B3 Flashcards
outline the role of organelles in the production, transport and release of proteins from eukaryotic cells
- DNA in nucleus codes for proteins
- ribosomes + RER produce proteins
- mitochondria produce ATP for protein synthesis
- golgi apparatus package/modify proteins
- vesicles transport proteins
- the vesicles fuse with the cell-surface membrane
- they release proteins via exocytosis
contrast how the optical microscope and TEM work
- TEM uses electrons, optical uses light
- TEM allows greater resolution, so with TEM, smaller organelles can be seen and organelles can be seen in more detail
- TEM view only dead/dehydrated specimens (in a vacuum)
optical can view live specimens - TEM focuses using magnets, optical uses lenses
- TEM requires thinner specimens
- TEM requires more complex preparation
2 ways in which the nucleotides in DNA are different to the nucleotides in RNA
DNA contains thymine and deoxyribose
RNA contains uracil and ribose
describe how you could make a temporary mount of a piece of plant tissue to observe starch grains in cells using an optical microscope
add a drop of water to glass slide
obtain thin section of plant tissue and place on water on slide
stain with iodine in potassium iodide
lower cover slip with mounting needle
describe binary fission in bacteria
replication of circular DNA
replication of plasmids
division of cytoplasm to produce daughter cells
how can environmental conditions be changed to increase the growth rate of bacterial cells
- increase glucose concentration- increases respiration
- increase oxygen concentration- increases respiration
- increase temperature- increase enzyme activity
increase concentration of nucleotides- increases DNA synthesis - increase concentration of phosphate- increases DNA/RNA/ATP
describe and explain the arrangement of genetic material in prophase
- chromosomes are becoming visible- because they are condensing
- chromosomes are arranged randomly/not aligned- no spindle activity
the fixed position occupied by a gene on a DNA molecule
locus
describe the role of spindle fibres and the behaviour of chromosomes during each of prophase, metaphase, anaphase
- in prophase, chromosomes condense
- in late prophase/metaphase, centromeres attach to spindle fibres
- in metaphase, chromosomes line up at the equator of the cell
- in anaphase, centromeres divide
- in anaphase, chromatids from each pair are pulled to opposite poles of the cell
- in anaphase, spindle fibres shorten
why does preventing the formation of spindle fibres stop the cell cycle?
centromeres cannot attach to spindle- no metaphase
chromatids cannot separate on spindle- no anaphase
how do you ensure the calculated mitotic index is accurate
- repeat count- ensure figures are correct
- standardise counting- count only whole cells
how could a chemical stop cell division
- stops anaphase
- by stopping spindle fibres forming and attaching to centromeres
- preventing separation of sister chromatids
- so no new cells can be made
how can you tell that cells are undergoing mitosis (microscope observation)
- individual chromosomes are visible- they have condensed
- each chromosome is made up of 2 chromatids because DNA has replicated
- the chromosomes are nor arranged in homologous pairs, which they would be if it was meiosis
describe how the structure of the chromosomes could differ along its length to result in stain binding to more in some airs
differences in base sequences
differences in interaction with histones
differences in condensation/supercoiling
homologous pair
2 chromosomes that carry the same genes in the same place, but may not have the same alleles for those genes
describe the appearance and behaviour of chromosomes during mitosis
PROPHASE
- chromosomes condense
- chromosomes appear as 2 sister chromatids, joined at centromere
METAPHASE
- chromosomes line up at equator
- chromosomes attach to spindle fibres
- by their centromere
ANAPHASE
- centromeres divide
- sister chromatids pulled to opposite poles of the cell
TELOPHASE
- chromosomes uncoil to become longer/thinner
what shows that a cell is in anaphase?
chromosomes are in 2 groups at poles of cell
V-shame shows that sister chromatids have been pulled apart at centromeres
in root squash, why:
- take cells from tip?
- firmly squash tip?
