Formative Qs Flashcards
Define the terms:
Km
Vmax
Km = substrate conc that gives 1/2 maximal rate
Vmax = max obtainable rate when all active sites are filled with substrate
What is the shape of a graph showing how rate of enzyme catalysed reaction varies with:
Enzyme conc
Substrate conc
What are the axes
With enzyme conc: straight line
With substrate conc: hyperbolic
X (horizontal)= [substrate] or [enzyme]
Y (vertical) = velocity (V)
Distinguish between competitive & non-competitive inhibitor
Competitive: binds to active site of an enzyme. Affects Km of enzyme for substrate
Non-competitive: binds somewhere on enzyme other than active site. Affects vmax of reaction
Give an example of an enzyme regulated allosterically.
Name allosteric activators & inhibitors for this enzyme
Phosphofructokinase (PFK)
Activator: AMP, ADP, fructose 2,6-bisphosphate
Inhibitor: ATP, citrate, H+
Draw a peptide bond
What are the key features of a peptide bond
Trans orientation of C=O & N-H grps
Rigid
Planar
Describe the key features of an alpha helix & explain how its stabilised
Right handed
3.6 aa per turn
R grps lie on outside of helix
Stabilised by H bonds that form btw amide hydrogen & carbonyl oxygen running along length of helix
List the bonds that can maintain the tertiary structure of a protein
Covalent (disulphide) Ionic (salt bridge) Hydrogen bonds Van der Waals interactions Hydrophobic interactions
Explain how a fall in pH can lead to the denaturation of a protein
Will cause change in ionisation state of the side chains of aa’s in the protein
Can affect hydrogen & ionic bond formation, causing changes to protein structure
How would the oxygen dissociation curve for Hb change if concentration of 2,3-BPG was increased
What are the axes for the dissociation curve
Curve shifts to the right
X= pO2 Y= % saturation
Explain what is meant by the Bohr effect & explain its physiological relevance
Lowering affinity of Hb for O2 caused by binding of CO2 or H +
Metabolically active tissues produce CO2 & other acidic compounds (e.g. Lactate)
Causes decrease in affinity of Hb for O2
O2 therefore released at sites of most need
What amino acid change occurs in sickle cell heamoglobin
Glutamate to Valine in beta subunits
Explain why acidosis can precipitate a sickle cell crisis
Causes shift on Hb conformation to favour T state (low affinity)
Exposes hydrophobic patch containing Val residue on surface if molecule
HbS polymerises via hydrophobic region & can trigger sickle cell crisis
GGTCGTACCATCGCT
represent the molecule as a double-stranded DNA molecule (i.e. write
down the given sequence and its complementary sequence) and indicate the polarity.
Assuming that the given sequence is the coding strand, show the mRNA transcript.
What is the enzyme responsible for this process called?
5’GGTCGTACCATCGCT3’
3’CCAGCATGGTAGCGA5’
5’GGUCGUACCAUCGCU3’
RNA polymerase
Name the 3 types of RNA processing that occur in eukaryotic pre-mRNA & indicate the function of each
5’ capping: prevents degradation
3’ tailing/polyadenation: prevents degradation
Splicing: allows diff lvl of regulation of gene expression
What is a ribosome & what is its function
A complex of rRNAs & many proteins
A mini ‘protein factory’, making polypeptides during process of translation by reading mRNA template
How do you calculate risk of a person being a carrier for a trait, where there is information about inheritance patterns in the last 3 generations (2 generations of which, carrier status is not known)
Multiply the risk in the 2 previous unknown generations only
In all secreted proteins, what is contained in:
Pre segment
Pro segement
Pre = signal sequence Pro = after removing signal sequence
In protein modification, what does glycosylation do?
