Yusuf_Ruweyda_BSB50120_8932602

Lecture 3: Proteins, Carbohydrates and Lipids

Introduction to Proteins

• Proteins are large organic macromolecules essential for life.

• Comprised of 20 different amino acids, which vary by their R groups.

• Linked by peptide bonds to form polypeptide chains.

• Characterized by four levels of 3D structure, with folding critical to their function.

• Plays numerous roles within cells, including structural support, movement, immunity, catalysis (through enzymes), communication, transport, and storage.

Structure and Composition of Proteins

• Fundamental components of all living cells, constituting over 50% of dry mass.

• Contain amino acids, composed of carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sometimes sulfur (S).

• Functions include:

  • Structural: Creating frameworks within cells.

  • Movement: Enabling muscle contractions.

  • Immunity & Protection: Antibodies to defend against pathogens.

  • Catalysis: Acting as enzymes to speed up biochemical reactions.

  • Communication: Serving as signals and receptors to relay information.

  • Transport: Moving substances across cell membranes.

  • Storage: Storing amino acids and other molecules.

Amino Acids and Their Structures

• Proteins are constructed as chains of amino acids (polypeptides).

• Amino Acid Structure:

  • Comprised of an amino group, carboxyl group, hydrogen atom, and variable R group (side chain).

  • Amino acids can exist as L-isomers or D-isomers based on the orientation of the amino group.

Amino Acid Properties

• Side chains (R groups) determine:

  • Folding characteristics: The 3D shape of the protein.

  • Charge at cellular pH: Can be positive or negative.

  • Hydrophobicity: R groups can be hydrophobic (water-hating) or hydrophilic (water-loving).

• Amino acids are coded for by mRNA, which corresponds to amino acids through codons during protein synthesis.

Peptide Bonds and Polypeptide Formation

• Peptide bonds formed through condensation reactions link amino acids.

• Each bond formation releases a water molecule.

• Polypeptides have an amino end (N-terminus) and a carboxyl end (C-terminus).

Levels of Protein Structure

1. Primary Structure: Linear sequence of amino acids (N-terminus to C-terminus).

2. Secondary Structure: Folding/coiling into repeating patterns such as alpha-helices and beta-pleated sheets.

3. Tertiary Structure: Overall 3D shape resulting from interactions between side chains of amino acids.

4. Quaternary Structure: Assembly of multiple polypeptide chains into a single functional protein.

Protein Function and Effects on Structure

• Correct amino acid sequence essential for proper function (e.g., sickle cell anemia caused by a single amino acid change in hemoglobin).

• Conditions such as pH, temperature, and salt concentration can affect protein conformation (denaturation).

• Chemical factors like co-factors and co-enzymes are crucial for enzyme activity.

Lecture 4: Carbohydrates

Introduction to Carbohydrates

• Carbohydrates are biological molecules, often referred to as sugars.

• Types: Monosaccharides (simple sugars), oligosaccharides (2-10 sugars), and polysaccharides (many sugars).

• Functions include energy storage, structural components, and involvement in cell-cell recognition.

Structure of Carbohydrates

• Carbohydrates consist of carbon, hydrogen, and oxygen, commonly with the formula CnH2nOn.

• Isoforms: Same molecular formula but different structures (e.g., glucose vs. fructose).

• Monosaccharides can be classified as aldoses or ketoses based on their functional groups.

Polysaccharides Overview

• Polysaccharides differ in structure and function:

  • Storage: Starch (plants), glycogen (animals).

  • Structural: Cellulose (plants), chitin (exoskeletons).

• Polysaccharides form through glycosidic bonds, which create long chains and branched structures.

Lipids

Characteristics of Lipids

• Lipids consist of carbon and hydrogen, primarily hydrophobic (insoluble in water).

• Includes fats, phospholipids, steroids, and waxes, each with distinct functions.

• Fatty acids can be saturated (no double bonds) or unsaturated (one or more double bonds).

Fat Structure

• Fats are formed by glycerol and fatty acids through dehydration reactions.

• Triacylglycerol (triglycerides): Consists of glycerol and three fatty acids.

Fatty Acid Classification

1. Saturated Fatty Acids: Solid at room temperature, found in animal fats.

2. Unsaturated Fatty Acids: Liquid at room temperature, found in oils (plant and fish).

Phospholipids and Membrane Structure

• Form lipid bilayers essential for cell membranes, with hydrophobic tails and hydrophilic heads creating a semi-permeable barrier.

• Glycolipids are important for cell communication and recognition.

Other Lipids

• Cholesterol: Integral to cell membranes, precursor for steroid hormones.

• Carotenoids and Waxes: Play various biological roles, including pigments and structural functions in organisms.

Conclusion

• Proteins, carbohydrates, and lipids are fundamental macromolecules in biological systems, each serving vital functions essential for life.