AP Biology AP Biology 1.5 Lipids Study Notes- New Syllabus Effective 2025

AP Biology 1.5 Lipids Study Notes- New syllabus

AP Biology 1.5 Lipids Study Notes – AP Biology – per latest AP Biology Syllabus.

LEARNING OBJECTIVE

Describe the structure and function of lipids.

Key Concepts:

Triglycerides
Phospholipids
Steroids

AP Biology-Concise Summary Notes- All Topics

1.5.A .1

Lipids are a class of substances that are insoluble in water (and other polar solvents) but are soluble in nonpolar sub stances (like ether or chloroform).

Saturated fatty Acids

• A saturated fatty acid has a single covalent bond between each pair of carbon atoms, and each carbon has two hydrogens bonded to it (three hydrogens bonded to the last carbon). You can remember this by thinking that each carbon is “saturated” with hydrogen.

• A monounsaturated fatty acid has one double covalent bond and each of the two carbons in this bond has only one hydrogen atom bonded to it.

• A polyunsaturated fatty acid is like a monounsaturated fatty acid except that there are two or more double covalent bonds.

Unsaturated fatty Acids

Unsaturated fatty acids are characterized by the presence of one or more carbon-carbon double bonds, leading to “kinks” in their structure and a liquid state at room temperature, unlike saturated fatty acids. They are classified as monounsaturated (one double bond) or polyunsaturated (more than one double bond).

Here’s a more detailed breakdown:

1. Definition & Structure:

Unsaturated Fatty Acids: Fatty acids with one or more carbon-carbon double bonds (C=C) in their hydrocarbon chain.
Saturated Fatty Acids: Fatty acids with only single bonds between carbon atoms (C-C).
Double Bonds: These double bonds introduce “kinks” or bends in the fatty acid chain, preventing them from packing tightly together, leading to a liquid state at room temperature.
Hydrocarbon Chain: The long chain of carbon atoms (C) and hydrogen atoms (H) that forms the tail of the fatty acid.
Carboxylic Acid Head: The end of the fatty acid with a carboxyl group (-COOH).

2. Types of Unsaturated Fatty Acids:

Monounsaturated Fatty Acids (MUFAs): Contain one double bond.
- Examples: Oleic acid (found in olive oil).
Polyunsaturated Fatty Acids (PUFAs): Contain two or more double bonds.
- Examples: Linoleic acid (omega-6, found in vegetable oils) and alpha-linolenic acid (omega-3, found in flaxseed oil).
- Essential Fatty Acids (EFAs): Some PUFAs, like linoleic and alpha-linolenic acids, are considered essential because the human body cannot synthesize them and must obtain them from the diet.
Cis vs. Trans: Depending on the position of hydrogen atoms around the double bond, unsaturated fatty acids can be classified as cis or trans.
- Cis: Hydrogen atoms on the same side of the double bond.
- Trans: Hydrogen atoms on opposite sides of the double bond (often produced through partial hydrogenation of oils).

3. Health Implications:

Health Benefits:
Unsaturated fats, particularly MUFAs and PUFAs, are often considered beneficial for heart health and overall well-being.
PUFA Benefits:
Omega-3 and omega-6 fatty acids are essential for various bodily functions, including brain health, inflammation, and heart health.

They can help reduce the risk of heart disease, stroke, and certain types of cancer.
MUFA Benefits:
Can help lower LDL (bad) cholesterol levels.

May improve blood vessel function.
Dietary Sources:
MUFAs: Olive oil, avocados, nuts (almonds, peanuts, walnuts), seeds (pumpkin, sunflower).

PUFAs: Fatty fish (salmon, tuna, mackerel), flaxseeds, chia seeds, walnuts, soybean oil, canola oil.

4. Unsaturated Fatty Acids and Food:

Oils:
Most unsaturated fats are liquid at room temperature and are commonly found in oils.
Food Preservation:
The double bonds in unsaturated fatty acids make them susceptible to oxidation (rancidity) when exposed to oxygen.
Antioxidants:
Antioxidants can help protect unsaturated fats from oxidation and extend the shelf life of foods.

