Comprehensive Biology: DNA, Cell Division & Reproduction

A comprehensive set of 102 vocabulary flashcards covering DNA structure, replication, protein synthesis, cell division, genetics, epigenetics, reproductive anatomy, hormonal regulation, and cancer prevention.

Q: What does DNA stand for and what is its primary function?

Deoxyribonucleic acid. It holds genetic information that determines the type of proteins a cell can produce, thus determining cell structure and function.

Q: Fill in the blanks: In non-dividing cells, DNA appears as a tangled network of thread-like structures called ____. In dividing cells, these become tightly coiled structures called ____.

chromatin; chromosomes

Q: What are the four nitrogen bases found in DNA and what are their complementary pairing rules?

Adenine (A) pairs with Thymine (T); Guanine (G) pairs with Cytosine (C).

Q: How many hydrogen bonds typically form between Adenine-Thymine (A-T) base pairs compared to Guanine-Cytosine (G-C) base pairs in DNA?

A-T pairs are held by 2 hydrogen bonds; G-C pairs are held by 3 hydrogen bonds.

Q: What are the three essential components that make up a DNA nucleotide?

1. Deoxyribose sugar
2. A phosphate group
3. A nitrogen base

Q: When discussing DNA, what do the terms 5' and 3' refer to concerning its directionality?

The 5' end has a phosphate group attached to the 5th carbon of the deoxyribose sugar; the 3' end has a hydroxyl (-OH) group attached to the 3rd carbon.

Q: In what specific direction is DNA always read?

DNA is always read and synthesized in the 5' → 3' direction.

Q: Fill in the complete structural hierarchy of DNA packaging, starting from DNA and leading up to the chromosome: DNA → ____ → ____ (composed of 8 histones) → ____ → ____.

histones; nucleosome; chromatin fibres; chromosome

Q: Describe three key differences between mitochondrial DNA (mtDNA) and nuclear DNA (nDNA).

1. Mitochondrial DNA is small and circular, unlike linear nuclear DNA.
2. It is not wrapped around histone proteins, as nuclear DNA is.
3. It contains a very limited number of genes (only 37), compared to the thousands in nuclear DNA.

Q: What specific types of molecules do the 37 genes found in mitochondrial DNA primarily code for?

The 37 mitochondrial genes code for transfer RNA (tRNA), which helps in protein synthesis, and enzymes essential for cellular respiration.

Q: Explain the concept of semi-conservative DNA replication.

In semi-conservative DNA replication, each new DNA molecule formed consists of one original parental strand and one newly synthesized strand.

Q: Outline the four main steps involved in the process of DNA replication.

1. DNA helicase unwinds strands: The enzyme DNA helicase separates the two DNA strands, creating replication forks.
2. Free nucleotides pair: Complementary free-floating nucleotides in the nucleus pair with the exposed bases on each parental strand.
3. DNA polymerase forms backbone: DNA polymerase forms strong phosphodiester bonds to create the sugar-phosphate backbone of the new strand.
4. Two identical DNA molecules result: The process yields two DNA molecules, each identical to the original and composed of one old and one new strand.

Q: What is the specific role of DNA ligase during DNA replication?

DNA ligase is an enzyme that joins together the short DNA segments known as Okazaki fragments on the lagging strand, effectively sealing nicks in the backbone.

Q: Why is the lagging strand synthesized discontinuously in Okazaki fragments during DNA replication?

The lagging strand is synthesized discontinuously because DNA polymerase can only synthesize new DNA in the 5' → 3' direction, requiring it to work away from the replication fork on one of the strands, forming short segments before they are joined.

Q: Explain why DNA remains in the nucleus while proteins are synthesized on ribosomes in the cytoplasm.

DNA is too large to exit the nucleus. Therefore, its genetic information is copied into messenger RNA (mRNA), which is small enough to travel to the cytoplasmic ribosomes where proteins are built.

Q: List three key structural differences between DNA and RNA.

1. Sugar type: RNA contains ribose sugar, while DNA contains deoxyribose.
2. Strandedness: RNA is typically single-stranded, whereas DNA is double-stranded.
3. Nitrogenous bases: RNA contains uracil (U) instead of thymine (T), which is found in DNA.