- where mitotic division occurs
- to make thin layer of cells to allow light to pass through
optical microscope
- uses light to form an image
the wavelength of light will determine the resolution of the microscope - max. RESOLUTION of 0.2um
cannot view: ribosomes, ER, lysosomes
mitochondria may be visible
nucleus is visible - max. MAGNIFICATION around x1,500
- 2D image
- image = virtual on retina, viewed via eyepiece lens
electron microscope
- uses electrons to form an image
- have higher resolution than optical so more detail- uses very short wavelengths
- max. RESOLUTION 0.0002 um
- max. MAGNIFICATION around x1,500,000
- the e- are negatively charged and so focused by electromagnets
- because electrons are deflected/absorbed by molecules in the air, a vacuum has to be created in microscope chamber
TEM
- use condenser electromagnets to focus a beam of electrons from an electron gun, which is transmitted through a specimen.
- denser parts of the specimen absorb more electrons, which makes them look darker on the image
–> electron shadow - 2D
- image produced = micrograph
MAGNIFICATION x500,000
TEM strength/weakness
give high resolution images
so can see internal structures of organelles e.g. chloroplasts
however, for this reason, can only be used on thin specimens
SEM
- scan a beam of e- across a specimen
this knocks off electrons from the specimen, which are gathered in a cathode ray tube to form an image - the image produced shows the surface of the specimen and can be 3D- gives depth of field
MAGNIFICATION x100,000
SEM strength/weakness
can be used on thick specimens
however, give lower resolution images than TEM
cannot observe internal cell structures
black and white image seen
reflected beam of electrons is observed
magnification
the degree to which the size of the image is larger than the specimen itself
resolution/ resolving power
the degree to which it is possible to distinguish between two adjacent points that are very close together
to improve resolution in a light microscope…
use an objective lens with a short focal length
film of immersion oil (with refractive index) on slide- allows light to be refracted from specimen to the objective lens, minimises scatter
importance of stains in light microscopes
iodine in potassium iodide
acetic orcein
methylene blue
gentian violet
if an object is transparent, it will allow light waves to pass through it and therefore will not be visible
some stains bind to specific cell structures
iodine in potassium iodide: stains starch grains
acetic orcein: stains DNA dark red
methylene blue: stains DNA
gentian violet: stains baceterial cell walls
evaluation of light microscopes
advantages
- no vacuum
- specimen can be alive
- large field of view
- cheap, portable
- no technical expertise required
- natural colours can be seen
- preparation of specimens = less harsh than EM
- less likely to produce artefacts
disadvantages
- low magnification
- low resolution
advantages/ disadvantages of EM compared to LM
advanages
- higher magnification
- higher resolution
- ultrastructure can be viewed
- SEM gives depth of field
disadvantages
- specimen is dead- under vacuum
- specimen needs to be dehydrated
- therefore requires vacuum pump
- contained within sealed chamber
- natural colours cannot be seen
- large, expensive, not portable
- requires room temperature control
- high voltage required (safety + cost)
- artefacts likely
staining in electron microscopes
+ differential staining
heavy positively charged metal ions
e.g. osmium, lead, uranium
makes organelles distinct
organelles and membranes absorb negative electrons differently
electrons are unable to pass through stained areas, produces electron shadows
differential staining:
more than one stain is used to treat the specimens
this allows different parts of a particular structure to be differentiated e.g. nucleolus in nucleus
what is cell fractionation
the process where cells are broken up and the different organelles they contain are separated out
before fractionation, the tissue is placed in a solution which is:
COLD
to reduce enzyme activity that might break down organelles
OF THE SAME WATER POTENTIAL AS THE TISSUE
to prevent organelles bursting or shrinking due to osmotic loss or gain of water
BUFFERED
so that the pH does not fluctuate
any change in pH could alter the structure of the organelles or affect the functioning of enzymes
–> to prevent denaturing of enzyme/protein
the stages of cell fractionation
HOMOGENATION
- cells are broken up by a homogenate, to release the organelles from the cell
FILTRATION
- the homogenate is filtered through a gauze to remove any complete cells, large tissue or debris
- the organelles are much smaller than the debris so pass through the gauze and are not filtered out
–> resulting solution = filtrate
ULTRACENTRIFUGATION
the fragments in the filtered homogenate are separated in a centrifuge.
this spins the homogenate at a very high speed to create a centrifugal force
- the tube of filtrate is spun in the centrifuge at a low speed
- the heaviest organelles, the nuclei, are forced to the bottom of the tube, where they form a pellet
- the supernatant is removed, leaving nuclei sediment
- the supernatant is spun in the centrifuge at a higher speed
- the chloroplast/mitochondria form a pellet at the bottom
- the process is continued so with each increase the next heaviest organelle is sedimented and separated out.
