Introduction to cell biology
Characteristics common to all cells
➔ Arise from pre-existing cells
➔ DNA stored in chromosomes
➔ Proteins synthesised on ribosomes
➔ A selectively permeable plasma membrane encloses every
cell that allows nutrients to enter the cell and wastes to leave
the cell
➔ Subcellular components are suspended in cytosol
Cells vary in size from 10-100micro meters (x10^-6), vary in sizes
due to different functions and environments
➔ Nerve and muscle cells can be a meter long!
➔ Most cells and organelles cannot be seen macroscopically
and require a microscope
Prokaryotic cell - bacteria
➔ Nucleoid: DNA concentrated in the center but not enclosed by a
membrane
➔ Little or no internal structures or organelles
➔ Ribosomes found outside of the nucleoid region that synthesize proteins
➔ Plasma membrane encloses cytoplasm and then there is a rigid cell wall
after the PM
➔ Glycocalyx: Outer coating on the cell wall consisting of a capsule or
slime layer
➔ A capsule which has a protective role
➔ Fimbriae: Attachment to other bacteria
➔ Flagella: Locomotion, filament is attached to a ‘motor’ via a ‘hook which
rotates and crosses through the cell wall and the plasma membrane
allowing the flagella to rotate, bend and flex thus propelling the cell
Eukaryotic cells - Animals, plants and fungi
Endomembrane system:
➔ Nucleus:
● Membrane enclosed phospholipid bilayer (so contains an inner
and outer membrane) with pores to allow movement out of
mRNA and ribosomes etc.
● Contains majority of cell DNA wrapped around histones to form
nucelosomes, collectively known as chromatin
● Contains the nucleolus in the center where rRNA (ribosomal RNA) is made
and ribosomes form, only present before replication
➔ Endoplasmic reticulum: Continuous with the nucleus
● Rough: Contains ribosomes to make proteins to insert in the ER which are
destined for secretion or membrane bound organelles.
, ● Smooth: Does not contain ribosomes and is tubular shaped. Synthesis and
transport of nutrients e.g. lipids, hormones, stores calcium and plays a role in
detoxification
➔ Golgi apparatus: Recieves proteins from the RER in a vesicle and fuses with the
membrane to enter on the cis side undergo modifications as it moves to the trans
side. Transported in a vesicle either to an organelle or to the plasma membrane for
secretion. Some vesicles also transport certain proteins back to the ER.
➔ Lysosomes: Contain active hydrolytic enzymes and fuse with either food vacuoles or
damaged organelle to digest
Other components:
➔ Ribosomes: Made up of a small and large subunit, exist in the cytosol or bound to the
ER
➔ Mitochondria: Contain an outermembrane and inner membrane in folds known as
cristae, in the center is matrix
● Contains free ribosomes and mitochondrial DNA
● Respiratory digestive enzymes for the citric acid cycle in the inner membrane
and matrix
➔ Chloroplasts (plastids): Found only in plants and
algae and are the site of photosynthesis to produce
glucose
● Bound by an outer and an inner membrane
● Contains thylakoids: a 3rd internal membrane
network containing photosynthetic apparatus
● Also contains chloroplast DNA, ribosomes,
stroma and granum
➔ Cytoskeleton: Interconnecting protein structure within the cytoplasm, made of:
microtubules, microfilaments and intermediate filaments
● Maintains cell shape
● Faciliates cell movement
● Facilitates movement of components within the cell e.g. vesicles
Microfilaments Intermediate filaments Microtubules
➔ Two intertwined ➔ Many proteins e.g. ➔ Hollow tubes with
strands of actin keratin supercoiled tubulin molecules
➔ Maintains cell shape into thick cabels forming a
as can bear tension ➔ Maintains cell shape surrounding wall
➔ Muscle contraction ➔ Anchorage of ➔ Maintenance of cell
➔ Cell motility nucelus and certain shape
➔ Cell division other organelles ➔ Cell motility
(cleavage furrow ➔ Formation of nucelar ➔ Chromosome
formation) lamina movements in cell
division
➔ Organelle
movements
,Vesicles contain a motor protein which attaches to the microtubule
network to follow and find the golgi. ATP induces a conformational
change which allows the motor protein to move along.
➔ Cilia and flagella: Contain microtubules with small motor proteins to enable the cilia
and flagella to bend and flex upon conformational ATP induced change.
● A basal body is a protein structure found at the base, it is formed from a
centriole and several additional protein structures, and is, essentially, a
modified centriole.
