Chapter 1 Flashcards
Summary of the Key Points
Commonalities Among All Living Things
Despite the enormous variety in shape, size, and external appearance, all cells share a fundamental internal chemistry. They use similar types of molecules, undergo comparable chemical reactions, and rely on the same core processes.
DNA as the Genetic Blueprint
Genetic information in all organisms is stored in DNA molecules composed of four nucleotide building blocks. These nucleotides, arranged in different sequences, form genes that are copied and transmitted during cell replication.
RNA and Proteins
DNA is transcribed into RNA, and most RNA molecules are translated into proteins. This directional flow of information (DNA → RNA → Protein) is known as the central dogma of molecular biology. Proteins themselves, built from 20 standard amino acids, serve an array of vital roles—from catalyzing chemical reactions to forming cellular structures.
Same Biochemical Machinery
All organisms share many of the same enzymes, structural proteins, and other macromolecules, providing strong evidence for a common evolutionary origin. Subtle differences in how, when, and where genes are turned on help produce the tremendous diversity of life we see around us.
According to the central dogma of molecular biology, which sequence best describes how genetic information flows within the cell?
A. RNA → DNA → protein
B. Protein → DNA → RNA
C. DNA → RNA → protein
D. Protein → RNA → DNA
C. DNA → RNA → protein
Which of the following statements best supports the idea that all living organisms share fundamentally similar biochemistry?
A. Different organisms use entirely different sets of amino acids to build proteins.
B. All living organisms rely on the same four nucleotide building blocks to form DNA.
C. Only bacteria and archaea carry genetic information in DNA; eukaryotes use proteins for this.
D. Viruses encode their genes in lipids rather than in DNA or RNA.
B. All organisms—from bacteria to humans—use the same four nucleotides to form DNA.
Why can proteins carry out such a vast array of functions, even though all proteins are made from the same 20 amino acids?
A. Each cell type uses a different set of amino acids to assemble its proteins.
B. The order in which amino acids are linked can vary enormously, producing proteins with unique shapes and chemical properties.
C. The amino acid sequence is identical for all proteins, but they are modified by lipids after translation.
D. Most proteins rely on carbohydrates for their basic structure, making amino acids irrelevant.
B. Variation in the sequence of the same 20 amino acids creates the wide variety of protein structures and functions.
Living cells are able to self-replicate, meaning they duplicate their DNA and other components, then divide into daughter cells that repeat the same cycle.
A central feedback loop drives this self-replication: DNA encodes the information for making proteins, and proteins catalyze the replication of DNA as well as the transcription of DNA into RNA and the translation of RNA into more proteins.
Proteins also facilitate the metabolic processes—breaking down nutrients and fueling biosynthesis—that keep this self-replicating system active.
Viruses contain genetic material (DNA or RNA) but are not considered truly living because they lack the machinery to self-replicate. Instead, they rely entirely on the host cell’s enzymes and processes to make copies of themselves.
Why are viruses generally excluded from the category of living organisms?
A. They use amino acids different from those used by most cells.
B. They can encode genetic material in DNA or RNA but lack the ability to replicate it without a host cell’s machinery.
C. They lack mutations in their genetic material and therefore cannot evolve.
D. They perform metabolism at a much faster rate than typical cells.
Viruses must parasitize a host cell’s replication machinery to copy their genetic material, which disqualifies them from being considered truly “living.”
Which of the following statements best explains why all modern cells share fundamental features such as DNA, RNA, and proteins?
A. Complex modern cells invented their core machinery independently on multiple occasions.
B. Random mutations cannot introduce any significant changes in cellular machinery.
C. All present-day cells have descended from a single common ancestor, inheriting its molecular toolkit.
D. The genetic code changed repeatedly over time, leading to completely different biochemistries.
C. All living cells today are believed to have evolved from the same ancestral cell, and they have retained that cell’s essential molecular machinery.
Which of the following best describes the major distinction between prokaryotic and eukaryotic cells?
