MCAT Biology CH 2: Cell Cycle, Mitosis, Meiosis & Reproductive System

What is the main focus of Chapter 2 in the MCAT Biology playlist?

Reproduction, including the cell cycle, mitosis, meiosis, and the reproductive system.

What are the four main stages of the cell cycle?

G1, S, G2, and M phases.

What does the G1 phase of the cell cycle stand for?

Gap 1, where the cell grows and carries out normal functions.

What occurs during the S phase of the cell cycle?

DNA replication, where each chromosome makes an exact copy of itself.

What is the purpose of the G2 phase?

Final preparations for cell division, including organelle replication.

What does the M phase of the cell cycle encompass?

Mitosis and cytokinesis, where the cell divides into two daughter cells.

What is interphase?

The collective term for G1, S, and G2 phases when the cell is not dividing.

What is the G0 phase?

A resting state where the cell is alive but not preparing to divide.

What is the role of the G1 to S checkpoint?

To assess the condition of DNA and determine if it is safe to replicate.

What protein is crucial at the G1 to S checkpoint?

p53, known as the guardian of the genome.

What does the G2 to M checkpoint ensure?

That the cell has grown sufficiently and all organelles are properly duplicated.

What are cyclins?

Regulatory proteins whose concentrations fluctuate throughout the cell cycle.

What are cyclin-dependent kinases (CDKs)?

Enzymes that are activated when bound to cyclins and drive the cell cycle forward.

What happens if checkpoint proteins like p53 are mutated?

Cells may divide uncontrollably, leading to cancer.

What is the main purpose of mitosis?

To evenly divide genetic material between two daughter cells.

What type of cells undergo mitosis?

Somatic cells, which are all body cells except sperm and egg.

What is the end result of mitosis?

Two identical diploid daughter cells.

What are the stages of mitosis?

Interphase, prophase, metaphase, anaphase, and telophase.

What is cytokinesis?

The final physical separation of the cytoplasm during cell division.

How does the cell cycle ensure accurate DNA replication?

Through checkpoints and molecular regulators like cyclins and CDKs.

What is the significance of sister chromatids?

They are identical strands of DNA connected at the centromere, formed during S phase.

What happens during prophase?

Chromatin condenses into visible chromosomes, and the nuclear envelope begins to break down.

What occurs during metaphase?

Chromosomes align at the cell's equatorial plane.

What happens during anaphase?

Sister chromatids are pulled apart to opposite poles of the cell.

What occurs during telophase?

Nuclear envelopes reform around each set of separated chromosomes.

What is the role of transcription factors in the cell cycle?

They initiate the expression of genes required for the next stage of the cell cycle.

What is the relationship between cyclins and CDKs?

Cyclins activate CDKs, which then drive the cell cycle progression.

What is the importance of checkpoints in the cell cycle?

They prevent the cell from progressing if conditions are not favorable, ensuring genomic integrity.

What phases comprise interphase before mitosis?

G1, S, and G2 phases.

What happens during the S phase of interphase?

DNA is copied, resulting in two sister chromatids for each chromosome.

What is the role of centromeres?

They hold sister chromatids together after DNA replication.

What are centrosomes?

Structures made up of two centrioles that organize the mitotic spindle.

What is the function of microtubules during mitosis?

They form the mitotic spindle, which pulls chromosomes apart.

What are kinetochores?

Protein complexes on top of centromeres that serve as attachment points for spindle fibers.

What occurs during prophase?

Centrosomes move apart, spindle fibers grow, kinetochores form, chromatin condenses, and the nuclear membrane breaks down.

What happens during metaphase?

Chromosomes align along the metaphase plate, attached to spindle fibers via kinetochores.

What occurs during anaphase?

Sister chromatids are pulled apart at the centromere toward opposite poles.

What is telophase?

A new nuclear envelope forms around each set of chromosomes, which begin to decondense.

What is the difference between diploid and haploid cells?

Diploid cells have two copies of each chromosome (46 total), while haploid cells have one copy (23 total).

What is the purpose of meiosis?

To produce four non-identical haploid cells for sexual reproduction.

What happens during Prophase I of meiosis?

Homologous chromosomes pair up and exchange DNA through crossing over.

What is synapsis?

The pairing of homologous chromosomes during Prophase I.

What are tetrads?

Structures formed by paired homologous chromosomes during Prophase I, consisting of four chromatids.

What is crossing over?

The exchange of DNA segments between homologous chromosomes at chiasmata.

What is the outcome of crossing over?

The creation of recombinant chromosomes that increase genetic diversity.

What happens during Metaphase I of meiosis?

Tetrads line up at the metaphase plate in random orientation.

What occurs during Anaphase I of meiosis?

Homologous chromosomes are separated and pulled to opposite poles, while sister chromatids remain together.

What happens during Telophase I?

A nuclear envelope begins to form around each set of chromosomes, followed by cytokinesis.

