U1 definitions Flashcards
give an example of an external death signal
lymphocytes
they bind to a surface receptor protein and trigger a protein cascade within the cytoplasm
give an example of an internal death signal
DNA damage
causes the activation of tumour suppressor proteins (ie, p53)
which can trigger DNA repair, arrest the cell cycle or cause programmed cell death
explain how apoptosis can be triggered
- can occur during normal cell growth and development (embryo development)
- during metamorphosis
- can also be triggered to kill cells that have begun to divide in an uncontrolled manner (tumour formation)
what is apoptosis
programmes cell death triggered by cell death signals which can be either internal or external
explain what causes tumour formation
an uncontrolled increase in the rate of the cell cycle. when a proto-oncogene (a normal gene involved in the control of cell growth or division) mutates to form a tumour-promoting oncogene.
explain what causes degenerate diseases
an uncontrolled decrease in the rate of the cell cycle.
eg. Alzheimer’s/dementia, Parkinson’s disease
describe the G1 checkpoint
- cyclins build up during G1
- retinoblastoma protein (Rb) acts as a tumour suppressor in G1 by inhibiting the transcription of genes that code for proteins needed for DNA replication.
- phosphorylation of G1 cyclin- CDKs inhibits Rb, allowing the transcription of genes that code for proetins needed for DNA replication
- the cell then progresses from G1 to S phase where DNA replication occurs.
describe the G2 checkpoint
- the success of DNA replication and any damage to DNA is assessed.
- then cells can progress to the M phase where mitosis occurs
describe the metaphase checkpoint
(controls progression from metaphase to anaphase)
- progression is halted until the chromosomes are aligned correctly on the metaphase plate and securely attach to the spindle microtubules.
what is the G0 resting state?
cells go into this non-dividing state when the go-ahead signal is not reached at the G1 checkpoint.
when may cells initiate apoptosis?
in the absence of growth factors
what is Rb?
Retinoblastoma
it can act as a tumour suppressor by inhibiting the transcription of genes which encode for proteins involved in DNA replication
what is p53?
a tumour suppressing protein capable of stimulating the arrest of the cell cycle, DNA repair or destruction of the cell BY THE ACTIVATION OF CASPASES.
what’s a tumour promoting oncogene?
a mutated proto-oncogene gene that has the potential to cause cancer
what is metamorphosis?
the process that involves a significant change in an organism’s physical form during development.
MTOC
microtubule organising centre
structure found in eukaryotic cells from which microtubules and attach to spindle fibres.
cyclic GMP
a second messenger for visual transduction
it is present in high concentrations in photoreceptor cells
what is a transcription factor?
a protein that binds to specific DNA sequences, thereby controlling the rate of transcription of genetic information from DNA to mRNA
state why the cell culture should contain serum?
because they contain growth factors that promote life and proliferation.
describe what is meant by a monoclonal antibody?
stocks of identical antibodies that are specific to a particular antigen
when is vital staining used?
with a haemocytometer in order to identify and count viable cells because the stain can distinguish between alive and dead cells. (cell viability can be estimated with a live/dead ratio)
dead cells will take up trypan blue, alive cells will not.
disadvantages of using a haemocytometer
- without vital staining, its impossible to distinguish between alive and dead cells
- the numbers obtained are only an estimate
- small cells are difficult to locate.
what are aseptic techniques?
aseptic techniques eliminate unwanted microbial contaminants from the cell culture.
it involves the sterilisation of equipment and culture media by heat or chemical means and subsequent exclusion of microbial contaminants.
what do immunoassay techniques rely on?
stocks of monoclonal antibodies
an antibody specific to the protein antigen is linked to a chemical label.
what is a label?
often a reporter enzyme produces a colour change, but chemiluminescence, fluorescence radioactivity and other reporters can be used
western blotting
a technique used after SDS PAGE electrophoresis.
in western blotting, the separated proteins from the gel are transferred (blotted) onto a solid medium
fluorescence microscopy
uses specific fluorescent labels to bind to and visualise certain molecules or structures within cells or tissues.
why do many culture media exist?
to promote the growth of specific types of cells and microbes
plating out of a liquid microbial culture on solid media allows…
the number of colony-forming units to be counted and the density of cells in the culture estimated.
when is serial dilution often needed?
to achieve a suitable colony count
why is the plasma membrane too small to carry out all of the vital functions carried out by the membrane?
because eukaryotic cells have a relatively small surface area to volume ratio
therefore eukaryotic cells have a system of internal membranes that increase the total area of the membrane.
what are phospholipids?
synthesised in the ER
a type of lipid that forms the main component of the cell membrane
how do molecules move through the Golgi apparatus?
in vesicles that bud off from the ER and fuse to the next one in the stack
what does the addition of various sugars form?
glycoproteins
the ability of oxygen to bind to haemoglobin is dependant on what?
the prosthetic haem group
example of secreted proteins that require proteolytic cleavage of inactive precursors to become active?
digestive enzymes
what can the interactions of R groups be influenced by?
