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