Prokaryotic Cells: Structure and Function

• Cells are the fundamental unit of life, and all cells have structures to perform functions, store and transmit information, provide energy, and serve as a selectively permeable barrier.
• Phylogeny indicates three broad domains, bacteria, archaea, and eukarya.

Prokaryotes

• Prokaryotes lack a membrane-bound nucleus.
• They contain a single, supercoiled, circular chromosome composed of DNA and proteins and are located in a region called the nucleoid.
• Prokaryotes may also contain small, supercoiled, circular DNA molecules called plasmids, that usually contain genes that help the cell adapt to environmental conditions.
• Most bacteria contain a plasma membrane surrounding the cytoplasm, ribosomes, and a stiff cell wall.
• Some bacteria have membrane-bound organelles that perform specialized tasks such as storing calcium ions, holding magnetite crystals, generating energy from ammonium ions, and organizing enzymes for building organic compounds.
• Prokaryotes contain protein fibers that form the basis of the cytoskeleton, assisting in cell division, and maintaining cell shape.

Cell Wall

• Most prokaryotes have a cell wall that forms a protective “exoskeleton”.
• It is composed of a tough, fibrous layer and surrounds the plasma membrane.
• Many prokaryotic species have an additional layer that is outside the cell wall and is composed of glycolipids.

Prokaryotic External Structures

• Many prokaryotes have structures that extend from their plasma membrane.
• Some have flagella, which are long filaments that rotate to propel the cell, and fimbriae, which are needle-like projections that promote attachment to other cells or surfaces.

Eukaryotes

• Most eukaryotic cells are larger than most prokaryotic cells: eukaryotic organisms range in size from microscopic algae to 100-meter-tall redwood trees.
• Eukaryotic cells are generally multicellular or unicellular include organisms like protists, fungi, plants and animals.
• Eukaryotic cells have a lower surface area-to-volume ratio, making it difficult for molecules to diffuse across the entire cell.
• Eukaryotic organelles break up the large cell volume into smaller compartments that allows for the membrane of organelles to provide surface for attachment of more proteins.
• The compartmentalization also allows for separation of incompatible chemical reaction and increases the efficiency of chemical reactions as well as distinct cytosol.
• Eukaryotic cells are generally much larger than prokaryotic cells and the cytoplasm is compartmentalized into a larger number of distinct organelles
• chromosomes in eukaryotes are enclosed in a membrane-bound nucleus.
• Eukaryotic cells also feature a diverse and dynamic cytoskeleton.

Nucleus

• Eukaryotes are surrounded by a double-membrane nuclear envelope with pore-like openings, where the inside surface is linked to nuclear lamina.
• Eukaryotes also have distinct regions in the nucleus called the nucleolus and ribosomal RNA is synthesized and ribosome subunits are assembled.
• The nucleus functions in information storage and processing and contains the cells linear chromosomes with each taking a distinct area.
• Densely packed sections of DNA reside on the periphery, with loosely packed sections of DNA toward the interior.
• The nuclear envelope is perforated with openings called nuclear pore complexes connecting the inside with the cytosol and consists of about 30 different proteins.
• Nuclear proteins contain a 17-amino-acid-long nuclear localization signal (NLS) or “zip code” that marks them for transport through the nuclear pore complex, allowing them to entire the nucleus directly.

Ribosomes

• Ribosomes are molecular machines that manufacture proteins are not considered organelles which are free in the cytosol to manufacture proteins that remain in the cytosol or are imported to other organelles, while some are attached to the endoplasmic reticulum.
• Ribosomes consist of large and small subunits, both containing ribosomal rRNA molecules and protein.

Endoplasmic Reticulum

• The endoplasmic reticulum (ER) forms A network of membrane-bound tubes and sacs, some studded with ribosomes, it is also and extension of the nuclear envelope.
• There are two types, the first is rough ER (RER) studded with ribosomes to synthesize shipped proteins to another organelle, inserting into the plasma membrane, or secreted to the cell exterior.
• Proteins manufactured on the RER move to the lumen, or in the inside of the sac-like structure where they are folded and processed.
• Proteins in the RER have a message to carry to other cells, act as membrane transporters or catalyze reactions.
• Smooth ER lacks ribosomes and contains enzymes that catalyze reactions involving lipids as well as synthesize fatty acids and phospholipids needed by the organism, it reserves calcium ions and can break down lipids.

Golgi Apparatus

• The Golgi Apparatus is the site of protein processing, sorting, and shipping consisting of membrane sacs or cisternae.
• The cis side of the Golgi apparatus is located closest to the nucleus receiving from RER.
• The trans side faces, ships, and moves material toward the plasma membrane in membranous vesicles.

Lysosomes

• Lysosomes ar found only in animal cells as single-membrane-bound structures containing approximately 40 different digestive enzymes.
• Lysosomes are recycle structures that can digest macromolecules like food, waste and send out monomers, enzymes are acid hydrolases working best at pH 5.0 and utilize proton pumps in membranes to maintain internal pH.
• Lysosomes also participate in autophagy, phagocytosis, and a receptor-mediated endocytosis to deliver materials
• Receptor-mediated endocytosis happens when macromolecules outside the cell are bound to receptor proteins, after which the cell membrane folds off to form an early endosome.
• Plasma membrane pinches off transport vesicles to bring things into the cell.

Vacuoles

• Vacuoles are generally large storage centers for water and ions, found in plants and fungal cells, and they tend to lack lysosomes.
• They help maintain cell volume, are filled with protein in seed, contain pigments in petals or fruit, and my contain noxious compounds to protect leaves for being eaten.