temperature (can be denatured), pH
which phosphate is transferred during the phosphorylation reaction?
the terminal phosphate
what does the phosphate group add?
negative charges
what does the phospholipid bilayer act as a barrier to?
ions and most uncharged polar molecules
some molecules such as oxygen and CO2 can pass through by simple diffusion
what are channels?
multi-subunit proteins with the subunits arranged to form water-filled pores that extend across the membrane
what does the sodium-potassium pump account for in many organisms?
a high proportion of the basal metabolic rate
signalling molecules may have different effects on different target cell types due to?
differences in the intracellular signalling molecules and pathways that are involved
what do neurotransmitters bind to?
receptors at a synapse
in cone cells, different forms of opsin combine with retinal to give different photoreceptor proteins each with a maximal sensitivity to which specific wavelengths?
red, green, blue or UV
explain how the receptors of hydrophilic signalling molecules transduce the signal across a cell membrane?
by converting an extracellular signal into an intracellular signal.
the receptor changes conformation
this often involves G proteins and cascades of phosphorylation.
phosphorylation cascades allow more than one pathway to be activated.
G proteins relay signals from activated receptors which have bound to target proteins such as enzymes and ion channels.
suggest why parasite abundance is a useful way for females to assess males?
a low parasite count means that the individual has a better parasite or disease-resistant genes (fitness).
this makes him desirable for mating as these genes will be passed onto the offspring.
in which proteins do quaternary structures exist?
ones with 2 or more polypeptide chains connected.
what are the receptors of hydrophobic signalling molecules?
transcription factors.
why is it advantageous for females to be inconspicuous?
they will be better camouflage and so they will better protect their young.
what term is used to describe the activation of cellular response as a result of a signal molecule binding to plasma membrane protein?
signal transduction
what type of proteins are the receptors for steroid hormones?
TRANSCRIPTION FACTORS
give one factor that can affect the set of proteins expressed by a given cell type?
cellular stress
metabolic activity of the cell
response to signalling molecules
diseased versus healthy cells
describe how vesicles are able to move around a cell?
along microtubules (to other membranes)
define a risk assessment?
it involves identifying possible risks and the control measures to minimise them.
what do many allosteric proteins consist of?
multiple subunits (have quaternary structure)
what are allosteric enzymes?
enzymes that change conformation in response to a modulator that binds to their allosteric site altering the activity of the enzyme.
what is the phospholipid bilayer a barrier to?
ions and most uncharged polar molecules
why do different cell types have different channel and transporter proteins?
to perform specialised functions
describe the method of using a colourimeter to measure turbidity or concentration?
- the instrument must be calibrated using a blank as a baseline ( usually only the solvent used in making the resolutions or a sample of the culture medium).
- light is passed through the sample.
- an electronic sensor detects how much light has been absorbed by the sample.
this is proportional to concentration and turbidity .
The secondary structure of a protein can be altered more easily than the primary structure. Explain this in terms of the bonds involved.
-secondary structure is based on hydrogen bonding whereas the primary structure is based on covalent bonding.
this means that secondary structure can be altered more easily as hydrogen bonding is an intermolecular interaction that is more easily broken as they are weaker than covalent bonding.
how is a microbial culture started?
by an inoculum of microbial cells plated onto a solid agar medium or in a broth of suitable nutrients.
digestive enzymes are an example of what?
secreted proteins which require proteolytic cleavage to become activated.
what allows proteins to carry out a wide range of functions?
the diversity of R groups
- hydrophobic
- basic
- acidic
- polar
what allows ligands to bind to proteins?
r groups not involved in folding have receptors for ligands
what are allosteric interactions?
occurs when the binding of a ligand to the receptors on allosteric site, they change conformation and alter the activity of the cell
what are channel proteins
multisubunit proteins with subunits arranged to form water-filled pores that extend across the membrane
- in animals and plants they are highly selective.
how do transporter proteins transfer the solute across the membrane?
binding of the specific substance causes the protein to undergo a conformational change to transport the substance across the membrane.
how may a signal produce multiple different responses?
different cell types may show a species-specific response
how does a wave of depolarisation pass along the length of a neuron?
`depolarisation of the first region of a neuron causes the next region to depolarise and go through the same cycle of events, allowing the action potential to travel rapidly along the neuron, region after region.
describe what happens when the action potential reaches the end of a neuron?
vesicles containing neurotransmitters to fuse with the membrane, releasing neurotransmitters into the synapse which causes a response in connecting cells.
what does restoration of the resting membrane potential allow?
inactive voltage-gated channels to return to a conformation which allows them to open again in response to depolarization.
suggest how steroid hormones can have different effects on different tissues?
different responses to different responses to signalling molecules and they have different signal transduction pathways.
what does native gel electrophoresis use to separate proteins?
size, shape and charge
what does SDS-PAGE use to separate proteins?
Size alone
state the three types of structures which make up the cytoskeleton
microfilaments, intermediate filaments and microtubules
where do spindle microtubules attach to chromosomes?
kindochores of the centromere region
