module 2; cells Flashcards
describe the structure & function of the nucleus
structure:
nuclear envelope - double membrane
nuclear pores
nucleoplasm - granular jelly-like material
chromosomes - protein bound, linear DNA
nucleolus
function:
site of DNA replication & transcription (makes mRNA)
carries genetic code for each cell
describe the structure & function of the endoplasmic reticulum
structure:
rough & smooth ER have folded membranes called cisternae
rough ER have ribosomes on cisternae
function:
RER - protein synthesis
SER - synthesis & store lipids & carbohydrates
describe the structure & function of the golgi apparatus & vesicles
structure:
folded membrane - making cisternae
secretary vesicles pinch off cisternae
function:
adds carbs to proteins to form glycoproteins
produces secretary enzymes
secretes carbs
transports, modify & stores lipids
forms lysosomes
molecules that are ‘labelled’ with destination
finished product is transported to the cell surface in golgi vesicles when they fuse with membranes then content released
describe the structure & function of lysosomes
structure:
bags of digestive enzymes - can contain 50 different enzymes
function:
hydrolyse phagocytic cells
breaks down dead cells fully (autolysis)
exocytosis - releases enzymes outside of cell to destroy material
digests worn out organelles for reuse
describe the structure & function of the mitochondria
structure:
double membrane
inner membrane - called cristae
fluid centre - called mitochondrial matrix
loop of mitochondrial DNA
function:
site of aerobic respiration
site of ATP production
DNA to code for enzymes needed in respiration
describe the structure & function of ribosomes
structure:
small - made up of 2 subunits of protein &. rRNA
80s - largest ribosome found in eukary cells
70s - smaller found in prokary cells, mitochondria & chloroplasts
function:
site of protein synthesis
describe the structure & function of the vacuole
structure:
filled with fluid
single membrane - tonoplast
function:
make cells turgid - provides support
temporary store of sugars & amino acids
pigments may colour petals to attract pollinators
describe the structure & function of chloroplasts
structure:
double membrane
has thylakoids (folded membranes with pigment)
fluid-filled stroma contains enzymes for photosynthesis
function:
site of photosynthesis
describe the structure & function of the cell wall
structure:
plant cells - made of microfibrils with cellulose polymers
fungi cells - made of chitin
function:
provides structural strength to the cell
describe the structure & function of the plasma membrane
structure:
phospholipid bilayer - molecules embed within & attached on outside
function:
controls entrance & exit of molecules
what are the differences between eukaryotic and prokaryotic cells?
prokary cells are smaller, don’t have membrane-bound organelles, have smaller ribosomes, don’t contain nucleus & have cell walls made of murein
some prokary cells could also have plasmids, capsule around cell &/or flagella
describe the structure & function of a virus
are acellular & non-living
structure:
genetic material
capsid
attachment protein
function:
replicates inside of cells - difficult to destroy without harming host cell
define magnification
refers to how many times larger the image is compared to the object
define resolution
the minimum distance between 2 objects in which they can still be viewed as separate
what are the 3 types of microscopes?
optical (light) microscope
transmission electron microscope
scanning electron microscope
explain how a optical (light) microscope works
a beam of light condensed to create the image
what are the advantages & disadvantages of using an optical (light) microscope?
advantages:
colour images
can view living samples
disadvantages:
poorer resolution - as light as a longer wavelength
lower magnification
small organelles inside cell are not visible
explain how an electron microscope works
a beam of electrons is condensed to create the image
electromagnets are used to condense the beam
what are the advantages & disadvantages of using an electron microscope (scanning or transmission)?
advantages:
higher resolving power as electrons have a short wavelength
higher magnification
disadvantages:
black & white images - samples need to be stained
sample must be in vacuum (has to be non-living) - as electrons are absorbed by air
explain the process of how a transmission electron microscope (TEM) creates an image
- very thin specimens & placed in vacuum
- electron gun produces beam of electrons that pass through specimens
- some parts absorb electrons & appear dark
- image produced is 2D & shows detailed images of internal structure of cell
explain the process of how a scanning electron microscope (SEM) creates an image
- specimens don’t need to be thin as electrons aren’t transmitting through
- electrons are beamed onto surface & electrons are scattered in different ways depending on contours
- 3D image produced
how can magnification be calculated?
