What is the most promising place for extraterrestrial life in our solar system?

🪐🌑Just two decades ago, scientists expected that the sixth largest of Saturn’s moons, Enceladus, to be a frozen ice ball.

🌑🌊However, in 2005, robotic spacecraft Cassini sent to study Saturn and its rings and moons detected plumes of water vapor and icy particles erupting from geysers on the surface, revealing the existence of a global ocean between the moon's icy shell and its rocky core ⬆️.

❗️In 2023, researchers announced that that they had found phosphorous in the ocean on Enceladus.

ℹ️Of the six elements required for life (carbon, hydrogen, nitrogen, oxygen, and sulfur were already found on Enceladus), phosphorus was the only one building block that astronomers had not yet detected in material from Enceladus.

‼️According to scientists, this one of the most important space discoveries of 2023 makes Enceladus the most promising place for extraterrestrial life in our solar system.

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What are 2023 remarkable climate highlights?

🔴 2023 is confirmed as the warmest calendar year in global temperature data records going back to 1850.

🌐 2023 had a global average temperature of 14.98°C, 0.17°C higher than the previous highest annual value in 2016.

🔴 2023 was 0.60°C warmer than the 1991-2020 average and 1.48°C warmer than the 1850-1900 pre-industrial level.

🔴 Almost each month in 2023 was warmer than the corresponding month in any previous year.

🌐🌊 Global average sea surface temperatures (SSTs) reached record levels for the time of year from April through December.

🇦🇶 Antarctic sea ice reached all-time minima in February 2023 and record low extents for the corresponding time of the year in 8 months.

🔥 A large number of extreme events (heatwaves, floods, droughts and wildfires) were recorded across the globe. Estimated global wildfire carbon emissions in 2023 increased by 30% with respect to 2022 driven largely by wildfires in Northern America.

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What are notable global heat and cold records for 2023?

☀️🇺🇸Hottest temperature in the Northern Hemisphere: 53.9°C (129.0°F) at Saratoga Spring, USA, July 16

❄️🇷🇺Coldest temperature in the Northern Hemisphere: -62.7°C (-80.9°F) at Tongulah, Russia, January 18

☀️🇦🇺Hottest temperature in the Southern Hemisphere: 49.5°C (121.1°F) at Roebourne, Australia, December 31

❄️🇦🇶Coldest temperature in the Southern Hemisphere: -83.2°C (-117.8°F) at Concordia, Antarctica, July 25

🔺🇸🇳Highest 2023 average temperature in the Northern Hemisphere: 32.2°C (90.0°F) at Matam, Senegal

🔻🇮🇩Highest 2023 average temperature in the Southern Hemisphere: 29.7°C (85.5°F) at Surabya AP, Indonesia

🥵A total of 175 monthly national/territorial heat records beaten or tied in 2023

🥶A total of nine monthly national/territorial cold records beaten in 2023

ℹ️Earth’s all-time record for hottest yearly average temperature was 32.9°C (91.2°F) at Makkah, Saudi Arabia, in 2010 and 2016.

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What drug made 2023 a revolutionary year for weight loss?

✔️ Wegovy, initially prescribed for diabetes, emerged as a revolutionary weight-loss drug. Never before has there been an approved weight loss medicine that is so effective and yet also considered reasonably safe.

✔️ Wegovy is the newest glucagon-like peptide-1 receptor agonist (GLP-1RA). Glucagon-like peptide-1 (GLP-1) is an incretin, a metabolic hormone secreted from the L-cells of the small intestine and colon and specialized cells in the brainstem within a few minutes of eating.

✔️ In a two-year trial, Wegovy participants shed 15% body weight, dwarfing the control group's 3%. Trials also hinted at its potential benefits like reducing heart attack and stroke risks and aiding addiction treatment.

✔️ However, Wegovy's side effects, like nausea and a potential risk of thyroid cancers, caution against unbridled optimism.

ℹ️ Global obesity affects 650 million adults, surpassing undernourished populations at 735 million.

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What is the smallest common denominator of life?

📍 Cells are the smallest common denominator of life.

📌 Some cells are organisms unto themselves; others are part of multicellular organisms.

📌 All cells are made from the same major classes of organic molecules: nucleic acids, proteins, carbohydrates, and lipids.

