Lipids Structure and Function
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Questions and Answers

What structure is formed by the complementary base pairing in RNA?

  • Alpha helix
  • Double helix
  • Beta sheet
  • Hairpin loop (correct)

    • Which of the following statements is true regarding DNA as an information molecule?

  • DNA can catalyze chemical reactions
  • Sequence of bases does not convey meaning
  • DNA is less stable than RNA
  • DNA carries information for cell growth and reproduction (correct)

    • Which characteristic makes RNA more diverse than DNA?

  • RNA is composed only of single strands
  • RNA is always double-stranded
  • RNA can catalyze reactions (correct)
  • RNA contains only uracil

    • What contributes to the stability of the DNA double helix structure?

    <p>Hydrophobic interactions</p> Signup and view all the answers

    What is one key role of the negatively charged phosphate groups in DNA?

    <p>They make DNA hydrophilic overall.</p> Signup and view all the answers

    What role do hydrophilic heads and hydrophobic tails play in the formation of lipid bilayers?

    <p>Hydrophilic heads interact with water and hydrophobic tails face each other.</p> Signup and view all the answers

    What effect does the presence of double bonds in the hydrocarbon tails of phospholipids have on membrane permeability?

    <p>Prevents close packing of hydrocarbon tails, resulting in increased membrane permeability.</p> Signup and view all the answers

    How does the length of the hydrocarbon tail affect membrane permeability?

    <p>Longer tails decrease permeability due to tighter packing of the phospholipids.</p> Signup and view all the answers

    What is the impact of adding cholesterol to a membrane composed of phospholipids?

    <p>Cholesterol increases the density of the hydrophobic section, reducing permeability.</p> Signup and view all the answers

    Which type of substances typically crosses a phospholipid bilayer most rapidly?

    <p>Small nonpolar molecules.</p> Signup and view all the answers

    What is the primary function of carbohydrates in plants during photosynthesis?

    <p>To store chemical energy</p> Signup and view all the answers

    Which type of linkage forms when a fatty acid is bonded to glycerol?

    <p>Ester linkages</p> Signup and view all the answers

    What structural feature distinguishes steroids from other types of lipids?

    <p>A bulky, four-ring structure</p> Signup and view all the answers

    What major role do phospholipids play in cells?

    <p>Cell membrane formation</p> Signup and view all the answers

    Which of the following carbohydrates is primarily used for energy storage in animals?

    <p>Glycogen</p> Signup and view all the answers

    Which property makes lipids primarily hydrophobic?

    <p>High proportion of nonpolar C–C and C–H bonds</p> Signup and view all the answers

    What is a characteristic of unsaturated fatty acids?

    <p>They form triglycerides that are liquid and can be oils.</p> Signup and view all the answers

    Which polysaccharide is known for providing structural support in plant cell walls?

    <p>Cellulose</p> Signup and view all the answers

    What distinguishes a deoxyribonucleotide from a ribonucleotide?

    <p>Deoxyribonucleotide has an H at the 2′ carbon.</p> Signup and view all the answers

    Which bases are classified as pyrimidines?

    <p>Cytosine, Thymine, and Uracil</p> Signup and view all the answers

    What type of bond forms the backbone of nucleic acid chains?

    <p>Phosphodiester bond</p> Signup and view all the answers

    What does Chargaff’s rule state about the relationship between purines and pyrimidines in DNA?

    <p>The number of adenine equals the number of thymine, and cytosine equals guanine.</p> Signup and view all the answers

    Which of the following statements accurately describes the structure of DNA?

    <p>Complementary bases pair as A - T and C - G.</p> Signup and view all the answers

    What describes the directionality of nucleic acid strands?

    <p>Sequences are written in a 5′ to 3′ direction.</p> Signup and view all the answers

    Who contributed to the understanding of DNA's structure through X-ray crystallography?

    <p>Rosalind Franklin and Maurice Wilkins</p> Signup and view all the answers

    Which statement correctly describes the difference between RNA and DNA?

    <p>RNA uses ribose sugar, while DNA uses deoxyribose.</p> Signup and view all the answers

    What role do carbohydrates play in cells?

    <p>Involved in cell recognition and identity</p> Signup and view all the answers

    Which polysaccharide is found in the bacterial cell wall?

    <p>Peptidoglycan</p> Signup and view all the answers

    What type of linkages can form in starch?

    <p>Both α-1,4-glycosidic and α-1,6-glycosidic linkages</p> Signup and view all the answers

    What happens to glycosidic linkages during the process of hydrolysis?

    <p>They are broken</p> Signup and view all the answers

    Why are carbohydrates considered hydrophilic?

    <p>Due to polar carbonyl and hydroxyl groups</p> Signup and view all the answers

    What is the significance of glycoproteins and glycolipids in terms of cell function?

    <p>They play a role in cell recognition and signaling.</p> Signup and view all the answers

    Which carbohydrate is a storage polysaccharide in animals?

    <p>Glycogen</p> Signup and view all the answers

    What key feature differentiates the structural role of cellulose from starch?

    <p>Cellulose has β-1,4-glycosidic linkages while starch has α-linkages.</p> Signup and view all the answers

    What does the term 'hydroxyl group' refer to in carbohydrates?

    <p>A functional group with the formula –OH</p> Signup and view all the answers

    Study Notes

    Lipids Structure and Function

    • Lipids are largely nonpolar and hydrophobic, meaning they repel water.
    • This is due to their high proportion of nonpolar C–C and C–H bonds.
    • A fatty acid is a hydrocarbon chain attached to a carboxyl (–COOH) functional group.
    • Fatty acids can be saturated or unsaturated.

    Types of Lipids Found in Cells

    • Lipids are characterized by their insolubility in water, not a shared chemical structure.
    • This insolubility is based on the high proportion of nonpolar C–C and C–H bonds.

    Fats

    • Made of 3 fatty acids linked to glycerol.
    • Also called triglycerides.
    • When their fatty acids are polyunsaturated, they are liquid and form oils.
    • Their primary role is energy storage.
    • Fats form by dehydration reactions between the hydroxyl group of glycerol and the carboxyl group of a fatty acid (ester linkage).

    Steroids

    • Distinguished by a bulky, four-ring structure.
    • Steroids differ from one another by the functional groups attached to the carbons in the rings.
    • Examples: Hormones such as estrogen and testosterone, cholesterol.

    Phospholipids

    • They contain two hydrocarbon chains.
    • They are amphipathic: meaning they contain hydrophilic and hydrophobic regions.
    • Phospholipids primarily form cell membranes.

    Phospholipid Bilayer

    • The hydrophilic heads face the solution.
    • The hydrophobic tails face one another.
    • The formation of a bilayer is spontaneous and requires no energy.
    • Bilayers have selective permeability which means that small molecules move across quickly.
    • Nonpolar molecules also move across quickly.
    • Charged or large polar substances cross slowly or not at all.

    How Does Lipid Structure Affect Membrane Permeability?

    • Number of double bonds in the phospholipid’s hydrophobic tail: Double bonds in a hydrocarbon chain prevent close packing of the tails which makes membranes more permeable.
    • Length of the hydrocarbon tail: Longer hydrocarbon tails make membranes less permeable.
    • Number of cholesterol molecules in the membrane: Adding cholesterol increases the density of the hydrophobic section, which decreases membrane permeability.

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    Related Documents

    BLG143 2024 Lecture Notes on Nucleic Acids PDF

    Description

    Explore the essential aspects of lipids, including their structure, types, and functions in biological systems. Understand the differences between fatty acids, triglycerides, and steroids, as well as their roles in energy storage and cellular functions.

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