order of organelles heaviest –> lightest
nuclei
chloroplasts
mitochondria
lysosomes
ER
ribosomes
cell fractionation to obtain chloroplasts- exam q
homogenise the leaf AND filter
in cold, isotonic, buffered solution
centrifuge and remove nuclei pellet
centrifuge supernatant and the chloroplasts settle out
cell surface membrane
- description
-function
- the membrane on the surface of animal cells and inside cell walls of other cells
- ususally made of lipids and protein
- regulates the movement of substances in/out the cell
- has receptor molecules, which allow it to respond to chemicals like hormones
nucleus
- description
- function
- nuclear envelope: double membrane which contains many nuclear pores.
controls entry and exit of substances between nucleus and cytoplasm - chromosomes: protein bound linear DNA
- nucleolus: small spherical region in nucleoplasm, makes RNA and assembles ribosomes
- nucleoplasm: granular, jelly-like material that makes up the bulk of the nucleus
- rough ER: continuous with the nuclear envelope outer membrane
- controls cell activities (by controlling DNA transcription)
- retains the genetic material - DNA + chromosomes
mitochondrion
- description
-function
- double membrane: controls entry and exit of materials
- cristae: provide a large surface area for attachment of enzymes and proteins involved in respiration
(more cristae increase metabolic activity) - matrix: contains proteins, lipids, ribosomes and DNA that control protein production
- also contains many enzymes involved in respiration
- site of aerobic respiration where ATP is produced
- found in large numbers in cells that are very metabolically active and require lots of energy
chloroplast
- structure
- function
- chloroplast envelope: double plasma membrane surrounding the chloroplast- highly selective to what enters/ exits
- thylakoid membranes: internal membranes containing chlorophyll, where light absorbtion, stage 1 of photosynthesis, takes place
- grana: stacks of thylakoids
- lamellae: thin, flat pieces of thylakoid membrane connecting grana
- stroma: thick, fluic-like matrix where stage 2 of photosynthesis, synthesis of sugars, occurs
- also contains other structures such as starch grains
- granal membrane provide a large surface area for attachment of chlorophyll, electron carriers and enzymes that carry out stage 1 of photosynthesis. attached in a highly ordered fashion.
- fluid of the stroma has all enzymes needed for the production of sugar in stage 2 of photosynthesis
contains DNA and ribosomes: can quickly and easily manufacture proteins necessary for photosynthesis
RER
- description
- function
- system of membranes enclosing a fluid filled space
- continuous with outer membrane of nucleus
- surface is covered in ribosomes
- increases surface area for protein and glycoprotein synthesis
- provides a pathway for the transport of materials, especially proteins, throughout the cell
SER
- description
- function
- lacks ribosomes on its surface
- often more tubular in appearance
- continuous with outer membrane of nucleus
- synthesise, store and transport lipids and carbohydrates
- cells that manufacture, store and transport lots of proteins, lipis and carbs have extensive ER
golgi apparatus
- description
- function
- stacks of membranes that make up flattened sacks- cisternae
with small hollow structures- vesicles - form lysosomes
- produce secretory enzymes
- the proteins and lipids produced in the ER are passed through the golgi in a strict sequence
- the golgi modifies the proteins, often adding non-protein elements
- also ‘labels’ proteins so they can be sorted and sent to correct place
golgi vesicle
- description
- function
- produced by the golgi apparatus
- small, fluid-filled sac surrounded by membrane
- stores lipids and proteins made by the golgi
- transports them out of the cell via the cell surface membrane
lysosome
- description
- function
- formed when a vesicle from the golgi apparatus contains enzymes called lysozymes
- has no clear internal structure
- isolate a specific enzyme from the cell before releasing it- either to outside the cell or into a phagocytotic vessel
- hydrolyse material ingested by phagocytotic cells
- digest invading cells
- release enzymes to the outside of the cell (exocytosis) to destroy material outside the cell
- digest worn out organelles so useful chemicals they are made of can be re-used
- completely break down cells after they have died (autolysis)
ribosome
- description
- function
- a very small (cytoplasmic granule) organelle
- either floats in cytoplasm or is associated with RER
- made of 2 sub-units ,which are made of protein and ribosomal RNA
- the site of protein synthesis
80s= in Euk., 25nm diameter
70s= in Prok., mitochondria and chloroplasts, slightly smalller
cell wall
- description
- function
- a rigid structure that surrounds cells in plants, algae and fungi
plants: cellulose
algae: cellulose and glycoprotein
fungi: chitin (nitrogen containing polysaccharide) + glycal + glycoprotein
in a plant: the cell wall is made of microfibrils of cellulose embedded in a matrix
- microfibrils give considerable mechanic strength to prevent bursting by osmotic gain
- gives overall mechanical strength to the plant
- allows water to move along it- aids water movement through the plant.