📌 Cells can be placed in 2️⃣ major categories as a result of ancient evolutionary events:

1️⃣ Prokaryotes, such as bacteria and archaea, with their cytoplasmic genomes, are single cells.

2️⃣ Eukaryotes, with their nuclear-encased genomes and other subunits. Some eukaryotes, like amoebae, are free-living, single-celled entities. Other eukaryotic cells are part of multicellular organisms. For instance, all plants and animals are made of eukaryotic cells — sometimes even trillions of them.

📌 Though they are small, cells have evolved into a vast variety of shapes and sizes. Together they form tissues that themselves form organs, and eventually entire organisms.

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What are intracellular molecules’ functions?

Intracellular organic molecules include:

🧬2️⃣ Nucleic acids contain and help express a cell's genetic code.
Deoxyribonucleic acid (DNA) contains all of the information required to build and maintain the cell.
Ribonucleic acid (RNA) has several roles associated with expression of the information stored in DNA.

⚪️ Proteins are made from chains of smaller molecules called amino acids, and serve catalytic and structural functions. E.g., proteins called enzymes convert cellular molecules into other forms that might help a cell meet its energy needs, build support structures, or pump out wastes.

🔴 Carbohydrates provide energy and can be of 2️⃣ types:
✔️simple carbohydrates are used for the cell's immediate energy demands
✔️complex carbohydrates serve as intracellular energy stores and also play a crucial role in cell recognition.

🟡 Lipids are components of cell membranes, involved in energy storage and relaying signals.

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What is found inside a prokaryotic cell?

A prokaryotic cell ⬆️ is usually small and relatively simple in structure.

Its components are ⬇️:

Capsule: layer of carbohydrates that surrounds the cell wall of some bacteria and helps them attach to surfaces

Cell wall: consists of peptidoglycans that give the cell structure and protection

Cell/plasma membrane, which encloses the cytoplasm and separates the cell from the environment

Cytoplasm: region enclosed by the cell membrane, where genetic material and processes occur

Nucleoid: region that contains DNA

Plasmids: independently reproducing DNA

Ribosome: performs protein synthesis

Flagella: thin, tail-like structures that aid movement

Pili/sex pilus: short, rod-shaped structures involves in attachment to surfaces and DNA transfer

Fimbriae: thin, hair-like structures used for attachment

Vesicles: sacs released by the membrane that perform a variety of functions

Vacuoles: storage sacs found in some bacterial cells

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What are key eukaryote features?

Plant and animal cells ⬆️ are examples of eukaryotic cells.

They have a true nucleus and membrane-bound compartments with specific functions – organelles.

Here are key eukaryote features ⬇️

Nucleus: contains DNA and oversees all cell processes

Nucleolus: site of ribosome biogenesis

Plasma membrane: encloses the cell

Cytoplasm: region between the nuclear and the plasma membranes

Cell wall: supports and protects plant, algae, and fungi cells

Centrosomes and Centrioles: play a role in cell division

Mitochondria: provide chemical energy

Chloroplasts: traps energy for photosynthesis in plant cells

Lysosomes: digests excess or worn-out organelles, food particles, and engulfed viruses or bacteria

Ribosomes: perform protein synthesis

Endoplasmic reticulum (ER): synthesizes proteins (rough ER) and lipids (smooth ER)

Golgi apparatus: sorts, packages, and processes proteins

Vesicles and vacuoles: membrane-bound storage and transportation sacs

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How scientists were discovering the cell?

While the invention of the telescope made the Cosmos accessible to human observation, the light microscope opened up smaller worlds, showing what living forms were composed of.

🔬 The cell was first discovered and named by an English “natural philosopher” Robert Hooke (1635-1703) in 1665. Using three lenses and a stage light, he improved the design of his compound microscope ⬆️, which allowed to see tiny pores in a piece of cork. Hooke came to call his discovery “cells”, “small rooms” in Latina, because they reminded him of the cells in a monastery. However, Hooke didn't realize at that time that “cells” could be alive.

🔬🦠 The first man to witness a live cell was a Dutch scientist, often called the “father of microscopy”, Anton van Leeuwenhoek (1632-1723), who, in 1674, described the algae Spirogyra and also protozoa and bacteria that he called “animalcules”. He was also the first to observe and describe spermatozoa in 1677.