Q: What are the three main types of RNA, and what is the primary function of each in protein synthesis?

1. rRNA (ribosomal RNA): Forms the structural and catalytic core of ribosomes, where proteins are synthesized.
2. mRNA (messenger RNA): Carries the genetic code from DNA in the nucleus to the ribosomes in the cytoplasm.
3. tRNA (transfer RNA): Delivers specific amino acids to the ribosome according to the mRNA codons during protein synthesis.

Q: Define and differentiate between a triplet, a codon, and an anticodon in terms of their location and role in gene expression.

Triplet: A sequence of three consecutive nitrogen bases on a DNA molecule.
Codon: A sequence of three consecutive nitrogen bases on an mRNA molecule that specifies a particular amino acid or a stop signal.
Anticodon: A sequence of three complementary nitrogen bases found on a tRNA molecule that pairs with a specific mRNA codon during translation.

Q: Which specific codon serves as the start signal for translation, and what amino acid does it code for?

The start codon is AUG; it codes for the amino acid methionine.

Q: Describe the main steps involved in the process of transcription, from initiation to termination.

1. RNA polymerase binds promoter: RNA polymerase recognizes and binds to a specific DNA sequence called the promoter, signaling the start of a gene.
2. DNA unwinds, complementary mRNA forms: The DNA double helix unwinds, and RNA polymerase synthesizes a complementary mRNA strand using one DNA strand as a template.
3. Enzyme hits stop code, mRNA is released: RNA polymerase continues until it encounters a stop sequence on the DNA, at which point the newly formed mRNA molecule is released.

Q: Differentiate between introns and exons in eukaryotic gene expression.

Introns are non-coding regions within a gene that are removed from the pre-mRNA transcript during a process called splicing. Exons are the coding regions of a gene that remain in the mature mRNA and are eventually translated into protein.

Q: What are the 5' cap and 3' poly-A tail, and what is their primary function in mRNA processing?

The 5' cap is a modified guanine nucleotide added to the 5' end of mRNA, and the 3' poly-A tail is a long chain of adenine nucleotides added to the 3' end. Both are protective modifications that prevent mRNA degradation and aid in its translation and export from the nucleus.

Q: Outline the main steps of translation, the process of protein synthesis, from initiation to termination.

1. Ribosome binds mRNA at AUG: A ribosome attaches to the mRNA molecule and scans for the start codon (AUG).
2. tRNA brings amino acids: Transfer RNA (tRNA) molecules, each carrying a specific amino acid, bring their amino acids to the ribosome, matching their anticodons to the mRNA codons.
3. Ribosome moves codon to codon, peptide bonds form: The ribosome moves along the mRNA, reading codons sequentially. Peptide bonds form between adjacent amino acids, creating a polypeptide chain.
4. Translation stops at stop codon: The process continues until the ribosome encounters a stop codon on the mRNA, signaling the termination of protein synthesis and release of the polypeptide.

Q: What are the three primary biological purposes of mitosis?

Mitosis serves for: 1. Growth: Increasing the number of cells in a multicellular organism. 2. Tissue repair: Replacing damaged or worn-out cells. 3. Asexual reproduction: In unicellular organisms, it is the primary mode of reproduction.

Q: List the four main phases of the eukaryotic cell cycle and briefly describe what occurs in each.

1. G1 (Gap 1): Cell grows and carries out normal metabolic functions.
2. S (Synthesis): DNA replication occurs, synthesizing a complete copy of the cell's genome.
3. G2 (Gap 2): Cell continues to grow and synthesizes proteins and organelles in preparation for mitosis.
4. M (Mitosis): The cell undergoes nuclear division (mitosis) and cytoplasmic division (cytokinesis).

Q: List the distinct stages of mitosis in their correct order, followed by the final process of cell division.

Prophase, Metaphase, Anaphase, Telophase, followed by Cytokinesis.

Q: What is the final outcome of a single mitotic division regarding the resulting daughter cells?

Mitosis results in two genetically identical diploid (2n) daughter cells.

Q: Define the term "diploid" in the context of chromosome number, and provide an example for humans.

Diploid describes a cell or organism having two complete sets of chromosomes, one from each parent. In humans, the diploid number (2n) is 46 chromosomes.

