Chapter 1: Cells: the fundamental units of life

Who first coined the term 'cell' (from the Latin 'cellula') after observing cork tissue under a 30x microscope?

Robert Hooke

Which 17th-century scientist first observed 'animalcules' and posited that motility is a fundamental quality of life?

Antonie van Leeuwenhoek

"According to the classic cell theory, what is the origin of all living cells?"

They are formed by the growth and division of pre-existing cells.

How did Louis Pasteur's 'swan-neck flask' experiment contribute to the development of cell theory?

It disproved the theory of spontaneous generation by showing that microbes only grow in nutrient broth when exposed to airborne microorganisms.

What distinction does modern cell theory make regarding the flow of energy that was absent in the classic version?

"It specifies that energy flow, including metabolism and biochemistry, occurs within cells."

"In the context of modern cell theory, what is the relationship between an organism's total activity and its individual cells?"

The activity of an organism depends on the total activity of its independent cells.

What mnemonic is often used to define the seven characteristics required to classify an organism as 'alive'?

"MRS GREN (Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition)"

Why are viruses generally considered 'genetic zombies' or non-living entities despite containing biomolecules?

They cannot reproduce by their own efforts and must parasitize the reproductive machinery of a host cell.

The flow of genetic information from DNA to RNA to protein is known as the _____.

central dogma

Which specific chemical machinery is responsible for translating an RNA molecule into a linear sequence of amino acids?

Ribosomes

"In the central dogma, the process of synthesizing an RNA molecule from a DNA template is called _____."

transcription

"Why is life described as an 'autocatalytic process' involving DNA, RNA, and proteins?"

"Polynucleotides provide the sequence information to make proteins, while proteins catalyze the replication and transcription of those polynucleotides."

The 'RNA world' hypothesis proposes that RNA preceded DNA because it can perform which two essential functions simultaneously?

Storing genetic information and catalyzing chemical reactions.

Why is the deoxyribose sugar in DNA considered an evolutionary advantage over the ribose sugar in RNA for genomic storage?

The deoxyribose-phosphate backbone makes DNA chemically much more stable than RNA.

Which molecular fossils in modern cells provide the strongest evidence for a primordial 'RNA world'?

Ribozymes (such as the rRNA in the large ribosomal subunit).

What is the primary structural difference between prokaryotic and eukaryotic cells regarding their genetic material?

"Eukaryotic cells contain their DNA within a distinct nucleus, whereas prokaryotic cells lack a nuclear envelope."

Archaea and Bacteria are the two major divisions of which cell category?

Prokaryotes

Which specific group of archaea is thought to be the direct ancestor of the eukaryotic lineage due to their close association with partner cells?

Asgard archaea

"According to the endosymbiotic theory, mitochondria evolved from which type of organism?"

An aerobic bacterium.

Which scientist is credited with providing the comprehensive evidence for the endosymbiotic theory in the 20th century?

Lynn Margulis

What evidence from organelle genomes supports the endosymbiotic origin of mitochondria and chloroplasts?

They possess their own circular DNA molecules with sequences similar to bacterial genomes.

"If mitochondria are removed from a eukaryotic cell, why can the cell not regenerate them de novo?"

"The genetic instructions required to produce new mitochondria are contained within the mitochondrial genome, not the nuclear genome."

"By what process do mitochondria and chloroplasts reproduce, mirroring their prokaryotic ancestors?"

Binary fission

From which parent is mitochondrial DNA exclusively inherited in humans?

The mother (maternal lineage).

Which eukaryotic organelle is responsible for the final oxidation of food molecules to produce ATP?

Mitochondrion

The _____ is a labyrinthine compartment where lipids and proteins are synthesized for the cell's membranes and for export.

endoplasmic reticulum

"Which organelle acts as a stack of flattened, membrane-enclosed sacs that modifies and packages molecules made in the ER?"

The Golgi apparatus

"Which organelle is responsible for intracellular digestion, breaking down food particles or unwanted organelles?"

