Lecture Chapter 6 tour of the cell 9 27 11 All organisms are made of cells The cells is the simplest collection of matter that can live Cell structure is correlated to cellular function All cells are related by their descent from earlier cells To study cells biologist use microscopes and the tools of biochemistry Thought usually too small to be seen by the unaided eye cells can be complex Scientists use microscopes to visualize cells too small to see the naked eye In a light microscope LM visible light passes through Microscopy The quality of an image depends on Magnification the ratio of an objects image size to its real size Resolution the measure of the clarity of the image of the minimum distance of 2 distinguishable points Contrast visible differences in parts of the sample Use different methods for enhancing visualization of cellular structures Brightfield unstained Brightfield stained Phase contrast Differential interference contrast Fluorescence Confocal LM s can magnify effectively to about 1000 times the size of the actual specimen VAious techniques enhance contrast and enable cell components 2 basic types of electron microscopes Ems are used to study subcellular structures Scanning electron microscope SEMs focus a beam of electrons Transmission electron microscopes TEMs Cell fractionation takes the cells apart and separates the major organelles from one another Ultracentrifuges fractionate cells into their components parts Cells fractionation enables scientists to determine the functions of organelles Biochemistry and cytology Eukaryotic cells The basic structural and function unit of every organism is 1 of the 2 types of cells prokaryotic or eukaryote Only organisms of the Domains Bacteria and Archea Only Comparing Basic features of all cells plasma membrane semifluid substance called cytosol Chromosomes carry genes Ribosomes make proteins Prokaryotic cells are characterized by having No nucleus DNA in an unbound region called nucleoid No membrane bound organelles Cytoplasm bound by the plasma membrane Eukaryotic cells are characterized by having DNA in a nucleus that is bounded by a membranous nuclear envelope Membrane bound organelles Cytoplasm in the region between the plasma membrane and nucleus Eukaryotic cells are generally larger than prokaryotic Plasma membrane Is a selective barrier that allows sufficient passage of oxygen nutrients and waste to service the volume of every cell The general structure of a biological membrane is a double layer of phospholipids Limitations of cells The logistics of carrying out cellular metabolism sets limits on the size of cells The surface area to volume ratio of a cell is critical As the surface area increases by a factor of n2 the volume increases by a factor of n3 Small cells have a greater surface area relative to volume A panoramic view of the eukaryotic cell Eukaryotic cells have extensive and elaborate arranged internal membranes which form organelles Plant and animal cells have most of the same organelles but with some differences Plants cells have chloroplast central vacuole cells wall plasmadesmata Animal cells centrioles lysosomes flagella The eukaryotic cells genetic instructions are housed The nucleus contains most of the cells genes and is usually the most conspicuous organelle The nuclear envelope encloses the nucleus separating Pore regulate the entry and exit of molecules from the nucleus In the nucleus DNA and proteins form genetic material called chromatin Chromatin condenses to form discrete chromosomes The nucleus is located within the nucleus and is the site of ribosomal RNA rRNA synthesis Ribosomes protein factories are particles made of ribosomal RNA and protein carry out protein synthesis in 2 locations in the cytosol on the outside of the endoplasmic reticulum ER The endomembrane system regulates protein traffic and performs metabolic functions Components of the endomembrane system nuclear envelope endoplasmic reticulum Golgi apparatus lysosomes vacuoles plasma membrane These components are either continuous or connected via transfer by vesicles The ER bio accounts for more than half of the total membrane in many eukaryotic cells The ER membrane is continuous with the nuclear envelope There are 2 distinct regions of ER smooth ER which lacks ribosomes rough ER with ribosomes studding its surface Functions of smooth ER synthesizes lipids metabolizes carbohydrates detoxifies poison stores calcium Functions of rough ER has bound ribosomes which secrete glycoproteins proteins covalently bonded to carbohydrates distributes transport vesicles proteins surrounded by membranes is a membrane factory for the cell The Golgi apparatus consists of flattened membranous sacs called cisternae Functions modifies products of the ER manufactures certain macromolecules sorts and packages materials into transport vesicles Lysosomes Digestive compartments is a membranous sac of hydrolytic enzymes that can digest macromolecules Lysosomal enzymes can hydrolyze proteins fats polysaccharides and nucleic acids Some types of cell can engulf another cell by phagocytosis this forms a food vacuole A lysosomes fuses with the food vacuole and digest the molecules Lysosomes also use enzymes to recycle the cells own Vacuoles A plant cell or fungal cell may have 1 or several vacuoles Food vacuoles are formed by phagocytosis Contractile vacuoles found in many fresh water protists pump extra Mitochondria and chloroplast Lecture chapter 6 9 29 11 Lecture chapter 7 The role of membrane carbohydrates in cell cell recognition Cells recognize each other by binding to surface molecules often carbohydrates on the plasma membrane Membrane carbohydrates may be covalently bonded to lipids forming glycolipids or more commonly to proteins forming glycoproteins Carbohydrates on the external side of the plasma membrane vary among species individuals and even cell types in an individual Synthesis and sidedness of membranes Membranes have distinct inside and outside faces The asymmetrical distribution of proteins lipids and associated carbohydrates in the plasma membrane when the membrane is built by the smooth ER and Golgi apparatus Membrane structure results in selective permeability A cell must exchange materials with its surroundings a process controlled by the plasma membrane Plasma membranes are selectively permeable regulating the cells molecular traffic Hydrophobic nonpolar molecules such as hydrocarbons can dissolve in the lipid bilayer and
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