eukaryotic cells generalized eukaryotic cells and the organelles of eukaryotic cells. essentials ch...
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Eukaryotic Cells
Generalized eukaryotic cells and the organelles of eukaryotic cells. Essentials Ch 1 and 2
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The Eukaryotic Cell
All cells of the human body are eukaryotic cells
Each contains a nucleus (as you may know RBC do lose their nucleus, but develop from nucleated cells)
Eukaryotic cells are more complex than the other general type of cell; the bacterial cell
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A typical eukaryotic cell
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No such thing as typical Eukaryotic Cell
The cells of the body are quite different in appearance and function from one tissue type to another
They share many organelles common, but have unique character as to how they utilize the complement of organelles
In discussions of tissues always examine the use each cell puts to its organelles
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Scale
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Nuclear Text reference
Junqueria p.48 -54 Relevant figures 3-1 - 3-8
Essentials
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Nucleus
Nucleus structure Nuclear envelope Nucleolus Nucleoplasm
ChromatinDNANuclear laminaNucleoskeleton
Nuclear Pore
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Functions of Nucleus
Repository for the information that is required to run the cell
DNA is the molecule in the nucleus which contains the information
Information containing regions are referred to as genes
Multiple genes reside on linear chromosomes
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Functions of Nucleus 2
Nucleus also functions in faithfully copying the DNA information and passing it to the next generation
Nucleus is fundamental in beginning the process of Gene Expression whereby the information is accessed and utilized to produce rRNA, tRNA and Proteins
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Flow of Information
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Nuclear Envelope
Visible using light microscopeComplex structure under EM
Double lipid bilayer• Inner membrane• Outer membrane
Covered on cytoplasmic surface with polyribosomes
Internal surface nuclear lamina Nuclear cisternae (Nuclear space)
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Nucleolus
Site where genes for ribosomal RNA is amplified (hence the intense staining)
Multiple copies of rRNA genes are expressed at High level by RNA Polymerase I
Sub-assembly of small and large ribosomal subunits occurs here
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Nucleolar Organizing Regions - Nucleolus 2
Regions within Nucleolus Nucleolar organizer DNA - rRNA genes Associated with this NOR DNA is pars fibrosa
Pars fibrosa is composed of primary transcripts of rRNA genes
Third region is pars granulosa15-20 nm particles which contain the maturing
subassembled ribosomes
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Nucleoplasm
Chromatin Euchromatin - diffuse lighter staining Heterochromatin - dense darker staining
Nuclear Laminins Intermediate filaments - nucleoskeleton Have a chromatin binding function Thought to organize chromatin in the to aid in
gene expression
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Structure of Chromatin
Chromatin is made up of DNA and primarily histone proteins
Structural organizationLevels of Chromatin packing p252
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Nuclear Pore Complex
Formed where there is a fusion of two membranes
Intricate protein structure called NPCDiameter of entire complex 120 nmMass 120 million DaConsists of 100 or more different
polypeptides
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Nuclear Pore Complex 2
Structure has an octagonal arrayRings of eight subunitsA central granule is prominentThis central granule called transporter has
a poreTransporter pore is much smaller than the
overall size of the NPC
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Nuclear Pore Complex 3
Proteins smaller than 60,000 Da can diffuse through the pores Histone proteins average 20,000 Da and
therefore freely diffuse back into the nucleus
Proteins larger than 60,000 Da require specialized signals and also require docking and ATP energy
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Nuclear Pore Complex 4
Nuclear localization signal - an example of how the transporter works for large proteins
8 - 30 amino acids rich in arginine and lysine in a protein that is to be imported back into the nucleus
Cytosolic receptor protein recognizesDocking with NPCTransporter opens like iris diaphragm using ATP
and passes protein into the nucleoplasm
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Nuclear Matrix
Component that fills the space between chromatin fibers Composed of proteins, metabolites and ions If we remove the proteins, metabolites and
ions, remainder is nucleoskeleton Nucleoskeleton continous with the nuclear
lamina (Intermediate filaments class of cytoskeletal elements)
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Karyotype
The condensed chromosomes of of the dividing cell (metaphase chr) are used in karyotyping individuals
Essentials Fig 8-2 p. 247Junqueria fig 3-7 p. 57 Note the chromosomes are ordered based
on size
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G - banding
It is sometimes difficult to tell chromosomes of similar size apart
Giemsa’s stain produces unique banding patterns to individual chromosomes
Fluorescent dyes have also been used and now multiple fluorescent stains are being used to give cytogeneticists even more information
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Plasma Membrane
General characteristics 7.5 to 10 nm across, surrounding the cell Composed of Phospholipids, Cholesterol,
other lipids and ProteinsProteins are found either running into or through
the lipid bilayer = integral or intrinsic OR the protein may be associated with either leaflet of the lipid bilayer = peripheral or extrinsic.