cell vacuole
- description
-function
- a fluid- filled sac bound by a single membrane- tonoplast
- contains cell sap- weak solution of sugars/ salts
- contains amino acids + sugars as temporary food store
- also contains some pigments
- helps maintain turgor pressure inside the cell + keep cell turgid to stop wilting
- isolates unwanted chemicals inside cell
- pigments attract pollinating insects
differentiation
when a cell becomes specialised to carry out a specific function
categories of specialisation (3)
- changes in the number of a particular organelle
- change in the shape of the cell
- changes in the contents of the cell
tissue
a collection of similar cells that work together to perform a specific function
organ
a collection of tissues that are coordinated to provide a variety of functions
organ systems
the way in which certain organs work together as a single unit
eukaryotes vs prokaryotes
eukaryotes
- larger
- have a nucleus bound by a nuclear envolope
- DNA associated with proteins called histones
- no plasmids- DNA = linear
- membrane-bound organelles
- chloroplasts present in plants + algae
- ribosomes = larger (80s)
- cell walls made by cellulose in plants
- have a phospholipid bilayer cell membrane
- ATP production occurs in mitochondria
- may have an undulipodia
prokaryotes
- smaller
- have no nucleus or nuclear envelope
- DNA is not associated with proteins
- some DNA in form of plasmids
- no membrane-bound organelles
- no chloroplasts, only bacterial chlorophyll associated with the cell surface membrane in some bacteria
- ribosomes = smaller (70s)
- cell walls made of murein (peptidoglycan)
- may have an outer mucilaginous layer - capsule
- ATP production occurs in folded regions of the cell-surface membrane- mesosomes
- may have flagella
bacteria- structure
- all bacteria possess a cell wall made of murein (peptidoglycan) a polymer of polysaccharides and peptides
- many bacteria further protect themselves by secreting a capsule of mucilaginous slime around this wall
- inside the cell = cell-surface membrane, cytoplasm, 70s ribosomes
- 70s ribosomes = smaller than 80s in eukaryotes
- bacteria store food reserves as glycogen granules and oil droplets
- the genetic material in bacteria is in the form of a circular strand of DNA
separate from this are plasmids. these can reproduce themselves individually and may give antibiotic resistance. they are also used as vectors in genetic engineering
roles of structures in a bacterial cell
- cell wall
- capsule
- cell surface membrane
- circular DNA
- plasmid
- flagellum
- physical barrier that excludes certain substances, protects against mechanical damage and osmotic lysis
- protects bacterium from other cells and helps cells stick together for further protection
- acts as a differentially permeable layer, controlling entry + exit of chemicals
- possesses the genetic information for the replication of bacterial cells
- possesses the genetic information for the replication of bacterial cells
- possess genes that may aid bacterial cells’ survival in adverse conditions e.g. antibiotic resistance
- may be more than one- used for locomotion
viruses- structure
- acellular, non-living particles
- unlike bacteria: no plasma membrane, no cytoplasm, no ribosomes
- smaller than bacteria
- contain nucleic acid e.g. DNA or RNA as genetic material
- can only multiply inside living host cells
- the nucleic acid is enclosed within a protein coat- capsid
- some viruses are further surrounded by a lipid envelope
- the capsid/lipid envelope has attachment proteins which are essential to allow the virus to identify and attach onto the host cell
virus replication
- attach to host with receptor proteins
- inject DNA
- DNA becomes part of host’s DNA
- host begins producing virus proteins through metabolic functions
what does mitosis produce
two daughter cells that have the same number of chromosomes as the parent cell and each other
except in the rare event of a mutation, the genetic make-up of the two daughter nuclei produced by mitosis is identical to that of the parent nucleus
what does meiosis produce
four daughter cells each with half the number of chromosomes of the parent cell
mitosis is always preceded by a period in which the cell is not dividing: interphase
describe interphase
- a period of considerable cellular activity
- includes DNA replication
- the state a complete parent cell is in when it has all 46 chromosomes that have been replicated
- after replication, the two copies of DNA remain joined at the centromere
- there are two centrioles at opposite ends of the cell
