Digestion and Human Health - Notes

Food

• Food provides both matter and energy to the body.
• The body transforms food into matter and energy.

6.1 – The Molecules of Living Systems

• This section covers:
  1. The chemical nature of carbohydrates, lipids, proteins, and nucleic acids.
  2. How carbohydrates, lipids, and proteins are synthesized and broken down.
  3. Tests to identify macromolecules.

Macromolecules

• Macromolecules are large, complex organic molecules.
• Organic molecules contain carbon bonded to hydrogen and other atoms like oxygen, sulfur, and nitrogen.

Four Classes of Macromolecules

• The four classes of macromolecules are:
  • Carbohydrates
  • Lipids
  • Proteins
  • Nucleic acids

Macromolecules as Polymers

• Macromolecules are polymers.
  • Poly means many.
• Polymers are long molecules formed by linking many small, similar subunits (monomers) together.
  • Example: linking railroad cars to form a train (A-A-A-A-A-A-A-A-A-A-).

Assembling & Disassembling Molecules

• The body builds complex macromolecules from monomers (smaller similar subunits) through assembling.
• The body breaks down macromolecules into monomers through disassembling.
• Dehydration Synthesis and Hydrolysis Reactions are key processes.

Hydrolysis and Dehydration Synthesis

• Dehydration Synthesis: removes a water molecule to link monomers.
• Hydrolysis: adds a water molecule to break down polymers.

Key Terms Review

• Macromolecules: Large complex organic molecules.
• Organic Molecules: Contain carbon bonded to hydrogen and other atoms (O, S, N).

Macromolecule Formation

• Macromolecules are formed by dehydration synthesis, where a water molecule (H_2O) is removed to join monomers.

Dehydration Synthesis

• Dehydration synthesis is the synthesis of macromolecules, which removes water (H_2O).

Macromolecule Breakdown

• Macromolecules are broken down by hydrolysis, where water (H_2O) must be added.

Hydrolysis Reaction

• Hydrolysis is a reaction where macromolecules are broken down by adding water (H_2O).

Assembling & Disassembling Molecules

• Dehydration Synthesis: synthesis of macromolecules.
• Hydrolysis Reaction: macromolecules are broken down.

Carbohydrates

• Composed of carbon, hydrogen, and oxygen, in a 1:2:1 ratio (CH_2O).

Types of Carbohydrates

• Three types of carbohydrates (saccharides):
  • Monosaccharide: 1 sugar unit.
  • Disaccharide: 2 sugar units.
  • Polysaccharide: many (>2) sugar units.

Classification of Carbohydrates

• Simple Sugars: monosaccharides and disaccharides.
• Complex Carbohydrates: polysaccharides.

Monomers of Carbohydrates

• Monomers (building blocks) of all carbohydrates are monosaccharides (C6H{12}O_6).
  • Most common:
    • Glucose
    • Fructose (fruit & plants)
    • Galactose (milk)

Disaccharides Formation

• Disaccharides are formed when 2 monosaccharides are joined together through dehydration synthesis.

Examples of Disaccharides

• Examples of disaccharides:
  • glucose + glucose = Maltose (malt sugar)
  • glucose + fructose = Sucrose (table sugar)
  • glucose + galactose = Lactose (milk sugar)

Production of a Disaccharide

• Two monosaccharides combine through dehydration synthesis by removing (H_2O) to form a disaccharide and then a polysaccharide.

How Plants Store Energy

• Plants store energy as polysaccharides, specifically starch (e.g., potatoes).
• Structural polysaccharides include cellulose, found in cell walls of plants.
  • Humans lack the enzymes to digest cellulose.

How Animals Store Energy

• Animals store energy as polysaccharides, specifically glycogen, which is highly branched and stored in the liver.

Structural Differences

• Starch, glycogen, and cellulose are all polysaccharides consisting of glucose subunits, but they have different structures.

Lipids

• Diverse group of macromolecules that are all insoluble in water.
• Provide 2.25 times more energy per gram than other biological molecules.

Functions of Lipids

• Functions:
  • Fats & oils: long-term energy storage molecules.
  • Phospholipids: components of cell membranes.
  • Steroids: sex hormones like estrogen & testosterone.

Subunits of Lipids

• Subunits:
  • 1 glycerol molecule (a 3-carbon chain).
  • 3 fatty acids (composition may vary).
  • Triglyceride = fat.

Saturated vs. Unsaturated Fats

• Saturated: C-C single bonds, saturated with hydrogen, solid at room temperature, animal-derived, associated with cardiovascular diseases.
• Unsaturated: C=C double bonds, not saturated with hydrogen, liquid at room temperature, plant-derived, healthier choice.

