CELL STRUCTURE AND FUNCTION
Cytoplasm
● Refers to all the organelles (excluding nucleus) and cytosol within cell membrane
● Cytosol is an aqueous solute rich matrix; contains about 90% water, and dissolved in it:
○ Various essential ions and soluble organic molecules (sugars, amino acids)
○ Soluble proteins (e.g. enzymes)
○ Cytoskeleton (network of fine strands of globular and fibrous proteins, which provide
infrastructure and support to cell)
Organelles
● Membranous organelles - compartmentalised spaces within cytoplasm surrounded by
membranes which are structurally and biochemically similar to plasma membrane
● Non-membranous organelles - not enclosed by a membrane
Membranous Organelles
[Advantages]
● Presence of membranes surrounding organelles allows maintenance of characteristic
differences between contents of organelle and cytosol
○ Compartmentalisation of specific reactions provide different local environments for
which incompatible processes can occur simultaneously
● Presence of membranes also helps to increase membrane surface area
○ Internal membranes allow for embedding of enzymes and proteins that mediate
many cellular reactions
○ Greater membrane surface area increases efficiency of reactions by providing
optimal enzyme concentration for reactions to occur
Copyright © 2019 tonyndr
, Nucleus
● Largest organelle in animal cell; usually spherical/oval with size of between 5-20 μm
● Encloses genetic material and protects DNA from metabolically active cytoplasm
[Nuclear Envelope]
● Double membrane separating contents of nucleus from cytoplasm
● Each membrane is a lipid bilayer
○ Outer membrane is continuous with membrane of endoplasmic reticulum
○ Inner and outer membranes are continuous with each other; region between them is
known as the perinuclear space (continuous with ER lumen)
○ Nuclear envelope is perforated by nuclear pores, made up of a large protein complex,
which allows macromolecules (e.g. mRNA, rRNA) to exit nucleus and proteins (e.g.
enzymes) to enter and exit nucleus
[Nucleoplasm]
● Aqueous matrix within nucleus, containing proteins, metabolites, ions, RNA, and chromatin
● Chromatin is composed of coils of DNA wound around basic histones, and exists in two
forms:
○ Euchromatin (loosely coiled chromatin) - appears as light-coloured patches in
electron micrograph of nucleus
○ Heterochromatin (tightly coiled chromatin) - appears as dark-coloured patches in
electron micrograph of nucleus
[Nucleolus]
● Appears as a dense mass in nucleus when viewed under electron microscope
● Composed of DNA carrying rRNA genes, RNA and protein, which functions to synthesise
ribosomal RNA (rRNA) that forms a component of ribosomes
Membranous Organelles (Involved in Endomembrane System)
● Endomembrane system consists of a number of inter-related membrane sacs within
cytoplasm of cell, related either by direct physical continuity or by transfer of membrane
segments (vesicles)
● Functions in part to manufacture proteins and lipids
● Includes the rough and smooth endoplasmic reticulum, Golgi apparatus, lysosomes and
vesicles
● Plasma membrane is not part of the endomembrane system but it continuously interacts with
its components by receiving and producing vesicles
(A) Endoplasmic Reticulum
● Consists of an extensive network of hollow, membranous tubules/sacs/sheets called
cisternae (singular: cisterna)
● Cisternal space/lumen - internal space of ER, continuous with perinuclear space
● Specialised structures for functions:
○ Extensive network of cisternae increases membrane surface area for synthesis of
polypeptides (rER) or lipids (sER)
Copyright © 2019 tonyndr
Cytoplasm
● Refers to all the organelles (excluding nucleus) and cytosol within cell membrane
● Cytosol is an aqueous solute rich matrix; contains about 90% water, and dissolved in it:
○ Various essential ions and soluble organic molecules (sugars, amino acids)
○ Soluble proteins (e.g. enzymes)
○ Cytoskeleton (network of fine strands of globular and fibrous proteins, which provide
infrastructure and support to cell)
Organelles
● Membranous organelles - compartmentalised spaces within cytoplasm surrounded by
membranes which are structurally and biochemically similar to plasma membrane
● Non-membranous organelles - not enclosed by a membrane
Membranous Organelles
[Advantages]
● Presence of membranes surrounding organelles allows maintenance of characteristic
differences between contents of organelle and cytosol
○ Compartmentalisation of specific reactions provide different local environments for
which incompatible processes can occur simultaneously
● Presence of membranes also helps to increase membrane surface area
○ Internal membranes allow for embedding of enzymes and proteins that mediate
many cellular reactions
○ Greater membrane surface area increases efficiency of reactions by providing
optimal enzyme concentration for reactions to occur
Copyright © 2019 tonyndr
, Nucleus
● Largest organelle in animal cell; usually spherical/oval with size of between 5-20 μm
● Encloses genetic material and protects DNA from metabolically active cytoplasm
[Nuclear Envelope]
● Double membrane separating contents of nucleus from cytoplasm
● Each membrane is a lipid bilayer
○ Outer membrane is continuous with membrane of endoplasmic reticulum
○ Inner and outer membranes are continuous with each other; region between them is
known as the perinuclear space (continuous with ER lumen)
○ Nuclear envelope is perforated by nuclear pores, made up of a large protein complex,
which allows macromolecules (e.g. mRNA, rRNA) to exit nucleus and proteins (e.g.
enzymes) to enter and exit nucleus
[Nucleoplasm]
● Aqueous matrix within nucleus, containing proteins, metabolites, ions, RNA, and chromatin
● Chromatin is composed of coils of DNA wound around basic histones, and exists in two
forms:
○ Euchromatin (loosely coiled chromatin) - appears as light-coloured patches in
electron micrograph of nucleus
○ Heterochromatin (tightly coiled chromatin) - appears as dark-coloured patches in
electron micrograph of nucleus
[Nucleolus]
● Appears as a dense mass in nucleus when viewed under electron microscope
● Composed of DNA carrying rRNA genes, RNA and protein, which functions to synthesise
ribosomal RNA (rRNA) that forms a component of ribosomes
Membranous Organelles (Involved in Endomembrane System)
● Endomembrane system consists of a number of inter-related membrane sacs within
cytoplasm of cell, related either by direct physical continuity or by transfer of membrane
segments (vesicles)
● Functions in part to manufacture proteins and lipids
● Includes the rough and smooth endoplasmic reticulum, Golgi apparatus, lysosomes and
vesicles
● Plasma membrane is not part of the endomembrane system but it continuously interacts with
its components by receiving and producing vesicles
(A) Endoplasmic Reticulum
● Consists of an extensive network of hollow, membranous tubules/sacs/sheets called
cisternae (singular: cisterna)
● Cisternal space/lumen - internal space of ER, continuous with perinuclear space
● Specialised structures for functions:
○ Extensive network of cisternae increases membrane surface area for synthesis of
polypeptides (rER) or lipids (sER)
Copyright © 2019 tonyndr
