cell organelles
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The organelles of animal and plant cells are similar to each other except that __________ are present only in animal cells, and ___________ are present only in plant cells.
ORGANELLES
Animal and plant cells have organelles.
Organelles compartmentalize functions within the cell.
MITOCHONDRIAElectron micrographs of cells show
mitochondria as rod like structures.0.5μ,m-1 μm in diametre 7 μm in length
BIOMEDICAL IMPORTANCEINNER MEMBRANEComponent of electron transport
system.Impermeable to most ions and large
molecules e.g; H,Na,ATP,GTP ,Pyruvate,Citrate etc.
For transport special carriers are present e.g Adenine nucleotide carrier system(ATP-ADP Transport)
Complex II,Succinate dehydrogenase
Complex V,ATP Synthetase complex.
OUTER MEMBRANEPermeable to all ions
MatrixInclosed by inner mitochondrial
membrane.Contain enzymes of: Citric acid cycle β oxidation of fatty acids Amino acid oxidation Urea and heme synthesis
NADFADADP,PiMitochondrial DNACircular DNA,has information for 13
mitochondrial proteins and some RNAsMitochondrial cytochrome P450 system
P450 system is involved in the hydroxylation of cholesterol to steroid hormones(placenta,adrenal cortex,ovaries and testes)
Bile acid Synthesis (liver)Vitamin D formation(kidney)Mitochondria plays a key role in
aging.Cytochrome C component of ETC plays a main role in cell death and Apoptosis.
MITOCHONDRIAL DISEASES.Fatal infantile mitochondrial
myopathy and renal dysfunction.MELAS(Mitochondrial
encaphalopathy lactic acidosis and stroke)
Myoclonic epilepsy etc.
ENDOPLASMIC RETICULUM
BIOMEDICAL IMPORTANCEROUGH ERBiosynthesis of proteins.Special proteins called CHAPERONS
are present ,involved in proper folding of proteins.
Protein glycosylation
SMOTH ERSynthesis of lipids,cholesterol and
steroid hormones.Detoxification of endogeneous and
exogeneous substancesMicrosomal cytochrome P450
monoxygenase system(Xenobiotic metabolism)
Elongation of fatty acidsDesaturation of fatty acidsOmega oxidation of fatty acidsSynthesis of other
organelles ,peroxisomes and lysosomes in association with Golgi Apparatus.
_________ ___________GOLGI APPARATUS
Function: Packages, modifies, and transports materials to different location inside/outside of the cell.
Appearance: Stack of pancakes
Consists of a stack of curved saccules.
Receives protein and also lipid-filled vesicles from the ER, packages, processes, and distributes them within the cell or for export out of the cell (secretion).
Also encloses digestive enzymes into membranes to form lysosomes.
Golgi complex is the site for the formation of carbohydrate side chains of glycoproteins and mucopolysacchrides(GAGs)
It gives rise to acroblast of spermatozoa that is converted to acrosome.It contains lysosomal enzymes and proteinases invoved in the fertilization of ovum.
LYSOSOMESExtracellular digestion of both
intracellular and extracellular substances.
Single limiting membrane.Acidic pH 5.They have group of enzymes called
HYDROLASES.The enzymes destined to inter lysosomes has mannose at their ends,which change to manose 6 phosphate and enter into the lysosomes.
BIOMEDICAL IMPORTANCE
BONE REMODELING An osteoclast breaks the bone
matrix down into fragments by means of secreated acid and lysosomal hydrolases.It completes the breakdown by endocytosis and lysosomal digestion of the fragment.
THYROXIN PRODUCTION.
LIPOFUSCIN. Age pigment wear and tear pigment.DISEASES OF LYSOSOMESRelease of lysosomal enzymes in
response to ionizing rediations,some carcinogens,silca particles,dust,hypoxia,heat and certain drugs leading to cell death, mutaions in genome and malignancies.
Lysosomal storage diseases
PEROXISOMESFirst observed by electron microscopy in
animal cells (1950s), then in plant cells (1960s)
Christian deDuve (1965)Isolated from liver cells by centrifugationCalled them peroxisomes because they
generate and destroy H2O2
Single membrane
Roughly spherical0.2 - 1.7m
Composition varies
BIOMEDICAL IMPORTANCERich in enzymes.50 Enzymes have been demonstrated in
them.Proteins called PEROXINS are involved
in the various stages of their production.These are involved in the metabolism of
lipids i.e.plasmalogens,cholesterol.Involved in the β oxidation of very long
and branched chain fatty acids.Shortens the chain of cholesterol in the
formation of bile acids.
Peroxisomes are involved in the production and detoxification of H ₂O₂
PEROXYSOME PROLIFERATOR ACTIVATED RECEPTOR(PPARs).
PPARs α:expresses genes hepatic enzymes for β oxidation and formation of ketone bodies.
PPARsγ:express genes encoding for protein synthesis involved in lipid synthesis and storage in the fat cells.
PPARsδ:express genes encoding proteins of liver and muscles involved in the β oxidation of fatty acids and dissipation of free energy as heat.
Adrenoleukodystrophy: Deficiency in -oxidation of very long-chain fatty acids
Zellweger syndrome: Defect in protein import, giving rise to “ghost peroxisomes”
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An apparent amorphous mass enclosed by a nuclear envelope,Literally mean central core of the body or object.
Within:Chromosomes
ChromatinNuclear matrix
Fibrillar networkNucleoli
r-RNA and ribosomesNucleoplasm
Fluid of the nucleus
NUCLEUS
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The nuclear envelopeComponents:
Two cellular membranesBarrier to ions, solutes, macromolecules
Membranes fused to form poresComplex assemblies of proteins
Outer membraneRibosomesContinuous with RER
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Inner membraneBound to nuclear lamina
Filamentous networkNuclear lamina
Supports envelopeAttachment of chromatin
Nuclear lamina fibersProteins – lamins superfamily – Intermediate filaments of cytoplasm.
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The nuclear pore complex (NPC)Large numbers of proteins – synthesized in cytoplasm and transported into the nucleus
RNAs manufactured in nucleus – transported to cytoplasm
NPC is made up of about 50 proteins called nucleoporins.
Show both selective and non selective movements of ions and substances.
Larger proteins(RNA polymerases)need special mechanisms to move from cytoplasm into the nucleus.Signal system….
Expenditure of energy by GTP hydrolysis.RNA move from nucleus to cytoplasm
through these pores.
The nuclear envelopeComponents:
The nuclear pore complex (NPC)
Eukaryotic Nucleus - Structure
ChromatinRepresents substance of chromosomes.Each chromatid in a chromosome represents one
DNA molecule that occurs in a highly condensed form.
The nucleic acids present in the chromatin is mostly DNA but small ammount of RNA is also present.
Chromatin is a combination of DNA and protein.The most abundant proteins are histones(5
types),NUCLEOSOMES.Other proteins include enzymes like DNA and RNA
polymerases,Protins involved in the regulation of DNA transcription and replication.
Chromatin occurs in two forms, Euchromatin Stains lightly,partially or completely uncoiled,active transcription. Hetrochromatin Stains deeply,highly
coiled,generally inactive include noncoding regions,telomere and centromere.
Constitutive heterochromatinFacultative X chromosome inactivation, bar
b0ody.
NUCLEOLUSAlso called micronucleus.Nucleolonema,network of Strands containing RNA. Size varies depending upon the activity.
Nucleoli are formed around specific genetic loci called nucleolar organizing regions (NORs).
Consists of two parts. Fibrillar part.(site for rRNA
transcription).Genes for 28s,18s and 5.8s are located there.
Granular part.(assembly of ribosomal subunits takes place there).
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