Q: What is the primary purpose of meiosis, and how does it relate to sexual reproduction?

The main purpose of meiosis is to produce four haploid gametes (sex cells) from a single diploid cell. This process halves the chromosome number, ensuring that when two gametes fuse during fertilization, the resulting zygote has the correct diploid chromosome number for sexual reproduction.

Q: Define the term "haploid" in the context of chromosome number, and provide an example for human gametes.

Haploid describes a cell or organism having a single set of unpaired chromosomes. In humans, the haploid number (n) for gametes is 23 chromosomes.

Q: Explain the process of 'crossing over' and during which stage of meiosis does it occur?

Crossing over is the exchange of genetic material between non-sister chromatids of homologous chromosomes. It occurs during prophase I of meiosis, leading to increased genetic variation.

Q: What is the key difference in chromosome separation between Anaphase I of meiosis and Anaphase of mitosis?

In Anaphase I of meiosis, homologous chromosomes separate and move to opposite poles, while sister chromatids remain attached. In mitotic anaphase, sister chromatids separate and move to opposite poles.

Q: Compare the products of mitosis versus meiosis in terms of cell number, ploidy, and purpose.

Mitosis: Produces 2 diploid cells, primarily for growth and tissue repair.
Meiosis: Produces 4 haploid cells, specifically for sexual reproduction and genetic diversity.

Q: List four major sources of genetic variation that contribute to diversity within a species.

1. Random assortment of chromosomes during meiosis.
2. Crossing over between homologous chromosomes.
3. Non-disjunction (errors in chromosome separation).
4. Random fertilisation of gametes.

Q: Define non-disjunction and explain its consequence in terms of gametes.

Non-disjunction is the failure of homologous chromosomes or sister chromatids to separate properly during meiosis (or mitosis). This results in gametes (or cells) with an abnormal number of chromosomes (e.g., too many or too few).

Q: What genetic condition is known as "Trisomy," and provide a common example.

Trisomy is a chromosomal abnormality characterized by the presence of an extra chromosome, meaning there are three copies of a particular chromosome instead of the usual two. A common example is Trisomy-21, also known as Down syndrome, where there are three copies of chromosome 21.

Q: Describe the chromosomal abnormality and key characteristics of Turner Syndrome.

Turner Syndrome is a genetic condition affecting females, characterized by the presence of only one X chromosome (XO monosomy) instead of the usual two (XX). Individuals typically exhibit short stature, sterility, and generally normal intelligence.

Q: Describe the chromosomal abnormality and key characteristics of Klinefelter Syndrome.

Klinefelter Syndrome is a genetic condition affecting males, characterized by the presence of an extra X chromosome (XXY) instead of the usual XY. Affected individuals often have small testes, sterility, and may exhibit some feminine physical traits (e.g., breast development).

Q: What is epigenetics, and how does it differ from traditional genetics?

Epigenetics refers to heritable changes in gene expression that occur without altering the underlying DNA sequence. These changes can switch genes on or off, influencing how cells read and express genes, unlike genetic mutations which involve changes to the DNA sequence itself.

Q: What is acetylation in the context of epigenetics, and how does it influence gene expression?

Acetylation is the addition of acetyl groups to histone proteins. This modification loosens the chromatin structure, making DNA more accessible to transcription machinery, thereby increasing gene expression (turning genes on).

Q: What is DNA methylation, and what is its effect on gene expression?

DNA methylation is the addition of methyl groups to specific cytosine bases, primarily at CpG sites, within the DNA molecule. This modification typically leads to the condensation of chromatin and the silencing of genes (turning genes off).

Q: List several environmental factors that are known to influence and modify an individual's epigenome.

The epigenome can be modified by environmental factors such as severe stress, nutritional factors (e.g., diet deficiencies or excesses), and exposure to toxins or drugs.

Q: Why are testes located externally, and what is the optimal temperature requirement for spermatogenesis?

Testes are located externally in the scrotum because spermatogenesis (sperm production) requires a temperature of approximately 2 \deg C below normal body temperature for optimal activity.

Q: Describe the contributions of the seminal vesicles, prostate gland, and bulbourethral glands to semen composition.

