Phospholipids and amphipathic molecules
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Question
Define a phospholipid.
Answer
A lipid made of **one glycerol, two fatty acids and a phosphate-containing head**.
Question
Define amphipathic.
Answer
Having **both a hydrophilic (water-loving) part and a hydrophobic (water-fearing) part** in the same molecule.
Question
What does hydrophilic mean?
Answer
**Water-loving** — attracted to and mixes with water.
Question
What does hydrophobic mean?
Answer
**Water-fearing** — does not mix with water; repelled by it.
Question
Which part of a phospholipid is the hydrophilic head?
Answer
The **phosphate group** (with the glycerol) — it is **polar**, so it is attracted to water.
Question
Which part of a phospholipid is hydrophobic?
Answer
The **two fatty-acid tails** — they are **non-polar**, so they are repelled by water.
Question
Why is a phospholipid amphipathic?
Answer
Because the **same molecule** has a **hydrophilic head AND hydrophobic tails**.
Question
How is a phospholipid built?
Answer
By **condensation reactions** that join the fatty acids and phosphate to glycerol, **releasing water (H₂O)**.
Question
How does a phospholipid differ from a triglyceride?
Answer
Both use one glycerol, but a phospholipid has **2 fatty acids + a phosphate head**, while a triglyceride has **3 fatty acids and no phosphate**.
Question
How do phospholipids behave in water?
Answer
They **self-arrange into a bilayer**: hydrophilic heads face the water on both sides, hydrophobic tails tuck into the middle.
Question
What is a phospholipid bilayer the basis of?
Answer
The **cell (plasma) membrane** — the boundary around every cell.
Question
In a phospholipid bilayer, where do the hydrophobic tails point?
Answer
**Inwards**, towards the middle — away from the water on both sides.
Question
Give an example of a molecule that is NOT amphipathic.
Answer
A **triglyceride** (fully hydrophobic) or **glucose** (fully hydrophilic) — each is only one or the other.
Question
What is the backbone of a phospholipid?
Answer
**Glycerol** — the fatty-acid tails and the phosphate head all attach to it.
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Topic 2.1 hub
Carbohydrates and lipids
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