Key Differences Between Saturated and Unsaturated Fats

• Saturated Fats:
  • C-C single bonds only.
  • Saturated with H – bonded to the maximum # of H atoms
  • Fat is solid at RT
  • Animal
  • Associated with cardiovascular diseases
• Unsaturated Fats
  • C=C double bonds.
  • Not saturated with H – not bonded to the maximum # of H atoms
  • Fat is liquid at RT
  • Plant
  • Healthier choice

Proteins

• Greatest structural complexity & functional diversity; makes up most cellular structures.

Functions of Proteins

• Functions:
  • Transport – hemoglobin (O_2 carrying molecule in blood).
  • Blood clotting – fibrin.
  • Support – collagen.
  • Immunity – antibodies.
  • Catalysis – enzymes.
  • Muscle action – actin & myosin.
  • Chemical messengers – some hormones.

Subunits of Proteins

• Subunits (monomers): amino acids.

Amino Acid Structure

• Amino Acid Structure includes:
  • Amino Group
  • Carboxylic Acid Group
  • R Group (Side Chain)
  • \alpha- carbon
• Chemical formula of Amino Acid:
  • H_2N-CHR-COOH

Unique Group in Amino Acids

• The R-group is unique to each amino acid.
• There are 20 a.a.’s - The body makes 11, other 9 = essential a.a.’s must obtain from diet.

Formation of Proteins

• Amino acids are bonded together in long chains to form proteins by dehydration synthesis.
  • The bond between amino acids is called a peptide bond.

Protein Structure

• Attraction and repulsion between R-groups of amino acids causes twisting and turning of the strand.
• Quaternary Structure: 4 polypeptide chains

R Groups and Protein Structure

• Charged R groups attract water (outside of protein).
  • E.g., enzymes, hemoglobin.
• Uncharged R groups repelled by water (inside of protein).
  • E.g., keratin in fingernails.

Protein Functions

• Transport – hemoglobin
• Blood clotting – fibrin
• Support – collagen
• Immunity – antibodies
• Catalysis – enzymes
• Muscle action – actin & myosin
• Chemical messengers – some hormones

Structural and Functional Diversity of Proteins

• Why are proteins more structurally and functionally diverse than carbohydrates and lipids?

Reasons for Protein Diversity

• There are 20 different amino acid R-groups, which provide a large number of possible combinations, resulting in the vast variety of proteins.
• Also, the 3D structure of the protein is highly complex due to the attraction/repulsion of the different R-groups of the various amino acids in the protein.
• The final shape of a protein’s three-dimensional structure determines its properties, and therefore the functions, of the protein.

Nucleic Acids

• Function: contain the chemical code that directs growth and development.
  • Determine how a cell functions and the characteristics it has.
• There are 2 types of nucleic acids
  • 1. DNA – deoxyribonucleic acid Contains genes – information needed to build the cell
  • 2. RNA – ribonucleic acid Involved in making a protein

Nucleotides

• Nucleic acids consist of long chains of linked subunits called nucleotides.
  • These subunits contain phosphate, a sugar, and a nitrogen base.

Vitamins

• Organic compounds that often help enzymes function.
• Small amounts needed by the body for tissue development, growth, and resistance to disease.
• Vitamins are coenzymes – chemicals needed to make enzymes function.

Minerals

• Minerals are inorganic compounds.
• Small amounts needed by the body.
• Help some chemical reactions to happen.
• Help build bones/cartilage.
• Readily absorbed into the bloodstream.
• Essential parts of molecules such as hemoglobin, hormones, enzymes, and vitamins.

Testing for Macromolecules

Benedict’s Reagent

• Tests for monosaccharides.
  • Reagent is light blue; it changes color in the presence of monosaccharides & some disaccharides.

Iodine Test

• Iodine Test for the presence of starch (polysaccharide)
  • yellow -----> blue/black

Biuret Reagent

• Tests for proteins.
  • Binds to peptide bonds
  • Blue ----> purple

Biuret’s Reagent

• Tests for the presence of polypeptides and proteins
  1. Light blue – no change (solution remains blue) - Proteins not present ( - )
  2. The solution turns from blue to violet (deep purple) - Proteins are present ( + )
  3. The solution turns from blue to pink - Peptides are present ( + ) (Peptides - short chains of amino acid residues)

Translucent Test

• Translucent test for fats (brown paper bag)
  • (+) Translucent (grease spot)
  • (-) nontranslucent (no grease spot)