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Top Ten Organelles

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Sarah Milanko

on 13 March 2011

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Transcript of Top Ten Organelles

Ten Cell
Orgnelles Nucleus Mitochondrion Ribosomes Endoplasmic Reticulum Golgi Body Choloroplast Lysosomes Vacuoles Cell Wall Is a large, spherical organelle,
surrounded by a double-layered membrane.
Controls cell activities (Contains DNA). Plasma Membrane 10. Partially permeable, flexible barrier made of phospholipid molecules.
Responsible for recognition, adhesio and chemical communication between cells. Credits:
plasma membrane: en.labs.wikimedia.org Organelles composed of many folded layers of membrane.
Involved in the energy transformations the release energy for use by the cell.
Tiny spherical organelles which are the sites of the production of proteins.
Located in the cytosol and sometimes associated with the Endoplasmic Reticulum.
A network of intracellular membranes, linked with the plasma membrane and other membranous organelles.
If the Endoplasmic Reticulum is rough it is associated with ribosomes, if it is smooth it is lacking in ribosomes.
It is involved in the production, processing, transport and storage of materials within the cell. Stacks of flattened membranous sacs, linked with the ER.
Modifies and packages proteins into membrane bound vesicles in preparation for their secretion from the cell. 1. 2. 3. 4. http://en.wikipedia.org/wiki/File:Peptide_syn.png micro.magnet.fsu.edu micro.magnet.fsu.edu Membrane bound, liquid filled sac.
Keep a variety of substances separate from the cell contents.
Provide physical support through turgid and storage in plant cells; larger in plant cells, smaller in animal cells.
May be involved in intracellular digestion (food vacuoles) or water balance (contractile vacuoles). http://en.wikipedia.org/wiki/File:Mitochondria,_mammalian_lung_-_TEM.jpg http://en.wikipedia.org/wiki/File:Animal_mitochondrion_diagram_en_(edit).svg Top Ten
Organelles. The Nucleus 1. Structures

• The nucleus is the largest cellular organelle in animals, occupying about 10% of total cell volume in mammals.
• It is enclosed in a double membrane and communicates with the surrounding cytosol via numerous nuclear pores in its nuclear envelope.
• It appears as a dense, roughly spherical organelle.
• The cell nucleus contains the majority of the cell's genetic material, in the form of chromosomes (DNA).This material is responsible for providing the cell with its unique characteristics. When a cell is dividing, the nuclear chromatin (DNA and surrounding protein) condenses into chromosomes that are easily seen by microscopy.
• Nucleoplasm, also known as karyoplasm, is the matrix present inside the nucleus. Mitochondria Structure
• The mitochondrion has outer and inner membranes, composed of phospholipid bilayers and proteins. These membranes create five distinct compartments within the mitochondria; the outer membrane (associated with the ER membrane), the intermembrane space, the inner membrane, the cristae (creates a larger surface area and enhances the inner membrane's ability to produce ATP) and the matrix.
• The large amount of proteins in the mitochondria's inner membrane reflect its function; production of the cells energy (ATP).
• A small fraction of the cell's genes are located instead in the mitochondria.

More information about the Inner membrane:
The inner mitochondrial membrane contains proteins with five types of functions:
1. Those that perform the redox reactions of oxidative phosphorylation
2. ATP synthase, which generates ATP in the matrix
3. Specific transport proteins that regulate metabolite passage into and out of the matrix
4. Protein import machinery.
5. Mitochondria fusion and fission protein. Ribosomes Structure

• The ribosomal subunits of prokaryotes and eukaryotes are quite similar. The various ribosomes share a core structure, which is quite similar despite the large differences in size.
• Prokaryotes have 70S ribosomes, each consisting of a small (30S) and a large (50S) subunit.
• Eukaryotes have 80S ribosomes, each consisting of a small (40S) and large (60S) subunit.
• The ribosomes found in chloroplasts and mitochondria of eukaryotes also consist of large and small subunits bound together with proteins into one 70S particle.
• The mRNA comprises a series of codons that dictate to the ribosome the sequence of the amino acids needed to make the protein.
Reticulum Structure

• The endoplasmic reticulum is composed of an extensive membrane network of cisternae (sac-like structures). These are held together by the cytoskeleton.
• There are three varieties of ER; rough endoplasmic reticulum (studded with protein-manufactoring ribosomes), smooth endoplasmic reticulum (connected to the nuclear envelope) and sarcoplasmic reticulum (a special type of smooth SER, found in striated muscles).
• The quantity of RER and SER in a cell can quickly interchange from one type to the other, depending on changing metabolic needs.