Peroxisomes

• Peroxisomes, which bud from the ER, are are globular organelles bound by a single membrane containing enzymes.
• Peroxisomes form in the center of oxidation reaction processes that produce hydrogen peroxide H2O2 .
• Peroxisomes contain enzyme catalyse for detoxification and specialized form in plant are called glyoxysomes, oxidizing fats for an energy storage compound.

Mitochondria

• Mitochondria are the eukaryotic power generators that supply ATP.
• They have two membranes where the inner is folded, forming cristae with the solute in the membrane is mitochondrial matrix, where the mitochondria contain their own DNA and manufacture ribosomes.

Chloroplasts

• Chloroplasts are organelles utilized for sugar-manufacturing and photosynthesis , utilizing light energy to produce chemical energy.
• Chloroplast have three membranes which contain stacked stacks of flattened sacs in stacks called thylakoids arranged into grana that is within the stroma.
• Chloroplast store their own ribosomes and DNA(cpDNA).

Theory of Endosymbiosis

• The Endosymbiosis theory describes how bacteria develop an enclosed mutually beneficial relationship over time with a host .
• Chloroplast and Mitochondrial are said to may have been the results.
  • Contain their own DNA
  • Synthesizing thier own ribosomes.
  • Growth and division independently of the cell.

Cytoskeleton

• The cytoskeleton constitutes protein fibers gives cells structural stability, aids movement, transports materials and structure.
• The major differences between cells is the type, size and numbers of organelles and its specialized functions
• Cells are dynamic living things with interacting parts and moving molecules, consuming ~10 million ATP molecules per second.
• Cellular enzymes catalyze >25,000 times a second, and each phospholipid move the organelle in 1 minute as for the hundreds of mitochondria, are replaced after 10 days.

Systems

• Cell systems include: -Nuclear transportation. -Endomembrane in manufacturing and shipping of proteins. -Cytoskeleton system. The nuclear lamina is a transport mechanism which consists of 2 membranes composed of a lipid bilayer which works in conjuction with the endoplasmic reticulum. The inside layer links with fibrous proteins providing shape and support

Nuclear Transportation

• RNA and ribosomes and the product are processed at the synthesized before exported out.
• Messenger RNA caries is constructed within the cytoplasm before transported for synthesis
• In the case of needing proteins inside of the nucleus, they must be imported as well through proteins for ribosomes in the nucleus need a NLS"nuclear localization signal" to enter.
• Importins proteins transport other proteins by binding to large molecules, and to fold them.

Endomembrane

• Proteins in the found in organelles must to transported with special proteins from the cytosol, after which they signal when the organelles are appropriated.
• Proteins the RER moves the final changes. After transport the vesicle moves towards Golgi

Secretory Pathway

• The pathway details the steps and synthesis of proteins, involving vesicles from the RER and the Golgi, integrating everything. Pulse case process
• the pulse involves: -Pancreatic Cells exposing certain protein or radioactive enzymes for 3 minutes as the enzymes grow in culture.
• The chase involes:
  • Removal or nonradioactive amino acids that are added during protein production.
  • Lablled proteins over a duration of time.

Signal Hypothosis

• Protein enters a part of the ER with free ribosomes, the hypothesis goes, that protein requires zip codes a sequence directs the polypeptide toward the RER
• A signal sequence combines RER movement through several process: -1. Receptor Binding -2. Channel Synthesis -3. growing with lumen -Protein foldings with removal before releasing signal peptidase. -In RER the proteins are modified inside, by adding a carbohydrate indicator, creating glycoprotein -It then forms a transfer of cis
• As the final step it enters the Golgi -Modified and exiting through transport, - Molecular tags determine transport -Postal codes are required for destination.

Recycling

• Large digestion molecules utilize processes such as: -Ensocytosis with vesicles cutting off membrane -2 types for process +Receptor mediated where molecules attach to membrane before enclosing to form a vesicle, followed by a early endosome and proton pumps. +Phagocytosis with the absorption of smaller cells , fusing for lysosomal enzymes.
  • Autophagy, a process which cleans cytoplasm and utilizes enzymes, fusing lysosomes with the cytoplasm during organelle digestion.

Cellular and Cytoskeleton

• Cells require a cytoskeleton that is is dynamic, and is responsible for structural integrity, altering their shape and helping them move
• The Three types include Actin Filaments forming strands and a helix for movement, Intermediated FIlaments for structural or stable support that the cell is lacking, and Microtubules that are hollow and stable.
• Actin filments has the smallest filaments made of globular filaments for polymerization. They move the body in a long bundle and are found under the plasma.
• Cell crawl, Muscle contraction, the cytosis,and cytoplasm flow are the four functions.

###Intermediated Filaments

• Provide movement or supports, a flexible cell that holds in place.
• Intermediate filaments are composed a number of proteins including keratin and neurolamin.
• Functions of the filament are to provide shape, create links in mesh and secure support as the cell divides.

Microtubules

• are tube made of protein called tubulin and polarized , growing at each end. Inside this structure the main support component.
• The origin in animals stems from the centrosomes
• Microtubules have several task -Separate chromosomes -Vessel transport -Energy assistance -Structural frame -Stability -Motor proteins -Kinesin required from movement converting ATP. Kinesin will bind at different location (tail in vesicle and stalk to the head)

Cilia

• Flagellas and similar structures are used in cells for movement, the prokaryotic version of movement. Eukayotic structure has microtubial and is surrounded. These use axoneme at basal body.
• the process is identical in cells and growth at the other location has to be spanned to reach body.
• Dynein protein arms are how the movement moves to link. Axoneme bend through all of bridge location.

Explore the structure and function of prokaryotic cells, organisms lacking a membrane-bound nucleus. Learn about their key components like the nucleoid, plasmids, plasma membrane, cell wall, and specialized organelles for survival and adaptation. Understand how prokaryotes, including bacteria, thrive in diverse environments.