Comprehensive Study Notes: Atoms, Bonding, Reactions, and Basic Biochemistry
Page 1
Atom notation explained
¹¹H means:
Atomic number (bottom left) = 1 → 1 proton
Mass number (top left) = 1 → 1 proton + 0 neutrons
³₁H means:
Atomic number = 1 → 1 proton
Mass number = 3 → 1 proton + 2 neutrons
✅ Correct Answer: They are isotopes.
💡 Why?
Isotopes are atoms of the same element (same number of protons) but different numbers of neutrons.
Both atoms are hydrogen (atomic number 1), but:
¹H has 0 neutrons
³H has 2 neutrons
So they’re isotopes of hydrogen: specifically, protium (¹H) and tritium (³H).
❌ Why the other options are incorrect:
Polymers: Polymers are long chains of molecules, not individual atoms.
They contain 1 and 3 protons: Both have 1 proton—atomic number defines that.
They are compounds: Compounds are made of two or more different elements bonded together. These are single atoms.
They each contain 1 neutron: ¹H has 0 neutrons, ³H has 2 neutrons.
Atom N: ¹⁴₇N
Atomic number = 7 → Nitrogen has 7 protons and 7 electrons (in a neutral atom).
🌀 Electron Configuration of Nitrogen
Shell 1 holds 2 electrons
Shell 2 holds up to 8 electrons
Page 2
The Identity of an Atom
The atomic number is what determines the element.
Atomic number = number of protons in the nucleus.
So…
✅ Correct Answer: protons in an atom
💡 Why?
If you change the number of protons, you change the atomic number, which means you're now dealing with a completely different element.
○ Example: Carbon has 6 protons → if you add one, it becomes nitrogen (7 protons).
❌ Why the other options don’t work:
Particles in the nucleus: That includes both protons and neutrons—only changing protons changes the element.
Electrons circling the nucleus: Changing electrons affects charge, not the element.
Neutrons in an atom: That creates isotopes, not new elements.
What determines electron arrangement?
The text notes: Electron Configuration of Nitrogen
Shells and electron counts lead to understanding valence electrons.
Page 3
What are isotopes?
Isotopes are atoms of the same element (same number of protons) but with different numbers of neutrons.
That means they have the same atomic number, same number of electrons, and same chemical behavior—but different mass numbers.
✅ Correct Answer: have different numbers of neutrons
❌ Why the other options are incorrect:
Different numbers of electrons: Only changes if the atom is an ion—not an isotope.
React differently with other atoms: Isotopes of the same element react the same way chemically.
Different atomic numbers: That would make them different elements, not isotopes.
What makes an atom reactive?
Reactivity is all about how eager an atom is to bond with others.
That eagerness comes from unpaired electrons in the valence shell (the outermost shell).
Atoms “want” to fill or empty their valence shell to become stable—like noble gases.
✅ Correct Answer: the existence of unpaired electrons in the valence shell
🔍 Why the other options don’t work:
Average distance of the outermost shell: Affects energy levels, but not directly reactivity.
Page 4
Potential energy of the valence shell
Doesn’t explain why atoms bond—unpaired electrons do.
Sum of potential energies of all shells
Too broad—reactivity is driven by the outer shell only.
Mass number = 15, Atomic number = 7
Atomic number = # of protons = 7
Mass number = protons + neutrons → So: Neutrons = 15 − 7 = 8
❌ Protons repel electrons
Nope! Protons are positively charged, electrons are negatively charged → they attract each other.
❌ Protons attract other protons
Not quite. Protons repel each other because they have the same charge. They're held together in the nucleus by the strong nuclear force, not attraction.
❌ Most of an atom's volume is filled with matter
Actually, atoms are mostly empty space! The nucleus is tiny, and electrons zip around in a huge cloud.
✅ Electrons determine the atom's size
Yes! The electron cloud defines how big the atom is. The farther out the electrons orbit, the larger the atom appears.
❌ All of the above
Page 5
An atom has 8 protons, 8 neutrons, and 8 electrons. Another isotope of the same element might have 10 neutrons.
Because only one statement is true, this one’s out.
"All the electrons in an atom have similar amounts of energy" ❌ False.
Electrons in outer shells have more energy than those in inner shells.
"The valence shell has higher energy than other occupied shells" ✅ True!
"Electrons must lose energy to move from the first to the second shell" ❌ False.
Electrons must gain energy to move to a higher shell, not lose it.
