Topic 1 - Cell Biology Flashcards
cell theory
- cells are the fundamental building blocks of all living organisms
- the cell is the smallest unit of life
- cells come from pre-existing cells
exceptions to cell theory
- striated muscle
- fungi
- giant algae (e.g. acetabularia)
how do striated muscle tissues contradict the cell theory?
- they’re made up of muscle fibre
- muscle fibres are similar to cells in the sense that they’re both surrounded by a membrane, form by cell division (from pre-existing cells), and have their own genetic material & energy release system
- but they’re much larger than most animal cells (around 30mm)
- for comparison, most human cells are < 0.3mm
- oh and they have as many as several hundred nuclei…
how do fungi contradict the cell theory?
- they’re made up of narrow thread-like structures (hyphae)
- hyphae are white in color with a fluffy appearance and a cell membrane & cell wall
- oh and each hypha has more than one nuclei
- in some types of fungi they’re divided into small cell-like sections called septa
- in aseptate fungi there are no septa
how do giant algae contradict the cell theory?
- algae are unicellular organisms
- the species acetabularia is significantly larger than regular cells (can grow to length of 100mm)
which functions of life do unicellular organisms carry out?
- almost all of them, except movement (many unicellular organisms can move but some remain in a fixed position/rely on external forces to move them)
- because of this, unicellular organisms tend to have more complex cellular structures than multicellular organisms
functions of life
- nutrition
- metabolism
- growth
- response
- excretion
- homeostasis
- reproduction
nutrition
obtaining food to provide energy and materials needed for growth
metabolism
chemical rxns inside the cell (including cell respiration to release energy)
growth
irreversible increase in size
response
ability to react to changes in environment
excretion
getting rid of waste products of metabolism
homeostasis
keeping conditions inside the organism within tolerable limits
reproduction
producing offspring (can be sexual or asexual)
why are there limitations on cell size
- to maximise surface area : volume ratio
significance of cell surface area
- the rate of movement is dependent on surface area
if SA is too small:
- substances can’t enter the cell as quickly as they’re required to + waste products will accumulate as they’re produced more rapidly than they are excreted
- cells may overheat coz metabolism produces heat faster than it’s lost over the cell’s surface
multicellular organisms
organisms consisting of a single mass of cells that have been fused together
difference between unicellular colonies and multicellular organisms
- unicellular colonies are made up of unicellular organisms that cooperate but are’t fused to form a single cell mass
- multicellular organisms are made up of a single mass of cells that come together to form an organism with distinctive overall properties (emergent properties)
emergent properties
- arise from the interaction of the component parts of a complex structure
- individual units of a multicellular organism will not show emergent properties - this can only be observed when all the parts are put together
- “the whole is greater than the sum of its parts”
division of labor
when different cells perform different functions in a multicellular organism
tissue
- a group of cells that specialize to perform the same function
- occurs due to cell differentiation
differentiation
- the development of cells in a specific way to carry out specific function(s)
- involves the expression of some genes but not others in a cell’s genome
why is differentiation important in a cell?
- can carry out their role more efficiently
- develop the ideal structure with the necessary enzymes needed the carry out all the chemical reactions associated with the function
how does differentiation occur?