A. Prokaryotes have no plasma membrane, whereas eukaryotes do.
B. Prokaryotic cells contain a nucleus; eukaryotic cells do not.
C. Prokaryotic cells lack a defined nucleus and most membrane-bound organelles, whereas eukaryotic cells have them.
D. Prokaryotes are always large and multicellular, while eukaryotes are exclusively single-celled organisms.
C. Prokaryotes do not have a true nucleus or most other membrane-bound organelles, whereas eukaryotes possess these structures.
Which of the following best characterizes a eukaryotic cell?
A. It has no true nucleus and only one type of organelle, the mitochondrion.
B. It may be single-celled or part of a multicellular organism, and it contains a nucleus plus a variety of other membrane-bound organelles.
C. It can survive only in anaerobic environments because it lacks mitochondria.
D. It is usually smaller than a prokaryotic cell and lacks any internal compartments.
B. Eukaryotic cells, whether single-celled or multicellular, contain a nucleus and typically possess many different membrane-enclosed organelles.
Which statement best explains the primary function of mitochondria in eukaryotic cells?
A. They store hereditary information and control gene expression.
B. They capture energy from sunlight to produce sugar molecules.
C. They perform the final steps of food molecule oxidation and generate ATP, consuming oxygen in the process.
D. They digest foreign organisms after endocytosis.
C. Mitochondria carry out cell respiration, converting the energy from food molecules into ATP while consuming oxygen.
Which statement best describes the primary function of chloroplasts in plant cells?
A. They break down old or unwanted cellular components.
B. They house the cell’s genetic information in the form of chromosomes.
C. They carry out photosynthesis, generating sugar molecules and releasing oxygen using sunlight.
D. They oxidize sugars to release energy in the form of ATP.
C. Chloroplasts capture the energy of sunlight to synthesize sugars and release oxygen in the process of photosynthesis.
What best describes the primary benefit that extensive internal membranes provide to eukaryotic cells?
A. They immediately destroy all imported nutrients to prevent overfeeding.
B. They form separate, specialized compartments that contain distinct sets of enzymes and molecules for specific functions.
C. They limit the cell’s surface area, preventing excessive transport across the membrane.
D. They store all of the cell’s genetic information in each separate membrane compartment.
B. Internal membranes create specialized compartments within the cell, each equipped with the enzymes and molecular machinery needed for particular functions.
Which statement best describes the primary function of the rough endoplasmic reticulum (RER) in eukaryotic cells?
A. It stores calcium ions for signaling.
B. It synthesizes and modifies proteins that will be secreted or inserted into membranes.
C. It degrades damaged organelles and large molecules.
D. It is the site of most ATP production in the cell.
B. The RER, studded with ribosomes, is chiefly responsible for synthesizing secretory and membrane proteins and for initial modifications of these proteins.
Which of the following functions is most closely associated with the smooth endoplasmic reticulum?
A. Assembly of ribosomal subunits
B. RNA transcription and processing
C. Lipid synthesis and detoxification of harmful substances
D. Final protein packaging and sorting for secretion
C. Smooth ER is specialized for lipid synthesis (including phospholipids) and the detoxification of various compounds.
Which of the following best describes the primary function of the Golgi apparatus in eukaryotic cells?
A. It is the main site of ATP production and oxidative phosphorylation.
B. It degrades unwanted proteins and recycles their components.
C. It receives vesicles from the ER, processes and modifies proteins (e.g., glycosylation), then packages them for secretion or delivery to other cell compartments.
D. It functions only in lipid synthesis and steroid hormone production.
C. The Golgi apparatus modifies, sorts, and packages proteins (among other molecules) received from the ER, then directs them to their proper destinations.
Which statement best explains how the Golgi apparatus and the endoplasmic reticulum (ER) cooperate in protein secretion?
A. Proteins synthesized on free cytosolic ribosomes spontaneously assemble at the Golgi without involvement of the ER.
B. Proteins destined for secretion or certain organelles are first processed in the ER, then sent to the Golgi in vesicles for further modification and packaging.
C. The Golgi apparatus supplies the raw amino acids to the ER, which assembles them into secretory proteins.
D. Proteins are synthesized in the Golgi and transported to the ER for glycosylation before secretion.
B. Secretory proteins are initially synthesized and partially modified in the ER, then travel via transport vesicles to the Golgi for additional modifications (such as glycosylation) and final packaging for secretion.
