Biology Unit 2 carbohydrates, lipids, proteins and nucleic acids.

Organic Macromolecules Overview

• Definition: Large, carbon-based molecules found in all living things.

• Elements present: Mainly carbon (C), hydrogen (H), oxygen (O); smaller amounts of other elements.

• Macromolecules vs. Inorganic molecules:

  • Macromolecules: Large, contain long hydrocarbon chains.

  • Inorganic molecules: Do not have long hydrocarbon chains.

Types of Organic Macromolecules

1. Carbohydrates

   • Function: Provide energy for the body.

   • Example: Sugars, starches.

2. Lipids

   • Function: Provide energy, store energy, and make up cell membranes.

   • Example: Fats, oils, phospholipids.

3. Proteins

   • Function: Provide energy, build and repair tissues, act as enzymes.

   • Example: Meat, eggs, enzymes.

4. Nucleic Acids

   • Function: Store genetic information (DNA, RNA).

   • Example: DNA, RNA.

Key Points

• Organic macromolecules are essential for life.

• Carbohydrates, lipids, and proteins primarily supply energy.

• Nucleic acids carry genetic information.

Carbohydrates

• Definition: Sugars and starches; organic macromolecules that provide energy.

• Solubility: Soluble in water.

• Composition: Made of carbon (C), hydrogen (H), and oxygen (O) in a 1:2:1 ratio.

• Structure: Form long hydrocarbon chains.

Types of Carbohydrates

• There are three main types (to be detailed later).

Importance of Carbohydrates

• Often criticized due to high-sugar/starch foods, but essential for all.

• Energy source: Provide quick energy for the body.

• Needs vary by activity:

  • Marathon runner: Needs lots of carbohydrates for instant energy.

  • Wrestler: Needs more fat and protein (slower energy) for endurance over time.

Key Point

• Carbohydrates are vital for energy, but the amount needed depends on activity and lifestyle.

Types of Carbohydrates

Functions of Carbohydrates

1. Energy Source

   • Provide 75% of the energy from our food.

   • Instant energy in humans:

     • Glycogen (polysaccharide stored in liver & muscle) breaks down into glucose for quick energy.

   • Instant energy in plants:

     • Starch (plant storage polysaccharide) breaks down into glucose for functions like respiration.

2. Structural Role

   • Certain polysaccharides help form biological structures.

   • In plants:

     • Cellulose → key component of cell walls.

   • In arthropods (e.g., ants, spiders):

     • Chitin → forms hard exoskeletons to protect soft tissues.

Lipids

• Definition: Organic macromolecules made of carbon (C), hydrogen (H), and oxygen (O) in different proportions than carbohydrates.

• Solubility: Hydrophobic → insoluble in water.

  • Reason: Hydrocarbon bonds are non-polar, making it hard to mix with polar water molecules.

Functions of Lipids

1. Energy Source

   • Supply energy for the body, similar to carbohydrates.

2. Primary Form of Fat

   • Main source of stored fat in the body.

3. Other Roles

   • Structural components (e.g., cell membranes)

   • Signaling molecules (e.g., steroids)

   • Useful in products like soaps.

Examples of Lipids

• Butter

• White fat on bacon

• Olive oil

• Steroids

• Soaps

Types of Lipids

Nucleic Acids

• Definition: Organic macromolecules that store genetic information in cells.

• Types:

  1. DNA (Deoxyribonucleic acid) – stores hereditary information.

  2. RNA (Ribonucleic acid) – helps in protein synthesis and gene expression.

Composition

• Made of nucleotides linked by covalent bonds.

• Nucleotide Structure:

  1. Five-carbon sugar (deoxyribose in DNA, ribose in RNA)

  2. Nitrogenous base (either a purine or pyrimidine)

     • Purines: 6-sided ring fused to 5-sided ring (Adenine, Guanine)

     • Pyrimidines: 6-sided ring (Cytosine, Thymine in DNA, Uracil in RNA)

  3. Phosphate group

Nitrogen Base Pairing

Types of Nucleic Acids: DNA vs RNA

Functions of Nucleic Acids

1. Preserve Genetic Information

   • Store the hereditary information of living cells.

   • DNA is responsible for replicating itself and directing RNA replication.

2. Direct Cellular Activities

   • DNA controls cell growth, division, and death.

   • Determines what a cell can or cannot do.

3. Protein Synthesis

   • DNA directs RNA to synthesize proteins.

   • Flow of genetic information:

     DNA → mRNA → Protein\text{DNA → mRNA → Protein}DNA → mRNA → Protein

   • Other RNA types assist in protein synthesis:

     • mRNA (messenger RNA): Carries instructions from DNA.

     • rRNA (ribosomal RNA): Forms part of ribosomes.

     • tRNA (transfer RNA): Brings amino acids to build proteins.

Proteins

• Definition: Large, complex macromolecules that make up >50% of the dry mass of cells.

• Composition: Carbon (C), Hydrogen (H), Nitrogen (N), Oxygen (O).

• Monomers: Amino acids (all proteins are made from the same 20 amino acids).

• Sources:

  • Some proteins are made by the body.

  • Others must be obtained from diet to supply essential amino acids.