"All of the above" ❌ Incorrect, since only one statement is true.
Given: 6 protons • 6 neutrons • 6 electrons
What defines the element?
The number of protons = atomic number
Atomic number 6 = Carbon (C)
✅ Correct Answer: C; it has 6 protons
❌ Why the other options don’t work:
N; it has 6 electrons: Not enough to define the element; protons define the element.
N; it has 6 protons: Not correct for nitrogen.
C; it has 6 electrons: True for a neutral atom, but protons define the element.
O; its mass number is 12: Oxygen has 8 protons → atomic number 8.
Page 6
Chemists assign atoms to chemical elements by counting their protons
Which of the following is the key characteristic that is ultimately responsible for the unique chemical properties of each element?
Each element has a unique number of protons.
🧪 What is a mole?
A mole is a counting unit—like a dozen, but way bigger.
1 mole = 6.022 imes 10^{23} particles (Avogadro’s number)
So a mole of anything—sugar, vitamin C, atoms, ions—means you have that many molecules or particles, regardless of their size or mass.
❌ Why the other options don’t work:
Volume: Different substances have different densities and molecular sizes.
Number of atoms: Mole counts vary with molecular size; a mole of different substances won’t have the same total atom count.
Mass: Different molecules have different molar masses—so their masses will be different even if you have 1 mole of each.
An element is a pure substance made of only one kind of atom. Examples: Carbon (C), Oxygen (O), Hydrogen (H).
which of the following is a trace element required by all living organisms?
IODINE
Radioactive decay happens when an atom’s nucleus is unstable, often due to:
Too many neutrons
Too few neutrons
Imbalance in nuclear forces
Correct Answer: Imbalance in nuclear forces
Page 7
Which four of the 92 naturally occurring elements make up approximately 96% of the mass of the human body?
Carbon, Hydrogen, Nitrogen, Oxygen
Trace elements are required by organisms in only minute quantities (less than 0.01% of mass).
Which of the following is a trace element that is required by humans and other vertebrates?
IODINE
Why iodine?
Iodine is essential for making thyroid hormones, which regulate metabolism, growth, and development.
Deficiency can lead to goiter or other thyroid issues.
❌ Why the other options don’t count as trace elements:
Nitrogen: Needed in large amounts for proteins and DNA.
Calcium: Crucial for bones and muscles—needed in bulk.
Phosphorus: Key part of DNA, ATP, and bones—also needed in large amounts.
Potassium: Vital for nerve and muscle function—required in significant amounts.
Trace elements are required by organisms in only minute quantities (less than 0.01% of mass).
Which of the following is a trace element that is required by all organisms? IRON
Given only a mass number, one can deduce the number of in each atom of an element. What is the mass number?
Mass number = protons + neutrons
Page 8
It tells you the total number of particles in the nucleus, but not how many of each.
✅ Correct Answer: protons plus neutrons
❌ Why the other options don’t work:
Neutrons: You need the atomic number (protons) to subtract from the mass number.
Protons: Mass number alone doesn’t tell you how many protons—need atomic number.
Electrons: Only equal to protons in a neutral atom, and mass number doesn’t include electrons.
Protons plus electrons: Mass number doesn’t include electrons at all—just nucleus particles.
Oxygen has an atomic number of 8 and a mass number of 16. What is the atomic mass of an oxygen atom?
Given: Atomic number = 8 → 8 protons; Mass number = 16 → 8 protons + 8 neutrons
⚖ What is atomic mass measured in?
Atomic mass is typically expressed in daltons (Da) or atomic mass units (amu).
1 proton ≈ 1 dalton, 1 neutron ≈ 1 dalton
So: 8 protons + 8 neutrons = ~16 daltons
✅ Correct Answer: approximately 16 daltons
❌ Why the other options don’t work:
8 daltons: That’s just the number of protons—not the full mass.
Protons repel electrons
❌ Protons repel electrons
Protons attract other protons
❌ Not quite. Protons repel each other because they have the same charge. They’re held together in the nucleus by the strong nuclear force, not attraction.
Most of an atom's volume is filled with matter
❌ Actually, atoms are mostly empty space! The nucleus is tiny, and electrons zip around in a huge cloud.
Electrons determine the atom's size
✅ Yes, the electron cloud defines how big the atom is.
Page 9
An atom has 16 protons, 16 neutrons, and 16 electrons? (Example context from decay section)
16 grams Way too large—grams are used for moles, not single atoms.
