(2) cells: cell structure Flashcards
Advantages of light microscopes?
- can examine live specimens
- cheap
- portable (can take into field)
- coloured images can be seen
Disadvantages of light microscope?
limited powers of magnification (x1500)
limited power of resolution (200nm)
staining of specimens may lead to artefacts
Advantages of an electron microscope?
high level of magnification (x500000)
excellent power of resolution
disadvantages of electron microscope?
specimen’s must be dead (observed in a vacuum)
preparations of specimens likely to produce artefacts
V expensive (£75000)
cannot be moved
images only in black and white
process of using an transmission electron microscope?
- Specimens covered in resin and frozen to form a solid block
- thinly sliced and stained with heavy metals (gold)
- As electrons pass through specimen, E’s absorbed by stained parts and the ones that pass focused by electromagnets onto a fluorescent screen/photograph film (only views dead samples)
process of using a scanning electron microscope?
- Specimen coated with a thin layer metal to improve conductivity and contrast
- electrons are reflected from the surface of the specimen producing a 3D image
properties of prokaryotic cells
- 0.1-10 micrometer in diameters
dna is circular and free in cytoplasm
small ribosomes 70s
very few organelles and not membrane bound
properties of eukaryotic cells
- 10-100 micrometer in diameter
- DNA inside distinct membrane bound nucleus
- dna = linear, at rewatched to his tones and condensed into visible chromosomes before cell division
- large ribosomes 80s
- complex membrane system many organelles
cell membrane
made of many phospholipids
holds a cell together and regulated what enters and leaves the cytoplasm as it is a selectively permeable barrier
cytoplasm
(cytosol + organelles minus nucleus)
comprises a liquid called and all the organelles suspended in it
what are the features of the nucleus?
nuclear envelope: double membrane often with ribosomes on its surface, controls the entry and exit of materials in and out of the nucleus and contains the reactions taking place within it
nuclear pores: allows passage of large molecules out of the nucleus (3000 in each)
nucleoplasm: granular jelly like material that makes up the bulk of the nucleus
chromosomes with protein bound linear DNA
nucleolus: small spherical region sin nucleoplasm, manufactures ribosomal RNA and assemblies ribosomes
what is the function of the nucleus?
acts as the control centre of the cell through the production of mRNA and tRNA and hence protein synthesis
retains the genetic material of the cell in the form of DNA and chromosomes
manufactures ribosomal RNA and ribosomes
what structures make up a mitochondrion?
double membrane that controls the entry and exit of material
inner membrane is folded to form extensions known as Cristae, provide a large surface area for the attachment of enzymes and other proteins involved in respiration
matrix: liquid the cristae projects into
contains proteins lipids and ribosomes and DNA and enzymes used in respiration to produce ATP
what is the function of mitocondria?
they are the sites of aerobic respiration and produce ATP
what are the main features of chloroplasts?
chloroplast envelope: double plasma membrane, highly selective in what it allows to enter / leave cells
grana: stacks of thylakoids, which contains chlorophyll
where first stage of photosynthesis takes place
stroma: fluid filled matrix where 2nd stage of photosynthesis takes place
how are chloroplasts adapted to their function of carrying out photosynthesis?
granal membrane provide a large surface area for attachment of chlorophyll, electron carriers and enzymes that carry our the first stage of photosynthesis
fluid of stoma possessesall the enzymes needed to make sugars in the second stage of photosynthesis
chloroplasts contain both DNA and ribosomes so they can quickly n easily manufacture proteins needed for photosynthesis
feature of the rough endoplasmic reticulum and its function?
series of cisternae with ribosomes present on the outer surface of the membrane
provides a large surface area for the synthesis of proteins and glycoproteins
packages new protein into a vehicle for transport
provides a pathway of for the transport of materials esp. proteins throughout the cell
feature of the smooth endoplasmic reticulum and its function?
series of branching tubes
synthesises and stores and transports lipids and carbohydrates
what is the function of Golgi apparatus?
stacks of cisternae and formed through the fusing of vesicles
secrets carbohydrates
transports modifies and stores lipids
adds carbohydrates to proteins to form glycoproteins
forms lysosomes
what are the functions of lysosomes?
vesicles containing digestive enzymes
hydrolyse material ingested by phagocytise cells
release enzymes to the outside of the cell to destroy material around the cell
digest worn out organelles so that useful chemicals they’re made of can be reused
autolysis: completely break down cells after they have died
features and function of ribosomes?
small non-membranous organelles responsible for protein synthesis
2 subunits, one large n one small each containing ribosomal RNA and protein
80S found in eukaryotic cells
70S found in prokaryotic cells, slightly smaller
features of the cell wall and its function?
consists of a number of polysaccharides such as cellulose
middle lamella (thin layer) marks boundary between adjacent cell walls and cements adjacent cells together
function: provide mechanical strength in order to prevent the cell bursting under the pressure created by the osmotic entry of water
what is cell fractionation and what are the 3 stages?
