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Molecular Biology - Carbohydrates and Lipids

Grade 11IBBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Molecular biology explains living processes in terms of the chemical substances involved, primarily focusing on carbon-based compounds such as carbohydrates, lipids, proteins, and nucleic acids.

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Carbohydrates are composed of carbon (CC), hydrogen (HH), and oxygen (OO), typically in the ratio of 1:2:11:2:1. They serve as short-term energy sources and structural components.

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Monosaccharides (e.g., glucose C6H12O6C_6H_{12}O_6 and ribose C5H10O5C_5H_{10}O_5) are the monomers of carbohydrates, which join via condensation reactions to form disaccharides and polysaccharides.

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Condensation reactions involve the loss of a water molecule (H2OH_2O) to form a covalent bond (glycosidic bond in carbohydrates, ester bond in lipids).

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Lipids are a diverse group of hydrophobic organic compounds, including triglycerides, phospholipids, and steroids. Triglycerides are formed from one glycerol and three fatty acids.

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Fatty acids can be saturated (no double bonds), monounsaturated (one C=CC=C double bond), or polyunsaturated (multiple C=CC=C double bonds).

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Unsaturated fatty acids can be ciscis isomers (hydrogen atoms on the same side of the double bond) or transtrans isomers (hydrogen atoms on opposite sides).

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Lipids are more suitable for long-term energy storage in humans than carbohydrates because they provide roughly 37 kJg−137 \text{ kJg}^{-1} of energy compared to 17 kJg−117 \text{ kJg}^{-1} for carbohydrates.

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The Body Mass Index (BMIBMI) is used as a screening tool to identify possible weight problems in adults.

📐Formulae

C6H12O6+C6H12O6→C12H22O11+H2OC_6H_{12}O_6 + C_6H_{12}O_6 \rightarrow C_{12}H_{22}O_{11} + H_2O

BMI = \frac{mass\text{ (kg)}}{height^2\text{ (m^2)}}

Glycerol+3×Fatty Acids→Triglyceride+3H2O\text{Glycerol} + 3 \times \text{Fatty Acids} \rightarrow \text{Triglyceride} + 3H_2O

CnH2nOn (General formula for monosaccharides)C_nH_{2n}O_n \text{ (General formula for monosaccharides)}

💡Examples

Problem 1:

Calculate the BMIBMI of a student who has a mass of 65 kg65\text{ kg} and a height of 1.75 m1.75\text{ m}. Determine the weight status based on the standard BMIBMI categories.

Solution:

BMI=651.752=653.0625≈21.22BMI = \frac{65}{1.75^2} = \frac{65}{3.0625} \approx 21.22

Explanation:

Using the formula BMI=massheight2BMI = \frac{mass}{height^2}, we divide 65 kg65\text{ kg} by the square of 1.75 m1.75\text{ m}. A BMIBMI of 21.2221.22 falls within the 'Normal weight' range (18.518.5 to 24.924.9).

Problem 2:

Compare the energy storage efficiency of 10 g10\text{ g} of fat versus 10 g10\text{ g} of glycogen.

Solution:

Energy from Fat=10 g×37 kJg−1=370 kJ\text{Energy from Fat} = 10\text{ g} \times 37\text{ kJg}^{-1} = 370\text{ kJ} Energy from Glycogen=10 g×17 kJg−1=170 kJ\text{Energy from Glycogen} = 10\text{ g} \times 17\text{ kJg}^{-1} = 170\text{ kJ}

Explanation:

Lipids (fats) contain more than twice as much energy per gram as carbohydrates (glycogen). Additionally, lipids are hydrophobic and do not require H2OH_2O for storage, whereas glycogen is stored with water, making lipids much more mass-efficient for long-term storage.

Problem 3:

Identify the type of reaction that occurs when a glucose molecule (C6H12O6C_6H_{12}O_6) and a fructose molecule (C6H12O6C_6H_{12}O_6) combine to form sucrose (C12H22O11C_{12}H_{22}O_{11}).

Solution:

Condensation reaction\text{Condensation reaction}

Explanation:

Two monosaccharides combine to form a disaccharide and one molecule of H2OH_2O. This is a condensation reaction because a water molecule is 'condensed' out to form the glycosidic bond.

Carbohydrates and Lipids - Revision Notes & Key Diagrams | IB Grade 11 Biology