24 daltons That would mean extra neutrons—not true for oxygen-16.
8 grams Again, grams are for bulk amounts, not individual atoms.
🧪 What’s happening in this decay?
Phosphorus-32 has:
15 protons (atomic number)
17 neutrons (mass number 32 − 15)
In beta decay, a neutron turns into a proton, and an electron (beta particle) is emitted.
🔄 What changes?
The atom gains 1 proton → atomic number increases from 15 to 16
Mass number stays the same → still 32
So the new atom has:
16 protons
16 neutrons
Mass number = 32
✅ Correct Answer: sulfur-32 (atomic number 16)
❌ Why the other options don’t work:
Negatively charged phosphorus-32 ion: This isn’t ionization—it’s nuclear decay.
Phosphorus-31: That’s a different isotope, not the result of this decay.
Positively charged phosphorus-31 ion: Wrong isotope and wrong process—this isn’t about losing electrons.
Page 10
The chemical behavior of an atom depends primarily upon which of the following?
✅ Correct Answer: the number of electrons in the valence shell
💡 Why?
The valence shell is the outermost electron shell.
The number of electrons in that shell determines how an atom bonds, reacts, and interacts with other atoms.
Atoms with full valence shells (like noble gases) are stable and unreactive.
Atoms with unpaired or missing electrons in the valence shell are more reactive.
❌ Why the other options don’t work:
Number of protons: Defines the element, but not its chemical behavior.
Total number of electrons: Doesn’t matter unless you know how they’re arranged.
Number of electron shells: Affects size and energy, but not reactivity directly.
Number of neutrons: Influences isotopes and stability, not chemical behavior.
How does the formation of covalent bonds differ from the formation of ionic bonds between two atoms?
Correct Answer: Covalent bonds involve the sharing of electrons between atoms; ionic bonds involve the transfer of electrons from one atom to the other.
🔬 Why this is correct:
Covalent bonds: Atoms share electrons to fill their valence shells. Example: In H₂O, oxygen shares electrons with hydrogen.
Ionic bonds: One atom transfers electrons to another, creating charged ions that attract each other. Example: In NaCl, sodium gives up an electron to chlorine → Na⁺ and Cl⁻ attract.
❌ Why the other options don’t work:
Sharing of pairs vs. single electrons: Covalent bonds can involve sharing of electron pairs; ionic bonds don’t involve sharing at all.
Molecules vs. compounds: Both covalent and ionic bonds can form compounds; this doesn’t explain the bonding mechanism.
Transfer vs. electrical attraction: Ionic bonds do involve electrical attraction—but only after the electron transfer. The key difference is sharing vs. transferring.
Page 11
Chemical equilibrium is reached when __.
✅ Correct Answer: the forward and reverse reactions occur at the same rate so that the concentrations of reactants and products have stabilized at a particular ratio.
💡 Why?
Chemical equilibrium doesn’t mean the reaction stops—it means the rate of the forward reaction equals the rate of the reverse reaction.
The concentrations of reactants and products stay constant, but not necessarily equal.
It’s a dynamic balance, not a freeze-frame.
❌ Why the other options don’t work:
Matter destroyed/created: Not correct—law of conservation.
Reverse reaction begins: That can happen before equilibrium is reached.
All reactants converted: That's completion, not equilibrium.
Matter is conserved: True in general, but not specific to equilibrium.
Which of the following correctly describes any chemical reaction that has reached equilibrium?
✅ Correct Answer: The rate of the forward reaction is equal to the rate of the reverse reaction
💡 Why?
At chemical equilibrium, the reaction doesn’t stop—it just reaches a point where the forward and reverse reactions happen at the same rate.
The concentrations of reactants and products remain constant, but they don’t have to be equal.
It’s a dynamic balance, not a complete conversion or freeze.
❌ Why the other options don’t work:
The reaction is now irreversible: No, equilibrium is reversible.
Concentrations are equal: Not necessarily—just stable, not equal.
Both reactions have halted: False—they’re still happening, just at equal rates.
Page 12
Water molecules have a polarity, which allows them to be electrically attracted to other water molecules and other polar molecules by weak chemical bonds known as _.
✅ Correct Answer: hydrogen bonds
💡 Why?
Water is polar:
Oxygen pulls electrons more strongly, creating partial negative charge on O and partial positive charges on H.
This polarity allows water molecules to form weak attractions between the partially positive hydrogen of one molecule and the partially negative oxygen of another.
