Chapter 4 A Tour of the Cell Intro Cytoskeleton system of protein fibers that provide structural support and enables movement Leeuwenhoek better lenses blood sperm pond water animalicules Hooke 1665 discovered cells cellulae little rooms on a piece of cork 4 1 Microscopes LM were the first microscopes 1600s visible light is passed through a specimen then through lenses bend light to magnify Magnification increase in image size compared to actual size Resolution ability to distinguish two nearby objects as separate o Human eye 1 mm o LM 2 micrometer 1 micro 10 3 mm o EM 2 nm 1nm 10 3 micrometer Cell theory all living things are composed of cells all cells come from cells EM 1950s beam of electrons through specimen or onto its surface can explore cell ultrastructure and complex internal anatomy use electromagnet lenses to bend path of electrons o SEM study architecture of cell surface 3D o TEM details of internal structure electron beam through thin section of specimen section is stained w atoms of heavy metals 4 2 Small cell size related to the need to exchange materials across the plasma membrane Cells must be large enough to house enough DNA protein molecules and structures to survive and reproduce Must be small the need to have a surface area large enough to service the volume of a cell no activity in chicken egg but a lot in embryo Surface to Volume ratio o Large cells have less surface area relative to their volume p 54 o Smaller cells have larger ratio long skinny neurons Plasma membrane o forms flexible boundary between living cell and its surroundings o Very thing structure correlates to function o Phospholipid head w negative charged phosphate group Hydrophilic tail with 2 nonpolar fatty acids Hydrophobic Form bilayer contains diverse proteins floating Regulate flow of materials into the cell membranes proteins form channels that shield ions and polar molecules as they pass through hydrophobic center of the membrane other proteins serve as pumps that use energy to transport molecules in or out of cell 4 3 Prokaryotic cells are structurally simpler than eukaryotic cells Prokaryotic Bacteria and Archea o Nucleoid coiled region of DNA no membrane surrounds the nucleus o Ribosomes of prokaryotes are smaller and differ somewhat from euk Molecular different are basis for action of antibiotics which target pro ribosomes Protein synthesis is blocked in invading bacteria o Rigid cell wall surrounds plasma membrane helps protect cell and maintain shape penicillin prevents formation of these walls o Outter capsule helps glue cells to surroundings same as surface projections cilia short attch and flagella long movement Eukaryotic all other forms of life protists fungi plants o Have membrane enclosed nucleus which houses DNA membrane enclosed organelles that perform specific functions BOTH o Bound by plasma membrane o Interior of cell is filled with cytosol jellylike fluid o Have one or more chromosome carry genes made of DNA o Contain ribosomes make proteins according to gene instructions o Inside of the cells is called cytoplasm in eukaryotes it is region between nucleus and plasma membrane 4 4 Eukaryotic cells are partitioned into functional compartments Contain nucleus and organelles each bound by a membrane with a lipid and protein composition that suits its function 4 basic functional groups 1 The nucleus and ribosomes carry out the genetic control of the cell 2 Organelles involved in manufacture distribution and breakdown of molecules ER golgi lysosomes vacuoles peroxisomes 3 Mitochondria in all cells and chloroplasts in plant cells function in energy processing 4 Structural support movement and communication between cells cytoskeleton plasma membrane and plant cell wall Cellular metabolism chemical activities of the cell collectively occur w in organelles Fluid filled spaces w in organelles are sites where specific chemical conditions are maintained Except lysosomes and centrosomes organelles and structures in animal cells are in plant cells animal have flagella only some plant sperm have it Plant cell rigid cell wall contains cellulose o Plasmodesmata cytoplasmic channels that connect adjacent cell walls o Chloroplast photosynthesis o Large central vacuole stores water and chemicals The Nucleus and Ribosomes 4 5 The nucleus contains the cell s genetic instructions coded in DNA DNA organized into chromosomes called chromatin when not divided control cell activities by directing protein synthesis appears as a diffuse mass in the nucleus Nuclear envelope double membrane enclosing the nucleus each membrane is a separate phospholipid bilayer w associated proteins Nucleolus site where rRNA is synthesized according to instruction in DNA proteins from cytoplasm are assembled w this rRNA to form ribosomes exit to cytoplasm and become functional mRNA directs protein synthesis moves into cytoplasm where ribosomes translate it into aa sequence of proteins carry out commands from the nucleus written in mRNA to build proteins 4 6 Ribosomes make proteins for use in the cell and for export Pancreas produces digestive enzymes has millions of ribosomes Free ribosomes suspended in cytosol bound ribosomes attached to the outside of the endoplasmic reticulum or nuclear envelope Proteins made on free rib function w in cytosol enzymes that catalyze 1st steps of sugar breakdown for cellular respiration Bound rib make proteins that will be inserted into membranes packaged in organelles or exported from a cell The Endomembrane System 4 7 Many organelles are connected in the endomembrane system Endomembrane system nuclear envelope ER golgi lysosomes vacuoles Internal membranes in eukaryotic cells involved in cell function plasma membrane some of these are physically connected other are lined w vesicles pm these interact in synthesis distribution storage and export of molecules o Divides cell into dif compartments require dif conditions ER largest component of em extensive network of flattened sacs w tubules membranes are continuous w nuclear envelope and when vesicles bud from it they travel to many other compartments o Encloses a space that is separate from the cytosol 4 8 The endoplasmic reticulum is a biosynthetic workshop Smooth ER outer surface lacks attached ribosomes o Enzymes important in synthesis of lipids oils phospholipids steroids o Vertebrae steroids sex hormones Liver process harmful substances More drugs more smooth ER detoxifying enzymes higher Barbiturate abuse decrease