Cells Flashcards
Cell membrane structure
phospholipid bilayer with embedded intrinsic and extrinsic proteins
cell membrane function
selectively permeable barrier
controls passage of substances in and out the cell
barrier between internal and external cell environment
Nucleus structure
nuclear pores, nucleolus, DNA and nuclear envelope
Nucleus function
site of transcription and pre-mRNA splicing - mRNA production
site of DNA replication
nucleolus make ribosomes
nuclear pore allows movement of substances to/from cytoplasm
mitochondria structure
double membrane with inner membrane folded into cristae
ribosomes in the matrix
small, circular DNA
enzymes in the matrix
mitochondria function
site of aerobic respiration
Produces ATP
Chloroplast structure
Thylakoid membranes stacked to form grana, linked by lamella
stroma contains enzymes
contains starch granules, small circular DNA and ribosomes
Chloroplast function
Chlorophyll absorbs light for photosynthesised to produce organic molecules
organisms containing chloroplasts
plants
algae
Golgi apparatus structure
fluid-filled, membrane-bound sacs
vesicles at edge
Golgi apparatus function
modifies proteins received from RER
packages them into vesicles to transport to cell membrane for exocytosis
makes lysosomes
Lysosome structure
type of golgi vesicle containing digestive enzyme
lysosomes function
contains digestive enzymes
e.g lysozymes to hydrolyse pathogen/cell waste products
Rough endoplasmic reticulum function
site of protein synthesis
fold polypeptides to secondary and tertiary structure
packaging into vesicles to transport to Golgi
smooth endoplasmic reticulum function
synthesises and processes lipids
cell wall function
provides structural strength, rigidity and support to cell
helps resist osmotic pressures
ribosome structure
small and large subunit
made of protein and rRNA
free floating in cytoplasm and bound to RER
70 in prokaryotes, mitochondria and chloroplasts
Ribosome function
site of translation in protein synthesis
rough endoplasmic reticulum structure
system of membranes with bound ribosomes
continuous with nucleus
smooth endoplasmic reticulum structure
system of membrane with no bound ribosomes
cell wall structure
in plant, fungal and bacterial cells
plants - made of microfibrils of cellulose
fungi - made of chitin
bacteria - murein
cell vacuole structure
fluid-filled
surrounded by a single membrane called a tonoplast
contrast prokaryotic and eukaryotic cells
prokaryotic cells are smaller
prokaryotes have no membrane bound organelles
prokaryotes have smaller ribosomes
prokaryotes have no nucleus-
circular DNA not associated with histones
prokaryotic cell wall made of
murein instead of cellulose/ chitin
occasional features of prokaryotes
plasmids - loops of DNA
capsule surrounding cell wall - helps agglutination + adds protection
flagella for movement
cell vacuole function
makes cells turgid - structural support
temporary store of sugars, amino acids
coloured pigments attract pollinators
protein carriers
Bind with a molecule which causes a change in shape of the protein
this change in shape enables the molecule to be released to the other side of the membrane
Protein channels
tubes filled with water enabling water-soluble ions to pass through the membrane
selective
channel proteins only open in the presences of certain ions when they bind to the protein
features of viruses
non-living and acellular
contain genetic material, capsid and attachment proteins
some contain a lipid envelope and enzymes
3 types of microscopes
optical
scanning electron microscopes
transmission electron microscopes
magnification
image/actual
how many times larger the image is compared to the object
resolution
the minimum distance between 2 objects which can still be viewed as separate
determined by the wavelength of light
optical microscopes
beam of light used to create image
glass lens used for focusing
2D coloured image produced
Evaluate optical microscopes
poorer resolution as long wavelength of light - small organelles not visible
lower magnification
can view living samples
simple staining method
vacuum not required
TEM
beam of electrons passes through the sample used to create an image
focused using electromagnets
2D, black and white image produced
can see internal ultrastructure of cell
structures absorb electrons and appear dark
evaluation TEMs
Highest resolving power
high magnification
extremely thin specimens
required
complex staining method
specimen must be dead
vacuum required
SEM
Beam of electrons pass across
sample used to create image
focused using electromagnets
3D, black and white image
produced
electrons scattered across
specimen producing image
Evaluation SEM
High resolving power
high magnification
thick specimens usable
complex staining method
specimen must be dead
vacuum required
Why calibrate eyepiece graticule?
Calibration of the eyepiece is
required each time the objective
lens is changed
calibrate to work out the
distance between each division at that magnification
Homogenisation
Process by which cells are broken open so organelles are free to be separated
done using homogeniser
purpose of cell fractionation
break open cells and remove cell debris
so organelles can be studied
homogenisation conditions
Cold reduces enzyme activity
preventing organelle digestion
Isotonic prevents movement of water by osmosis - no bursting / shrivelling of organelles
Buffered resists pH changes
preventing organelle + enzyme damage
Ultra-centrifugation
Homogenate solution filtered to remove cell debris
solution placed in a centrifuge which spins at a low speed
initially
then increasingly faster speeds to separate organelles according to their density
Differential centrifugation
supernatant first out is most dense = nuclei
spun at higher speeds
chloroplasts > mitochondria > lysosomes
binary fission
involves circular DNA plasmids replicating
cytokinesis creates 2 daughter nuclei
each daughter cell has 1 copy of circular DNA and a variable number of plasmids
cell cycle
interphase
nuclear division - mitosis or meiosis
cytokinesis
interphase
Longest stage in the cell cycle
when DNA replicates (S-phase) and organelles duplicate while cell grows (G1&G2-phase)
DNA replicates and appears as two sister chromatids held by centromere
mitosis
One round of cell division
two diploid, genetically
identical daughter cells
growth and repair (e.g. clonal
expansion)
comprised of prophase,
metaphase, anaphase and
telophase
prophase
Chromosomes condense and
become visible
nuclear envelope disintegrates
in animals - centrioles separate & spindle fibre structure form
metaphase
Chromosomes align along
equator of cell
spindle fibres released from
poles now attach to centromere and chromatid
anaphase
Spindle fibre contracts (using
ATP) to pull chromatids,
centromere first, towards
opposite poles of cell
centromere divides in two
telophase
Chromosomes at each pole
become longer and thinner
again
spindle fibres disintegrate +
nucleus reforms
mitotic index
Used to determine proportion of cells undergoing mitosis
Calculated as a percentage OR decimal
num of cells in mitosis/ total num of cells
X100