- all cells in a multicellular organism have the same set of genes
- this is so that they can specialize in every possible way (if required)
- but in most cell types, less than half of these genes are ever used/needed
- cell differentiation occurs bc a diff sequence of genes is expressed in diff cell types
- so the key to development is the control of gene expression
gene expression
when a gene is being used in a cell
types of stem cells
- embryonic stem cell
- adult stem cell
- cord blood stem cell
properties of embryonic stem cells
- totipotent
- can divide an infinite number of times
- more risk of becoming tumour cells compared to adult stem cells
- less chance of genetic damage due to accumulation of mutations (variation) than with adult stem cells
- likely to be genetically different from an adult patient receiving the tissue
- the removal of cells from the embryo will kill the embryo (ethical issue)
properties of cord blood stem cells
- easily obtained and stored
- commercial collection and storage services available
- fully compatible with the tissues of the adult that grows from the baby (no rejection problems)
- limited capacity to differentiate (can only naturally develop into blood cells)
- limited quantities of stem cells from one baby’s cord
- the umbilical cord is discarded whether or not stem cells are taken from it (no ethical issues)
properties of adult stem cells
- difficult to obtain - there are very few of them and they’re buried deep in tissues
- less growth potential & differentiation capacity than embryonic stem cells (pluripotent but not totipotent)
- less chance of malignant tumors developing compared to embryonic stem cells
- fully compatible with the adult’s tissues (no rejection problems)
- removal of stem cells won’t kill the adult from which the cells are taken (no ethical issues)
possible uses of embryonic stem cells
- produce regenerated tissues
- provide means for healing diseases where a particular cell type has been lost/is malfunctioning
- (potentially) provide whole replacement organs
stargardt’s disease
- also known as Stargardt’s macular dystrophy
- genetic disease developing in children between 6 and 12
- mostly due to recessive mutation of ABCA4 gene
- this causes a membrane protein used for active transport in retina cells to malfunction
- so photoreceptive cells in the retina degenerate
- causing vision to worsen over time (potentially leading to blindness)
role of stem cells in treating stargardt’s disease
- embryonic stem cells can be developed into retina cells
- was initially done with mice cells which were then injected into the eyes of mice with a condition similar to Stargardt’s disease
- the cells were not rejected, didn’t cause complications, etc, and instead caused an improvement in vision
leukemia
- type of cancer
- all cancers start with mutations occur in genes controlling cell division
- for a cancer to develop, several specific mutations must occur in this genes in one cell
- once the mutation occurs, the cell grows and divides repeatedly to produce more and more cells
- for leukemia, abnormally large quantities of WBCs are produced
problem with only using chemotherapy treatment for leukemia
- cancer cells in the bone marrow must be destroyed
- this can be done by treating the patient with chemicals to kill dividing cells (chemotherapy)
- however, to remain healthy, the patient should be able to produce WBCs needed to fight diseases
- if chemo is used, stem cells that can produce blood cells would be killed as well
role of stem cells in treating leukemia
- A large needle is inserted into a large bone (usually the pelvis) and fluid is removed from the bone marrow
- Stem cells are extracted from this fluid and are stored by freezing (as these are adult stem cells, they only have the potential for producing blood cells)
- A high dose of chemotherapy drugs is given to the patient to kill all cancer cells, causing the bone marrow to lose its ability to produce blood cells
- The stem cells are then returned so they can re-establish themselves in the bone marrow and begin producing blood cells again
ethics of stem cell research
- currently, techniques for extraction of embryonic stem cells will kill the embryo
- some scientists argue that IVF (in vitro fertilisation) can be used to produce embryos
- however, others argue that it’s unethical to create human lives just to obtain stem cells
- furthermore, IVF involves hormone treatment for women (with some associated risk) along with an invasive surgical procedure
totipotent
potential to differentiate into all types of cells (including embryonic tissue)
pluripotent
potential to differentiate into multiple types of cells
resolution
making the separate parts of an object distinguishable by eye
maximum resolution of light microscope
0.3 micron or 200 nanometres
why is there a limit to the resolution of light microscopes?