1. Seminal vesicles: Add a sugary, fructose-rich fluid that provides energy for sperm motility.
2. Prostate gland: Adds an alkaline fluid that neutralizes the acidity of the vaginal tract, protecting sperm.
3. Bulbourethral glands: Add lubricating mucus to the urethra.

Q: Outline the complete pathway of sperm from its production site to its exit from the male body.

Seminiferous tubules → Epididymis → Vas deferens → Urethra.

Q: What is the corpus luteum, and what happens to it if pregnancy does not occur?

The corpus luteum is a hormone-secreting structure formed in the ovary from the ruptured follicle after ovulation. If pregnancy does not occur, it degenerates into a non-hormone-producing scar tissue called the corpus albicans.

Q: What are fimbriae, and what is their role in the female reproductive system?

Fimbriae are finger-like projections located at the end of the fallopian (uterine) tube nearest the ovary. Their role is to sweep the ovulated egg from the surface of the ovary into the fallopian tube.

Q: List the correct sequence of cell development during spermatogenesis, from the least differentiated germ cell to a mature sperm.

Spermatogonium → Primary spermatocyte → Secondary spermatocyte → Spermatid → Spermatozoon (mature sperm).

Q: Describe the three main structural parts of a mature human sperm cell and the primary function of each part.

1. Head: Contains the haploid nucleus with genetic material and the acrosome, an enzyme-filled cap that helps penetrate the egg.
2. Midpiece: Contains numerous mitochondria to provide ATP for flagellar movement.
3. Tail (Flagellum): A long, whip-like structure providing propulsion for movement.

Q: Describe the unique timing and pauses in the process of oogenesis (egg development).

Oogenesis begins in females before birth, with primary oocytes pausing at prophase I. This pause continues until puberty, when one oocyte per cycle matures and restarts meiosis. The secondary oocyte then pauses again at metaphase II until fertilization occurs, which triggers the completion of meiosis II.

Q: Compare the number of functional gametes produced from one primary spermatocyte versus one primary oocyte.

One primary spermatocyte undergoes meiosis to yield 4 functional spermatozoa (sperm). In contrast, one primary oocyte undergoes meiosis to yield only 1 functional ovum (egg) and 2 or 3 small, non-functional polar bodies.

Q: List the main stages of follicular development in the ovarian cycle, in chronological order.

Primary follicle → Secondary follicle → Graafian follicle (mature follicle) → Ovulation → Corpus luteum.

Q: Outline the major phases and characteristic days of a typical 28-day menstrual cycle.

1. Days 1-4: Menstruation (shedding of endometrium).
2. Days 5-12: Pre-ovulation/Proliferative phase (endometrium rebuilds).
3. Days 13-15: Ovulation (release of egg).
4. Days 16-20: Secretion/Luteal phase (endometrium prepares for implantation).
5. Days 21-28: Pre-menstruation (if no fertilization, corpus luteum degenerates).

Q: For the following reproductive hormones, state their primary function: FSH, LH, Estrogen, Progesterone.

1. FSH (Follicle-Stimulating Hormone): Stimulates the growth and development of ovarian follicles in females and spermatogenesis in males.
2. LH (Luteinizing Hormone): Triggers ovulation and corpus luteum formation in females; stimulates testosterone production in males.
3. Estrogen: Primarily responsible for building and thickening the uterine endometrium during the proliferative phase, and development of female secondary sexual characteristics.
4. Progesterone: Primarily responsible for maintaining the thick, secretory endometrium for potential implantation and inhibiting uterine contractions.

Q: Where does fertilization typically occur in the female reproductive system?

Fertilization typically occurs in the uterine (fallopian) tubes.

Q: Outline the main steps involved in human fertilization, from sperm contact to zygote formation.

1. Sperm penetrate corona radiata: Multiple sperm initially bind to and penetrate the outer layers of the egg, called the corona radiata.
2. One enters egg: A single sperm then successfully penetrates the zona pellucida and fuses with the egg cell membrane.
3. Egg completes meiosis II: The entry of the sperm triggers the egg to complete its second meiotic division (meiosis II).
4. Pronuclei fuse to form zygote: The male and female pronuclei (haploid nuclei from sperm and egg, respectively) fuse, forming a diploid zygote, marking the beginning of embryonic development.

Q: What is the typical average volume of an ejaculate and the approximate number of sperm it contains?

