Molecular Biology of the Cell MBC高等分細生U1-1

C) Tube worms (Riftia pachyptila)

Explanation: The giant tube worms, Riftia pachyptila, live in symbiosis with sulfur-oxidizing bacteria, which provide nourishment to the worms by harnessing geochemical energy.

B) A segment of DNA that corresponds to a single protein or RNA molecule.

Explanation: A gene is defined as a segment of DNA that encodes for a specific protein or RNA molecule, including variants and non-coding functions.

C) It guides the processes of DNA interpretation and copying

Explanation: The directionality of DNA strands is crucial for the consistent reading and copying of genetic information, similar to how text is read from left to right.

B) Ribose

Explanation: RNA contains ribose as its sugar component, while DNA contains deoxyribose, which is a key difference between the two nucleic acids.

B) By separating DNA strands and using them as templates

Explanation: The cell replicates its DNA by separating the paired strands and using each as a template for creating a new complementary DNA strand.

B) They carry amino acids to the ribosome and match them to codons in mRNA.

Explanation: tRNAs are responsible for bringing specific amino acids to the ribosome, where they recognize codons in mRNA through their anticodons.

B) A binds to T, and C binds to G

Explanation: The base-pairing rule states that adenine (A) pairs with thymine (T) and cytosine (C) pairs with guanine (G), which is crucial for the formation of complementary DNA strands during replication.

B) To guide the synthesis of proteins

Explanation: mRNA serves as an intermediary that carries genetic information from DNA to the ribosomes, where it guides the synthesis of proteins according to the genetic instructions.

C) By forming weak bonds with complementary segments

Explanation: RNA molecules can recognize and bind to other molecules by forming weak bonds with complementary segments of their own sequence, allowing for selective interactions.

C) They all are made of cells

Explanation: The text states that despite their diversity, all living organisms share the common feature of being made of cells.

B) Understanding cell evolution

Explanation: The text indicates that a deeper understanding of cells and their evolution is crucial for tackling the grand historical problems of life on Earth.

C) To gather raw materials and replicate hereditary information

Explanation: A single cell serves as the vehicle for hereditary information and has the machinery to gather raw materials from the environment to construct new cells in its own image.

B) Nucleotides

Explanation: Nucleotides are the monomers that make up DNA, consisting of a sugar, a phosphate group, and a nitrogenous base.

C) DNA

Explanation: All living cells on Earth store their hereditary information in the form of double-stranded DNA, which is a fundamental characteristic of cellular biology.

C) Replication

Explanation: DNA replication is the process by which a double-stranded DNA molecule is copied to produce two identical DNA molecules, ensuring the hereditary information is preserved.

C) Individual cell

Explanation: The individual cell is defined as the minimal self-reproducing unit of living matter, emphasizing its fundamental role in life.

B) They are the principal catalysts for chemical reactions

Explanation: Proteins serve as the principal catalysts for almost all chemical reactions in the cell, highlighting their essential role in cellular processes.

B) There is astonishing variety in individual particulars and astonishing constancy in fundamental mechanisms

Explanation: The text highlights a counterpoint in biology between the astonishing variety of individual organisms and the astonishing constancy of fundamental biological mechanisms.

B) Geochemical energy

Explanation: Organisms living near hydrothermal vents thrive on geochemical energy derived from reactions between available chemicals, forming a unique ecosystem powered by this energy source instead of sunlight.

B) To maintain the cell's integrity as a coordinated chemical system

Explanation: The plasma membrane is crucial for maintaining the integrity of the cell, allowing it to function as a coordinated chemical system by regulating what enters and exits.

B) They act as catalysts for chemical reactions

Explanation: Proteins function as catalysts in cells, facilitating various biochemical reactions, which is essential for maintaining cellular processes.

B) They provide a universal language for genetic information

Explanation: DNA sequences serve as a universal language for genetic information, allowing for the characterization and comparison of living organisms.

