Chapter 5 Lipids Membranes Cell Compartments Part 1 Membrane Structure Function I Lipids Phospholipids A Phospholipids are amphipathic hydrophilic phobic B When placed in water the polar heads spontaneously orient to interact with water and the tails orient to interact with each other making sphere C Membranes are fluid lipids move rotate migrate within a layer but never switch layers 1 Fluidity critical to function cell changes membrane chem to keep fluidity constant under changing conditions D Variable 1 Tails of phospholipids can be variable in their saturation bent vs straight not always 1 bent 1 straight a Tighter packing due to more saturated long straight fatty acid tails increased weak interactions between phospholipids less membrane fluidity 2 Head groups may differ in size shape or charge Stabilize fluidity of animal membranes II Lipids Cholesterol III Proteins A Contained in most 99 9 of membranes B Bigger than phospholipids move less C Give membrane function Classified by function 1 Allow materials to move across membrane transporter 2 Receive info from environment transmit it into the cell receptor ex senses 3 Catalyze reactions enzymes could be flipped to other side of membrane 4 Anchor cell to other cells or help maintain cell shape Anchors D Give the membrane structure Classified by structure 1 irremovable unless membrane is destroyed Integral membrane proteins a Transmembrane proteins many IMP s that span the membrane b Take form of alpha helices secondary structure through weak noncovalent interactions 2 Peripheral Membrane Proteins temporarily associate with membrane lipid or proteins IV All membrane components are not uniform Part 2 Membrane Function Selective Barriers Membranes Are Selectively Permeable Based On I Incoming molecule s size II Incoming molecule s charge III Hydrophilic nature IV Transmembrane concentration gradient diffusion force A Protein can facilitate diffusion 1 Channels just open let it flow 2 Carriers proteins that bind to a molecule change shape which transports molecules across the membrane not the same thing as a channel B Osmosis diffusion of H2O 3 Active transport use energy protein transporters to move against gradient 1 Ex in kidneys aquaporin protein utilized in absorbing excess H2O into nephrons 2 Water diffuses across membranes in response to relative solute concentrations a Hypertonic environment more concentrated than cell b Isotonic concentration to cell c Hypotonic less concentrated than the cell cell environment relative to outside environment d Effect of carrying tonicity fig 5 14 i These 3 are describing environment relative to cell but can be flipped to describe i Hypertonic environment outside cell cells shrink H2O leaves cell Isotonic no change H2O in H2O out ii iii Hypotonic cells swell H2O rushes in Part 3 Introduction to Cells Vary in size are much bigger the molecules they contain I Typical PROKARYOTIC Structure A Plasma membrane B Cell wall made of peptidoglycan C Glycocalyx outer gelatinous covering D Flagella sometimes present can be grown reabsorbed as needed E Pilli to attach or pick up DNA covers surface F Ribosome lots present G Nucleoid region where circular chromosome is found H Transcription translation both happen in prokaryotes II Typical EUKARYOTIC Cell Structure A More variable externally B More complex internally C Everything inside the membrane is the cytoplasm 1 Nucleus is often not considered part of the cytoplasm 2 Cytosol region inside the plasma membrane but outside the organelles a 20 50 of cell volume b Site of chemical reactions c Contains ribosomes ribosomes are not organelles d Contains dense network of protein filaments cytoskeleton i Provides cell shape organization movement ii Dynamic highly regulated iii Protein constituting cytoskeleton is extremely dense all over the cell D Plasma membrane is part of the endomembrane system ES a membrane network in eukaryotic cells 1 ES includes membrane membrane bound organelles which all interact Endomembrane System I Nuclear Envelope A 2 layers of protein pore containing membrane that surrounds the nucleus B Small molecules ions diffuse through pores large ones are actively transported C Chromatin very well organized DNA wrapped around histones D Nucleolus sub region where ribosomal subunits are assembled small large E Continuous with Endoplasmic Reticulum A Network of membranes enclosing a lumen II Endoplasmic Reticulum Has 2 subdivisions that can change into one another B Rough E R in protein synthesis no ribosomes lipid synthesis studded with ribosomes active C Smooth E R D Factory of the cell E Fig 5 20 F Amount of rough ER vs smooth varies depending on cell type time 1 Ex Liver cells lots of smooth for detox metabolism Tolerance to alcohol comes from increased production of smooth ER 2 Ex 2 Pancreatic cells lots of rough ER to produce insulin digestive enzymes proteins G Protein Sorting 1 Translation starts in free ribosomes in cytosol 2 Proteins are then sorted based on their AA sequence a If translation is completed on a free ribosome the protein will do one of the following Fig 5 23 i Stay in the cytosol ii Go to nucleus iii Go to chloroplast plants iv Go to mitochondria b If ribosome moves associates with ER before completion of translation because of protein s AA sequence the protein will stay in the ER s lumen stay in ER s membrane or move on to Golgi apparatus III Golgi Apparatus A Vesicles bud from ER and bring product to Golgi series of enclosed compartments B Processes sorts lipids proteins from ER 1 Glycosylation adding sugar to a molecule 2 Proteolysis big proteins get cut into pieces C Synthesizes carbohydrates D Vessicles bud from Golgi and go to membrane for exocytosis of products A ER Golgi insertion to membrane exocytosis out of cell IV Summary of Excretory Pathway Biosynthetic Pathway 1 How insulin is made 2 How proteins for membrane are made instead of being released they implant 3 Material can also move in opposite direction from Golgi back to ER V Lysosomes A Recycling centers B Breaks down organic molecules C Acidic pH 4 8 D Contain acid hydrolases enzymes that work in acidic conditions use water to break down molecules E Lyse all 4 types of macromolecules 1 Lyse the cell s own molecules autophagy 2 Lyse material taken into the cell via endocytosis F Tay Sachs 1 Caused by lack of lysosomal enzyme a Hexosaminidase b Hex enzyme breaks down fatty acids 2 Without enzyme fatty acids accumulate in brain cells 3 Progressive
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