describe prophase
EARLY PROPHASE
- the chromatids become visible under a light microscope as they are coiling and supercoiling, becoming shorter and thicker
- centrioles (in animal cells) begin to move to opposite poles of the cell
LATE PROPHASE
- centrioles move completely round to opposite poles of the cell
- from each of the centrioles, spindle fibres develop (from protein threads) which span from pole to pole
–> called spindle apparatus
plant cells lack centrioles but still develop spindle apparatus, so centrioles are not essential to spindle fibre formation
- the nucleolus disappears and the nuclear envelope breaks down, leaving the chromosomes in the cytoplasm
- the chromosomes are drawn towards the equator of the cell by the spindle fibres attached to the centromeres
describe metaphase
- chromosomes are seen to be made up of two chromatids, joined by centromere
- the centromeres are attached to the spindle fibres- they are pulled along to line up at the equator of the cell
describe anaphase
- the centromeres split in two and the spindle fibres pull the individual chromatids apart
- the chromatids move to their opposite poles - now called chromosomes
- the energy for this is provided by mitochondria which gather round the spindle fibres
describe telophase
- the chromosomes reach their poles
- the two groups of chromosomes have the full amount of DNA
- they become longer and thinner, finally disappearing, leaving widely spread chromatin
- spindle fibres disintegrate
- nuclear envelope and nucleolus re-form
describe cytokinesis
- general
- animal cells
- plant cells
- the cytoplasm divides, forming two new cells, each with the exact same DNA
- each cell is the same as each other and the original cell
- filaments of actin attached to inner surface of plasma membrane contract + pull membrane inwards
- division furrow forms and deepens, eventually splitting parent cell
- cell plate forms
- extends outwards until it meets plasma membrane
what is the mitotic index
the ratio between the number of cells in a population undergoing mitosis
cell division in prokaryotes- binary fission
- the circular DNA molecule replicates and both copies attach to the cell membrane
- plasmids also replicate
- the two sets of genetic material migrate to opposite poles
- the cytoplasmic contents must be divided to give both new cells the machinery to sustain life
- the cell membrane begins to grow between the two DNA molecules and begin to pinch inward, dividing the cytoplasm in two
- a new cell wall forms between the two DNA molecules, dividing the original cell into two
- a new cell wall forms between the two DNA molecules, dividing the original cell into two identical daughter cells, with a single copy of circular DNA and variable numbers of copies of plasmids
replication of viruses
- as viruses are non-living, they cannot undergo cell division
- they replicate by attaching to their host cell with attachment proteins on their surface
- they inject their nucleic acid into the host cell
- the genetic information on the injected viral nucleic acid provides the instructions for the host cell’s metabolic activities to start producing the viral components, nucleic acids, enzymes and structural proteins which are assembled into new viruses
the importance of nucleic acids
- mitosis is important in organisms as it produces daughter cells that are genetically identical to the parent cells
this is useful for:
GROWTH
when two haploid cells e.g. sperm and ovum fuse together to form a diploid cell, it has all of its genetic information needed to form the new organism. if the new organisms is to resemble its parents, all the cells that grow from this original cell must be genetically identical. mitosis ensures this happens
REPAIR
if cells are damaged or die, it is important that the new cells produced have identical structure and function to the ones that have been lost
REPRODUCTION
single celled organisms divide by mitosis to give two new organisms, each new being genetically identical to parent
what is the cell cycle and what cells undergo it
only some cells in multicellular organisms retain the ability to divide
those that do not divide continuously undergo a regular cycle of division separated by periods of cell growth
1. INTERPHASE: occupies most of the cell cycle, ‘resting phase’ as no division takes place
2. NUCLEAR DIVISION: when the nucleus divides into 2/4
3. CYTOKINESIS: cytoplasm divides
cancer and the control of mitosis
- cancer is a group of diseases caused by a growth disorder of cells