C) 100 million

Explanation: It is estimated that there are more than 10 million, perhaps up to 100 million living species on Earth today, highlighting the vast biodiversity present.

C) DNA

Explanation: All cells store their hereditary information in the same linear chemical code, which is DNA, making it a universal feature of life.

B) They convert nitrogen gas into usable nitrogen compounds

Explanation: Nitrogen-fixing bacteria play a crucial role in converting atmospheric nitrogen (N2) into forms that can be utilized by plants, which cannot fix nitrogen on their own.

B) Through templated polymerization

Explanation: Cells replicate their hereditary information by templated polymerization, where the sequence of nucleotides in an existing DNA strand guides the formation of a new strand.

C) They consist of both hydrophobic and hydrophilic parts

Explanation: Amphiphilic molecules have both hydrophobic (water-insoluble) and hydrophilic (water-soluble) components, allowing them to form structures like bilayers in aqueous environments.

C) Cell

Explanation: The text emphasizes that all living things are made of cells, which are described as the fundamental units of life, capable of growing and dividing.

B) By feeding on other living things or organic chemicals

Explanation: Living organisms obtain their free energy in various ways, including feeding on other living things or the organic chemicals they produce.

B) 64

Explanation: The number of distinct triplets (codons) that can be formed from four nucleotides is 4^3, which equals 64 possible codons.

B) By adjusting the rate of transcription and translation independently.

Explanation: Cells regulate gene expression by controlling the transcription and translation rates of different genes based on their needs, rather than producing all proteins continuously.

C) To guide the synthesis of proteins

Explanation: RNA plays a crucial role in expressing genetic information by guiding the synthesis of proteins through the processes of transcription and translation.

C) Flexible single-stranded backbone

Explanation: The single-stranded nature of RNA, along with its flexible backbone, allows it to bend and fold into specific shapes, which can be crucial for its function.

B) The structure, function, and behavior of cells

Explanation: Cell biology is defined in the text as the study of the structure, function, and behavior of cells, which is essential for understanding life.

D) 20

Explanation: There are 20 different types of amino acids that can be linked together to form proteins, unlike DNA and RNA which have only 4 types of nucleotides.

C) The phenomenon of heredity

Explanation: Heredity is central to the definition of life, distinguishing living organisms from non-living processes, as it involves the transmission of genetic information from parents to offspring.

C) Transcription

Explanation: Transcription is the first step in gene expression, where segments of DNA are used as templates to synthesize RNA molecules, which then guide protein synthesis.

C) Double-stranded DNA

Explanation: Every cell on our planet stores its genetic information in the same chemical form, which is double-stranded DNA.

B) They spontaneously aggregate to form bilayers

Explanation: Phospholipids, due to their amphiphilic nature, spontaneously aggregate in water to form bilayers, which are fundamental to the structure of cell membranes.

C) It forms the basis for self-replicating behavior in living organisms

Explanation: The feedback loop between proteins and polynucleotides is crucial for the autocatalytic and self-reproducing nature of living cells.

B) It specifies a single amino acid in a protein.

Explanation: Each triplet of nucleotides, or codon, in mRNA codes for a specific amino acid, which is essential for protein synthesis.

B) Hydrogen, Carbon, Nitrogen, Oxygen, Sulfur, Phosphorus

Explanation: DNA, RNA, and proteins are composed of six essential elements: hydrogen, carbon, nitrogen, oxygen, sulfur, and phosphorus, which are abundant in the nonliving environment.

C) DNA double helix

Explanation: The two strands of DNA twist around each other to form a double helix, which is a fundamental structure of DNA that allows for its stability and function.

B) They hold the two strands of DNA together

Explanation: Hydrogen bonds form between complementary bases on opposite strands of DNA, holding the two strands together in a double helix structure.

B) From sunlight

Explanation: Plants harness energy from sunlight to create their own small organic molecules, distinguishing their energy acquisition method from that of animals, which consume other living things.

B) To drive complex chemical processes specified by hereditary information

Explanation: Living organisms consume free energy to maintain their organization and to drive complex chemical processes that are dictated by their hereditary information.