Lysosomes

What is the function of peroxisomes in the eukaryotic cell?

They provide a contained environment for reactions that generate and utilize hydrogen peroxide to inactivate toxic molecules.

"The aqueous, concentrated mixture of large and small molecules that fills the space outside the organelles is called the _____."

cytosol

Which component of the cytoskeleton is primarily responsible for the contractile force in muscle cells?

Actin filaments

Which cytoskeletal filaments are the thickest and help pull duplicated chromosomes apart during cell division?

Microtubules

Which type of microscope is required to see the fine details of organelles such as the internal membranes of mitochondria?

Electron microscope

What is a major advantage of super-resolution fluorescence microscopy over standard light microscopy?

It allows researchers to observe cellular components with precision beyond the traditional limit of resolution of light.

"Which modern imaging technique allows for the high-resolution visualization of molecules in their native, frozen state without the need for dyes?"

Cryo-electron microscopy (cryo-EM)

Why is the yeast Saccharomyces cerevisiae considered a powerful model organism for studying eukaryotic cell biology?

"It is a simple, single-celled eukaryote that reproduces rapidly and shares many fundamental mechanisms with human cells."

"In Paul Nurse's experiments, what was the significance of replacing a mutant yeast $Cdc2$ gene with a human version?"

"The human gene functioned perfectly in the yeast cell, proving that the molecular machinery of the cell cycle is highly conserved across evolution."

What is the common name for the model organism Drosophila melanogaster?

Fruit fly

Which model organism was the first multicellular eukaryote to have its entire genome sequenced?

The nematode worm Caenorhabditis elegans

The total genetic information carried by all the chromosomes of a cell is its _____.

genome

Approximately how many protein-coding genes are found in the human genome?

"$20,000$"

How does the genome size of the fruit fly compare to that of the bacterium E. coli?

"The fruit fly has roughly 14,000 genes, which is more than three times as many as E. coli (approx. 4,300 genes)."

"Which organelle, found only in plants and algae, contains three membrane layers and its own internal stacks of chlorophyll?"

Chloroplast

The process by which animal cells engulf large particles or even other cells is known as _____.

endocytosis

The process by which cells release intracellular materials into the external environment via vesicles is known as _____.

exocytosis

What structural role do intermediate filaments play within the cytoskeleton?

They serve to strengthen the cell mechanically.

"In the context of cell respiration, which gas is utilized by mitochondria to extract energy from food?"

Oxygen

Why is ribose easier to produce in 'primitive Earth' simulations than deoxyribose?

"Ribose is readily formed from formaldehyde, whereas deoxyribose requires a more complex protein-catalyzed reaction from ribose."

"According to the preface, which virus is discussed across several chapters to illustrate viral structure and vaccine development?"

SARS-CoV-2

How are eukaryotic cells typically related in size to bacteria?

"They are usually $1,000$ to $10,000$ times larger in volume."

What is the function of transport vesicles in the eukaryotic cytoplasm?

They ferry molecules between one membrane-enclosed organelle and another.

"In all living cells, DNA is a double helix composed of two strands that are _____ and _____ to each other."

antiparallel and complementary

What specific chemical bonds hold together the G-C and A-T base pairs in a DNA molecule?

Hydrogen bonds

Why is the cytosol described as being 'crowded and dynamic'?

It is packed with molecules of many sizes so tightly that it behaves more like a water-based gel than a liquid solution.

Which specific yeast species is used to study the 'cell division cycle' due to its distinct appearance as it divides?

Schizosaccharomyces pombe (fission yeast)

Which model organism is a small weed used to study the genetics and molecular biology of plants?

Arabidopsis thaliana (Mustard plant)

The genetic material of a eukaryotic cell is contained in a set of _____.

chromosomes

"In the context of the endosymbiotic theory, which ancestor is proposed to have formed the nuclear envelope by infolding its plasma membrane?"

An ancestral anaerobic archaeon.

Which model organism is a transparent fish used to study the development of vertebrate tissues?

