Eukaryotic Cell Biomolecules PDF

THE EUKARYOTIC CELL  MEMBRANE STRUCTURE Cell membrane: ▪ dynamic fluid structures ▪ Most of their molecules move about in the plane of the membrane ▪ encloses the cell and defines its boundaries; ▪ maintains the essential differences between the cytosol and the...

THE EUKARYOTIC CELL  MEMBRANE STRUCTURE Cell membrane: ▪ dynamic fluid structures ▪ Most of their molecules move about in the plane of the membrane ▪ encloses the cell and defines its boundaries; ▪ maintains the essential differences between the cytosol and the extracellular environment;  Membrane structure Common general structure of biological membranes: ▪ Thin film of lipid and protein molecules held together by non covalent interactions  Membrane structure LIPID MOLECULES Arranged as a continuous double layer about 5 nm thick; Provide the basic fluid structure Impermeable barrier to water soluble molecules Assemble spontaneously into bilayers even under artificial conditions.  Membrane structure LIPID MOLECULES Constitute about 50% of the mass of animal cells About 5x106 lipid molecules per 1µm 1µm area of lipid bilayer or 109 lipid molecules in the plasma membrane of a small animal cell  Membrane structure LIPID MOLECULES All are amphiphilic/ amphipathic: – Has hydrophilic/water- loving/polar end – hydrophobic/ water- fearing/nonpolar end; insoluble in water, uncharged; cannot form energetically favorable interactions with water  MEMBRANE PROTEINS Perform most of the membrane’s specific task Give each type of CM its characteristic functional properties Amounts and types found in a membrane are highly variable Example: myelin membrane w/c serves as electrical insulation of nerve cell axons has less than 25% protein of its mass.  Another example: membranes involved in ATP production like internal membranes of mitochondria and chloroplast - approximately 75% is protein There are always more lipid molecules than protein molecules in CM – about 50 lipid molecules for each protein molecule in CM that are 50% protein by mass Membrane protein function: ▪ transport ▪ enzymatic activity ▪ signal transduction ▪ intercellular joining ▪ cell-cell recognition ECM attachment  TRANSMEMBRANE PROTEINS Amphiphilic Hydrophobic regions – pass through the membrane & interact w/ the hydrophobic tails of the lipid molecules in the interior of the bilayer where they are sequestered away from water.  TRANSMEMBRANE PROTEINS Hydrophilic regions are exposed to water on either side of the membrane Covalent attachment of a FA chain that inserts in the cytosolic monolayer of the lipid bilayer increases the hydrophobicity of some of the transmembrane proteins  PERIPHERAL MEMBRANE PROTEINS do not extend into the hydrophobic interior of the lipid bilayer Bound to either face of the membrane by non-covalent interactions with other membrane proteins  PERIPHERAL MEMBRANE PROTEINS Can be released from the membrane by: gentle extraction procedures ▪ exposure to solutions of very low or high ionic strength ▪ Extreme pH All of these interfere w/ protein-protein interactions but leave the lipid bilayer intact NUCLEUS. spherical, oval, largest structure of the of the cell; contains almost all of the cell’s hereditary information. ▪ Nuclear envelope double membrane structure that surrounds the nucleus. ▪ Nuclear pores control the movement of substances between the nucleus and cytoplasm. ▪ Nucleoli spherical bodies, condensed regions of chromosomes where rRNA is synthesized Nuclear DNA contains histones 165 bp of DNA + 8 molecules histones =nucleosome Chromatin – threadlike appearance of DNA when not reproducing Chromosomes – chromatin becomes short, thick bodies during cell division  Packaging DNA 11 nm Nucleosomes Metaphase Chromosome 30 700 nm nm 200 nm Looped Domains Tight helical fiber 2 nm Protein scaffold B DNA Helix  Packaging DNA 11 nm Histone octomer Histone proteins Nucleosome B DNA Helix 2 nm  karyotyping Normal Trisomy 21 ENDOPLASMIC RETICULUM ▪ Extensive network of flattened membranous sacs or tubules called cisterns ▪ Continuous w/ the nuclear envelope Rough ER studded with ribosomes Smooth ER no ribosomes on its surface; synthesize SER enzymes in liver cells help phospholipids, fats, release glucose in the bloodstream steroids like estrogens and inactivate/detoxify drugs. and testosterone RIBOSOMES ▪ Sites of protein synthesis ▪ Proteins synthesized to attached ribosomes enter cisterns w/in ER for processing and sorting ▪ In some cases, enzymes attach the proteins to RER is a factory for carbohydrates to form synthesizing secretory glycoproteins or to phospholipids. proteins and membrane molecules. ▪ These molecules may be incorporated into organelle membranes or plasma membrane. GOLGI COMPLEX ▪Transport vesicles formed by the budding off of the An organelle consisting of 3 synthesized proteins from the membrane surface. to 20 cisterns – often curved, ▪Proteins are released through the fusion of the giving the organelle a transport vesicle w/ the cistern complex cuplike shape ▪Proteins are modified and move from one cistern to ▪ proteins synthesized by the another via transfer vesicles that bud from the cistern’s attached ribosomes are edges. initially transported in this ▪Enzymes in the cisterns modify the proteins to form glycoprotein, glycolipids and lipoproteins. organelle. Proteins ---- ER ---- formation ------ transport vesicle ----- proteins modified into glyco, from