Homeostasis and cell protection, movement, nutrition, communication, energy production, renewal Flashcards
What is homeostasis?
Process of keeping internal variables within a normal range of values
Give 3 examples of internal variables regulated by homeostatic mechanisms?
Blood glucose level, temperature, blood pressure
When carbohydrates are eaten, how does homeostasis regulate blood glucose levels?
Pancreatic beta cells detect rise in blood glucose level
Pancreatic beta cells release insulin which binds to hepatocyte and skeletal muscle receptors
Cells take up extra glucose in blood and store it as glycogen, until blood glucose level is restored to a normal value
How does a negative feedback loop work?
Stimulus changes variable so that value isn’t in normal range
Receptor detects change
Control centre compares change to reference value, instructs effector to make adjustment to restore normal value
What 2 substances can’t pass through the phospholipid bilayer of the plasma membrane by passive diffusion?
Large molecules, charged/polar molecules
Why can’t charged/polar molecules move through the phospholipid bilayer by passive diffusion?
They are repelled by the neutral, hydrophobic tails of the phospholipids
Why can’t large molecules passively diffuse through the phospholipid bilayer?
They are too big to fit between the individual phospholipids
What is a phosphatidylserine?
Negatively-charged phospholipid that faces outwards in a normal cell, and is important in signaling phagocytes
How does phosphatidylserine signal to phagocytes that its cell is apoptotic?
The phosphatidylserine turns to face outwards, which attracts phagocytes
In which condition are glycolipids on outside of the plasma membrane important?
Inflammation
How can cell polarity be maintained
Give 6 examples of substances that passively diffuse through the phospholipid bilayer?
Oxygen, carbon dioxide, urea, steroids, water, alcohol
What size do ions/molecules need to be to require transport through fast channels and slow carrier proteins?
Over 75 daltons
What does the Multidrug Resistant (MDR) Protein carry out of cells, and what is the consequence of this substance being removed from the cell?
Chemotherapy drugs pumped out of cell which causes cell to become resistant to treatment
What does cytoplasm contain that increases cell osmolarity?
Charged metabolites
What is cell osmolarity?
Process of measurement of solute concentration
If cell cytoplasm has high osmolarity, what substance will diffuse into the cell?
High osmolarity attracts water
How does a cell prevent lysis from excess water entering the cell?
Na-K ATPase pump constantly pumps sodium and chloride ions
If a cell is injured and can’t produce energy, how will the Na-K ATPase pump be affected?
Pump will fail, so excess water will enter cell and lysis occurs
What occurs in endocytosis?
Large molecule is taken into the cell by cell membrane invagination, which buds off to form an endosome (vesicle)
After an endosome has fused with a lysosome and the extracellular material has been ingested, what happens to the receptors coating the endosome?
Receptors are recycled back to the cell plasma membrane
What is another name for receptor-mediated endocytosis?
Claritin-dependent endocytosis
What occurs in receptor-mediated endocytosis?
Large molecule binds to cell surface receptors then Claritin proteins are used to coat the forming endosome before it buds off
Give 2 examples of extracellular ligands/molecules that use receptor-mediated endocytosis?
Transferrin (iron transporter), bad cholesterol
What occurs in caveolin-mediated endocytosis?
Large molecule binds to cell surface receptors then Caveolin proteins are used to coat the forming endosome before it buds off
Give an example of an extracellular ligand/molecule that uses caveolin-mediated endocytosis?
Vitamins
What is exocytosis?
Export of large molecules through fusion of the vacuole membrane with the cell membrane
What occurs in transcytosis?
Large molecule endocytosed at one area of plasma membrane, exocytosed at another area of membrane
What are 2 surfaces in the plasma membrane, and where are they located relative to organ lumen?
Apical membrane faces towards organ lumen
Basolateral membrane faces away from organ lumen
Give an example of a molecule transported by transcytosis?
Antibodies passing breastmilk through intestinal cells
In cystic fibrosis, which channel protein is defective?
Transmembrane chloride channel protein
How does cystic fibrosis lead to infections?
Defective transmembrane chloride channel causes airways to be coated by thick mucus, which traps bacteria in lungs and causes infection
What structure in the cell allows cell movement?
Cytoskeleton
What is the main component of the cytoskeleton that controls cell shape and movement?
