Detailed Notes on Nucleic Acids, Proteins, and Cell Membranes

DNA Base Triplets and Genetic Code

  • Each amino acid has multiple DNA base triplet codes, similar to synonyms.
  • A gene on DNA has at least three times as many bases as amino acids in the protein it codes for.
  • DNA contains thousands of base pairs.
  • The 4 base pairs allow for a great variety of proteins, similar to how the 26 letters of the alphabet can form countless words.
  • Diversity in the genetic code stems from different base-pair sequences and lengths.

Nucleic Acids and Proteins Summary

  • There are two nucleic acids: DNA and RNA.
  • DNA contains instructions for building proteins.
  • DNA is composed of sugar, phosphate, and nitrogenous bases.
  • Nitrogenous bases pair up: adenine-thymine (A-T) in DNA, adenine-uracil (A-U) in RNA, and guanine-cytosine (G-C) in both DNA and RNA.
  • Proteins are structural and functional components of cells.
  • Proteins are made of amino acids and their sequence is determined by DNA.
  • Examples of proteins include enzymes, hormones, antibodies, and hemoglobin.

The Living Cell Membrane

  • The cell membrane separates a cell's protoplasm from its external surroundings.
  • It regulates what enters and leaves the cell.
  • Cell membranes are exclusive to living cells.
  • Cells obtain nutrients from the environment and dispose of waste into it.
  • The cell membrane is involved in transporting materials in and out of the cell.

Cell Membrane Composition

  • The membrane comprises two layers of phospholipids (lipids with phosphate groups).
  • Each phospholipid molecule has a hydrophilic (water-attracting) head and hydrophobic (water-repelling) tails.
  • The hydrophilic heads face the outer aqueous environment and cytoplasm, while hydrophobic tails face inward, away from water.
  • Protein molecules, including glycoproteins (proteins with sugar molecules), are embedded within the phospholipid bilayer.

Glycoproteins and Cell Identity

  • Glycoproteins provide cells with a unique identity, differing between organisms and individuals.
  • They help distinguish, for example, type A from type B red blood cells.
  • The immune system recognizes foreign invaders by identifying glycoprotein structures on their cell membranes.
  • This recognition explains why transplanted organs are often rejected.

Functions of Proteins in the Cell Membrane

  • Some proteins act as gatekeepers, controlling paths through the membrane.
  • For example, nerve cells have specialized protein gatekeepers for potassium and sodium ions.
  • Other proteins act as receptor sites for hormones, which are chemical messengers that facilitate cell communication.
  • Insulin attaches to specific receptor proteins, causing the membrane to allow sugar from the blood to enter.
  • Some proteins use cell energy to transport materials into or out of the cell which are called transport proteins.

Liposomes

  • Liposomes are double-layered spheres, about the size of a cell, that lipids can assemble into.
  • Liposomes can fuse with the cell membrane and deliver their contents into the cell.
  • Liposomes can be used to target tumor tissues in conjunction with cancer-fighting medications.
  • Using liposomes helps to reduce unwanted side effects on healthy tissues and allows patients to tolerate higher doses of anti-cancer drugs.

Liposomes and Gene Therapy

  • Liposomes can be used to improve the efficiency of gene therapy, which introduces new genes into a person's cells to correct genetic diseases or flaws.
  • Researchers have successfully inserted DNA into liposomes, which then fuse with target cells, similar to endocytosis.

Math Formula

  • The arrangement of the bases is called a permutation. The formula for calculating the total number of permutations (P) when selecting (r) items from a total of (n) items, with repetition allowed and order being important, is: P=nrP = n^r