(3) Cell structure Flashcards
what is the ultrastructure of the cell
the internal structure of each cell type that suits it for its job
what is a eukaryotic cell
plant/ animal cell with a distinct nucleus and membrane bounded organelles
what is a prokaryotic cell
bacterial cell
no nucleus
what is the general structure of the nucleus
spherical double membrane (nuclear envelope) nuclear pores at least one nucleolus between 10-so micrometers in diameter
what is the nuclear envelope
a double membrane that surrounds the nucleus. the outer membrane is continuous with the ER and often has ribosomes on its surface
controls entry and exit of materials in and out of the nucleus
what are nuclear pores
allow the passage of large molecules such as mRNA out of the nucleus. around 3000 pores in each nucleus each 40-100 nm in diameter
what is the nucleoplasm
granular, jelly like material that makes up the bulk of the nucleus
what are chromosomes
where genetic information is stored as protein-bound, linear DNA
what is the nucleolus
small spherical region within the nucleoplasm
manufactures ribosomal RNA and assembled the ribosomes
what are the functions of the nucleus
manufacture ribosomal RNA and ribosomes
retain generic material of the cell in the form of DNA and chromosomes
act as the control centre of the cell through the production of mRNA and tRNA and hence protein synthesis
what is the role of the double membrane
controls the entry and exit of material. the inner membrane is folded to form extensions known as cristae
what are cristae
extensions of the inner membrane
provide a large SA for the attachment of enzymes and other proteins involved in respiration
what is the matrix in a mitochondria
contains proteins, lipids, ribosomes and DNA that allows the mitochondria to control the production of some of their own proteins
where are most enzymes for respiration found
the matrix of a mitochondria
what do mitochondria produce
ATP (the energy carrier molecule)
why do epithelial cells in the intestine have a lot of mitochondria
because mitochondria produce ATP which releases energy and epithelial cells in the intestine need a lot of ATP in the process of absorbing substances from the intestines via active transport
what is the chloroplast envelope
double plasma membrane surrounding the organelle that is highly selective in what it allows to enter and exit
what is the grana of a chloroplast
location of light absorption (first stage of photosynthesis)
stacks of up to 100 disc like structures called thylakoids which contain chlorophyll
what is the stroma of a chloroplast
a fluid filled matrix containing starch grains. The location of the 2nd stage of photosynthesis ( synthesis of sugar)
how are chloroplasts adapted for their function (3 ways)
1) granal membranes provide large SA for the attachment of chlorophyll, electron carriers and enzymes that carry out the first stage of photosynthesis
2) fluid in the stroma possess all the enzymes needed to make sugars in the second stage of photosynthesis
3) chloroplasts contain both dna and ribosomes so they can quickly and easily manufacture some of the proteins needed for photsynthesis
what is the structure of the rough endoplasmic reticulum
tubules and flattened sacs surrounded by double membrane covered in ribosomes
continuous with outer nuclear membrane
what is the function of the rough endoplasmic reticulum
protein and glycoprotein synthesis (large SA)
provides a pathway for the transport of materials, especially proteins, throughout the cell
what is the structure of the smooth endoplasmic reticulum
more tubular appearance than RER.
