Cellular Biology Flashcards
What is the role of SER?
Synthesis of carbs and lipids, storage of molecules and drug detoxification in the liver and kidneys
What is the role of RER?
Ribosomes: mRNA –> protein
ER: folds and modifies proteins produced by ribosomes
What is the role of the Golgi apparatus?
Synthesis and packaging of secretions (packing enzymes into vesicles for exocytosis)
What is the role of lysosomes?
Originate at Golgi and contain digestive enzymes, work to defend against disease, remove debris (autophagy and autolysis)
What is the role of peroxisomes?
Originate at RER and are involved in fatty acid metabolism and detoxification of free radicals
What does the cell cytoskeleton consist of?
Actin microfilaments, intermediate filaments, tubulin micotubules
What is the role of actin microfilaments in the cell cytoskeleton?
Maintain cell shape, facilitate movement (with aid of myosin) for organelle and vesicle movement
What is the role of intermediate filaments in the cell cytoskeleton?
Provide tensile strength
What is the role of microtubules in the cell cytoskeleton?
Provide cell scaffold and forms tracks for movement and mitotic spindle
What is hyaluronic acid a type of?
Glycosaminoglycan
What type of collagen is in the basement membrane?
Type 4 (floor, four)
What is elastin?
Polymer of tropoelastin associated with fibrillin to form elastic fibres
What is fibronectin?
Present in ECM and plasma (soluble form) and works to bind cells and ECM, cellular attachment and matrix organisation (guides cell migration, development and repair)
What are the principle components of the extracellular matrix?
GAGs, proteoglycans, fibrous proteins and basement membrane
What are tight junctions?
Cellular junction which prevents molecules from passing across the epithelium
What are adherens junctions?
Tethers adjacent cells together
What are desmosomes?
Resists mechanical stress
What are gap junctions?
Allow passage of small molecules between adjacent cells
What are hemidesmosomes?
Anchors epithelia to the basement lamina
Why are non-cilia present on nearly all cells?
Act as sensory antennae
What are pseudopodia?
Cell protrusions which are involved in cell crawling
Outline the 4 main phases of the cell cycle
G1 and G2 - allows monitoring of internal and external environment to ensure suitable to progress, as well as checkpoints
S - chromosome duplication
M - mitosis
Describe prophase
Chromatin condenses, nucleolus disappears, nuclear envelope breaks down, sister chromatids join at centromere, centrioles move to opposite poles, microtubules form radiating array and chromosomes attach by a kinetochore
Describe metaphase
Chromosomes align in mid-line, cohesion holds chromatids together and at this point is broken down except for at centromere
Describe anaphase
Securin hydrolysed (inhibitor of separase) –> separase hydrolyses remaining cohesion separating the sister chromatids –> elongation of polar microtubules pulls chromatids to opposite poles
Describe telophase
Chromosomes reach opposite poles, chromatin uncoils, nuclear envelope reforms, contractile ring of actin and myosin pinches the cell until it cleaves into two daughter cells
When does random recombination occur?
In prophase I between homologous pair of non-sister chromatids due to crossing over of chromatid tails at the chiasmata
What is the role of cyclin-dependent kinases (CDKs) in the cell cycle?
Act at different parts of the cell cycle and must be active in order for the cell cycle to progress. Cyclins activate CDKs and cyclin-dependent kinase inhibitors (CKIs) inhibit CDKs and prevent cell cycle progression
Name the three checkpoints in the cell cycle
End of G1, End of G2, Spindle checkpoint (metaphase of M)
Describe the checkpoint just prior to the S phase in mitosis
If there is an issue in the environment (growth factors, cell size, DNA damage, nutrients), progression is halted by CKI p16 which inhibits CDK4 OR 6 so that it can’t be activated.
Describe the checkpoint at the end of G2 phase in mitosis
If there is an issue in the environment (cell size, DNA damage, DNA replication), then phosphatase is inactivated in order to inhibit the cyclin-CDK
If there is no issue then a phosphatase is activated to remove the inhibitory phosphates ont he CDK1-cyclin B complex to allow cell cycle progression
Describe the spindle checkpoint in mitosis
Occurs during metaphase whereby the tension in the microtubules is ‘sensed’ and if it is normal then this initiates entry into anaphase
What may cause retinoblastoma?
Mutation in RB1 gene leading to non-functional Rb protein in retinal cells and E2F proteins are therefore free to drive cell cycle (proliferation) with the need for CDK activation –> tumour of the retina
Outline 2 anti-mitotic chemotherapy drugs
Vinca alkaloids - prevent microtubule formation
Taxanes - prevent microtubule disassembly
Outline 2 biologic chemotherapy drugs
Antibody-drug conjugate - antibody works to target the drug to tumour cells
Antibody-GFR inhibitors - antibodies bind to growth factor receptors to prevent signalling
Describe what happens during apoptosis
Membrane blebbing –> membrane shrinkage –> apoptotic body formation –> nuclear collapse (fragmentation and chromatin condensation) –> engulfment by macrophages
Which molecules are involved in the initiation and execution of apoptosis?
