BCHEM 151: Biochemistry Lecture 1

BCHEM 151: Biochemistry - Lecture 1

• Course: Biochemistry 151
• Lecturer: Amma Larbi, PhD
• Lecture Topic: Elemental Composition of Cells
• Study Objectives:
  • Origin of elements
  • List of elements in living cells
  • Reasons for the inclusion/exclusion of elements in cells
  • Role of carbon in forming compounds

Introduction

• Living cells/organisms are formed from elements organized into recognizable structural components.
• Atoms/elements are the basic building blocks in biochemistry, while cells are fundamental building blocks in other contexts

Origin of Elements

• Elements formed through:
  • Big Bang
  • Fusion reactions in stars
  • Artificial synthesis

The Big Bang Theory

• Explosion of incredibly hot, dense primordial matter.
• Led to the formation of Hydrogen and Helium.
• Gravity brought together gas clouds that collapsed into galaxies and stars.
• Elements beyond Hydrogen and Helium were formed in the centers of these stars, then released upon their explosion.

Fusion Reactions in Stars

• High temperatures and reactant concentrations are essential in the stellar core for forming elements.
• High temperatures overcome electrostatic repulsion between positively charged nuclei.
• Fusion reactions release heat and light, contributing to the star's formation from gas clouds.
• Star explosion releases a considerable amount of energy.

Stellar Lifecycles

• Majority of visible stars emit light through hydrogen fusion into helium.
• Hydrogen in stars is used up; faster in larger stars.
• Star core temperature drops and the star collapses.
• The heat releases causes the core temperature to rise and ignite helium, subsequently becoming bigger and redder.
• Fusion processes continue (fusion of helium and other elements)
• The largest atom formed through fusion is iron.
• Elements larger than iron form from neutrons produced in star explosions capturing nuclei of iron atoms.

Laboratory Synthesis of Elements

• Elements beyond atomic number 92 (transuranium elements) are synthesized by high-energy particle accelerators(in cyclotrons)
• Example: Californium created through the fusion of C-12 and U-238.

Elements Utilized to Form Cells

• Over 117 elements exist, but only a fraction are found in cells.
• Earth's most abundant element percentages: Oxygen (48.86%), Iron (18.84%), Silicon (13.96%), Magnesium (12.42%)
• Carbon percentage in Earth is ~0.10%
• Main Ions in biological systems: (e.g., Cu²⁺, Mg²⁺, Ca²⁺, Na⁺, K⁺)
• Major elements (Bulk elements) found in organic molecules: CHONPS (carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur).
• Trace elements: involved in crucial processes, including Na, K, Mg, Ca, B, V, Mn, Fe, Co, Ni, Cu, Zn, Si, Se, Cl, Br, and Cr.

Striking Features of Major Elements

• Majority are p-block elements.
• Capable of forming covalent bonds.
• Non-metals
• Relatively small atomic sizes.
• Neither too reactive nor inert.

Why is Carbon Unique?

• Carbon exhibits an ideal size for forming stable covalent bonds.
• Tetravalent nature allowing forming chains through catenation.
• Ability to form multiple bonds with other atoms and itself.

Other Elements Capable of Multiple Bonds

• Silicon (group IVA) is also tetravalent.
• Si-Si bonds are rare and weak due to the larger size of Silicon atoms.
• Silicon has strong Si-O bonds, creating stable inert chains.
• Carbon is preferred in living organisms despite Silicon's abundance.

Properties of Nitrogen and Boron:

• Nitrogen's ability to form bonds and the effects of lone electron pairs on the stability of N-N bonds.
• Boron's electron deficiency and impact on boron compound stability.

Reasons for Excluding Certain Elements:

• Artificial nature of some elements
• Inert nature of some elements
• Toxic nature of some elements
• Radioactivity of some elements

Non-Essential Elements with Beneficial Roles

• Some elements that aren't crucial for life still provide benefits, such as:
  • Lithium compounds for schizophrenia treatment.
  • Platinum/gold complexes in treating cancer and arthritis.
  • Kaolin (aluminum-containing mineral) as an anti-diarrheal agent.

Additional Resources

• YouTube videos on Stellar Hypothesis, from the Big Bang to the Present, and Beyond the Big Bang explosion (videos are provided).