1.5.A .2

Steroids

Steroids are characterized by a backbone of four linked carbon rings. Examples of steroids include cholesterol (a component of cell membranes) and certain hormones, including testosterone and estrogen.

Cholesterol

Cholesterol, a waxy, fat-like substance, is essential for building healthy cells, hormones, and vitamin D, but excess levels can lead to plaque buildup in arteries, increasing the risk of heart disease.

What is Cholesterol?

Definition:
Cholesterol is a type of lipid (fat) that’s found in all animal cells.
Importance:
Your body needs cholesterol for various functions, including:
Building cell membranes

Producing hormones (like estrogen and testosterone)

Synthesizing vitamin D

Digesting fats
Sources:
Your liver produces all the cholesterol your body needs.

Cholesterol is also found in foods from animal sources, such as meat, poultry, eggs, and dairy products.
Lipoproteins:
Cholesterol travels through the bloodstream in particles called lipoproteins, which are combinations of fat and protein.

LDL (Low-Density Lipoprotein): Often called “bad” cholesterol because high levels can contribute to plaque buildup in arteries.

HDL (High-Density Lipoprotein): Often called “good” cholesterol because it helps remove cholesterol from the body.

Cholesterol and Health

High Cholesterol (Hyperlipidemia):
When you have too much cholesterol in your blood, it can lead to a buildup of plaque in your arteries, a condition called atherosclerosis.
Atherosclerosis:
This buildup can narrow or block arteries, potentially leading to:
Coronary artery disease: Reduced blood flow to the heart, potentially causing a heart attack.

Stroke: Reduced blood flow to the brain.
Risk Factors:
Unhealthy lifestyle: Diet high in saturated and trans fats, lack of exercise, smoking, and obesity.

Genetics: Family history of high cholesterol.

Age: Cholesterol levels tend to rise as you get older.

Medical Conditions: Diabetes, high blood pressure, and certain other conditions can contribute to high cholesterol.
Symptoms:
High cholesterol often has no noticeable symptoms, making regular cholesterol screenings important.
Diagnosis:
A blood test called a lipid panel measures total cholesterol, LDL, HDL, and triglycerides.
Treatment:
Lifestyle changes: Diet rich in fruits, vegetables, and whole grains, regular exercise, and maintaining a healthy weight.

Medications: Statins and other cholesterol-lowering drugs may be prescribed in some cases.

Cholesterol Levels

Total Cholesterol:
Desirable:Less than 200 mg/dL (5.17 mmol/L)
Borderline High:200 to 239 mg/dL (5.17 to 6.18 mmol/L)
High:240 mg/dL (6.21 mmol/L) or greater
LDL Cholesterol:
Optimal:Less than 100 mg/dL (2.59 mmol/L)
Near Optimal:100 to 129 mg/dL (2.59 to 3.34 mmol/L)
High:160 mg/dL (4.14 mmol/L) or greater
HDL Cholesterol:
Low:Less than 40 mg/dL (1.04 mmol/L) for men, less than 50 mg/dL (1.30 mmol/L) for women
High:60 mg/dL (1.55 mmol/L) or greater

Phospholipids

A phospholipid looks just like a lipid except that one of the fatty acid chains is replaced by a phosphate group (–PO3 2–). An additional and variable group of atoms is attached to the phosphate group. The two fatty acid “tails” of the phospholipid are nonpolar and hydrophobic and the phosphate “head” is polar and hydrophilic. A phospholipid is termed an amphipathic molecule because it has both polar (hydrophilic) and nonpolar (hydrophobic) regions. Phospholipids are often found oriented in sandwich like formations with the hydrophobic tails grouped together on the inside of the sandwich and the hydrophilic heads oriented toward the outside and facing an aqueous environment. Such formations of phospholipids provide the structural foundation of cell membranes.

AP Biology 1.5 Lipids Study Notes