hydrogen-oxygen atom ratio of 2:1
    • They are also known as saccharides and are the most abundant organic compound in living organisms
    • The empirical formula of carbohydrates is (CH2O)n or CnH2nOn
    • Produced through photosynthesis, an endothermic reductive condensation of carbon dioxide requiring light energy and the pigment chlorophyll
    • Major source of metabolic energy in plants and for animals that rely on plants for food

    Classification of Carbohydrates

    • Based on the degree of polymerization, carbohydrates are divided into four major categories: monosaccharides, disaccharides, oligosaccharides, and polysaccharides.

    Monosaccharides

    • The simplest carbohydrates that cannot be hydrolyzed into smaller carbohydrates
    • Building blocks of disaccharides and polysaccharides, also known as simple sugars
    • Two types: aldose and ketose
      • Aldose: contains an aldehyde group
      • Ketose: contains a ketone group

    Examples of Monosaccharides

    • Glucose, mannose and galactose (C6H12O6)
      • The same molecular formula (C6H12O6) and are isomers
      • Stereoisomers as they have the same structure but differ in the spatial arrangement of the atoms
      • Epimers are carbohydrates that vary in one position for the placement of the -OH group
        • Glucose is the C-2 epimer of mannose, and C-4 epimer of galactose
    • Fructose (C6H12O6)
      • Differs in structure from glucose, mannose, and galactose
      • It has a ketone group rather than an aldehyde group
      • Hence a structural isomer
    • Ribose (C5H10O5) and deoxyribose (C5H10O4)
      • Both are aldopentose: a monosaccharide containing five carbon atoms that has an aldehyde functional group at one end
      • Ribose sugar has a hydroxyl (OH) group at position 2, whereas deoxyribose sugar has a hydrogen (H) atom at position 2

    Functions of Monosaccharides

    • Glucose is the main and important source of energy in humans, central to energy consumption
    • Galactose is an essential carbohydrate for cellular metabolism, contributing to energy production and storage, obtained from milk sugar (lactose)
    • Mannose is a constituent of mucoproteins and glycoproteins required for proper body functioning
    • Fructose is found in fruits and honey; metabolized by the liver to produce glucose, glycogen, lactate, and fatty acids in humans
    • Ribose is a component of ribonucleotides from which ribonucleic acid (RNA) is built, necessary for coding, decoding, regulation, and expression of genes
    • Deoxyribose, along with phosphate, makes up the sugar-phosphate backbone in deoxyribonucleic acid (DNA), the genetic materials for living organisms

    Disaccharides

    • Consist of two sugar units, can be broken (hydrolyzed) into two monosaccharides
    • The hydroxyl group of one monosaccharide combines with the hydrogen of another monosaccharide through a covalent bond, releasing a molecule of water
    • The covalent bond formed between the two sugar molecules is known as a glycosidic bond

    Examples of Disaccharides

    • Maltose (glucose + glucose)
    • Cellobiose (glucose + glucose)
      • Differ in glycosidic bonds
    • Sucrose (glucose + fructose)
    • Lactose (glucose + galactose)

    Sources of Disaccharides

    • Maltose naturally exists in fruit, such as apples, oranges, peaches, blueberries, and cranberries
    • Cellobiose occurs naturally as a basic component of cellulose, a substance produced by plants
    • Sucrose can be found in sugarcane, sugar beets, dates
    • Lactose naturally occurs in milk

    Functions of Disaccharides

    • Maltose is an important intermediate in starch and glycogen digestion
    • Cellobiose is a product of cellulose breakdown and plays a role in the metabolism of certain organisms that can utilize it
    • Sucrose is a product of photosynthesis, providing essential carbon and energy for growth and development in plants
    • Lactose is a source of energy in animals, primarily serving as a carbohydrate found in milk

    Oligosaccharides

    • Compounds that yield 3 to 10 molecules of the same or different monosaccharides on hydrolysis
    • Linked to either lipids or amino acid by N- or O-glycosidic bonds known as glycolipids or glycoproteins
      • N-linked oligosaccharides: involves the attachment of oligosaccharides to asparagine
      • O-linked oligosaccharides: involves the attachment of oligosaccharides to threonine or serine

    Functions of Oligosaccharides

    • Glycoproteins are carbohydrates attached to proteins, function as cell-surface receptors, cell-adhesion molecules, immunoglobulins, and tumor antigens
    • Glycolipids are carbohydrates attached to lipids that are important for cell recognition and modulate membrane proteins that act as receptors