tubules surrounded by a double membrane and no ribosomes on surface
what is the function of the smooth endoplasmic reticulum
synthesises, stores and transports lipids and carbohydrates
which kind of cells have an extensive ER
cells that manufacture and store large quantities of carbohydrates, proteins and lipids. for example liver an secretory cells
what is the structure of the golgi apparatus
similar to the SER but more compact. consists of a stack of membranes that are made up of flattened sacs or cisternae with vesicles
what are the 5 functions of the golgi apparatus
1) add carbohydrates to proteins to form glycoproteins
2) produce secretory enzymes
3) secrete carbohydrates (those used in making plant cell walls)
4) transport, modify and store lipids
5) form lysosomes
what is chromatin
a material that makes up chromosomes. made up of dna and a protein called histone
how do bacteria protect themselves
by having a murein/ peptidoglycan cell wall (a polymer of polysaccharides and peptides)
Also, some bacteria further protect themselves by having a slime (mucilaginous) capsule around this wall
in what form does bacteria store food reserves
as glycogen granules and oil droplets
what is the form of the genetic material in bacteria
a main circular strand of dna and then smaller circular pieces of dna called plasmids
what is the role of plasmids in a bacterial cell
they can reproduce independently and can provide antibiotic resistance by producing enzymes that break down antibiotics
they are used as vectors (carriers of genetic material) in genetic engineering
what is the role of the cell wall in a bacterial cell and what is it made of
physical barrier that excludes certain substances and protects against mechanical damage and osmotic lysis (bursting of cell due to pressure)
made of murein or peptidoglycan and is 10-80 nm thick
what is the role of the capsule in a bacterial cell
protects bacterium from other cells and helps groups of bacteria to stick together for further protection
what is the role of the cell surface membrane in a bacterial cell
acts as a differentially permeable layer which controls the entry and exit of chemicals
what is the role of the flagellum in a bacterial cell
may be more than 1
used for locomotion (allows cell to move)
what is a virus
an acellular non living particle that only exists in a host cell
how big is a virus
smaller than bacteria
20-300 nm
what are attachment proteins in a virus
attached to the lipid envelope (if this is not present then the capsid) these are essential to allow the virus to identify and attach to a host cell
why can electron microscopes distinguish between objects only 0.1nm apart but light microscopes can with 0.2um apart
light rays have a relatively long wavelength but electrons have a shorter wavelength
define magnification
how many times bigger the image is when compared to the object
define resolution
the minimum distance apart that 2 objects can be in order for them to appear separate. higher resolution means higher clarity.
what is cell fractionation
the process where cells are broken up and the different organelles are separated out
before cell fractionation, the tissue is placed in a cold buffered isotonic solution. why is the solution cold, buffered and isotonic
1) cold- to reduce enzyme activity that may break down the organelles
2) isotonic (same water potential as the tissue) prevents organelles bursting or shrinking as a result of osmotic gain/ loss of water
3) buffered- so pH doesn’t fluctuate which could alter organelle structure or enzyme function
what are the 2 stages to cell fractionation
homogenation and ultracentrifugation
what happens in homogenation
cells are broken up by a homogeniser (blender) which releases the organelles from the cell. the homogenate is then filtered to remove any debris
what are the 6 steps of ultracentrifugation
- tube of filtrate is placed in the centrifuge and spun at a slow speed
- heaviest organelles (nuclei) are forced to bottom of tube where they form a thin sediment
- the supernatent (fluid at top of tube) is removed, leaving sediment of the nuclei
- supernatent is spun in the centrifuge at a faster speed than before
- mitochondria is forced to bottom of tube
- process is continued so that at each increase in speed, the next heaviest organelle is sedimented and separated.
what is the order of the organelles that are deposited in ultracentrifugation
nucleus chloroplasts ER mitochondria lysosomes ribosomes
what are the 2 advantages of electron microscopes
1) electron beam has a very short wavelength so the microscope can resolve objects well
2) as electrons are negatively charged, the m=beam can be focused using electromagnets
how does a transmission electron microscope work
the beam of electrons is focused onto the specimen by a condenser electromagnet. the beam passes through a thin section of the specimen. some parts of the specimen absorb the electrons so appear dark and others allow the electrons to pass through and appear light. image is produced on screen to show a photomicrograph
the resolving power of the TEM is 0.1nm. why is this not always acheived
difficulties preparing the specimen limit the resolution that can be achieved
higher energy electron beam is required that can destroy the specimen
what are 4 limitations of the TEM
1) whole system must be in a vacuum so living specimens can’t be observed
2) complex staining process is required and image is not in colour
3) specimen must be very thin
4) image may contain artefacts making it difficult to see what really exists
how does a SEM work
similar to a tem but the sem directs a beam of electrons onto the surface of a specimen from above rather than below like with a tem.
