NMAT Biology
Complete guide to Cell Biology, Genetics, Human Anatomy & Physiology
Cell Biology
Cell Structure and Function
The cell is the basic structural and functional unit of all living organisms. Understanding cellular components is fundamental to medical education as many diseases originate at the cellular level.
Key Organelles to Remember
- Cell Membrane: Phospholipid bilayer that is selectively permeable. Contains transport proteins (channels, carriers) and receptor proteins for cell signaling.
- Nucleus: Contains genetic material (DNA). Bounded by nuclear envelope with nuclear pores. Houses the nucleolus where ribosomal RNA is synthesized.
- Mitochondria: "Powerhouse of the cell" - produces ATP through cellular respiration. Has its own DNA (maternal inheritance). Double membrane structure.
- Endoplasmic Reticulum: Rough ER (studded with ribosomes) for protein synthesis. Smooth ER for lipid synthesis and detoxification.
- Golgi Apparatus: Modifies, packages, and ships proteins. Produces lysosomes.
- Lysosomes: Contain hydrolytic enzymes for intracellular digestion. Involved in autophagy and apoptosis.
- Ribosomes: Sites of protein synthesis. Found free in cytoplasm or attached to rough ER.
Cell Division
Mitosis (Somatic Cell Division)
Produces 2 identical diploid (2n) daughter cells
- Prophase: Chromatin condenses into chromosomes, nuclear envelope breaks down, spindle fibers form
- Metaphase: Chromosomes align at the cell's equator (metaphase plate)
- Anaphase: Sister chromatids separate and move to opposite poles
- Telophase: Nuclear envelope reforms, chromosomes decondense
- Cytokinesis: Cytoplasm divides, producing two daughter cells
Meiosis (Germ Cell Division)
Produces 4 haploid (n) gametes
Meiosis I: Homologous chromosomes separate
- Crossing over occurs during Prophase I
- Increases genetic variation
Meiosis II: Similar to mitosis
- Sister chromatids separate
- Results in 4 unique haploid cells
NMAT Tip: Mitosis vs Meiosis
Remember: Mitosis = 2 identical cells (for growth/repair),Meiosis = 4 unique cells (for reproduction). A common question asks about where each occurs and their purposes.
Genetics
Mendelian Genetics
Mendel's Laws
- Law of Segregation: Each parent contributes one allele for each trait. Allele pairs separate during gamete formation.
- Law of Independent Assortment: Genes for different traits are inherited independently of each other (applies to genes on different chromosomes).
- Law of Dominance: When two different alleles are present, one (dominant) may mask the expression of the other (recessive).
Key Terms
Genotype: The genetic makeup (e.g., Aa, BB)
Phenotype: The observable trait
Homozygous: Two identical alleles (AA or aa)
Heterozygous: Two different alleles (Aa)
Dominant: Expressed when one or two copies present
Recessive: Only expressed when homozygous
Codominance: Both alleles fully expressed
Incomplete Dominance: Blended phenotype
DNA Structure and Replication
DNA Structure
- Double helix structure discovered by Watson and Crick
- Sugar-phosphate backbone (deoxyribose sugar + phosphate groups)
- Nitrogenous base pairs: Adenine-Thymine (2 H-bonds), Guanine-Cytosine (3 H-bonds)
- Antiparallel strands: One runs 5' to 3', the other 3' to 5'
Central Dogma of Molecular Biology
Transcription
- Occurs in the nucleus
- RNA polymerase reads DNA template
- Produces mRNA (messenger RNA)
- Uses uracil (U) instead of thymine (T)
Translation
- Occurs at ribosomes (cytoplasm)
- mRNA codons read in triplets
- tRNA brings amino acids
- Produces polypeptide chains (proteins)
Human Anatomy & Physiology
Cardiovascular System
Heart Structure & Function
- 4 Chambers: Right atrium, Right ventricle, Left atrium, Left ventricle
- Blood Flow: Body → RA → RV → Lungs → LA → LV → Body
- Valves: Tricuspid (R), Bicuspid/Mitral (L), Pulmonary, Aortic
- SA Node: Natural pacemaker (60-100 bpm)
- Cardiac Output: Heart Rate × Stroke Volume
Blood Components
- RBCs: Carry O₂ (hemoglobin)
- WBCs: Immune defense
- Platelets: Clotting
- Plasma: Fluid portion (55%)
Blood Pressure
- Systolic: Ventricular contraction
- Diastolic: Ventricular relaxation
- Normal: 120/80 mmHg
- Hypertension: >140/90 mmHg
Respiratory System
Gas Exchange
- Pathway: Nose/Mouth → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli
- Alveoli: Site of gas exchange, surrounded by capillaries
- Diaphragm: Primary muscle of respiration
- External Respiration: O₂ enters blood, CO₂ leaves (lungs)
- Internal Respiration: O₂ enters tissues, CO₂ enters blood
Digestive System
Digestive Pathway
Mouth → Esophagus → Stomach → Small Intestine → Large Intestine → Rectum
- Mouth: Mechanical digestion, salivary amylase (starch → maltose)
- Stomach: HCl + Pepsin (protein digestion), produces chyme
- Small Intestine: Main site of absorption; villi increase surface area
- Liver: Produces bile for fat emulsification
- Pancreas: Releases digestive enzymes and bicarbonate
- Large Intestine: Water absorption, houses gut bacteria
Nervous System
Central Nervous System (CNS)
- Brain: Cerebrum, Cerebellum, Brainstem
- Spinal Cord: Reflex arcs, nerve pathways
- Protected by meninges and CSF
Peripheral Nervous System (PNS)
- Somatic: Voluntary control
- Autonomic: Involuntary
- Sympathetic (fight/flight) vs Parasympathetic (rest/digest)
Ecology
Levels of Organization
Organism → Population → Community → Ecosystem → Biome → Biosphere
Energy Flow
- Producers (Autotrophs): Convert sunlight to chemical energy (photosynthesis)
- Primary Consumers: Herbivores that eat producers
- Secondary Consumers: Carnivores that eat herbivores
- Tertiary Consumers: Top predators
- Decomposers: Break down dead organic matter
10% Rule
Only about 10% of energy is transferred from one trophic level to the next. The rest is lost as heat through metabolic processes. This is why food chains rarely exceed 4-5 levels.
Biogeochemical Cycles
Carbon Cycle
Photosynthesis, respiration, combustion, decomposition
Nitrogen Cycle
Nitrogen fixation, nitrification, denitrification
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