Cellular Organization and Molecular Genetics: Study Notes for Anatomy & Physiology

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Cellular Organization

Cell Membrane Structure and Function

The cell membrane is a selectively permeable barrier that surrounds the cell, maintaining homeostasis and mediating communication with the environment.

Structure: Composed primarily of a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.
Phospholipids: Amphipathic molecules with hydrophilic heads and hydrophobic tails; form the bilayer structure.
Membrane Proteins: Integral and peripheral proteins serve as channels, receptors, enzymes, and anchors.
Functions: Protection, transport, cell signaling, and cell recognition.
Example: The sodium-potassium pump is an integral membrane protein that maintains ion gradients.

Transport Mechanisms Across Membranes

Cells exchange substances with their environment through various transport mechanisms.

Passive Transport: Movement of molecules down their concentration gradient without energy input (e.g., simple diffusion, facilitated diffusion, osmosis).
Active Transport: Movement against the concentration gradient, requiring energy (e.g., sodium-potassium pump).
Osmosis: Diffusion of water across a semipermeable membrane.
Isotonic, Hypotonic, Hypertonic Solutions: Describe the relative solute concentrations and their effects on cell volume.
Example: Red blood cells in a hypotonic solution swell due to water influx.

Cellular Organelles and Their Functions

Organelles are specialized structures within cells that perform distinct functions.

Nucleus: Contains genetic material (DNA); controls cell activities.
Endoplasmic Reticulum (ER): Rough ER synthesizes proteins; smooth ER synthesizes lipids.
Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.
Lysosomes: Contain digestive enzymes for intracellular digestion.
Peroxisomes: Break down fatty acids and detoxify harmful substances.
Mitochondria: Site of cellular respiration and ATP production.
Cytoskeleton: Provides structural support, cell shape, and facilitates movement.

Cellular Metabolism and Energy Production

Cells obtain energy through the breakdown of glucose and other nutrients.

Glycolysis: Anaerobic breakdown of glucose to pyruvate, producing ATP.
ATP Production: Most ATP is produced by oxidative phosphorylation in mitochondria.
Reactive Oxygen Species (ROS): Byproducts of metabolism; antioxidants like vitamin C and E neutralize ROS.
Example: Muscle cells require large amounts of ATP for contraction.

Cell Division and Chromosomes

Cell division is essential for growth, repair, and reproduction.

Mitosis: Produces two genetically identical daughter cells; used for growth and repair.
Meiosis: Produces gametes with half the chromosome number; introduces genetic diversity.
Chromosome Structure: DNA is packaged into chromosomes; humans have 46 chromosomes (23 pairs).
Example: Skin cells divide by mitosis to replace damaged tissue.

Molecular Genetics

DNA and RNA Structure and Function

DNA and RNA are nucleic acids that store and transmit genetic information.

DNA Structure: Double helix composed of nucleotides (adenine, thymine, cytosine, guanine).
RNA Structure: Single-stranded; uracil replaces thymine.
Functions: DNA stores genetic information; RNA is involved in protein synthesis and gene regulation.
Types of RNA: mRNA (messenger), tRNA (transfer), rRNA (ribosomal), and others.
Example: mRNA carries genetic code from DNA to ribosomes for protein synthesis.

DNA Replication and Transcription

Genetic information is copied and expressed through replication and transcription.

DNA Replication: Process by which DNA makes an exact copy of itself before cell division.
Transcription: Synthesis of RNA from a DNA template.
Key Elements: Promoters, RNA polymerase, and transcription factors.
Example: During S phase of the cell cycle, DNA is replicated.

Translation and Protein Synthesis

Proteins are synthesized based on genetic instructions.

Translation: Process by which ribosomes synthesize proteins using mRNA as a template.
Genetic Code: Set of rules by which nucleotide sequences are translated into amino acids.
Protein Structure: Primary, secondary, tertiary, and quaternary levels.
Example: Hemoglobin is a quaternary protein composed of multiple polypeptide chains.

Genetic Variation and Inheritance

Genetic diversity arises from mutations, recombination, and independent assortment.

Alleles: Different forms of a gene; can be dominant or recessive.
Homozygous vs. Heterozygous: Homozygous individuals have identical alleles; heterozygous have different alleles.
Genotype vs. Phenotype: Genotype is the genetic makeup; phenotype is the observable trait.
Example: Blood type is determined by specific alleles inherited from parents.

Biotechnology and Genetic Engineering

Modern techniques allow manipulation of genetic material for research and medicine.

Genetic Engineering: Direct modification of an organism's DNA.
Knock-outs: Genes are intentionally disrupted to study their function.
DNA Fingerprinting: Technique used for identification based on unique DNA patterns.
Example: CRISPR-Cas9 is a tool for precise gene editing.

Comparison of Cell Types

Cells can be classified based on structure and function.

Cell Type	Characteristics	Example
Prokaryotic	No nucleus, simple structure	Bacteria
Eukaryotic	Nucleus, membrane-bound organelles	Human cells
Somatic	Body cells, diploid	Skin cells
Gametes	Sex cells, haploid	Sperm, egg

Key Equations

ATP Yield from Glucose:
Central Dogma of Molecular Biology:

Additional info: Some explanations and examples have been expanded for clarity and completeness.