they are limited by the wavelength of light (400-700nm)
resolution of light microscopes vs electron microscopes
- electron microscopes have res of 200x greater than light microscopes (0.001 micron)
- light microscopes reveal the structure of cells
- electron microscopes reveal the ultrastructure
prokaryote
- simplest cell structure, no compartments
- first organisms to evolve on Earth
- mostly small in size and can be found almost everywhere
- unicellular
- filled with cytoplasm
components of a prokaryote
- nucleoid (not nucleus)
- plasma membrane
- cell wall
- cytoplasm
- pili
- flagella
- ribosomes (70S)
nucleoid
- contains naked DNA
- stores genetic info that controls the cells and will be passed on to daughter cells
cell wall & plasma membrane
- prokaryotic cell wall protects and maintains cell shape
- some bacteria have a polysaccharide layer outside the cell wall that allows them to adhere to structures
- plasma membrane is semi-permeable
- prokaryotic membranes are similar to eukaryotic membranes
- control substances moving into and out of the cell
- contains integral and peripheral proteins
- substances pass through by either active or passive transport
cytoplasm
- contains enzymes used to catalyse chemical reaction of metabolism and also contains DNA in a region called the nucleoid
- ribosomes are found here
pili & flagella
helps bacteria adhere to each other for the exchange of genetic material
flagella
- made of protein called flagellin
- helps bacteria move around
- a motor protein spins the flagella like a propeller
binary fission
- i.e. cell division
- used in asexual reproduction
- this is how prokaryotes reproduce
binary fission process
- the single circular chromosome is replicated
- the two copies move to opposite ends of the cell
- division of the cytoplasm follows
- the daughter cells are genetically identical
eukaryote
- compartmentalized
- more complex than prokaryotes
components of a eukaryote
- nucleus
- rough endoplasmic reticulum
- golgi apparatus
- lysosome (uncommon in plants)
- mitochondrion
- ribosomes (80S)
- plasma membrane
- vesicles
- centrosome
- cilia and flagella
- vacuoles
- cell wall
- chloroplast (plant and algal cells only)
structure of nucleus
- has a double membrane (nuclear membrane)
- the nuclear membrane has pores (nuclear pores)
- nucleus contains chromosomes consisting of DNA associated with histone proteins
- histones are proteins that coil DNA
- chromatin are spread through the nucleus
- there are some dense areas of chromatin around the edges of the nucleus
chromatin
uncoiled chromosomes in the nucleus
function of nucleus
- site of DNA replication
- also site of DNA transcription to form mRNA
- mRNA is exported via nuclear pores to the cytoplasm
structure of rough endoplasmic reticulum
- consists of cisternae
- 80S ribosomes are attached to the cisternae
cisternae
flattened membrane sacs
function of rER
- synthesize protein for secretion from the cell
- proteins synthesized by rER ribosomes pass into the cisternae
- vesicles bud off from the cisternae and move to the golgi apparatus
structure of golgi apparatus
- consists of cisternae
- not as long as rER cisternae, and are often curved
- unlike rEr, they aren’t attached to robosomes
- they have many vesicles nearby
function of golgi apparatus
processes proteins brought in vesicles from the rER
structure of lysosome
- spherical with a single membrane
- formed from golgi vesicles
- contain high concentrations of proteins
- specifically digestive enzymes
function of lysosome
digestive enzymes in lysosome can break down:
- ingested food in vesicles
- organelles in the cell
- can even be used to destroy the entire cell
structure of mitochondrion
- has double membrane
- also has cristae
- contains matrix
- usually spherical/ovoid
cristae
when the inner membrane invaginates (like in mitochondria)
matrix
fluid found in mitochondria
function of mitochondria
- produces ATP for the cell via aerobic respiration
