Cell Structure and Organelles

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Organelle Mitochondria Chloroplast Golgi Endoplasmic reticulum

Plant or Animal Plants and animals Plants Plants and animals Plants and animals Plants and animals Plants and animals Plants and animals Primarily plants Plants and animals Plants Plants

Function Energy transducer--Big ATP producer Energy transducer--produces sugar Packages and modifies synthetic products Nascent proteins are placed inside for modification and transport Boundary of the cell; exchange with the environment Site of hereditary information; control of cell activity Site of protein synthesis; often associated with ER Storage; excretion; water balance Movement; production of currents Cell to cell communication Protection; fluid pressure; support Cytoskeleton elements; motor proteins

Plasma membrane Nucleus Ribosomes Central vacuole Cilia/flagella Plasmadesmata Cell wall

Microfilaments, microtubules, Plants and intermediate filaments animals

3 Fundamental Parts of a Cell

1. Cell Membrane (plasma membrane, plasmalemma ) - protectively surrounds the cytoplasm. - plasma membrane in plants and prokaryotes is usually covered by a cell wall - serves to separate and protect a cell from its surrounding environment - regulates passage of materials in and out of the cell. Semi-permeable (limited passage) & Permeable (pass freely) Active energy is recquired for bigger molecules to pass through. - made mostly from a double layer of lipids hydrophobic molecules (heads) and hydrophilic molecules (tails). Hence, the layer is called a phospholipid bilayer. - allows communication with other cells. Cell wall - non-living composed of cellulose. Plant cellulose (liquim & pectin) Fungi (chitin) Bacteria (peptidoglycan) Fluid mosaic model - because the heads of phospholipids are hydrophilic in associate with the liquid part of the cell, therefore substances can pass in and out of the cell. It also has structural arrangement of proteins and lipids. Phospholipids - 2 fatty acids + 1 phosphate grp. (phosphorus & oxygen) Dietary lipids - 3 fatty acids + 1 glycerol 2. Cytoplasm - region where main activities take place - cytoplasm is bounded by a cell or plasma membrane, nucleoplasm is bounded by a nuclear membrane. These two types are protoplasm. Cytosol - consist of thick semi-fluid aggregate chemical compounds. Largely water - complex mixture of cytoskeleton filaments, dissolved molecules, and water that fills much of the volume of a cell - reservoir for entry and exit of materials in cell.

Cytomembrane - various structures and internal membrane

Mitochondria and Chloroplasts – eukaryotes only - the power generators Mitochondria are self-replicating organelles that occur in various numbers, shapes, and sizes in the cytoplasm of all eukaryotic cells. Mitochondria play a critical role in generating energy in the eukaryotic cell. Mitochondria generate the cell's energy by oxidative phosphorylation, using oxygen to release energy stored in cellular nutrients (typically pertaining to glucose) to generate ATP. Mitochondria multiply by splitting in two. Respiration occurs in the cell mitochondria. Organelles that are modified chloroplasts are broadly called plastids, and are involved in energy storage through photosynthesis, which uses solar energy to generate carbohydrates and oxygen from carbon dioxide and water.[citation needed] Mitochondria and chloroplasts each contain their own genome, which is separate and distinct from the nuclear genome of a cell. Both organelles contain this DNA in circular plasmids, much like prokaryotic cells, strongly supporting the evolutionary theory of endosymbiosis; since these organelles contain their own genomes and have other similarities to prokaryotes, they are thought to have developed through a symbiotic relationship after being engulfed by a primitive cell. Endoplasmic reticulum – eukaryotes only The endoplasmic reticulum (ER) is the transport network for molecules targeted for certain modifications and specific destinations, as compared to molecules that will float freely in the cytoplasm. The ER has two forms: the rough ER, which has ribosomes on its surface and secretes proteins into the cytoplasm, and the smooth ER, which lacks them. Smooth ER plays a role in calcium

