1. Cell Structure
Methods of studying cells
The principles and limitations of optical microscopes, transmission
electron microscopes and scanning electron microscopes. Measuring
the size of an object viewed with an optical microscope. The
difference between magnification and resolution. Use of the formula:
magnification = size of image size of real object Principles of cell
fractionation and ultracentrifugation as used to separate cell
components. Students should be able to appreciate that there was a
considerable period of time during which the scientific community
distinguished between artefacts and cell organelles.
Light TEM SEM
Convex lens manipulates Beam of electrons fired Beam of electrons
direction of light which at a sample, scattered across surface
enters the eye and light electromagnetic lenses of specimen to form 3D
rays reflect off object are used to condense image
and lenses into eye and focus the electrons
2D 2D 3D
Coloured Black and white Black and white
cheap expensive expensive
Living dead dead
Low resolution Highest resolution High resolution
Low magnification High magnification High magnification
Very thin specimens Very thin specimens
Magnification is the increase in size of an object when viewed through a
microscope whereas resolution is the ability of the microscope to distinguish
between 2 separate points.
Homogenisation - blending
Ice cold - reduces enzyme activity
pH buffer - prevents denaturation of proteins
Isotonic - prevents osmosis in or out of organelles
Filtration
Removes debris and large cells
Centrifugation
Spin in a centrifuge at a low speed
Keep the pellet (dense stuff) and pour out supernatant
Repeat until everything has been separated
,Eukaryotic cell structure
The structure of eukaryotic cells, restricted to the structure and
function of:
• cell-surface membrane
• nucleus (containing chromosomes, consisting of protein bound,
linear DNA, and one or more nucleoli)
• mitochondria
• chloroplasts (in plants and algae)
• Golgi apparatus and Golgi vesicles
• lysosomes (a membrane-bound organelle that releases hydrolytic
enzymes)
• ribosomes
• rough endoplasmic reticulum and smooth endoplasmic reticulum
• cell wall (in plants, algae and fungi)
• cell vacuole (in plants).
CELL WALL
Cellulose in plant cells
Contain many polysaccharides
Thin layer – the middle lamella which marks the boundary between
adjacent cell walls and cements adjacent cells together
Mechanical strength to prevent bursting under pressure created by
osmotic entry of water
Allow water to pass along it
Cell wall in algae made of either cellulose or glycoproteins or a mixture
Cell wall in fungi made of chitin, glycan and glycoproteins
VACUOLE
Single membrane bound fluid filled sac – single membrane called a
tonoplast
Contains a mixture of mineral salts, sugars, amino acids, waste, pigments
Support herbaceous plants by making cells turgid
Sugars and amino acids – temporary food store
Pigments colour petals attracting insects
NUCLEUS
, Nuclear envelope Double membrane to enclose and
protect DNA
Outer membrane continuous with the
rer membranes - makes perinuclear space
(between inner + outer membranes)
continuous with the lumen of the rer -
easy transport of substances
Nuclear pores Occupied by RNA-protein complexes,
entry of nucleotides for replication and
exit of mRNA for protein synthesis
Small molecules pass through pores by
diffusion but large molecules like partly
completed ribosomes by active transport
Nucleoplasm Chromatin granules made of DNA and
associated proteins - condense to form
chromosomes during cell division
Nucleolus Produces partly completed ribosomes, co -
enzymes, nucleotides, proteins and RNA
(mainly ribosome synthesis)
MITOCHONDRIA
Double membrane Isolates reactions of the Kreb’s
cycle and electron transfer chain from
the cytoplasm - allows high
concentrations of enzymes and
substrates to be maintained which
increases the rate of respiratory
reactions.
