Internal organization

of cells

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All cells except the Bacteria

Larger (about 20-60 µm) and more complex Definite nucleus surrounded by a membrane An evolutionary development following the

prokaryotes – common “ancestors”

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Protoplasm = Cytoplasm + nucleus Cytoplasm = Cytosol + organelles Cytosol = a clear aqueous solution

containing dissolved substances (eg ions, sugars etc)

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An organelle – a small organ

They are permanent structures in the

cytosol with specific functions

Each organelle has a specific structure

to fulfill a specific function(s)

The most organelles represent unique compartments surrounded by membranes

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The organelles

Ø Nucleus = replication, transcription – contains

genetic information

Ø Endoplasmic reticulum (ER) – several functions

Ø Ribosomes – protein synthesis

Ø Golgi-bodies – secretion

Ø Lysosomes – intracellular digestion

Ø Peroxisomes and glyoxysomes

Ø Mitochondria – cellular respiration

Ø Plastids (e.g. chloroplasts – photosyntesis;

amyloplasts – store starch)

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and animal cells

Plant cells have cell walls

Plant cells have a large vacuole(s)

Plant cells have chloroplasts

Plant cells do not have centrioles

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Ø Non-membranous protein filaments within the cytosol

Ø Microfilaments (actin) filaments – muscle contraction

Ø Intermediate filaments – structural stability for a variety of cells

Ø Microtubules – part of centrioles, cilia and flagella

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Erg(Greek) = work

Products formed because of the work done by the

protoplasm

Ergastic substances = products of cell metabolism

Ø  Oil droplets

Ø  Protein crystals (reserve proteins)

(Visible in potato cells)

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Ø  The matrix provides a barrier for the transport of polar

and ionic compounds

Ø  Whereas proteins perform the dynamic functions of the

membrane

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Ø The boundary between the cell and its

environment

Ø It forms an integral part of the cytoplasm

Ø Maintains the integrity of the cell – keeps the

contents inside and the outside out

Ø Differentially permeable, controls what enters

or exits the cell

Ø Proteins act as “channels”, “gates” or

“carriers” for ions and polar substances

Ø Certain carriers apply energy (ATP) to force

substances through the membrane 13

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Ø Plasmalemma is concerned with cellular communication

Ø Special surface markers (glycoproteins and glycolipids) serve as “antennae” to detect substances outside the cell:

Ø Hormone receptors

Ø Antigens – determine blood types (groups) – react with specific antibodies

Ø Cell identity markers – determine tissue specificity

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Ø The largest and most obvious structure in the cell

Ø Present in all eukaryotic cells

Ø Except in mature red blood cells and sieve tube elements in plants

Ø Multinucleate cells

Ø Nucleus surrounded by a double membrane

Ø Inner membrane smooth, outer one granular

Ø Outer membrane continuous with granular

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ER

Ø  Double membrane with pores

Ø  Nuclear membrane encloses an amorphous, granular nucleoplasm (karyolymph) in which the chromatin network (or chromosomes) and one or two nucleoli occur

Ø  Chromosomes originate during nuclear divisions – from the chromatin network

Ø  Genes on chromosomes –

replicated during cell division

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(mRNA)

DNA

(rRNA)

Transcription

RNA

(tRNA)

Translation

Replication Protein

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Ø One nucleolus occurs for every haploid set of

chromosomes

Ø Site for the production of ribosomal RNA

Ø Ribosomal RNA and ribosomal protein (from the

cytosol) are combined as ribosome subunits

Ø Ribosome subunits leave nucleus through the

pores

Ø Subunits combine with a mRNA in the cytosol

as functional ribosomes

The nucleolus is therefore regarded as the

ribosome factory of the cell

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