Principles Of Cellular Function Flashcards
(23 cards)
How is water distributed through the body compartments? How do age and gender affect total body water?
- Total body water (TBW) is 60% body weight
- 2/3 (40%) ICF
- 1/3 (20%) ECF -> 1/4 Plasma, 3/4 Interstitial - Age
- Body water decreases with age - Gender
- Body water higher in males
What are the buffer systems in the BLOOD?
- Carbonic acid/Bicarbonate system
- Main buffer - Plasma proteins
- Free carboxyl and amino groups - Haemoglobin
- Imidazole groups of histidine residues
- Deoxygenated Hb better than oxygenated Hb
Explain the carbonic acid/bicarbonate system
- H2CO3 H + HCO3
- Reaction sped up in the presence of carbonic anhydrase found intracellularly
- Increase acid/H in blood will shift the equilibrium to the left -> Forms more carbonic acid
- Increase OH in blood will shift the equilibrium to the right -> To replace H used up with OH to form H20 - Buffering system linked to
- Renal system -> Removes HCO3
- Respiratory system -> Removes CO2
What are the major buffers in CELLS and how do they work?
- Hprotein H + Protein
2. H2PO4 H + HPO4
Describe the Henderson-Hasselbach equation
pH = pKa + log [A-]/[HA]
- Most effective when [A-]/[HA] = 1, so pH = pKa
Outline the different ways in which a substance can cross a cell membrane.
- Passive
- Diffusion
- Facilitated diffusion - Active
- Endocytosis -> Phagocytosis by leukocytes
- Exocytosis -> Golgi apparatus to extracellular
- Ion channels
- Active transport via transport protein
> Primary active transport - Na/K ATPase pump
> Secondary active transport - Na/glucose transporter
Can you please explain the process of secondary active transport?
- The movement of an ion down its electrochemical gradient provides energy to another substrate/ion to move against its electrochemical gradient
- Eg. Na/glucose transporters, Na/amino acids transporters
Describe the Na/K pump
- Energy-dependant pump requiring ATP to ADP as energy source
- Transports 3Na out of cell + 2K into cell against its electrochemical gradient for each ATP molecule
Describe the synthesis and metabolism of cAMP. Discuss the function of cAMP.
- Cyclic adenosine monophosphate
- Intracellular secondary messenger
- Formed from ATP by adenyl cyclase into cAMP
- Metabolised by Phosphodiesterase - Functions
- Intracellular secondary messenger
- Stimulates protein synthesis
- Activates cAMP-related element-binding protein (CREB) to alter transcription of genes
What are the major factors determining plasma glucose level? List the hormones which affect plasma glucose levels.
- Overall determined by intake/glucose entering blood stream vs output/glucose leaving blood stream
- Dietary carbohydrate intake
- Cells uptake of glucose
- Liver glycogenolysis, gluconeogenesis, glycogenesis
- Renal filtration and reabsorption of glucose
- Hormonal effects -> insulin, glucagon, cortisol, thyroid hormone - Hormones affecting glucose level
- Reduce BSL -> Insulin, Insulin-like growth factor 1 and 2
- Increase BSL -> Glucagon, Cortisol, Catecholamines
What are the potential pathways for glucose metabolism in the body.
- Aerobic
- Anaerobic
- Glycogen
- Pentoses
What are the types of immunoglobulin and clinical significance of each
- Immunoglobulin A
- Found in mucous membranes
- Important in mucous secretions - Immunoglobulin D
- Antigen recognition by B cells - Immunoglobulin E
- Anaphylaxis
- Histamine release by mast cells and basophils - Immunoglobulin G
- Infection causing complement activation
- Crosses the placenta and breast milk - Immunoglobulin M
- Infection causing complement activation
- First to be produced
- Largest immunoglobulin
Draw a typical immunoglobulin molecule and label the parts
- Fab = Antigen-binding portion
- Antigen-binding site
- Fc = Effector portion
- Hinge
- Variable region
What are the features of innate vs acquired immunity?