the beam is passed back and forth across specimen in a regular pattern which created a 3d image
how does the SEM produce the 3d image
computer analysis of the pattern of scattered electrons and secondary electrons produced
what is the resolving power of the TEM
0.1nm
what is the resolving power of the light microscope
0.2 um
what is the resolving power of the SEM
20nm
how does a cell become specialised when they all contain the same genes
every cell contains all the genes for it to develop into any cell but only some are expressed (turned on) in any one cell at any one time
what are epithelial tissues
sheets of cells that line the surface of organs and have a protective or secretory function
what 3 tissues are the stomach made up of
muscle- churn and mix stomach contents
epithelium- protect stomach wall and produce secretions
connective- hold tissues together
what 5 tissues make up a leaf
palisade mesophyll- made up of leaf palisade cells that carry out photosynthesis
spongy mesophyll- gaseous diffusion
epidermis- protection and gaseous diffusion
phloem- transport organic materials away from leaf
xylem- transport water and ions into leaf
why are arteries and veins organs but capillaries are not when they have the same function
capillaries are made up of only epithelium but arteries and veins are made up of many tissues eg epithelial, muscle
what is the difference between mitosis and meiosis
mitosis produces 2 daughter cells that have the same number or chromosomes as the parent cells. meiosis produces 4 daughter cells each with half the number of chromosomes as the parent cell
what is the structure of a chromosome
after dna replication, the 2 chromatids are joined by a centromere
what is the order of the stages in mitosis
interphase prophase metaphase anaphase telophase cytokinesis
what happens during interphase
the period where the cell is not dividing. has 3 stages: G1, S and G2
what happens during prophase
chromosomes first become visible
centrioles move to the poles
spindle fibres develop from the centrioles to make spindle apparatus
nucleolus disappears and nuclear envelope breaks down
what happens in metaphase
chromosomes are seen to be made up of 2 chromatids joined by a centromere
chromosomes are pulled along the spindle apparatus and arrange themselves along the equator of the cell
what happens during analysts
centromeres divide and spindle fibres pull the individual chromatids apart
chromatids move to respective poles and are now chromosomes
how is cancer controlled
chemicals that destroy the spindle are used to treat cells so chronometer remain at the equator and don’t reach the poles
what happens during telophase
chromosomes reach their respective poles and become longer and thinner then disappear leaving only widely spread chromatin
spindle fibres disintegrate and nuclear envelope and nucleolus re form
what happens during cytokinesis
cytoplasm divides
what are the 4 steps of binary fission
1) circular dna molecule replicates and both copies attach to cell membrane
2) plasmids replicate
3) cell membrane begins to grow between the 2 dna molecules and pinches inwards, dividing cytoplasm in two
4) new cell wall forms between the 2 molecules of dna and original cell divides into 2 identical daughter cells
how to viruses replicate
by attaching to their host cell with the attachment proteins on their surface
they inject their nucleic acid into the host cell this provides instructions for the host cells metabolic processes to start producing vital components which are assembled into new viruses
what are the 3 stages of the cell cycle
interphase nuclear division (mitosis or meiosis) cytokinesis
how does chemotherapy work
disrupts the cell cycle by:
preventing dna from replicating
inhibiting the metaphase stage of mitosis by interfering with spindle formation
what is a problem with chemotherapy
they also disrupt the cell cycle of normal cells but the drugs are more effective against rapidly dividing cells
what are the 4 functions of lysosomes
1) hydrolyse material ingested by phagocytise cells eg white blood cells
2) release enzymes to outside the cell in order to destroy material around the cell
3) digest worn out organelles so the chemicals they’re made of can be re used
4) break down cells after they have died (autolysis)
what do lysosomes contain
proteases lipases
lysozymes (hydrolyse the cell walls of certain bacteria)
what are the 2 types of ribosomes
80S- found in eukaryotes (25nm in diameter)
70S- prokaryotes
what does the cell wall contain
microfibrils and cellulose (embedded in a matrix)
what is the middle lamella
thin layer which marks the boundary between adjacent cell walls and cements adjacent cells together
what are 3 functions of the cellulose cell wall
to provide mechanical strength in order to prevent the cell bursting under pressure created by osmosis
mechanical strength to whole plant
to allow water to pass along it and so contribute to the movement of water through the plant
what is a vacuole
fluid filled sac bounded by a single membrane called the tonoplast
contains a solution of mineral salts, sugars, amino acids, wastes and pigments
what are 3 functions of plant vacuoles
support herbaceous plants by making cells turgid
sugars and amino acids may act as a temporary food store
pigments colour petals to attract insects for pollination
