Cell Cycle and Genetics

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Explore the cell cycle and cellular division in eukaryotic cells, leading to the creation of identical daughter cells, and contrast it with prokaryotic binary fission. Understand Mendelian inheritance and the genetic variation it explains, along with the structure and function of DNA. Delve into gene expression and its regulation, and how developmental biology and evolution shape life.

Summary

Outline

The Cell Cycle and Cellular Division

The cell cycle is an essential series of events in eukaryotic cells leading to cell division and the creation of two genetically identical daughter cells. It consists of interphase, during which the cell grows and replicates its DNA, and the mitotic phase, which includes mitosis and cytokinesis. Mitosis is subdivided into prophase, metaphase, anaphase, and telophase, and results in the segregation of duplicated chromosomes into two new nuclei. Cytokinesis is the process that divides the cytoplasm, completing cell division. In contrast, meiosis is a specialized cell division that produces four non-identical haploid cells, each with half the number of chromosomes, which is crucial for sexual reproduction. This process includes two successive divisions: meiosis I and meiosis II, and introduces genetic diversity through processes such as crossing over and independent assortment.

Cell undergoing mitosis with visible X chromosomes, spindle fibers attached to centromeres and daughter cells in interphase on the blue background.

Prokaryotic Cell Division and Binary Fission

Prokaryotic cell division occurs through binary fission, a simpler and quicker process than eukaryotic cell division. In this process, the single, circular DNA molecule replicates, and the cell grows, with the two copies of DNA attaching to different parts of the cell membrane. A septum then forms in the center of the cell, and the cell membrane pinches inward, eventually dividing the cell into two genetically identical daughter cells. The protein FtsZ plays a critical role in septum formation by assembling into a Z-ring at the future site of the septum. This process ensures the propagation of the prokaryotic species and can occur rapidly under favorable conditions.

Mendelian Inheritance and Genetic Variation

Mendelian genetics is the study of how traits are inherited through discrete units of inheritance known as genes. Gregor Mendel's laws of inheritance include the law of segregation, which states that allele pairs separate during gamete formation, and the law of independent assortment, which asserts that genes for different traits are distributed to gametes independently. However, the law of independent assortment can be affected by genetic linkage, where genes located close together on the same chromosome tend to be inherited together. The chromosome theory of inheritance integrates Mendel's principles with the behavior of chromosomes during meiosis and has been expanded by molecular genetics to include the structure and function of genes at the DNA level.

DNA Structure and Function

DNA is the molecule that carries the genetic instructions for life. Its structure is a double helix composed of two strands of nucleotides, with each strand consisting of a sugar-phosphate backbone and nitrogenous bases. The sequence of these bases encodes genetic information. DNA replication is a semiconservative process, meaning each new DNA molecule consists of one original and one new strand. Mutations in the DNA sequence can lead to changes in the genotype and potentially the phenotype of an organism. While some mutations are harmful, others contribute to the genetic diversity within a population, which is a key element of evolution.

Gene Expression and Regulation

Gene expression is the process by which the information encoded in a gene is used to direct the synthesis of a functional gene product, usually a protein. This process involves two main steps: transcription, where DNA is copied into messenger RNA (mRNA), and translation, where mRNA is used as a template to assemble amino acids into a protein. The regulation of gene expression is critical for cell function and differentiation and can occur at multiple levels, from DNA accessibility in the chromatin to post-translational modifications of proteins. Regulatory proteins, such as transcription factors, and non-coding RNAs are key players in gene regulation, ensuring that genes are expressed at the right time, place, and amount.

Development, Genes, and Evolution

Developmental biology studies how organisms grow and develop from a single cell into a complex structure. This process is controlled by a network of genes, including the highly conserved developmental-genetic toolkit, which guides the formation of body plans and structures. Evolution is the process by which populations of organisms change over time through mechanisms such as natural selection, genetic drift, and gene flow. Natural selection favors individuals with traits that improve survival and reproductive success. Over time, these changes can lead to the emergence of new species, a process known as speciation. Phylogenetics, the study of the evolutionary relationships among species, provides insights into the history of life on Earth and the common ancestry of all living organisms.

Cell Cycle and Genetics

Cell Cycle

Interphase

During interphase, the cell grows and replicates its DNA

Mitotic Phase

Mitosis

Mitosis is the process of dividing duplicated chromosomes into two new nuclei

Cytokinesis

Cytokinesis is the process of dividing the cytoplasm, completing cell division

Meiosis

Meiosis I

Meiosis I is the first division in the process of creating four non-identical haploid cells

Meiosis II

Meiosis II is the second division in the process of creating four non-identical haploid cells

Prokaryotic Cell Division

Binary Fission

Binary fission is the process of prokaryotic cell division, resulting in two genetically identical daughter cells

Septum Formation

The protein FtsZ plays a critical role in forming a septum during prokaryotic cell division

Mendelian Inheritance

Laws of Inheritance

Law of Segregation

The law of segregation states that allele pairs separate during gamete formation

Law of Independent Assortment

The law of independent assortment states that genes for different traits are distributed to gametes independently

Genetic Linkage

Genetic linkage can affect the law of independent assortment by causing genes located close together on the same chromosome to be inherited together

DNA Structure and Function

DNA Structure

DNA is a double helix composed of two strands of nucleotides, with each strand containing a sugar-phosphate backbone and nitrogenous bases

DNA Replication

DNA replication is a semiconservative process, resulting in two new DNA molecules each consisting of one original and one new strand

Mutations

Mutations in the DNA sequence can lead to changes in an organism's genotype and potentially its phenotype

Gene Expression and Regulation

Gene Expression

Transcription

Transcription is the process of copying DNA into mRNA

Translation

Translation is the process of using mRNA to assemble amino acids into a protein

Gene Regulation

Gene regulation is critical for cell function and differentiation and can occur at multiple levels, from DNA accessibility to post-translational modifications of proteins