THE CELL
Basic cell functions:
• Obtain nutrients and oxygen
• Perform chemical reactions to obtain energy
• Eliminate carbon dioxide and waste products
• Synthesise proteins and cell components
• Adapt and respond to environmental changes
Cell theory
• Cells are the building blocks of all living organisms
• All cells come form the division of pre-existing cells
• Cells are the smallest units that perform vital physiological functions
Define: Homeostasis
• Homeostasis refers to the existence or maintenance of a stable internal
environment
• Each cell maintains homeostasis at the cellular level
• Homeostasis at higher level reflects combined coordinated action of many cells
Cell Interior
• Nucleus
• Cytoplasm: is a watery solution of minerals, gases, organic molecules, and cell
organelles that is found between the cell membrane and the nucleus
o Cytosol: is the water portion of the cytoplasm and many chemical
reactions take place within it.
o Cell organelles (membranous/non-membranous): are intracellular
structures often bounded by their own membranes, that have specific
functions in cellular metabolism
Cell exterior
• Extracellular fluid (interstitial fluid)
Cell membrane
• Physical isolation
• Regulation of exchange with the environment
• Communication between the cell and its environment
• Structural
Written by: Cynthia Richardin 1
,Structure of the Nucleus
• Nuclear envelope: a barrier that surrounds the nucleus, interrupted by nucleus pores
• Chromatin: a network of fibres made of protein and DNA. When cells divide,
chromatin condenses into chromosomes
• Nucleolus: coiled structure composed of ribonucleic acid (RNA) and proteins
associated with DNA.
Functions of a nucleus
• Stores & transmits genetic information in form of DNA to synthesise proteins
Cell organelles
• Membranous organelles are surrounded by lipid membrane and always in contact
with the cytosol
Endoplasmic reticulum (ER):
Is an extensive network of membranous tubules that extend from the nuclear membrane to
the cell membrane. The ER is a passageway for the transport of the materials necessary for
cell function within the cell.
• Structure:
o Network of membranous channels extending throughout the cytoplasm
o There are two forms:
§ Granular (rough) with ribosomes attached
§ Agranular (smooth)
• Function:
o Rough ER: packaging and transport of proteins secreted by cells or
distributed to other cell organelles
o Rough ER has numerous ribosomes on its surface
o Smooth ER:
§ Lipid synthesis
§ Storage and release of calcium for muscle contraction and other cell
activities
Golgi Apparatus
• Structure:
o Stack of flattened membranes (cisternae) containing chambers
o Found near the nucleus
• Function
o Storage, alteration and packaging of secretory products and lysosomal
enzymes
o For transport to plasma membrane
• Types of vesicles:
o Secretory vesicles – exocytosis
o Membrane renewal vesicles
o Lysosomes
Written by: Cynthia Richardin 2
,Lysosomes:
Lysosomes are single membrane structures that contain digestive enzymes. When certain
white blood cells engulf bacteria, the bacteria are digested and destroyed by these
enzymes.