by using the IAM formula
magnification = image size / actual size
what is an eye piece graticule & what is it used for?
its a scale on a glass disc
its used to measure the size of the object that is being viewed under the microscope
what is cell fractionation?
its where cells are broken open to release the contents of an organelle so it can be studied
how should cells be prepared for cell fractionation?
cells must be prepared in a cold, isotonic & buffered solution
cold - to reduce enzyme activity, when cells break open enzymes are released which could damage organelles
isotonic - must be same water potential to prevent osmosis, organelles could shrivel/burst
buffered - solution has pH buffer to prevent damage to organelles
describe the process of cell fractionation
- homogenisation:
cell broken open (homogenised) using a blender
cells blended in cold, isotonic & buffered solution
solution filtered to remove large debris - ultracentrifugation
filtered solution spun at different speeds in centrifuge
organelles separate according to their densities
what is differential centrifugation?
centrifuge spins & centrifugal forces cause pellets of the most dense organelles to form at the bottom.
centrifuge is spun at low speed & process is repeated at faster speeds.
each time supernatant is removed leaving behind a pellet of organelles.
supernatant spun again to remove next pellet of organelles.
what is the order of density for organelles (from most to least)?
nuclei - most dense
chloroplasts
mitochondria
lysosomes
endoplasmic reticulum
ribosomes - least dense
how do eukaryotic cells replicate?
eukary cells enter cell cycle and divide by mitosis/meiosis
how do prokaryotic cells replicate?
prokary cells replicate by binary fission
how do viruses replicate?
viruses don’t undergo cell division (they are non-living) so they replicate inside host cells by injecting their nucleic acid in cell
what are the stages in the cell cycle?
3 stages:
1. interphase (G1, S & G2)
2. nuclear division (mitosis / meiosis)
3. cytokinesis
name & describe the first stage of cell division
interphase (longest stage) is where organelles double, cell grows & then DNA replicates
name & describe the second stage of cell division
nuclear division can be either mitosis (creating 2 identical diploid cells) / meiosis (creating 4 genetically different haploid cells)
what is the difference between mitosis & meiosis?
mitosis creates cells with identical DNA for growth & repair
meiosis creates gametes
name & describe the last stage of cell division
cytokinesis is the division of the cytoplasm to create new cells
name the stages of mitosis
prophase, metaphase, anaphase & telophase
describe what occurs during prophase
chromosomes condense & become visible
nucleolus disappears
in animal cells - centrioles separate & move to opposite poles of cell
why are centrioles important in prophase?
responsible for creating spindle fibres which are released from both poles to create spindle apparatus - which attaches to centromere and chromatids on chromosome in later stages
do plants have centrioles?
no, they only have the spindle apparatus
describe what occurs during metaphase
chromosomes align along equator of the cell
spindle fibres released from poles now attach to centromere & chromatid
describe what occurs during anaphase
spindle fibres start to retract & pull centromere & chromatids towards opposite poles
separated chromatids are now chromosomes
this stage requires ATP - provided by by respiration in mitochondria
describe what occurs during telophase
chromosomes at each pole become longer & thinner
spindle fibres disintegrate & nucleus starts to reform
how is the mitotic index calculated?
mitotic index = (no.of cells in mitosis/ total no.of cells) x 100
name & describe the process of cell division in prokaryotic cells
binary fission:
1. replication of the circular DNA & of plasmids
2. division of cytoplasm to produce 2 daughter cells - each with copy of circular DNA & plasmids
describe the structure of the plasma membrane
membranes described as fluid-mosaic model as it has a mixture & movement of phospholipids, proteins, glycoproteins & glycolipids
these molecules arranged within bilayer forms partially permeable membrane