Cell in health & disease Flashcards
Define homeostasis
process by which internal variables are kept within a normal range of values.
e.g. blood pressure, temp, blood glucose.
Kept within normal ranges by using NEGATIVE FEEDBACK loop
Give example of positive and negative feedback loop
negative feedback - control of blood sugar by insulin
positive feedback loop - coagulation (clotting) cascade
What 9 housekeeping functions are needed to keep cells alive?
Protection- plasma membrane
Nutrition- methods of entering or exiting cell
Movement- cytoskeleton
Communication- cell receptors
Energy generation- ATP & mitochondria
Recycling & renewable- cell cycle, cell matrix, stem cells
Proteins- ribosomes, rough endoplasmic reticulum, smooth endoplasmic reticulum & Golgi body
Waste disposal- autophagy & heterophagy
Growth factors
List main functions of mitochondria
- Generation of ATP (by oxidative phosphorylation w/in inter membrane space).
- Source of molecules used to create proteins, nucleic acids and lipids (intermediate metabolism).
- Regulation of apoptosis (programmed cell death).
- Source of reactive oxygen species.
- Production of haem (for haemoglobin).
- Generation of heat.
What can damage mitochondria?
Toxins
lack of blood supply
Trauma
What is the function of lysosome?
membrane-bound organelles
contain enzymes which breaking down proteins, nucleic acids, carbohydrates & lipids.
function as the digestive system of the cell degrading material taken up from outside the cell & digesting obsolete components of the cell itself
What is the function of Golgi apparatus?
protein modifications
glycosylation of proteins and lipids
What is the function of rough endoplasmic reticulum?
Production of proteins & lipids
production of all of the cell organelles.
Ribosomes translate mRNA into proteins- these proteins fold in the endoplasmic reticulum.
Sugars can also be added to proteins in the RER.
If proteins misfold they are degraded or if this is excessive a stress response is triggered which can then initiate apoptosis.
What is the function of smooth endoplasmic reticulum?
site of steroid & lipoprotein synthesis.
Make drugs less hydrophobic allowing their export.
Release & storage of calcium ions that regulate muscle contraction.
Where is the cytoskeleton found? What are the 4 components ?
Found in cytoplasm
1. Actin microfilaments- controls cell shape & movement
2. Microtubules- forms cilia & flagella (i.e. movement) & participate in chromatid separation during mitosis
3. Nuclear membrane lamins- maintain structure of nucleus & regulate gene transcription
4. Intermediate filaments eg. cytokeratin- give strength to cells
What is the function of tight functions & anchoring junctions in relation to movement?
They hold cell together
Help w/ cell polarity
Does this by- desmosomes attach intracellular cytoskeleton of adjacent cells together using
Cadherine proteins at these junctions
Hemidesmosomes- attach cell to extra-cellar matrix
Give example of disease that affects tight junctions
Pemphigus vulgaris
Skin disease- antibodies are directed against Desmoglein-3
Keratinocytes fall apart
causes blisters & erosions
List the 7 ways in which molecules can move across membranes (nutrition) & give one example of a substance which uses each method
- Passive diffusion eg. oxygen, CO2, polar molecules (H2O) & hydrophobic molecules
- Fast channel proteins (using concentration gradients) eg. sodium.
- Slow carrier proteins eg. amino acids- use ATP
- Endocytosis (receptor or caveolae mediated) eg. LDL (receptor-mediated) and folate (caveolae-mediated).
- Exocytosis- large molecules
- Phagocytosis eg. bacteria.
- Trancytosis eg. antibodies from breast milk passing through intestinal cells into baby.
Which ion channel is damaged in the disease cystic fibrosis?
cystic fibrosis transmembrane regulator or CFTR
- responsible for chloride transport across cell membranes.
- leads to the secretion of sticky thick mucus
What is caveolae-mediated endocytosis?
uptakes vitamins & works by forming cavities in the plasma membrane produced by folding
What is receptor mediated endocytosis?
Uptake of LDL & transferrin (iron transporter).
Used to allow larger molecules to enter cell.
1.Receptors bind to the solute
2. The plasma membrane then folds & creates a vesicle
3.Vesicle then fuses w/ lysosome & releases its contents.
4. Receptors are recycled back to the plasma membrane
What is transcytosis?
Movement of endoyctosed vesicles from the apical to the basolateral plasma membrane
i.e between the top & bottom/ sides of the cell
List 4 mechanisms by which cells communicate
- Autocrine signalling- occurs at a neuromuscular junction- acetylcholine travels from nerve, across the synaptic space, to the receptor on muscle cell.
