MCAT Biology Lecture Notes

Introduction

• Utilized Milestone review sheets to prepare for MCAT.
• Scored in the 100th percentile.
• Review sheets covered all essential information for the exam.
• Practice exams helped solidify knowledge.
• Purpose: Efficiently go through review sheets and clarify complex topics.

Parts of the Cell

Prokaryotes

• Nucleoid: DNA region, no nucleus but nucleoid where most DNA can be found.

Eukaryotes

• Nucleolus: Found within nucleus, no membrane, produces ribosomes.
• Ribosomes: Present in both prokaryotes and eukaryotes, essential for protein synthesis.
• Peroxisomes: Breakdown materials (e.g., waste products).
• Endoplasmic Reticulum (ER):
  • Rough ER: Studded with ribosomes, synthesizes proteins.
  • Smooth ER: Involved in detoxification and lipid synthesis.
• Golgi Apparatus: Modifies and distributes proteins, only in eukaryotes, functions similar to a packaging system.
  • COPII: Anterograde transport (ER to Golgi).
  • COPI: Retrograde transport (Golgi to ER).
  • Clathrin: Transport between plasma membrane and Golgi.
• Centrioles: Nine groups of microtubules involved in chromosome separation during anaphase.
• Lysosomes: Recycling centers, single membrane, produced by Golgi.
• Plasmids: Circular DNA in prokaryotes, can carry genes beneficial for survival.

Bacteria and Gram Staining

Shapes

• Bacilli: Rod-shaped.
• Cocci: Spherical.
• Spirilla: Spiral-shaped.

Oxygen Requirements

• Obligate Aerobes: Require O2.
• Obligate Anaerobes: Cannot survive in O2.
• Facultative Anaerobes: Can survive with or without O2.
• Aerotolerant Anaerobes: Do not use O2 but can tolerate its presence.

Gram Staining

• Gram-Positive: Purple, thick peptidoglycan cell wall.
• Gram-Negative: Pink, thin peptidoglycan cell wall and outer membrane.

Differences Between Eukaryotes and Prokaryotes

• Eukaryotes: ETC in mitochondria, large ribosomes, reproduce via mitosis.
• Prokaryotes: ETC in cell membrane, small ribosomes, reproduce via binary fission.
  • Plasmids can carry DNA, contribute to variations, and integrate into the genome forming episomes.

Miscellaneous

• Prions: Infectious proteins causing misfolding, e.g., mad cow disease.
• Viroids: Plant pathogens.
• Cytoskeleton Components:
  • Microfilaments (Actin): Smallest, involved in cell motility.
  • Microtubules (Tubulin): Largest, involved in movement within the cell.
  • Intermediate Filaments (Keratin, Desmin): Provide structural support.

Tissues

Types

• Epithelia: Covers surfaces and organs, forms outer layers.
  • Types: Simple (one layer), stratified (multiple layers), pseudostratified (one layer with varying lengths), cuboidal (cube-shaped), columnar (column-shaped), squamous (flat).
• Connective Tissue: Supports and structures other tissues and organs.
  • Types: Bone, cartilage, tendon, blood. Provides support via stroma and extracellular matrix.

Genetic Recombination in Bacteria

• Transformation: Uptake of genetic material from the environment.
• Conjugation: Transfer of DNA via a conjugation bridge.
• Transduction: Transfer of DNA using bacteriophages (bacteria viruses).
• Transposons: Sequences of DNA that can move around in the genome.

Viruses

• Structure: Capsid (protein coat), envelope (some viruses), virions (individual virus particles).
• Viral DNA/RNA: Can be single or double-stranded, positive or negative sense. Retroviruses use reverse transcriptase.
• Bacteriophages: Can undergo lytic or lysogenic cycles.
  • Lytic cycle: Produces new virions leading to cell lysis.
  • Lysogenic cycle: Virus remains dormant until activated.