- fat is digested here if it’s being used as an energy source
structure of ribosomes
- appear as dark granules
- no membrane
- prokaryotic ribosomes are 70S while eukaryotic ribosomes are 80S
- 80S are slightly larger than 70S
- can be free-floating in cytoplasm or stuck to rER
- they are constructed in a region of the nucleus called the nucleolus
function of ribosomes
- site of protein synthesis
- contributes to protein synthesis by translating messenger RNA
- free ribosomes synthesize protein and release them directly into the cytoplasm
structure of chloroplasts
- has a double membrane
- contains stacks of thylakoids
- usually spherical/ovoid
- may contain starch grains if they have been photosynthesizing rapidly
thylakoids
flattened sacs of membrane
function of chloroplasts
produce glucose and a variety of other organic compounds through photosynthesis
structure of vacuoles/vesicles
- organelles consisting of a single membrane
- contains fluids
- vesicles are small version of vacuoles
- many plant cells have vacuoles that are over 50% of the cell volume
function of vacuoles
- some animals absorb foods from outside to digest them inside vacuoles
- some unicellular organisms use vacuoles to expel excess water
function of vesicles
- generally used to transport materials inside the cell
structure of microtubules
- small cylindrical fibres
function of microtubules
- moves chromosomes during cell division
- has other roles but they’re not relevant in IB hehe
centrosome
- made up of 2 centrioles perpendicular to each other
- each centriole consists of 2 groups of 9 triple microtubules
function of centrosome
- anchor point for microtubules during cell division
- anchor for cilia/flagella
structure of cilia/flagella
- whip-like structures
- project from cell surface
- contain a ring of 9 double microtubules and a pair of microtubules in the center
- flagella are larger than cilia and usually only one is present
- cilia are smaller and many are present
function of cilia/flagella
- movement
- cilia can also be used to create a current in the fluid around the cell
function of endocrine gland cells
secretes hormones into the bloodstream
function of exocrine gland cells ub tge oabcreas
- secrete digestive enzymes into a duct
- they’re carried into the small intestine to digest foods
palisade mesophyll
- cell type that carries out the most photosynthesis
- roughly cylindrical
hydrophilic
substances that are attracted to water
hydrophobic
substances that are repulsed by water
amphiphatic
substances that are partly hydrophilic and partly hydrophobic
phospholipids
- amphipathic substances
- hydrophilic head (phosphate group)
- hydrophobic tail (hydrocarbon chains)
phospholipid bilayers
- phospholipids are arranged into double layers when mixed into water
- tails face inward while heads face the water on either side
- stable structures
function of phospholipid bilayer
forms the basis of all cell membranes
functions of membrane proteins
- hormone-binding sites (hormone receptors)
- immobilized enzymes with active site on the outside (e.g. in small intestine)
- cell adhesion to form tight junctions between groups of cells (in tissues and organs)
- cell-to-cell communication (e.g. receptors)
- channels for passive transport (allows hydrophilic substances to pass via facilitated diffusion)
- pumps (for active transport, uses ATP)
integral proteins
- hydrophobic on at least part of their surface
- embedded in the hydrocarbon chain in the center of the membrane
- most integral proteins are transmembrane
transmembrane
- transmembrane substances extend all the way across the membrane
- their hydrophilic parts project through the regions of phosphate heads on either side
peripheral proteins
- hydrophilic on their surface
- so they’re not embedded in the membrane
- most are attached to integral proteins (this is reversible)
- some have a single hydrocarbon chain to anchor the protein to the membrane surface
