MDSC 515 MAIN EXAMINATION SET 2025/2026
QUESTIONS AND SOLUTIONS GRADED A+ TIP
✔✔transcription factors - ✔✔-signal transduction pathways influence gene transcription
through activation and nuclear localization of transcription factors
-cause up regulation of genes or have a wide-spread effect on gene expression
-modular - one component acts with DNA and the other with proteins
-alterations in these pathways can lead to cancer or other diseases (c-MYC in
tumorigenesis - this is a growth signal it when it is inappropriately activated then there is
excessive growth)
✔✔microRNA - ✔✔-transcribed into RNA but not translated into proteins
-modulates the translation of target mRNA into proteins
-is silenced post-transcription - either cleaved or repressed
-DICER aids in its maturity (cleaves RNA into miRNA which guides target mRNA for
degradation)
-mRNA degradation or reduced protein production
✔✔DICER1 syndrome - ✔✔-mRNA associated with these mutations - can lead to
tumours
-juvenile granulose cell tumour, sertoli-leydig cell tumour and cystic nephroma
✔✔long non-coding RNA - ✔✔-modulate gene expression in many ways
-XIST: transcribed from the X chromosome and plays a role in its inactivation
-forms a cloak on the x-chromosome from which it was transcribed -causes x-
inactivation
✔✔epigenetic factors - ✔✔-affect transcription and translation but not directly the DNA
-factors beyond the coding/non-coding portion of DNA that affect gene expression
✔✔Histones - ✔✔-DNA wrapped around a central structure
-heterochromatin is condensed and euchromatin is dispersed
-areas that are unwound control gene expression (euchromatin)
-modifications: methylation (activation or repression), acetylation (activation) and
phosphorylation (activation or repression)
-DNA methylation - transcriptional silencing of methylated DNA
-many of these processes are reversible so theoretically possible to alter dysregulated
processes in diseases
✔✔cytoplasmic organelles - ✔✔-housekeeping functions are compartmentalized in
membrane bound organelles
-keeps the cell safe from activities of certain enzymes and chemical species
-creation of unique intracellular environments
,✔✔cytoskeleton - ✔✔-ability of a cell to adopt a certain shape, maintain polarity and
organize relationships of intracellular organelles
-classes of proteins: thin filaments (actin), intermediate filaments, thick filaments
(myosin) and microtubules (connecting cables for molecular motor proteins during
transport)
✔✔thin filaments - ✔✔-helical polymers of singular globular actin or G-actin
with the help of ATP, G-actin can polymerize into F-actin
-actin filaments are polar and grow at different rates at the different ends
-polymer can continuously grow at plus end and disassemble at its minus end
-F-actin into bundles that control cell shape and movement
✔✔thick filaments - ✔✔-different subtypes of myosin are found in different types of
tissue
-move along actin filaments
-myosin has a pivot point it bends around - acts as a molecular motor
-myosin in muscle is myosin II subfamily - dimers, each head binds two subunits -
myosin light chains
-actin and myosin in muscle cells lead to contraction of muscle
✔✔actin and myosin - ✔✔-isoforms present in almost all cell types
-fibroblast-like cells - utilize actin stress fibres in wound healing
-motile cells - cell locomotion
-neurons and epithelial cells - intricate actin and myosin filament networks - cell can
extend processes to distant locations
-form adhesion belts at the level of tight junctions
✔✔intermediate filaments - ✔✔-strings that connect different parts of the cells together
-tensile strength - allow cells to bear mechanical stress
-major structural proteins in skin and hair
-large family with tissue specific patterns of expression
✔✔microtubule structure - ✔✔-polymerized heterodimers of alpha and beta tubular
proteins in constantly elongating or shrinking hollow tubes with a defined polarity
-circumferential wall with a hollow core
-plus end has three times the growth rate of the minus end
✔✔microtubule function - ✔✔-consisits of two centroles that are oriented at right angles
toward each other
-minus end associates with proteins that surround the centrosome and the plus ends
radiate through the cytoplasm
-multiple functions: framework of membranes, project down the axon of neurons, play a
role in alignment of chromosomes and separation during cellular division
✔✔microtubules in motility - ✔✔-cilium formed by microtubules
,-central structure connected to outer tubules by radial spokes
-outer tubules connect to neighbours by dynein or nexin
✔✔cytoskeleton in cell-cell/cell-matrix interactions - ✔✔-adhesion to extracellular matrix
is through integrins within hemidesmosomes
-inter-epithelial adhesion (interactions of cells and their cytoskeletons): tight junctions,
desmosomes (anchoring junctions), adhering junctions and gap (communicating)
junctions
-creation of apical and basolateral surface for cell polarity
✔✔tight junctions - ✔✔-seal adjacent cells together to create a continuous barrier
-restricts movement of ions and molecules between cells
-forms a mesh-like network between cells
-separation of apical and basolateral domains to maintain cell polarity
✔✔anchoring junctions - ✔✔-attaches cells and their cytoskeletons to other cells or to
the extracellular matrix through transmembrane glycoproteins called cadherins
-anchor proteins link the cytosolic domains of cadherins to the intermediate filaments
-when attaching between cells = desmosomes
-when attaching cell to the extracellular matrix = hemidesmosomes - connector proteins
are called integrins
✔✔adhering junctions - ✔✔-belt that encircles an entire epithelial cell just below the
tight junction
-mediated by extracellular domains of the cadherin family
-epithelial cells form a polarized epithelium if the cells are close enough to form
adhering junction
-disruption leads to loss of epithelial organization - can cause metastasis
✔✔gap junctions - ✔✔-connect the cytosol of one cell to another
-chemicals or signals to pass from one cell to the other
-pores
permeability affected by pH and calcium
-critical for cell-cell communication
✔✔endoplasmic reticulum - ✔✔-site of synthesis of secreted proteins, transmembrane
proteins and plasma membranes for organelles - initial site of synthesis for all molecules
destined for export
-continuous sheet around a lumen which has domains: rough has ribosomes and
smooth does not
✔✔Rough endoplasmic reticulum - ✔✔-membrane bound ribosomes translate mRNA
into protein
-proteins secreted into lumen and integrated into the membrane
-signal sequences on the N-terminus
, chaperone molecules keep protein molecules in the ER until modification into the proper
conformation - if this fails it is degraded
✔✔exported proteins - ✔✔-signal sequences are localization signals for ribosomes
-signal recognition particle binds to a signal sequence and localizes to the receptor
-once they bind the translocon opens its tunnel and the protein travels completely
through the membrane and does not come in contact with the core just ends up on the
other side
✔✔membrane bound proteins - ✔✔-do not fully translocate through the RER membrane
-carry a stop-transfer sequence - translocon dissembles and the hydrophobic
membrane segment goes to the hydrophobic core
-there can also be start-transfer sequence - acts both to bind a signal recognition
particle and hydrophobic membrane spanning segment
✔✔transition to the golgi - ✔✔-secretory and membrane proteins congregate in the
transitional zone of the RER
-vesicles pick off from the transitional zine and fuse with the golgi complex
-modified from cis to trans (groups go from same side of double bond to opposite sides)
✔✔Golgi apparatus - ✔✔-step-wise glycosylation of lipids and proteins
-cis-golgi network recycles proteins back to the RER
-trans-golgi network dispatched proteins to other organelles and the plasma membrane
or to secretory vesicles for extracellular release
-exocytosis can be constitutive (continuous release to maintain homeostasis) or
regulated (occurs in response to a specific stimuli)
-golgi is especially prevalent in cells for secretions - goblet cells, bronchial epithelium,
plasma cells
✔✔smooth ER - ✔✔-the transition zone from the RER to transport vesicles moving to
the golgi
-lipid and steriod synthesis in specialized cells
-more prevalent in cells that synthesize steroid hormones or cells that catabolize lipid-
soluble molecules - contains enzymes (p450) to modify cholesterol hormones
-sequesters intracellular calcium which is involved in a lot of cellular signalling pathways
-in muscles - the sarcoplasmic reticulum is specialized and important in the contraction
and relaxation of muscles
✔✔lysosomes - ✔✔-contain enzymes for recycling components - acid hydrolyses
-membrane is resistant to the enzymes within and has proton pumps to maintain the
acidic pH inside
-lysosome enzymes initially synthesized in the ER and modified in the golgi before
being transported in vesicles to the lysosomes
✔✔autophagy - ✔✔-cells accumulate waste during metabolism
