C889 Molecular and Cellular Biology
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Free C889 Molecular and Cellular Biology Questions
1. Explain the significance of the tertiary structure in proteins and how it differs from the secondary structure.
- Tertiary structure is the overall three-dimensional shape, while secondary structure involves local folding patterns like alpha helices and beta sheets.
- Tertiary structure is the linear arrangement of amino acids, while secondary structure is the association of multiple polypeptides.
- Tertiary structure is the spatial organization of amino acids, while secondary structure refers to the overall shape of the protein.
- Tertiary structure is the combination of different proteins, while secondary structure is the sequence of amino acids.
Explanation
The tertiary structure of a protein refers to its overall three-dimensional shape, which is stabilized by interactions among the side chains of amino acids, such as hydrogen bonds, disulfide bridges, ionic bonds, and hydrophobic interactions. This structure is critical because it determines the protein’s functional properties, including binding, enzymatic activity, and interactions with other molecules. In contrast, the secondary structure involves local folding patterns of the polypeptide chain, primarily alpha helices and beta sheets, which contribute to the protein’s stability but do not define its complete 3D conformation.
2. If a scientist were to disrupt the process of cell differentiation in a developing embryo, what potential effects might this have on the organism?
- The organism would likely develop normally with no effects.
- The organism may have improperly formed tissues and organs, leading to developmental issues.
- The organism would only experience changes in its reproductive cells.
- The organism would become entirely composed of unspecialized cells.
Explanation
Cell differentiation is the process by which unspecialized cells become specialized to perform specific functions, forming tissues and organs in a developing organism. Disrupting this process can prevent proper tissue and organ formation, leading to developmental abnormalities and potentially non-viable offspring. While all cells might not remain entirely unspecialized, the failure of differentiation can severely impact the organism’s overall structure and function, highlighting the critical role of this process in embryonic development.
3. Explain how the presence of a nucleus in eukaryotic cells contributes to their complexity compared to prokaryotic cells.
- It allows for the storage of genetic information in a protected environment.
- It enables eukaryotic cells to reproduce faster than prokaryotic cells.
- It prevents eukaryotic cells from undergoing differentiation.
- It eliminates the need for membrane-bound organelles.
Explanation
The nucleus in eukaryotic cells serves as a protected compartment for storing genetic material (DNA), separating transcription and replication from the rest of the cytoplasm. This organization allows for more precise regulation of gene expression, complex control over cellular processes, and coordination of activities that support the larger size and functional diversity of eukaryotic cells. The presence of a nucleus, along with other membrane-bound organelles, contributes to the overall complexity of eukaryotic cells compared to prokaryotic cells, which lack these internal compartments.
4. Explain how amino acids are linked together to form proteins and the significance of this process.
- Amino acids are linked by hydrogen bonds, which stabilize protein structure.
- Amino acids are polymerized through condensation reactions to form peptide bonds, which are crucial for protein structure.
- Amino acids are synthesized in the nucleus and then transported to the ribosomes.
- Amino acids are converted into carbohydrates before being assembled into proteins.
Explanation
Amino acids are linked together through condensation reactions that form peptide bonds, which involve the removal of a water molecule between the carboxyl group of one amino acid and the amino group of the next. This process creates a polypeptide chain, which is the primary structure of a protein. The sequence of amino acids determines the protein’s folding and function, making peptide bond formation critical for the structure and biological activity of proteins. Proper assembly of amino acids into polypeptides is essential for enzymatic activity, cellular signaling, structural support, and numerous other cellular functions.
5. What does the endosymbiosis theory propose about the origin of eukaryotic cells?
- Eukaryotic cells evolved from prokaryotic cells through a series of mutations.
- Eukaryotic cells originated from the fusion of multiple prokaryotic cells.
- Eukaryotic cells originated through a symbiotic relationship between different species.
- Eukaryotic cells are a result of spontaneous generation in primordial soup.