An average human ejaculate is approximately 3 mL in volume and typically contains between 150 and 300 million sperm.

Q: Define a zygote and explain its significance in embryonic development.

A zygote is a diploid cell formed by the fusion of a male and female pronucleus during fertilization. It is the first cell of a new organism and marks the initiation of embryonic development.

Q: List several common sources or types of carcinogens.

Carcinogen sources include: UV radiation (from sunlight), X-rays and other ionizing radiation, oncogenic viruses (e.g., HPV), and chemical carcinogens such as alcohol, asbestos, and tobacco smoke.

Q: Name several effective strategies for preventing cancer.

Cancer prevention strategies include: avoiding smoking and exposure to secondhand smoke, using sun protection (e.g., sunscreen, protective clothing), maintaining a healthy diet high in fibre and low in fat, limiting alcohol consumption, and using protective gear when handling hazardous chemicals.

Q: Given a DNA strand 5'-ATCGTA-3', provide its complementary DNA strand, the corresponding mRNA sequence, and the tRNA anticodons.

Given DNA strand: 5'-ATCGTA-3'.
Complementary DNA strand: 3'-TAGCAT-5'.
Corresponding mRNA: 5'-AUCGUA-3' (U replaces T).
Corresponding tRNA anticodons: 3'-UAGCAU-5'.

Q: If an organism has 24 chromosomes in its somatic cells, what would be the chromosome number in its gametes and in its zygote?

For an organism with 24 chromosomes in its somatic cells (2n = 24):
Its gametes would have 12 chromosomes (n = 12).
Its zygote would have 24 chromosomes (2n = 24).

Q: Describe the key physiological events occurring in a female's reproductive cycle around Day 18 (assuming a 28-day cycle).

Around Day 18, the corpus luteum is active and secretly primarily progesterone and some estrogen. The uterus is in its secretory phase, characterized by the production of glycogen-rich mucus to support a potential embryo, and the endometrium is maintained in a thick state.

Q: Compare the nature and effects of mutations occurring in DNA versus those occurring in mRNA.

DNA mutations: Are permanent changes to the genetic code, can be inherited by daughter cells or offspring, and can affect all proteins produced from that gene.
mRNA mutations: Are temporary, affect only one specific batch of protein molecules produced from that mRNA transcript, and are not inheritable.

Q: Explain the biological importance of genetic variation within a population.

Genetic variation is crucial because it provides the raw material for natural selection, allowing a population to adapt to changing environmental conditions. It increases the survival chances of a species under stress (e.g., disease outbreaks, climate change) by ensuring that some individuals will have traits that are beneficial, countering uniform susceptibility to challenges.

Q: List four fundamental functional properties of DNA.

DNA possesses the following functional properties:

1. It is heritable (passed from parent to offspring).
2. It encodes information to direct cellular processes and build organisms.
3. It enables species comparison due to its universal genetic code.
4. It can replicate accurately to ensure faithful transmission of genetic information.

Q: What type of bond links the sugar-phosphate backbone of a DNA strand, and what is its strength?

The sugar-phosphate backbone in DNA is linked by strong covalent bonds called phosphodiester bonds.

Q: How are the carbons numbered in the deoxyribose sugar of a nucleotide?

Each deoxyribose sugar in a nucleotide has five carbons, which are conventionally labeled 1' (one prime) to 5' (five prime).

Q: Which specific carbons in a nucleotide are involved in establishing the 5' and 3' directionality of a DNA strand?

The 5' carbon of one nucleotide attaches to a phosphate group, forming the 5' end of a strand. The 3' carbon bears a hydroxyl (-OH) group, to which the next nucleotide is added, allowing for strand extension.

Q: Define a nucleosome in the context of DNA packaging.

A nucleosome is the fundamental repeating unit of chromatin structure, consisting of a segment of DNA wound around a core of eight histone proteins.

Q: How many nitrogen bases (a triplet/codon) are required to code for a single amino acid?

Three bases (known as a triplet on DNA or a codon on mRNA) code for one amino acid.

Q: Provide amino acid meanings for the following mRNA codons: CAG, UUA, and CCC.

CAG codes for Valine; UUA codes for Leucine; CCC codes for Proline.