ribosomes of transport vesicle fuse w/GA cistern glycolipids, lipo, then released Processed proteins ▪Secretory proteins ▪Incorporated into the plasma membrane ▪Stored in storage vesicles - lysosome LYSOSOME – formed from Golgi complexes that look like membrane-enclosed spheres Single membraned and lack internal structure Contain 40 kinds of digestive enzymes that break down various molecules including bacteria Abundant in human WBC. VACUOLE – space/cavity in the cytoplasm that is enclosed by a membrane called tonoplast. ▪ Plant cell – occupies 5-90% of the cell volume depending on the type of cell ▪ Some serve as storage of proteins, sugars, organic acids and inorganic ions; also metabolic poisons and wastes (in plants) ▪ help bring food to the cell ▪ May take up water enabling plant cells to increase in size and provide rigidity to leaves and stems. MITOCHONDRIA ▪ Spherical/rod-shaped; appear throughout the cytoplasm ▪ Double-membrane : outer smooth, inner series of folds (cristae) ▪ Center part – matrix ▪ No. in the cell varies; liver has 1000-2000 mitochondria ▪ Contains 70s ribosomes and some DNA of their own as well as the machinery needed to replicate, transcribe and translate the info encoded by their DNA. ▪ Can reproduce on their own by growing and dividing in two. CHLOROPLAST – found in green algae and plants ▪ Membrane-enclosed structure containing pigment chlorophyll and enzymes required for photosynthesis ▪ Thylakoids – flattened membrane sacs that contain chlorophyll ▪ Grana – stacks of thylakoids PEROXISOME they are surrounded by only a single membrane; do not contain DNA or ribosomes. lacking a genome, all of their proteins are encoded in the nucleus. usually contain one or more enzymes that use molecular oxygen to remove hydrogen atoms from specific organic substrates(designated here as R) in an oxidation reaction that produces hydrogen peroxide (H2O2): RH2 + H2 R + H2O2 -contains 50 different enzymes that are involved in different biochemical pathways PEROXISOME ▪ Liver and kidney cells – peroxisomes detoxify toxic molecules that enter the bloodstream; 25% of the ethanol we drink is oxidized to acetaldehyde by catalase when excess H2O2 accumulates in the cell, catalase converts it to H2O through the reaction : 2 H2O2 2 H2O + O2 YEAST AND PLANTS: FA oxidation -Oxidation of uric acid, amino ANIMALS : FA oxidation (also happens in the mitochondria); synthesize cholesterol and acids and fatty acids dolichol (also synthesized in the ER) CENTROSOME – located near the nucleus ▪ Two components: pericentriolar area and centriole ▪ Pericentriolar material – region of the cytosol composed of a dense network of small protein fibers; organizing center for the mitotic spindle; microtubule formation in nondividing cell. Centrioles – composed of nine clusters of three microtubules (triplets) arranged in a circular pattern = 9 + 0 array 9 refers to nine clusters of microtubules and the 0 refers to the absence of microtubules in the center  CELLULAR COMPARTMENTALIZATION Advantages of compartmentalization (closed parts surrounded by a single layer or two layers of lipids): 1. Allow the cell to carry out different metabolic activities due to the established physical boundaries. *confine molecules within a region, isolate cellular conditions like pH, enzyme systems * Mitochondria – cytosol has an oxidizing environment which converts NADH to NAD+ 2. to generate a specific micro-environment to spatially or temporally regulate a biological process. As an example, a yeast vacuole is normally acidified by proton transporters on the membrane. 3. to establish specific locations or cellular addresses for which processes should occur. *transcription factor – directed to a nucleus where it promotes transcription of certain genes  Tissues: groups of cells with a common structure and function (4 types) 1- Epithelial: outside of body and lines organs and cavities; held together by tight junctions basement membrane: dense mat of extracellular matrix Simple: single layer of cells Stratified: multiple tiers of cells Cuboidal (like dice) Columnar (like bricks on end) Squamous (like floor tiles) mucous membrane 2- Connective: bind and support other tissues; scattered cells through matrix; 3 kinds: A-Collagenous fibers (collagen protein) B- Elastic fibers (elastin protein) C-Reticular fibers (thin branched collagen fibers) Loose connective tissue: binds epithelia to underlying tissue; holds organs 1-Fibroblasts- secretes extracellular proteins 2-Macrophages- amoeboid WBC’s; phagocytosis 3-Adipose tissue- fat storage; insulation Fibrous connective tissue: parallel bundles of cells 1-Tendons- muscles to bones 2-Ligaments- bones to bones; joints (BOBOLI) Cartilage: collagen in a rubbery matrix (chondroitin); flexible support Bone: mineralized tissue by osteoblasts Blood: liquid plasma matrix; erythrocytes (RBC’s) carry O2; leukocytes (WBC’s) immunity 3-Nervous: senses stimuli and transmits signals from 1 part of the animal to another Neuron: functional unit that transmits impulses Dendrites: transmit impulses from tips to rest of neuron Axons: transmit impulses toward another neuron or effector 4- Muscle: capable of contracting when stimulated by nerve impulses; myofibrils composed of proteins actin and myosin; 3 types: A- Skeletal: voluntary movement (striated) B- Cardiac: contractile wall of heart (branched striated) C- Smooth: involuntary activities (no striations)