- Paracrine signalling- where a cell produces & secretes a messenger that binds to its own receptors. Occurs during cell development or to amplify a response. e.g. malignant tumours can survive by producing Growth Factors
- Endocrine signalling- Targets the cells in the immediate vicinity. e.g. Growth factors are involved in generation of blood vessels, wound healing, cell movement & cancer spread via this mechanism
- Synaptic signalling- involves a mediator being released into the bloodstream and travelling to a distant target e.g. FSH from the pituitary gland targets follicles cells in the ovaries.
List 5 signal types which cells can respond to
Pathogens
Damage to neighbouring cells
Contact w/ neighbouring cells
Contact w. extracellular matrix
Secreted molecules e.g. growth factors
List 4 possible outcomes following a ligand binding to a cell surface receptor & give 1 example of ligand associated w/ each
- Ion channel opens e.g. neurotransmitters at neuromuscular junction
- G-protein is activated e.g. hormones
- A tyrosine kinase is activated e.g. epidermal growth factors
- Latent transcription factor is activated e.g. interferon
Explain 2 ways cells detect signals
- Cell surface receptors - usually transmembrane proteins.
- Intracellular receptors - transcription factors. These receptors are activated by lipid-soluble ligands e.g. Vit D, oestrogen, testosterone or steroid hormones
Describe function of a transcription factor & given 1 example of a transcription which facilitates cell division & 1 which stops it
Transcription factor- protien which controls rate of transcription of genetic info from DNA to messenger RNA by binding to specific DNA sequence
MYC- facilities cell division
P53 stops division
List 5 functions of growth factors
- Stimulate activity of proteins needed for cell survival, growth & division.
- Promote entry of cells into the cell cycle
- Relieve blocks on cell cycle progression
- Prevent apoptosis
- Enhance synthesis of cell components
Give 2 examples of growth factors & explain how they work
- Epidermal Growth Factor - causes squamous epithelial cells of the epidermis to divide and wound healing to begin.
- Platelet Derived Growth Factor - causes scar tissue formation & supports healing
List 4 functions of extracellular matrix
- Anchors cells- maintains their polarity & supports cell migration
- Control cell proliferation
- Provides a scaffold for tissue repair/ regeneration
- Created tissue microenvironment
Describe the components of the extracellular matrix? Examples of conditions?
- Collagen - major structural protein that has triple helical structure which is strengthened by lateral cross links of covalent bonds which Need Vit C to maintain strength
- E.g. Osteogenesis Imperfecta & Ehlers-Danlos Syndrome are genetic collagen defects. - Elastin - provides elasticity = important in skin or heart valves. Elastin is made from a protein called Fibrillin.
- E.g. Marfan’s syndrome- caused by mutation in fibrillar-1 gene- heart defects & lens dislocations seen - Integrins - glycoproteins that cross cell membranes to link cells to the outside world. Important for cell shape, movement & division. Mediate interaction between white blood cells & lining of blood vessels in inflammation
- Hydrated gels - important for resistance to compression & lubrication. Also important in joint cartilage. e.g. proteoglycans
What drives cell cycle progression?
Driven by proteins called cyclins & cyclin-associated enzymes called cyclin-dependent kinases (CDKs)
Where are the checkpoints in the cell cycle & what happens at each checkpoint?
- G1/S (synthesis) checkpoint (start)- to check if nutrition, environment & cell size are favourable for replication & that all DNA is intact
- G2/ M mitosis checkpoint- to check that DNA has been completely replicated
- Metaphase/ anaphase checkpoint- to check that all DNA is intact & if all chromosomes are attached to mitotic spindle
*Look at diagram on notes
What enforces cell cycle checkpoints & given example of 1 of these? What is the consequence of defective cell cycle enforcer?
Cyclin- dependent kinase inhibitors (CDKIs) stop cell cycle & enforce checkpoints
E.g. P16
Defective CDKI checkpoint proteins allow cells w/ DNA damage to replicate increasing risk of malignancy
What is the difference between embryonic stem cells & adult stem cells?
Embryonic stem cells- totipotent stem cells- can give rise to all types of differentiated tissues
Adult stem cells- can only replace cells in the tissue in which they reside & these checks are found in stem cell niches in many organisms
Give 2 properties of stem cells
- Self-renewal- the capacity of stem cells to retain their numbers
- Asymmetric division- capacity of stem cells to generate 2 daughter cells- 1 which will differentiate into mature cells & 1 which remains undifferentiated & retains self- renewal capacity
Name some stem cell niches
- Area around blood vessels in bone marrow.
- Bulge region of hair follicle.
- Limbus of cornea
- Crypts of Gastrointestinal tract