Outer membrane is permeable to
small molecules such as sugars, salts
and nucleotides, the inner membrane is
selectively permeable - enables the
mitochondrion to control the chemical
composition of the matrix, optimising
conditions for enzyme activity
Inner membrane is spanned by proteins
(porins) -allows entry of pyrovic acid
and oxygen and the exit of ATP and
Methods of studying cells
The principles and limitations of optical microscopes, transmission
electron microscopes and scanning electron microscopes. Measuring
the size of an object viewed with an optical microscope. The
difference between magnification and resolution. Use of the formula:
magnification = size of image size of real object Principles of cell
fractionation and ultracentrifugation as used to separate cell
components. Students should be able to appreciate that there was a
considerable period of time during which the scientific community
distinguished between artefacts and cell organelles.
Light TEM SEM
Convex lens manipulates Beam of electrons fired Beam of electrons
direction of light which at a sample, scattered across surface
enters the eye and light electromagnetic lenses of specimen to form 3D
rays reflect off object are used to condense image
and lenses into eye and focus the electrons
2D 2D 3D
Coloured Black and white Black and white
cheap expensive expensive
Living dead dead
Low resolution Highest resolution High resolution
Low magnification High magnification High magnification
Very thin specimens Very thin specimens
Magnification is the increase in size of an object when viewed through a
microscope whereas resolution is the ability of the microscope to distinguish
between 2 separate points.
Homogenisation - blending
Ice cold - reduces enzyme activity
pH buffer - prevents denaturation of proteins
Isotonic - prevents osmosis in or out of organelles
Filtration
Removes debris and large cells
Centrifugation
Spin in a centrifuge at a low speed
Keep the pellet (dense stuff) and pour out supernatant
Repeat until everything has been separated
,Eukaryotic cell structure
The structure of eukaryotic cells, restricted to the structure and
function of:
• cell-surface membrane
• nucleus (containing chromosomes, consisting of protein bound,
linear DNA, and one or more nucleoli)
• mitochondria
• chloroplasts (in plants and algae)
• Golgi apparatus and Golgi vesicles
• lysosomes (a membrane-bound organelle that releases hydrolytic
enzymes)
• ribosomes
• rough endoplasmic reticulum and smooth endoplasmic reticulum
• cell wall (in plants, algae and fungi)
• cell vacuole (in plants).
CELL WALL
Cellulose in plant cells
Contain many polysaccharides
Thin layer – the middle lamella which marks the boundary between
adjacent cell walls and cements adjacent cells together
Mechanical strength to prevent bursting under pressure created by
osmotic entry of water
Allow water to pass along it
Cell wall in algae made of either cellulose or glycoproteins or a mixture
Cell wall in fungi made of chitin, glycan and glycoproteins
VACUOLE
Single membrane bound fluid filled sac – single membrane called a
tonoplast
Contains a mixture of mineral salts, sugars, amino acids, waste, pigments
Support herbaceous plants by making cells turgid
Sugars and amino acids – temporary food store
Pigments colour petals attracting insects
NUCLEUS
, Nuclear envelope Double membrane to enclose and
protect DNA
Outer membrane continuous with the
rer membranes - makes perinuclear space
(between inner + outer membranes)
continuous with the lumen of the rer -
easy transport of substances
Nuclear pores Occupied by RNA-protein complexes,
entry of nucleotides for replication and
exit of mRNA for protein synthesis
Small molecules pass through pores by
diffusion but large molecules like partly
completed ribosomes by active transport
Nucleoplasm Chromatin granules made of DNA and
associated proteins - condense to form
chromosomes during cell division
Nucleolus Produces partly completed ribosomes, co -
enzymes, nucleotides, proteins and RNA
(mainly ribosome synthesis)
MITOCHONDRIA
Double membrane Isolates reactions of the Kreb’s
cycle and electron transfer chain from
the cytoplasm - allows high
concentrations of enzymes and
substrates to be maintained which
increases the rate of respiratory
reactions.
Outer membrane is permeable to
small molecules such as sugars, salts
and nucleotides, the inner membrane is
selectively permeable - enables the
mitochondrion to control the chemical
composition of the matrix, optimising
conditions for enzyme activity
Inner membrane is spanned by proteins
(porins) -allows entry of pyrovic acid
and oxygen and the exit of ATP and