Plant cells Animal cells
Cellulose cell wall: protects cell and Lacks a cellulose cell wall
maintains shape
Central vacuole: Storage and breakdown of No central vacuole
waste products
Chloroplasts: Photosynthetic organelle No chloroplasts
Do not contain centrioles Contain centrioles
Microscopy
Three parameters
➔ Magnification of an image
➔ Resolution (clarity) of an image
➔ Contrast: Difference in brightness between light and dark in the image
Types
➔ Light microscopes (LM)
● Used to visualise whole cells and large subcellular organelles e.g. nucleus
● Can view cell movement and functions in real time
● Generally low quality
, ➔ Fluorescence microscope
● Used to visualise whole cells and large subcellular organelles e.g. nucleus
● Can view cell movement and functions in real time
● Black background with fluorescent colours.
➔ Transmission electron microscope (EM):
● Use electromagnets to focus a beam of electrons through the specimen,
resolution is 2nm (very high quality)
● Used to study internal cell structure, organelles, proteins and nucleic acids
● Kills cells
➔ Scanning electron microscope (SEM):
● Cells/tissue is coated with gold and a scan excites electrons on the cell
surface which can be detected, resolution is 10nm)
● Used to study cell surface and generate 3D images
● Kills cells
Cell fractionation
➔ Homogenize cells and then centrifuge homogenized cells to separate for size and
density
➔ Centrifugation is conducted 4 times with the supernatant layer being removed and
re-centrifuged
➔ This process first isolates larger organelles and then reduces to smaller components
1. 1000g for 10 minutes - Gives pallet rich in nuclei and cellular debris
2. Supernatant poured and spun at 20,000 g for 20 mins and pellet rich in
mitochondria and (chloroplasts if plant)
3. 800g for 60 mins giving pellet rich in microsomes
4. 150,000g, 3 hours for pellet rich in ribosomes
5. Ribosomes are then the part studied
Cell membrane structure
➔ Plasma membrane, forms a barrier to regulate movement of molecules into and out
of the cell
➔ Eukaryotic cells have membrane bound organelles with a similar structure to outer
membrane
➔ Fluid mosaic model: The membrane is a mosaic of protein molecules floating in a
phospholipid bilayer (7-8nm thick)
● Hydrophilic head and hydrophobic tail which orient themselves in the
phospholipid bilayer
● Glycerol molecule attaches head to tail, phosphate group in the middle and a
phosphate-linked group on top (other small molecules can be attached here)
● Fatty acids make up the hydrophobic tail and rarely ‘flip flop’ as unstable
position and the hydrophilic head can’t pass through the hydrophobic tails.
➔ Fluidity of the plasma membrane:
Characteristics common to all cells
➔ Arise from pre-existing cells
➔ DNA stored in chromosomes
➔ Proteins synthesised on ribosomes
➔ A selectively permeable plasma membrane encloses every
cell that allows nutrients to enter the cell and wastes to leave
the cell
➔ Subcellular components are suspended in cytosol
Cells vary in size from 10-100micro meters (x10^-6), vary in sizes
due to different functions and environments
➔ Nerve and muscle cells can be a meter long!
➔ Most cells and organelles cannot be seen macroscopically
and require a microscope
Prokaryotic cell - bacteria
➔ Nucleoid: DNA concentrated in the center but not enclosed by a
membrane
➔ Little or no internal structures or organelles
➔ Ribosomes found outside of the nucleoid region that synthesize proteins
➔ Plasma membrane encloses cytoplasm and then there is a rigid cell wall
after the PM
➔ Glycocalyx: Outer coating on the cell wall consisting of a capsule or
slime layer
➔ A capsule which has a protective role
➔ Fimbriae: Attachment to other bacteria
➔ Flagella: Locomotion, filament is attached to a ‘motor’ via a ‘hook which
rotates and crosses through the cell wall and the plasma membrane
allowing the flagella to rotate, bend and flex thus propelling the cell
Eukaryotic cells - Animals, plants and fungi
Endomembrane system:
➔ Nucleus:
● Membrane enclosed phospholipid bilayer (so contains an inner
and outer membrane) with pores to allow movement out of
mRNA and ribosomes etc.
● Contains majority of cell DNA wrapped around histones to form
nucelosomes, collectively known as chromatin
● Contains the nucleolus in the center where rRNA (ribosomal RNA) is made
and ribosomes form, only present before replication
➔ Endoplasmic reticulum: Continuous with the nucleus
● Rough: Contains ribosomes to make proteins to insert in the ER which are
destined for secretion or membrane bound organelles.
, ● Smooth: Does not contain ribosomes and is tubular shaped. Synthesis and
transport of nutrients e.g. lipids, hormones, stores calcium and plays a role in
detoxification
➔ Golgi apparatus: Recieves proteins from the RER in a vesicle and fuses with the
membrane to enter on the cis side undergo modifications as it moves to the trans
side. Transported in a vesicle either to an organelle or to the plasma membrane for
secretion. Some vesicles also transport certain proteins back to the ER.
