Bio

Absolutely. Based on what you’re describing, your Bio 201 test is covering introductory chemistry + biological molecules. We can study it at exactly that level—not crazy chemistry, but enough to recognize what’s happening and answer test questions.

🧬 BIO 201 TEST — MASTER STUDY GUIDE

1. The 4 major biological molecules

There are four major classes:


*Lipids aren’t technically polymers in the same way proteins/carbs/nucleic acids are, but glycerol + fatty acids is the basic structure you’ll commonly need to recognize.

🔥 Easy way to remember

Carbs = quick energy
Lipids = long-term energy + membranes
Proteins = workers
Nucleic acids = information


2. Carbohydrates 🍞

Made primarily of:

C + H + O

Often roughly in a 1:2:1 ratio.

Monosaccharide

One sugar.

Examples:

  • Glucose

  • Fructose

  • Galactose

Disaccharide

Two sugars joined together.

Example:

  • Sucrose = glucose + fructose

Polysaccharide

Many sugars joined together.

Examples:

  • Starch → plant energy storage

  • Glycogen → animal energy storage

  • Cellulose → plant cell walls

Test trap 🚨

Glucose → immediate/quick energy

Glycogen → stored carbohydrate in animals

Starch → stored carbohydrate in plants

Cellulose → structure in plants


3. Lipids 🥑

Lipids include:

  • Fats

  • Oils

  • Waxes

  • Phospholipids

  • Steroids

They’re mostly hydrophobic, meaning they don’t mix well with water.

Triglyceride

A typical fat contains:

1 glycerol + 3 fatty acids

Saturated vs. unsaturated

Saturated fat

  • No carbon-carbon double bonds

  • Usually straighter

  • Can pack tightly

Unsaturated fat

  • Has one or more C=C double bonds

  • Has bends/kinks

  • Doesn’t pack as tightly

Phospholipids

SUPER important because they’re major components of cell membranes.

They have:

Hydrophilic head → likes water

Hydrophobic tails → avoid water

So:

Head = water-loving
Tail = water-fearing


4. Proteins 🥩

Proteins are made of amino acids.

Amino acids are connected by peptide bonds.

Proteins can function as:

  • Enzymes

  • Transport proteins

  • Receptors

  • Structural proteins

  • Hormones

  • Antibodies

  • Movement proteins

Amino acid basic structure

Every amino acid has:

  • Amino group

  • Carboxyl group

  • Hydrogen

  • Central carbon

  • R group

The R group is what differs between amino acids.

There are 20 common amino acids used to build proteins.


5. Nucleic acids 🧬

Two major ones:

DNA

  • Stores genetic information

RNA

  • Helps use genetic information to make proteins

Their building blocks are nucleotides.

Each nucleotide has:

  1. Sugar

  2. Phosphate group

  3. Nitrogenous base

DNA bases:

A, T, C, G

RNA bases:

A, U, C, G

Remember:

DNA has T
RNA has U


💧 6. Water as a molecule

This is probably one of the biggest sections based on what you’ve been studying.

Water = H₂O

One oxygen is covalently bonded to two hydrogens.

But water is polar.

Why?

Oxygen pulls electrons toward itself more strongly than hydrogen does.

So you get:

Oxygen → slightly negative (δ−)

Hydrogens → slightly positive (δ+)

Think:

O = negative side
H = positive side


⚡ 7. Covalent bonds

A covalent bond occurs when atoms share electrons.

Example:

H₂O

Oxygen shares electrons with two hydrogen atoms.

There are two major types you should know:

Nonpolar covalent

Electrons are shared relatively equally.

Example:

O₂

Polar covalent

Electrons are shared unequally.

Example:

H₂O

Oxygen pulls harder on the shared electrons.


🧲 8. Ionic bonds

Ionic bonds involve transfer of electrons.

One atom loses an electron → becomes positive

Another gains an electron → becomes negative

Opposite charges attract.

Example:

NaCl

Na → loses electron → Na⁺

Cl → gains electron → Cl⁻

Then:

Na⁺ ↔ Cl⁻

That’s an ionic attraction.

Don’t confuse:

Covalent = SHARE

Ionic = TRANSFER


🫱🏽‍🫲🏾 9. Hydrogen bonds

Hydrogen bonds are weaker than covalent bonds.

They happen because of attractions between partial charges.

For example, between water molecules:

Hδ+ ——— Oδ−

The slightly positive hydrogen of one water molecule is attracted to the slightly negative oxygen of another.

That’s a hydrogen bond.

Important distinction:

Inside one H₂O molecule:

O—H = covalent bond

Between two H₂O molecules:

H···O = hydrogen bond

That’s a VERY common test question.


🎱 10. The octet rule

Atoms generally become more stable when their outer electron shell has 8 electrons.

This is the octet rule.

Atoms can achieve this by:

  • Gaining electrons

  • Losing electrons

  • Sharing electrons

For example:

Sodium

Na has 1 valence electron.

It can lose that electron:

Na → Na⁺

Now its outer shell is more stable.

Chlorine

Cl has 7 valence electrons.

It can gain 1:

Cl → Cl⁻

Now it has 8.

That’s why Na and Cl can form NaCl.


🧠 The BIG connection

This is where your professor may start combining concepts.

Imagine:

H₂O

Oxygen has 6 valence electrons.

It wants 2 more to reach an octet.

So oxygen forms two covalent bonds with hydrogen.

But oxygen pulls the shared electrons more strongly.

Therefore:

H₂O is polar.

Because water molecules are polar, they can form:

hydrogen bonds with each other.

And those hydrogen bonds help explain water’s unusual properties.