SCIENCE

## Summary of Key Biological Concepts

Here's a structured summary of the biological concepts you provided, organized for clarity and emphasis on key points:

**1. Thyroid Gland & Metabolism:**

* **Hormones:** Produces T4 (thyroxine) and T3 (triiodothyronine) to regulate metabolism.

* **Cellular Impact:** Thyroid hormones stimulate cellular activity, affecting protein synthesis and oxygen use.

* **Homeostasis:** Maintains balanced bodily functions like heart rate, temperature, and energy expenditure.

* **Disorders:**

* Hypothyroidism (underactive): Slows metabolism, leading to fatigue, weight gain, and cold intolerance.

* Hyperthyroidism (overactive): Speeds metabolism, causing weight loss, increased heart rate, and heat intolerance.

**2. Adrenal Glands & Stress Response:**

* **Hormones:** Secretes adrenaline (epinephrine), noradrenaline (norepinephrine), and cortisol.

* **Stress Response:** Prepares the body for "fight or flight" by increasing heart rate, blood pressure, and energy availability.

* **HPA Axis:** Part of the hypothalamic-pituitary-adrenal axis, involved in cortisol production.

* **Chronic Stress:** Prolonged stress leads to elevated cortisol, negatively impacting the immune system, metabolism, and mental health.

**3. Female Reproductive System:**

* **Ovaries:** Produce eggs (ova) and hormones (estrogen, progesterone).

* **Fallopian Tubes:** Transport eggs to the uterus; site of fertilization.

* **Uterus:** Where a fertilized egg implants and develops during pregnancy.

* **Key Processes:**

* Ovulation: Egg release from ovary.

* Endometrium: Uterine lining that thickens for implantation.

* Cervix: Uterine opening connecting to the vagina.

* **Fertilization:** Typically occurs in the fallopian tube. Cilia help move the egg.

**4. Menstrual Cycle:**

* **Phases:**

* Menstrual: Bleeding (shedding of uterine lining).

* Follicular: Egg maturation. FSH (follicle-stimulating hormone) is key.

* Ovulation: Egg release (triggered by LH - luteinizing hormone).

* Luteal: Uterine lining thickening (progesterone from corpus luteum).

* **Hormones:** FSH, LH, estrogen, and progesterone play crucial roles.

**5. Nervous System & Homeostasis:**

* **Sensory Input:** Detects changes via receptors.

* **Signal Transmission:** Electrical impulses travel along neurons to the CNS (brain and spinal cord).

* **Integration & Response:** Brain processes input and signals effectors (muscles/glands).

* **Negative Feedback:** Counteracts changes to maintain stability (set point).

* **Examples:** Temperature regulation, blood pressure control, blood glucose control.

* **Key Terms:** Homeostasis, feedback mechanism, receptor, effector.

**6. DNA Replication:**

* **Key Enzymes:**

* DNA Helicase: Unwinds DNA.

* DNA Primase: Synthesizes RNA primers.

* DNA Polymerase: Builds new DNA strand.

* DNA Ligase: Joins DNA fragments.

* Single-Stranded Binding Proteins: Stabilize single DNA strands.

**7. RNA Types:**

* **mRNA (messenger RNA):** Carries protein coding sequences from DNA to ribosomes. Contains codons.

* **tRNA (transfer RNA):** Carries amino acids to ribosomes during protein synthesis.

* **rRNA (ribosomal RNA):** Forms the core of ribosomes and catalyzes peptide bond formation.

**8. DNA Replication Errors (Mutations):**

* **Types:** Insertions, deletions, point mutations, double-strand breaks, repeat expansion/contraction.

* **Causes:** Deoxyribonucleotides, free radicals, purines, oxygen.

* **Repair Mechanisms:** Proofreading, base excision repair (BER), homologous/non-homologous end-joining repair.

**9. Central Dogma of Molecular Biology:**

* **Flow of Information:** DNA → RNA → Protein.

* **Processes:** Replication, transcription, translation.

**10. Types of Mutations:**

* **Point Mutations:** Missense (amino acid change), silent (no change), nonsense (stop codon).

* **Frameshift Mutations:** Insertion/deletion altering the reading frame.

* **Chromosomal Alterations:** Translocations, duplications, deletions.

**11. Effects of Mutations:**

* **Range:** No effect (silent) to significant changes in protein function (disease, lethality).

