Unit 2: Living Things

Characteristics of Life

Organization, energy use, homeostasis, metabolism, reproduction, evolution, and cellular structure.

Why are cells microscopic?

To maintain a high surface area to volume ratio for efficient nutrient supply and demand.

Prokaryotic Cell Domains

Divided into two domains: Bacteria and extremophile Archaea.

Prokaryotic Cell Wall

Protective outer barrier composed of peptidoglycans.

Eukaryotic Compartmentalization

Distinctive feature featuring internal membrane-bound compartments called organelles.

Functions of the Nucleus

Stores genetic information, assembles ribosomes, and performs transcription.

Nuclear Pores

Passages through the nuclear envelope regulating active and passive transport.

Ribosomes

Non-membrane-bound complexes of ribosomal proteins and rRNAs that synthesize proteins.

Smooth Endoplasmic Reticulum

Lacks ribosomes; site of lipid, fatty acid desaturation, and cholesterol synthesis.

Rough Endoplasmic Reticulum

Studded with ribosomes; synthesizes proteins for export or the endomembrane system.

Golgi Apparatus

Series of flattened lipid bilayer sacs that sort, modify, and package molecules.

Lysosomes

Vesicles with low internal pH (4.5-5.0) containing digestive enzymes.

Mitochondria Structure

Double lipid bilayer organelle with cristae, a matrix, and its own DNA.

Chloroplast Structure

Organelle containing thylakoid disks, grana, and stroma for photosynthesis.

Extracellular Matrix

Network of proteins outside cells providing structural support and mediating cell communication.

Gorter's RBC Experiment

Demonstrated that plasma membranes are phospholipid bilayers via a 2:1 surface area ratio.

Fluid Mosaic Model

Plasma membranes are dynamic, fluid structures allowing lateral diffusion of proteins and lipids.

Regulating Membrane Fluidity

Cells adjust fatty acid chain length and degree of unsaturation.

Role of Cholesterol

Amphipathic lipid that stabilizes membrane fluidity across temperatures; absent in prokaryotes.

Plasma Membrane Permeability

Permeable to nonpolar molecules; impermeable to large polar molecules and ions.

Simple Diffusion

Passive movement of molecules down concentration gradients without proteins or ATP.

Facilitated Diffusion

Passive transport down concentration gradients using selective channel or carrier proteins.

Carrier Protein Types

Uniporters, symporters, and antiporters transporting specific molecules across membranes.

Protein Kinetics

Channel proteins display linear kinetics; carrier proteins display saturation kinetics.

Active Transport

Movement of molecules against concentration gradients using carrier proteins and ATP.