These weak attractions are hydrogen bonds and are responsible for water’s properties.
❌ Why the other options don’t work:
Nonpolar covalent bonds: Involve equal sharing of electrons—water is polar.
Van der Waals interactions: Very weak and non-specific—not the main force between water molecules.
Polar covalent bonds: True within a water molecule, but not between molecules.
Ionic bonds: Involve full electron transfer—not relevant to water’s intermolecular bonding.
Many of water's emergent properties, such as its cohesion, its high specific heat, and its high heat of vaporization, result from the fact that water molecules _.
✅ Correct Answer: are attracted to each other by partial negative and positive charges on the oxygen and hydrogen atoms, respectively
💡 Why?
Water is a polar molecule:
Oxygen has a partial negative charge
Hydrogen has a partial positive charge
This polarity allows water molecules to form hydrogen bonds with each other.
❌ Why the other options don’t work:
Very small: True, but not the cause of those specific properties.
Extremely large: False—water is a small molecule.
In constant motion: Also true, but not the direct cause.
Tend to repel each other: No—water molecules attract via hydrogen bonding.
An acid is a substance that _.
✅ Correct Answer: increases the hydrogen ion concentration of an aqueous solution
💡 Why?
Acids release H⁺ ions (hydrogen ions) when dissolved in water.
This increase in hydrogen ion concentration is what gives acids their low pH and characteristic reactivity.
Example: HCl (hydrochloric acid) → dissolves in water → H⁺ + Cl⁻
❌ Why the other options don’t work:
Forms covalent bonds: Not unique to acids.
Reduces hydrogen ion concentration: That’s what bases do.
Is a versatile solvent: Water is a solvent, not acids in general.
Contains hydrogen: True, but not all hydrogen-containing substances are acids.
pH of 6 is how many times more acidic than a pH of 9?
How the pH scale works:
The pH scale is logarithmic, meaning each unit change = 10× difference in hydrogen ion concentration.
So going from pH 9 to pH 6 is a 3-unit drop → 10^3 = 1000
✅ Correct Answer: 1,000
💡 What this means:
A solution with pH 6 is 1,000 times more acidic than one with pH 9.
That’s why even small changes in pH can have big biological effects—especially in enzymes and cellular processes.
Q uestion Correct Answer Why It’s Right
1 cohesion
2 hydrogen bonds
3 neutral
4 100 times more acidic
5 An increase in hydrogen ion concentration means a decrease in pH scale units.
6 A solution that could buffer the bleach and ammonia would remove excess OH⁻ ions.
7 Chlorine is filling its third electron shell. Chlorine gains an electron to complete its outer shell.
8 between an oxygen and a hydrogen atom of different water molecules. Hydrogen bonds form between molecules, not within.
9 Oxygen is more electronegative than the hydrogen atoms. It pulls electrons closer, making water polar.
10 polar covalent
11 (Bonus) two polar covalent bonds
12 (Bonus) polar covalent …………. hydrogen
Page 13
Water’s emergent properties are driven by hydrogen bonding between water molecules.
Hydrogen bonds: weak attractions between the partially positive H and partially negative O of neighboring water molecules.
Water’s polarity underlies its solvent abilities and many of its unique properties (cohesion, surface tension, heat capacity, etc.).
The term “polarity” arises from unequal sharing of electrons in a polar covalent bond within a water molecule.
Page 14
An acid is a substance that increases the hydrogen ion concentration of an aqueous solution. (Re-stated)
The pH scale is logarithmic: a change of 1 pH unit corresponds to a 10× change in [H⁺].
If pH goes from 9 to 6, the solution becomes 1000× more acidic.
Buffers help stabilize pH by neutralizing excess OH⁻ or H⁺ ions.
Chlorine is filling its third electron shell; it gains an electron to complete its outer shell when forming ions.
Hydrogen bonding explanations: Bonds form between a hydrogen atom and an electronegative atom (like oxygen) in a different molecule (intermolecular) rather than within the same molecule.
Some Q&A highlights:
Between an oxygen and a hydrogen atom of different water molecules — Hydrogen bonds.
Oxygen is more electronegative than hydrogen; this causes polarity in H₂O.
Polar covalent bonds are the intra-molecular bonds in H₂O; hydrogen bonds are the inter-molecular bonds.
Page 15
Hydration, cohesion, and surface tension in water are linked to hydrogen bonding.
Cohesion is water molecules sticking to each other due to hydrogen bonding.
