Organelles

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eukaryotic cell consists of (4 things)

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1. plasma or cell membrane
2. one or more nuclei, surr by nuc membrane which contains most of DNA
3. cytoplasm
4. basic set of organelles that form specialized compartments

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ex of cytoplasmic struct that are not surr by a membrane

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various cytoskeletal filaments, lipid droplets, or centrioles

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advantages of specialized compartments

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1) membranes surr them increase the cell surface and contain enzymes
2) compartment can have a unique composition of sp functions

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3 maj mech by which cells move materials

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1. mvmt across membrane (transmembrane transp)
2. gated transport
3. vesicular transport

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mvmt across membrane --- small uncharged particles

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simple diff

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mvmt across membrane---- small water sol molecules move through membranes using

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active or facilitated transp via carrier proteins or channels

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mvmt across membrane---- proteins in process of synthesis

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can move across cell membranes in special channels (ex membranes surr RER, perioxisomes, mitochon)

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mvmt via vesicular transp --- uptake by vesicles into cell are by

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endocytosis and phagocytosis

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mvmt via vesicular transp --- sel transp of vesicles occurs when one memb fuse with another carrying cargo. this occurs in which pathways

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biosynthetic secretory pathway and endycytic pathway

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mvmt via vesicular transp--- 3 types of coated vesicles

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1) clathrin coated vesicles: mvt into cell from plasma membrane and from golgi to cell surface
2) COPII coated vesicles mvmt of material from ER to and throuh the golgi memb
3) COPI coated vesicles: gen involved with retrieval of memb and contents (golgi back to ER)

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mvmt via vesicular transp ---- pinocytotic vesicles are

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clathrin independent

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basic fcn of plasma membrane

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1) selective barrier
2) formed by complex mix of lipids an dproteins
3) constant state of dynamic flux or can be tethered
4) 7.5 to 10 nm thickness
5) viewed in TEM

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enzymatically active areaas of cell membrane contain higher proportion of

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proteins

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lipid rafts

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enriched in cholesterol and sphingolipids and are less fluid than most plasma membranes

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membranes under TEM, plasma membrane is resolved since

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there is a deposition of osmium on hydrophillic groups of lipid bilayer that produces electron densities

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plasma membrane has trilaminar appearance designated as a

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unit membrane, outer electron dense layer and inner electron dense layer and intermed electron lucent layer

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membrane proteins form about what percent of membrane mass and include what kind of proteins

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50% of membrane mass and contain integral proteins and peripheral proteins

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membranes demonstrate fluidity but also can be tethered which means they

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do not move

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both lipids and proteins have what on their extracell surfaces

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oligosaccharide chains forming glycolipids and glycoproteins at surface that together form a glycocalyx that has an overall neg charge

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integral membrane proteins are involved with what functions

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transport (pumps and channels)
cell receptors, struct proteins, enzymes, molecules involved with cell adhesion

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since many proteins and lipids can move within membrane, structure called tight junction exists where

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at luminal border of adj epithelial cells (this tight junction is also called zonula occludens)

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tight junction / zonula occludens function is to

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limit the mvmt of proteins and lipids within memb to lateral surface or to apical surface so that diff surf of cell can contain diff molecules and therefore diff fcns

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organelles: interphase nucleus
size and bounded by how many memb

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6-10 micrometers dia, bounded by two unit membranes

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functions of nucleus

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protection, replication, synthesis, expression of genome
also synthesis of ribosomal components

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dna is transcribed into

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mRNA

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shape of nucleus and number per cell

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differs in acc with the shape of cell, some cells contain more than one nucleus (hundreds in skeletal muscle)

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nuclear envelope

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comprised of two unit membranes continuous with each other at circ openings called nuc pores

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perinuclear cisterna

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space between two membranes in nuclear envelope
outer memb contain with RER, studded with ribosomes

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nuclear envelope interrupted by

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nuclear pore complexes, with 8 fold symm, gated ch for nuc

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fibrous lamina

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layer of intermed filaments, just inside inner membrane of nuc envelope
polypeptides called lamins A, B, C

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when lamins are phosphorylated

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the fibrious lamina and nuc envelope disassemble

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nuclear envelope segregates the fcns of

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nucleus and cytoplasm

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in interphase, the chromatin adj to centromeres of chromosomes

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is assoc with fibrous lamina

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chromatin

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genetic material when not condensed to form chromosomes. fibrillar mass which fills most of nucleus.