QUESTIONS AND SOLUTIONS GRADED A+ TIP
✔✔transcription factors - ✔✔-signal transduction pathways influence gene transcription
through activation and nuclear localization of transcription factors
-cause up regulation of genes or have a wide-spread effect on gene expression
-modular - one component acts with DNA and the other with proteins
-alterations in these pathways can lead to cancer or other diseases (c-MYC in
tumorigenesis - this is a growth signal it when it is inappropriately activated then there is
excessive growth)
✔✔microRNA - ✔✔-transcribed into RNA but not translated into proteins
-modulates the translation of target mRNA into proteins
-is silenced post-transcription - either cleaved or repressed
-DICER aids in its maturity (cleaves RNA into miRNA which guides target mRNA for
degradation)
-mRNA degradation or reduced protein production
✔✔DICER1 syndrome - ✔✔-mRNA associated with these mutations - can lead to
tumours
-juvenile granulose cell tumour, sertoli-leydig cell tumour and cystic nephroma
✔✔long non-coding RNA - ✔✔-modulate gene expression in many ways
-XIST: transcribed from the X chromosome and plays a role in its inactivation
-forms a cloak on the x-chromosome from which it was transcribed -causes x-
inactivation
✔✔epigenetic factors - ✔✔-affect transcription and translation but not directly the DNA
-factors beyond the coding/non-coding portion of DNA that affect gene expression
✔✔Histones - ✔✔-DNA wrapped around a central structure
-heterochromatin is condensed and euchromatin is dispersed
-areas that are unwound control gene expression (euchromatin)
-modifications: methylation (activation or repression), acetylation (activation) and
phosphorylation (activation or repression)
-DNA methylation - transcriptional silencing of methylated DNA
-many of these processes are reversible so theoretically possible to alter dysregulated
processes in diseases
✔✔cytoplasmic organelles - ✔✔-housekeeping functions are compartmentalized in
membrane bound organelles
-keeps the cell safe from activities of certain enzymes and chemical species
-creation of unique intracellular environments
,✔✔cytoskeleton - ✔✔-ability of a cell to adopt a certain shape, maintain polarity and
organize relationships of intracellular organelles
-classes of proteins: thin filaments (actin), intermediate filaments, thick filaments
(myosin) and microtubules (connecting cables for molecular motor proteins during
transport)
✔✔thin filaments - ✔✔-helical polymers of singular globular actin or G-actin
with the help of ATP, G-actin can polymerize into F-actin
-actin filaments are polar and grow at different rates at the different ends
-polymer can continuously grow at plus end and disassemble at its minus end
-F-actin into bundles that control cell shape and movement
✔✔thick filaments - ✔✔-different subtypes of myosin are found in different types of
tissue
-move along actin filaments
-myosin has a pivot point it bends around - acts as a molecular motor
-myosin in muscle is myosin II subfamily - dimers, each head binds two subunits -
myosin light chains
-actin and myosin in muscle cells lead to contraction of muscle
✔✔actin and myosin - ✔✔-isoforms present in almost all cell types
-fibroblast-like cells - utilize actin stress fibres in wound healing
-motile cells - cell locomotion
-neurons and epithelial cells - intricate actin and myosin filament networks - cell can
extend processes to distant locations
-form adhesion belts at the level of tight junctions
✔✔intermediate filaments - ✔✔-strings that connect different parts of the cells together
-tensile strength - allow cells to bear mechanical stress
-major structural proteins in skin and hair
-large family with tissue specific patterns of expression
✔✔microtubule structure - ✔✔-polymerized heterodimers of alpha and beta tubular
proteins in constantly elongating or shrinking hollow tubes with a defined polarity
-circumferential wall with a hollow core
-plus end has three times the growth rate of the minus end
✔✔microtubule function - ✔✔-consisits of two centroles that are oriented at right angles
toward each other
-minus end associates with proteins that surround the centrosome and the plus ends
radiate through the cytoplasm
-multiple functions: framework of membranes, project down the axon of neurons, play a
role in alignment of chromosomes and separation during cellular division
✔✔microtubules in motility - ✔✔-cilium formed by microtubules
,-central structure connected to outer tubules by radial spokes
