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U-M BIOLOGY 172 - Unit 2: Cell Structure

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BIO 172 1st Edition Lecture 11Outline of Last Lecture I. Exam on Monday, so we started a new section today!Outline of Current Lecture I. Cell StructureII. Endomembrane SystemCurrent LectureCell Structure:Bacteria cells versus Eukaryotic:Bacteria lack nuclear membranes. Bacteria usually lack organelles, so they are less organized than eukaryotes. Bacterial are usually much smaller than eukaryotes because they lack those membrane-bound organelles.Cellular ORGANIZATION of Prokaryotes:Cell wall: farthest outside. Most prokaryotes have a cell wall.Plasma membrane: this encircles the organelles and chromosomes.Cytoskeleton: actin-type protein MreB.MreB: a protein that forms structures for support in the cell. Helps the cell keep its shape, and bacteria have MreB rather than Actin that eukaryotes have.Nucleoid: where the chromosome is housed. The chromosome is folded; it becomes supercoiled/compacted DNA that is held together by proteins associated with the DNA of bacteria.Histone-like Proteins: bacteria do not have histones like Eukaryotes do… but they have histone-like proteins that carry out a similar role: keeping DNA compacted. (Because Histones in eukaryotes keep DNA wound around themselves).Plasmid: a small circular DNA molecule. These help transfer antibiotic resistance to bacteria, byencoding genes that help resistance to drugs. If a plasmid gets to a cell that could not cause an infection, the plasmid can transfer and then that cell WOULD be able to infect.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Flagellum: allows bacteria to move, considered an organelle. H+ is the energy.Pilus: important for genetic sharing.Part of a prokaryotic cell wall is the Glycan Chain: many sugar chains peptide-bonded together.This Cross Link provides support for the bacteria cell, and stops it from bursting.MreB helps to support the cell by lining its cell wall, and then letting the cell keep its shape.If/when MreB is depleted in a cell, the cell will lose its shape and then not be able to divide properly. This causes the cell to die.FtsZ ring and cell division:FtsZ is used in cell division universally among prokaryotes (bacteria and archaea).It has a relation that eukaryotes use, called Tubulin.FtsZ attaches to the prokaryotic cell membrane, forming a ring at the center of the cell, not coating the membrane but touching it in a ring shape: (FtsZ monomers polymerize to form the ring! A visual of the ring is the yellow arch in the picture below)FtsZ responsible for prokaryotic cell division (cytoinesis).FtsZ forms a ring at the mid-cell position, so that during replication, the cell is doubled but that ring can split it into two cells.After going through full replication, and once cell(s) are separated enough, the chromosomes are separated too.The FtsZ will form a ring structure between those, and attach to cell membrane and form a ring. Then FtsZ contracts and pulls membrane inward. It’ll pinch off and generate two distinct cells.Eukaryotic Cells:Typical ANIMAL cell feature: Nucleus, DNA, and transcription. mRNA needs to be exported from the nucleus before RNA can be synthesized.Mitochondria: where the ATP is made.Plasma membrane: composed of phospholipids, proteins bound to membrane allow cell to take in things.Cytoskeletal elements: allow for framework within animal cell. To keep its shape, and associate with proteins.Endoplasmic Reticulum (ER): protein and lipid synthesis.Lysosomes: break down/degrade macromolecules.Golgi: take proteins and lipids, modify them, sort them, and send them to a specific place.PLANT cell features: Distinctions from animal cells:Cell wall, cellulose. Both used for structure and support.Vacuoles: allows plant cell to have the shape it has. Plant wilting in summer is because vacuole doesn’t have enough water in it to keep it upright.Turgor pressure: The mechanism for getting water into a plant cell. An animal cell couldn’t handle that pressure since it has no cell wall!Chloroplasts: use light to make sugar.The Endomembrane System:Nuclear envelope: integrated network. Nucleus and nuclear envelope(has outer folding sheets, which are rough ER and smooth ER. Rough is where protein synthesis happens, to make vesicles which move things from the rough ER to the Golgi).Each Golgi fold has different enzymes within it. Depending on the specific enzyme, the Golgi willmodify and sort a vesicle… then the vesicle is sent wherever it needs to go.The NUCLEUS: is large, and organized. The NUCLEAR ENVELOPE is the double-membrane that surrounds it. There is a distinct region called the NUCLEOLUS…Nucleus is used for information storage, processing, and holding the chromosomes. Ribosomal RNA synthesis happens in the NUCLEOLUS.**Mitochondria also holds DNA, it’s not all contained in the nucleus. Nuclear envelope is double layered, and the thing keeping those layers together is called Lamina. It keeps the two membranes together.Entrance/Exit of the Nucleus: Nuclear pore: allows mRNA to be captured and moved out, allows proteins into nucleus. Endoplasmic Reticulum: made of complex out-foldings of outer nuclear membrane. Rough because Ribosomes are associated. The rough ER modifies proteins and directs their transportation.Smoothhas no ribosomes, but synthesis of lipids and carbohydrates happens here, and hormones produced.After leaving the Rough ER…The protein ends up in the Golgi apparatus! Here, the Golgi modifies the protein further and determines where the protein will actually end up.SRP = Signal Recognition ParticleAny protein destined for the ER lumen or secretion use SRP.Signal recognition particle: complex part of ribonucleo-protein. Protein and RNA component. A new polypeptide is formed by ribosome… SRP binds to signal sequence (orange string of amino acids in picture below) and the SRP can then bind to a receptor! SRP can then be removed, andtranslation will take up again. Then the protein is sent through a pore. Then the signal sequence is cleaved, and the protein is released to the lumen of the ER and then can move towards the golgi!Export of Proteins, using major secretory system:In the Endoplasmic Reticulum, a protein signal is required to start exporting proteins! That signal is usually located at the beginning of the protein being exported. Once the protein is exported, the signal sequence is removed.The E.R. inserts


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