Summary of "Химические основы живых организмов"

Overview

Lecture by Akimov Les (biology-olympiad preparation) introducing “Chemical foundations of living organisms.”
Purpose: explain basic chemistry concepts needed for deeper biology topics (biochemistry, molecular biology, cellular respiration, photosynthesis) and to provide a solid foundation for olympiad-level biology.

Matter: anything that has mass and volume (examples: air, microphone). Not matter: forms of energy (light), fields, purely imagined things.
Substance (chemical substance): a form of matter with specific chemical and physical properties (melting/boiling points, chemical reactivity).
- Elements: cannot be decomposed into simpler substances by chemical means (example: oxygen gas).
- Compounds: substances that can be chemically decomposed into other substances (example: water → hydrogen + oxygen; glucose → C, H, O).
Mixtures: physical combinations of substances that retain their individual identities (examples: tea, air, milk, blood, cytosol). Mixing does not produce a new chemical substance.

The four most abundant elements in living organisms: oxygen (O), carbon (C), hydrogen (H), nitrogen (N) — together ≈ 96% of organismal mass.
Other important elements (~4%): calcium (Ca), phosphorus (P), potassium (K), sulfur (S), magnesium (Mg), chlorine (Cl), etc.
Trace elements: present in very small amounts but biologically essential (examples: boron, chromium, cobalt, copper, iron, molybdenum, silicon, zinc, vanadium). Note: some elements (e.g., lead) are toxic despite being present in trace amounts.

Atomic → molecular → organelle → cell → tissue → organ → organ system → organism

Above organism: population → ecosystem (not covered in detail but noted).

Atom: smallest part of an element that retains the element’s properties.
Subatomic particles:
- Proton: charge +1, mass ≈ 1 dalton
- Neutron: charge 0, mass ≈ 1 dalton
- Electron: charge −1, mass ≈ 0 (negligible compared to proton/neutron)
Nucleus contains protons and neutrons; electrons form an electron cloud / orbitals around the nucleus.
Atomic number = number of protons; atomic mass ≈ protons + neutrons.
Ions: atoms with unequal numbers of protons and electrons (positive = cation, negative = anion).
Isotopes: atoms of the same element differing in neutron number (e.g., C‑12, C‑13, C‑14). Isotopes behave chemically like the element but differ in mass and some physical/decay properties.

Proton +1, Neutron 0, Electron −1 — memorize charges and approximate masses.

Electrons occupy shells (energy levels) around the nucleus. The first shell holds 2 electrons; higher shells hold more (biology usually focuses on first two/three shells).
Electrons prefer to occupy orbitals singly before pairing (Hund’s rule). Unpaired electrons in the outer shell determine an atom’s valence (bonding capability).
Typical valences (examples):
- Hydrogen: 1 unpaired → valence 1
- Carbon: 4 unpaired → valence 4 (forms 4 covalent bonds, e.g., CH4)
- Nitrogen: 3 unpaired → valence 3 (forms 3 covalent bonds, e.g., NH3; can form N≡N triple bond)
- Oxygen: 2 unpaired → valence 2 (forms 2 covalent bonds, e.g., H2O)
Electron transitions between energy levels: moving to a higher level requires energy (absorption); falling to a lower level releases energy (heat, light).

Covalent bonds: atoms share pairs of valence electrons.
- Single, double, triple bonds (examples: H–H single in H2; O=O double in O2; N≡N triple).
- Molecule examples: H2, O2, H2O, CH4, NH3, CO2.
Polar vs nonpolar covalent bonds:
- Electronegativity: an atom’s tendency to attract electrons.
- If bonded atoms differ significantly in electronegativity (e.g., O vs H), the shared electrons are pulled closer to the more electronegative atom → polar covalent bond with partial charges (δ− on O, δ+ on H in water).
- If electronegativities are similar (e.g., C–H, H–H, O–O), the bond is nonpolar.
Ionic bonds: complete transfer of electrons creating oppositely charged ions (example: NaCl — Na+ and Cl−). Ionic solids form crystal lattices and often dissolve in water.
Hydrogen bonds: weak interactions where a hydrogen covalently bonded to an electronegative atom (N or O) is attracted to another electronegative atom. Important because they:
- Are much weaker than covalent bonds (approx. ~20× weaker) but strong enough to stabilize structures (water cohesion, protein secondary structure, DNA base pairing).
- Are reversible and essential for dynamic biological processes (e.g., ligand–receptor interactions).
Van der Waals interactions: very weak, short-range forces that occur when atoms/molecules are in close contact; collectively can be significant.

Carbon isotopes in the atmosphere: mostly C‑12, some C‑13 (~1.1%), trace C‑14.
Living organisms exchange carbon with the environment (C‑14 uptake continues while alive). After death, uptake stops and C‑14 decays.
C‑14 half-life ≈ 5,730 years. Measuring residual C‑14 fraction in a fossil relative to atmospheric levels allows age estimation.
Example: if a fossil has 1/8 of atmospheric C‑14, that corresponds to 3 half-lives → 3 × 5,730 ≈ 17,190 years (≈ 17,000 years).

Memorize subatomic particles (proton, neutron, electron), their charges and approximate masses (use daltons for atomic mass).
Know atomic number (protons) vs atomic mass (protons + neutrons).
Predicting bonding and molecule formation:
- Count valence (outer-shell) electrons and unpaired electrons to determine likely covalent bonds.
- Apply Hund’s rule: electrons fill orbitals singly before pairing.
- Consider electronegativity differences to decide polar vs nonpolar covalent vs ionic bonding.
Radiocarbon dating: measure the ratio of C‑14 in sample vs expected living level and apply half-life decay (each half-life halves the amount).
Recommended background reading/viewing: Wikipedia for definitions; Kurzgesagt (or similar visual channels) for scale/size visualizations (lecturer’s recommendation).

Several transcription errors and mislabelled element symbols occurred in subtitles. Correct conventional symbols: O = oxygen, C = carbon, H = hydrogen, N = nitrogen.
Some organization names in the introduction were garbled; they are ministry/educational organizations related to Kazakhstan.