Caspases
Initiation - caspase 2, 8 and 9
Execution - caspase 3, 6 and 7
What is involved in necrosis?
Membrane disruption, respiratory poison and hypoxia lead to ATP depletion, metabolic collapse, cell swelling and rupture –> inflammation
Name the two stages of differentiation
Specification and differentiation
Describe the two stages of differentiation
Specification - when a cell is capable of differentiating autonomously when placed in a neural environment but not when in a non-neutral environment (reversible process)
Diferentiation - cell differentiates autonomously when placed even into another embryonic region
Describe autocrine signalling
When a ligand binds to receptors on the same cell or group of cells
Describe contact-dependent signalling
When a membrane-bound signalling molecule binds to a complementary target cell
Describe paracrine signalling
Where the cell releases signals to the local cells
Describe synaptic signalling
When there is neurotransmitter release over the synapse to the dendrites
Describe endocrine signalling
Secretes chemical signal into the blood/lymphatics where it circulates and reaches distant target cells
Outline the intracellular pathway triggered by receptor binding
Signal + receptor bind –> relay proteins in cell –> adaptor proteins (don’t convey signal, just connect) –> relay proteins –> messenger proteins (convey from one part of cell to another) –> amplifier proteins –> transducer proteins (signal conversion) –> bifurcation proteins spread signals between many pathways –> integrator protein (integrate different signals) –> latent gene regulatory proteins activated near cell surface –> migrate to the nucleus to stimulate gene transcription
How does ACh action differ on cardiac and skeletal muscle?
Inhibitory effect on cardiac muscle (slows HR), excitatory effect on skeletal muscle (contraction)
How can signals elicit different responses in cells?
Varies according to receptor proteins, particular signal subset and intracellular machinery
How does an enzyme active site bind to the substrate?
Has amino acid side chains which align to bind the substrate through hydrogen bonding, salt bridges and hydrophobic interaction
Define absolute specificity
Enzyme which only catalyses one type of reaction for a single substrate
Define group specificity
Enzyme which catalyses one type of reaction for similar substrates
Define linkage specificity
Enzyme which catalyses one type of reaction for a specific type of bond
What is a cofactor?
Non-protein component of an enzyme required for it’s activity
What is a prosthetic group?
A non-dissociable co-factor
What is an apoenzyme?
An enzyme lacking a cofactor, and is therefore inactive
What is a holoenzyme?
An enzyme with a cofactor, an activated enzyme
What is a coenzyme?
A dissociable non-protein component which participates in the enzyme reaction and frequently interacts with multiple enzymes
What is an isoenzyme?
Different forms of an enzyme, which catalyse the same reaction, in different tissues of the body
What is a proenzyme/zymogen?
When an enzyme is initially synthesised in an inactive form and requires proteolytic conversion to activate
How do competitive inhibitors work?
Have a structure similar to the substrate and compete for the active site of the enzyme
How do non-competitive inhibitors work?
Bind to an allosteric site of the enzyme and distorts the shape of the active site to prevent substrate binding
Which molecule is involved in adhering a cell to it’s basement membrane?
Laminin
Describe the structure of collagen
Every 3rd amino acid is glycine which allows it to have a tight, coiled structure
Why are fatty acids important in the body?
Energy store, precursors of phospholipids (cell membrane), needed as we can’t make omega 3 or 6 fatty acids,
Why is cholesterol important in the body?
It’s a precursor of vitamin D and bile acids
Describe how statins and phytosterols work
Statins - target cholesterol synthesis to prevent amount
Phytosterols - reduce cholesterol uptake from the diet
What is a secondary active transporter?
Where uphill solute transport is possible if coupled to the downhill movement of another solute/ion
What is a primary active transporter?
Uphill solute transport possible if coupled to ATP hydrolysis
Define symport and antiport
Symport - when the transport molecule and ion move in the same direction
Antiport - when the transport molecule and ion move in different directions
What is CFTR and what’s it’s function?
Chloride ion channel on the plasma membranes of the lung, intestine and pancreatic epithelia which is required to release chloride in order to allow outflow of sodium and water to reduce the viscosity of surface mucus
What is the consequence of a CFTR mutation?
Viscous mucus reduces function of epithelial cells, causes chronic infection, inflammation and fibrosis
What is a chiral carbon?
A carbon atom that covalently bonds to 4 different groups
What are the different types of enantiomer?
D-form (most common) - when the -OH group is attached to the right of the chiral carbon
L-form - when the -OH group is attached to the left of the chiral carbon
What is an amino sugar?
A sugar which has an amine (NH2) group in place of -OH in a sugar molecule
Describe the structure of glycogen
Glucose monomers with alpha-1,4 glycosidic bonds and alpha-1,6 glycosidic bonds for branches
What is heparin?
Molecule that activates antithrombin III (the main inhibitor of thrombin and factor Xa) allosterically to thin the blood (an anticoagulant)
What are bacterial lipopolysaccharides (LPS)?
Present on bacteria, and stimulates innate immune cells via TLR4 recognition of the bacterial LPS and causes an inflammatory reaction and a signalling cascade designed to clear infection
