GBIO 1000 — Unit II Flashcards

Three tenets of cell theory

1. All organisms are made of one or more cells. 2. Cells are the basic units of structure and function in living things. 3. All cells come from preexisting cells.

Exception to "all cells come from preexisting cells"

The origin of the first cell, which arose through chemical evolution from nonliving molecules forming self-replicating systems rather than coming from a prior cell.

How cell theory illustrates unity and diversity

Unity: All organisms are composed of cells. Diversity: Cells differ widely in size, shape, structures, and specialized functions.

Reason cells are generally small in size

High surface-area-to-volume ratio allows efficient transport of nutrients, oxygen, and wastes; volume increases faster than surface area as cell size increases.

Cell

The smallest structural and functional unit capable of carrying out all life processes.

Basic components shared by all cells

Plasma membrane, cytoplasm, DNA (genetic material), and ribosomes.

Plasma membrane

The selectively permeable outer boundary of a cell that regulates the entry and exit of substances.

Cytoplasm vs. Cytosol

Cytoplasm encompasses everything inside the plasma membrane except the nucleus; cytosol is specifically the fluid portion of the cytoplasm.

Key distinction between prokaryotes and eukaryotes

Prokaryotes lack a nucleus and membrane-bound organelles, whereas eukaryotes possess a membrane-bound nucleus and organelles.

Organisms with prokaryotic cells

Bacteria and Archaea.

Organisms with eukaryotic cells

Animals, plants, fungi, and protists.

Location of prokaryotic DNA

In the nucleoid region, which is not enclosed by a membrane.

Organelle

A specialized structure within a cell that performs a specific cellular function.

Evolutionary relationship between prokaryotes and eukaryotes

Prokaryotes evolved first; eukaryotes evolved later from prokaryotic ancestors. Modern prokaryotes have also continued to evolve for billions of years.

Endosymbiotic hypothesis

The theory that mitochondria and chloroplasts originated as free-living prokaryotes that were engulfed by an ancestral eukaryotic cell and established a permanent symbiotic relationship.

Organelles explained by endosymbiosis

Mitochondria (from aerobic bacteria) and chloroplasts (from photosynthetic cyanobacteria).

Evidence supporting the endosymbiotic hypothesis

Mitochondria and chloroplasts possess circular DNA, bacterial-type ribosomes, binary fission-style division, double membranes, and sizes similar to bacteria.

Structures present in plant cells but absent in animal cells

Cellulose cell wall, chloroplasts, and a large central vacuole.

Function of the plant cell wall

Located outside the plasma membrane, it provides structural support, protection, and maintains cell shape.

Chloroplast function

Converts light energy into chemical energy stored in sugars through photosynthesis.

Vacuole

A membrane-bound storage organelle; in plant cells, the central vacuole stores water and maintains turgor pressure.

Endomembrane system

A network of internal membranes that synthesize, modify, package, transport, and recycle cellular molecules.

Components of the endomembrane system

Nuclear envelope, rough and smooth endoplasmic reticulum, Golgi apparatus, lysosomes, vesicles, vacuoles, and plasma membrane.

Cell structures excluded from the endomembrane system

Mitochondria, chloroplasts, ribosomes, cytoskeleton, and centrosomes/centrioles.

Rough endoplasmic reticulum (rough ER) function

Contains surface ribosomes and synthesizes proteins destined for secretion, membrane insertion, or organelle delivery.

Smooth endoplasmic reticulum (smooth ER) function

Synthesizes lipids, detoxifies chemicals/drugs, and stores calcium ions.

Golgi apparatus function

Modifies, sorts, and packages proteins and lipids into vesicles for transport to destination sites.

Lysosome function

Contains hydrolytic digestive enzymes to break down waste, worn-out cell parts, and ingested materials.

Vesicles

Small, membrane-bound sacs that transport materials within or outside the cell.

Structural composition of the plasma membrane

A phospholipid bilayer embedded with proteins, cholesterol, and carbohydrate chains.

Phospholipid structure

A lipid molecule consisting of a hydrophilic phosphate head and two hydrophobic fatty-acid tails.

Hydrophilic

Water-loving; having an affinity for water, as seen in phospholipid heads.

