Cell Biology: Origins of Life, Cell Types, and Organelles

Comprehensive question-and-answer review flashcards covering the origin of life, domains of life, microscopy, viruses, cellular structures, and eukaryotic organelles.

What is the "Goldilocks zone"?

The habitable zone around a star where conditions are just right for liquid water.

How might hydrothermal vents have contributed to the origin of life?

They are fissures on the seafloor that may have provided the energy and chemistry for early life.

What did the Miller-Urey experiment demonstrate?

It was a classic test showing that organic molecules could form from inorganic precursors.

What does the RNA world hypothesis propose?

The theory that early life used RNA for both genetic storage and catalytic activity.

What is a ribozyme?

An RNA molecule capable of acting as an enzyme (catalysis).

What is LUCA?

Last Universal Common Ancestor; the shared ancestor of all current life on Earth.

What does the endosymbiosis theory propose about eukaryotic organelles?

The theory that eukaryotic organelles (mitochondria/chloroplasts) evolved from engulfed prokaryotes.

What are the primary characteristics of the Archaea domain?

Single-celled prokaryotic organisms often found in extreme environments.

What key structural features distinguish prokaryotic cells from eukaryotic cells?

Prokaryotic cells lack a nucleus and membrane-bound organelles, while eukaryotic cells contain a nucleus and membrane-bound organelles.

What is cell differentiation?

The process by which unspecialized cells develop into specific structures with distinct functions.

How do transmission electron microscopes (TEM) and scanning electron microscopes (SEM) differ?

TEM looks through specimens, while SEM looks at surfaces.

How is magnification defined in microscopy?

The ratio of an object's image size to its real size.

What is a viral capsid?

The protein shell enclosing a virus's genetic material.

What is a viral envelope?

An outer membrane layer stolen from the host cell.

How does the lytic cycle differ from the lysogenic cycle in viruses?

The lytic cycle destroys the host immediately, while the lysogenic cycle integrates viral DNA into the host genome.

How do bacterial cell walls differ in composition from plant cell walls?

Bacterial walls are made of peptidoglycan, while plant walls are made of cellulose.

What is the distinction between cytoplasm and cytosol?

Cytoplasm is the entire region inside the cell membrane (minus the nucleus), while cytosol is just the fluid portion.

What are microtubules and what are their functions in the cell?

Thick, hollow cytoskeleton fibers used for cell shape and moving organelles.

What are microfilaments and what are their functions?

Thin cytoskeleton fibers (actin) used for cell movement and support.

How do cilia and flagella differ in length and quantity?

Cilia are short and many, whereas flagella are long and few.

What is the function of microvilli?

Folds in the plasma membrane that increase surface area for absorption.

What process occurs inside the nucleolus?

Ribosomes are assembled in this dense region inside the nucleus.

What is the physical difference between chromatin and chromosomes?

Chromatin is loose, uncoiled DNA, whereas chromosomes are tightly packed DNA ready for cell division.

How do rough endoplasmic reticulum and smooth endoplasmic reticulum differ in structure and function?

Rough ER has ribosomes and modifies proteins, while smooth ER lacks ribosomes and synthesizes lipids.

What is the role of the Golgi apparatus?

It acts as the cell's post office by modifying, sorting, and packaging proteins and lipids.

What is the primary function of lysosomes?

They are sacs filled with digestive enzymes to break down waste.

What is the primary function of the mitochondrion?

Known as the powerhouse of the cell, it produces ATP via aerobic respiration.

What is the function of chloroplasts?

The site of photosynthesis in plants and algae.

“Goldilocks Zone”: The habitable zone around a star where conditions are neither too hot nor too cold for liquid water to exist on a planet's surface. Liquid water is considered essential for the emergence of life

“Goldilocks Zone”:/

A famous 1951 simulation of early Earth's atmosphere (water, methane, ammonia, hydrogen) exposed to electrical sparks (lightning). It successfully produced amino acids and other organic compounds, proving that the building blocks of life can arise spontaneously from inorganic matter.

Miller-Urey Experiment:/

Fissures on the seafloor that release geothermally heated water rich in minerals. Many scientists hypothesize that life originated here because they provide abundant chemical energy and protection from harsh UV radiation without needing sunlight.

The most recent shared ancestral population from which all current life on Earth descended (Bacteria, Archaea, and Eukarya). LUCA lived roughly 3.5 to 3.8 billion years ago, utilized a genetic code based on DNA/RNA, and used ATP for energy.

LUCA/

A theory proposing that RNA was the first genetic material to evolve before DNA and proteins. This is because RNA can both store genetic information (like DNA) and catalyze chemical reactions (like protein enzymes).

An RNA molecule capable of acting as an enzyme to catalyze specific biochemical reactions. Ribozymes provide strong structural evidence for the RNA World Hypothesis.

