Biology 1050 Cell Structure, Membranes & Homeostasis Notes PDF 2024

Biology 1050 Introduction to Cell & Molecular Biology Topic 3A Cell Structure, Membranes and Homeostasis Copyright © Macmillan Learning  1665: Robert Hooke and Cells - Hooke built a microscope to examine thin sections of dried cork samples from plants. - He...

Biology 1050 Introduction to Cell & Molecular Biology Topic 3A Cell Structure, Membranes and Homeostasis Copyright © Macmillan Learning  1665: Robert Hooke and Cells - Hooke built a microscope to examine thin sections of dried cork samples from plants. - He observed that the samples were made up of small cavity structures. - He was the first to name these cavities “cells”.  Cell Theory All organisms are made up of cells. The cell is the fundamental unit of life. Cells come from preexisting cells.  Prokaryotic and Eukaryotic Cells Cells can be classified as prokaryotes or eukaryotes. Prokaryotic cells (What Domain(s)?) lack a nucleus and have no internal compartmentalization. Eukaryotic cells (What Domain(s)?) have a nucleus and internal membrane- bound organelles.  Prokaryotes vs. Eukaryotes Prokaryotes Eukaryotes Nucleus No (nucleoid region) Yes Chromosome(s) Haploid Diploid Transcription Cytoplasm Nucleus location Translation location Cytoplasm Cytoplasm Size Small (average size of 1−2 Larger (average size of 10- micrometers) 20 micrometers) Ratio of surface area High (compared to Low (compared to to volume eukaryotic cells) prokaryotic cells) Internal organization No organelles Contains organelles (e.g. mitochondria, chloroplasts) Cell membrane Hopanoids Sterols (e.g. cholesterol) additions - Moderate the fluidity and - Moderate the fluidity and rigidity of cell membranes. rigidity of cell membranes. Hopanoids are located in the membranes of bacteria. They modulate the fluidity of the membranes by interacting with the phospholipids to form a highly ordered membrane bilayer and increase the rigidity of the membranes.  Cholesterol Cholesterol is found in many animal cell membranes. Cholesterol has both polar and nonpolar regions and associates into cell membranes. Cholesterol can impact membrane fluidity.  All Cells Are Defined by a Cell Membrane The major lipids found in the cell membranes are phospholipids. Phospholipids have a hydrophobic tail (nonpolar region) and a hydrophilic head (polar region). Therefore, phospholipids are amphipathic. Lipid Structures: Micelle and Bilayer Bilayers and liposomes Micelles are formed by are formed by phospholipids with large phospholipids with small bulky heads and a heads and two single hydrophobic tail. hydrophobic tails.  Lipid Structures: Liposome (or lipid vesicle) When in water, phospholipids spontaneously form a liposome, wherein polar heads and nonpolar tails associate with one another in a bilayer. Membranes are self-healing because they will spontaneously reform.  Membranes Are a Fluid Mosaic Lipids and proteins are found in the membrane, forming a mosaic. Lipids are able to move laterally within the membrane. Lipid movement is affected by the nature of the phospholipid tails.  Saturated vs. Unsaturated - Van der Waals interactions between the fatty acid tails help stabilize the membrane. - Because these interactions are weak, membrane lipids are able to move in the plane of the membrane. Thus, the membrane is fluid. Which of the following graphs correctly illustrates the effect of temperature on membrane fluidity? A B C Which of the following graphs correctly illustrates the effect of phospholipid fatty acid tail length on membrane fluidity? A B C Which of the following graphs correctly illustrates the effect of the number of double bonds on membrane fluidity? A B C  Cholesterol Cholesterol is found in many animal cell membranes. Cholesterol has both polar and nonpolar regions and associates into cell membranes. Cholesterol can impact membrane fluidity.  Cholesterol and Fluidity Cholesterol acts like a “buffer” for membrane fluidity.  Proteins in the Membrane Proteins of the membrane include: transporters that move ions and molecules. receptors that allow the cell to receive signals from the environment. enzymes that catalyze chemical reactions in the cell. anchors that attach to other proteins such as actins or cytoskeleton that help to maintain cell structure and shape.  Integral and Peripheral Proteins Integral membrane proteins are permanently associated with the membrane and can cross the entire membrane. Peripheral membrane proteins are temporarily associated with either side of the membrane. Examples of Integral Membrane Proteins - Sodium-Potassium pump - Aquaporins - ATP synthase Examples of Peripheral Membrane Proteins - Cytochrome c - Phospholipases - Glycolipid transfer proteins Which one of the following is considered an integral membrane protein? A. a protein capable of diffusing throughout the cytoplasm of a cell B. a protein attached to a transmembrane protein via hydrogen bonding C. a protein attached to a phospholipid via ionic bonding with the head group of the lipid molecule D. a protein with one end in the cytoplasm and the other end in the extracellular space  Evidence for the Fluid Mosaic Model Is there movement in the membrane? Proteins are fluorescently labeled. One specific region of the membrane is targeted by a laser and photobleached. Researchers then observe the membrane to see if the bleached area remains, or if fluorescent proteins return to the bleached area.  Proteins Do Move in the Membrane Fluorescence returns to the bleached area, showing that proteins are mobile throughout the membrane.