Proteins Flashcards
What are the characteristics of globular proteins
Compact
soluble
hydrophilic residues outside and hydrophobic residues hidden
What are the characteristics of fibrous proteins
Elongated
repeating amino acid sequences
insoluble due to high hydrophobic amino acid content
What are the two oxygen binding proteins and what are their functions
Myoglobin: O2 store
Haemoglobin: o2 transport
What are the characteristics of myoglobin
highest conc in skeletal and cardiac muscles small protein contains haem prosthetic group Globular protein 8 alpha- helices
What is the haem group
tightly bound to protein
essential for biological activity
What are the advantages of haem associating with protein molecule
Fe atoms kept in Fe2+ form
Binding of other small molecules is inhibited
What are the characteristics of haemoglobin
Four polypeptide chains, containing a haem group each, held together by non-covalent interactions, in a tetrahedral array with overall spherical shape, quaternary structure
Adult: 2 a and 2 B chains
What if O2 affinity for Hb dependent on
pH and CO2
What is the result of oxygen binding to Hb
Alters tertiary and quaternary structure
when one subunit is bound to oxygen the altered shape allows for an increased affinity to oxygen for the other subunits
What is the tense state
more salt bridges between subunits so low affinity for O2
What is the relaxed state
Fewer salt bridges so high affinity for O2
What is the Bohr effect
If pH goes down then decrease of affinity of Hb for O2
Increased CO2 or lactic acid will lower pH
What is BPG (bisphosphoglycerate)
BPG decreases affinity of Hb for O2 so causing more oxygen to be released in high altitude and hypoxia where BPG levels are high
What are the three haemoglobin regulators
H+, CO2, BPG
They act at different sites so their effects are additive
What are the characteristics of Foetal haemoglobin
Binds O2 more strongly than adult
2 a 2 y
What are two inherited disorders which affect haemoglobin synthesis, structure and function
Sickle cell anaemia
B- thalassaemia
How can mutations affect Hb
Amount synthesised structure stability of Hb affinity for O2 affinity for regulators
Why do mutations not always cause disease
Position
Type
What is collagen
Family of fibrous proteins insoluble fibres high tensile strength At least 12 different types of collagen Always consists of three strands
What are the three grouping of collagen types
fibril-forming
network-forming
fibril- associated
What is the primary structure of collagen
Gly- X- Y repeating
What is the secondary structure of collagen
Left handed helix
3.3 residues per turn
What is the quaternary structure of collagen
Triple helix
Right handed twist
What are collagenases
Enzymes used in growth, tissue remodelling, tissue repair by breaking down collagen
What is osteogenesis imperfecta
A range of inherited disorders characterised by increases risk of bone fractures
mutations in type 1 collagen
spontaneous mutation
severity depends on nature of mutation
What is the relevance of enzymology to medicine
drug action
biochemical defects in enzymes underlie disease
clinical diagnosis/prognosis
What are enzymes and how do they work
Biological catalysts of chemical reactions
Specific action on particular substrates
increase rate at which equilibrium is reached but do not shift the position of equilibrium
What is an assay
A procedure for measuring the biochemical or immunological activity of a sample
What is Michaelis constant
Km = (k2 + k3)/ k1
Measure of the affinity of an enzyme for its substrate
What factors affect enzyme activity
Substrate conc
Temperature
pH
Inhibitors
How do irreversible inhibitors work
covalent modification of amino acid side chains in the active site
What is the IC50
Inhibitory conc that knocks out 50% of the activity
What cofactors are essential for enzyme function
metal ions
coenzyme
vitamins
What happens if you have a G6PDH deficiency and are exposed to drugs which produce free radicles
Haemolytic crisis
What is the function of protein kinases
phosphorylation of enzymes
What is the function of protein phosphatases
removal of phosphate groups
What are the four types of control of enzyme activity
Inhibition (reversible or irreversible)
Feedback regulation
Covalent modification
Proteolytic activation
How can enzyme presence indicate tissue damage
reduced levels of secreted enzymes in blood indicate damage to secreting tissues
Presence of intracellular enzymes in serum indicates tissue damage
Why is time after injury crucial for using enzymes as indicators for damaged cells
the half-life of enzymes in the blood stream varies
What does the unit IU mean
measure of enzyme activity
1 IU is the amount of activity that will convert 1 micromole of substrate per minute under standard defined conditions