Hydrogen bonds contribute to water’s high surface tension and heat-related properties.
pH and acidity basics recap: A decrease in pH means an increase in hydrogen ion concentration.
Buffers: stabilize pH by neutralizing extra OH⁻ or H⁺ ions as needed.
Example questions reviewed (via answers):
1 cohesion
2 hydrogen bonds
3 neutral
4 1000× more acidic
5 More H⁺ → lower pH
6 Buffers neutralize OH⁻ ions
7 Chlorine gains electron to complete outer shell
8 Hydrogen bonds form between molecules
9 Oxygen is more electronegative → water is polar
10 Polar covalent bonds
11 Two polar covalent bonds
12 Polar covalent… hydrogen (hydrogen bonds)
Page 16
Additional item clarifications:
7. Chlorine gaining an electron to complete its outer shell reflects achieving a stable electron configuration.
8. Hydrogen bonds occur between molecules (intermolecular).
9. Oxygen’s electronegativity creates polarity in water.
Polar covalent bonds are the intra-molecular bonds in H₂O.
Two polar covalent bonds exist within a water molecule (H–O and H–O).
Between polar covalent (within molecule) and hydrogen bonds (between molecules).
Page 17
Lactose and digestion basics:
Lactose intolerance = lack of lactase enzyme → can't break down lactose (milk sugar).
Organic compounds are defined by the presence of carbon atoms.
Carbon can form up to four covalent bonds (not six).
Hydrocarbons are organic compounds (not inorganic).
Page 18
Isomers: same molecular formula, different structures → different properties.
Hydroxyl group (-OH) is found in alcohols.
Carboxyl group (-COOH) is a carbon double-bonded to oxygen and single-bonded to hydroxyl.
Amino group (-NH₂) found in amino acids and proteins.
Amino acids contain both carboxyl (-COOH) and amino (-NH₂) groups.
Disaccharides form when two monosaccharides link and release water (dehydration synthesis).
Digestion versus dehydration synthesis:
Digestion uses hydrolysis to break bonds (water-involved).
Example notes:
Most animals cannot break down cellulose; starch is easier to digest because cellulose has β-linkages that many animals cannot digest, whereas starch has α-linkages that are easier to digest.
Fats have long nonpolar hydrocarbon chains, making them hydrophobic.
Summary of key ideas:
Hydrophobic vs hydrophilic properties influence solubility and membrane behavior.
Page 19
Lipids and their features:
3 Hydrophobic: fatty acid chains repel water.
4 Unsaturated: double bonds introduce kinks; usually liquid at room temperature.
5 Phospholipid basics: one glycerol, one phosphate group, and two fatty acids. This is the basic structure of a phospholipid, key to cell membranes.
6 Steroids: lipids with a four-ring structure (e.g., cholesterol).
7 Phospholipids: form the bilayer of cell membranes — hydrophilic heads, hydrophobic tails.
Enzymes and proteins:
8 Enzymes speed up chemical reactions by lowering activation energy.
9 The chemical properties of their R groups (side chains) determine each amino acid’s traits.
10 The sequence of amino acids in the polypeptide chain determines the protein’s shape and function.
11 (Bonus) Peptide bonds form between amino acids during protein synthesis.
12 (Bonus) The primary structure — the sequence of amino acids in the polypeptide chain — is foundational for protein folding and higher structures (secondary, tertiary, quaternary).
Page 20
The central dogma of molecular biology:
DNA → RNA → Protein
The genes in DNA direct the synthesis of an RNA molecule, which is used to build (direct the synthesis of) a protein.
Central dogma summary: DNA is transcribed to RNA, which is translated into protein.
Study guide:
DNA (Deoxyribonucleic Acid): The molecule that carries genetic information in cells.
RNA (Ribonucleic Acid): A single-stranded molecule that plays a crucial role in coding, decoding, regulation, and expression of genes.
Protein: Large, complex molecules essential for the structure, function, and regulation of the body's cells, tissues, and organs.
Transcription: The process of copying a segment of DNA into RNA.
Translation: The process wherein RNA is decoded by a ribosome to produce a specific polypeptide or amino acid chain, ultimately folding into a functional protein.
I. Atom Structure and Identity
Atom Notation
Atomic number (bottom left): number of protons (defines the element).
Mass number (top left): number of protons + neutrons.
Isotopes
Same element (same protons), different number of neutrons.
Example: ¹H (protium, 0 neutrons) and ³H (tritium, 2 neutrons).