- Innate immunity
- Defence mechanism present even before infection
- E.g: Phagocytes, NK cells, complements
- Important in early phases of infection
- Triggered by cellular receptors -> Toll-like receptors - Acquired immunity
- Defence mechanism against infection
- Cellular mediated -> T cells -> Recognizes antigen on antigen-presenting cells (APC), major histocompatibility complex (MHC), human leukocyte antigen (HLA) -> Protects against intracellular microbes
- Humoral mediated -> B cells -> Protects against extracellular microbes -> Releasing antibodies
How do cells communicate with one another?
- Cell-to-cell
- Gap junctions - Chemical mediators in the ECF
- Neural -> Neurotransmitters in synapses
- Autocrine -> Cell produces messenger that acts on itself
- Paracrine -> Cell produces messenger that acts on neighbouring cells
- Endocrine -> Hormone and growth factor secreted from another site and circulating in blood or lymph
- Juxtacrine -> Molecules attached to receptor of membrane that attaches to another cell
How do receptors respond to variations in messenger?
- Upregulation of receptors
- Deficient messenger causes increase in receptors - Downregulation of receptors
- Excess messenger causes decrease in receptors
How do messengers act? What are the actions of second messengers?
- Open or close ion channels
- Produce cAMP
- Produce cGMP
- Increase activity of tyrosine kinase
- Activates phospholipase-C to produce intracellular IP3, DAG
- Increase serine, threonine
Name the principal ketone bodies. How are ketone bodies produced and metabolised? In which clinical situation do they accumulate in the body?
- Principal ketone bodies are
- Acetoacetate
- Acetone
- B-hydroxybutyrate - Metabolism of ketone bodies
- Produced in mitochondria of liver and all tissues
- Substrate -> Fatty acids, AcetylCoA
- Fatty acids undergo B-oxidation to form AcetylCoA -> Enters citric acid cycle -> Yields 11 ATP, 1 GTP - Ketones accumulate in ketosis metabolic acidosis during
- Starving/fasting
- Diabetes (T1DM)
- High fat low carbohydrate diet
Describe the structure, mechanism of action and function of the Na/K pump
- Structure
- Antiport
- 2a + 2b subunits
- a-subunit binds Na + ATP intracellularly and K extracellularly
- b-subunit does not have Na or K binding site - Mechanism of action
- Na binds to a-subunit intracellularly
- ATP also binds to a-subunit intracellularly
- ATP converted to ADP
- Causes change in protein configuration
- Na expelled out of cell
- K then binds to a-subunit extracellularly
- Dephosphorylates a-subunit to return protein to original configuration
- K released into cell - Function of pump
- Maintains electrochemical gradient -> Pumping 3 Na out, 2 K in
- Co-transport of other molecules -> Glucose in small intestine
What is normal serum osmolality? What substances contribute to serum osmolality? How does plasma differ in composition intracellularly vs extracellularly?
- Normal serum osmolality is 290mOsm/L
- Substances
- Mainly ions (270mOsm) -> Na, K, Cl, HCO3
- Rest (20mOsm) -> Other cations, anions, urea, glucose, protein - Difference in plasma composition
- Intracellularly -> High K, PO4, proteins
- Extracellularly -> High Na, Cl
What is the difference between diffusion and osmosis? Define tonicity.
- Diffusion is
- Movement of solutes through semi-permeable membrane down its concentration gradient
- Governed by Fick’s Law - Osmosis is
- Movement of SOLVENT/water molecules through membrane impermeable to solutes
- Down its concentration gradient to area of high concentration of SOLUTES - Tonicity is osmolality of a solution relative to plasma osmolality
- Isotonic -> Same osmolality as plasma
- Hypotonic -> Lower osmolality than plasma
- Hypertonic -> Higher osmolality than plasma
What is the genesis of the membrane potential?
- Due to difference in concentration and electrochemical gradient of Na + K intracellularly and extracellularly
- Maintained by Na/K pump
- Pumps 3 Na out and 2 K in
What are the phases of protein synthesis? Describe the process of protein secretion from cells.
- Protein synthesis has 2 phase
- Transcription of DNA into mRNA in nucleus
- Translation of mRNA into amino acid chain by ribosome with help of tRNA in cytoplasm - Protein secretion has 2 pathways
- Amino acid/polypeptide produced are cleaved and secreted out of cell by ATP-dependent membrane transporters
- Amino acid/polypeptides are transporters into endoplasmic reticulum to be modified, packaged and secreted by exocytosis
