3.Thecell

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Lakeside Academy, Buchans**We aren't endorsed by this school

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SCIENCE 131

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Biology

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Dec 16, 2024

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Uploaded by jessikim0729

Reference: Campbell BIOLOGY, Canadian Edition, Reece et al. (2012)Topic: The CellSuggested Readings: Chapter 6: page 103, 107-127 The Cell All of life is made of cells – this fundamental idea prompted the research of many scientists to examine the cell and together the cell theory is composed of three fundamental concepts: 1.The smallest fundamental unit of life is the cell 2.All of life is made of cells, it can be unicellular or multicellular 3.A cell must come from a pre-existing cell Cells can be divided into two categories: Prokaryotes (e.g., bacteria or archaea) or Eukaryotes (e.g., plants, animals, fungi)Prokaryotes (e.g., Bacteria):Prokaryotes are very small single-celled organism (about 0.5- 10 um), it is simple and does not contain any organelles. Generally, bacteria are composed of the following structures: oPlasma membrane – lipid bilayer of phospholipids enclosing the cytoplasm oGenetic material – usually a circular chromosome. The DNA (deoxyribonucleic acid, a type of nucleic acid) is not enclosed, but it is not floating around within the cell either, it is usually organized in a region called the nucleoid regionoCytosol – a jelly-like fluid composed of mostly water to keep the internal environment ofthe cell at its optimal functioning capacityIn prokaryotes, the cytoplasm refers to all the material within the cell, so the cytosol, ribosomes, and cytoskeletonoRibosomes – a complex of RNA (ribonucleic acid, a type of nucleic acid) and proteins that synthesize proteins oCytoskeleton – protein filaments involved in cell shape and movementoCell wall – found in nearly all bacteria to help maintain its shape and provide protection oOther components: Flagella – tail for movementPili – short hairs for attachment Prokaryotes versus Eukaryotes: While the domains Bacteria and Archaea are all composed of prokaryotes, the domain Eukarya (protists, fungi, plants, and animals) are all composed of eukaryotes There are a few major differences between prokaryotes and eukaryotes: oEukaryotes have internal compartmentalization or organization; organelles (membrane-bound structures with a specialized form and function – allowing several processes to begoing on simultaneously)Page 1of 3

Reference: Campbell BIOLOGY, Canadian Edition, Reece et al. (2012)oThe DNA in a eukaryote is enclosed inside an organelle called a nucleus and is linear (notcircular)oEukaryotic cells are larger – about 10 – 100 um A eukaryotic cell could not grow infinitely, however, there are constraints based on the metabolic requirements of the cellAs the cell grows larger, the surface area to volume ratio decreases rapidly, and the time it takes for nutrients, gases, or wastes to cross the plasma membrane would be too great to support the life of the cellEukaryotic cell:A eukaryotic cell is highly complex. Generally, it is composed of the following: oPlasma membrane – lipid bilayer of phospholipids embedded with diverse proteins, lipids, and carbohydrates suited to the cell’s functionoNucleus – an organelle that contains most of the genes in the eukaryotic cells (some are in the mitochondria and chloroplasts). Nuclear envelope - encloses the nucleus and is composed of a double membrane and is perforated by nuclear pores which play an important role in regulating the entry and exit of proteins and RNAs Nuclear lamina - is a netlike array of protein filaments that will help the nucleus maintain its shape and help organize genetic material Chromatin – the genetic material of the cells are long strands (not circular) of DNA associated with proteins (histones) to help coil and organize the DNA. The complex of DNA and proteins is called chromatin. When the cell is undergoing cell division and the chromatin is further condensed it is referred to as chromosomesEach Eukaryotic species has a characteristic number of chromosomes Nucleolus – the site of ribosomal RNA synthesis oRibosomes – a complex of RNA and proteins which are either free in the cytosol or attached to the rough endoplasmic reticulum that plays a major role in protein synthesisoRough Endoplasmic Reticulum (RER) – organelle composed of a network of tubes that play a role in phospholipid and protein synthesis As the protein is synthesized, the chain is threaded into the RER where it will be folded into its functional shapeOr if the proteins need carbohydrates to be attached, it is within the RER where they are added to make the final glycoproteinIf the proteins need to travel to another location within the cell (i.e., the Golgi apparatus) they will be wrapped in a membrane in bubbles called vesicles oSmooth Endoplasmic Reticulum – an organelle that is an extension of the RER without ribosomes attached, plays a role in membrane and lipid synthesis, carbohydrate metabolism, storage of calcium ions, and detoxification Page 2of 3

Reference: Campbell BIOLOGY, Canadian Edition, Reece et al. (2012)Detoxification usually involves adding hydroxyl groups – OH to drug molecules, making them easier to flush from the body oGolgi apparatus – an organelle that helps synthesize, modify, sort, and secrete the products of the cell oMitochondrion – organelle where aerobic cellular respiration takes place, where the most adenosine triphosphate (ATP) is generated oLysosome – organelle that hydrolyzes organelles and macromolecules (a bag of hydrolytic enzymes)oPeroxisome – organelle involved in metabolic functions producing hydrogen peroxide asa by-product which is then converted to wateroMicrovilli – projections of the plasma membrane that help increase the cell’s surface areaoCytoskeleton – protein filaments involved in cell shape and movementMicrofilaments – thinnest – actin filaments, help in cell movement Intermediate filaments – only found in cells of animals, reinforce the shape of the cellMicrotubules – thickest – shape and support the cell, serve as tracts along whichorganelles can move within the cell, involved in cell division, the main component in cilia (move like the motion of an oar) and flagella (move like the motion of a fish) oCentrosome – a region where the cell’s microtubules are initiated; contains a pair of centrioles; plays a role in cell division oFlagellum – a long tail-like structure composed of microtubules within an extension of the plasma membrane used for motility oVacuoles/vesicles – organelles that play a role in nutrient or waste storage Food vacuoles are formed when a cell takes in nutrients through phagocytosis – these are then fused with a lysosome to help break down the nutrients Contractile vacuoles help pump out excess waterPlant cells differ in that they have:oCell wall – an outer layer made of cellulose, other polysaccharides, and proteins to helpsmaintain the cell’s shape, protect it from mechanical damage, prevent it from taking up excess water and help against the force of gravity oCentral vacuole – a large organelle that functions in the storage and breakdown of waste products, hydrolysis of macromolecules and plays a major role in plant growth oChloroplasts – a photosynthetic organelle that can convert sunlight into chemical energyoPlasmodesmata – cytoplasmic channels through the cell walls that connect the cytoplasm of adjacent cells Fungi cells differ in that they have: oCell wall – an outer layer made of chitin to helps maintain the cell’s shape and protect it from mechanical damage Page 3of 3