• Structure: vesicles containing digestive enzymes
• Function: intracellular removal of damaged organelles or pathogens
Peroxisomes:
• Structure: vesicles containing degradative enzymes
• Function: catabolism of fats and other organic compounds, neutralisation of toxic
compounds generated in the process
Proteasome:
Proteasome is a barrel-shaped organelle made up of enzymes that cut protein molecules
apart (protease enzyme). Proteins that are to be destroyed are tagged by a protein called
ubiquitin and are carried into the proteasome for destruction
Mitochondrion:
The powerhouse of the call
• It has a double membrane
• Outer membrane surrounds the organelle
• Inner membrane contains numerous folds (cristae)
• Cristae increase the surface area exposed to the fluid content of matrix
• Metabolic enzymes in the matrix catalyse the reaction that provide energy for cellular
functions
• Adenosine triphosphate (ATP) is produced, which provides energy to the cell (~95%)
Ribosomes:
Ribosomes are very small structures made up of protein and ribosomal RNA. They are the
sites of protein synthesis
• Structure: fixed to the rough ER or are free ribosomes scattered in the cytoplasm
Each ribosome consists of protein and RNA molecules
• Function: synthesis of proteins from amino acids using information carried by RNA
molecules from DNA in the nucleus
Proteins synthesised on free ribosomes pass into cytosol proteins synthesised by ER go to
Golgi apparatus
Other cell structures ~
Centrioles:
Are a pair of rod-shaped structures perpendicular to one another, located just outside the
nucleus. Their function is to organise the spindle fibres during cell division. The spindle
fibres are contracting proteins that pull the two sets of chromosomes apart, towards the end
of the original cell as it divides into two new cells
Written by: Cynthia Richardin 3
, • Direct movement of chromosomes in the cell division
• Organise the cytoskeleton
• Cytoplasm surrounding them is the centrosome
Cilia:
Cilia and flagella are mobile thread-like projections through the cell membrane, each is
anchored by a basal body just within the membrane. Cilia are usually shorter than flagella,
and an individual cell has many of them on its free surface
• Anchored by a basal body
• Movement of materials (fluids) across cell surface
Proteosomes:
• Breakdown and recycling of damaged or abnormal proteins (contains protein-
digesting enzymes called proteases)
Cytoskeleton:
Protein microfilaments that shape to a cell, support the membrane and microvilli and
provide for attachment and movement.
• Proteins organised in fine filaments or slender tubes
• Provides skeletal strength and flexibility
Microvilli:
The function is to increase a cells surface area for absorption
• Increase surface area to facilitate absorption of extracellular materials
Muscle cells
1. Smooth muscle:
• Involuntary
• Found in the walls of internal organs
o Blood vessels
o Gastrointestinal tract
2. Cardiac muscle:
• Involuntary
• Found in the heart
3. Skeletal muscle (40% of body weight)
• Voluntary
• Connected to bones for articulation/movement
Written by: Cynthia Richardin 4
Basic cell functions:
• Obtain nutrients and oxygen
• Perform chemical reactions to obtain energy
• Eliminate carbon dioxide and waste products
• Synthesise proteins and cell components
• Adapt and respond to environmental changes
Cell theory
• Cells are the building blocks of all living organisms
• All cells come form the division of pre-existing cells
• Cells are the smallest units that perform vital physiological functions
Define: Homeostasis
• Homeostasis refers to the existence or maintenance of a stable internal
environment
• Each cell maintains homeostasis at the cellular level
• Homeostasis at higher level reflects combined coordinated action of many cells
Cell Interior
• Nucleus
• Cytoplasm: is a watery solution of minerals, gases, organic molecules, and cell
organelles that is found between the cell membrane and the nucleus
o Cytosol: is the water portion of the cytoplasm and many chemical
reactions take place within it.
o Cell organelles (membranous/non-membranous): are intracellular
structures often bounded by their own membranes, that have specific
functions in cellular metabolism
Cell exterior
• Extracellular fluid (interstitial fluid)
Cell membrane
• Physical isolation
• Regulation of exchange with the environment
• Communication between the cell and its environment
• Structural
Written by: Cynthia Richardin 1
,Structure of the Nucleus
• Nuclear envelope: a barrier that surrounds the nucleus, interrupted by nucleus pores
• Chromatin: a network of fibres made of protein and DNA. When cells divide,
chromatin condenses into chromosomes
• Nucleolus: coiled structure composed of ribonucleic acid (RNA) and proteins
associated with DNA.
Functions of a nucleus
• Stores & transmits genetic information in form of DNA to synthesise proteins
Cell organelles
• Membranous organelles are surrounded by lipid membrane and always in contact
with the cytosol
Endoplasmic reticulum (ER):
Is an extensive network of membranous tubules that extend from the nuclear membrane to
the cell membrane. The ER is a passageway for the transport of the materials necessary for
cell function within the cell.