➔ Lysosomes: Contain active hydrolytic enzymes and fuse with either food vacuoles or
damaged organelle to digest
Other components:
➔ Ribosomes: Made up of a small and large subunit, exist in the cytosol or bound to the
ER
➔ Mitochondria: Contain an outermembrane and inner membrane in folds known as
cristae, in the center is matrix
● Contains free ribosomes and mitochondrial DNA
● Respiratory digestive enzymes for the citric acid cycle in the inner membrane
and matrix
➔ Chloroplasts (plastids): Found only in plants and
algae and are the site of photosynthesis to produce
glucose
● Bound by an outer and an inner membrane
● Contains thylakoids: a 3rd internal membrane
network containing photosynthetic apparatus
● Also contains chloroplast DNA, ribosomes,
stroma and granum
➔ Cytoskeleton: Interconnecting protein structure within the cytoplasm, made of:
microtubules, microfilaments and intermediate filaments
● Maintains cell shape
● Faciliates cell movement
● Facilitates movement of components within the cell e.g. vesicles
Microfilaments Intermediate filaments Microtubules
➔ Two intertwined ➔ Many proteins e.g. ➔ Hollow tubes with
strands of actin keratin supercoiled tubulin molecules
➔ Maintains cell shape into thick cabels forming a
as can bear tension ➔ Maintains cell shape surrounding wall
➔ Muscle contraction ➔ Anchorage of ➔ Maintenance of cell
➔ Cell motility nucelus and certain shape
➔ Cell division other organelles ➔ Cell motility
(cleavage furrow ➔ Formation of nucelar ➔ Chromosome
formation) lamina movements in cell
division
➔ Organelle
movements
,Vesicles contain a motor protein which attaches to the microtubule
network to follow and find the golgi. ATP induces a conformational
change which allows the motor protein to move along.
➔ Cilia and flagella: Contain microtubules with small motor proteins to enable the cilia
and flagella to bend and flex upon conformational ATP induced change.
● A basal body is a protein structure found at the base, it is formed from a
centriole and several additional protein structures, and is, essentially, a
modified centriole.
Plant cells Animal cells
Cellulose cell wall: protects cell and Lacks a cellulose cell wall
maintains shape
Central vacuole: Storage and breakdown of No central vacuole
waste products
Chloroplasts: Photosynthetic organelle No chloroplasts
Do not contain centrioles Contain centrioles
Microscopy
Three parameters
➔ Magnification of an image
➔ Resolution (clarity) of an image
➔ Contrast: Difference in brightness between light and dark in the image
Types
➔ Light microscopes (LM)
● Used to visualise whole cells and large subcellular organelles e.g. nucleus
● Can view cell movement and functions in real time
● Generally low quality
, ➔ Fluorescence microscope
● Used to visualise whole cells and large subcellular organelles e.g. nucleus
● Can view cell movement and functions in real time
● Black background with fluorescent colours.
➔ Transmission electron microscope (EM):
● Use electromagnets to focus a beam of electrons through the specimen,
resolution is 2nm (very high quality)
● Used to study internal cell structure, organelles, proteins and nucleic acids
● Kills cells
➔ Scanning electron microscope (SEM):
● Cells/tissue is coated with gold and a scan excites electrons on the cell
surface which can be detected, resolution is 10nm)
● Used to study cell surface and generate 3D images
● Kills cells
Cell fractionation
➔ Homogenize cells and then centrifuge homogenized cells to separate for size and
density
➔ Centrifugation is conducted 4 times with the supernatant layer being removed and
re-centrifuged
➔ This process first isolates larger organelles and then reduces to smaller components
1. 1000g for 10 minutes - Gives pallet rich in nuclei and cellular debris
2. Supernatant poured and spun at 20,000 g for 20 mins and pellet rich in
mitochondria and (chloroplasts if plant)
3. 800g for 60 mins giving pellet rich in microsomes
4. 150,000g, 3 hours for pellet rich in ribosomes
5. Ribosomes are then the part studied
Cell membrane structure
➔ Plasma membrane, forms a barrier to regulate movement of molecules into and out
of the cell
➔ Eukaryotic cells have membrane bound organelles with a similar structure to outer
membrane
➔ Fluid mosaic model: The membrane is a mosaic of protein molecules floating in a
phospholipid bilayer (7-8nm thick)
● Hydrophilic head and hydrophobic tail which orient themselves in the
phospholipid bilayer
● Glycerol molecule attaches head to tail, phosphate group in the middle and a
phosphate-linked group on top (other small molecules can be attached here)
● Fatty acids make up the hydrophobic tail and rarely ‘flip flop’ as unstable
position and the hydrophilic head can’t pass through the hydrophobic tails.
➔ Fluidity of the plasma membrane:
