Cell Biology flashcards

Question 1

Which of the following statements best describes the role of weak interactions in biological systems?

Accepted Answer

They allow for dynamic interactions, flexibility, and reversibility in biological molecules.

Question 2

A segment of DNA contains 150 base pairs. If 40% of these base pairs are Guanine-Cytosine (G-C) pairs, how many hydrogen bonds are present in this segment?

Accepted Answer

First, calculate the number of G-C pairs: 150 base pairs * 0.40 = 60 G-C pairs. Each G-C pair has 3 hydrogen bonds, so 60 * 3 = 180 hydrogen bonds from G-C pairs. Next, calculate the number of Adenine-Thymine (A-T) pairs: 150 - 60 = 90 A-T pairs. Each A-T pair has 2 hydrogen bonds, so 90 * 2 = 180 hydrogen bonds from A-T pairs. The total number of hydrogen bonds is 180 + 180 = 360 hydrogen bonds.

Question 3

Distinguish between the O-H bonds within a water molecule and the hydrogen bonds that form between different water molecules.

Accepted Answer

The O-H bonds within a single water molecule are covalent bonds, formed by the sharing of electrons between oxygen and hydrogen atoms. In contrast, hydrogen bonds occur between different water molecules, representing an attractive force between a hydrogen atom covalently bonded to an electronegative atom (like oxygen) and another electronegative atom on a separate molecule.

Question 4

Explain how hydrogen bonds contribute to the unique properties of water and their significance in biological contexts.

Accepted Answer

Hydrogen bonds between water molecules are responsible for many of water's unique properties, such as its high boiling point, cohesion, surface tension, and excellent solvent capabilities. Biologically, these properties are vital for maintaining cellular environments, facilitating nutrient transport, and regulating temperature within organisms.

Question 5

A scientist is studying a newly discovered protein that maintains its tertiary structure even under conditions that typically disrupt hydrogen bonds. Which of the following interactions is most likely playing a significant role in stabilizing this protein's tertiary structure under these conditions?

Accepted Answer

Ionic interactions (salt bridges), which are stronger than hydrogen bonds.

Question 6

Describe the nature of Van der Waals forces and their biological importance, particularly considering their individual weakness.

Accepted Answer

Van der Waals forces are weak attractions caused by temporary fluctuations in electron distribution, occurring between all atoms and molecules, even non-polar ones. Individually, they are extremely weak and effective only at very short distances. However, their biological importance arises when thousands occur simultaneously, contributing significantly to the stabilization of protein folding, cell membranes, and molecular recognition processes.

Question 7

Which of the following interactions is incorrectly matched with its primary biological role?

Accepted Answer

Hydrophobic interactions: Primary structure of proteins

Question 8

Explain why G-C base pairs are considered stronger than A-T base pairs in DNA structure.

Accepted Answer

G-C base pairs are stronger than A-T base pairs because they form three hydrogen bonds, whereas A-T base pairs form only two hydrogen bonds. The greater number of hydrogen bonds in G-C pairs results in a more stable interaction, requiring more energy to separate.

Question 9

A researcher observes that a particular enzyme loses its specific 3D shape and function when exposed to a non-polar solvent. This suggests the disruption of which type of weak interaction that is crucial for maintaining the protein's folded structure?

Accepted Answer

Hydrophobic interactions, which drive non-polar molecules to avoid water.

Question 10

Define a hydrogen bond and list the electronegative atoms commonly involved in its formation.

Accepted Answer

A hydrogen bond forms when a hydrogen atom covalently bonded to an electronegative atom is attracted to another electronegative atom. The electronegative atoms usually involved in hydrogen bonding are oxygen (O), nitrogen (N), and fluorine (F).

Question 11

A protein's primary structure is maintained by what type of chemical bond?

Accepted Answer

The primary structure of a protein, which refers to the linear sequence of amino acids, is maintained by covalent peptide bonds. These strong bonds link individual amino acids together to form the polypeptide chain.

Question 12

Which of the following accurately describes the relative strengths of chemical bonds and weak interactions from strongest to weakest?

Accepted Answer

Covalent bond > Ionic bond > Hydrogen bond > Van der Waals forces

Question 13

How do multiple weak interactions collectively contribute to the stability of biological structures, despite a single weak interaction being easily broken?

Accepted Answer

While a single weak interaction can be easily broken, the cumulative effect of many weak interactions acting together creates strong and stable biological structures. This allows for both the necessary stability and the flexibility and reversibility required for dynamic biological processes.

Question 14

Consider a scenario where a drug is designed to inhibit an enzyme by binding to its active site. Which type of weak interaction would be most critical for the initial recognition and reversible binding of the drug to the enzyme, assuming the drug is non-polar?

Accepted Answer

Van der Waals forces, effective at short distances for non-polar interactions.

Question 15

What is the primary difference between hydrophobic interactions and other weak interactions like hydrogen bonds or ionic interactions?

Accepted Answer

The primary difference is that hydrophobic interactions are not actual chemical bonds. Instead, they result from the tendency of non-polar molecules to avoid water, leading to their aggregation and the exclusion of water molecules. This is distinct from hydrogen bonds (attraction between electronegative atoms and H) and ionic interactions (attraction between oppositely charged ions), which are direct attractive forces.

Question 16

Which of the following statements best describes the primary structure of an enzyme?

Accepted Answer

The linear sequence of amino acids in the polypeptide chain, encoded by a gene.

Question 17

Explain the concept of 'specificity' in enzyme function and how it relates to the active site.

Accepted Answer

Enzyme specificity means that each enzyme typically catalyzes only one specific reaction or a limited set of closely related reactions. This high specificity arises from the precise arrangement of amino acids within the enzyme's active site, which allows it to interact selectively with specific substrate molecules, much like a 'lock and key' mechanism.

Question 18

A researcher is studying a novel enzyme that functions optimally at 30°C and a pH of 7.0. If they conduct an experiment where the temperature is raised to 50°C, what would be the expected effect on the enzyme's activity and why?

Accepted Answer

Raising the temperature to 50°C, significantly above the enzyme's optimum of 30°C, would likely lead to a decrease in enzyme activity, or even complete loss of function. This is because high temperatures can break the bonds holding the enzyme's specific three-dimensional shape, particularly around the active site, causing it to denature. Once denatured, the substrate can no longer fit into the active site, and the enzyme cannot regain its proper activity.

Question 19

Consider an enzyme that catalyzes a reaction with a rate of 0.5 µmol/min at 25°C. If the enzyme has an optimal temperature of 37°C and a Q10 value of 2 (meaning the reaction rate doubles for every 10°C increase in temperature within its functional range), what would be the approximate reaction rate...

Accepted Answer

To calculate the approximate reaction rate at 35°C: The temperature increases by 10°C (from 25°C to 35°C). With a Q10 value of 2, the reaction rate would double. Therefore, the approximate reaction rate at 35°C would be 0.5 µmol/min * 2 = 1.0 µmol/min.

Question 20

Define 'metabolic reactions' and explain the critical role enzymes play in sustaining life through these reactions.

Accepted Answer

Metabolic reactions encompass all the chemical reactions that occur within a cell or organism to keep it alive. Enzymes are crucial for sustaining life because they act as biological catalysts, significantly speeding up the rate of these metabolic reactions. Without enzymes, these reactions would proceed too slowly to support life, as exemplified by the digestion of a meal taking weeks instead of hours.

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