Cell Biology: Mitosis, Meiosis, and Cellular Processes

Posted on Sep 24, 2024 in Biology

Mitosis

Mitosis, the process of dividing a nucleus into two identical copies of DNA, consists of several stages:

Prophase

Dispersed chromatin begins to condense.

Metaphase

Chromatin reaches maximum condensation, making chromosomes visible.

Anaphase

The chromatids of each chromosome separate, with one chromatid from each pair moving to opposite cell poles.

Telophase

The chromatids, now daughter chromosomes, are enveloped by a nuclear membrane and begin to decondense. Finally, two daughter nuclei are formed.

Cytoplasm Division

This is the final phase of mitosis. In animal cells, filaments form to constrict and separate the two daughter cells. In plant cells, a cell plate (phragmoplast) forms between the daughter cells.

Meiosis

Meiosis is the cell division process of sex cells. It consists of two divisions:

First Meiotic Division

The most significant difference from mitosis occurs during prophase I.

Prophase I

Homologous chromosomes pair up and exchange genetic material.

Metaphase I

The metaphase plate forms, consisting of two pairs of homologous chromosomes.

Anaphase I

Homologous chromosomes separate, with one chromosome from each pair moving to opposite cell poles.

Telophase I

Two daughter cell nuclei are formed.

Second Meiotic Division

Prophase II

The function of prophase II is to separate the chromatids of each chromosome.

Metaphase II

Daughter chromosomes align at the metaphase plate.

Anaphase II

The chromatids of each chromosome separate and migrate to their respective cell poles.

Telophase II

Sexual gametes are produced. These haploid cells contain half the number of chromosomes as the parent cell. The biological significance of meiosis is to increase genetic diversity.

Eukaryotic Cells

Eukaryotic cells, such as animal and plant cells, store their DNA within a nucleus that is enclosed by a double membrane.

Prokaryotic Cells

Prokaryotic cells, such as bacteria, have their DNA dispersed in the cytoplasm.

Anabolism

Anabolism involves building complex molecules from simpler ones, requiring ATP.

Catabolism

Catabolism involves breaking down complex molecules into simpler ones, releasing energy.

For example, gluconeogenesis is an anabolic reaction, while glycolysis is a catabolic reaction.

Carbohydrates

Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen (CHO). They are classified as monosaccharides, disaccharides, and polysaccharides. Their functions include:

  • Energy: Glucose is the primary sugar used by cells for energy.
  • Reserve: Starch serves as the reserve sugar in plants, while glycogen serves this role in animals.
  • Structural: Cellulose provides structural support in plants, while chitin serves a similar function in fungi and insects.

Lipids

Lipids are organic compounds composed of carbon, hydrogen, and oxygen (CHO) and are mostly insoluble in water. They are classified as fats, waxes, phospholipids, and steroids. Their functions include:

  • Energy: Fats are the primary energy reserve in animals.
  • Regulatory: Some vitamins and hormones are steroids, which regulate various vital processes.
  • Structural: Phospholipids form cell membranes, providing protection and structure.

Proteins

Proteins are organic biomolecules composed of carbon, hydrogen, oxygen, and nitrogen (CHON). Their structure is divided into primary, secondary, tertiary, and quaternary levels. Their functions include:

  • Structural: Collagen provides strength to bones and cartilage, while keratin forms nails and hair.
  • Transport: Hemoglobin transports oxygen in the blood.
  • Regulatory: Insulin regulates blood sugar levels.
  • Contractile: Proteins enable muscle contraction.
  • Immune Defense: Antibodies protect against pathogens.
  • Enzymes: Enzymes act as biocatalysts, speeding up chemical reactions.

Nucleic Acids

Nucleic acids are biomolecules composed of carbon, hydrogen, oxygen, nitrogen, and phosphorus (CONP). They are divided into DNA and RNA.

DNA consists of two strands of nucleotides, forming a double helix structure. It carries genetic information.

RNA is found in both the nucleus and cytoplasm and consists of a single strand of nucleotides. There are three main types of RNA:

  • Messenger RNA (mRNA): Carries genetic information from DNA to ribosomes for protein synthesis.
  • Ribosomal RNA (rRNA): Forms part of the structure of ribosomes.
  • Transfer RNA (tRNA): Transports amino acids to ribosomes for protein synthesis.

Food Chain

Autotrophic organisms, such as plants, produce organic matter from inorganic matter through photosynthesis.

Heterotrophic organisms, such as animals, obtain organic matter by consuming other organisms.

Fermentation

Fermentation is a catabolic process that cells use to degrade organic compounds and obtain ATP in the absence of oxygen. The end products of fermentation are organic matter (e.g., ethanol) and energy. Fermentation is less efficient at producing energy than cellular respiration.

Cellular Respiration

Cellular respiration is a catabolic process that breaks down organic matter to produce ATP in the presence of oxygen. It occurs in three stages:

  1. Glycolysis: Glucose is broken down into smaller molecules.
  2. Krebs Cycle: Organic matter is completely oxidized to inorganic molecules.
  3. Electron Transport Chain: Electrons from the oxidation of molecules are passed along a chain of proteins, generating ATP.

Animal Cell

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