BIO 120 Exam #2: Cells, Membranes, Homeostasis

Cell theory: The cell is the fundamental unit of life; organisms are made of cells, and cells come from preexisting cells.
Cell structure and function are closely related.
Cells are classified as prokaryotes or eukaryotes, differing in internal compartmentalization.
Prokaryotic cells lack a nucleus and extensive internal membrane-enclosed compartments; these include bacteria and archaea, typically smaller than eukaryotes.
Eukaryotic cells have a nucleus and other internal compartments called organelles; these include animals, plants, fungi, and protists.

Cell membranes contain lipids, proteins, and carbohydrates.
Phospholipids have both hydrophilic and hydrophobic regions, spontaneously forming liposomes in water.
Membranes are fluid, so membrane components move laterally.
Membrane fluidity is affected by fatty acid chain length, carbon-carbon double bonds, cholesterol, and temperature.
Membranes contain transmembrane proteins or peripheral proteins.

The cell membrane maintains homeostasis by controlling the movement of substances.
Selective permeability arises from the combination of lipids and proteins in cell membranes.
Selective permeability of cell membranes is critical for maintaining homeostasis.
Passive transport involves molecules moving by diffusion from high to low concentration areas.
Passive transport occurs by simple or facilitated diffusion.
Active transport moves molecules from low to high concentration areas, requiring energy.
Primary active transport uses ATP; secondary active transport uses energy stored in an electrochemical gradient.
Animal cells maintain size and shape using protein pumps that actively move ions.
Plants, fungi, and bacteria have a cell wall that maintains cell size and shape.
The cytoskeleton also helps to maintain cell shape.

The endomembrane system is an interconnected membrane set in eukaryotes, defining spaces in the cell.
It includes the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vesicles, and the cell membrane.
The nucleus, enclosed by a double membrane (nuclear envelope), houses the genome.
The endoplasmic reticulum connects to the outer nuclear envelope, producing proteins and lipids for cell use or export.
The Golgi apparatus communicates with the endoplasmic reticulum using transport vesicles, receives lipids/proteins, and directs them.
Lysosomes break down macromolecules into simpler compounds.

Mitochondria and chloroplasts harness energy and likely evolved from free-living prokaryotes.
Mitochondria harness energy from chemical compounds.
Chloroplasts harness sunlight to build sugars in plant and algal cells.
ATP: Bonds linking phosphate groups in ATP have high potential energy that can be harnessed for use by the cell.

The first and second laws of thermodynamics govern energy flow in biological systems.
First Law of Thermodynamics: Energy cannot be created or destroyed
Second law of thermodynamics: There is an increase in entropy in the universe

Chemical reactions involve the breaking and forming of bonds.
In a chemical reaction, atoms themselves do not change, but which atoms are linked to each other changes.
Gibbs free energy (G) is the amount of energy available to do work.
Three thermodynamic parameters define a chemical reaction: Gibbs free energy (G), enthalpy (H), and entropy (S).
Exergonic reactions are spontaneous (∆G < 0) and release energy.
Endergonic reactions are nonspontaneous (∆G > 0) and require energy.
The change of free energy in a chemical reaction is described by ∆G = ∆H – T∆S.
The hydrolysis of ATP is an exergonic reaction that drives many endergonic reactions in a cell.
In cells, nonspontaneous reactions are often coupled to spontaneous ones.

Enzymes, protein catalysts, increase the rate of chemical reactions.
Enzymes reduce the free energy level of the transition state between reactants and products, reducing the activation energy needed.
During catalysis, the substrate and product form a complex with the enzyme, stabilized by transient covalent bonds, weak noncovalent interactions.
The active site of an enzyme is small and has a very specific spatial arrangement.
An enzyme is highly specific for its substrate and the type of reaction it catalyzes.
Kinetics is the study of rates of chemical reactions, with the Michaelis-Menten model describing how enzymes affect the rate.
Environmental factors, such as temperature and pH, affect enzyme activity.
Activators increase enzyme activity.
Inhibitors reduce enzyme activity and can act competitively or noncompetitively.
Allosteric enzymes bind activators and inhibitors at sites other than the active site, changing shape and activity.
Allosteric enzymes are often found at the start of a metabolic pathway or at crossroads.

The cytoskeleton includes microfilaments, intermediate filaments, and microtubules that help maintain cell shape.
Microfilaments are helical polymers of actin monomers.
Intermediate filaments are polymers of proteins that differ depending on cell type.
Microtubules are hollow polymers of tubulin dimers.
Microfilaments and microtubules are dynamic and can assemble/disassemble rapidly.
Motor proteins use ATP to change shape and move.
Microfilaments associate with myosin to transport substances and cause shape changes, like muscle contraction.
Microtubules associate with dynein and kinesin to transport substances.
Microtubules are in cilia, rodlike structures extending from the cell surface.
Motile cilia move cells or fluid; nonmotile cilia often act as sensory structures.
Some prokaryotic cells have protein polymers similar to microtubules and microfilaments.

The extracellular matrix provides structural support and informational cues.
It’s an insoluble protein and polysaccharide meshwork secreted by cells, supporting cells, tissues, and organs.
In plants, it’s the cell wall, mainly cellulose.
In animals, it is abundant in connective tissue.
Collagen is the primary component of connective tissues in animals.
A specialized extracellular matrix (basal lamina) is under epithelial cell layers.
The extracellular matrix can influence cell shape and gene expression.