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How the scientific study of cells was founded and developed?

ℹ️ Cytology or Cell biology is the scientific study of cells.

📍 German scientists Theodore Schwann (1810–1882) and Mattias Schleiden (1804–1881) studied cells of animals and plants respectively. They identified key differences and similarities between the two cell types and in 1838-39 put forth the idea that cells were the fundamental units of both plants and animals. Thus, Schwann and Schleiden are generally regarded as the first scientists to establish cell theory.

☑️ However, both Schwann and Schleiden misunderstood how cells grow.
▪️ Schleiden believed that cells were “seeded” by the nucleus and grew from there.
▪️ Similarly, Schwann claimed that animal cells “crystalized” from the material between other cells. He summarized his observations into three conclusions about cells:
✅ The cell is the fundamental unit of structure, physiology, and organization in living things.
✅ The cell retains a dual existence as a distinct entity and a building block in the construction of organisms.
❌Cells form by free-cell formation, similar to the formation of crystals (spontaneous generation).
Today it is known that the first two tenets are correct, but the third is clearly wrong.

📍 Another piece of the cell theory puzzle was identified by another German researcher Rudolf Virchow (1821-1902) in 1855, who stated that all cells are generated by existing cells – Omnis cellula e cellula: “All cells only arise from pre-existing cells”.

📍 The key tenets of the modern cell theory are:
✅ All known living things are made up of cells.
✅ The cell is the structural & functional unit of all living things.
✅ All cells come from pre-existing cells by division. (Spontaneous Generation does not occur).
✅ Cells contain hereditary information, which is passed from cell to cell during cell division.
✅ All cells are basically the same in chemical composition.
✅ All energy flow (metabolism & biochemistry) of life occurs within cells.

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How is the proper growth and replication of cells ensured?

The process which is vital for the growth, development, repair, and maintenance of living organisms is called the cell cycle. It is a series of events that cells go through to grow, replicate their DNA, and divide.

The two broad phases of the cell cycle are:
1️⃣ Interphase, during which cells grow, replicate their DNA and organelles, and prepare for division.
2️⃣ Mitosis, a process of cell division that results in two genetically identical daughter cells from a single parent cell.

ℹ️ The term “mitosis” was coined by Walther Flemming (1843-1905) in 1882 while documenting the process of chromosomal division in salamander larvae. The term comes from the Greek word ‘mitos’ meaning ‘thread,’ referring to the thread-like appearance of chromosomes during mitosis. Other names for the process are ‘karyokinesis’ (Schleicher, 1878) and ‘equatorial division’ (August Weismann, 1887).

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What are cell cycle phases in detail?

1️⃣ Interphase, the period preceding mitosis, is the longest phase of the cell cycle and has three distinct sub-stages.
🔻G1 Phase (Gap 1): right after cell division cells increase in size, produce RNA and synthesize proteins. Importantly, this phase ensures that everything is in place for DNA synthesis to occur in the next phase.
🔻S Phase (Synthesis): the cell’s DNA replicates, and at the end of this phase, each chromosome consists of two chromatids attached at the centromere.
🔻G2 Phase (Gap 2): the cell continues growing and prepares for mitosis, ensuring that all the DNA has been replicated without any errors.

2️⃣ Mitosis or the M phase, has multiple steps:
🔻Prophase: Chromosomes condense and become visible, the nuclear envelope starts to disintegrate, and the mitotic spindle begins to form.
🔻Metaphase: Chromosomes line up along the cell’s equatorial plate, and spindle fibers attach to the centromeres.
🔻Anaphase: Sister chromatids are pulled apart towards opposite poles of the cell.
🔻Telophase: The chromatids or chromosomes move to opposite ends of the cell and two nuclei form.
🔻Following mitosis (or as its final step), the cell undergoes cytokinesis where the cytoplasm divides, creating two daughter cells.