    Polysaccharides

    • A chain of more than 10 monosaccharides join together through glycosidic bond formation, also known as glycans
    • Unlike mono- and disaccharides, polysaccharides are not sweet and generally not soluble in water

    Important Polysaccharides

    • Starch: an energy storage polysaccharide found in plants, digestible for humans
    • Glycogen: an energy storage polysaccharide formed in the liver in animals
    • Cellulose: a structural polysaccharide found in the cell wall of plants
      • Indigestible for humans but acts as digestive fiber to promote gut health

    Other Polysaccharides

    • Chitin: provides important structural stability to fungal cell walls
    • Peptidoglycan: an essential component of bacterial cell walls

    Carbohydrates

    • Monosaccharides are single sugar molecules, examples are glucose, fructose, galactose, and mannose.
    • Disaccharides are two sugar molecules, examples are maltose, cellobiose, lactose, and sucrose.
    • Oligosaccharides are 3-10 sugar molecules.
    • Polysaccharides are more than 10 sugar molecules, examples are starch, glycogen, and cellulose.

    Amino Acids

    • Organic compounds mostly made up of carbon, hydrogen, and nitrogen
    • Structure consists of a hydrogen atom, a carboxyl group, an amino group, and a side chain (R-group)
    • The α-carbon, carboxyl, and amino groups are common to all amino acids
    • The R-group is the only unique feature in each amino acid
    • Exist in two mirror image forms, L and D (except for glycine, which has a R-group as hydrogen atom)
    • Most amino acids found in cells and proteins are in the L configuration
    • 20 different amino acids make up protein building blocks

    Essential Amino Acids

    • Cannot be synthesized by the cell and must be obtained from diet
    • Help the body repair muscle tissues and form precursor molecules for neurotransmitters

    Non-Essential Amino Acids

    • Can be produced by the cell
    • Involved in proper brain function, the production of red blood cells and white blood cells, and the removal of toxins from the body

    Amino Acid Classification

    • Non-polar Side Chains (Hydrophobic): alanine (A), valine (V), leucine (L), glycine (G), isoleucine (I), methionine (M), tryptophan (W), phenylalanine (F), and proline (P)
    • Polar Side Chains: serine (S), threonine (T), cysteine (C), tyrosine (Y), asparagine (N), and glutamine (Q)
    • Positively Charged (Basic): lysine (K), arginine (R), histidine (H)
    • Negatively Charged (Acidic): aspartic acid (D), glutamic acid(E)

    Proteins

    • Biological macromolecule made up of one or several chains of amino acids linked to each other by peptide bonds forming a polypeptide chain.

    Peptide Bond

    • The amine group of one amino acid reacts with the carboxylic acid of another amino acid, forming an amide group (CO−NH).
    • A dehydration-condensation reaction
    • Formation of a peptide bond is catalyzed by a ribosome
    • Peptide: short chains of amino acids linked by peptide bonds
    • Polypeptide: a longer, continuous, unbranched peptide chain

    Protein Structure

    • Primary Structure: linear sequence of amino acids linked together to form a polypeptide chain, determined by the encoding sequence of nucleotides in the gene (DNA).
    • Secondary Structure: local patterns, such as α-helix and β-strands, stabilized by hydrogen bonds.
      • α-helix: coiled structure with 3.6 amino acids per turn of the helix. Hydrogen bonds form between C=O groups and N-H groups in the polypeptide backbone.
      • β-strands: flat, side-by-side arrangement of polypeptide chains linked together by hydrogen bonds. Can be organized to form sheets and barrels.
    • Tertiary Structure: overall folding of the polypeptide chains, involving further folding of the secondary structure. Stabilized by H-bonds, electrostatic forces, disulfide linkages, and Vander Waals forces.
      • Gives rise to two major molecular shapes called fibrous and globular.
      • Fibrous: long and narrow, structural (maintains cell shape), repetitive amino acid sequence, less sensitive to changes in pH and temperature, typically insoluble in water, examples: collagen, myosin, fibrin, actin, keratin, elastin.
      • Globular: round/spherical, functional (biological functions), irregular amino acid sequence, more sensitive to changes in pH and temperature, typically soluble in water, examples: Haemoglobin, myoglobin, immunoglobin, insulin, enzymes.
    • Quaternary Structure: spatial arrangement of various tertiary structures; composed of two or more smaller protein chains (subunits). Describes the number and arrangement of multiple folded protein subunits in a multi-subunit complex (example: hemoglobin, DNA polymerase).