Why are endocytosis and exocytosis essential for eukaryotic cells?
A. They allow the membrane to remain static, never changing its composition.
B. They facilitate the selective import of macromolecules, particles, and even entire cells (via endocytosis) and the export of secreted molecules and waste (via exocytosis).
C. They are passive processes that do not require energy input or membrane remodeling.
D. They do not involve vesicles or changes in the plasma membrane and occur only under starvation conditions.
B. Endocytosis and exocytosis enable a eukaryotic cell to dynamically exchange material with its surroundings and regulate both uptake and secretion via vesicular transport.
Which of the following correctly pairs a cytoskeletal filament type with one of its primary functions?
A. Intermediate filaments → driving muscle contraction
B. Microtubules → separating duplicated chromosomes during cell division
C. Actin filaments → forming the mitotic spindle that segregates chromosomes
D. Microtubules → strengthening animal cells against mechanical stress
B. Microtubules play a major role in separating duplicated chromosomes during cell division.
Which of the following statements best describes the primary role of ribosomes in the cell?
A. They degrade damaged proteins.
B. They synthesize lipids for membrane formation.
C. They serve as the site of protein synthesis by translating mRNA into polypeptides.
D. They store genetic material for future cell divisions.
C. Ribosomes translate the genetic information in mRNA into polypeptide chains, thus serving as the cell’s machinery for protein synthesis.
Why are ribosomes in bacteria, archaea, and eukaryotes considered similar yet distinct structures?
A. Only bacterial ribosomes contain ribosomal RNA; others lack rRNA entirely.
B. They all have large and small subunits containing both RNA and proteins, but their size, rRNA sequences, and protein compositions differ across these domains.
C. Archaeal and eukaryotic ribosomes are identical in structure and composition; only bacterial ribosomes differ significantly.
D. Prokaryotes lack a small subunit, whereas eukaryotes lack a large subunit.
B. All cells have ribosomes made of RNA and proteins, but each domain’s ribosomes differ in subunit size and specific rRNA/protein composition.
How do plasmodesmata and bacterial cell walls differ in terms of function and composition?
A. Plasmodesmata are channels through which cells can exchange cytoplasm and solutes, whereas bacterial cell walls are rigid structures made chiefly of peptidoglycans providing osmotic protection.
B. Plasmodesmata provide mechanical support, while bacterial cell walls allow free exchange of nucleic acids.
C. Plasmodesmata exist only in animal cells, and bacterial cell walls occur only in plant cells.
D. They share the same basic chemical structure, as both are composed of collagen fibers and proteoglycans.
A. Plasmodesmata form direct channels between adjacent plant cells to facilitate solute and water transport, whereas bacterial cell walls are primarily peptidoglycan-based barriers that maintain cell shape and protect against osmotic stress.
Which of the following statements best distinguishes the extracellular matrix (ECM) of animal cells from the cell walls in plants and fungi?
A. The ECM in animals primarily consists of collagen and proteoglycans; the cell walls of plants and fungi are built mainly from cellulose or chitin.
B. Plant and fungal cell walls contain proteins similar to collagen but lack carbohydrates.
C. Animal ECM lacks all proteins and is composed solely of cellulose.
D. Both structures are identical in composition but differ in thickness.
A. The animal ECM typically contains collagen and proteoglycans, whereas plant and fungal cell walls are built primarily from cellulose (plants) or chitin (fungi).
Why do biologists rely heavily on model organisms such as E. coli, S. cerevisiae, and Arabidopsis thaliana to understand fundamental cellular processes?
A. Model organisms each represent an entirely unique genetic code.
B. Experimental findings in model organisms rarely apply to other species due to evolutionary differences.
C. Model organisms are relatively easy to grow and manipulate, and they share basic cellular mechanisms with more complex organisms (including humans).
D. There are no differences in complexity among the species chosen as model organisms.
C. Model organisms are convenient to study experimentally and retain core cellular processes that are broadly representative of other, more complex species.