What is N linked & O linked glycosylation
Adds oligosaccharide (sugar), Important for protein folding/stability/interacting with other proteins (gives specificity) N linked = add nitrogen (N glycosidic bind) O linked = add oxygen (O glycosidic bond)
Describe the key features of collagen
Make of 3 alpha polypeptide chains (2x alpha 1, 1x alpha 2)
Primary sequence = glycine-x-y
x & y normally = proline (maintains alpha shape) & hydroxyproline (increases interchain H bonds)
Arranged in a left hand triple helix (n.b. Is not an alpha helix)
Gives high tensile strength
An extracellular protein (needs to be secreted from cell)
Basic unit = tropocollagen
Describe how collagen is synthesised & secreted
Synthesised as preprocollagen in cell RER
(Pre = marks for secretion, pro = prevents formation of collagen fibres in cell)
proline & lysine residues hydroxylated
(Adds OH; need O2, Vit C, Fe2+; stabikised triple helix)
Hydroxylysine residues glycosylated with glucose & galactose
3 pro-alpha chains assemble
Intra & inter chain disulfide bonds form
Forms a triple helix = procollagen
Secreted from Golgi into cytoplasm
Packaged into secretory vesicles & secreted by exocytosis
N & C terminal peptides cleaved by procollagen peptidases = tropocollagen
Tropocollagen molecules assemble into fibrils with crosslinking = mature collagen fibres
What is contained in pre pro insulin
Pre = signal sequence Pro = c peptide Insulin = a & b peptide
Describe the processing of insulin to form active insulin
Why is C peptide a good marker of endogenous insulin
Signal sequence cleaved by signal peptidase - makes pro insulin
C peptide cleaved by endopeptidase - makes insulin
Active insulin = a & b peptides joined by 2 disulphide bridges
C peptide secreted with active insulin
Describe the regulatory mechanisms of the blood clotting cascade
Positive feedback activation:
Thrombin (enzyme making fibrin clot) feeds back and acts on orevious factors (can form clot from small amt of factor)
Inactive zymogens at low conc:
Prevents clotting being activated accidentally
Amplification of signal:
A cascade - enzyme activates other enzymes = increased number of affected molecules
Localised clotting factor to site of damage:
Negative Gla domains on many clotting factors attract Ca2+
Termination of clotting by multiple processes
Describe the methods of termination of the blood clotting cascade
Inhibit enzymes:
Specific inhibitors e,g, AT3 activated by heparin binding
Conc of zymogens:
Dilute clotting factors by blood flow/removal by liver
Digest proteases:
E.g. By protein C
Break down clot (fibrinolysis): By pkasminogen (activated by streptokinase)
Describe how the blood clotting cascade is initiated
Damage to membranes activates intrinsic & extrinsic pathway:
Intrinsic: damaged membrane of vessel promotes binding of factor 11
Extrinsic: trauma releases tissue factor (3)
Zymogens are activated by proteolytic cleavage (mainly proteases): chop off part of a protein
Robertsonian translocation:
Can it be balanced?
What type of gametes can be produced
Yes (normal phenotype): may loos genetic material but may not loos genetic info if all DNA info retained from the 2 chromosomes (2 p arms lost; no genetic info here)
Normal, balanced carrier, trisomy, monosomy
(Depending on how chromosomes line up & split on metaphase plate)
Uniparental disomy:
What kind of daughter cells are possible
When fertilised by a normal parent, what combinations are possible?
What happens if empty daughter cell fertilised with daughter cell with both copies of a chromosome?
1 daughter cell with both pairs of a chromosome, the other with none
Trisomy, monosomy, normal
May inherit both copies of one chromosome from one parent (uniparental disomy)
Due to monosomic & trisomic rescue
But some chromosomes (e.g. XX) have one coy silenced
Describe recombination frequency
How to estimate recombination frequency from a pedigree for an X linked recessive condition
Crossing over of genetic info: how often can it occur
Just look at male offspring from affected female & whether gametes have crossed over or not
(Cant be sure of genotype of females)
Describe protein import into the mitochondrial matrix
Unfolded amphipathic helix binds to import receptor Fed thru TOM pore in outer membrane Moves thru TIM pore in inner membrane Signal sequence cleaved Protein folds
Describe import of protein into the nucleus
Importin binds protein to NLS (the signal)
Ran-GTP binds Importin to nucleus
Conformational change displaces protein
Importin & Ran-GTP recycled & returned to cytoplsam
Signal retained
Describe the secretory pathway (protein processing in the ER)
Signal sequence at N terminus Recognised by/binds to SRP binds to SRP receptor on ER membrane Protein secreted into ER signal sequence cleaved Protein folds in ER packaged into vesicles & secreted
Describe the mechanisms of keeping a protein in the ER
Contains a KDEL sequence at C terminus
If packaged (& folded) into secretory vesicle:
sequence binds to KDEL receptor in cis Golgi
retrograde transport back to ER
Signal retained
No energy required
Describe targeting of a protein to the lysosome
Mannose 6 P added post translationally Signal patch distinguishes lysosomal proteins from other mannose proteins Delivered folded via vesicle Binds to M6P receptor in trans golgi Phosphate removed by phosphatase