Golgi Body Structure
• The Golgi apparatus is found in both plant and animal cells.
• It is composed of stacks of membrane-bound structures known as cisternae (singular: cisterna).
• Each cisterna comprises a flat, membrane enclosed disc that includes special Golgi enzymes which modify or help to modify cargo proteins that travel through it.

Chloroplast Structure
• Chloroplasts are found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts are members of a class of organelles known as plastids.
• They are observable as flat discs contained by an envelope that consists of an inner and an outer phospholipid membrane. Between these two layers is the intermembrane space. It also has reticulations, or many infoldings, filling the inner spaces.
• The chloroplast has its own DNA, which codes for redox proteins involved in electron transport in photosynthesis; this is termed the 'plastome'.

• Lysosomes contain acid hydrolase enzymes. These break up waste materials and cellular debris.
• They are found in animal cells, while in yeast and plants the same roles are performed by lytic vacuoles.
• At pH 4.8, the interior of the lysosomes is acidic compared to the slightly alkaline cytosol (pH 7.2). The lysosome maintains this difference in pH by pumping protons (H+ ions) from the cytosol across the membrane via proton pumps and chloride ion channels. The lysosomal membrane protects the cytosol, and therefore the rest of the cell, from the degradative enzymes within the lysosome. The cell is additionally protected from any lysosomal acid hydrolases that leak into the cytosol, as these enzymes are pH-sensitive and do not function as well in the alkaline environment of the cytosol.

Plasma Membrane Cell Wall Vacuole Lysosomes Structures
• A vacuole is a membrane-bound organelle present in all plant and fungal cells and some protist, animal and bacterial cells. Its structure varies according to the needs of the cell.
• Vacuoles are filled with water containing inorganic and organic molecules including enzymes in solution, though in certain cases they may contain solids which have been engulfed.
• Vacuoles are formed by the fusion of multiple membrane vesicles and are effectively just larger forms of these.
• Cell walls are commonly misconstrued as being rigid; they will bend rather than hold a fixed shape. Their flexibility is apparent when a plant wilts (the stems and leaves begin to droop), or in seaweeds (they bend in water currents).
• A cell wall has considerable tensile strength.
• Hydraulic turgor pressure creates their rigidity, as well as the wall structure itself.
• The composition, properties and form of the cell wall may change during the cell cycle and depend on growth conditions.