Hydrophobic

Water-fearing; repelled by water, as seen in phospholipid tails.

Formation of the phospholipid bilayer

Hydrophilic heads face outward toward aqueous fluid inside and outside the cell, while hydrophobic tails face inward away from water, forming a barrier.

Fluid Mosaic Model

Model describing the membrane as fluid (lipids and proteins move laterally) and mosaic (composed of a diverse array of embedded proteins, lipids, and carbohydrates).

Transmembrane proteins

Proteins spanning the entire phospholipid bilayer, functioning in transport, signal reception, or enzymatic activity.

Cell-surface (peripheral) proteins

Proteins attached to one surface of the membrane that aid in cell signaling, recognition, or structural attachment.

Role of cholesterol in animal cell membranes

Stabilizes membrane fluidity, preventing it from becoming overly rigid at low temperatures or overly fluid at high temperatures.

Four major functions of the plasma membrane

Physical barrier, selective transport, cellular communication via receptors, and cell recognition/attachment.

Four primary functions of membrane proteins

Transport, receptor/signal transduction, enzymatic activity, and cell recognition or structural attachment.

Selective permeability

Property of cellular membranes that allows certain substances to pass through more easily than others.

Cellular principle illustrated by inner mitochondrial membrane folds

Compartmentalization and surface area optimization: folded membranes create distinct reaction environments and maximize surface area for ATP synthesis.

Diffusion

Net movement of particles down a concentration gradient from an area of higher concentration to lower concentration.

Osmosis

Diffusion of water across a selectively permeable membrane from higher free-water concentration to lower free-water concentration.

Concentration gradient

Difference in the concentration of a substance across a distance or membrane.

Direction of water movement in osmosis

Toward the region with higher solute concentration (lower free-water concentration).

Isotonic solution

A solution with solute concentration equal to that inside the cell, resulting in no net movement of water.

Animal cell response to an isotonic solution

Remains normal (stable size) because rates of water influx and efflux are equal.

Hypotonic solution

A solution with lower solute concentration than the cell, causing water to enter the cell.

Animal cell response to a hypotonic solution

Swells and may burst (undergoes lysis) as water flows into the cell.

Plant cell response to a hypotonic solution

Becomes turgid (firm); the rigid cell wall prevents the cell from bursting.

Hypertonic solution

A solution with higher solute concentration than the cell, causing water to flow out of the cell.

Animal cell response to a hypertonic solution

Shrivels (undergoes crenation) as water leaves the cell.

Plant cell response to a hypertonic solution

Loses water causing the plasma membrane to pull away from the cell wall (undergoes plasmolysis).

Simple diffusion

Passive transport directly across the phospholipid bilayer, typical for small nonpolar molecules like $O_2$ and $CO_2$.

Facilitated diffusion

Passive transport down a concentration gradient assisted by transport proteins (channels or carriers) for ions and polar molecules.

Passive transport vs. Active transport

Passive transport moves substances down their concentration gradient without ATP; active transport uses energy (ATP) to move substances against their gradient.

Endocytosis

Bulk transport process in which a cell takes in extracellular material by invaginating its plasma membrane to form a vesicle.

Exocytosis

Bulk transport process where internal vesicles fuse with the plasma membrane to release contents outside the cell.

Transport mechanism for very large molecules

Vesicular or bulk transport: endocytosis brings large molecules into the cell, and exocytosis releases them.

Phagocytosis

Cell eating; a form of endocytosis where a cell engulfs large particles, microbes, or debris.

Pinocytosis

Cell drinking; a form of endocytosis where a cell ingests droplets of extracellular fluid and dissolved solutes.

Receptor-mediated endocytosis

Selective endocytosis triggered when specific extracellular molecules (ligands) bind to targeted cell-surface receptors.

Function of the sodium-potassium pump

Uses $1$ ATP to transport $3\,Na^+$ ions out of the cell and $2\,K^+$ ions into the cell, both against their concentration gradients.

Physiological importance of the sodium-potassium pump

Maintains membrane potential for nerve and muscle function, regulates cell volume, and maintains ion gradients for secondary active transport.