-outer tubules connect to neighbours by dynein or nexin
✔✔cytoskeleton in cell-cell/cell-matrix interactions - ✔✔-adhesion to extracellular matrix
is through integrins within hemidesmosomes
-inter-epithelial adhesion (interactions of cells and their cytoskeletons): tight junctions,
desmosomes (anchoring junctions), adhering junctions and gap (communicating)
junctions
-creation of apical and basolateral surface for cell polarity
✔✔tight junctions - ✔✔-seal adjacent cells together to create a continuous barrier
-restricts movement of ions and molecules between cells
-forms a mesh-like network between cells
-separation of apical and basolateral domains to maintain cell polarity
✔✔anchoring junctions - ✔✔-attaches cells and their cytoskeletons to other cells or to
the extracellular matrix through transmembrane glycoproteins called cadherins
-anchor proteins link the cytosolic domains of cadherins to the intermediate filaments
-when attaching between cells = desmosomes
-when attaching cell to the extracellular matrix = hemidesmosomes - connector proteins
are called integrins
✔✔adhering junctions - ✔✔-belt that encircles an entire epithelial cell just below the
tight junction
-mediated by extracellular domains of the cadherin family
-epithelial cells form a polarized epithelium if the cells are close enough to form
adhering junction
-disruption leads to loss of epithelial organization - can cause metastasis
✔✔gap junctions - ✔✔-connect the cytosol of one cell to another
-chemicals or signals to pass from one cell to the other
-pores
permeability affected by pH and calcium
-critical for cell-cell communication
✔✔endoplasmic reticulum - ✔✔-site of synthesis of secreted proteins, transmembrane
proteins and plasma membranes for organelles - initial site of synthesis for all molecules
destined for export
-continuous sheet around a lumen which has domains: rough has ribosomes and
smooth does not
✔✔Rough endoplasmic reticulum - ✔✔-membrane bound ribosomes translate mRNA
into protein
-proteins secreted into lumen and integrated into the membrane
-signal sequences on the N-terminus
, chaperone molecules keep protein molecules in the ER until modification into the proper
conformation - if this fails it is degraded
✔✔exported proteins - ✔✔-signal sequences are localization signals for ribosomes
-signal recognition particle binds to a signal sequence and localizes to the receptor
-once they bind the translocon opens its tunnel and the protein travels completely
through the membrane and does not come in contact with the core just ends up on the
other side
✔✔membrane bound proteins - ✔✔-do not fully translocate through the RER membrane
-carry a stop-transfer sequence - translocon dissembles and the hydrophobic
membrane segment goes to the hydrophobic core
-there can also be start-transfer sequence - acts both to bind a signal recognition
particle and hydrophobic membrane spanning segment
✔✔transition to the golgi - ✔✔-secretory and membrane proteins congregate in the
transitional zone of the RER
-vesicles pick off from the transitional zine and fuse with the golgi complex
-modified from cis to trans (groups go from same side of double bond to opposite sides)
✔✔Golgi apparatus - ✔✔-step-wise glycosylation of lipids and proteins
-cis-golgi network recycles proteins back to the RER
-trans-golgi network dispatched proteins to other organelles and the plasma membrane
or to secretory vesicles for extracellular release
-exocytosis can be constitutive (continuous release to maintain homeostasis) or
regulated (occurs in response to a specific stimuli)
-golgi is especially prevalent in cells for secretions - goblet cells, bronchial epithelium,
plasma cells
✔✔smooth ER - ✔✔-the transition zone from the RER to transport vesicles moving to
the golgi
-lipid and steriod synthesis in specialized cells
-more prevalent in cells that synthesize steroid hormones or cells that catabolize lipid-
soluble molecules - contains enzymes (p450) to modify cholesterol hormones
-sequesters intracellular calcium which is involved in a lot of cellular signalling pathways
-in muscles - the sarcoplasmic reticulum is specialized and important in the contraction
and relaxation of muscles
✔✔lysosomes - ✔✔-contain enzymes for recycling components - acid hydrolyses
-membrane is resistant to the enzymes within and has proton pumps to maintain the
acidic pH inside
-lysosome enzymes initially synthesized in the ER and modified in the golgi before
being transported in vesicles to the lysosomes
✔✔autophagy - ✔✔-cells accumulate waste during metabolism