Types of cell walls:
• In plants, the strongest component of the complex cell wall is a carbohydrate called cellulose, which is a polymer of glucose. Plants also have a secondary cell wall which is an additional, thicker layer of cellulose which increases wall rigidity. The secondary cell wall is composed of cellulose (35-50%), xylan, a type of hemicellulose (20-35%) and lignin, a complex phenolic polymer (10-25%).
• In bacteria, peptidoglycan forms the cell wall.
• Fungi possess cell walls made of the glucosamine polymer chitin,
• Algae typically possess walls made of glycoproteins and polysaccharides.
• Unusually, diatoms have a cell wall composed of silicic acid. Function
• The cell membrane separates the interior of all cells from the outside environment.
• It is selectively-permeable in relation to ions and organic molecules and controls the movement of substances in and out of cells.
• Cell membranes are involved in a variety of cellular processes such as cell adhesion, ion conductivity and cell signaling and serve as the attachment surface for the extracellular glycocalyx and cell wall and intracellular cytoskeleton.
• The cell membrane also plays a role in anchoring the cytoskeleton to provide shape to the cell, and in attaching to the extracellular matrix and other cells to help group cells together to form tissues.
• In addition, membranes in prokaryotes and in the mitochondria and chloroplasts of eukaryotes facilitate the synthesis of ATP through chemiosmosis.
2. 3. 4. 5. 6. 7. 8. 9. 10. notesforpakistan.blogspot.com micro.magnet.fsu.edu http://en.wikipedia.org/wiki/File:Peptide_syn.png http://en.wikipedia.org/wiki/File:Mitochondria,_mammalian_lung_-_TEM.jpg http://www.google.com.au/imgres?imgurl=http://creationrevolution.com/wp-content/uploads/2010/11/Golgi-Apparatus-and-ER.jpg&imgrefurl=http://creationrevolution.com/2010/11/golgi-apparatus-steel-industry-of-the-simple-cell-%25E2%2580%2593-part-6/&usg=__zTsxQWsSYZ2ho_ATogzGJOYbXLE=&h=920&w=1057&sz=244&hl=en&start=0&zoom=1&tbnid=GHQDvD6CgwWnTM:&tbnh=148&tbnw=170&ei=G-xyTY6YDoi8vwO569CvBg&prev=/images%3Fq%3Dgolgi%2Bbody%26um%3D1%26hl%3Den%26rlz%3D1I7GGLD_en%26biw%3D1328%26bih%3D630%26tbs%3Disch:1&um=1&itbs=1&iact=hc&vpx=502&vpy=111&dur=5228&hovh=209&hovw=241&tx=132&ty=100&oei=G-xyTY6YDoi8vwO569CvBg&page=1&ndsp=18&ved=1t:429,r:2,s:0 http://en.wikipedia.org/wiki/File:Plagiomnium_affine_laminazellen.jpeg The differences between the bacterial and eukaryotic ribosomes are exploited by pharmaceutical chemists to create antibiotics that can destroy a bacterial infection without harming the cells of the infected person. Due to the differences in their structures, the bacterial 70S ribosomes are vulnerable to these antibiotics while the eukaryotic 80S ribosomes are not. Did you know Function

• Ribosomes translate mRNA into protein, also known as protein biosynthesis.
• In bacterial cells, several ribosomes usually work parallel on a single mRNA, forming what is called a polyribosome or polysome. Link between Structure and Function:

• All of the catalytic activity of the ribosome is carried out by the RNA; the proteins reside on the surface and stabilize the structure. www.wikipedia.org
Various Authours, Heinemann Biology VCE Units 1 and 2, 2007, Victoria, Australia Bibliography Functions
• The main function of the cell nucleus is to control gene expression and mediate the replication of DNA during the cell cycle.
• Gene expression first involves transcription, in which DNA is used as a template to produce RNA.
• RNA produced from this process is messenger RNA (mRNA), which then needs to be translated by ribosomes to form a protein. As ribosomes are located outside the nucleus, the mRNA that is produced then needs to be exported. Nuclear envelope and pores
• The nuclear envelope (nuclear membrane) consists of two cellular membranes, an inner and an outer membrane.
• The nuclear envelope allows the nucleus to control its contents and separates them from the cytoplasm. This is important for controlling processes on either side of the nuclear membrane.
• The outer nuclear membrane is continuous with the membrane of the rough endoplasmic reticulum (RER) and is also studded with ribosomes.
• Sometimes called a suborganelle, the nucleolus is a discrete densely stained structure found in the nucleus. It is not surrounded by a membrane.
• The main roles of the nucleolus are to synthesize rRNA and assemble ribosomes.

Other subnuclear bodies:
Cajal bodies - involved in a number of different roles related to RNA processing.
PIKA - function remains unclear.
PML bodies - believed to play a role in regulating transcription.
Paraspeckles - dynamic structures which alter in response to changes in cellular metabolic activity.
Speckles - rich in splicing snRNPs and other splicing proteins necessary for pre-mRNA processing. Disruption of the outer membrane permits proteins in the intermembrane space to leak into the cytosol, leading to certain cell death. Did you know

• The Golgi apparatus is integral in modifying, sorting, and packaging macromolecules synthesized by the cell for cell secretion (exocytosis) or use within the cell.
• It primarily modifies proteins delivered from the rough endoplasmic reticulum but is also involved in the transport of lipids around the cell, and the creation of lysosomes.
• In this respect it can be thought of as similar to a post office; it packages and labels items which it then sends to different parts of the cell.
• The GA is also a major site of carbohydrate synthesis.
Autophagy may also lead to autophagic cell death, a form of programmed self-destruction, or autolysis of the cell, which means that the cell is digesting itself. Did you know Function
• Lysosomes digest dying cells or larger extracellular material, like foreign invading microbes (a process called autophagy) and perform endocytosis (recycle receptor proteins from the cell surface).
• Lysosomes also help repair damage to the plasma membrane by serving as a membrane patch, sealing the wound.