Cell Cycle and Reproduction

Cell Cycle Phases

• Interphase: Majority of the cycle.
  • G1 Phase: Cell growth and preparation for DNA replication.
  • S Phase: DNA replication.
  • G2 Phase: Further cell growth and preparation for mitosis.
• Mitosis (M Phase):
  • Prophase: DNA condenses, centrioles move to opposite poles.
  • Metaphase: Chromosomes align in the middle.
  • Anaphase: Chromatids separate.
  • Telophase: Nuclear membrane reforms, cytokinesis divides the cell.

Meiosis

• Meiosis I: Homologous chromosomes separate.
  • Prophase I: Crossing over occurs.
  • Metaphase I: Homologous chromosomes align in the middle.
  • Anaphase I: Homologous chromosomes separate.
  • Telophase I: Two haploid cells form.
• Meiosis II: Similar to mitosis; chromatids separate, resulting in four haploid cells.
• Nondisjunction: Error in chromosome separation, leads to conditions like Down syndrome.

Male Reproductive System

• Pathway (SEVE(N) UP): Seminiferous tubules -> Epididymis -> Vas deferens -> Ejaculatory duct -> Urethra -> Penis.
• Glands:
  • Seminal Vesicles and Prostate Gland: Produce alkaline fluid to survive female reproductive tract acidity.
  • Bulbourethral Glands: Produce fluid to cleanse and lubricate urethra.
• Spermatogenesis: Formation of sperm in seminiferous tubules.
• Sertoli Cells: Support spermatogenesis.
• Leydig Cells: Produce testosterone.

Female Reproductive System

• Ovaries: Produce ova, controlled by FSH and LH.
• Hormones:
  • Estrogen: Develops reproductive tract, thickens uterine wall.
  • Progesterone: Maintains and protects endometrium.
• Menstrual Cycle:
  • Follicular Phase: FSH stimulates follicle development.
  • Ovulation: LH surge causes egg release.
  • Luteal Phase: Estrogen and progesterone prepare for potential pregnancy.
• Uterus: Site of implantation and fetal development.

Embryogenesis and Development

• Fertilization: Sperm meets egg in the ampulla of the fallopian tube, leading to a zygote.
• Cleavage: Zygote undergoes rapid cell division, forms morula.
• Blastulation: Formation of the blastula with a fluid-filled cavity (blastocoel).
• Gastrulation: Formation of three germ layers: ectoderm, mesoderm, endoderm.
  • Ectoderm: Forms skin, nervous system, etc.
  • Mesoderm: Forms muscles, bones, circulatory system, etc.
  • Endoderm: Forms internal organs like the gut and lungs.
• Neurulation: Formation of the neural tube, which becomes the central nervous system.
• Stem Cells:
  • Totipotent: Can become any cell type.
  • Pluripotent: Can become any cell type except placental.
  • Multipotent: Can become multiple cell types but limited.

Nervous System

• Types of Neurons: Afferent (sensory), efferent (motor), interneurons.
• Action Potentials: All-or-nothing response, depolarization and repolarization phases mediated by sodium and potassium ions.
• Synapse:
  • Chemical Synapse: Neurotransmitters released from presynaptic neuron to postsynaptic neuron.
  • Neurotransmitter Removal: Breakdown, reuptake, or diffusion.
• Reflex Arc: Simple pathway involving sensory and motor neurons for quick responses.
• Central Nervous System (CNS): Brain and spinal cord.
• Peripheral Nervous System (PNS): Somatic (voluntary control) and autonomic (involuntary control).
  • Autonomic Split: Sympathetic (fight-or-flight) and parasympathetic (rest-and-digest).

Endocrine System

• Hormone Types:
  • Peptide Hormones: Hydrophilic, use receptors on cell surface (e.g., insulin).
  • Steroid Hormones: Lipophilic, pass through cell membrane, affect nuclear receptors (e.g., estrogen, testosterone).
  • Amino Acid-Derivative Hormones: Combination traits (e.g., epinephrine).
• Glands and Hormones:
  • Hypothalamus: Regulates pituitary gland.
  • Pituitary Gland: Divided into anterior and posterior sections.
  • Pancreas: Insulin, glucagon.
  • Thyroid: T3, T4, and calcitonin.
  • Parathyroid: PTH, regulates calcium.
  • Adrenal Cortex: Cortisol, aldosterone.
  • Adrenal Medulla: Epinephrine, norepinephrine.

