Case Study 7 - Objectives PDF

**1) Explain how temperature varies throughout a sample 28-day cycle.** **a) What happens to body temperature on the day before vs day after ovulation?** **b) Which days represent the days of peak fertility?** Peak fertility occurs in the **five days leading up to ovulation** and the **day of ovu...

**1) Explain how temperature varies throughout a sample 28-day cycle.** **a) What happens to body temperature on the day before vs day after ovulation?** **b) Which days represent the days of peak fertility?** Peak fertility occurs in the **five days leading up to ovulation** and the **day of ovulation** itself. These include: - Days 11--16 in a typical 28-day cycle, with ovulation most commonly occurring on Day 14. - Sperm can survive for up to five days in the reproductive tract, so intercourse during these days can result in conception. **c) Which days represent the days of low fertility?** The least fertile days are: - The **early days of the cycle** (Days 1--7), when menstruation occurs, and there is no mature egg ready for fertilization. - The **luteal phase** (Days 17--28), after ovulation has occurred, as the egg has either been fertilized or has disintegrated, and hormone levels prepare for menstruation. 2\) Explain why 28-days is the average length of a woman's cycle that only applies to certain individuals. **a) Between the follicular phase and luteal phase, which one is more consistent between each cycle?** The **luteal phase** (the second half of the cycle) is generally **more consistent** in length across cycles for most individuals. It typically lasts about 12--14 days after ovulation, as it corresponds to the lifespan of the corpus luteum, which secretes progesterone and supports early pregnancy if fertilization occurs. The **follicular phase** (the first half of the cycle) is more **variable**. It starts on the first day of menstruation and ends with ovulation. Its length depends on how quickly the follicles in the ovaries develop and how soon the body reaches the hormonal threshold for ovulation. This phase can fluctuate significantly, causing variations in cycle length. **3) Explain the role of hormones in the regulation of the ovarian cycle.** **a) What would cause the hypothalamus to secrete more GnRH?** The hypothalamus secretes **gonadotropin-releasing hormone (GnRH)** in response to: - Low levels of estrogen and progesterone (such as at the start of the cycle, during menstruation). - Positive feedback from high levels of estrogen just before ovulation. GnRH signals the anterior pituitary to release **FSH** and **LH**. **b) Which hormone(s) stimulates the follicles to mature?**  **Follicle-Stimulating Hormone (FSH)**: Primarily responsible for stimulating the growth and maturation of ovarian follicles.  **Luteinizing Hormone (LH)**: Works synergistically with FSH, particularly later in the follicular phase, to aid in the final stages of follicular maturation. **c) Which hormone(s) does a maturing follicle secrete?** Estrogen: As follicles mature, granulosa cells within the follicle secrete increasing levels of estrogen. This rising estrogen levels: - Stimulate the thickening of the endometrium. - Provide positive feedback to the hypothalamus and pituitary (leading to the LH surge that triggers ovulation). **d) Which hormone(s) triggers ovulation?** - The luteinizing hormone (LH) surge, caused by high estrogen levels, triggers ovulation. This event occurs around the midpoint of the cycle (typically Day 14 in a 28-day cycle). **e) Where does the corpus luteum come from and which hormone(s) does it secrete?**  The corpus luteum forms from the ruptured follicle after ovulation.  It secretes: - Progesterone: Maintains and prepares the endometrium for possible implantation of a fertilized egg. Estrogen: Supports the endometrium and inhibits further FSH and LH release to prevent another ovulation during the same cycle. **f) What is hCG, where does it come from, and how does it prevent shedding of the endometrium?**  Human Chorionic Gonadotropin (hCG): - A hormone secreted by the developing embryo\'s trophoblast cells after implantation (around 6--10 days post-fertilization).  Function: - Maintains the corpus luteum, ensuring continued secretion of progesterone and estrogen. - These hormones prevent the shedding of the endometrium and maintain the uterine lining for the developing pregnancy. **4) Explain the role of hormones in the regulation of the menstrual cycle.** **a) Which hormone(s) causes the thickening of the uterine lining (endometrium)?