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Cell Organelles
Sunday, 13 July 2014

9:41 AM

Describe and interpret drawings and photographs of typical animal and plant cells as seen under the electron microscope, recognising the following membrane
systems and organelles: rough and smooth endoplasmic reticulum, Golgi body, mitochondria, ribosomes, lysosomes, chloroplasts, cell surface membrane, nuclear
envelope, centrioles, nucleus and nucleolus
...
) (For practical assessment, students may be required to
operate a light microscope, mount slides and use a graticule
...

Organelle

Structure

Function

Endoplasmic Reticulum

Rough Endoplasmic Reticulum
• Originates from outer membrane of nuclear envelope
• Consists of a network of flattened membrane-bound
sacs called cisternae (cisterna) with ribosomes
attached on the outer surface
• Typically appears as pairs of parallel lines running
through the cytoplasm

Rough Endoplasmic Reticulum

Nucleus

Largest organelle within the eukaryotic cell; spherical or
• Contains hereditary material
ovoid in shape
a
...
Nucleoplasm
○ Semi-fluid matrix that fills the nucleus
c
...
Nucleolus
○ One or more may be found
○ Responsible for the synthesis of ribosomal RNA
(rRNA)

Smooth Endoplasmic Reticulum
• Consists of a series of interconnected tubules
• Lacks ribosomes

• Proteins are synthesised by attached ribosomes and
are transported through cisternae to their
destinations or packaged in vesicles and dispatched
to other parts of the cell or across the membrane
(exocytosis)

Internal cisternae of both endoplasmic reticulum are
continuous

• Folding and modification of proteins here
Smooth Endoplasmic Reticulum
• Synthesis of lipids

• Metabolism of carbohydrates

• Detoxification of drugs and poisons
• Storage of calcium ions for contraction in muscle
cells
Ribosome

• Composed of ribosomal RNA and ribosomal protein to form • Site of protein synthesis
a ribonucleoprotein
• Found attached to endoplasmic reticulum or suspended in

Bio Notes Page 1

• Found attached to endoplasmic reticulum or suspended in
cytosol
• Consists of two subunits: 60S and 40S to form 80S (30S and
50S to form 70S in prokaryotes) [Measure of sedimentation
during centrifugation, not size)
• Can occur in clusters called polyribosomes; allows for
simultaneous synthesis of many polypeptide chains from a •
single mRNA

Golgi Apparatus

• Consists of sacks of flattened membrane-bound sacs • Sorts, packages and modifies proteins before
cisternae (cisterna) - and a system of associated vesicles transporting them to another cellular location (usually
Golgi vesicles
for exocytosis)
• Cisternae are continuously being formed at the cis face and
are continuously being broken down into vesicles at the
trans face
• A vesicle that buds from the endoplasmic reticulum adds
its membrane and contents of its lumen to the Golgi body • Forms lysosomes
by fusing with its cis face
• Involved in the formation of new cellular membrane;
during cytokinesis, Golgi vesicles move to the region
between two newly formed daughter nuclei, and their
membranes fuse to form the new cell surface membrane
of the daughter cells

• Bound by a double membrane
• Outer: Smooth, continuous
• Inner: Gives rise to thylakoid/lamellae which extend
throughout the interior
• Interior is filled with gel-like matrix called stroma
• Thylakoids are staked to form grana (granum)
• Stacks of grana are joined by intergranal lamellae, and
contain photosynthetic pigments
• Contains chloroplast DNA (ctDNA/cpDNA/PltdDNA) and
70S ribosomes

Bio Notes Page 2

• Site for photosynthesis

Mitochondria

• Bound by a double membrane
• Outer: Smooth, continuous
• Inner: Gives rise to cristae which extend throughout
the interior
• Intermembrane space between the inner and outer
membranes
• Gel-like matrix in inner membrane, containing 70S
ribosomes and mitochondrial DNA (mDNA)

• Site of aerobic and anaerobic respiration

Lysosome

• Formed by Golgi body
• Contains hydrolytic enzymes surrounded by a single
membrane
• Contents are acidic and have a low optimum pH

• Engulf and digest worn-out or damaged organelles within
the cell (autophagy)

Centrioles

• Self-digestion of cell through release of contents into the
cell (autolysis)
...
Each
triplet is attached to each other by fibrils
• Microtubules are made up of long hollow tubes called
tubulins

Bio Notes Page 3



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