The unit of life
Red blood cell
Nerve cell
Skeletal muscle cell
Epithelial cell
Plasma membrane: Outer boundary of the cell
Cytoplasm: Contains organelles and cytosol
Cytosol: Fluid portion
Organelles: Specialized structures within the cell
Cytoskeleton: Framework that provides structure
Nucleus: Contains genetic material
Composed of phospholipids with hydrophilic heads and hydrophobic tails
Separates intracellular fluid (cytosol) from extracellular fluid (ECF)
Polar (hydrophilic) head
Nonpolar (hydrophobic) tails
A schematic structure shows how phospholipids arrange themselves in water
In water, phospholipids spontaneously form bilayers
Polar heads face water, and nonpolar tails face each other
This arrangement is crucial for cell membrane structure
Describes the cell membrane as a mosaic of components:
Integral proteins (transmembrane proteins)
Peripheral proteins
Cholesterol
Glycoproteins and glycolipids
Provides fluidity and flexibility to the membrane
Channels: Allow substances to pass through the membrane
Carriers: Bind and transport substances into or out of the cell
Receptors: Bind to ligands to initiate cellular responses
Enzymes: Catalyze biochemical reactions
Structural support: Connect with other proteins for cell support
Linker proteins: Connect adjacent cells in tissues
Concentration gradient: Difference in concentration across a membrane
Equilibrium: Achieved when molecules are evenly dispersed
Example:
Two glucose solutions separated by a divider
Removal of the divider leads to diffusion until equilibrium is reached
Simple diffusion: Nonpolar molecules moving through the phospholipid bilayer
Facilitated diffusion: Uses channel or carrier proteins to transport polar/ionic molecules across the membrane
Movement of water across a selectively permeable membrane
Water moves to balance solute concentrations on both sides of the membrane
Isotonic: Equal solute concentration inside and outside the cell (normal state)
Hypertonic: Higher solute concentration outside the cell (causes crenation)
Hypotonic: Lower solute concentration outside the cell (can cause lysis)
Na+/K+ pump: Transports sodium out and potassium into the cell against their concentration gradients using ATP
Phagocytosis (cell eating): Engulfing of large particles like bacteria
Particle binds to receptor
Pseudopods surround the particle, forming a phagosome
Phagosome fuses with lysosome for digestion
Pinocytosis (cell drinking): Engulfing of small particles or liquids
Process of expelling materials from the cell via vesicles that fuse with the plasma membrane
Passive transport: Moves substances down their concentration gradients without energy
Simple diffusion: Molecules cross without assistance
Facilitated diffusion: Molecules move with the help of transport proteins
Osmosis: Movement of water
Active transport: Moves substances against their concentration gradients using energy
Primary active transport: ATP-driven pumps
Secondary active transport: Uses gradients created by primary transport
Mitochondrion: ATP synthesis
Lysosome: Digestion of macromolecules
Rough Endoplasmic Reticulum (RER): Protein synthesis and modification
Smooth Endoplasmic Reticulum (SER): Lipid synthesis and detoxification
Golgi Apparatus: Modifies, sorts, and packages proteins
Contains nucleolus, chromatin, and is surrounded by a nuclear envelope with pores
Chromatin: DNA and proteins (histones); condenses to form chromosomes during cell division
Interphase (G1, S, G2 phases)
G1: Cell growth
S: DNA replication
G2: Prepare for division
M phase: Cell division (Mitosis and Cytokinesis)
Genetic information flow:
DNA -> mRNA -> Protein
Transcription: DNA is transcribed into mRNA
Translation: mRNA is translated into a polypeptide at the ribosome
Each sequence of three nucleotides (codon) specifies an amino acid
Transcription: DNA to pre-mRNA, introns removed to form mature mRNA
Translation: mRNA guides the assembly of amino acids into polypeptides using tRNA
Posttranslational modification: Polypeptide folding and modification into functional proteins in the cytosol or ER.