**  Estrogen: Stimulates the thickening of the endometrium during the proliferative phase. It promotes cell division and the development of blood vessels in the lining.  Progesterone: Further enhances the endometrium during the secretory phase, making it glandular and nutrient-rich to support a potential embryo. **b) Where does the above hormone come from?**  Estrogen: Secreted by the developing ovarian follicles (specifically, granulosa cells) during the follicular phase.  Progesterone: Secreted by the corpus luteum in the ovary after ovulation during the luteal phase. **c) What triggers the endometrium to be shed (menses)?** The shedding of the endometrium (menses) is triggered by: - A drop in progesterone and estrogen levels, which occurs when the corpus luteum degenerates (if no fertilization and implantation take place). - This hormonal decline causes the uterine blood vessels to constrict, depriving the endometrium of oxygen and nutrients, leading to its breakdown and eventual shedding. **5) Illustrate (drawing, chart, etc.) how the negative feedback system involving the hypothalamus, pituitary gland, and ovaries functions. Be sure to include these hormones: GnRH, FSH, LH, estrogen, and progesterone.** **6) Predict the day of ovulation based on the total length of an individual's cycle given that the luteal phase is consistently \~ 14 days for this individual.** **a) On which day would ovulation occur for an individual with a 24-day cycle?** Day 10 **b) On which day would ovulation occur for an individual with a 28-day cycle?** Day 14 **c) On which day would ovulation occur for an individual with a 30-day cycle?** Day 16 **7) How do birth control pills work?** **a) What hormones are contained in birth control pills?** - Combination Pills: Contain both synthetic estrogen (typically ethinyl estradiol) and progestin (a synthetic form of progesterone). These are the most common type. - Progestin-Only Pills (Mini Pills): Contain only synthetic progestin and are used for individuals who cannot take estrogen, such as those with a higher risk of blood clots. The hormones in birth control pills mimic pregnancy-like hormonal levels, providing negative feedback to the hypothalamus and pituitary to prevent the hormonal cascade needed for ovulation. **8) Transcribe and translate DNA template sequences using an mRNA codon table.** **a) Identify type(s) of mutation(s) by comparing two DNA sequences.** Compare two DNA sequences and identify mutations: - **Substitution**: One base is replaced with another (e.g., A→GA \\rightarrow GA→G). - Effect depends on whether the substitution is **silent** (no amino acid change), **missense** (changes the amino acid), or **nonsense** (creates a stop codon). - **Insertion**: One or more bases are added. - Can cause a **frameshift mutation**, altering the reading frame. - **Deletion**: One or more bases are removed. - Also causes a **frameshift mutation** unless the deletion is a multiple of three. **b) Explain how mutations found in introns or exons would affect the final protein product.**  **Introns**: Mutations here generally have no effect on the final protein product since introns are spliced out during RNA processing. However, mutations in intron splicing sites can disrupt splicing and cause abnormal proteins.  **Exons**: Mutations here can directly alter the amino acid sequence of the protein: - **Missense mutation**: Alters one amino acid, potentially affecting protein function. - **Nonsense mutation**: Produces a stop codon, truncating the protein. - **Frameshift mutation**: Changes the reading frame, likely resulting in a dysfunctional protein. **c) Explain how alternative splicing would affect the final protein product.**  Alternative splicing allows a single gene to produce multiple protein isoforms by including or excluding specific exons during RNA processing.  This can result in: - Proteins with different functional domains. - Isoforms suited for specific tissues or developmental stages. - Variations in protein stability, localization, or activity. **d) Understand that hormones can regulate the expression of genes by promoting different alternative splicing pathways.** Hormones can regulate alternative splicing by: - Modifying splicing factor activity: Hormones like **estrogen** or **cortisol** can activate signaling pathways that influence splicing factors, altering how pre-mRNA is spliced. - Changing the availability of splicing machinery in a tissue-specific manner. - Promoting or repressing specific splicing pathways, which may adapt the final protein isoform to the needs of a cell under hormonal influence.