the process of separating cell organelles from each other
3 stages:
homogenisation
filtration
ultracentrifugation
why must the sample of tissue be placed in a cold isotonic buffer solution before being homogenised?
ice cold - to reduce the activity of enzymes that break down organelles
isotonic - to prevent water moving organelles which would cause them to expand and become damaged
buffered solution - prevents enzymes from becoming denatured
what is the process of homogenisation?
tissue containing solution is homogenised where the machine grinds the cell up and breaks the plasma membrane of the cells and releases the organelles into a solution called homogenate
what happens during filtration?
homogenate is filtered through a gauze to separate any large cell debris or tissue debris that were not broken up
leaves the filtrate that contains a mixture of organelles
what happens in ultracentrifugation?
filtrate is placed into a tube and into the centrifuge where it is spun on a low speed to separate the heaviest organelles (nuclei)
which settle at the booth known as the pellet and the solution on top is the supernatant
supernatant placed into another tube and spun at a higher speed to extract a different organelle in the pellet
what is the order of mass from heaviest to lightest in ultracentrifugation
nuclei
chloroplasts
mitochondria
lysosomes
endoplasmic reticulum
ribosomes
what are the 2 groups of prokaryotes?
bacteria and archea
what is the role and characteristic of the mesosome in a prokaryotic cell?
it is the unfolding of the cell membrane and thought to be involved in respiration, attachment and replication of DNA and secretion
what is the cells wall made of in prokaryotic cells?
peptidoglycan
a polymer of aminoacids and sugars in
what are the characteristics of the DNA in a prokaryotic cell?
not associated with proteins but is freely suspended in the cytoplasm usually coiled up and referred to as the nucleoid or genephore
what can only some prokaryotic cells have and what are the roles of them?
- plasmid: possesses genes that may aid the survival of bacteria in adverse conditions
- pili (spikes in outside of cell): hollow protein structures used during bacterial conjugation
- flagellum: long helical tube, which rotate to provide locomotion powered by protein motors
what are the characteristics of viruses?
smaller than bacteria (20-300nm)
contain nuclei acid (single or double strand) -> can have DNA or RNA depending on species
contains capsid which is a protein coat that holds the nuclei acid
what is the difference between mitosis and meiosis?
mitosis produces 2 daughter cells that are genetically identical to the parent cells and each other
meiosis produces 4 daughter cells that are genetically different, and have half the amount of chromosomes of the parent cells
why do cells divide?
development: increase in complexity from a single zygote
growth: involves an increase in size through an increase in cell number
replacement: many cells within a multicellular organism are constantly dying and being repaired
asexual reproduction: process that produces identical clones
what are the 3 phases of the cell cycle?
interphase:
Nuclear division
cytokinesis
what are the stages in interphase and what happens in each one?
G1: the new cell grows and carries out its normal cell functions such as protein synthesis and respiration
S phase: cells DNA is replicated so that each chromosome is double structured
-> energy is also saved up in the form of ATP, ready for process of cell division
G2: (second gap/growth phase): followed by a central checkpoint, where the cell checks and repairs damage to its DNA before proceeding to mitosis
mitosis: what happens during prophase?
prophase: chromatin condenses and becomes inactive, centrioles migrate in pairs to opposite poles and the nuclear and nucleolus break up
mitosis: what happens during metaphase?
mitotic spindle grows further and attaches to the centromere of each chromosome
the fibres then, arrange the chromosomes to line up along the cell equator
mitosis: what happens during anaphase?
centromere of each chromosome breaks, sister chromatids separate into daughter chromosomes
the cell starts to elongate as cytokinesis begins
mitosis: what happens during telophase?
the new nuclear membranes and nucleoli form
chromosome start to unwind back into chromatin and are no long visible under the microscope
what happens during cytokinesis?
the cell will completely divide in to two daughter cells as the cytoplasm and cell membrane separates
what is the process that allows prokaryotic cells to divide?
explain
binary fission
circular DNA molecule replicated and both copies attach to the cell membrane , plasmids also replicated
the cell membrane begins to grow between the two DNA molecules and begins to pinch inwards, dividing the cytoplasm into 2
a new cell wall forms between the two molecules of DNA, dividing the original cell into two identical daughter cells, each with a single copy of circular DNA and a variable number of copies of the plasmids
how do viruses replicate?
cannot go under cell division as they are non living
they replicate by:
attaching to their host cell with the attachment proteins on the surface
then they inject their nuclei acid into the cell, and the genetic info on the injected viral nuclei. Acid then provides the ‘instructions’ for the hosts cell metabolic processes to start producing the viral components, nuclei acid, enzymes and structural proteins, which are assembled into new viruses
what is cancer a result of and what does it lead to?
result of damage to the genes that regulate mitosis and the cell cycle
leads to uncontrolled growth and division of cells, and as a consequence a group of abnormal cells called a tumour develops and expands in size
becomes cancerous if it changes from benign to malignant
how does chemotherapy disrupt the cell cycle and treat cancer?
prevents DNA from replicating
inhibiting the metaphase stage of mitosis by interfering with spindle formation
