Biological Chemistry 1: Elemental Composition of Cells

Biological Chemistry 1 (BIOL 157) - Lecture 1: Elemental Composition of Cells

• Study Objectives: This lecture covers the origin of elements, the elements in living cells, why some elements are in cells and others are not, and why carbon forms so many compounds.

Introduction

• All living cells and organisms are composed of intricately organized elements that form characteristic structures. Atoms combine to form molecules, which form cells, tissues, organs, organ systems, and finally, the organism.

Origin of Elements

• Elements are formed through various processes:
  • Big Bang
  • Fusion reactions in stars,
  • Artificial synthesis.

The Big Bang Theory

• An infinitely hot and dense primordial matter exploded, forming hydrogen and helium.
• Gravity brought together gas clouds, forming vast galaxies and billions of stars.
• Elements beyond hydrogen and helium were formed in the centers of stars and released upon their explosions.

Fusion Reactions in Stars

• Extremely high temperatures in stellar cores are necessary for fusion reactions.
• High temperatures overcome electrostatic repulsion between positively charged nuclei, allowing them to fuse.
• Fusion reactions produce heat and light, contributing to the formation and lifetime of stars.
• An enormous amount of energy is released during these reactions, leading to star explosions.

Elements Formed in Stars

• Hydrogen fusion forms helium.
• Helium fusion forms beryllium, then carbon, then oxygen.
• Iron is the largest atom formed by fusion.

Larger Elements Formation

• Elements larger than iron are formed when neutrons from exploding stars are captured by iron nuclei.

Laboratory Synthesis of Elements

• Elements with atomic numbers greater than 92 (transuranium elements) are artificially synthesized using high-energy particles in cyclotrons to fuse target nuclei. For example, Californium was made this way.

Elements in Living Cells

• Not all elements found on Earth are found in cells. (Less than a third).

• Percentage of atoms on earth: Oxygen (48.86%) Iron (18.84%) Silicon (13.96%) Magnesium (12.42%)

• Percentage of carbon in cells is around 0.10 %

• There's a similarity in the concentration of main ions in seawater and blood plasma (Cu²⁺, Mg²⁺, Ca²⁺, Na⁺, K⁺, etc.)

• Living cells utilize CHONPS (Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, Sulfur) for many organic molecules.

• Trace elements (those not CHONPS) are sometimes necessary components of biological systems, and are usually found in cell fluids.

Striking Features of Major Elements in Cells

• Primarily p-block elements
• Their ability to form covalent bonds, being non-metals.
• Their relatively small atomic sizes/numbers.
• Not overly reactive nor inert.

Why Carbon Forms Many Compounds

• Carbon's ideal size allows for stable covalent bonding.
• It's tetravalent, meaning it can form four bonds.
• Carbon has the power of catenation—forming chains with itself.
• Carbon can form multiple bonds.

Other Elements with Bonding Capabilities

• Silicon is tetravalent and can form chains like carbon. However, Si-Si bonds are rare, and Si-O bonds are very stable. Silicon is substantially more abundant than carbon in the Earth's crust, but carbon is preferentially incorporated in living cells.

Nitrogen Properties

• Nitrogen forms N-N bonds with less energy than C-C bonds. N atoms have lone pairs which repel during bond formation, and this reduces overall bond energy. This makes extended nitrogen chains unstable.

Boron Properties

• Boron has three valence electrons; it forms electron-deficient compounds, limiting the stability of boron compounds.

Reasons for Excluding Certain Elements

• Artificial nature
• Inert nature
• Toxicity
• Radioactivity

Non-Essential Elements with Beneficial Uses

• Some elements, though not essential for life, can be valuable (e.g., Lithium for schizophrenia treatment, platinum/gold for cancer/arthritis treatments, Kaolin for diarrhea).