Plasma Membrane Structure and Components

Fluid Mosaic Model Principles

The plasma membrane is a dynamic structure composed of lipids, proteins, and carbohydrates. The fluid mosaic model describes the membrane as a flexible bilayer of phospholipids with embedded proteins and other molecules.

• Phospholipid bilayer: Provides barrier and fluidity.

• Integral and peripheral proteins: Facilitate transport, signaling, and structural support.

• Carbohydrate chains: Involved in cell recognition and adhesion.

Example: Glycoproteins on the membrane surface act as cell identity markers.

Glycolytic Composition

Glycocalyx refers to the carbohydrate-rich area on the cell surface, important for protection and cell interactions.

• Composed of glycoproteins and glycolipids.

• Functions in immunity and cell recognition.

Types of Cell Junctions

Classification and Functions

Cell junctions are specialized structures that connect adjacent cells, maintaining tissue integrity and communication.

• Tight junctions: Prevent leakage of extracellular fluid.

• Desmosomes: Provide mechanical strength.

• Gap junctions: Allow direct communication via ions and small molecules.

Membrane Transport Mechanisms

Substances That Can Diffuse Directly Through the Plasma Membrane

Small, nonpolar molecules such as oxygen and carbon dioxide can diffuse directly through the lipid bilayer.

• Simple diffusion: Movement down concentration gradient without energy input.

Types and Characteristics of Passive Transport

Passive transport does not require cellular energy and relies on concentration gradients.

• Simple diffusion

• Facilitated diffusion: Uses membrane proteins for transport.

• Osmosis: Diffusion of water across a semipermeable membrane.

Effects of Hypertonic, Hypotonic, Isotonic Solutions on Cells

Solution tonicity affects cell volume and function.

• Hypertonic: Cells lose water and shrink.

• Hypotonic: Cells gain water and may burst.

• Isotonic: No net water movement; cell volume remains stable.

Endocytosis Types and Mechanisms

Endocytosis is the process by which cells internalize substances.

• Phagocytosis: Engulfment of large particles.

• Pinocytosis: Uptake of fluids and small molecules.

• Receptor-mediated endocytosis: Specific uptake via receptor binding.

Sodium-Potassium Pump (Transport Type)

The sodium-potassium pump is an example of active transport, moving ions against their concentration gradients using ATP.

• Maintains cellular electrochemical gradients.

Secondary Active Transport Mechanism

Uses energy from the movement of one substance down its gradient to transport another substance against its gradient.

• Example: Glucose transport coupled with sodium influx.

Cell Signaling

Chemical Signaling, G Protein-Linked Receptor Signaling

Cells communicate via chemical signals that bind to receptors, triggering intracellular responses.

• G protein-coupled receptors (GPCRs): Activate intracellular signaling cascades.

• Second messengers: cAMP, Ca2+, etc.

Genetic Material Organization and Function

Organization of DNA in the Nucleus

DNA is packaged into chromosomes within the nucleus, associated with histone proteins.

• Chromatin: DNA-protein complex.

• Chromosomes: Condensed chromatin during cell division.

Functions of Types of RNA in Protein Synthesis

RNA types play distinct roles in protein synthesis.

• mRNA: Carries genetic code from DNA to ribosome.

• tRNA: Brings amino acids to ribosome.

• rRNA: Forms ribosome structure and catalyzes peptide bond formation.

Definition of Semiconservative DNA Replication

Each new DNA molecule consists of one original and one new strand.

• Semiconservative replication: Ensures genetic continuity.

Lysosome Functions

Lysosomes are organelles containing digestive enzymes for breaking down cellular waste and foreign material.

• Autophagy and defense against pathogens.

Definition of a Gene

A gene is a segment of DNA that encodes a functional product, usually a protein.

Enzymes in DNA Replication

Several enzymes coordinate DNA replication:

• DNA helicase: Unwinds DNA.

• DNA polymerase: Synthesizes new DNA strands.

• Ligase: Joins DNA fragments.

Transcription vs Translation

Transcription: Synthesis of mRNA from DNA template. Translation: Synthesis of protein from mRNA template.

Base Pairing Rules (mRNA Codon and tRNA Anticodon)

Base pairing ensures accurate genetic information transfer.

• DNA: A-T, C-G

• RNA: A-U, C-G

Codon: Three-base sequence on mRNA. Anticodon: Complementary three-base sequence on tRNA.

Genetic Code Redundancy

Multiple codons can encode the same amino acid, providing error tolerance.

mRNA Processing

Pre-mRNA undergoes modifications before translation:

• 5' cap addition

• Poly-A tail addition

• Splicing to remove introns

Signal Recognition Particle (SRP) Role

SRP directs ribosomes to the endoplasmic reticulum for protein synthesis.

Genetic Theory of Aging

Suggests aging is influenced by genetic factors such as telomere shortening and accumulation of mutations.

Endocrine System Overview

Endocrine vs Exocrine Glands

Glands are classified based on their secretion methods.

Tissue Organization

Epithelial Tissue Classifications

Epithelial tissues are classified by cell shape and layers.

• Shapes: Squamous, cuboidal, columnar

• Layers: Simple (one layer), stratified (multiple layers)

Cell Types in Each Connective Tissue

Connective tissues contain various cell types:

• Fibroblasts: Produce fibers and ground substance.

• Adipocytes: Store fat.

• Chondrocytes: Cartilage cells.

• Osteocytes: Bone cells.

Connective Tissue Extracellular Matrix Composition

The extracellular matrix consists of protein fibers (collagen, elastin) and ground substance (proteoglycans, glycoproteins).

Connective Tissue Origin

All connective tissues originate from mesenchyme, an embryonic tissue.

Connective Tissue Fiber Types

• Collagen fibers: Provide strength.

• Elastic fibers: Provide elasticity.

• Reticular fibers: Form supportive networks.

Epithelial Membranes

Composed of epithelial and connective tissue layers, forming body coverings and linings.

• Mucous membranes: Line cavities open to exterior.

• Serous membranes: Line closed cavities.

• Cutaneous membrane: Skin.

Tissue Repair Stages and Inflammation

Tissue repair involves several stages:

• Inflammation: Response to injury, increased blood flow.

• Organization: Formation of granulation tissue.

• Regeneration: Replacement of damaged tissue.

Germ Layer Origins of Tissues

During embryonic development, three germ layers give rise to all tissues:

• Ectoderm: Forms nervous tissue and epidermis.

• Mesoderm: Forms muscle, connective tissue, and blood.

• Endoderm: Forms epithelial linings of digestive and respiratory tracts.