Q: How and where is a replication fork formed during DNA replication?

A replication fork, which is a Y-shaped structure, is formed when the enzyme DNA helicase unwinds and separates the two strands of the DNA double helix.

Q: What is the specific role of ATP (adenosine triphosphate) in the process of DNA replication?

ATP provides the necessary energy to activate free nucleotides, making them suitable for incorporation into the new DNA strand by DNA polymerase.

Q: What is the primary function of the enzyme DNA ligase during DNA replication, particularly on the lagging strand?

DNA ligase is crucial for sealing nicks (gaps) in the newly synthesized DNA strands and for joining the Okazaki fragments together on the lagging strand.

Q: What hormonal event triggers the LH (Luteinizing Hormone) surge, and what is the direct consequence of this surge in the female reproductive cycle?

Rising levels of estrogen, typically around day 14 of the menstrual cycle, trigger an LH surge. This surge is directly responsible for inducing ovulation.

Q: Explain the negative feedback mechanism of high progesterone levels during the luteal phase of the menstrual cycle.

High levels of progesterone during the luteal (secretory) phase inhibit the release of FSH (Follicle-Stimulating Hormone) and LH (Luteinizing Hormone) from the pituitary gland. This negative feedback prevents the development of new ovarian follicles and subsequent ovulation.

Q: Describe the major hormonal changes that occur if fertilization does not happen in a menstrual cycle, and what body process these changes initiate.

If fertilization does not occur, the corpus luteum degenerates, leading to a significant drop in estrogen and progesterone levels. This decline in hormones removes the inhibition on FSH and LH, causing their levels to rise, which in turn initiates the next menstrual cycle and menstruation.

Q: Describe the crucial hormonal event that occurs if fertilization does happen, and how it impacts the corpus luteum and endometrium.

If fertilization occurs, the developing embryo begins to secrete human chorionic gonadotropin (hCG). This hCG acts to maintain the corpus luteum, preventing its degeneration. The sustained corpus luteum continues to produce progesterone, which is essential to preserve the uterine endometrium for pregnancy.

Q: Which primary hormone is responsible for thickening the endometrium during the proliferative phase of the menstrual cycle?

Estrogen is the primary hormone responsible for thickening and rebuilding the uterine endometrium during the proliferative phase.

Q: Which hormone is primarily responsible for maintaining the thick endometrium and stimulating the secretion of nutrient-rich mucus during the secretory phase of the menstrual cycle?

Progesterone is the primary hormone that maintains the thick endometrium, making it receptive to implantation, and stimulates the secretion of nutrient-rich mucus during the secretory phase.

Q: Explain the negative feedback loop between estrogen and FSH (Follicle-Stimulating Hormone) during the follicular phase.

Low levels of estrogen initially stimulate the release of FSH. However, as the ovarian follicles grow and produce increasing amounts of estrogen, this rising estrogen then exerts negative feedback on the pituitary gland, inhibiting further FSH release.

Q: What are "secondary sexual characteristics," and provide examples.

Secondary sexual characteristics are physical traits that develop during puberty but are not directly involved in reproduction. Examples include voice deepening and body hair growth in males, and breast development and widening of hips in females.

Q: Define "menarche" and "menopause" in the context of the female reproductive life.

Menarche is the term for a female's first menstrual period, signaling the onset of fertility. Menopause is the permanent cessation of menstrual cycles, typically occurring between 45 and 55 years of age, indicating the end of reproductive capacity.

Q: In transcription, differentiate between the "template strand" and the "coding strand" of DNA.

The template strand (or antisense strand) of DNA is the strand that RNA polymerase reads to synthesize a complementary mRNA molecule. The coding strand (or sense strand) of DNA is the non-template strand; it has a sequence identical to the mRNA transcript (with thymine instead of uracil).

Q: What is a promoter sequence, and what is its role in transcription?

A promoter sequence is a specific region of DNA located upstream of a gene. It serves as the binding site for RNA polymerase, signaling the start point for transcription.

Q: What three key modifications occur during mRNA processing in eukaryotes before the mRNA exits the nucleus?

The three key modifications are:

1. The addition of a 5' cap (a modified guanine nucleotide) to the beginning.
2. The addition of a 3' poly-A tail (a long chain of adenine nucleotides) to the end.
3. Intron splicing, where non-coding intron sequences are removed, and exons are ligated together.
   These processes prepare the mRNA for export and translation.

