Zusammenfassung der Ressource
Eukaryotic Cells
- These cells have a true nucleus
- Nucleus
- Nuclear envelope
- A double membrane surround the nucleus
- The outer membrane is continuous
with the endoplasmic reticulum
- Functions:
- Controls entry and exit of substances
- Contains reactions inside the nucleus
- Nuclear pores
- Function:
- Allow passage of
large molecules like
mRNA our of the
nucleus
- Nucleoplasm
- Granular jelly-like
material making up the
bulk of the nucleus
- Nucleolus
- Small spherical region of the
nucleus (can be more than one)
- Function:
- rRNA manufactured and ribosomes
assembled here
- Chromosones
- it is protein bound
- (Wrapped
around proteins
called histones)
- Linear DNA
- In a straight
line
- Ribosomes
- Small granules found
in all cells
- Tend to be in
cytoplasm or
associated with ER
- Made of two subunits
made of rRNA and
many proteins
- Not enclosed by a membrane
- Function:
- Sit of protein synthesis
- Endoplasmic reticulum
- Continuous with the outer nuclear membrane
- Cells that store lots of proteins, carbs and lipids have a very extensive ER
- Rough ER (RER)
- This has
ribosomes present
on the outer
surface of the
membranes
- Functions:
- Large surface area for
synthesis of proteins
- Pathway for transport of materials
- Smooth ER (SER)
- This has no ribosomes
and is more tubular in
appearance
- Functions:
- Synthesises, stores
and transfers lipids
- Synthesises, stores and transports carbs
- There is only one cisternae per cell
- Depending on how
the sample is cut,
there may appear to
be more
- Golgi Apparatus
- Spreads throughout the cytoplasm
- More compact than the SER
- Stack of membranes
that make up flatten
sacs or cisternae
- Also has small vesicles
- Very well developed in secretory cells
- e.g. epithelial cells lining the intestines
- Functions:
- Add carbs to glucose to form glycoproteins
- Produces secretory enzymes
- Secrete carbs such as those in plant cell walls
- Transports, modifies and stores lipids
- The vesicles
- They are small
rounded hollow
structures
- Functions:
- Transport substances
to and from the Golgi
apparatus
- Some of these being lysosomes
- Lysosomes
- Vesicles produced
by the Golgi
apparatus
- Contains enzymes
like proteases and
lipases
- Also contain lysozymes
- An enzyme that can
hydrolyse some
bacterial cell walls
- Functions:
- Hydrolyse material engulfed by
phagocytic cells
- Release enzymes to the outside
of the cell to destroy material
around the cell
- This is called exocytosis
- Digest worn out
organelles so that
chemicals may be
reused
- Completely break down cells after they have died
- This is called autolysis
- Mitochondria
- This is enclosed by a double membrane
- This controls the
entry and exit of
substances
- The inner membrane is
folded to form extensions
called cristae
- This provides a larger surface area for
enzymes and other proteins involved in
aerobic respiration
- The matrix contains
protein, lipid, ribosomes
and DNA.
- Many enzymes found
it respiration are found
here
- Functions:
- Site of aerobic respiration
- This is releasing
energy from food
- Produces ATP
- This is very
important in
active transport
- Going against the conc.
gradient requires lots of ATP
- Lots of these are
needed in muscle
cells for contraction
- Because muscle
contraction needs ATP
- Chloroplasts
- Function
- Site of photosynthesis
- Chloroplast envelope
- A double plasma membrane
- It is highly selective
- Thylakoids
- Disc like membrane structures
- Contain chlorophyll
- Arranged in
stacks called
grana
- (Or one granum)
- Stroma
- Fluid filled matrix
- Containing things like:
- Starch granules
- DNA
- Ribosomes
- Enzymes
- Adaptions:
- Large surface area for
chlorophyll in grana
- Stroma contains
enzymes for second
stage of photosynthesis
- DNA and ribosomes for quick
synthesis of proteins for
photosynthesis
- Vacuoles
- Fluid filled sacs bound by a single membrane
- Plants usually have one large central
- The membrane of the vacuole is called the tonoplast
- It contains mineral
salts, sugars, amino
acids, wastes and
sometimes pigments
- Functions:
- Support
herbaceous
plants by making
cells turgid
- Temporary stock of
sugar and amino acids
- Holds pigment
- Cell walls (plants)
- Made up of cellulose microfibrils
embedded in a matrix
- Matrix consists of other
polysaccharides such as
hemicellulose and pectin
- The middle lamella is
the boundary
between cells and
cements cells
together
- Functions:
- Stop the cell bursting under turgor
pressure when water moves in by
osmosis
- It adds mechanical strength
- Allows water to move along it
- Contributing to water movement
- Cell fractionation
- Homogenisation
- 1. Tissue to be used is
chopped up and placed in
an isotonic buffer solution
(between 2 and 4 degrees)
- Isotonic = of the same water potential as tissue
- It is isotonic so that the cell does not
burst or shrink
- 2. The buffered tissue
is placed in a
homogeniser and the
tissue is
homogenised
- Homogenised = blended
- 3. This breaks up the
cells in the tissue and
releases the
organelles
- 4. The homogenate is
then filtered to remove
complete cells and large
debris
- The solution is cold
to reduce enzyme
activity
- It is buffered to keep the pH the
same, so it prevents change in
organelles or functioning of enzymes
- Ultracentrifugation
- The principle is that the heavy
organelles fall to the bottom in the
first sediment, leaving the
supernatant which can be spun
again
- 1. Homogenised tissue
placed in centrifuge and
spun at low speed
- 2. After spinning
sediment will be
at the bottom,
supernatant will
be clear liquid
- 3. Take supernatant and
spin it again faster to get
even smaller organelles
in sediment
- 4. Take the supernatant out and
spin again even faster keep
repeating until you get the
organelles you want
- Sediment 3 will
contain
organelles like
lysosomes
- Sediment 4 would
contain ribosomes
- Sediment 2 will
contain organelles like
mitochondria
- Sediment 1 will
contain heaviest
organelles e.g.
nucleus
- Cell specialisation
- Tissues
- A collection of similar cells that perform
a specific function
- e.g. xylem tissue in plants
- Organs
- A combination of tissues
that perform one major
function
- e.g. Stomachs in animals
- 1. Muscle churns and mixes
stomach contents
- 2. Epithelium produces
secretions and protects
stomach wall
- 3. Connective tissue holds
together the other tissues
- Organ systems
- A number of organs working together
- e.g.
- Digestive system
- Stomach, pancreas, liver, mouth and anus
- Respiratory system
- Lungs, mouth, trachea, bronchus and diaphram
- Circulatory system
- Heart, blood vessels