protein content of plasma membranes
- the more active the membrane, the higher its protein content
- myelin sheaths only use their membrane as insulators so the protein count is only 18%
- most membranes are about 50%
- highest protein contents are on membranes of chloroplasts and mitochondria (75%)
cholesterol and cell membranes (general)
- type of lipid (but it’s neither fat nor oil, it’s a steroid)
- most of it is hydrophobic so it’s attracted to the hydrocarbon tails but one end is hydrophilic due to a hydroxyl group (-OH)
- the hydrophilic end is attracted to the phosphate heads on the periphery of the membrane
- so cholesterol is positioned between phospholipids in the membrane
- vesicles containing neurotransmitters at synapses contain the highest cholesterol concentration (30% of lipids in the membrane is cholesterol)
role of cholesterol in cell membranes
- fluidity of animal cell membranes must be controlled
- too fluid = less able to control which substances pass through
- not fluid enough = movement of the cell and substances within it would be restricted
- cholesterol disrupts the regular packing of hydrocarbon tails of phospholipid molecules
- this prevents them from crystallizing/behaving as a solid
- but it also restricts molecular motion, reducing membrane fluidity
- and it also reduces permeability to hydrophilic particles
- due to its shape, cholesterol helps membranes curve into a concave shape (this is especially helpful in the formation of vesicles during endocytosis)
formation of a vesicle
- a small region of a membrane is pinched off from the rest
- membrane proteins carry out this process using ATP
endocytosis
- formation of vesicles inside the cell
- contains the material that was transported into the cell
- this is a method of taking materials into the cell
examples of endocytosis
- typically water and solutes are transported
- sometimes larger molecules that can’t pass through the plasma membrane
- in the placenta, proteins (including antibodies) from the mother are absorbed into the foetus via endocytosis
- some cells (e.g. paramecium) take in large undigested food particles via endocytosis
- some types of white blood cells take in pathogens via endocytosis and kill them
process of vesicle movement in cells
- protein is synthesized by ribosomes and accumulate in the cisternae of the rER
- vesicles containing the proteins bud off and carry them to the golgi apparatus
- the vesicles fuse with the golgi apparatus
- golgi apparatus processes the proteins into their final forms
- after that, vesicles bud off containing the final form of the proteins and move to the plasma membrane (where the protein is secreted)
process of vesicle movement in growing cells
- area of the plasma membrane needs to increase in a growing cell
- phospholipids are synthesized next to the rER and are inserted into the rER membrane
- ribosomes on rER synthesize membrane proteins
- which are also inserted into the membrane
- vesicles bud off the rER and move to the plasma membrane
- they fuse with it to increase the area of the plasma membrane
exocytosis
process by which a vesicle fuses with the plasma membrane to eject its contents from the cell
uses of exocytosis
- release of digestive enzymes from gland cells
- expelling waste products/materials (e.g. removal of excess water from unicellular organisms)
diffusion
- the spreading out of particles in liquids and gases
- down a concentration gradient
- happens due to continuous random motion of particles
types of diffusion
- simple diffusion
- facilitated diffusion
- osmosis
- active transport
simple diffusion
- passive diffusion
- particles pass between the phospholipids in membrane
- can only happen if the phospholipid bilayer is permeable to those particles
- non-polar substances (e.g. oxygen) can easily diffuse in/out
simple diffusion: why is it easier for non-polar particles (compared to polar particles) to pass through the phospholipid bilayer?
