Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

CELLS









They lack a nucleus and other membrane-bound
organelles eg
...
Bacteria





Has nucleus and cell surface membrane and
cytoplasm
Have chromosomes (DNA containing protein
called histone – helix)
Eg
...

Bacteriophages consist of a core of double stranded
DNA bounded by protein coat as a sheath
...
Phages
invade bacteria and phage DNA is injected into the
bacterium
...
The phage DNA
replicates to form many copies which are then
packaged in the new protein coats
...

Retroviruses consist of a core of RNA bounded by a
protein coat and a lipid bilayer containing
glycoproteins
...
Viral DNA invades
into host DNA where viral protein and new copies of
RNA are made
...


MICROSCOPY
Light microscope
 Light refracted by glass lenses
 Uses light to produce images
 Image formed on the retina/ recorded
on photographic film
 Position of cell surface membrane,
nuclear and tonoplast membranes can
be labelled but not membrane as the
detail of membrane structure can’t be
seen under LM

Electron microscope
 Electron beams refracted by electromagnetic lenses
 Uses electrons to produce images
 Image formed on fluorescent screen or recorded on
photographic film
 EM can magnify further than LM because electrons have
shorter wavelength than light
 Only dead material used as it must be vacuum inside as
air molecules would deflect the electron beam

Adv
 View living
cells/process
eg
...
x2000
 Low resolution
 Limited in cellular
detail

Transmission EM
 Electrons passes through a very thin
specimen
 Produce image have high resolution
 Used for very high magnification

Adv
 Magnifies objects
up to x500 000
 High resolution

Dis
 Only dead specimens can be
observed
 Image in black and white
 Lit of preparation is required –
can cause artefacts

Scanning EM
 Electrons bounce off the surface of the image
 Lower resolution and magnification
 3D image of surface

Resolution – ability to see two adjacent points as distinct entities
x 1000

MAGNIFICATION

mm

Object – specimen viewed using a microscope

um

Image – object presented in a micrograph
Magnification = measured size of image/true size

x 1000

/1000000

CELL ULTRASTRUCTURE

nm

Detail of a cell when viewed through an EM
Animal cell

Plant cell

Fungal cell

No cell wall present
No chloroplasts for p/s
Small temporary vacuoles

Chitin cell wall
None
Possess vacuoles

Possess centrioles which are
used in nuclear division

Cellulose cell wall which is fully permeable
Chloroplasts for p/s
Large permanent vacuole (surrounded by
the tonoplast) for turgor support
Cell joined by middle lamella – made up of
calcium pectate

Store glycogen
Have both lysosomes
No plasmodesmata

Store starch
No lysosomes or centrioles
Have plasmodesmata

Cell often multinuclear as
new call walls don’t always
form
Store glycogen
Have lysosomes
No plasmodesmata

Membrane bound organelles – structures surrounded by membrane that perform particular function in a cell

NUCLEUS

RIBOSOMES

RER/SER

GOLGI APPARATUS

LYSOSOMES

MITOCHONDRIA

STRUCTURE
Largest organelle enclosed with an
envelope (double membrane)
containing chromatin with DNA and
histones (protein that help support
and protect DNA); more densely
packed=heterochromatin (darker) &
less densely packed=euchromatin
(lighter); nucleoli appears darker
than heterochromatin and it
contains DNA; outer membrane is
encrusted with ribosome - RER

FUNCTION
DNA codes for rRNA used for protein
synthesis; isolate chromasomes form
cytoplasm where reaction takes
place, DNA is protected from
damage; mRNA carries genetic code
from DNA through nuclear pores into
cytoplasm to ribosome; ribosomes
are transported out of the nucleolus
into cytoplasm; rRNA synthesised by
nucleolus; pores in envelope allow
large molecules in (eg
...
ribosomes)
Small bodies of protein and RNA
Site of polypeptide synthesis; free
either free in cytoplasm or attached
ribosomes produce proteins that will
to RER (visible as small black dots in
function within the cytoplasm
EM micrographs); they are made of
Not protein synthesis because
protein, RNA occur in groups called
polypeptides may be transported to
polyribosomes creating hot spots of
Golgi where finish protein
protein synthesis
(quaternary) is formed or conjugated
A membrane system that extends
ER is joined with nuclear envelope ,
throughout the cytoplasm; 3D
facilitating the transport of the
membrane system enclosed sacs
mRNA ; primary structure is
called cisternae; some ER has
synthesised on RER and the 2nd -3rd
ribosomes dotted along the outside
structure are developed in cisternae;
membrane=RER; other parts of ER
SER synthesises lipids (eg,
don’t have ribosome attached=SER;
phospholipids), detoxification
RER provide scaffolding for
(process of removing toxic
ribosomes to make protein
substance) of drug and carbohydrate
metabolism
Series of curved flattened sacs
Polypeptides are combined to form
(cisternae) have small vesicles
quaternary structure or modified:
entering/leaving the Golgi body;
carbohydrate added forming
vesicles contain newly synthesised
glycoprotein, lipid added forming
protein pinch off from RER at
lipoprotein, prosthetic groups or
forming face (closest to the nucleus); cofactors added forming enzymes;
finished protein pinched off from
protein can be labelled,
maturing face (furthest away from
packaged/sorted for export vesicles
nucleus)
transport the protein within the cell
or fuse with the cell membrane to
release their contents outside cell
Vesicles produced by the Golgi
It fuses with other vesicles
contain hydrolytic enzymes; it has
containing sth that has to be
thick membrane to prevent enzymes destroyed or digested (eg
...
muscle, liver cell);

