Biología celular: Ciclo celular y tumores

Cell and Nuclear Division

• Cells in multicellular organisms do not grow to sizes as large as shown in diagrams, for illustrative purposes only.
• Cell size affects the efficiency of diffusion. Smaller cells have a greater surface area to volume ratio, making diffusion more efficient for exchanging materials with the environment.

Multicellular Organisms

• Large organisms are multicellular, composed of many cells.
• Cells possess distinct properties and perform specific functions in the body.
• There are different types of cells that make up different tissues, and these different tissues carry out different functions.
• The genome is the complete set of genes in an organism.

Human Embryonic and Fetal Development

• Stages of development include fertilized egg, 2-cell stage, 4-cell stage, 8-cell stage, 16-cell stage, blastocyst, foetus - 4 weeks, foetus - 10 weeks, foetus - 16 weeks, foetus - 20 weeks.
• Visual representations of these stages are provided.

Stem Cells

• Stem cells have the potential to divide and differentiate along different pathways, forming various cell types.
• Stem cells are visualised and examples of cells they differentiate into are shown: muscle cells, blood cells, nerve cells, cardiac cells, intestinal cells, and liver cells.

Cell Division

• All organisms need to produce new cells for growth, maintenance, and reproduction.
• A single cell divides into two daughter cells.
• The parent cell disappears, unlike reproduction in animal parents.
• New cells are formed only by the division of pre-existing cells.

Roles of Mitosis and Meiosis

• Mitosis produces genetically identical cells and 2n is the diploid number of chromosomes.
• Meiosis halves the chromosome number from diploid 2n to haploid n and generates genetic diversity.

Chromosomes

• Each chromosome is made up of tightly coiled DNA around histone proteins, which are structural proteins.
• The coiled DNA/chromosome structure is the condensed form.
• The uncoiled DNA/chromatin structure is the relaxed state.
• Sister chromatids are two identical copies of a chromosome that are held together.
• The centromere is a constriction point in the chromosome that joins the sister chromatids.

Chromatin

• Electron micrograph/microscopic image of chromatin is presented.

Chromosome Structure

• Chromatin/chromosome structure is explained with a diagram
• Key structural components like telomeres, nuclear pores, solenoids, chromatin fiber, DNA helix (double helix), and histones are labelled.

Cell Cycle

• The cell cycle is a series of events that occur between one cell division and the next.
• It has two main phases: interphase and cell division.
• Interphase is composed of three phases: G1, S, and G2.
• Each phase is characterized by specific events
• G1 phase: Cell growth, protein synthesis, organelles duplication.
• S phase: DNA replication, chromosome duplication.
• G2 phase: Preparation for mitosis, protein synthesis for division.

Interphase Steps

• Cell growth, protein synthesis, copying of organelles, DNA replication occur in specific phases of the cell cycle.
• G1 phase: Initial period of growth and preparation for DNA replication.
• S phase: DNA synthesis occurs to create a duplicate of each chromosome.
• G2 phase: The final growth period for preparation and organization for the division process.

DNA Replication

• DNA replication is necessary for both mitosis and meiosis.
• Early interphase: Single chromatid before DNA replication
• Prophase: Replicated chromosome with two chromatids
• Metaphase: Arrangement of chromosomes on the metaphase plate
• Anaphase: Separation of sister chromatids
• Stages are accompanied by diagrams and explanations of the processes

Microtubules Organizing Centres (MTOCs)

• Microtubules move and separate chromosomes during mitosis.
• MTOCs are regions in the cell where microtubules are organized.
• Astral microtubules and kinetochore microtubules (K-fibres) are labelled and explained

Kinetochore

• Protein structures called kinetochores are assembled on centromeres of chromatids.
• The kinetochore acts as a motor for microtubules by removing tubulin subunits.
• Kinetochores are essential in moving chromosomes during cell division, by attaching to microtubules and pulling them towards opposite poles.

Tubulin

• Microtubules are made up of tubulin protein, consisting of alpha-tubulin and beta-tubulin subunits.

Phases of Mitosis

• Mitosis is the process by which a cell's nucleus divides to form two identical nuclei.
• Prophase, metaphase, anaphase, and telophase are stages.
• Diagrams and descriptions of the events in each phase are included.