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chromatin appears .... when staining with basophilic dyes such as heterochromatin

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appears densely staining when highly condensed and less active. when more actively transcribed, stains with less basophilia (euchromatin)

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chromatin composed of

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largely of coiled DNA protein complexes.

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densely packed dark staining clumps of chromatin (heterochromatin) are

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usually not capable of being expressed (transcribing RNA)

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more loosely packed lighter staining chromatin (euchromatin) is

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more actively expressed (capable of transcribing RNA)

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2 meanings of chromosome

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1) darkly stained rod like body during mitosis and meiosis. formed of condensed chromatin, allow genetic mat to be halved during mitosis
2) structure consisting of coiled strands of DNA bound to basic proteins which composed of genetic elements.

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basic unit of chromosome

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nucleosome: has core of 4 types of histones wrapped by DNA

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nucleolus made of

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dense aggregates of protein and nuc acid. may be more than one in nucleus. site of transcription of ribosomal DNA by RNA polymerase I and synthesis of 2 maj subunits of ribosome (ribosomal RNA)

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nucleolus composed of three components:

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1) nucleolar organizing DNA
2) nucleolonema with granular and fibrillar regions
-- pars fibrosa
-- pars granulosa

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number and size of nucleoli related to

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number of ribosomes produced and to protein synthetic activity of cell

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polyribosomal proteins are synth in

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cytoplasm
then enter nucleus and assoc with ribosomes in nucleolus

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nuclear matrix

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comprised mainly of proteins and exists within the nucleus

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functions of RNA (mRNA, tRNA, ribosomal RNA)
where are they synth

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all synthesized in nucleus and assoc with proteins made in cytoplasm that have moved into nucleus. resulting subunits of ribosomes exit nuc through nuc pore

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ribosomes are composed of two subunits:

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large (60S) and small (40S) each is a complex of rRNA and proteins

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protein or polypeptide synthesis is initiated when

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small ribosomal subunit binds so mRNA and tRNA in cytoplasm. then large ribosomal subunit becomes attracted to complex

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ribosomes play a key role in

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translating the message carried by strand of mRNA

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how many ribosomes can simult translate the same mRNA

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several. since bound to same mRNA the ribosomes appear as whorls in electron micrographs called polysomes

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accumulations of ribosomes are

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basophilic (due to content of acidic phosphate groups)
stain hematoxylin indicating sites in cell involved with prot synth

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proteins or polypeptides destined for use in cytoplasm

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are synth on ribosomes that are free in cytoplasm

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polypeptides destined for secretion to become enzymes in lysosomes or to become integral memb proteins

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become bound to RER

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RER is found as

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a series of membrane limited flattened interconnecting cisternae with ribosome son cytoplasmic surfaces of the membranes

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RER is prominant in cells that are

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specialized for protein synth
invovled in synth of both proteins and lipids of many cell memb

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RER synthesizes proteins that are not destined for use in cytoplasm, but for

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a) secretion out of cell by exocytosis
b) to be inserted into other membrane bound organelles through vesicular transp to lysosome or endosome compartment
c) to form integral memb proteins

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cells specialized for secretion will have: (4 things)

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a) euchromatic nuclei
b) abundant RER
c) prominant golgi app
d) often will have dense membrane bounded secretory products

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protein modification in RER include:

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a) cleavage of signal sequences
b) initial core glycosylation of glycoproetins (addn of core mannose containing oligosacc)
c) post translational mod of protein
d) polypeptide folding
e) assembly of multichain proteins

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proteins that are synth in RER move to

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golgi via transport vesicles coated by coatamers

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golgi app functions:

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major site of carb synthesis and both cis and trans golgi networks are sorting stations for material moving within GA

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golgi app also functions:

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further modifies protein by glycosylation of proetins and lipids and phosphorylation or sulfation of glycoproteins

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golgi app also brings about:

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intracell sorting an dpackaging of proteins in memb bound vesicles
some ferried to endosomes some secreted directly

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structure of golgi app

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consists of a stack of 3-10 flattened membrane bound cisternae wtih dilated rims. assoc with small vesicles

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golgi app freq resides near

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nucleus and assoc with cell center inccluding microtubule organizing center and centrioles

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regions of golgi app

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cis golgi network (formgin face) region where transfer vesicels have budded from RER fuse wtih golgi membranes
sorting station

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mvmt via vesicular transp ---- pinocytotic vesicles are

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clathrin independent

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basic fcn of plasma membrane

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1) selective barrier
2) formed by complex mix of lipids an dproteins
3) constant state of dynamic flux or can be tethered
4) 7.5 to 10 nm thickness
5) viewed in TEM

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enzymatically active areaas of cell membrane contain higher proportion of

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proteins

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lipid rafts

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enriched in cholesterol and sphingolipids and are less fluid than most plasma membranes

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membranes under TEM, plasma membrane is resolved since

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there is a deposition of osmium on hydrophillic groups of lipid bilayer that produces electron densities

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lysosomes are major

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digestive organelles of the cell
contain hydrolases

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lysosomes are how many unit membrane

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single
prevents hydrolytic enzymes from digesting the cytoplasm

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what kind of pH on lysosomes

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low pH. created and maintained by membrane bound ATP driven proton pumps (exch Na+ for H+)

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materials to be digested in lysosomes taken up by

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endocytosis (also drinking by pinocytosis)
receptor mediated endocytosis, and phagocytosis or are formed by autophagy

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proteosomes are

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multi-hydrolase enzyme complexes that digest single cytoplasmic proteins that have been misfolded or are short term regulators

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SER lacks what which is why it is called smooth

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lacks ribosomes on surface

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fcns of SER

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synth of steroid hormones
detoxifies lipid sol drugs
synth phospholipids for cell memb
involved with glucose mobilization and storage
ca ion sequestration
can have high Ca conc in lumen
in sk and cardiac muscle: called sarcoplasmic retic

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mitochon present in all cells except

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mature RBC

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structure of mitochon

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flexible, mobile, self replicating (circlular dna and small ribosomes, most of proteins coded for by nuc DNA and made on cytoplasmic ribosomes)

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fcns of mitochondria

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pyruvate is conv to AChA, which enters Krebs cycle, oxidized into CO2 and reducing equiv

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parts of cytoskeleton:

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microtubules, microfilaments (actin filaments), intermediate filaments

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microtubules are

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unbranched tub structures, support force generating components

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microfilaments (actin filaments)

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inv with motility of cytoplasmic components and membrane proteins) prov force needed to divide cytoplasm into two during cyto kinesis
supportive meshwork

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myosin is the

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molec motor that moves actin filaments causing muscle contraction

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intermediate filaments

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neurofilaments in nerve cells, keratins in epithelial cells, vimentin related such as desmin in muscle, vimentin in fibroblasts and endothel, glial fibrillary acidic proteins in astrocytes, and nuclear lamins

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cell junctions: 3 groups

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occluding jcns, anchoring jcns, communicating jcns

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occluding junctions function to

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regulate flow of material from lumen/surface of epithelium to lateral intercell space bet epith cells (include zonula occludens)

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anchoring junctions

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provide adhesion bet cells
inc desmosome

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communicating jcns (gap jcns) consist of patches of

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specialeized memb proteins on two adj cell membranes containing transmemb channels or sm pores
connexons that permit diffusion
little elec resistance bet cells at gap jcns

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connexons consist of

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six integral mem proteins in circ arrangement called connexins

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gap jcns occur between

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epithelial cells and other such as cardiac muscle cells, bone cells, smooth muscle cells, and nerve cells