Explanation
The endosymbiosis theory suggests that eukaryotic cells arose when certain prokaryotic cells established symbiotic relationships within other cells. For example, mitochondria and chloroplasts are believed to have originated as free-living bacteria that were engulfed by ancestral eukaryotic cells, leading to mutual benefits. This theory explains the presence of double membranes and their own DNA within these organelles. It does not involve spontaneous generation or simple mutations, but rather a cooperative evolutionary event.
6. Explain the significance of the presence of membrane-bound organelles in eukaryotic cells compared to prokaryotic cells.
- They allow for compartmentalization of cellular processes.
- They increase the size of the cell.
- They are responsible for cell division.
- They provide structural support to the cell.
Explanation
Membrane-bound organelles in eukaryotic cells, such as the nucleus, mitochondria, endoplasmic reticulum, and Golgi apparatus, enable compartmentalization of cellular processes. This separation allows different biochemical reactions to occur in specialized environments, increasing efficiency and regulation within the cell. For example, the nucleus houses genetic material and transcription processes, while mitochondria focus on energy production. Prokaryotic cells lack these organelles, so their processes occur in the cytoplasm, making compartmentalization a distinguishing feature of eukaryotes that enhances cellular complexity and functionality.
7. What is cell differentiation?
- The process by which cells can attach together to form a multicellular organism
- The process by which cells acquire different DNA sequences as they develop
- The process by which cells become specialized in different types
- The process by which cells express specific genes only when needed
Explanation
Cell differentiation is the process by which unspecialized cells, such as stem cells, develop into specialized cells with distinct structures and functions. This specialization enables the formation of tissues and organs with unique roles, such as muscle contraction, nerve signaling, or hormone secretion. Differentiation is critical for the development, growth, and maintenance of multicellular organisms, allowing cells to perform specific tasks efficiently. It does not involve changing DNA sequences or merely turning genes on or off, but rather the development of cell type-specific functions.
8. What is the role of DNA molecules in the synthesis of proteins?
- They catalyze the formation of bonds between amino acids.
- They determine the sequence of amino acids in a protein.
- They transfer amino acids from the cytoplasm to the nucleus.
- They supply energy for protein synthesis.
Explanation
DNA contains the genetic instructions for synthesizing proteins. The sequence of nucleotides in a gene dictates the order of amino acids in a polypeptide chain, which is ultimately expressed as a functional protein. This information is transcribed into RNA, which is then translated at ribosomes to assemble amino acids in the correct sequence. DNA does not directly catalyze bond formation, transport amino acids, or supply energy for synthesis; its primary role is informational.
9. Explain the difference in physical state and structure between saturated and unsaturated fatty acids.
- Saturated fatty acids are solid at room temperature due to their straight chains, while unsaturated fatty acids are liquid because of their kinks from double bonds.
- Saturated fatty acids are liquid at room temperature and have kinks, while unsaturated fatty acids are solid due to their straight chains.
- Both saturated and unsaturated fatty acids are solid at room temperature.
- Both types of fatty acids have the same structure and physical state.
Explanation
Saturated fatty acids have no double bonds between carbon atoms, resulting in straight hydrocarbon chains that pack closely together. This tight packing causes them to be solid at room temperature. Unsaturated fatty acids contain one or more double bonds, creating kinks in their chains that prevent close packing, making them liquid at room temperature. The presence or absence of double bonds directly influences the fatty acid’s structure and physical properties, which also affects membrane fluidity and the behavior of fats in biological systems.
10. Which cellular structure is absent in prokaryotic cells but present in eukaryotic cells?
- Cell membrane
- Ribosomes
- Nucleus
- Cytoplasm
Explanation
The nucleus is a membrane-bound organelle that houses the cell’s genetic material in eukaryotic cells. Prokaryotic cells lack a nucleus; their DNA is located in a nucleoid region that is not enclosed by a membrane. Both prokaryotic and eukaryotic cells have a cell membrane, ribosomes, and cytoplasm, but the presence of a true nucleus is a defining feature that distinguishes eukaryotes from prokaryotes.
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