Transcript Document
A tour through the Cell cont… The framework of a cell - the Cytoskeleton Organelles in action - Protein Synthesis Cytoplasm • • semi-fluid-like jelly within the cell division into three subdivisions: cytosol, cytoskeleton & organelles Cytoskeleton: •internal framework of the cell •gives the cytoplasm flexibility and strength •provides the cell with mechanical support •gives the cell its shape •can be rapidly disassembled in one area of the cell and reassembled in another •anchorage points for organelles and cytoplasmic enzymes •also plays a role in cell migration and movement by the cell Cytoskeleton: •three major components 1. microfilaments 2. intermediate filaments 3. microtubules microfilaments = thin filaments (7 nm) made up of a protein called actin -twisted double chain of actin subunits -forms a dense network immediately under the PM (called the cortex) -also found scattered throughout the cytoplasm -function: 1. anchor to membrane proteins 2. interaction with myosin = interacts with larger microfilaments made up of myosin - results in active movements within a cell (e.g. muscle cell contraction) 3. provide much of the mechanical strength of the cell 4. give the cell its shape 5. also provide support for cellular extensions called microvilli (small intestines) intermediate filaments = range from 8 to 12 nm in diameter -function: 1. impart strength to the cytoskeleton (like microfilaments) 2. support cell shape 3. anchors & stabilize organelles 4. transport materials within a cell microtubules = hollow rods or “straws” of 25 nm in diameter - made of repeating units of proteins called tubulin - function: 1. cell shape & strength 2. organelles: anchorage & movement 3. mitosis - form the spindle (chromosome movement) 4. form many of the non-membranous organelles - cilia, flagella, centrioles Organelles in Action • organelles attach to the cytoskeleton – held in place • each organelle has a distinct function • organelle of protein synthesis = Endoplasmic Reticulum – large organelle surrounded by a phospholipid bilayer and attached to the nucleus – can be found studded with ribosomes = Rough ER (protein synthesis) – parts found without ribosomes and make lipids = Smooth ER • organelle of protein modification and packaging = Golgi apparatus Protein synthesis • known as translation – translating the message found in DNA/RNA into a polypeptide chain protein • requires three things – 1. mRNA – messenger RNA transcribed from the DNA template – 2. tRNA – transfer RNA that carries the amino acids of the future protein – 3. ribosome – the “machine” of translation • • • • • • How are the instructions for assembling amino acids into proteins encoded in your DNA? first the DNA gets transcribed into a message = mRNA the mRNA gets exported out into the cytoplasm the mRNA gets bound by a ribosome tRNA molecules bring the correct amino acid into the ribosome amino acids are linked together mRNA • • • the mRNA nucleotide sequence is “read” by the ribosome in groups of 3 nucleotides = “codon” each codon codes for 1 of the 20 amino acids that make up proteins in eukaryotes all of these codons grouped together is called the “genetic code” the code is redundant - each amino acid can be coded for by more than one codon Protein Translation: The Genetic Code U UUU Phe U – serine – codons are: AGU, AGC – BUT arginine codons are: AGA and AGG First mRNA base (5 end of codon) in many cases the 3rd codon is important in defining the amino acid UUC UAU UCU UGU Tyr UCC A Cys U UAC UGC C UCA UAA Stop UGA Stop A UUG UCG UAG Stop UGG Trp G CUU CCU CAU CGU Leu His C G Ser UUA • e.g. alanine – GCU, GCC, GCA and GCG • the GC defines the amino acid as alanine • Second mRNA base A C CUC Leu CAC CCC CCA CUG CCG CAG AUU ACU AAU AUC Ile AUG CAA Met or start GUU Gln AAC ACC ACA AAA ACG AAG GCU GAU CGA C Arg CGG Asn Thr AUA CGC Pro CUA U AGU G Ser AGA U C AGC Lys A Arg A AGG G GGU U Asp G GUC GUA GUG GCC Val GCA GCG GAA GAG C GGC GAC Ala Glu GGA GGG Gly A G Third mRNA base (3 end of codon) • Building a protein: tRNA • • • • • where do the amino acids come from they are brought into the ribosome bound to tRNA molecules tRNA molecule consists of a single strand of RNA - about 80 RNA nucleotides long at one end – anticodon site for binding with the mRNA template at the other end – attachment site for the amino acid that corresponds to the mRNA codon 3 Amino acid attachment 5 site 5 3 Hydrogen bonds Amino acid attachment site Hydrogen bonds AAG Anticodon (a) Two-dimensional structure Anticodon 3 5 Anticodon (b) Three-dimensional structure (c) Symbol used in books Building a Protein: Ribosomes • machine of translation • made in the nucleolus in eukaryotic cells • comprised of two subunits of proteins (large and small) linked together – eukaryotes: small subunit = ~33 proteins + large subunit = ~50 proteins – subunits are exported out via nuclear pores Ribosomes • • within the large subunit are two sites for the binding of tRNAs – P-site or Peptidyl-tRNA site – “old” AA – A-site or aminoacyl-tRNA site – incoming AA and one E site/Exit site for the exit of the old tRNA off the ribosome Growing polypeptide Amino end Next amino acid to be added to polypeptide chain E tRNA mRNA 5 3 Codons (c) Schematic model with mRNA and tRNA Translation http://highered.mcgrawhill.com/sites/0072507470/student_view0/chapter3/animat ion__how_translation_works.html Organelles in Disease: The lysosome Lysosomes = “garbage disposals” -dismantle debris, eat foreign invaders/viruses taken in by endocytosis or phagocytosis -also destroy worn cellular parts from the cell itself and recycles the usable components = autophagy -form by the budding of vesicles off the Golgi and their fusion -acidic interior -1. contain enzymes that breakdown DNA, RNA (nucleases) and proteins (proteases) -2. contains enzymes for the breakdown of lipids and phospholipids Tay Sachs and lysosomes: human genetic disease -severe mental degradation -lysosomes lack one of the 40 required enzymes -results in a build up of fatty material on neurons -failure of nervous system communication -infantile form of the disease = death by 4 yrs -juvenile form = death from 5 to 15 yrs -adult onset – not fatal; progressive loss of nervous function -most common in Ashkenazi Jews, French Canadians and Cajun populations in Louisiana (same mutation as Jews) Organelles in Disease: The Peroxisome -only identified in 1954 -found in all cells – abundant in liver and kidney cells -major function is breakdown of long chain fatty acids -other functions: 1. synthesis of bile acids F-actin and peroxisomes 2. breakdown of alcohol by liver cells 3. anti-oxidant function - contains enzymes to break down dangerous chemicals made by the cell during metabolism Adrenoleukodystrophy and peroxisomes: -X linked disorder -1:20,000 to 1:50,000 births -peroxisomes can’t break down fatty acids properly -leads to a build up of big, saturated fatty acids on cells of throughout the body -can result in neuron death – not known why -lethargy, skin darkens, blood sugar drops, altered heart rhythm due to imbalanced electrolytes, paralysis, death *** slowed by a certain triglyceride found in rapeseed oil Lorenzo Odone = “Lorenzo’s Oil” (mixture of unsaturated fatty acids that slows the development of these saturated FAs)