All lipids present have amphipathic nature
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Plasma Membrane Functions
Membranes are indispensable to lifePrimary function is to form the barrier
between outside an inside the cellMembranes are highly selective
permeability barriersWhat goes out of and comes into the cell
is controlled by specific proteins
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Key Membrane Functions
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Key Membrane Functions
Create & MaintainGradients
[ion] differences fromone side to the other
Regulate flow ofinformation
Receptors – bindsignal (SignalTransduction)
Convert energy conversion of oneform of energy toanother (ETS)
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Fluid Mosaic Model
Overall organization of the PM is described as a fluid mosaic A sea of amphipathic lipids with proteins floating within and adhering to the lipids
Variation in lipidsGlycolipids & glycoproteins are restricted
to outer leaflet ; form glycocalyx
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Peripheral vs Integral Proteins
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PM Transport Processes
Passive transport Simple diffusion - few
molecules Facilitated diffusion -
ion channel or carrier protein
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PM Transport Processes 2
Active Transport - require energy Example Na+ K+ ATPase pump Antiport - two ions or molecules move in
opposite directions (Na+/K+ ATPase) Symport- two ions or molecules move in
same direction (Glucose symport) Uniport- single ion or molecule move in a
single direction (Ca+2 ATPase pump)
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Cytoplasm or Cytosol
Bounded by PM outside and ending at membrane of various membranous organelles
Aqueous environment full of Enzymes - example glycolytic enzymes Organelles Inclusions Cytoskeletal elements
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Organelles in Cytosol
Ribosomes Structure
Made up of rRNA and ribosomal proteinsHas two subunits - large and smallSizes of the two subunits determined by
sedimentation in a density gradientUnits are Svedberg’s or simply designated S
Individual or in Polyribosome complexes Function Translation
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Organelles in Cytosol 2
Endoplasmic reticulum Structure- membranous and continous with
outer lipid bilayer of nuclear envelope Two forms
Rough ER - membranous labyrinth which has an inner space referred to as the lumen; typically studded with ribosomes
Smooth ER- tubular membranous network which also has a lumen; typically has no ribosomes
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Organelles in Cytosol 3
Rough ER Function Start the process of Membrane-packaged
proteins Works in concert with Golgi Complex Produces
Secretory proteinsIntegral membrane proteinsLysosomal proteins
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Organelles in Cytosol 3
Smooth ER Function Steroid hormone synthesis occurs in SER rich
cells (Leydig cells of the testis) Drug detoxification - hepatocytes produces
elaborated SER in response to drugs like phenobarbital
Muscle Contraction and Relaxation involves release of Ca+2 ions from sarcoplasmic ret.
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Organelles in cytosol 4
Mitochondria (pl..) Mitochondrion (sing.) Structure - double membrane bound
organelle inner and outer membranesHas its own DNA and ribosomesDNA codes for some of the proteins of ETS and
tRNA’sOther proteins are coded for by nucleusDue to structure its has an intermembrane spaceThe inner most space is the matrix
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Mitochondria Functions
Structure helps to impart functionEnzymes of TCA cycle and -oxidation of
fatty acidsETS carrier proteins and ATP synthaseGenetic apparatus that codes for some of
the above functions
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Organelles in cytosol 5
Golgi complex Structure - series of disk-shaped cisternae or
saccules arranged in stacks Typical stack has flattened center and
rounded edge rims There is a distinct polarity to the stacks
Cis face is the forming face (RER --> cis-face)Trans face is the exiting face (Golgi -->
destination)
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Golgi functions
The Golgi complex processes membrane - packaged proteins synthesized in the RER Processing involves some proteins being
glycosylated All proteins being sorted into groups to be
shipped to a final functional destination Membrane recycling also occurs
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Organelles in cytosol 6
Clathrin Coated vesicles Clathrin is a protein with a Triskelion structure Clathrin is involved in receptor mediated
endocytosis Clathrin molecules form a molecular cage
around receptor coated pits and eventually around the vesicle that is brought into the cell
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Organelles in cytosol 7
Coatomer vesicles Coats vesicles - NOT IN CAGE FORM Coatomer is a large protein complex formed
by individual coat protein subunits called COP’s
Coatomer proteins mediate continous constitutive protein transport within cells
Represents a default system for bulk flow
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Organelles in cytosol 8
Lysosomes Structure - dense membrane bound organelle
with diverse shapes and sizes; identified by presence of acid phosphatase
Function - over 40 hydrolases (pH ~ 5)Digest materials brought into the cellDigest aged organelles marked for destructionApoptosis - cell suicide
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Organelles in cytosol 9
Peroxisomes (Microbodies) Structure - membrane bound spherical to
ovoid; identified by presence of catalase Structure often has a crystalline core
consisting of urate oxidase Function - oxidative enzyme complement
Oxidize some fatty acidsDetoxification of substances like ethanol
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Organelles in cytosol 10
Centrioles and centrosomesStructure - centrioles are 9 + 0 structures
made up of 9 triplets of microtubules Structure of centrosome is the centrioles +
surrounding matrix of proteinsCentrioles are the primary Microtubule
Organizing Centers (MTOC) of the cellThe centriole is (-) end the ends of MT (+)
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Centrosome + MT’s
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Inclusions in cytosol
Glycogen granules - polysaccharide storage form of glucose prominent in liver and muscle
Lipid droplets - an energy storage inclusion - lipid contains more energy available than carbohydrates like glucose
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Cytoskeleton
Microtubules Straight, hollow tubules 25 nm diameter and
several micrometers long Each tube consists of polymerized and
tubulin which first forms 13 protofilaments, which then role into tube
There is polarity to MT’s - centrioles become minus end with ends out in cell as + or growing end
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Microtubles
Functions Maintain cell shape Aid in the transport of macromolecules and
organelles in cytosol Allow for the movement of cilia, flagella and
chromosomes
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Cytoskeleton 2
Microfilaments Structure - Polymerized form of actin = F- actin
; double helix 6 nm in diameter Polarity - polymerized and depolymerized at + Abundant in periphery of cell Functions are many
Focal contact for cell with environmentLocomotion of nonmuscle cellsContractile ring in dividing cells
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Cytoskeleton 3
Intermediate filamentsStructure - 8 - 11 nm diameter ;
heterogenous group of proteins that make up intermediate filaments, but all have regions of conserved sequence
Function - Provide mechanical strengthsOnce laid down do not change rapidly
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Interactions among Organelles
Secretion of proteinsProduction of lysosomesProtein SortingEndocytosis, Exocytosis and PinocytosisSignal transduction via receptor ligand
interaction