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In Ultra-Structure of Cells students learn that all living things are made of cells, and cells are the smallest units that can be alive. Life on Earth is classified into five kingdoms, and they each have their own characteristic kind of cell. However the biggest division is between the cells of the prokaryote kingdom (the bacteria) and those of the other four kingdoms (animals, plants, fungi and protista), which are all eukaryotic cells. Prokaryotic cells are smaller and simpler than eukaryotic cells, and do not have a nucleus.
Prokaryote = "before carrier bag" i.e. without a nucleus
Eukaryote = "good carrier bag" i.e. with a nucleus
1.2.U.1 Prokaryotes have a simple cell structure without compartmentalisation
1.2.U.1 Prokaryotes have a simple cell structure without compartmentalisation
Be able to:
Outline the major differences between prokaryotic and eukaryotic cells.
List the functions of the following structures of a prokaryotic cell: cell membrane, nucleoid, plasmid, cytoplasm, ribosome, cell wall, pili, capsule, flagella- Define extracellular.
Contrast the size of eukaryotic and prokaryotic ribosomes
Prokaryotes are organisms that belong to the kingdom Monera and have been further classified into two distinct domains:
Archaebacteria – found in extreme environments like high temperatures, salt concentrations or pH (i.e. extremophiles)
Eubacteria – traditional bacteria including most known pathogenic forms (e.g. E. coli, S. aureus, etc.)
Characteristics of Prokaryotes
Prokaryotes are the single-celled organisms and much smaller than eukaryotic cells.
The size of most prokaryotes is between 1 µm and 10 µm, but can vary in size from 0.2 µm to 750 µm.
The prokaryotes are divided into two domains: the bacteria, unicellular microorganisms that have wide range of shapes and ubiquitous in habitat and the archaea, single-celled prokaryotic microorganisms similar to bacteria but possess some genes and several metabolic pathways that are closely related to those of eukaryotes.
Exists in different shapes like, coccus, bacillus, spirillum, coccobacillus, and spirochete. While some of the prokaryotes are pleomorphic i.e. do not possess constant shape and some exists as aggregate communities.
Features of Prokaryotes
Cell wall – rigid outer covering made of peptidoglycan; maintains shape and prevents bursting (lysis)
Slime capsule – a thick polysaccharide layer used for protection against dessication (drying out) and phagocytosis
Flagella – Long, slender projections containing a motor protein that enables movement (singular: flagellum)
Pili – Hair-like extensions that enable adherence to surfaces (attachment pili) or mediate bacterial conjugation (sex pili)
Cell membrane – Semi-permeable and selective barrier surrounding the cell
Cytoplasm – internal fluid component of the cell
Nucleoid – region of the cytoplasm where the DNA is located (DNA strand is circular and called a genophore)
Plasmids – autonomous circular DNA molecules that may be transferred between bacteria (horizontal gene transfer)
Ribosomes – complexes of RNA and protein that are responsible for polypeptide synthesis (70S prokaryote ribosome)
1.2.U.2 Eukaryotes have a compartmentalised cell structure
1.2.U.2 Eukaryotes have a compartmentalised cell structure
Be able to:
state the meaning and advantages of eukaryotic cells being “compartmentalized.”
Eukaryotes are organisms whose cells contain a nucleus (‘eu’ = good / true ; ‘karyon’ = nucleus)
They have a more complex structure and are believed to have evolved from prokaryotic cells (via endosymbiosis)
Prokaryotic cells are fundamentally different in their internal organization from eukaryotic cells. Notably, prokaryotic cells lack a nucleus and membranous organelles.The nucleus is bounded by the nuclear envelope, a double membrane with many nuclear pores through which material enters and leaves.
Eukaryotes can be divided into four distinct kingdoms:
Protista – unicellular organisms; or multicellular organisms without specialized tissue
Fungi – have a cell wall made of chitin and obtain nutrition via heterotrophic absorption
Plantae – have a cell wall made of cellulose and obtain nutrition autotrophically (via photosynthesis)
Animalia – no cell wall and obtain nutrition via heterotrophic ingestion
Eukaryotic Organelles
Nucleus - a membrane bound structure that contains the cell's hereditary (DNA) information and controls the cell's growth and reproduction. It is commonly the most prominent organelle in the cell.
Mitochondria - as the cell's power producers, mitochondria convert energy into forms that are usable by the cell. They are the sites of cellular respiration which ultimately generates fuel for the cell's activities. Mitochondria are also involved in other cell processes such as cell division and growth, as well as cell death.
Endoplasmic Reticulum - extensive network of membranes composed of both regions with ribosomes (rough ER) and regions without ribosomes (smooth ER). This organelle manufactures membranes, secretory proteins, carbohydrates, lipids, and hormones.
Golgi complex - also called the Golgi apparatus, this structure is responsible for manufacturing, warehousing, and shipping certain cellular products, particularly those from the endoplasmic reticulum (ER).
Peroxisomes - Like lysosomes, peroxisomes are bound by a membrane and contain enzymes. Peroxisomes help to detoxify alcohol, form bile acid, and break down fats.