- it is a result of damage to and subsequent mutation of genes that regulate mitosis and the cell cycle
this is due to: - ionising radiation
- x-rays/ gamma rays
- UV light
- tar from tobacco smoke
- viral infection
this leads to UNCONTROLLED CELL DIVISION
- as a consequence, a group of abnormal cells, a tumor, develops and constantly expands in size
- a tumor becomes cancerous if it changes from benign to malignant
the rate of mitosis + mutation + benign and malignant
- the rate of mitosis can be affected by the environment and growth factors
- it can also be controlled by two types of gene, that inhibit+ stimulate mitosis
- a mutation to one of these genes results in uncontrolled mitosis
- the mutant cells so formed are usually structurally and functionally different from normal cells
- most mutated cells die
however any that survive are capable of dividing to form clones of themselves and form tumours - malignant tumors grow more rapidly and are less compact than benign tumors
treatment of cancer
- how they work
- problems
- cancer treatment often involves killing dividing cells by blocking a part of the cell cycle
- in this way, the cell cycle is disrupted and cell division, hence cancer growth, ceases
drugs used to treat cancer (chemotherapy) usually disrupt the cell cycle by:
- preventing DNA replictation
- inhibiting the metaphase stage of mitosis by interfering with spindle formation
- the problem is they also disrupt the cell cycle of normal cells
- however, the drugs are more effective against rapidly dividing cells
- as cancer cells have a particularly fast rate of division they are damaged to a greater degree than normal cells
- those normal cells such as hair producing cells that also divide rapidly are also vulnerable to change.
why are eggs produced by meiosis genetically different
independent segregation
farmed female trout are treated so they produce diploid egg cells
the offspring produced from farmed trout are sterile
suggest and explain why
- 1 paternal, 2 maternal chromosome sets
- 3 copies of chromosomes
- chromosomes do not pair/split evenly
- so no meiosis
why does preventing the formation of spindle fibres stop the cell cycle
- centromeres cannot attach to spindle
- so no metaphase
- chromatids cannot separate on spindle
- so no anaphase
describe 2 aseptic techniques to use when transferring a sample to an agar plate
- open lid of petri dish as little as possible
to prevent unwanted bacteria contaminating dish - flame the wire loop
to maintain a pure culture
when looking at chromosomes, what is the evidence that the cell is undergoing mitosis
- individual chromosomes = visible bc they condensed
- each chromosome = made of 2 chromatids bc DNA has repliacted
- the chromosomes are not arranged in homologous pairs, which they would be if it was meiosis
describe the appearance and behaviour of chromosomes during mitosis
prophase
- chromosomes condense
- appear as 2 sister chromatids
metaphase
- chromosomes line up on equator
- chromosomes attach to spindle fibres
- by their centromere
anaphase
- centromeres split/divide
- sister chromatids pulled to opposite poles of cell
telophase
- chromosomes uncoil to become longer/ thinner
characteristic of cells in anaphase
chromosomes are in 2 groups at opposite poles of the spindle
v-shape shows that sister chromatids have been pulled apart at centromeres
why are light microscopes not good for identifying smaller organelles
- resolution is too low
- because wavelength of light is too long
a cell ingests bacteria and digests them in the cytoplasm
describe the role of one organelle in digesting the bacteria
- lysosomes
- fuse with vesicle
- release hydrolytic enzymes
give the structures found in all prokaryotes and eukaryotes
- cell membrane
- cytoplasm
- ribosomes
- DNA
suggest explanations for the faster rate of plasmid replication in cells growing in a culture with a high amino acid concentration
- amino acids are used in protein synthesis
- so more enzymes made for plasmid replication
- amino acids used in respiration
- so more energy/ ATP for plasmid replication
give 2 features of the chloroplast that allows protein to be synthesised inside the chloroplast
and one difference between this feature and a similar feature in the rest of the cell
- DNA
not associated with histones but nuclear DNA is - ribosomes
smaller than cytoplasmic ribosomes
80s/70s
why may no organelles be visible in a RBC
the cytoplasm of the RBC is filled with harmoglobin
name structures that cannot be viewed with an optical microscope
mitochondrion
ribosomes
ER
lysosome
cell-surface membrane
