【Biology】Chapter 1: Cells and Molecules — The Microscopic World That Makes Us
Hello everyone! Let’s set off on an adventure into the world of "Cells and Molecules" together.
You might be thinking, "Molecules are invisible and sound complicated..." but don't worry! In reality, what happens inside our bodies is actually quite easy to understand if we compare it to everyday events.
In this chapter, we will learn about the components that make up cells and the "energy mechanisms" that sustain life. This is foundational knowledge that frequently appears on exams, so let's master it!
1. Components of Cells: What are we made of?
If we were to take our bodies (cells) apart, what would we find? The truth is, most of it is water.
Ranking of Intracellular Components
- Water (approx. 70–85%): The most abundant!
- Proteins (approx. 10–18%): #1 in dry weight (weight excluding water)!
- Lipids
- Nucleic Acids (DNA and RNA)
- Carbohydrates/Inorganic Salts
Key Point: The Importance of Water
Water isn't just plain liquid. It plays two major roles:
① Function as a solvent: It dissolves various substances, making it easier for chemical reactions to occur.
② Temperature stability: Water has a "high specific heat capacity" (it is slow to heat up and slow to cool down), which helps keep our body temperature constant even when the air temperature changes.
Did you know?
In plant cells, the percentage of "carbohydrates" is slightly higher than in animals. This is because they have cell walls (cellulose)!
2. The Stars of Life: How Proteins Work
Muscles, skin, hair, and the "enzymes" that facilitate chemical reactions in the body—these are all proteins.
Amino Acids: The Building Blocks
Proteins are made of small units called amino acids connected like a chain.
・There are 20 types of amino acids in total.
・The bond between amino acids is called a peptide bond.
・A long chain of these is called a polypeptide.
Study Tip:
Think of a protein like a necklace. The design of the necklace (the properties of the protein) is determined by the order in which you arrange the 20 types of "beads" (amino acids)!
The Three-Dimensional Structure of Proteins
An amino acid chain isn't just a simple string; it folds into complex, specific shapes. When this shape is broken, it is called denaturation.
Example: An egg hardening when cooked is a classic example of "heat denaturation," where the heat changes the protein's shape.
【Summary】
・Proteins are made of 20 types of amino acids.
・The bond is called a peptide bond.
・If the shape changes, it loses its function (inactivation).
3. The Currency of Life’s Energy: ATP
We get energy from food, but we can't use that energy directly. It needs to be converted into a "user-friendly" form first. That is ATP (Adenosine Triphosphate).
The Structure of ATP
ATP is made of the following three parts:
① Adenine (base)
② Ribose (sugar)
③ Phosphoric acid (3 groups)
* Adenine + Ribose = Adenosine.
How Energy is Released
The bond between phosphate groups is called a high-energy phosphate bond; when this bond breaks, a large amount of energy is released.
\( ATP \rightarrow ADP \text{ (Adenosine Diphosphate)} + \text{Phosphoric acid} + \text{Energy} \)
Everyday Analogy:
ATP is like a "charged battery" or "cash." When your body wants to do something (like move a muscle or synthesize a substance), you pay with ATP to receive the energy!
Common Mistake:
People often think "ATP *is* the energy," but more accurately, it is a "substance that stores energy."
4. Chemical Reaction Supporters: Enzymes
Countless chemical reactions occur in the body at all times. Enzymes are responsible for making these happen smoothly. The true nature of an enzyme is a protein.
Characteristics of Enzymes
- Catalytic action: They assist in reactions without changing themselves.
- Substrate specificity: They only react with specific partners (substrates). Like a "lock and key" relationship.
- Optimal temperature/pH: There is a temperature and acidity level where they work best.
Step-by-Step: How Enzymes Work
1. An enzyme has a pocket called an "active site."
2. A "substrate" that fits perfectly plugs into it.
3. The reaction occurs, and the product is released.
4. The emptied enzyme moves on to the next reaction!
Important!
The optimal temperature for most enzymes is around 37°C (body temperature). If a fever gets too high, enzymes undergo denaturation and stop working, which is why high fevers are dangerous.
5. The Blueprint of Genetic Information: Nucleic Acids (DNA and RNA)
Finally, let’s briefly touch on nucleic acids, the blueprints of the cell.
Nucleotides
The basic unit of nucleic acids is the nucleotide.
・It is made of a set of phosphoric acid + sugar + base.
Differences between DNA and RNA
・DNA (Deoxyribonucleic acid): The sugar is deoxyribose. It has a double-helix structure. Stores genetic information.
・RNA (Ribonucleic acid): The sugar is ribose. Usually a single strand. Mediates protein synthesis.
【Summary Point】
・Think of DNA as the "master file" (original) and RNA as a "copy" (for working), and it becomes much easier to understand!
It might feel overwhelming with so many terms at first, but try to keep a relaxed mindset: "It's just about the tiny parts inside our bodies."
First, master these three points: "Proteins = amino acids," "ATP = energy currency," and "Enzymes = helpers made of protein."
Next, we'll look at how these molecules are assembled inside the cell. Good luck!