sequestration and release. Golgi apparatus – eukaryotes only The primary function of the Golgi apparatus is to process and package the macromoleculessuch as proteins and lipids that are synthesized by the cell. It is particularly important in the processing of proteins for secretion. The Golgi apparatus forms a part of the endomembrane system of eukaryotic cells. Vesicles that enter the Golgi apparatus are processed in a cis to trans direction, meaning they coalesce on the cis side of the apparatus and after processing pinch off on the opposite (trans) side to form a new vesicle in the animal cell. Ribosomes The ribosome is a large complex of RNA and protein molecules. They each consist of two subunits, and act as an assembly line where RNA from the nucleus is used to synthesise proteins from amino acids. Ribosomes can be found either floating freely or bound to a membrane (the rough endoplasmatic reticulum in eukaryotes, or the cell membrane in prokaryotes).[9] Lysosomes and Peroxisomes – eukaryotes only Lysosomes contain digestive enzymes (acid hydrolases). They digest excess or worn-out organelles, food particles, and engulfedviruses or bacteria. Peroxisomes have enzymes that rid the cell of toxic peroxides. The cell could not house these destructive enzymes if they were not contained in a membrane-bound system. These organelles are often called a "suicide bag" because of their ability to detonate and destroy the cell.[citation needed] Centrosome – the cytoskeleton organiser The centrosome produces the microtubules of a cell – a key component of the cytoskeleton. It directs the transport through the ER and the Golgi apparatus. Centrosomes are composed of two centrioles, which separate during cell division and help in the formation of themitotic spindle. A single centrosome is present in the animal cells. They are also found in some fungi and

algae cells.[citation needed] Vacuoles Vacuoles store food and waste. Some vacuoles store extra water. They are often described as liquid filled space and are surrounded by a membrane. Some cells, most notably Amoeba, have contractile vacuoles, which can pump water out of the cell if there is too much water. The vacuoles of eukaryotic cells are usually larger in those of plants than animals.

3. Nucleus cell nucleus is the most conspicuous organelle found in a eukaryotic cell. It houses the cell's chromosomes, and is the place where almost all DNA replication and RNA synthesis (transcription) occur. The nucleus is spherical and separated from the cytoplasm by a double membrane called the nuclear envelope. The nuclear envelope isolates and protects a cell's DNA from various molecules that could accidentally damage its structure or interfere with its processing. During processing, DNA is transcribed, or copied into a special RNA, called messenger RNA (mRNA). This mRNA is then transported out of the nucleus, where it is translated into a specific protein molecule. The nucleolus is a specialized region within the nucleus where ribosome subunits are assembled. In prokaryotes, DNA processing takes place in the cytoplasm. Nucleolus - composed of RNA. - site where subunits of ribosomes are found Messenger RNA (mRNA) carries information about a protein sequence to the ribosomes, the protein synthesis factories in the cell. It is coded so that every three nucleotides (a codon)

correspond to one amino acid. In eukaryotic cells, once precursor mRNA (pre-mRNA) has been transcribed from DNA, it is processed to mature mRNA. This removes its introns—non-coding sections of the pre-mRNA. The mRNA is then exported from the nucleus to the cytoplasm, where it is bound to ribosomes and translated into its corresponding protein form with the help of tRNA. In prokaryotic cells, which do not have nucleus and cytoplasm compartments, mRNA can bind to ribosomes while it is being transcribed from DNA. After a certain amount of time the message degrades into its component nucleotides with the assistance of ribonucleases. Transfer RNA (tRNA) is a small RNA chain of about 80 nucleotides that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation. It has sites for amino acid attachment and an anticodon region for codon recognition that binds to a specific sequence on the messenger RNA chain through hydrogen bonding. Ribosomal RNA (rRNA) is the catalytic component of the ribosomes. Eukaryotic ribosomes contain four different rRNA molecules: 18S, 5.8S, 28S and 5S rRNA. Three of the rRNA molecules are synthesized in the nucleolus, and one is synthesized elsewhere. In the cytoplasm, ribosomal RNA and protein combine to form a nucleoprotein called a ribosome. The ribosome binds mRNA and carries out protein synthesis.

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