Vacuole - these fluid-filled, enclosed structures are found most commonly in plant cells and fungi. Vacuoles are responsible for a wide variety of important functions in a cell including nutrient storage, detoxification, and waste exportation.
Centrioles - these cylindrical structures are found in animal cells, but not plant cells. Centrioles help to organize the assembly of microtubules during cell division.
Cilia and Flagella - cilia and flagella are protrusions from some cells that aid in cellular locomotion. They are formed from specialized groupings of microtubules called basal bodies
Organelles Found in Plant Cells Only
Chloroplast - this chlorophyll containing plastid is found in plant cells, but not animal cells. Chloroplasts absorb the sun's light energy for photosynthesis.
Cell Wall - this rigid outer wall is positioned next to the cell membrane in most plant cells. Not found in animal cells, the cell wall helps to provide support and protection for the cell.
Organelles Found In Animals Cells Only
Lysosome - membranous sacs filled with hydrolytic enzymes that will breakdown / hydrolysis of macromolecules (presence in plant cells is unsure)
Universal Organelles (found in both Prokaryotic and Eukaryotic Cells)
Ribosomes - these organelles consist of RNA and proteins and are responsible for protein production. Ribosomes are found suspended in the cytosol or bound to the endoplasmic reticulum.
Cytoskeleton - these structures are filamentous scaffolding within the cytoplasm (fluid portion of the cytoplasm is the cytosol). The cytoskeleton rovides internal structure and mediates intracellular transport (less developed in prokaryotes)
Plasma membrane - this is a phospholipid bilayer embedded with proteins (not an organelle, but a vital structure). The plasma membrane is a semi-permeable and selective barrier surrounding the cel
1.2.U3 Prokaryotes divide by binary fission.
1.2.U3 Prokaryotes divide by binary fission.
Be able to:
- Define asexual reproduction.
- Outline the four steps of binary fission.
Prokaryotic cells divide by binary fission. This involves the replication of their DNA and elongation of the cell such to the point that it will partition or divide into two cells. Binary fission is a form of asexual reproduction and this means that the two cells produced are genetically identical to the original cell.
1.2.U.4 Electron microscopes have a much higher resolution than light microscopes
1.2.U.4 Electron microscopes have a much higher resolution than light microscopes
Be able to:
- Define resolution.
- Compare the maximum resolutions of a light microscope with those of an electron microscope.
- List three example structures that are visible with electron microscopes but not with a light microscope
The electron microscope is a type of microscope that uses a beam of electrons to create an image of the specimen. It is capable of much higher magnifications and has a greater resolving power than a light microscope, allowing it to see much smaller objects in finer detail. They are large, expensive pieces of equipment, generally standing alone in a small, specially designed room and requiring trained personnel to operate them.
Transmission electron microscopes (TEM) generate high resolution cross-sections of objects
Scanning electron microscopes (SEM) display enhanced depth to map the surface of objects in 3D
1.2.A.1 Structure and function of organelles within exocrine gland cells of the pancreas and within palisade mesophyll cells of the leaf
1.2.A.1 Structure and function of organelles within exocrine gland cells of the pancreas and within palisade mesophyll cells of the leaf
Be able to:
State the function of an exocrine gland cell.
Describe the function of the following structures in an exocrine gland cell: plasma membrane, nucleus, mitochondria, Golgi apparatus, lysosomes, vesicles and endoplasmic reticulum
State the function of a palisade mesophyll cell.
Describe the function of the following structures in a palisade mesophyll cell: cell wall, plasma membrane, chloroplasts, vacuole, nucleus, and mitochondria.
Exocrine Gland Cells of the Pancreas
These are animal cells that are specialized to secrete large quantities of digestive enzymes.
They will have all the organelles of an animal cell but will have many ribosomes and rough ER to create the enzymes which are proteins and transport them outside the cell.
They have many mitochondria to supply the ATP needed for these processes.
An organelle is a tiny cellular structure that performs specific functions within a cell. Organelles are are embedded within the cytoplasm of eukaryotic and prokaryotic cells. In the more complex eukaryotic cells, organelles are often enclosed by their own membrane
Palisade Mesophyll cells carry out most of the photosynthesis in the leaf.
They have many chloroplasts to allow the cell to carry out the maximum levels of photosynthesis.
The cells are surrounded by a cell wall to hold the shape of and protect the cell and a plasma membrane to allow substances in and out of the cell.
They also have mitochondria which are membrane-bound organelles that carry out aerobic cellular respiration to create ATP.
They have vacuoles which are a large cavity in the middle of the cell that stores water and dissolved substances, e.g. sugars and metabolic by-products
They are basically plant cells with many chloroplasts.
1.2.S.1 Drawing of the ultrastructure of prokaryotic cells based on electron micrographs
1.2.S.1 Drawing of the ultrastructure of prokaryotic cells based on electron micrographs
Be able to:
Draw the ultrastructure of E.coli, including the cell wall, pili, flagella, plasma membrane, cytoplasm, 70s ribosomes, and nucleoid with naked DNA.
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