Q: Approximately how quickly can a ribosome assemble a protein molecule of 400 amino acids?

A ribosome can typically assemble a protein containing 400 amino acids in about 20 seconds.

Q: Explain how genes relate to the production of non-protein biomolecules like lipids and carbohydrates. Do genes code for them directly?

Genes do not directly code for lipids or carbohydrates. Instead, genes code for the enzymes that catalyze the metabolic pathways involved in building, modifying, and breaking down lipids and carbohydrates.

Q: List several biological and environmental factors that can influence or modulate gene activity and expression within a cell.

Gene expression can be modulated by a variety of factors, including: the cell's age, circadian rhythms (internal biological clocks), intercellular signals (e.g., hormones, growth factors), environmental cues (e.g., diet, chemicals, stress), and the cell's division status.

Q: Describe the effect of acetylation on chromatin structure and its consequence for gene transcription.

Acetylation, specifically the addition of acetyl groups to the tails of histone proteins, loosens the compact structure of chromatin. This 'opens up' the DNA, making it more accessible for transcription factors and RNA polymerase, thereby enhancing gene expression.

Q: What are CpG sites, and what is their significance in epigenetic gene regulation?

CpG sites are regions in the DNA molecule where a cytosine nucleotide is located next to a guanine nucleotide, linked by a phosphate group. These sites are important because they are frequently targeted for DNA methylation, an epigenetic modification that can lead to gene silencing.

Q: How do external environmental factors influence the epigenome, and what is the outcome regarding gene expression?

External environmental factors can alter an individual's epigenetic patterns, specifically by modifying DNA methylation or histone acetylation. These alterations can switch genes on or off, changing gene expression without changing the underlying DNA nucleotide sequence.

Q: Describe the key physiological events occurring in a female's reproductive cycle around Day 1 (assuming a 28-day cycle).

Around Day 1, the menstrual phase begins, where the uterine endometrium is shed. Concurrently, several ovarian follicles begin to develop, and hormone levels are low for estrogen and progesterone, while FSH (Follicle-Stimulating Hormone) levels typically start to rise.

Q: Describe the key physiological events occurring in a female's reproductive cycle around Day 14 (assuming a 28-day cycle).

Around Day 14, ovulation occurs, typically triggered by a surge in LH (Luteinizing Hormone). The uterine endometrium completes its proliferative phase, having thickened under the influence of rising estrogen, and progesterone levels are just beginning to rise as the follicle transforms into the corpus luteum.

Q: Describe the key physiological events occurring in a female's reproductive cycle around Day 21 (assuming a 28-day cycle).

Around Day 21, the corpus luteum is fully active in the ovary, secreting high levels of progesterone and some estrogen. The uterus is in its secretory phase, characterized by a thick, glandular endometrium prepared for implantation. Due to high progesterone, FSH and LH levels are suppressed via negative feedback.

Q: What hormones does the corpus luteum produce after ovulation, and what is their primary role?

After ovulation, the corpus luteum primarily produces progesterone, along with some estrogen. These hormones are crucial for maintaining the thickened uterine endometrium, preparing it for possible embryo implantation, and sustaining early pregnancy.

Q: How do typical oral contraceptive pills work to prevent pregnancy?

Oral contraceptive pills typically contain synthetic forms of estrogen and progesterone. These synthetic hormones primarily work by inhibiting the release of FSH (Follicle-Stimulating Hormone) and LH (Luteinizing Hormone) from the pituitary gland, thereby preventing ovulation. They can also thicken cervical mucus and thin the uterine lining.

Q: What are Sertoli cells, and what is their function in male reproduction?

Sertoli cells (also known as "nurse cells") are located within the seminiferous tubules of the testes. Their primary function is to support, nourish, and regulate the maturation of developing sperm cells from spermatogonia into spermatozoa.

Q: What is the epididymis, and what is its role in sperm maturation?

The epididymis is a coiled tube located on the posterior side of each testis. It serves as the primary site where sperm are stored and undergo final maturation, gaining motility and the ability to fertilize an egg, after their production in the seminiferous tubules.