B) Double-stranded with a sugar-phosphate backbone

Explanation: DNA is characterized by its double-stranded structure and a sugar-phosphate backbone, which provides stability and directionality.

C) Prokaryotic cells lack membrane-bound organelles

Explanation: Prokaryotic cells are characterized by their lack of membrane-bound organelles and a nucleus, distinguishing them from eukaryotic cells, which have these structures.

B) 300

Explanation: The minimum number of genes for a viable cell in contemporary environments is estimated to be around 300, indicating the complexity and essential functions required for life.

C) In deep ocean and inhospitable environments

Explanation: Lithotrophic organisms are mostly microscopic and inhabit extreme environments such as deep ocean floors and other areas that humans do not frequent.

B) It serves as a building block for DNA and RNA

Explanation: ATP (adenosine triphosphate) is crucial not only as a building block for DNA and RNA synthesis but also as a carrier of free energy needed for numerous chemical reactions in the cell.

B) They synthesize proteins

Explanation: Ribosomes are complex molecular machines that guide the synthesis of protein molecules, playing a crucial role in translation.

B) They specify the amino acid sequences of proteins

Explanation: Polynucleotides, such as DNA and RNA, contain the genetic information that dictates the sequence of amino acids in proteins.

B) Mycoplasma genitalium

Explanation: Mycoplasma genitalium is noted for having one of the smallest known genomes, with about 530 genes, and it serves as a model for understanding the minimal requirements for cellular life.

B) RNA contains uracil instead of thymine

Explanation: One of the distinguishing features of RNA is that it contains uracil (U) in place of thymine (T), which is found in DNA, affecting its structure and function.

D) Aerobic reactions

Explanation: Aerobic lithotrophs use molecular oxygen from the environment to derive energy, linking them to the products of past life, as atmospheric oxygen is a result of living organisms.

D) 400 genes

Explanation: The simplest known cells can survive with about 400 genes, indicating the minimal genetic requirements for life.

B) They are enclosed by a plasma membrane

Explanation: All cells are enclosed by a plasma membrane, which acts as a selective barrier, allowing the concentration of nutrients and retention of products, a fundamental characteristic of cellular structure.

C) Amino acids

Explanation: Amino acids are the monomers of proteins, differing from the monomers of DNA and RNA, which are nucleotides.

C) Catalyze chemical reactions

Explanation: Proteins act as enzymes to catalyze reactions, directing the majority of chemical processes in the cell.

C) Phototrophic

Explanation: Phototrophic organisms are those that harvest energy from sunlight, playing a crucial role in the ecosystem and contributing to the oxygen in the Earth's atmosphere.

C) Oxygen

Explanation: The oxygen in the Earth's atmosphere is a by-product of the biosynthetic activities of phototrophic organisms, which include bacteria, algae, and plants.

C) A sequence of amino acids

Explanation: A polypeptide is created by joining amino acids in a specific sequence, forming the structure of proteins.

B) Lithotrophic

Explanation: Lithotrophic organisms capture energy from energy-rich inorganic chemicals in their environment, making them essential for certain ecosystems, especially in extreme habitats.

C) How it specifies protein production

Explanation: In the 1950s, the mechanisms by which DNA translates genetic information into proteins were not understood, marking a significant area of scientific inquiry.

C) It decays toward chemical equilibrium and dies

Explanation: When a cell ceases to consume free energy, it begins to decay toward chemical equilibrium, ultimately leading to its death, emphasizing the critical role of energy in cellular life.

B) They have a temperature gradient from 2-3°C to over 350°C.

Explanation: Hot hydrothermal vents exhibit a significant temperature gradient, with extreme temperatures near the core and cooler temperatures in the surrounding ocean, creating unique habitats for various organisms.

B) Free energy and raw materials

Explanation: A living cell requires free energy from the environment and raw materials to drive the synthetic reactions necessary for growth and replication, highlighting the fundamental energy requirements for life.