Interphase-preceding Mitosis

• Chromosomes are dispersed in the nucleus
• All DNA is replicated and each chromosome consists of two chromatids containing identical DNA.

Prophase

• Chromosomes condense to form thicker, shorter structures, a process that continues throughout all of prophase.
• Microtubules grow from structures called microtubule organizing centers (MTOCs) towards opposite poles of the cell

Metaphase

• Chromosomes align at the equator of the cell.
• The nuclear membrane breaks down.
• Microtubules grow from the poles, attaching to the centromere of each chromatid.

Anaphase

• Sister chromatids separate and move to opposite poles of the cell
• Cohesin that held the sister chromatids together at the centromere is cut
• Chromosomes move to opposite sides/poles.

Telophase

• Chromosomes decondense.
• The nuclear membrane reforms around the chromosomes at each pole of the cell.
• Cytoplasmic division/cytokinesis begins.

Interphase following Mitosis

• Chromosomes in a cell consist of a single DNA molecule, dispersed throughout the nucleus.
• Cytokinesis produces completed cells through dividing the cytoplasm.
• Cell growth is very active

Cytokinesis

• The division of the cytoplasm to form two cells.
• In plant cells: new cell wall forms across the equator, with plasma membrane on both sides, dividing the cell in two.
• In animal cells: Plasma membrane is pulled inwards until it meets in the centre of the cell, dividing it in two using contractile proteins, like actin and myosin.
• Diagrams illustrating both plant and animal cytokinesis are included.
• Different types of cytokinesis (equal, unequal, occasional plant division) are explained.

Meiosis

• Halves the chromosome number, crucial for sexual reproduction.
• Meiosis involves two divisions of a cell, with a replication of DNA before the first division but not the second.
• Specific phases (Prophase I, Metaphase I, Anaphase I, Telophase I, Prophase II, Metaphase II, Anaphase II, Telophase II) are described, with diagrams highlighting the events that take place in each phase.
• The initial cell contains a diploid 2n number of chromosomes.
• The resulting/final cell contains a haploid n number of chromosomes.

Meiosis and Genetic Variation

• Meiosis contributes to genetic variation through crossing over, random orientation.

Non-Disjunction and Down Syndrome

• Non-disjunction is when chromosomes do not separate correctly during anaphase.
• This can lead to an abnormal number of chromosomes in the daughter cells, such as trisomy (e.g., Down Syndrome, trisomy 21).
• Errors during meiosis can result in non-disjunction, leading to incorrect chromosome numbers in gametes.

Data-based Questions: Parental Age and Non-disjunction

• Data suggests the link between parental age and the risk of non-disjunction, which leads to chromosomal abnormalities like Down syndrome.
• Analysis of factors that affect the rate of non-disjunction, including maternal age, needs further study.

Cyclins and Cell Cycle Control

• Proteins called cyclins direct the stages of the cell cycle, activating associated kinases.
• Checkpoints ensure only appropriate cells continue through the cycle and ensures cell proliferation does not happen excessively.

Consequences of Mutations in Genes that Control the Cell Cycle

• Loss of cell cycle control can lead to tumour formation.
• Oncogenes, proto-oncogenes and tumor-suppressor genes are defined and how mutations can lead to cancer
• The abnormal behavior of abnormal cells, such as rapid division and metastasis, can cause cancer.

Cancer

• Cancer is caused when cells divide repeatedly and form a single mass; called a primary tumour.
• Metastasis is the spread of cancer cells beyond the original site.
• Cells can invade nearby tissues and may also travel to other sites.

Mitotic Index

• The mitotic index is the ratio of cells in mitosis to the total number of cells.
• Doctors utilize this index to predict the rate of tumour growth in cancer.

Este cuestionario evalúa tu conocimiento sobre el ciclo celular, los proto-oncogenes, los genes supresores de tumores y la apoptosis. A través de diversas preguntas, explorarás conceptos fundamentales relacionados con la función de las ciclinas y el impacto de los mutágenos. ¡Prepárate para poner a prueba tu comprensión de estos temas clave en biología celular!