Download - 2013 Lecture 3 - Cell Organization - II
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Lecture 3
EukaryoticCell Structure
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Eukaryotic cells
` The main feature of eukaryotic cells is theirpossession of membrane-bound organelles` a structure or part that is enclosed within its own
membrane inside a cell and has a particularfunction(s)` more elaborate compartmentalisation of the cell
`
These organelles have specific roles defined bythe chemical reactions that take place withineach
` Characteristic of the` Protists` Fungi` Plants
` Animals
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Prokaryotes cf. Eukaryotes
PROKARYOTES EUKARYOTES
Members of the domainsArchaea and Bacteria. Members of the domainEukarya.
Appeared 3.5 billion years
ago.
Appeared 1.7 billion
years ago.Greater diversification
over longer existence;
more metabolic variationand diversity.
Lesser diversification
over shorter existence;
less metabolic variationand diversity.
Majority of all living
things.
Tiny minority of all
living things.
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Prokaryotes cf. Eukaryotes
PROKARYOTES EUKARYOTES
Unicellular. Unicellular and multicellular
forms.Typically 0.2-2.0 m. Typically 10-100 m.
Surface area to volume ratio
high; so metabolic rates high,and generation times short.
Surface area to volume ratio
low; so metabolic rates low,and generation times are
long.
No nucleus/nuclearmembrane; genetic material
in cytoplasm (nucleoid).
True nucleus, with nuclearmembrane.
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Prokaryotes cf. Eukaryotes
PROKARYOTES EUKARYOTES
Membrane-enclosed
organelles absent.'Internal' membranes, if
present, are invaginations
of plasma membrane.
Membrane-enclosed
organelles present; eachwith particular role in
cell.
Temporal, not physical
compartmentalisation:
lower efficiency of cellularfunctions.
Physical
compartmentalisation:
gives division of labourand greater efficiency.
Cells are less structurally
and functionally complex.
Cells are more complex.
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Prokaryotes cf. Eukaryotes
PROKARYOTES EUKARYOTES
Low DNA complexity; only
a single, loose, circular DNAmolecule and no histones.
High DNA complexity; DNA
divided into multiple tightly-bound, linear bundles
(chromosomes), and
associated with histones
(proteins involved in DNA
replication and gene
expression).
Satellite DNA structures,called plasmids, are
common; store many
important genes.
Plasmids are rare ineukaryotes.
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Prokaryotes cf. Eukaryotes
Circular DNA molecule if prokaryote
(left) and human chromosomes (right).
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Prokaryotes cf. Eukaryotes
Eukaryotic DNA is coiled around groups (cores) of proteinaceous histones.
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Prokaryotes cf. Eukaryotes
PROKARYOTES EUKARYOTES
Cells contain only one copy
of every gene (haploid, n).
Cells contain two (diploid,
2n) or more (polyploid; e.g.,4n) copies of every gene.
Reproduction usually
asexual (withoutinvolvement of gametes).
Both sexual and asexual
reproduction found.
Sexual reproduction rare;
does not involve meiosis.(Haploid cell cannot divide
to produce gametes with
half its gene complement.)
Sexual reproduction
common and involvesmeiosis. (E.g., one 2n cell
goes to one 4n cell, then to
four n cells, or gametes.)
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Prokaryotes cf. Eukaryotes
PROKARYOTES EUKARYOTES
Cell division involves binary
fission. (One n cell to one
2n cell, and then to two n
cells.)
Cell division is more complex
and by mitosis. (E.g., one 2n
cell to one 4n cells, and
then to two 2n cells.)
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Prokaryotes cf. Eukaryotes
Binary fission in bacteria. Mitosis in eukaryotes.
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Prokaryotes cf. Eukaryotes
PROKARYOTES EUKARYOTES
Ribosomes are small (70S). Ribosomes are larger (80S).
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Prokaryotes cf. Eukaryotes
PROKARYOTES EUKARYOTES
Cytoskeleton is either
absent or poorly developed
in cytoplasm; no or poor
cytoplasmic streaming.
Well developedcytoskeleton in cytoplasm
(with microtubules,
microfilaments, andintermediate filaments);
plays role in cell
organization and shape, andin cytoplasmic streaming.
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Prokaryotes cf. Eukaryotes
Fluorescentmicrograph
showing
cytoskeletalcomponents
in eukaryotic
epithelialcells.
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Prokaryotes cf. Eukaryotes
Cytoskeletal components form scaffolding and conveyor
belts within cell, holding components in place and moving
substances around.
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Prokaryotes cf. Eukaryotes
PROKARYOTES EUKARYOTES
Cell wall usually present and
is chemically complex; in
most bacteria (but not
archaea), it contains
peptidoglycan (a single large
polymer of protein and
carbohydrate).
Cell wall, when present, ischemically simple and has no
peptidoglycan (e.g., cellulose
cell wall of plant cells).