MICROTUBULES

inner-membrane which is folded to
form cristae that extend into matrix;
infolding gives inner mitochondrial
membrane greater surface area thus
no of enzymes that can be
embedded within the membrane
increases
Hollow cylinders/fibres formed from
the protein tubulin; they form
cytoskeleton (network of fibres that
maintains cell shape and keep
organelles anchored in place) which
aid movement of structures within
the cell; 9 triplets of microtubules in
a circular arrangement in centriole in
cytoplasm; animal and fungal cell
contain a pair of centrioles

many enzymes are involved in ATP
synthesis thus lots of cristae (with
more deeply infolded) are in active
cell

STRUCTURE
Cell surrounded by cell wall that lies
outside the cell membrane (1um
thick); main component
polysaccharide cellulose which is laid
down as microfibrils; each
microfibrils consists many cellulose
cross-linked to each other
Made up of many microfibrils
orientated in different, random
direction
When cell reaches full size additional
layers of cellulose is deposited; each
layer has microfibrils orientated in
same direction but additional layers
are orientated in different directions
to the other layers
Cell walls of adjacent cells are linked
by middle lamella made of
polysaccharide, pectin
Intermediate size between nucleus
and mitochondrion, bounded by
double membrane which encloses
stroma – light independent reaction;
thylakoids stacked=grana is where
chlorophyll (light dependent
reaction) is mostly concentrated; less
conc grana=inter-grana
Permanent in plant and fungal cells;
in cytoplasm; membrane of sap
vacuole in plant cells = tonoplast
Strands of cytoplasm between
neighbouring plant cells that pass
through pores in cell walls (cells are
joined by it); it allows direct
movement of large molecules to pass
through between cell

FUNCTION
It provides support as rigid structure
can support cell and important in
turgor – it restrict the outwards
expansion of protoplast as cell takes
in water by providing force against
high turgor pressure when cell lysis
in hypotonic; fully permeable
Loose arrangement gives the
strength necessary in cell wall
function
Lattice type arrangement gives the
strength necessary in cell wall
function

Centriole form spindle fibres during
cell division of animal and fugal cells
and centriole is constituents of cilia
and flagella; spindle fibres formed of
microtubules is important in
movement of chromosomes during
mitosis and meiosis

PLANT CELLS ONLY:

PLANT CELL WALL

PRIMARY CELL WALL

SECONDARY CELL WALL

MIDDLE LAMELLA

CHLOROPLASTS

LARGE VACUOLE

PLASMODESMATA

Calcium pectate forms a gel/cement
that acts as adhesive and hold
neighbouring cells together
Lipid droplets and starch grain
produced through p/s; site of p/s is
in palisade layer where most p/sing
cells with many chloroplasts (that
have many layered grana) are
present; chlorophyll is attached to
lamellae
For storage of ions/nutrients and
water and plays important part in
development of turgor for support
Gaps allow direct movement of
different kind of (large) molecules to
pass through between cells

FUNGAL CELLS

Multinucleate
= cells of
many species

Doesn’t p/s;
carbohydrate store;
lysosomes present

Fungi form long
elongated threads of
hyphae (long branching
structure) that spread
through substrate

Glycol-protein

MEASURING CELL LENGTH USING AN EYE PIECE GRATICULE AND A STAGE MICROMETER
Eyepiece graticule is calibrated before measuring cells:














As eyepiece scale represents different lengths depending on magnification used
Use stage micrometer (a special slide that has a calibrated scale of known length - 1mm divided into 100)
1mm=1000um thus each SEU is 1000/100 = 10um
At lower powers, we can estimate the width of the field of view by focusing on a clear ruler/graph paper
Estimate cell length by estimating the proportion of diameter of view that cell covers
0 values are superimposed
Find 100 SEUs = __ divisions, 1 division = 10um, __ x 10/100 = ___um per SEU
Cell length is calculated by __um per SEU x __SEUs (that cell covers)
Higher power, smaller __um/ size represented by 1 SEU/each division – increases precision
Measure cell length from middle lamella between adjacent cells
Increase reliability by measuring number of cells/repeat as cell length is variable or get average
Adjust the focusing knob – stage micrometer comes in/out of focus but eyepiece graticule is unaffected
Rotate the eyepiece lens – eyepiece graticule rotate but not stage micrometer

CELL SURFACE PLASMA MEMBRANE
It’s boundary of cell with outside world and of organelle with cytoplasm
...
Intrinsic proteins extending across the bilayer = transmembrane;
help provide stability and support as they help anchor the phospholipid molecules;
act as enzymes – it’s ideal place due to substrate availability and pH and need
replaced less often than other enzymes (eg
...

They have a hydrophilic channel running through them (can be permanently open or
controlled/gated)
Carriers – carry specific ions and molecules across the membrane because molecule
is large, charged or moving against conc gradient
...
The kinks/wave-like structure in unsaturated
hydrocarbon tails prevent them from packing close together thus more
movement
 Phospholipids with longer hydrocarbon chains decrease fluidity as
attractive forces among the tails will be greater
 At high temp, more fluid and less fluid at low temp as the phospholipid
bilayer freezes into a gel state
 Cholesterol acts as a temperature stability buffer
...
;
extrinsic protein attached
to either surface of the
membrane
Cell membrane differs in
number and types of
proteins they contain but
all have the same
phospholipid bilayer
Liver and muscle cells are
responsive to the
hormone insulin because
they have specific
receptor for the
attachment of insulin

Difference between virus and living cell:
Lack any metabolism eg
...
nuclei – chloroplast – mitochondria – ribosomes) size decreases

1
...

3
...

5
...

7

---