Actin filaments
Which 2 proteins form cilia and flagella?
Microtubules, motor proteins
What is cilia and flagella used for in mitosis?
Chromatin movement
What structure provides strength to cells?
Intermediate filaments
What intermediate filament is present in epithelial cells?
Cytokeratin
How can the origin of a cancer be determined by studying the cytokeratin in a cell?
Epithelial cells from different tissues have different cytokeratins present
What controls nucleus structure?
Nuclear membrane lamins
What is progeria?
Condition characterised by premature aging in children, due to irregular collapsing nuclear membrane
What proteins do desmosomes contain that allow cell-cell adhesion?
Cadherin
What part of each cell do desmosomes attach to adjacent cells?
Intracellular cytoskeletons
What attaches cells to the extracellular matrix?
Hemidesmosomes
What is the pathology of pemphigus vulgaris?
Condition where antibodies target Desmoglein-3 (desmosome component), causes keratinocytes to fall apart
What are 2 physical signs of pemphigus vulgaris?
Blisters, erosions
What is autophagy?
Process by which cell disposes of unnecessary/dysfunctional organelles and denatured proteins by ingesting it
What vesicles are formed by autophagy?
autophagosomes
What is heterophagy?
Cells ingest extracellular foreign materials
How is cellular waste destroyed in the cell?
Autophagosomes, phagosomes, endosomes fuse with lysosomes which contain digestive enzymes
How is waste removed from the cell?
Exocytosis
What process produces ATP, and where in the mitochondria does it occur?
Oxidative phosphorylation in intermembrane space
Why do rapidly growing cells produce intermediates?
Lipids, proteins, nucleic acid are produced instead of ATP
When rapidly growing cells produce lipids, proteins, nucleic acids instead of ATP, what is the by-product?
Oxygen species
What is thermogenin, and where is it found?
Mitochondrial carrier protein in inner membrane that generates heat, abundant in brown fat
What cellular process does the mitochondria regulate?
Apoptosis
What 3 factors can damage the mitochondria?
Trauma, low blood supply, toxins
How does mitochondrial damage affect ATP production?
Transition pore opens which causes ATP production to stop
Which parent is mitochondrial DNA inherited from?
Maternally inherited
What 3 conditions can cause mitochondrial diseases?
X-linked condition, autosomal disorder, random mutation
What is the process of communication at neuromuscular junctions?
Synaptic transmission
During synaptic transmission, what area does acetylcholine diffuse across, and what does it bind to on the post-synaptic membrane?
Diffuses across synaptic cleft and binds to acetylcholine receptor on the muscle cell
What is the function of autocrine signaling?
To amplify a response
What is the function of paracrine signaling?
To signal to adjacent cells, or cells in the immediate vicinity
What is the function of endocrine signaling?
To release mediators into bloodstream so that they can signal to distant target
What is a cell surface receptor?
Transmembrane protein with extracellular domains that binds to water-soluble ligand
What type of channel is opened when the ligand binds to a cell surface receptor?
Ion channel
What type of receptor are the 7 transmembrane receptors?
G-protein coupled receptor
When receptor tyrosine kinase is activated, what does it phosphorylate?
Phosphorylates tyrosine residue of specific intracellular proteins
How is the signaling of the receptor tyrosine kinase stopped?
Phosphatase removes phosphate group from the receptor
What 3 types of receptors does non-receptor tyrosine kinase activate?
Immune, cytokine, insulin receptors
What cells do pathogens signal to?
Innate immune cells
What does damage to neighbouring cells signal?
Wound healing
SIgnals produced by contact with neighbouring cells is mediated by which 2 factors?
Adhesion molecules, gap signaling junctions
What are 4 cellular responses to signals produced by growth factors?
Entry of cells into cell cycle
Removal of block on cell cycle progression
Prevent apoptosis
Enhance cell organelle synthesis
What is an intracellular receptor?
Transcription factor that causes DNA to be transcribed into RNA, upon binding to a lipid-soluble ligand
Why do intracellular receptors only bind to lipid-soluble ligands?
Ligands are fat-soluble so can cross the phospholipid bilayer, water-soluble ligands can’t cross so must enter with cell surface receptors
Do hormones and cytokines produce signals that trigger cellular response?
Yes
What transcription factor is activated by cell surface receptors?