- the center of membranes is hydrophobic
- ions with positive/negative charge can’t easily pass through
- polar molecules have a partial positive/negative charge so they can only diffuse at low rates
- small polar particles (e.g. ethanol, urea) diffuse more easily than large polar particles
facilitated diffusion
- passive diffusion
- channels in the plasma membrane help particles pass through the membrane (down a concentration gradient)
- these channels are made of protein with holes of a very narrow diameter
- the diameter and chemical properties of the channels ensure that only one type of particle can pass through that channel (e.g. sodium ions only, etc…)
benefits of facilitated diffusion
- cells can control what type of channels are synthesized
- so this way they can control what substances are diffused in/out
osmosis
- passive diffusion
- due to differences in concentration of solutes in water
- bonds between solutes and water serve to restrict movement of water molecules
- there is a net movement of water up a solute concentration gradient
- can happen in all cells because water molecules (despite being hydrophilic) are small enough to pass through the phospholipid bilayer
solute
- dissolved substances in water
- substances dissolve by forming intermolecular bonds with water molecules
aquaporins
- water channels in cells (facilitated diffusion)
- greatly increases membrane permeability to water
- at its narrowest point it’s only slightly wider than water molecules
- so water molecules pass in single file
- positive charges at its narrowest point prevent protons (H+) from passing through
cells with aquaporins
- kidney cells
- root hair cells
active transport
- it’s not diffusion; energy is needed (ATP)
- carried out by pump proteins
pump proteins
- used to transport substances in active transport
- globular proteins in cell membrane
- cell membranes contain many different pump proteins to allow the cell to control the content of cytoplasm
process of active transport
- the molecule/ion enters the pump protein and reaches a central chamber
- a conformational change to the protein occurs using energy from ATP
- the molecule/ion passes to the opposite side of the membrane
- the pump reverts to its original conformation and takes in more molecules/ions
axon
- part of a neuron (nerve cell)
- consists of a tubular membrane containing cytoplasm
- can be as narrow as 1 micron
- used to convey messages from one part of the body to another
- using nerve impulses
nerve impulse
- electrical form of communication between nerve cells
- involves rapid movement of sodium and potassium ions across the axon membrane of a neuron
- occur due to facilitated diffusion through sodium and potassium channels, because of concentration gradients
- the concentration gradients are built up by a sodium-potassium pump protein (active transport)
- one full cycle of the active transport of sodium-potassium uses 1 ATP
active transport process of sodium and potassium in neurons
- Pump opens to the inside of the axon, and 3 Na ions enter the pump and attach to binding sites
- ATP transfers a phosphate group from itself to the pump, causing the pump to change shape
- Pump closes to the inside of the axon and opens to the outside, releasing the 3 Na ions
- 2 K ions from outside enter and attach to binding sites
- Binding causes release of phosphate group, causing the pump to change shape
- Pump opens to the inside of the axon and closes to the outside, releasing the 2 K ions
- 1 ATP has been used up, and the cycle repeats
potassium channels in axons
- made up of 4 protein subunits with a narrow pore between them
- 0.3 nm wide at its narrowest point
- voltage-gated
facilitated diffusion process of potassium channels in axons
- K ions are < 0.3nm, but when dissolved, they become bonded to water molecules which makes them too big to pass through
- so the bonds between the K ions and water molecules are broken
- bonds form temporarily between the K ion and a series of amino acids at the narrowest point of the pore
- after the K ion passes through, it can be bonded with the water molecules again
voltage-gated protein channels
- voltages across membranes are due to imbalances in positive/negative charges
- if an axon has more positive charges outside than inside, protein channels are closed
- this is due to an extra globular protein subunit attached by a flexible chain of amino acids that can fit inside the pore to close it
creation of cells
- cells can only be formed from division of pre-existing cells
- there is a continuity of life from its origins on Earth to the cells in our bodies today
spontaneous generation
formation of living organisms from non-living matter
hypotheses for the origin of complex structures
- production of carbon compounds
- assembly of carbon compounds into polymers
- formation of membranes
- development of a mechanism for inheritance
production of carbon compounds from atmosphere
- Miller & Urey passed steam through a mixture of methane, hydrogen, and ammonia
- this mixture is a representative of early Earth’s atmosphere
- electrical discharges were used to simulate lightning
- amino acids and other carbon compounds needed for life were produced
assembly of carbon compounds into polymers
deep-sea vents carry chemical supplies of energy for the assembly of carbon compounds into polymers
deep-sea vents
- cracks in earth’s surface
- contains hot water carrying reduced inorganic chemicals (e.g. iron sulphide)
formation of membrane
- phospholipids or other amphipathic carbon compounds would have naturally formed bilayers
- these bilayers readily form vesicles resembling the plasma membrane of a small cell
development of an inheritance mechanism
- enzymes are needed to replicate DNA and pass genes on to offspring
- but genes are needed to create enzymes
- could be that in an earlier phase of evolution, RNA was the genetic material
- RNA can store information like DNA but is both self-replicating and can act as its own catalyst
theory of endosymbiosis
- larger prokaryotes took in smaller prokaryotes through endocytosis
- the larger prokaryotes allowed the smaller prokaryotes to live and reproduce in its cytoplasm
- the larger cells supply food while the smaller cells provide energy
- mutualistic/symbiotic relationship favored by natural selection
possible evidence: mitochondria and chloroplasts
evidence of mitochondria/chloroplasts being prokaryotes
- they have their own genes on a circular DNA molecule
- they have 70s ribosomes
- they transcribe their own DNA and use mRNA to synthesize their own proteins
- they can only be produced through division of pre-existing mitochondria/chloroplasts
mitosis
division of the nucleus into 2 genetically identical daughter nuclei
mitotic phases
- prophase
- metaphase
- anaphase
- telophase
cell cycle phases
- interphase
- cell division
interphase
- active phase in the life of a cell
- basically the cell’s living phase (when not reproducing)
- when metabolic reactions occur
- some of those reactions also occur during cell division (e.g. cell respiration)
- but others (e.g. DNA replication, protein synthesis) only occur in interphase
interphase phases
- G1 phase
- S phase
- G2 phase
S phase
cell replicates all genetic material in its nucleus
supercoiling
- DNA molecules are repeatedly coiled
- to make the chromosomes shorter, wider, and more condensed
- proteins called histones help with supercoiling and enzymes are also involved
why is supercoiling necessary?
