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HNC Cell Biology
LO3
| Question | Answer |
|---|---|
| Why do cells need to communicate with other cells? | To regulate: Nutrition, temperature response, metabolism rate, Excretion of waste & toxins, Repair when damaged, Identification as part of the body |
| How does body distinguish its own cells from invading cells | Through recognition of surface markers (antigens) found on all cells |
| What types of molecule are used as cell surface markers? | Glycoproteins (protein with attached carbohydrate group) and Glycolipids (lipid with an attached carbohydrate). |
| What structures are involved in communication between adjacent cells? | Through direct contact using structures such as desmosomes, tight junctions, gap junctions and plasmodesmata (plants only) |
| What are desmosomes? | localised patches that hold two cells together and allow materials to move around them. They connect the cytoplasm of two cells and form links through connecting filaments of cytoskeleton. |
| What are tight junctions? | Structures that form a leak-proof seal so that material has to enter cell from the apical surface of a tissue to the basolateral surface through a cell and can't pass between the cells. |
| What are gap junctions? | They are intracellular channels made up of 4 or 6 transmembrane proteins called connexins that connect the cytoplasm of neighbouring cells, and allow passage of ions, amino acids & sugars directly from cell to cell. |
| What are plasmodesmata? | Cylinder-like bridges connecting one cell wall with the other, lined by plasma membrane allowing exchange of ions, sugars, amino acids, RNA and small proteins between the cytoplasm of two adjacent PLANT cells. |
| What human body processes are gap junctions vital for? | Rhythmic contraction of the heart, communication via nerve impulses, contractions during labour |
| What are the two types of signalling between distal human cells? | Communication via chemical messengers (hormones) and communication via nerve impulses |
| What are hormones? | Small molecules released by endocrine glands that have an effect on a target tissue. |
| What does a hormone attach on a target tissue? | Hormone attaches to a hormone receptor (target molecule) |
| How does a hormone get to the target tissue? | Hormone gets to target tissue through the bloodstream |
| How specific is the hormone/hormone receptor interaction? | Hormone/hormone receptor interaction is very specific. A hormone can only have effects on cells that possess receptors for that hormone. |
| How many steps are there in the hormonal signalling (signal transduction) cascade | Three steps: Reception, Signal transduction and Response |
| What happens during Reception step of a signalling cascade? | Chemical signal (hormone a.k.a. ligand) finds its receptor & binds to it |
| What happens during Signal transduction step of a signalling cascade? | Binding of hormone (ligand) causes the receptor molecule to change shape, which activates an effector e.g. an enzyme |
| What happens during Response step of a signalling cascade? | depending on a signalling molecule an enzyme can be activated or inhibited or a Gene can be transcribed or silenced. |
| What are the two types of hormones by their chemical properties? | Water soluble peptide hormones (hydrophilic) and NON water soluble steroid hormones (hydrophobic) |
| Where is the hormone receptor for hydrophilic hormones found? | At the surface of a cell membrane |
| Why can't peptide hormones cross the cell membrane? | Because peptide hormones are hydrophilic and the lipid bilayer is hydrophobic. |
| What happens when a peptide protein binds a G-coupled hormone receptor? | Hormone receptor changes shape and attracts G-protein. GDP on G-protein is replaced by GTP. G-protein with GTP attached is activated. |
| What does activated G-protein do? | Activated G-protein goes to an effector (membrane bound enzyme). |
| What happens after activated G-protein is bound to effector? | Effector is activated and makes many molecules of second messenger (cAMP) |
| What does second messenger do? | Second messenger activates other cell enzymes and causes a response. |
| How is G-protein inactivated? | GTP on the G-protein is hydrolysed by a GTP-ase enzyme and converted to GDP. This inactivates G-protein |
| Name an example of an enzyme linked hormone receptor | Insulin receptor |
| Where is the receptor for hydrophobic hormones found? | Receptor for hydrophobic hormones is found on the inside of the cell |
| What happens in steroid hormone signalling? | Steroid hormone crosses the membrane, binds intracellular receptor which activates gene transcription in the nucleus. |
| What happens when the action potential reaches the end of a neurone? | Neurotransmitter is released and diffuses across the synapse |
| What happens when neurotransmitter reaches receptors on postsynaptic neurone? | Neurotransmitter causes Na+ channels open in the membrane of postsynaptic neurone and Na+ ions enter the cell |
| What effect does Na+ ions entering the nerve cell have? | The inside of the nerve cell becomes more positive |
| What happens to a nerve cell when the positive charge inside it reaches threshold value? | All the Na+ channels open more Na+ ions enter the cell and action potential is propagated. |
| How is the level of hydration sensed within human body? | Level of hydration is sensed by osmoreceptors in the pituitary gland |
| What hormone is produced by pituitary gland to regulate level of hydration in human body? | ADH (antidiuretic hormone) |
| What is the target tissue of ADH? | Target tissue of ADH are the tubules in the kidneys |
| What effect does ADH have on tubules in the kidneys? | It causes the tubules to re-absorb more water. |
| What effect does increased ADH have on urine? | Increased ADH makes urine more concentrated |
| List three examples of diseases caused by disruption to cell signalling? | Diabetes, Cancer, Parkinsonism |
| What can errors occur in the cell signalling pathway? | At the level of ligand, at the receptor level and the response level within the cell |
| What happens if the ligand is missing or mutated? | Without ligand No signal reaches the receptor |
| What happens if the receptor is missing, mutated or desensitized? | If receptor is missing ir desensitized even if ligand is present the signal is not passed on |
| What happens if the signalling pathway is disrupted at response level within the cell? | There is no response even if the ligand is bound to receptor |
| What causes type 1 diabetes? | Beta cells of pancreas are destroyed by the body |
| What effect does a lack of pancreas beta cells have on insulin production | Without pancreas beta cells causes insulin is not produced |
| What happens if there is no insulin produced? | Insulin does not bind to insulin receptor and glucose is not removed from the blood. Blood glucose level increases |
| Is insulin produced in type 2 diabetes? | Insulin is produced in type 2 diabetes, beta cells of pancreas are healthy. |
| What causes type 2 diabetes? | Insulin receptor is desensitized so even though insulin is present the glucose is not removed from the blood |
| Why is insulin receptor desensitized in type 2 diabetes? | insulin receptor becomes desensitized because of the high levels of blood glucose over many years due to poor diet and lack of exercise. |
| What causes cancer? | Uncontrolled division of cells brought on by mutations |
| What protein acts as a checkpoint for mutations | p53 acts as a checkpoint for mutations and stops cell division if any mutations are present |
| Why does mutation in p53 lead to increased chance of cancer? | Without p53 cells continue to divide even if mutations are present in DNA. This can cause new mutations to accumulate |
| What causes Parkinson's disease? | Parkinson's disease is caused by the lack of dopamine neurotransmitter in substantia nigra area of the brain |
| What does dopamine do? | Dopamine acts to inhibit acetylcholine release |
| What does acetyl choline do? | Acetylcholine causes muscle cells to move |
| What effect does an imbalance of dopamine and acetylcholine in Parkinson's have on movement? | Movement lacks coordination and control |
Created by:
dr.prorocic