Latent transcription factor
Give 3 reasons for why cell renewal is needed?
Cell growth, replacement, maintains homeostasis
What 2 proteins regulate cell cycle progression?
Cyclins, Cyclin-dependent Kinases
Why does the cell cycle have quality control checkpoints?
To ensure that any cells with genetic imperfections don’t complete replication
If a DNA abnormality is detected at a quality control checkpoint, what happens?
DNA repair mechanism
What happens to cells with severe abnormalities?
Apoptosis or enter state of senescence
Which active gene stops the cell cycle?
p53
What proteins enforce quality control checkpoints?
CDK inhibitors (CDKIs)
How do CDKIs interact with CDKs if a cell abnormality is detected?
CDKI have p16 gene which inhibits CDKs 4 and 6, so that cell cycle won’t progress
What condition can defective CDKIs increase the risk of?
Cancer, as more abnormal cells will mature
What do some cancer drugs target in order to stop abnormal cell cycle progression?
CDK 4 and 6
Why does the extracellular matrix anchor cells?
Cells are kept upright, so maintain the cell polarity
What factor and signal does the extracellular matrix use to control cell growth?
Integrin cell signals, growth factors
How is the extracellular matrix used in healing?
Provides scaffold for tissue renewal
What is the tissue microenvironment, that is produced by extracellular matrix?
Dynamic network of cellular and non-cellular component that collectively maintain homeostasis of an organ
Where is the extracellular matrix located, and how is it produced?
Secreted by cells to surround them in tissues
What is the major structural protein of the extracellular matrix?
Collagen
What vitamin is needed for collagen to maintain its strength?
Vitamin C
What is osteogenesis imperfecta?
Condition where patient presents with brittle bones, caused by genetic collagen defect in extracellular matrix
What is Ehlers-Danlos syndrome?
Condition where patient presents with fragile skin and unstable joints, caused by genetic collagen defect in extracellular matrix
What gives extracellular matrix the ability to stretch and recoil?
Elastin
What protein makes up elastin?
Fibrillin
Give 2 examples of where elastin is located in body?
Heart valves, skin
What is Marfan’s syndrome?
Condition where patient presents with heart valve problems producing a murmur, due to mutation of fibrillin-1 gene
What are integrins?
Transmembrane glycoproteins that bind cell to extracellular matrix
Give 2 examples of water-hydrated gels in the extracellular matrix?
Proteoglycans, hylaronans
What properties do water-hydrated gels give extracellular matrix?
Resistance to compression
Lubrication
Where is the presence of water-hydrated gel important?
Joint cartilage
What 2 properties give stem cells the ability to mediate the cycle of replacing dead cells to maintain homeostasis?
Self-renewal
They undergo asymmetric division to produce one daughter cell and one stem cell
What do totipotent/embryonic stem cells give rise to?
All cell types in differentiated tissue (embryonic, placental, adult)
What do adult/tissue stem cells give rise to?
Cell types in the tissue within within they reside
Give 2 examples of where multipotent stem cells are derived from?
Bone marrow, adipose tissue
Give 4 examples of cell types that multipotent stem cells give rise to?
Chondrocytes (cartilage)
Osteocytes (bone)
Adipocytes (fat)
Myocytes (muscle)
What is a stem cell niche?
Microenvironment in anatomical area where stem cells reside and receive stimuli to promote their differentiation
Where is the stem cell niche near bone marrow?
In areas surrounding blood vessels in bone marrow
Where is the stem cell niche in a hair follicle, and what happens if this niche is destroyed?
Bulge region, destruction causes permanent hair loss
Where is the stem cell niche in the cornea?
Limbus
Where is the stem cell niche in the GI tract?
Crypts
What are the Canals of Herring in the liver, where stem cell niches are found?
Small ducts that transport bile
Which region of the brain contains a neural stem cell niche, and which aggressive cancer can these cause?
Subventricular region, cause Glioblastoma
Which cells can be generated in a laboratory setting?
Pluripotent cells
Which genes are identified to mimic ‘stem’ ability of embryonic stem cells?
Genes who’s products reprogram somatic cells
How are induced Pluripotent Stem cells generated after reprogramming genes have been identified?
Genes introduced into fully differentiated cells
Why is regenerative medicine important?
Generated cells can be implanted without triggering immune response
