Biological Molecules

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Questions and Answers

Describe how the unique chemical properties of lipids, specifically their hydrophobic nature, contribute to the formation and maintenance of cellular membranes. Also explain how different types of lipids (e.g., phospholipids, cholesterol) contribute to the membrane's structure and fluidity?

The hydrophobic tails of lipids spontaneously assemble to exclude water, forming a bilayer. Phospholipids create the basic bilayer structure, while cholesterol modulates membrane fluidity by inserting itself into the bilayer.

Explain the role of condensation (dehydration) reactions in the formation of biological polymers. Provide specific examples of how these reactions occur in the synthesis of proteins, carbohydrates, and nucleic acids.

Condensation reactions remove a water molecule to link monomers. In proteins, amino acids form peptide bonds; in carbohydrates, sugars form glycosidic bonds; and in nucleic acids, nucleotides form phosphodiester bonds, all via dehydration.

The structures of both carbohydrates and proteins are closely tied to their functions within a cell. Compare and contrast how the specific arrangements and properties of their monomeric units (sugars and amino acids, respectively) dictate their diverse roles in cellular processes.

Carbohydrates' ring structures and hydroxyl groups make them ideal for energy storage and cell recognition. Proteins' diverse amino acid side chains allow for complex 3D structures that enable enzymatic catalysis, structural support, and signaling.

How do the properties of phosphodiester bonds contribute to the stability and function of DNA and RNA molecules, particularly in the context of genetic information storage and transfer?

Phosphodiester bonds link nucleotides, creating a stable backbone for DNA and RNA. Their specific arrangement allows for the encoding of genetic information, and their ability to be cleaved enables replication and transcription. Signup and view all the answers

Describe the roles that carbohydrates, proteins, and lipids play in the structure of the plasma membrane of a cell.

Lipids, specifically phospholipids, form the basic bilayer structure of the membrane. Proteins are embedded in or associated with the membrane to transport molecules or receive signals as well as provide structural support. Carbohydrates are involved in cell surface recognition and serve as a protective layer. Signup and view all the answers

Explain why humans can digest starch but not cellulose, referencing the specific types of glycosidic linkages involved.

Humans possess enzymes capable of hydrolyzing the alpha (α) glycosidic linkages present in starch. However, we lack enzymes that can break the beta (β) glycosidic linkages found in cellulose. Signup and view all the answers

Describe the amphipathic nature of phospholipids and how this property contributes to their function in cell membranes.

Phospholipids have a polar (hydrophilic) head and nonpolar (hydrophobic) tail, making them amphipathic. This allows them to form bilayers in aqueous solutions, which is the structural basis of cell membranes. Signup and view all the answers

In Tay-Sachs disease, the accumulation of GM2 ganglioside leads to neurodegeneration. Explain the underlying enzymatic defect and why this accumulation is particularly damaging to neurons.

A mutation in β-hexosaminidase A prevents the proper metabolism of GM2 ganglioside, leading to its accumulation. This accumulation is particularly damaging to neurons because interferes with cell-cell communication and neuronal plasticity. Signup and view all the answers

Describe the general chemical structure of an amino acid, highlighting the key components that contribute to its unique properties and its role as a building block of proteins.

Amino acids have a central carbon bonded to an amino group (NH2), a carboxyl group (COOH), a hydrogen atom, and a variable R-group. The R-group determines the amino acid's unique properties and its contribution to protein structure and function. Signup and view all the answers

How do the chemical features of triglycerides make them suitable for energy storage?

Triglycerides consist of glycerol and three fatty acids that feature hydrocarbon chains with polar COOH at one end. The long hydrocarbon chains enable efficient energy storage, as their oxidation yields a high amount of ATP. Moreover, their hydrophobic nature allows them to be stored in anhydrous form, maximizing energy density. Signup and view all the answers

Phospholipids contain both polar and nonpolar regions, making them amphipathic. How does this dual nature facilitate the formation of cellular membranes?

The amphipathic nature of phospholipids allows them to spontaneously form lipid bilayers in aqueous environments. The hydrophobic tails cluster inward, away from water, while the hydrophilic heads face outward, interacting with the aqueous surroundings. This arrangement creates a stable barrier that forms the basis of cellular membranes. Signup and view all the answers

Tay-Sachs disease involves the accumulation of GM2 ganglioside in neurons. What are the functional consequences of this accumulation, and why are neurons particularly vulnerable?

The accumulation of GM2 ganglioside disrupts normal cellular processes, particularly in neurons. This disruption leads to neurodegeneration and impairs cell-cell communication as well as neuronal plasticity. Neurons depend heavily on proper signalling pathways, leading to severe impairments in cellular function. Signup and view all the answers

Amino acids possess a uniform chemical backbone combined with variable R groups. Explain how this structural feature gives rise to the diverse range of protein structures and functions.

The uniform backbone allows for the formation of peptide bonds to create polypeptide chains. The immense diversity in protein structures and functions arise because the R-groups vary in size, shape, charge, hydrophobicity, and chemical reactivity, enabling different amino acids to impart distinct properties to the protein, influencing its folding, stability, and interactions. Signup and view all the answers

Consider a hypothetical polysaccharide composed of alternating glucose and galactose residues, linked β(1→4). If an enzyme can hydrolyze β(1→4) linkages, but only when both sugars are identical, explain why this polysaccharide would be resistant to breakdown by that enzyme.

The enzyme requires identical sugars on both sides of the β(1→4) linkage to hydrolyze it. Since glucose and galactose alternate, the enzyme cannot find a continuous sequence of either sugar to effectively bind and cleave the polysaccharide. Signup and view all the answers

Imagine a newly discovered disaccharide composed of two glucose molecules linked α(1→6). Predict how its digestibility and glycemic impact might differ from that of maltose, which is glucose α(1→4) glucose. Justify your prediction.

