Molecular biology flashcards

Molecular biology explores the chemical basis of life, focusing on the structure and function of biological molecules. Students must understand the properties of water and its biological importance, the structure of carbohydrates, lipids, proteins and nucleic acids, and how these molecules are built through condensation reactions and broken down by hydrolysis. A key area is DNA structure, replication, transcription and translation, including the role of enzymes such as DNA polymerase and RNA polymerase. Students must also understand enzyme function, including the induced fit model, factors affecting enzyme activity, and the role of inhibitors. Cellular respiration and photosynthesis are examined at the biochemical level, covering glycolysis, the Krebs cycle, the light-dependent and light-independent reactions, and the role of ATP as an energy currency throughout metabolism.

1. Card 1

   What type of reaction joins monomers together to form polymers in biological molecules?

   A condensation reaction, which releases a molecule of water each time two monomers are joined by a covalent bond.

2. Card 2

   Describe the induced fit model of enzyme action.

   The active site changes shape slightly when the substrate binds, creating a tighter fit that strains bonds in the substrate and lowers the activation energy of the reaction.

3. Card 3

   What are the four levels of protein structure?

   Primary (amino acid sequence), secondary (alpha helix or beta pleated sheet), tertiary (3D folding), and quaternary (multiple polypeptide chains together).

4. Card 4

   What is the difference between a saturated and an unsaturated fatty acid?

   A saturated fatty acid has no carbon-carbon double bonds; an unsaturated fatty acid has one or more double bonds, causing kinks that lower the melting point.

5. Card 5

   State the complementary base pairs found in DNA.

   Adenine pairs with thymine, and cytosine pairs with guanine, held together by hydrogen bonds between the two antiparallel strands of the double helix.

6. Card 6

   What is the role of DNA polymerase during DNA replication?

   DNA polymerase adds complementary nucleotides to the template strand in the 5' to 3' direction, producing two identical copies via semi-conservative replication.

7. Card 7

   Distinguish between transcription and translation.

   Transcription produces mRNA from a DNA template in the nucleus; translation uses the mRNA sequence to assemble a polypeptide at the ribosome.

8. Card 8

   What is the role of ATP in cellular metabolism?

   ATP (adenosine triphosphate) acts as the universal energy currency, releasing energy when hydrolysed to ADP and inorganic phosphate to drive cellular processes.

9. Card 9

   Where does glycolysis occur and what are its products?

   Glycolysis occurs in the cytoplasm and converts one glucose into two molecules of pyruvate, producing a net gain of 2 ATP and 2 NADH.

10. Card 10

    What is the difference between competitive and non-competitive enzyme inhibition?

    A competitive inhibitor blocks the active site directly; a non-competitive inhibitor binds elsewhere, changing the active site shape so substrate cannot bind effectively.

11. Card 11

    What happens during the light-independent reactions of photosynthesis?

    In the Calvin cycle, CO2 is fixed by RuBisCO and reduced using ATP and NADPH to produce G3P, which is used to regenerate RuBP and synthesise organic molecules.

12. Card 12

    Why is water described as a polar molecule and why does this matter biologically?

    Unequal sharing of electrons creates partial charges, making water polar. This allows hydrogen bonds to form, giving water high specific heat capacity and cohesion.

• Students often confuse transcription and translation, incorrectly stating that DNA is directly converted into protein without the intermediate mRNA stage.
• A common error is claiming that enzymes are destroyed or permanently changed after a reaction, when in fact they are biological catalysts that remain unchanged and can be reused.
• Many students incorrectly state that all lipids are hydrophobic, forgetting that phospholipids have a hydrophilic phosphate head, which is essential for understanding membrane structure.

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