    Denaturation Of Proteins

    • Loss of quaternary, tertiary, and secondary structures present in the native state.
    • Caused by changes in temperature, pH, or exposure to chemicals.
    • Can be reversible or irreversible.

    Protein Folding

    • Process by which a linear chain of amino acids acquires its functional three-dimensional structure.
    • Guided by hydrophobic interactions, formation of intramolecular hydrogen bonds, van der Waals forces.
    • Correct folding is important for protein function.
    • Misfolding can cause disorders and diseases, such as neurodegenerative disease.

    Chaperone Proteins

    • Assist protein folding in the cell.

    Ubiquitin–Proteasome System (UPS)

    • Degrades short-lived regulatory or structurally abnormal proteins

    Autophagy

    • Self-degradation process of the cell that removes unnecessary or dysfunctional components through a lysosome-dependent regulated mechanism

    Functions of Proteins

    • Structural: provide structural components (examples: collagen, keratin)
    • Contractile: mediate contraction of cardiac and skeletal muscle (examples: myosin, actin)
    • Transport: carry essential substances throughout the body (examples: haemoglobin, lipoproteins)
    • Storage: store nutrients (examples: casein, ferritin)
    • Hormonal: regulate body metabolism (examples: insulin, growth hormone)
    • Enzyme: catalyze biochemical reactions in cells (examples: trypsin, amylase)
    • Protection: recognize and destroy foreign substances (examples: immunoglobulins)

    Lipids

    • Organic compounds composed of hydrogen, carbon, and oxygen.
    • They are the building blocks for the structure and function of living cells.

    Structure

    • Made up of glycerol and fatty acids.
    • Glycerol is a three-carbon molecule with a hydroxyl group attached to each carbon.
    • Fatty acids have an acid group at one end and a hydrocarbon chain.
    • Fatty acids can be saturated or unsaturated.

    Physical Properties

    • Soluble in non-polar solvents (acetone, chloroform, alcohol).
    • Insoluble in water (hydrophobic).
    • Energy-rich molecules.
    • Can be liquid or solid at room temperature.
    • Greasy in texture.
    • Devoid of ionic charges.
    • Can be saturated or unsaturated.
    • Stored in adipose tissues.

    Chemical Properties

    • Hydrolysis of Triglycerides: Triglycerides can be broken down into glycerol and three fatty acids.
    • Saponification: Triglycerides react with a strong base to form fatty acid metal salts, which is used in soap-making.
    • Hydrogenation: Unsaturated fats are combined with hydrogen to produce saturated fats.
      • Unsaturated fats: Have at least one double bond in the fatty acid chain.
      • Saturated fats: Have only single bonds between carbon atoms.
      • Monounsaturated fats: Have one double bond.
      • Polyunsaturated fats: Have more than one double bond.
    • Halogenation: Unsaturated fatty acids react with halogens (Cl2, Br2, I2) to form halides and lose color.
    • Rancidity: Oxidation and hydrolysis of fats and oils cause rancidity, resulting in unpleasant odors.

    Classification of Lipids

    • Simple Lipids: Esters of fatty acids with alcohol.

      • Fats and oils: Esters of fatty acids with glycerol.
      • Waxes: Esters of fatty acids with high-molecular-weight, long-chain alcohols.

    • Complex Lipids: Esters of fatty acids with alcohols and other molecules.

      • Phospholipids: Composed of a hydrophilic head (phosphate group) and two hydrophobic tails (fatty acids) attached to an alcohol residue, essential for cell membranes.
        • Glycerophospholipids: Have a glycerol backbone.
        • Sphingolipids: Have a sphingosine backbone.
      • Glycolipids: Lipids with a carbohydrate attached by a glycosidic bond.
        • Glycoglycerolipids: Composed of glycerol, fatty acids, and carbohydrates, commonly found in plants.
        • Glycosphingolipids: Composed of sphingosine, fatty acids, and carbohydrates, predominant in animals and humans.

    • Derived Lipids: Lipids obtained after hydrolysis of simple and complex lipids.

      • Examples: Steroids, fatty acids, glycerol, ketone bodies, lipid-soluble vitamins, and hormones.