Respiratory System

• Air Pathway: Nasal cavity -> Pharynx -> Larynx -> Trachea -> Bronchi -> Bronchioles -> Alveoli.
• Alveoli: Site of gas exchange.
• Surfactant: Reduces surface tension within alveoli, prevents collapse.
• Spirometry: Measures lung volumes and capacities (e.g., tidal volume, vital capacity).
• Regulation: Medulla oblongata controls breathing rate based on CO2 and O2 levels.
• Pleurae: Membranes surrounding lungs (parietal and visceral).

Cardiovascular System

• Heart Pathway: Superior/inferior vena cava -> Right atrium -> Tricuspid valve -> Right ventricle -> Pulmonary artery -> Lungs -> Pulmonary vein -> Left atrium -> Mitral valve -> Left ventricle -> Aorta -> Body.
• Conduction System: SA node -> AV node -> Bundle of His -> Purkinje fibers.
• Blood Vessels: Arteries (carry blood away, thick walls), veins (carry blood to heart, thin walls), capillaries (site of gas exchange).
• Blood Composition: Plasma, erythrocytes (RBCs), leukocytes (WBCs), platelets.
• Blood Types: Based on antigens, important for transfusions (ABO, Rh factors).

Immune System

Innate Immunity

• Barriers: Skin, mucus, stomach acid, etc.
• Cells: Macrophages, neutrophils, eosinophils, basophils.

Adaptive Immunity

• B cells: Produce antibodies, memory B cells for quick future responses.
• T cells: Cytotoxic T cells (kill infected cells), helper T cells (coordinate immune response), regulatory T cells (prevent overactivity).
• Active Immunity: Exposure to antigen.
• Passive Immunity: Transfer of antibodies (e.g., maternal).

Digestive System

Pathway

• Oral Cavity: Mechanical digestion, salivary enzymes.
• Pharynx: Pathway for food and air.
• Esophagus: Propels food to stomach.
• Stomach: Acidic environment, enzyme pepsin.
• Small Intestine: Duodenum, jejunum, ileum, nutrient absorption.
• Large Intestine: Water and salt absorption, forms feces.

Accessory Organs

• Liver: Produces bile, detoxifies substances.
• Gallbladder: Stores and concentrates bile.
• Pancreas: Produces digestive enzymes and bicarbonate.

Excretory System

• Kidney Structure: Cortex, medulla, nephron.
• Nephron Function: Filtration, reabsorption, secretion.
• Hormones: Aldosterone and ADH regulate urine concentration.

Muscular System

• Types:
  • Skeletal Muscle: Voluntary, striated, multiple nuclei.
  • Smooth Muscle: Involuntary, non-striated, single nucleus.
  • Cardiac Muscle: Involuntary, striated, one or two nuclei.
• Muscle Contraction: Sliding filament model, role of calcium and ATP.

Skeletal System

• Structure: Axial and appendicular skeletons.
• Bone Remodeling: Osteoblasts (build), osteoclasts (resorb).
• Joints: Structures and functions of different joint types.
• Cartilage: Elastic tissue, found in joints.

Genetics and Evolution

• Genetics Concepts: Alleles, genotypes, phenotypes, dominance, penetrance, expressivity.
• Evolution Mechanisms: Natural selection, genetic drift, founder effect.
• Hardy-Weinberg Principle: Equilibrium conditions, allele frequencies in populations.
• DNA Experiments: Griffith, Avery-Macleod-McCarty, Hershey-Chase.

Summary

• Thorough review of high yield topics for MCAT Biology.
• Importance of understanding key concepts and practicing repeatedly.