Amino Acids

• Structure: Central carbon atom attached to:

  1. Amino group (–NH₂)

  2. Carboxyl group (–COOH)

  3. Hydrogen atom (H)

  4. R group (side chain) – unique for each amino acid

• Bonding:

  • Amino acids linked by peptide bonds

  • Formed between the amino group of one amino acid and the carboxyl group of another

Primary Structure of Proteins

• Definition: The most basic structure of a protein; a single linear chain of amino acids.

• Monomers: Amino acids – the building blocks of proteins.

  • Structure: Central carbon atom attached to:

    1. Amino group (–NH₂) – forms N-terminus of the chain

    2. Carboxyl group (–COOH) – forms C-terminus of the chain

    3. Hydrogen atom (H)

    4. Variable side chain (R group) – unique for each amino acid

• Polypeptide Chain:

  • The complete linear sequence of amino acids linked together forms a polypeptide chain.

  • Amino acids are joined by peptide bonds (covalent bonds between the amino group of one amino acid and the carboxyl group of the next).

  • Peptide bonds provide rigidity to the protein molecule.

• Example Proteins:

  • Oxytocin: Nonapeptide (9 amino acids in a linear chain)

  • Transthyretin: Transports Vitamin A and thyroid hormones in the blood

• Formation of Peptide Bonds:

  1. Condensation reaction – one water molecule is lost per bond

     • Amino group donates H

     • Carboxyl group donates OH

  2. Chain continues to grow, forming the protein

• Termini of the chain:

  • N-terminus: Free amino group at the start of the chain

  • C-terminus: Free carboxyl group at the end of the chain

econdary Structure of Proteins

• Definition: Produced by coiling and folding of certain regions of a single polypeptide chain.

• Purpose: Repeated coils and folds create a special arrangement, contributing to the protein’s shape.

Types of Secondary Structures

1. Alpha Helices (α-helices)

   • Shape: Coiled like a telephone cord.

   • Stabilization: Hydrogen bonds between the hydrogen of an amino group and the oxygen of a carboxyl group every fourth amino acid.

   • Length: Can range from 4 to 40+ amino acids; typically about 10 residues.

   • Example: Keratin in hair

2. Beta Sheets (β-sheets)

   • Shape: Folded regions of polypeptide chains lying side by side.

   • Stabilization: Repeated hydrogen bonds along the chain.

   • Example: Silk protein in spider webs

Hydrogen Bonds

• Role: Weak bonds that break easily but are repeated many times, providing support for the protein’s shape.

• Location: Between hydrogen in amino groups and oxygen in carboxyl groups along the polypeptide chain.

Tertiary Structure of Proteins

• Definition: The three-dimensional, fully folded and compact structure of a single protein molecule.

• Determining Factor: Interactions between amino acid R groups (side chains), which are unique for each amino acid.

Stabilizing Interactions

1. Hydrophobic Interactions

   • Non-polar R groups cluster in the interior of the protein to avoid water.

2. Van der Waals Interactions

   • Weak attractions that hold the hydrophobic clusters together.

3. Hydrogen Bonds

   • Form between polar R groups on the protein surface.

4. Ionic Interactions (Salt Bridges)

   • Occur between positively and negatively charged R groups.

5. Disulfide Bridges (Strong Covalent Bonds)

   • Form between two cysteine amino acids with sulfhydryl (-SH) groups.

   • Sulfur atoms bond to form a -S-S- bridge, bringing parts of the protein together.

Example Protein

• Myoglobin:

  • Found in muscles

  • Composed of 8 alpha helices folded into a compact globular protein

Quaternary Structure of Proteins

• Definition: Formed when two or more polypeptide chains (individual protein subunits) come together to form one large, functional protein molecule.

• Stabilizing Interactions:

  • Hydrogen bonds

  • Disulfide bridges

  • Other weak interactions that maintain the specific shape

Example Protein

• Collagen:

  • Found in skin, ligaments, tendons, and other vertebrate tissues

  • Composed of three helical subunits

  • Subunits intertwine to form a triple helix, giving collagen great strength

Denaturation of Proteins

• Definition: The process in which a protein loses its specific three-dimensional shape, causing it to become biologically inactive.

• Importance of Shape:

  • Protein function depends on its shape.

  • Shapes are determined by:

    • Amino acid sequence (primary structure)

    • Secondary and tertiary interactions (coils, folds, R-group interactions)

  • Different shapes = different functions (e.g., enzyme activity, structural support).

Causes of Denaturation

• Environmental changes can disrupt protein structure:

  • pH changes

  • Temperature changes

  • Salt concentration changes

  • Addition of alcohol, acids, urea, or heavy metals

Effects of Denaturation

• Protein unfolds, losing its original shape

• Protein becomes inactive

Examples

• Fried egg: Clear egg white turns opaque when heated

• Fever: Body enzymes temporarily denature at high temperature, causing sickness; normal temperature restores enzyme function

Functions of Proteins

1. Enzymatic Activity

   • Proteins as enzymes participate in and control almost all metabolic reactions.

   • Proper enzyme function is essential; malfunction can cause disorders.

2. Transport and Storage

   • Hemoglobin: Transports oxygen in the blood.

   • Ferritin: Stores iron in the liver.

3. Movement and Mechanical Support

   • Proteins aid in muscle contraction and movement.

   • Provide structural support (e.g., collagen for bone strength).

4. Defense

   • Antibodies: Protect against harmful agents like bacteria.

5. Regulation

   • Hormones: Proteins that influence cell activity and body functions.

Macromolecules Overview