⚪️ The G0 phase is a “resting” phase where the cell exits the cell cycle and stops dividing. Some cells, like neurons and muscle cells, enter this phase semi-permanently and may never undergo division again. It is crucial for:
✔️Conserving energy and resources in non-dividing cells.
✔️Specializing cells for specific functions.
✔️Regulation of the Cell Cycle:

🟩 Checkpoints tightly regulate the cell cycle to prevent errors:
✅ G1 Checkpoint ensures that the cell has adequate energy resources and that the surrounding environment is favorable for DNA replication. If conditions aren’t right, the cell can exit to G0 phase.
✅ G2 Checkpoint confirms that DNA has replicated properly.
✅ M Checkpoint (Spindle Assembly Checkpoint) occurs during metaphase in mitosis and ensures that all chromosomes properly align and attach to the spindle fibers.

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What happens if cells do not go through all checkpoints?

Not all cells go through all checkpoints of the cell cycle. Some fast-track through certain phases. Also, the time it takes for cells to complete the cycle varies. In humans, it ranges from two to five days for epithelial cells to an entire lifetime for certain neurons and cardiac cells.

Disruption in these regulatory checkpoints can lead to cells with damaged or missing genetic material.

Deregulation of the cell cycle can have grave consequences. When the checkpoints fail, it can result in:
🆘 Cells with incomplete or damaged DNA.
🆘 Uncontrolled cell division.

This uncontrolled division and growth of cells leads to the formation of tumors. Not all tumors are malignant, but those that are can invade nearby tissues and spread to other parts of the body (metastasis), leading to cancer ⬆️.

ℹ️ Cancer is a disease in which some of the body’s cells grow uncontrollably and spread to other parts of the body.

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Which type of cell division is crucial for sexual reproduction and genetic diversity?

🟢↔️🟢 A type of cell divison that ensures genetic diversity and the continuity of species through sexual reproduction is called meiosis.

It is the process that is not part of the cell cycle and where a cell replicates DNA once but divides twice, producing four cells that have half the genetic information of the original cell. It is how organisms produce gametes or sex cells, which are eggs in females and sperm in males.

Meiosis involves 2️⃣ divisions, so it’s typically broken down into meiosis I and meiosis II ⬆️.

✔️ Cells enter meiosis I from interphase, which is much like interphase in the cell cycle. When cells commit to meiosis, DNA replicates. It consists of:
Prophase I
Metaphase I
Anaphase I
Telophase I

✔️ Meiosis II is similar to mitosis but involves the division of haploid cells. It consists of:
Prophase II
Metaphase II
Anaphase II
Telophase II

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What are critical functions of meiosis?

Meiosis has several critical functions in organisms:

1️⃣ Production of Gametes is one of the primary functions. In animals, these gametes are the sperm and egg cells. In plants, meiosis leads to the formation of spores, which then develop into gametophytes that produce gametes.

2️⃣ Halving the Chromosome Number:
The chromosome number of a species remains constant from one generation to the next. By reducing the chromosome number by half, gametes form with a haploid (n) set of chromosomes. When two gametes fuse during fertilization, this restores the diploid (2n) number of chromosomes in the zygote, ensuring genetic stability across generations.

3️⃣ Promotion of Genetic Variation in multiple ways:
▪️Crossing-over: During prophase I, homologous chromosomes undergo crossing-over, where sections of chromatids exchange places. This results in new combinations of genes on each chromatid.
▪️ Independent Assortment: During metaphase I, how the pairs of homologous chromosomes line up at the metaphase plate is random. This means that different combinations of maternal and paternal chromosomes end up in each gamete.
▪️ Random Fertilization: The fusion of any sperm with any egg during fertilization adds another layer of genetic variability.

4️⃣ Evolutionary Significance:
The genetic variation introduced by meiosis provides raw material for natural selection. Organisms with advantageous genetic combinations are more likely to survive and reproduce, passing on those beneficial genes to their offspring. Over time, this leads to evolutionary changes in populations.

5️⃣ Repair of DNA Damage:
Before entering meiosis, cells undergo DNA repair mechanisms. If there’s damage to the DNA, the processes within meiosis, especially recombination, help correct certain types of damage. This ensures that genetic information passes to the next generation as accurately as possible.

6️⃣ Prevention of Chromosomal Abnormalities:
Gametes receive the correct number of chromosomes. Errors in this process lead to conditions like Down syndrome, where an individual has an extra chromosome 21.

✍️ Summary: meiosis maintains the chromosome number across generations, generates genetic diversity, aids in evolutionary processes, repairs DNA, and prevents chromosomal abnormalities.

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