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Prokaryotes cf. Eukaryotes
` Eukaryotes are composed of four kingdoms:
1. Kingdom Protista.
2. Kingdom Plantae.3. Kingdom Fungi.
4. Kingdom Animalia.
Protista Plantae Fungi Animalia
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Organelles
` Main feature of eukaryotic cells is their
possession oforganelles, i.e., membrane boundcompartments:
` inside the cell; and
` in which specific chemical reactions occur.
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Organelles
` Each organelle type has particular role within
the cell:
` Defined by the types of chemical reactionsorganelle can carry out.
` Organelles may be bound by:` A single membrane (e.g., Golgi, vesicles).
` A double membrane (e.g., nucleus,
mitochondria, chloroplasts).
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Organelles
Golgi apparatus (each compartment
surrounded by a single membrane).
Mitochondrion (surrounded by
double membrane).
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Organelles
` Several membrane-less structures sometimes
called organelles.
` They include:
1. Ribosomes (sites of protein synthesis).
2. The cytoskeleton` protein filaments
` structural and functional roles.
3. The extracellular matrix
` also has structural and functional roles.
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Organelles
` Advantages of compartmentalisation:
1. Division of labour between compartments:
2. Cell not a 'Jack of All Trades.'
3. Organelle's molecules kept away from other
molecules in cell:4. Prevents inappropriate reactions.
5. Allows many (sometimes incompatible) reactions
to coexist in same cell.
6. Allows greater diversity in resources cell can use.
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Organelles
` Advantages of compartmentalisation (contd):
7. Reactions can proceed more efficiently:
8. Chemicals could be concentrated withinparticular regions of the cell.
9. Environment within organelle can be madeoptimal for functions it performs (e.g., different
pH from rest of cell).
10. Membrane can regulate organelles uptake of rawmaterials and expulsion of wastes:
` Greater control of individual processes.
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Organelles
` Advantages of compartmentalisation (contd):
11. Different parts of a multistep process can
occur in different cellular compartments:` e.g., gene transcription takes place in nucleus
while translation occurs at ribosomesimultaneously.
` Greater control of overall process.
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Organelles
` Efficiency of compartmentalisation led to:
1. Greater variety and efficiency in
eukaryotic cell functions.
2. Specialisation of different types of cells
into tissues in multicellular eukaryotes.
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Organelles
Tissues of plant leaf, each with specialised cell types.
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Origin of organelles
` Theorised that organelles developed via the
process ofendosymbiosis:
1. Infolding of the plasma membrane, or
2. One cell ingested another (host), giving rise to
a permanent mutualism.` Eventually the ingested cell:
1. Lost some of its functions.2. Transferred many of its genes to host's DNA.
3. Became an organelle within the host cell.
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Origin of organelles
Endosymbiotic origin of mitochondria and chloroplasts.
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Nucleus
` Largest organelle in the cell` Double membrane:
` Associated with RER` Disintegrates for cell division` Nuclear pores
` ~ 9nm` Selective communication with cytoplasmprovide aqueous channels through the nuclear
envelopecomposed of multiple proteins, collectively referred
to as nucleoporins
` Transport of ribosomes, nucleotides & proteins
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Nucleus
` Site of DNA storage` Genetic control of cell metabolism
` Nucleolus produces ribosomes & RNA` The nuclear lamina is a dense`
~ 30 - 100 nm thick` fibrillar network composed of intermediate
filaments made oflamin that lines the
inner surface of the nuclear envelope
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Nucleus
Diagrammatic representation of structure of the eukaryotic nucleus.
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Nucleus
` Nucleoplasm:` fluid contained within the nucleus of a eukaryote in
which the chromosomes and nucleoli are found` Chromatin is the ground material
` fibrous complex of eukaryotic DNA and histone proteins` The extensive DNA of eukaryotic cells is tightly bound to
small basic proteins (histones) that package the DNA inan orderly way in the cell nucleus` assembled into individual repeating units called
nucleosomes
The basic structural unit of chromatin consisting of DNAwrapped around a histone core
` Histones are involved in a range of activities, including DNAreplication and gene expression
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Nucleosome
http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=cooper&part=A618&rendertype=figure&id=A622
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Nucleus
`Chromatin (nuclear ground
material) consists of1. Euchromatin2.
Heterochromatin3. Chromosomes
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Nucleus
1. Euchromatin`
found in both prokaryotes &eukaryotes` loosely organised chromatin
` appears as lightly staining bands` appreciable gene activity`
undergoes transcription
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Nucleus
2. Heterochromatin` only in eukaryotes` highly condensed DNA-protein
complex
` little or no transcription or geneactivity` protect chromosome integrity
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Nucleus
`Chromosomes`highly condensed chromatin`visible as strands`The carriers of genes, consisting of
long DNA molecules and associatedproteins
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Nucleus
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Nucleus
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Nucleus