Practice Exam For Cell Biology

Enzymes catalyze a chemical reaction by lowering the activation energy, which is the energy required to start the reaction. By lowering the activation energy, enzymes make it easier for the reactant molecules to reach the transition state, which is a high-energy intermediate that forms during the reaction. This transition state is crucial for the formation of the final product. Therefore, enzymes provide conditions favorable for the formation of this high-energy transition state, ultimately speeding up the reaction.

All of the above options are correct because proteins that have conserved amino acid sequences, conserved secondary structures, conserved tertiary structures, and similar functions are likely to be evolutionarily related. Conserved amino acid sequences indicate that these proteins have similar building blocks, which suggests a common ancestry. Conserved secondary structures and tertiary structures imply that these proteins have similar folding patterns, further supporting their evolutionary relationship. Additionally, proteins with similar functions are likely to have similar structures and sequences, as their function is determined by their structure. Therefore, all of the above options are valid explanations for the given answer.

Proteins can be regulated through various mechanisms such as allosteric regulation, feedback regulation, GTP-binding, and ATP-binding. Allosteric regulation involves the binding of a molecule to a site on the protein, which causes a conformational change and alters its activity. Feedback regulation occurs when the end product of a metabolic pathway inhibits an earlier step in the pathway. GTP-binding and ATP-binding are examples of proteins binding to these nucleotides, which can regulate their activity. Therefore, all of the mentioned options are ways in which proteins can be regulated.

The α helix and β sheet are formed by hydrogen bonding between atoms of the polypeptide backbone. In the α helix, the backbone forms a tightly coiled structure held together by hydrogen bonds between the carbonyl oxygen of one amino acid and the amide hydrogen of another amino acid, four residues away. In the β sheet, hydrogen bonds form between the carbonyl oxygen of one strand and the amide hydrogen of another strand, creating a sheet-like structure. These hydrogen bonds stabilize the secondary structures of proteins and are responsible for their stability and shape.

RNA in cells differ from DNA in that it is single stranded and can fold up into a variety of structures. Unlike DNA, which is typically double stranded, RNA exists as a single strand. This single-stranded nature allows RNA molecules to fold upon themselves and form intricate secondary and tertiary structures. These structures are crucial for RNA's various functions, such as catalyzing chemical reactions, regulating gene expression, and serving as a template for protein synthesis.

Prokaryotes are single-celled organisms that lack a nucleus and other membrane-bound organelles. They have a simple cell structure, with their DNA located in the cytoplasm rather than within a nucleus. The Golgi apparatus is a membrane-bound organelle involved in protein modification and transport, which is absent in prokaryotes. Therefore, the statement that prokaryotes have no Golgi apparatus is true.

Ef-Tu is an example of a GTP-binding protein. GTP-binding proteins, also known as G proteins, are involved in various cellular processes, including signal transduction and protein synthesis. Ef-Tu specifically plays a crucial role in protein synthesis by delivering aminoacyl-tRNA molecules to the ribosome during translation. It binds to GTP and undergoes conformational changes, allowing it to interact with other components of the translation machinery. Therefore, Ef-Tu is a prime example of a GTP-binding protein due to its involvement in protein synthesis and its ability to bind to GTP.

The correct answer is "enzyme performance." KM, or Michaelis constant, is a measure of how well an enzyme performs in converting substrate into product. It represents the concentration of substrate at which the enzyme is working at half of its maximum velocity. A lower KM value indicates a higher affinity between the enzyme and substrate, resulting in better enzyme performance.

The genetic code consists of 64 codons. This means that there are 64 different combinations of three nucleotides (A, T, G, and C) that can specify an amino acid or serve as stop signals. Each codon codes for a specific amino acid or a stop signal, allowing the correct sequence of amino acids to be determined during protein synthesis.