What is the significance of genetic variation in meiosis?

It ensures diversity in the offspring through processes like crossing over and random assortment.

How many rounds of division occur in meiosis?

Two rounds: Meiosis I and Meiosis II.

What is the result of meiosis?

Four non-identical haploid cells from one diploid cell.

What is the role of the spindle apparatus?

To facilitate the separation of chromosomes during cell division.

What happens to the nuclear membrane during prophase?

It begins to break down to allow spindle fibers access to the chromosomes.

What does the term 'haploid' refer to?

A cell with one copy of each chromosome, typical of gametes.

What is the chromosome count during anaphase?

The count temporarily doubles as sister chromatids are separated.

What occurs during Telophase I and Cytokinesis in meiosis?

A new nuclear membrane may form around each group of chromosomes, and the cell splits into two haploid daughter cells.

What is the main difference between Meiosis I and Meiosis II?

Meiosis I separates homologous chromosomes, reducing chromosome number, while Meiosis II separates sister chromatids, maintaining chromosome number.

What is the result of Meiosis II?

Four genetically unique haploid daughter cells.

What happens in Prophase II of meiosis?

The spindle forms again in each of the two haploid cells.

What is nondisjunction?

The failure of chromosomes to separate properly during meiosis, leading to gametes with an abnormal number of chromosomes.

What genetic condition can result from nondisjunction?

Down syndrome, caused by an extra copy of chromosome 21.

What is the ploidy of cells produced by mitosis?

Diploid (2n), resulting in two identical diploid cells.

What is the ploidy of cells produced by meiosis?

Haploid (n), resulting in four haploid cells.

Where does mitosis occur?

In all dividing cells of the body, such as skin, blood, and liver cells.

Where does meiosis occur?

In germline cells that give rise to sperm or egg, specifically for sexual reproduction.

What is the main purpose of meiosis?

To produce unique sex cells for reproduction.

What determines biological sex in humans?

The 23rd pair of chromosomes, known as the sex chromosomes.

What chromosomal combination results in a genetically female individual?

Two X chromosomes (XX).

What chromosomal combination results in a genetically male individual?

One X and one Y chromosome (XY).

What is the role of the SRY gene?

It triggers the development of testes during embryogenesis, leading to male reproductive structure development.

How do females (XX) inherit X-linked genes?

They have two alleles for each X-linked gene and can be homozygous dominant, homozygous recessive, or heterozygous.

What does it mean for a female to be a carrier of an X-linked disorder?

She has one normal allele and one mutated allele, typically not expressing the disorder but can pass the mutated allele to offspring.

Why are X-linked disorders more common in males?

Males are hemizygous for X-linked genes and will express any mutation present on their single X chromosome.

What are Sertoli cells?

Cells within the seminiferous tubules of the testes that provide structural and nutritional support to developing sperm.

What is the function of the testes?

To produce sperm and secrete testosterone.

What happens during Anaphase II of meiosis?

The sister chromatids are pulled apart toward opposite poles.

What is the outcome of meiosis in females?

Only one of the four haploid cells becomes a mature ovum; the others degenerate.

What is the difference between homologous chromosomes and sister chromatids?

Homologous chromosomes are pairs of chromosomes from each parent, while sister chromatids are identical copies of a single chromosome.

What is the role of the scrotum?

To house the testes and regulate their temperature for optimal sperm production.

What is the primary difference in chromosome behavior between mitosis and meiosis?

In mitosis, homologous chromosomes do not pair up, while in meiosis, they do pair up during Meiosis I.

What do Leydig cells secrete?

Testosterone and other androgens

Where do sperm mature and are stored?

In the epididymis

What is the function of the vas deferens?

To propel sperm toward the urethra during ejaculation

What do seminal vesicles produce?

A fluid rich in fructose for sperm energy

What is the function of the prostate gland?

To contribute an alkaline fluid that helps sperm survive in the vaginal environment

What do bulbourethral glands secrete?

A clear, lubricating mucus to prepare the urethra for semen

What is spermatogenesis?

The formation of sperm cells through meiosis

What is the first cell type in spermatogenesis?

Spermatogonium

What does a primary spermatocyte divide into?

Two secondary spermatocytes

What do secondary spermatocytes produce?

Two spermatids each after undergoing Meiosis II

What is spermiogenesis?

The maturation of spermatids into spermatozoa

What is contained in the head of a sperm?

The nucleus and acrosome

What is the function of the midpiece of a sperm?

To produce ATP for sperm movement

What is the role of the tail (flagellum) in sperm?

To propel the sperm forward

How long does spermatogenesis take?

About 64 to 72 days

What are the gonads in females?

The ovaries

What do ovaries produce?

Ova (eggs) and female sex hormones (estrogen and progesterone)

What is ovulation?

The release of a mature egg from the ovary

What is the infundibulum?

The part of the fallopian tube that captures the egg

What is the main role of the uterus?

To support and nourish a developing embryo