- in mitosis, the 2 chromosomes making up each chromosome separate and move to opposite poles
- the DNA molecules in these chromosomes are too long to fit in the nucleus
- so they must be packaged into much shorter structures
prophase
- supercoiling occurs here
- nucleolus breaks down
- microtubules grow from MTOCs to form a spindle-shaped array linking the two opposite poles of the cell
- at the end of prophase, the nuclear membrane breaks down
MTOC
microtubule organizing centre
metaphase
- microtubules continue growing and attach to centromeres on each chromosome
- the 2 attachment points on opposite sides of each centromere allow the chromatids of a chromosome to attach to different microtubules (from opposite poles)
- the microtubules are put under tension to test whether the attachment is correct
- if it is correct, the chromosomes remain aligned around the equator of the cell
anaphase
- each centromere divides to separate pairs of sister chromatids
- spindle microtubules pull the separated chromatids towards each pole
- mitosis produces 2 genetically identical nuclei as sister chromatids are pulled to opposite poles
telophase
- chromatids have reached the poles and are now chromosomes
- at each pole the chromosomes are pulled together near MTOC
- a nuclear membrane forms around each group of chromosomes (at opposite poles)
- the chromosomes uncoil and a nucleolus is formed
- the cell is dividing and the 2 daughter cells enter interphase
cytokinesis
- occurs after mitosis
- the stage when the two daughter cells separate from each other
- differs between animal and plant cells
cytokinesis in animal cells
- the plasma membrane is pulled inwards around the cell equator to form a cleavage furrow
- caused by a ring of contractile protein (actin and myosin)
- when the cleavage furrow reaches the centre, the cell pinches apart to form 2 separate daughter cells
cytokinesis in plant cells
- vesicles are moved to the equator where they fuse to form a tubular structure across the equator
- with the addition of more vesicles, the tubular structures merge to form 2 layers of membrane
- they develop into plasma membranes and connect to the pre-existing plasma membrane lining the perimeter of the cell
- thus cytoplasm is fully divided
- vesicles containing pectin and other substances are added and the substances are deposited via exocytosis
- this forms the middle lamella linking the 2 cell walls
- both daughter cells then bring cellulose to the equator and deposit them via exocytosis adjacent to the middle lamella
- thus forming their own cell walls adjacent to the equator
cyclins
- group of proteins
- used to ensure that tasks are performed at the correct time
- and to ensure that the cell only moves on to the next stage of a cycle when it’s appropriate
- there is a different type of cyclin for each phase/task
how do cyclins work?
- they bind to enzymes called cyclin-dependent kinases
- these kinases become active and attach phosphate groups together proteins in the cell
- the attachment triggers the other proteins to activate
- they then carry out phase-specific tasks
tumours
- abnormal groups of cells
- can develop at any stage in life in any part of the body
benign tumour
- when the abnormal group of cells adhere to each other and don’t invade other parts of the body
- they are unlikely to cause much harm
carcinoma
- malignant tumour
- occurs when the tumour cells detach to move elsewhere
- they develop into secondary tumours
- life-threatening
- diseases caused by malignant tumours are also known as cancer
carcinogens
chemicals/agents that cause cancer
mutagens
- agents that cause gene mutations
- they are all carcinogenic as mutations can cause cancer
mutation
random change(s) to the base sequence of genes
oncogene
- most genes won’t cause cancer if they mutate
- the few that do are called oncogenes
- they’re typically involved in the control of the cell cycle and cell division
- so mutations in the oncogenes can result in uncontrolled cell division, causing tumour formation
requirements for turning a cell into a tumour cell
- several mutations must occur
- specifically pertaining to oncogenes
metastasis
- the movement of cells from a primary tumour
- in order to set up secondary tumours in other parts of the body
organelle
- non-cellular structure
- carries out specific functions
eukaryotes vs prokaryotes
- eukaryotic DNA has proteins and chromosomes/chromatin while prokaryotic DNA is naked and in a ring form without protein
- eukaryotic DNA is enclosed in a nuclear envelope while prokaryotic DNA floats freely in the cytoplasm
- eukaryotes have mitochondria
- eukaryotes have 80s ribosomes while prokaryotes have 70s ribosomes
- eukaryotes have internal compartmentalization, forming organelles
- eukaryotes are typically > 10 micron while prokaryotes are typically < 10 micron
animal cells vs plant cells
- plant cells have a cell wall
- plant cells have chloroplasts
- animal cells usually don’t have vacuoles, or if they do, they’re small vacuoles
- plants store carbohydrates as starch while animals store carbohydrates as glycogen
- plant cells don’t contain centrioles in a centrosome
- animal cells are more flexible and rounded while plant cells are more rigid and often angular
component of bacterial cell walls
peptidoglycan
component of fungi cell walls
chitin
component of algae cell walls
cellulose
component of yeast cell walls
- glucan
- mannan
component of plant cell walls
cellulose
significance of the extracellular matrix of animal cells
- composed of collagen fibres and glycoproteins
- these form fibre-like structures to anchor the matrix to the plasma membrane
- thus strengthening the plasma membrane and allowing attachments between adjacent cells
- allows cell-to-cell interaction
- partially attributed to cell migration and movement