• Structure:
o Network of membranous channels extending throughout the cytoplasm
o There are two forms:
§ Granular (rough) with ribosomes attached
§ Agranular (smooth)
• Function:
o Rough ER: packaging and transport of proteins secreted by cells or
distributed to other cell organelles
o Rough ER has numerous ribosomes on its surface
o Smooth ER:
§ Lipid synthesis
§ Storage and release of calcium for muscle contraction and other cell
activities
Golgi Apparatus
• Structure:
o Stack of flattened membranes (cisternae) containing chambers
o Found near the nucleus
• Function
o Storage, alteration and packaging of secretory products and lysosomal
enzymes
o For transport to plasma membrane
• Types of vesicles:
o Secretory vesicles – exocytosis
o Membrane renewal vesicles
o Lysosomes
Written by: Cynthia Richardin 2
,Lysosomes:
Lysosomes are single membrane structures that contain digestive enzymes. When certain
white blood cells engulf bacteria, the bacteria are digested and destroyed by these
enzymes.
• Structure: vesicles containing digestive enzymes
• Function: intracellular removal of damaged organelles or pathogens
Peroxisomes:
• Structure: vesicles containing degradative enzymes
• Function: catabolism of fats and other organic compounds, neutralisation of toxic
compounds generated in the process
Proteasome:
Proteasome is a barrel-shaped organelle made up of enzymes that cut protein molecules
apart (protease enzyme). Proteins that are to be destroyed are tagged by a protein called
ubiquitin and are carried into the proteasome for destruction
Mitochondrion:
The powerhouse of the call
• It has a double membrane
• Outer membrane surrounds the organelle
• Inner membrane contains numerous folds (cristae)
• Cristae increase the surface area exposed to the fluid content of matrix
• Metabolic enzymes in the matrix catalyse the reaction that provide energy for cellular
functions
• Adenosine triphosphate (ATP) is produced, which provides energy to the cell (~95%)
Ribosomes:
Ribosomes are very small structures made up of protein and ribosomal RNA. They are the
sites of protein synthesis
• Structure: fixed to the rough ER or are free ribosomes scattered in the cytoplasm
Each ribosome consists of protein and RNA molecules
• Function: synthesis of proteins from amino acids using information carried by RNA
molecules from DNA in the nucleus
Proteins synthesised on free ribosomes pass into cytosol proteins synthesised by ER go to
Golgi apparatus
Other cell structures ~
Centrioles:
Are a pair of rod-shaped structures perpendicular to one another, located just outside the
nucleus. Their function is to organise the spindle fibres during cell division. The spindle
fibres are contracting proteins that pull the two sets of chromosomes apart, towards the end
of the original cell as it divides into two new cells
Written by: Cynthia Richardin 3
, • Direct movement of chromosomes in the cell division
• Organise the cytoskeleton
• Cytoplasm surrounding them is the centrosome
Cilia:
Cilia and flagella are mobile thread-like projections through the cell membrane, each is
anchored by a basal body just within the membrane. Cilia are usually shorter than flagella,
and an individual cell has many of them on its free surface
• Anchored by a basal body
• Movement of materials (fluids) across cell surface
Proteosomes:
• Breakdown and recycling of damaged or abnormal proteins (contains protein-
digesting enzymes called proteases)
Cytoskeleton:
Protein microfilaments that shape to a cell, support the membrane and microvilli and
provide for attachment and movement.
• Proteins organised in fine filaments or slender tubes
• Provides skeletal strength and flexibility
Microvilli:
The function is to increase a cells surface area for absorption
• Increase surface area to facilitate absorption of extracellular materials
Muscle cells
1. Smooth muscle:
• Involuntary
• Found in the walls of internal organs
o Blood vessels
o Gastrointestinal tract
2. Cardiac muscle:
• Involuntary
• Found in the heart
3. Skeletal muscle (40% of body weight)
• Voluntary
• Connected to bones for articulation/movement
Written by: Cynthia Richardin 4