The α(1→6) linkage in the new disaccharide is likely to result in slower hydrolysis compared to the α(1→4) linkage in maltose. This is because the α(1→6) linkage creates more steric hindrance, potentially making it harder for digestive enzymes to access and cleave the bond, leading to a lower glycemic response compared to maltose. Signup and view all the answers

A researcher is synthesizing a novel polysaccharide using enzymatic polymerization. They observe that the resulting polymer is highly branched, even though they are using a single type of monosaccharide and a single enzyme. Propose a reason for this outcome, considering the properties of sugar molecules.

The single monosaccharide likely has multiple hydroxyl (OH) groups available for glycosidic bond formation. The enzyme, while specific, may be capable of forming linkages at different positions (e.g., 1→4, 1→6) on the sugar, leading to branching at multiple points along the polysaccharide chain. Signup and view all the answers

Consider two polysaccharides: one is a linear polymer of glucose with β(1→4) linkages, and the other is a branched polymer of glucose with both α(1→4) and α(1→6) linkages. Explain how their structural differences would affect their physical properties (e.g., solubility, flexibility).

The linear β(1→4) linked polymer will likely be less soluble and more rigid due to its ability to form extensive hydrogen bonds between chains, resulting in a crystalline structure. The branched α(1→4) and α(1→6) linked polymer will be more soluble and flexible because the branches disrupt the chain packing, reducing crystallinity and increasing water accessibility. Signup and view all the answers

If you were designing a modified starch with the goal of creating a slow-release carbohydrate source, what specific changes to the starch's structure (branching, type of glycosidic linkages) would you consider implementing and why?

To create a slow-release carbohydrate, I would increase the proportion of α(1→6) linkages to create more branching and also incorporate some β(1→4) linkages. Increased branching provides more ends for enzymatic degradation but also introduces steric hindrance that slows down the overall process. The β(1→4) linkages would be more resistant to common amylases, further slowing digestion and release of glucose. Signup and view all the answers

Considering the chemical properties of amino acid side chains, how does the cellular environment (pH, ionic strength) influence the tertiary structure and function of a protein, and what implications does this have for protein-protein interactions?

Cellular environment (pH, ionic strength) strongly influences protein tertiary structure and function by affecting the ionization state and interactions of amino acid side chains, thus altering protein folding and stability. This, in turn, affects protein-protein interactions as binding interfaces and affinities are modulated by these environmental factors. Signup and view all the answers

How does the structural uniformity of nucleotides, particularly in the context of ATP, contribute to its role as a versatile short-term energy carrier?Elaborate on the chemical features that allow ATP to be used in a wide array of cellular processes.

The uniform chemical structure of nucleotides, especially ATP, facilitates its role as a versatile energy carrier by providing a consistent framework for enzymatic recognition and binding. Chemical features such as the high-energy phosphate bonds and the ability to be easily hydrolyzed contribute to ATP's broad applicability in cellular processes. Signup and view all the answers

In the context of maintaining order within a cell against the universal tendency towards disorder, describe the role of coupled reactions, particularly those involving ATP hydrolysis, in driving thermodynamically unfavorable processes.

Coupled reactions, especially involving ATP hydrolysis, drive thermodynamically unfavorable processes by utilizing the energy released from ATP breakdown to provide the necessary energy input for the unfavorable reaction to proceed. This energy coupling allows cells to create and maintain order. Signup and view all the answers

Given the list of ionizable amino acids, predict how changes in intracellular pH, caused by a cellular stress such as hypoxia, could affect the activity of an enzyme that relies on histidine residues at its active site for catalysis.

Changes in intracellular pH due to hypoxia can alter the protonation state of histidine residues at an enzyme's active site. If histidine is crucial for substrate binding or catalysis, alterations in its charge state can disrupt enzyme-substrate interactions, leading to a decrease or complete loss of enzyme activity. Signup and view all the answers

How does the cell leverage the polar, charged nature of nucleotides beyond energy transfer, particularly in the context of signal transduction pathways?

Beyond energy transfer, the polar, charged nature of nucleotides is leveraged in signal transduction pathways by facilitating protein-protein interactions, serving as signaling molecules (e.g., cAMP), and modulating enzyme activities through phosphorylation or nucleotide binding. Signup and view all the answers

Considering the diverse roles of amino acids, explain how post-translational modifications, such as phosphorylation or glycosylation, can modulate protein function beyond what is dictated by the primary amino acid sequence.

Post-translational modifications modulate protein function beyond the primary sequence by altering protein folding, stability, and interactions. Phosphorylation can change a protein’s charge and binding affinities, glycosylation can affect protein localization and recognition—fundamentally influencing a protein's activity, localization, and interactions independently of the original sequence. Signup and view all the answers

Describe the trade-offs a cell must manage when investing energy to create order. What mechanisms balance maintaining a low entropy state with the need to carry out diverse and sometimes energetically unfavorable reactions?

Cells balance maintaining a low entropy state with carrying out diverse reactions through coupled reactions, energy carriers like ATP, and compartmentalization. These mechanisms enable cells to perform energetically unfavorable reactions while efficiently managing overall energy expenditure and preventing excessive disorder. Signup and view all the answers

Flashcards

Biological Molecules

Small carbon-based molecules that form the building blocks of cells; the same across all living species.

Monomers and Polymers

Polymers constructed from smaller subunit molecules; the smaller molecules are called monomers.

Carbohydrates

Sugars that serve as energy storage and structural support for cells.

Lipids

Composed of fatty acids linked to glycerol, they are used for energy storage and to build membranes.