• Lysosomes fuse with vacuoles and dispense their enzymes into the vacuoles, digesting their contents. They are created by the addition of hydrolytic enzymes to early endosomes from the Golgi apparatus.
Some important enzymes found within lysosomes include:
• Lipase, which digests lipids
• Amylase, which digests amylose, starch, and maltodextrins
• Proteases, which digest proteins
• Nucleases, which digest nucleic acids
• Phosphoric acid monoesters.
  Did you know
In protists, vacuoles have the additional function of storing food which has been absorbed by the organism and assisting in the digestive and waste management process for the cell.
The function and importance of vacuoles varies greatly according to the type of cell in which they are present, as they are much more important in the cells of plants, fungi and certain protists, than those of animals and bacteria.
In general, the functions of the vacuole include:
• Isolating materials that might be harmful or a threat to the cell
• Containing waste products
• Containing water in plant cells
• Maintaining internal hydrostatic pressure or turgor within the cell
• Maintaining an acidic internal pH
• Containing small molecules
• Exporting unwanted substances from the cell
• Allows plants to support structures such as leaves and flowers due to the pressure of the central vacuole
• In seeds, stored proteins needed for germination are kept in 'protein bodies', which are modified vacuoles.

Vacuoles also play a major role in autophagy, maintaining a balance between biogenesis (production) and degradation (or turnover) of many substances and cell structures in certain organisms. They also aid in the lysis and recycling of misfolded proteins that have begun to build up within the cell. Function
• Mitochondria primarily produce ATP by oxidizing the major products of glucose, pyruvate, and NADH, produced in the cytosol.
• The central set of reactions involved in ATP production are collectively known as the citric acid cycle, or the Krebs Cycle.

• Mitochondria also regulate cellular metabolism, for example:
Regulation of the membrane potential.
Apoptosis-programmed cell death.
Calcium signaling.
Cellular proliferation regulation.
Regulation of cellular metabolism.
Certain heame synthesis reactions.
Steroid synthesis.

The endoplasmic reticulum (ER) is involved in heat production and is the most significant storage site of calcium in the cell. Function

• The cell wall offers protection against mechanical stress and permits the organism to build and hold its shape (morphogenesis).
• It limits the entry of large molecules that may be toxic to the cell.
• It further permits the creation of a stable osmotic environment by preventing osmotic lysis and helping to retain water.
• Another major function of the cell wall is to act as a pressure vessel, preventing over-expansion when water enters the cell.
• Key nutrients, especially water and carbon dioxide, are distributed throughout the plant from cell wall to cell wall in apoplastic flow. The pH is an important factor governing the transport of molecules through cell walls.
• Cell walls in some plant tissues also function as storage depots for carbohydrates that can be broken down and resorbed to supply the metabolic and growth needs of the plant. Structure
• The fluid mosaic model (phospholipid bilayer structure):
The cell membrane is primarily made of a thin layer of phospholipids. These spontaneously arrange so that the hydrophobic "tail" regions are shielded from the surrounding polar fluid, which causes the more hydrophilic "head" regions to associate with the cytosolic and extracellular faces of the resulting bilayer. This forms a continuous, spherical lipid bilayer. Functions
• The main functions of the endoplasmic reticulum are the facilitation of protein folding and the transport of synthesized proteins in sacs (cisternae).The endoplasmic reticulum can be referred to as the transportation system of an eukaryotic cell.
• The ER is also involved with the insertion of proteins into its membrane, glycosylation involving the attachment of oligosaccharides, disulfide bond formation, disulfide rearrangement and drug metabolism.
• Functions vary, depending on the type of endoplasmic reticulum and the type of cell in which it resides. Types of Endoplasmic Reticulum and their Functions:

The RER is fundamental in multiple functions:
• Lysosomal enzymes with a mannose-6-phosphate marker added in the cis-Golgi network.
• Secretion of proteins, either secreted constitutively with no tag, or regulated secretion involving clathrin and paired basic amino acids in the signal peptide.
• Integral membrane proteins that stay imbedded in the membrane as vesicles exit and bind to new membranes.
• Initial glycosylation as assembly continues.