Ribozyme:/

Catalysis: The process of speeding up a chemical reaction by lowering its activation energy using a catalyst (such as an enzyme or ribozyme) without being consumed by the reaction itself.

Endosymbiosis: A theory explaining how eukaryotic cells evolved. It states that free-living prokaryotes were engulfed by a larger host cell and formed a symbiotic relationship. Over time, these engulfed cells evolved into permanent organelles: mitochondria (from aerobic bacteria) and chloroplasts (from photosynthetic cyanobacteria).

🧬 2. The Domains of Life & Basic Cell Types

Archaea Domain: One of the three domains of life, consisting of single-celled prokaryotes that lack a nucleus and often thrive in extreme environments (extremophiles, like deep-sea vents or salt lakes). Their molecular machinery (like transcription and translation) closely mirrors eukaryotes rather than bacteria.

Bacteria Domain: A domain of life comprising true prokaryotic, single-celled organisms lacking a nucleus. They possess peptidoglycan cell walls and are found in almost every habitat on Earth.

Bacterium (plural: Bacteria): An individual single-celled organism belonging to the Bacteria domain.

Prokaryotic (noun: Prokaryote): Organisms (Bacteria and Archaea) whose cells lack a nucleus and membrane-bound organelles. Their DNA floats freely in a region called the nucleoid.

Eukaryotic (noun: Eukaryote; Eukarya Domain): Organisms (animals, plants, fungi, and protists) whose cells contain a distinct nucleus housing their DNA, along with specialized membrane-bound organelles.

Multicellularity: An evolutionary state where an organism is composed of many cooperating cells that are specialized for different functions, rather than living as a single independent cell.

Cell Differentiation: The process by which unspecialized cells (like stem cells) become specialized in structure and function (e.g., turning into a muscle cell vs. a nerve cell) through selective gene expression.

🔬 3. Cellular Structure: Boundaries, Support & Movement

Plasma (Cell) Membrane: A phospholipid bilayer featuring embedded proteins that encloses the entire cell. It is selectively permeable, tightly regulating what enters and exits the cell to maintain internal homeostasis.

Cell Wall (Bacterial vs. Plant): A rigid outer layer providing structural support and protection outside the plasma membrane.

Bacterial cell wall: Composed of peptidoglycan (a mesh of sugars and amino acids).

Plant cell wall: Composed of cellulose (a tough polysaccharide).

Cytosol: The fluid portion of the cytoplasm, consisting of water, dissolved ions, and molecules.

Cytoplasm: The entire contents of the cell within the plasma membrane, including both the fluid cytosol and all the suspended organelles (excluding the nucleus in eukaryotes).

Cytoskeleton: A network of protein filaments extending through the cytoplasm that maintains cell shape, secures organelles, and facilitates cellular movement.

Microtubule: Thick, hollow cylinders made of tubulin proteins. They form the "tracks" for moving vesicles, separate chromosomes during cell division, and make up the core of cilia and flagella.

Microfilament: Thin, solid rods made of actin proteins. They are responsible for cell movement, muscle contraction, and changing the cell's shape.

Cilium (plural: Cilia): Short, hair-like projections extending from the cell surface. They beat back and forth in rhythmic waves to move the cell through fluid or sweep fluids past the cell surface.

Flagellum (plural: Flagella): Long, whip-like appendages used primarily for locomotion. Prokaryotic flagella spin like propellers, while eukaryotic flagella move in a wave-like motion.

Microvillus (plural: Microvilli): Microscopic, finger-like folds of the plasma membrane that increase the surface area of a cell to maximize absorption (commonly found on cells lining the intestines).

Nucleus (plural: Nuclei): The command center of a eukaryotic cell that houses its genetic material (DNA).

Nuclear Envelope: A double membrane that encloses the nucleus, separating it from the cytoplasm. It contains nuclear pores that regulate the transport of macromolecules like RNA and proteins.

Nucleolus (plural: Nucleoli): A dense region inside the nucleus where ribosomal RNA (rRNA) is synthesized and combined with proteins to assemble ribosome subunits.

Chromatin vs. Chromosome: Two states of DNA inside the cell:

Chromatin: The loose, uncoiled, and accessible form of DNA bound to histone proteins, present when the cell is carrying out daily activities.

Chromosome: The highly condensed, tightly coiled structure that DNA packages into right before cell division, making it safe and easy to move.

Ribosome: A cellular structure made of RNA and protein that acts as the site of protein synthesis (translation). Ribosomes can float freely in the cytosol or bind to the rough endoplasmic reticulum.

Endoplasmic Reticulum (ER) (Smooth vs. Rough): A continuous network of membranous tubules and sacs.