Eukaryotic and Prokaryotic cells

Eukaryotic and Prokaryotic cells

What's a cell?

A cell is a basic unit of life, often described as a “bag” filled with viscous material, surrounded by a plasma membrane. It’s more than just a bag; it’s a complex, organized structure that serves as the building block of all living things. There are two main types of cells: prokaryotic and eukaryotic.

Prokaryotic Cells

Prokaryotic cells are single-celled organisms classified into the domains Bacteria and Archaea. The term “prokaryote” comes from Greek words meaning “before nucleus,” referring to their lack of a true nucleus. In contrast, eukaryotes (including animals, plants, fungi, and protists) have a defined nucleus.

Structures of Prokaryotic Cells.

1. Plasma Membrane: • A double layer of lipids that separates the cell from its environment. • Composed mainly of phospholipids, it controls the movement of substances in and out of the cell. 2. Cytoplasm: • A gel-like fluid where cellular components are suspended, similar to eukaryotic cytoplasm but without organelles. • Contains a cytoskeleton made of filamentous proteins that helps maintain shape and assists in division. 3. Ribosomes: • Smaller and structurally different from eukaryotic ribosomes, they have less rRNA and fewer proteins. • They function to build proteins by translating genetic messages. 4. Genetic Material: • Prokaryotic cells contain a single circular chromosome and may also have plasmids, which are small rings of DNA.

Prokaryotic Cell Wall.

Prokaryotic cells are surrounded by a rigid cell wall, primarily made of peptidoglycan, which provides structural support and protection from stress and lysis.

Appendages

• Flagella: Long, whip-like structures that enable movement toward nutrients or away from harmful substances. • Fimbriae: Short, hair-like structures that allow bacteria to adhere to surfaces and each other, playing a role in virulence. • Pili: Hair-like appendages used for attachment during bacterial conjugation, allowing DNA transfer.

Prokaryotic Ribosomes

Prokaryotic ribosomes are smaller and have a different composition than eukaryotic ribosomes but serve the same essential function: synthesizing proteins by translating messages from DNA.

Eukaryotic cells

Eukaryotic cells are one of the main types of cells. They are larger and more complex, organized into four kingdoms: protists, plants, fungi, and animals. Eukaryotic cells have a membrane-bound nucleus containing multiple linear chromosomes, and they contain various organelles that perform specific functions. While there are differences between plant and animal cells, all eukaryotic cells share common parts: cytoplasm, nucleus, cell membrane, and organelles.

Cytoplasm

fluid content inside the plasma membrane

Cytoplasm is the clear liquid in all cells, consisting of: 1. Cytosol: The fluid containing organelles. 2. Organelles: Specialized structures with functions like respiration and protein synthesis. 3. Cytoplasmic inclusions: Metabolically formed materials (like carbohydrates and proteins) for storage and secretion.

Nucleus

The nucleus is the cell’s control center, surrounded by a double membrane. It contains genetic material (DNA) organized as chromatin, which condenses into chromosomes during division. Nuclear pores regulate molecule transport, and the nucleolus synthesizes rRNA and assembles ribosomes for protein synthesis.

Cell membrane and her structure

The cell membrane surrounds all cells, performing many functions: it protects the integrity of cells, controls the movement of particles in and out, helps support the cell, and interacts with adjacent cell membranes. The fluid mosaic model describes the membrane as a mosaic of phospholipids, cholesterol, and proteins that can move freely in the membrane plane.

MEMBRANE LIPIDS Phospholipids are the major components of plasma membranes, forming a bilayer with hydrophilic heads facing the cytosol and extracellular fluid, while hydrophobic tails face each other. The lipid bilayer is semi-permeable, allowing only certain molecules to diffuse across. Cholesterol is another lipid component of animal cell membranes, helping maintain fluidity and is not present in plant cells.

PROTEINS Membrane proteins may extend partway into the plasma membrane, cross it entirely, or be attached to its inside or outside surface. Structural proteins help give the cell support and shape, receptor proteins help cells communicate with their external environment, and transport proteins transport molecules across membranes through facilitated diffusion.

MEMBRANE LIPIDS & PROTEINS

Organelles

They operate in the cells like organs work in our body, and every organells has a specifictask. They include: nucleus,ribosomes,endoplasmatic reticulum,Golgi apparatus, vacuoles,lysosomes,mithocondria and chloroplasts only in plants.

Ribosomes

Ribosomes are small organelles that are formed of RNA and proteins. Their only function is to assemble proteins and to translate the infos of DNA.

Carbohydrates

Carbohydrates are only present on the surface, and they're attached to proteins forming glycoproteins, if they're attached to lipids they form glycolipids

Endoplasmatic reticulum

Once that the proteins are synthesized by the ribosomes, they move thanks the endoplasmathic reticulum, that moves the proteins from one area to another area of the cell. The reticulum can be rough or smooth: the rough one has ribosomes attached to it; the smooth one doesn't have any ribosomes.