Zebrafish (Danio rerio)

What is the primary difference between a bacterium and an archaeon?

They belong to two distinct prokaryotic divisions that are only distantly related at the molecular level.

"What term refers to a free-living, nonphotosynthetic, single-celled, motile eukaryote that can act as a predator?"

Protozoan

Which technique allows for the localization of specific proteins within a cell using fluorescently labeled antibodies?

Fluorescence microscopy

What was the prevailing (but incorrect) scientific belief about genes until the 1920s?

That genes were made of proteins.

"The sequence of nucleotides in a gene is transcribed into an RNA molecule, which then dictates the sequence of _____ in a protein."

amino acids

What is the function of the nucleolus within the nucleus?

It is the site where ribosomal RNA is synthesized and ribosomal subunits are assembled.

Why is the human genome's protein-coding gene count described as a 'Shakespeare play' analogy in the text?

Knowing the sequence (the words) is not enough; one must understand how the genes (the elements) work together to produce the organism.

"In the endosymbiotic timeline, which organelle was acquired first: mitochondria or chloroplasts?"

Mitochondria

What is the primary role of the Golgi apparatus in a cell that secretes hormones?

Modifying and packaging hormones into vesicles for secretion (exocytosis).

Which model organism is commonly used to study the molecular genetics of mammalian immunology and human disease due to its similarity to humans?

The mouse (Mus musculus)

Which part of the eukaryotic cell is defined as everything outside the nucleus but inside the plasma membrane?

The cytoplasm

"In the autocatalytic system of a cell, what happens if the system is deprived of raw materials?"

It decays toward chemical equilibrium and 'dies'.

"According to modern cell theory, what determines the total activity of an organism?"

The combined activity of independent cells.

What was the significance of the 19th-century publications by Schleiden and Schwann?

"They documented that cells are the universal building blocks of all plant and animal tissues, signaling the birth of cell biology."

Which specific protein complex is responsible for degrading unwanted or damaged proteins in the cytosol?

Proteasomes

What chemical feature of the DNA sugar-phosphate backbone makes it more stable than that of RNA?

The presence of deoxyribose instead of ribose.

What do we call the process of gradual modification and adaptation that occurs in living organisms over generations?

Evolution

What makes an 'RNA world' plausible from a catalytic standpoint?

"RNA molecules can adopt diverse three-dimensional forms with chemically reactive sites, similar to proteins."

How does the 'Central Dogma' feedback loop enable cell reproduction?

"DNA provides the sequence for proteins, and those proteins then catalyze the replication of that DNA."

Why can cells look and behave very differently while still being fundamentally similar?

Cells can differ strongly in size, shape and function because they express different sets of genes and therefore produce different proteins. However, cells share fundamental chemistry: they use DNA as genetic information, RNA as an intermediate, proteins as major functional molecules, and many of the same basic chemical reactions and molecular mechanisms.

Why is cell specialization possible in a multicellular organism if its cells contain essentially the same DNA?

Different cell types selectively express different genes. Signals from the cell's environment and its developmental history influence which genes are active, causing different cells to produce different RNAs and proteins and therefore develop different structures and functions.

A nerve cell and a muscle cell have the same genome. Why can their structures and functions nevertheless be very different?

They use different parts of the genome. Different genes are expressed in the two cell types, producing different sets of proteins. Those proteins determine much of the cell's structure and behavior.

Why is the relationship between DNA, RNA and protein important for understanding how cells reproduce?

DNA stores sequence information, RNA carries/interprets that information, and proteins perform catalytic and structural functions. Proteins also catalyze the processes required to copy DNA and produce RNA and proteins. This creates a self-reinforcing system that allows cells to reproduce.

What makes the DNA → RNA → protein relationship more than simply a pathway for making proteins?

It is part of a feedback system: DNA provides information for making proteins, while proteins provide much of the machinery required to copy DNA, transcribe RNA and produce proteins. This interdependence supports cellular self-replication.

Why aren't viruses generally considered living organisms according to the book's reasoning?