* **Influencing Factors:** Gene function, mutation location, environment.

* **Examples:** Sickle cell anemia, cystic fibrosis, antibiotic resistance.

**12. UV Radiation & Mutations:**

* **Mechanism:** Damages DNA by forming pyrimidine dimers.

* **Lesions:** Cyclobutane pyrimidine dimers (CPDs), 6-4 photoproducts (6-4PPs).

* **Consequences:** Replication errors, mutations, potentially cancer.

**13. Antibiotic Resistance:**

* **Causes:** Mutations in target genes, silent mutations, loss-of-function mutations in regulators.

* **Measurement:** Mutation rate (frequency of mutants).

* **Influencing Factors:** Antibiotic treatment, mutator strains.

**14. Fossils & Evolution:**

* **Evidence:** Show how life has changed, relationships between organisms, simple to complex life progression.

* **Usage:** Radiometric dating, categorization, comparison.

**15. Homologous vs. Analogous Structures:**

* **Homologous:** Similar form and genetics due to common ancestry (divergent evolution). Example: Bird and bat wings (bones).

* **Analogous:** Similar function, different structure, independent evolution (convergent evolution). Example: Bird and bat wings (overall structure for flight).

**16. DNA & Amino Acid Sequences:**

* **Codons:** Three nucleotides coding for one amino acid.

* **Processes:** Transcription (DNA → mRNA), translation (mRNA → protein).

**17. Embryological Development:**

* **Stages:** Blastocyst, embryo, fetus.

* **Organ System Development:** Mesoderm, ectoderm, endoderm.

* **Hormones:** hCG.

**18. Puberty Hormones (Males):**

* **Testosterone:** Primary male sex hormone, secondary sex characteristics.

* **FSH:** Stimulates spermatogenesis.

* **LH:** Stimulates testosterone production.

* **DHT:** Initiates puberty.

* **Estrogen:** Affects reproductive health.

**19. Pregnancy Hormones:**

* **hCG:** Thickens uterine lining.

* **Estrogen:** Fetal growth, breast preparation.

* **Progesterone:** Uterine lining support, labor preparation.

* **Relaxin:** Loosens ligaments.

* **Oxytocin:** Uterine contractions, bonding.

* **Prolactin:** Breast milk production.

* **Adrenaline/Noradrenaline:** Stress response.

* **Beta-endorphins:** Pain relief.

**20. Pancreas & Diabetes:**

* **Hormones:** Insulin (lowers blood sugar), glucagon (raises blood sugar).

* **Diabetes Types:**

* Type 1: Pancreas doesn't produce enough insulin.

* Type 2: Insulin resistance.

* **Other Factors:** Pancreatitis, obesity, pituitary tumors, hyperaldosteronism.

**21. Menstrual Cycle Phases (Detailed):**

* **Menstruation:** Shedding of uterine lining.

* **Follicular:** Egg maturation.

* **Ovulation:** Egg release.

* **Luteal:** Corpus luteum produces progesterone.

**22. LH & Ovulation:**

* **Role:** Triggers ovulation, supports pregnancy.

* **Other Effects:** Puberty, testosterone production (males), menstrual cycle control (females).

**23. Progesterone's Function:**

* **Primary Role:** Prepares uterine lining for implantation.

* **Luteal Phase:** Levels rise after ovulation.

* **Pregnancy:** Supports early pregnancy.

* **Menstruation:** Drop in levels triggers shedding.

**24. Irregular Menstrual Periods:**

* **Causes:** Hormonal changes (puberty, menopause, thyroid disorders, PCOS), pregnancy, stress, lifestyle factors, infections, uterine fibroids/polyps, endometriosis, medications.

**25. Complementary Base Pairing:**

* **DNA:** A pairs with T, G pairs with C.

* **RNA:** A pairs with U, G pairs with C.

* **Importance:** Accurate replication, transcription, translation, DNA structure.

**26. Mutations & Base Pairing:**

* **Mutations:** Changes in DNA sequence (substitution, insertion, deletion).

* **Base Pairing's Role:** Ensures accurate replication and minimizes mutations.

**27. DNA as Evidence for Evolution:**

* **Shared Genetic Code:** Universal code suggests common origin.

* **Homologous Genes:** Similar genes in different species indicate shared ancestry.

* **DNA Comparisons:** Used to determine evolutionary relationships.