The job of rough E.R is the synthesis and modification of proteins: the Er synthesizes them with a ribosome attached on its membranes,later they modify those proteins, and then they the proteins are trasported into a vesicle.

While the smooth E.R has the job to synthesize lipids and phospholipids.The smooth ER also metabolizes carbohidrates with a detoxification role.

Golgi apparatus

The Golgi apparatus is formed by flattened discs,called cisternae;When the proteins it's out of the rough ER, reaches the Golgi apparatus and it's packaged in new vesicles, and it can be stored out or sented out of the cell. The part where the apparatus receives the proteins it's called cis-face, the part where they release the proteins it's called trans-face.

Lysosomes

Lysosomes contains 50 different digestive enzymes, that have the job to remove bacterias, viruses, food partycles;

Mitochondria

Mitochondria has the job to produce energy through the cellular respiration:in eukaryotic cells the cellular respiration happens in mitochondria;in prokaryotic cells the cellular respiration happens into both mitochondria and citoplasm or cell membrane.

The outer membrane of mitochondria is smooth, while the inner membrane has many folds called cristae. These folds increase the surface area for chemical reactions, which mainly occur on the inner membrane. The two membranes divide the mitochondrion into two parts: the intermembrane space and the mitochondrial matrix, which contains water and proteins (enzymes) involved in cellular respiration.Mitochondria have their own DNA and ribosomes, can produce their own proteins, and have some control over their reproduction. Their DNA is circular like that of bacteria and replicates through a process called binary fission. Mitochondrial DNA (mtDNA) encodes the proteins needed for cellular respiration

The outer membrane of mitochondria is smooth, while the inner membrane has many folds called cristae. These folds increase the surface area for chemical reactions, which mainly occur on the inner membrane. The two membranes divide the mitochondrion into two parts: the intermembrane space and the mitochondrial matrix, which contains water and proteins (enzymes) involved in cellular respiration. Mitochondria have their own DNA and ribosomes, can produce their own proteins, and have some control over their reproduction. Their DNA is circular like that of bacteria and replicates through a process called binary fission. Mitochondrial DNA (mtDNA) encodes the proteins needed for cellular respiration

Vacuoles

Vacuoles are found both in animal and in plant cells, but they are much larger in plant cells. They are storage organelles, storing food or any variety of nutrients usefull for cell survival. They can even store waste, so to protect the rest of the cell from contamination. Vacuoles are vescicles full of fluid, mainly made up of water, containing nutrients or waste, surrounded by a membrane. Plants may also use vacuoles to store water. Those tiny water bags help support plant cells. In plant cells, the vacuoles are much larger than in animal cells. Sometimes in these cells only one vacuole is present, that can take up more than half of the cell's volume. Some vacuoles contain pigments that give certain flowers their typical colors. The plant cell central vacuole also contains waste that tastes bitter to insects and animals.

Plant Cells

Animal and plant cells share several features, including a nucleus, cytoplasm, cell membrane, endoplasmic reticulum (E.R.), mitochondria, and ribosomes. Generally, plant cells are larger and often have a cuboid shape.Common parts of animal and plant cells:- Nucleus:Contains genetic material that controls cell activities.- Cytoplasm: The site of most chemical processes, controlled by enzymes.- Cell membrane: Regulates the movement of substances in and out of the cell.- Mitochondria:Where most energy is produced through cellular respiration.- Ribosomes: Sites for protein synthesis.- Endoplasmic reticulum: Involved in making and modifying proteins and lipids.

Extra parts found in plant cells:*- Cell wall: Provides rigidity, structural support, and helps with cell-to-cell interaction.- Chloroplast:Contains chlorophyll, which absorbs light energy for photosynthesis.- Large vacuole: Stores water, nutrients, and waste.

Chloroplasts

Plants are unique because they can perform photosynthesis, which is how they make food using sunlight. This process happens in specialized organelles called chloroplasts. Chloroplasts are oval-shaped and have two membranes: an outer membrane and an inner membrane. Both are made of a phospholipid bilayer and proteins, and the space between them is called the intermembrane space. Inside chloroplasts, there is a fluid called stroma, which contains small membranes called thylakoids. A stack of thylakoids is called a granum.

Thylakoids hold chlorophyll and other pigments that are essential for photosynthesis. To carry out photosynthesis, plants need carbon dioxide, water, and sunlight. During this process: - Chlorophyll absorbs sunlight. - This energy splits water molecules into hydrogen and oxygen. - Oxygen is released into the atmosphere from the plant leaves. - Hydrogen and carbon dioxide are used to create glucose, which is the main food source for plants.

Another key difference between plant and animal cells, in addition to chloroplasts, is the presence of a cell wall. The cell wall surrounds the plasma membrane and provides protection against mechanical and osmotic stress. It allows cells to create turgor pressure, which is the pressure of the cell contents pushing against the cell wall. Plant cells have high concentrations of dissolved molecules in their cytoplasm, causing water to enter the cell.

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