They have the same atomic number, same electrons, same chemical behavior, but different mass numbers.
Determining Element Identity
The atomic number (number of protons) defines the element.
Changing the number of protons changes the element.
Example: Carbon (6 protons) + 1 proton = Nitrogen (7 protons).
Electron Arrangement
Electrons occupy shells, determining electron configuration and valence electrons.
"The valence shell has higher energy than other occupied shells" - ✅ True.
Reactivity
Determined by the existence of unpaired electrons in the valence shell.
Atoms aim to fill or empty their valence shell for stability.
Atomic Mass
Measured in daltons (Da) or atomic mass units (amu).
1 \text{ proton} \approx 1 \text{ dalton}, 1 \text{ neutron} \approx 1 \text{ dalton}.
Example: Oxygen (8 protons, 8 neutrons) has an atomic mass of approximately 16 daltons.
II. Atomic Interactions and Properties
Subatomic Particle Roles
Protons: Positive charge, repel each other but held by strong nuclear force, define the element.
Electrons: Negative charge, attract protons, determine the atom's size (electron cloud).
Neutrons: No charge, affect mass number and isotopes.
Radioactive Decay
Occurs when an atom’s nucleus is unstable due to an imbalance in nuclear forces (e.g., too many or too few neutrons).
Example: Beta decay of Phosphorus-32 (15 protons, 17 neutrons) → neutron turns into proton → Sulfur-32 (16 protons, 16 neutrons).
Mole Concept
A counting unit: 1 mole = 6.022 \times 10^{23} particles (Avogadro’s number).
III. Elements and Life
Elements in Human Body
Carbon, Hydrogen, Nitrogen, Oxygen make up ~96% of human body mass.
Trace Elements
Required in minute quantities (less than 0.01% of mass).
Iodine: Essential for thyroid hormones.
Iron: Required by all organisms.
IV. Chemical Bonding and Water
Chemical Behavior
Primarily depends on the number of electrons in the valence shell.
Covalent Bonds
Involve the sharing of electrons between atoms.
Ionic Bonds
Involve the transfer of electrons from one atom to another, creating charged ions.
Water Properties
Polar molecule: Oxygen is more electronegative than hydrogen, creating partial negative charge on O and partial positive charges on H.
Hydrogen bonds: Weak attractions between partially positive H of one water molecule and partially negative O of another.
Responsible for water's emergent properties: cohesion, high specific heat, high heat of vaporization, solvation abilities.
V. Acids, Bases, and pH
Acid
Increases the hydrogen ion (H⁺) concentration of an aqueous solution.
pH Scale
Logarithmic scale where each unit change is a 10\times difference in H⁺ concentration.
Example: pH 6 is 1,000 times more acidic than pH 9 (10^3 difference).
Buffers
Stabilize pH by neutralizing excess OH⁻ or H⁺ ions.
VI. Organic Molecules
Organic Compounds
Defined by the presence of carbon atoms.
Carbon can form up to four covalent bonds.
Functional Groups
Hydroxyl group (-OH): Found in alcohols.
Carboxyl group (-COOH): Carbon double-bonded to oxygen and single-bonded to hydroxyl (found in fatty acids, amino acids).
Amino group (-NH₂): Found in amino acids and proteins.
Carbohydrates
Monosaccharides: Simple sugars.
Disaccharides: Formed by linking two monosaccharides via dehydration synthesis (releases water).
Digestion: Uses hydrolysis (adds water) to break bonds.
Cellulose vs. Starch: Cellulose has β-linkages (hard to digest), starch has α-linkages (easier to digest).
Lipids
Hydrophobic: Long nonpolar hydrocarbon chains.
Fats: Often saturated (solid at room temp) or unsaturated (double bonds, kinks, liquid at room temp).
Phospholipids: Glycerol + phosphate group + two fatty acids; form cell membrane bilayer (hydrophilic heads, hydrophobic tails).
Steroids: Lipids with a four-ring structure (e.g., cholesterol).
Proteins
Made of amino acids (contain both -COOH and -NH₂ groups).
R groups (side chains): Determine amino acid traits.
Peptide bonds: Form between amino acids during protein synthesis.
Primary structure: Sequence of amino acids, foundational for protein shape and function.
Enzymes: Proteins that speed up chemical reactions by lowering activation energy.
VII. Central Dogma
DNA → RNA → Protein
Genes in DNA direct RNA synthesis (transcription).
RNA directs protein synthesis (translation).