    Phospholipids

    • Major components of cell membranes, creating a phospholipid bilayer that separates the cell interior from the exterior.
    • Have hydrophobic tails facing inward and hydrophilic heads facing outward.
    • Influence membrane fluidity.
    • Act as second messengers in signaling transduction.
    • Precursors for bioactive lipids.
    • Control membrane protein function.
    • Involved in cellular trafficking and membrane remodeling.

    Glycolipids

    • Found on cell membranes of eukaryotic and some prokaryotic cells.
    • Attached to the lipid bilayer and extend into the extracellular environment.
    • Functions: cell recognition, cell-cell communication, signal transduction.

    Functions of Phospholipids and Glycolipids

    • Phospholipids:*
    • Structural role in biological membranes.
    • Membrane fluidity.
    • Cell signaling and communication.
    • Energy storage.
    • Precursors for bioactive lipids.
    • Membrane protein function.
    • Cellular trafficking and membrane remodeling
    • Glycolipids:*
    • Membrane stability.
    • Cell proliferation.
    • Calcium signaling
    • Cell recognition
    • Immune response
    • Surface receptors.

    Steroids

    • Lipids with fused ring structures.
    • Important components of cell membranes, altering membrane fluidity.
    • Examples: cholesterol, sex hormones (estradiol, testosterone).

    Cholesterol

    • Principal sterol in higher animals, found in various body tissues.
    • Structural component of cell membranes.
    • Regulates membrane fluidity.
    • Building block for steroid hormone synthesis (vitamin D, bile acids).
    • Stabilizes cell membranes at high temperatures.
    • Prevents aggregation of phospholipids at low temperatures.

    Fatty Acids

    • Carboxylic acids with an aliphatic chain, can be saturated or unsaturated.
    • Important dietary sources of energy for animals.
    • Important structural components of cells.

    Saturated Fatty Acids

    • Hydrocarbon chains contain no double bonds.
    • Associated with higher total plasma cholesterol and increased risk of heart disease and stroke.
    • Found in butter fat, meat fat, and tropical oils.

    Unsaturated Fatty Acids

    • Hydrocarbon chains contain double bonds.
    • Monounsaturated fatty acids: Have one double bond.
    • Polyunsaturated fatty acids: Have more than one double bond.
    • Found in avocado, fish oil.
    • Neuroprotective, antioxidant, anti-inflammatory effects and benefits for cardiovascular health.

    Polyunsaturated Fatty Acids (PUFA)

    • Omega-3 Fatty Acids: Have a double bond in the omega-3 position (third bond from the end).
      • Important in animal lipid metabolism and human physiology.
      • Types: α-linolenic acid (ALA), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA)
      • DHA and EPA are found in algae and fish, ALA is in plants.
      • Lower risk of cardiovascular disease with higher omega-3 intake.
    • Omega-6 Fatty Acids: Have a double bond in the omega-6 position. (sixth bond from the end).
      • Promote skin and hair growth.
      • Maintain bone health.
      • Regulate metabolism.
      • Support the reproductive system.
      • Found in nuts, seeds, eggs, and vegetable oils.

    Cis- and Trans- Fatty Acids

    • Cis-fatty acids: Hydrogen atoms are on the same side of the double bond.
      • Found naturally in some foods (nuts, fish, corn oil).
      • Generally considered beneficial.
    • Trans-fatty acids: Hydrogen atoms are on opposite sides of the double bond.
      • Predominantly found in artificial sources like fried foods, baked goods with hydrogenated vegetable oil.
      • Disrupt the body's ability to metabolize essential fatty acids.
      • Can alter phospholipid composition of the arterial walls and increase heart disease risk.

    Functions of Lipids

    • Energy storage.
    • Structural components of bio-membranes.
    • Metabolic regulators (steroid hormones).
    • Acts as surfactants, detergents, and emulsifying agents.
    • Electrical insulators in neurons.
    • Insulation against temperature changes (subcutaneous fat).
    • Protection for internal organs (fat pads).
    • Absorption of fat-soluble vitamins (A, D, E, K).
    • Second messengers in hormone action.

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    Lecture 2: Carbohydrates, Proteins, and Lipids PDF

    Description

    Test your knowledge of carbohydrates and their classification, including monosaccharides. This quiz covers the basics of their structure, function, and types. Understand the importance of these biomolecules in living organisms.

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