Viruses contain genetic material and other biomolecules, but they cannot reproduce independently. They depend on the molecular machinery of a host cell to make copies of themselves.

Why does evolution help explain both the unity and diversity of cells?

All present-day cells are thought to descend from a common ancestral cell, explaining their shared fundamental chemistry. Over billions of years, mutation and natural selection caused descendants to diverge and adapt to different environments, producing cellular diversity.

A mutation changes a protein so that a cell divides slightly faster. Why can this small difference become important at the population level?

If the faster-dividing cells survive and reproduce more successfully, their descendants increase faster than competing cells. Over many generations, even a small reproductive advantage can cause the advantageous variant to become predominant.

Why was microscopy so important for the development of cell biology?

Cells are generally too small to observe with the naked eye. Microscopy made cells and their internal structures observable, allowing scientists to recognize cells as the basic units of living organisms and later investigate their internal organization.

Why can't simply increasing magnification indefinitely solve the problem of seeing smaller cellular structures with a light microscope?

The limiting factor is resolution rather than magnification alone. Conventional light microscopy can resolve details down to roughly 0.2 μm because of the wavelength of visible light. Increasing magnification does not overcome this physical resolution limit.

You want to observe a living cell and follow its behavior over time. Why might light microscopy be preferable to electron microscopy?

Electron microscopy requires extensive specimen preparation and the specimen is examined under conditions that do not allow the cell to remain alive. Light microscopy can be used to observe living cells.

What is the fundamental difference between a TEM and an SEM?

A TEM transmits electrons through a very thin specimen and is therefore useful for examining internal ultrastructure. An SEM scans the surface and detects scattered/emitted electrons, producing detailed images of surface structure with strong three-dimensional appearance.

Why does electron microscopy provide higher resolution than conventional light microscopy?

Electrons have a much shorter wavelength than visible light, allowing much smaller structures to be resolved.

You need to determine the surface structure of a cell rather than its internal organelles. Which electron microscope would be more appropriate and why?

SEM, because it scans the specimen's surface and is particularly suited to revealing surface detail and producing images with a three-dimensional appearance.

Why is fluorescence microscopy especially useful when studying a particular protein inside a cell?

A protein can be specifically labeled with a fluorescent marker, allowing researchers to determine where that protein is located rather than simply seeing all cellular structures at once. The PowerPoint emphasizes dyes, probes, antibodies, tagged proteins and GFP as major developments in fluorescence microscopy.

What problem does super-resolution microscopy address?

It allows researchers to distinguish structures that are too close together to be resolved by conventional light microscopy. The book describes approaches capable of reaching roughly 20 nm resolution.

Why is cryo-EM particularly important for structural biology?

It allows very high-resolution determination of biomolecular structures, reaching approximately 3 Å in the lecture material. Structural information can then be used to understand molecular function.

A researcher wants to know the precise three-dimensional structure of a protein rather than simply where it is inside a cell. Why would a high-resolution structural method be more appropriate than ordinary fluorescence microscopy?

Fluorescence microscopy is excellent for locating labeled molecules in cells, whereas high-resolution structural techniques such as cryo-EM can reveal molecular structure at much finer resolution. The structure can then provide information about how the molecule functions.

Why is DNA sequence comparison useful for determining evolutionary relationships?

DNA contains inherited information and accumulates mutations over evolutionary time. Comparing sequences between organisms therefore provides a measure of their genetic similarity and evolutionary relatedness.

Why can morphological comparison alone be misleading when determining evolutionary relationships?

Unrelated organisms can have similar appearances, while closely related organisms can look very different. DNA sequence comparisons provide a more direct way to assess evolutionary relationships.

What are the three domains of life?

Bacteria, Archaea and Eukaryotes.

Why was DNA sequencing particularly important for distinguishing bacteria from archaea?

Both are prokaryotic and therefore lack a nucleus, so their outward appearance can be similar. Genome comparisons revealed that archaea are evolutionarily distinct from bacteria and are more closely related to eukaryotes than their appearance initially suggested.