Coupled transport (secondary active transport)

Mechanism where the downhill movement of one ion supplies energy to drive another substance uphill against its gradient.

Kinetic energy

Energy of motion, including molecular motion, muscle movement, and thermal energy (heat).

Potential energy

Stored energy resulting from spatial positioning or chemical structure, such as chemical bonds or electrochemical gradients.

Energy source driving cell metabolism

Chemical potential energy, predominantly stored within the molecular bonds of nutrients and ATP.

First law of thermodynamics

Energy cannot be created or destroyed; it can only be transformed from one form to another (Law of Conservation of Energy).

Second law of thermodynamics

Every energy transformation increases the entropy (disorder) of the universe, with some energy converting into unusable thermal energy.

Entropy

A thermodynamic measure of disorder, randomness, or energy dispersal within a system.

Homeostasis

Maintenance of stable, dynamic internal physiological conditions despite fluctuating environmental conditions.

Requirement of energy for homeostasis

Cells must continually expend energy to transport ions, synthesize molecules, repair structures, and maintain internal order against entropy.

Reactants vs. Products

Reactants are initial substances consumed in a chemical reaction; products are the ending substances formed by the reaction.

Substrate

The specific reactant molecule that binds to and is acted upon by an enzyme.

Activation energy

The initial energy barrier required to initiate a chemical reaction.

Enzyme

A biological catalyst (typically a protein) that accelerates chemical reactions by reducing activation energy.

Active site

The specific catalytic region of an enzyme where substrate molecules bind and undergo reaction.

Lock-and-key model

Model proposing that substrate molecules fit into an enzyme's active site as a rigid key fits into a lock.

Induced fit model

Model describing how binding of a substrate induces a subtle conformational change in the enzyme to optimize catalytic activity.

Exergonic reaction

A chemical reaction that releases net free energy (e.g., cellular respiration, ATP breakdown).

Endergonic reaction

A chemical reaction requiring net free energy input (e.g., photosynthesis, protein synthesis).

Anabolic reaction

Metabolic pathway that constructs complex molecules from simpler ones, requiring energy input (e.g., photosynthesis).

Catabolic reaction

Metabolic pathway that breaks down complex molecules into simpler units, releasing energy (e.g., cellular respiration).

Metabolic pathway

A series of sequential, enzyme-mediated chemical reactions where the product of one reaction serves as the substrate for the next.

Adenosine Triphosphate (ATP)

The primary energy currency of the cell, composed of adenine, ribose, and three phosphate groups.

Concept of ATP as a "biological universal"

ATP serves as the primary immediate energy donor across virtually all living organisms.

ATP hydrolysis reaction

Cleavage of the terminal phosphate yielding $ATP \rightarrow ADP + P_i + \text{energy}$, where $P_i$ is inorganic phosphate.

ATP regeneration reaction

Endergonic phosphorylation reaction: $ADP + P_i + \text{energy} \rightarrow ATP$, powered by energy from nutrient oxidation or light.

Three primary types of cellular work powered by ATP

Chemical work (anabolism), transport work (pumping solutes), and mechanical work (motility/muscle contraction).

Phosphorylation

Addition of a phosphate group to an organic molecule, transferring energy, increasing reactivity, or altering enzyme activity.

Cellular respiration

The enzyme-catalyzed catabolism of organic molecules (like glucose) to capture released energy in the form of ATP.

Primary purpose of cellular respiration

To convert chemical energy stored in nutrients into ATP to perform cellular work.

Balanced equation for aerobic cellular respiration

$$C_6H_{12}O_6 + 6 O_2 \rightarrow 6 CO_2 + 6 H_2O + ATP + \text{heat}$$

Cellular location of glycolysis

Cytosol (cytoplasm).

Cellular location of pyruvate oxidation and the Krebs cycle

Mitochondrial matrix.

Cellular location of the electron transport chain and ATP synthase

Inner mitochondrial membrane (cristae).

Three major stages of aerobic respiration

Glycolysis, Krebs cycle (citric acid cycle), and electron transport chain with chemiosmosis (linked by pyruvate oxidation).

Key net products of glycolysis per glucose molecule

$2$ pyruvate, net $2$ ATP, and $2\,NADH$.