Smooth endoplasmic reticulum
• The smooth endoplasmic reticulum has functions in several metabolic processes, including synthesis of lipids and steroids, metabolism of carbohydrates, regulation of calcium concentration, drug detoxification, attachment of receptors on cell membrane proteins and steroid metabolism.
• Smooth endoplasmic reticulum is found both animal and plant cells but serves different functions in each.
• The Smooth ER also contains the enzyme glucose-6-phosphatase which converts glucose-6-phosphate to glucose, a step in gluconeogenesis.
Sarcoplasmic reticulum
• The only structural difference between this organelle and the SER is the medley of proteins they have, both bound to their membranes and drifting within the confines of their lumens. This fundamental difference is indicative of their functions: the SER synthesizes molecules while the SR stores and pumps calcium ions. biochem.emory.edu answers.com phschool.com Function
• Chloroplasts capture light energy and transform it into the form of ATP, whilst reducing NADP to NADPH, in a complex set of processes called photosynthesis.
• The material within the chloroplast is called the stroma and contains one or more molecules of small circular DNA. It also contains ribosomes; however most of its proteins are encoded by genes contained in the host cell nucleus, with the protein products transported to the chloroplast.
• Within the stroma are stacks of thylakoids, the sub-organelles, which are the site of photosynthesis.
• Photosynthesis takes place on the thylakoid membrane; as in mitochondrial oxidative phosphorylation, it involves the coupling of cross-membrane fluxes with biosynthesis via the dissipation of a proton electrochemical gradient.
Link between Structure and Function:
• The cell nucleus controls the hereditary characteristics of an organism and is responsible for the protein synthesis, cell division, growth and differentiation.
• It is able to do this because it stores hereditary material, referred to as chromatins, in the form of long and thin DNA (deoxyribonucleic acid) strands. In conjunction, it regulates the integrity of genes and gene expression during mitosis and meiosis.
• It regulates protein synthesis as it transcribes messenger RNA (MRNA) for the production if protein synthesis.
Link between Structure and Function:
• As mentioned before, the highly folded inner membrane (cristae) creates a larger surface area and enhances the inner membrane's ability to produce ATP.
• The outer membrane allows the passage of most small molecules and ions but the crista does not, thus maintaining a closed space within the cell.
• The mitochondria is linked with the ER because it requires proteins to function. Link between Structure and Function:
• The ER is extensive, as it is a transport system of sorts.
• The nucleus sends copies of its DNA regarding protein synthesis (also known as mRNA) to the ER, hence the attachment between the nucleus and the ER.
• Smooth ER does not have ribosomes attached to its surface as it is involved (for example) in the synthesis of lipids, which help to build the cell membrane. Link between Structure and Function:
• The Golgi is near the rough ER as it modifies the proteins which come from the ER before they are exported from the cell.
• Like mitochondria and the ER, the cisternae present in the Golgi body enhance its functions. Link between Structure and Function:
• Cellulose is a structural carbohydrate and thus provides a protected framework for a plant cell to survive. In smaller plants, cell walls are slightly elastic. Wind can push them over and they are able to bounce back.
• Plasmodesmate are small holes in the wall that let nutrients, waste, and ions pass through. Water can also be lost through these holes but the cell wall will continue to maintain the cell's basic shape. Link between Structure and Function:
• Vacuoles are larger in cells which require structure; i.e plant cells.
• They are also able to isolate materials that might be harmful or a threat to the cell and contain waste products; resulting in connections with lysosomes. Link between Structure and Function:
• The phospholipid bilayer structure of a cell membrane (with specific membrane proteins) allows the membrane to be selective and control passive and active transport mechanisms. Link between Structure and Function:
• Chloroplasts also have many infoldings filling its intermembrane space; improving its functional capabilities.
• The stroma contain their own DNA, so they are able to function without instructions by the nucleus. Link between Structure and Function:
• Lysosomes contain many important enzymes which consume waste materials (held in
the vacuole, hence their fusion), digest dying cells and foreign invading microbes.
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