Cells and proteins - 3 Flashcards
what makes up the fluid mosaic model?
- phospholipid bilayer
- globular protein
what does the hydrophobic centre of a membrane allow?
allows oxygen and carbon dioxide to pass through since they are small non-polar molecules
what does the hydrophobic centre act as a barrier to?
acts as a barrier to the passage of charged ions and most polar molecules
what are integral proteins?
proteins embedded in the bilayer
what type of interactions do integral proteins form?
form strong hydrophobic interactions
what type of integral proteins span across the width of the membrane?
transmembrane proteins
what are peripheral proteins?
proteins that are not embedded in the bilayer
what type of bonds do peripheral proteins form?
form weak bonds to the surface of the membrane
whereabouts on the membrane do peripheral proteins bond to?
- heads of phospholipids
- integral proteins
what is a ligand?
any substance that can bind to a protein
what does a binding of a ligand cause?
- conformational change (change in shape)
- change in function
what does protein folding produce?
ligand-binding sites on the surface if the protein
what are ligand-binding sites complementary to?
complementary shape and chemistry to their ligand
what is DNA tightly coiled around?
histone proteins to form nucleosomes
how does DNA act as a ligand?
DNA binds since the negative-charged phosphates of DNA interact with positive-charged R groups on outside of histone
the active site of an enzyme is an example of what?
a ligand-binding site
when enzymes bind to the substrates is there a high or low affinity?
high affinity
what is a modulator?
molecules that bind to secondary sites of enzyme
what is a negative modulator?
inhibits enzyme activity
what is a positive modulator?
activates enzyme activity
how do modulators occur?
by altering the affinity to a substrate
what is co-operativity?
when binding of a molecule to a subunit increases affinity for the other subunits until saturated
explain haemoglobin as an example of co-operativity
- as oxygen binds to one subunit
- affinity of the other subunits change
- increases number of oxygen collected
what does addition/removal of a phosphate cause?
causes a reversible conformational change
what is the addition/removal of a phosphate carried out by?
carried out by enzymes
what is the addition/removal of a phosphate important for?
important in regulation of activity of proteins
what do kinases do?
- catalyse phosphorylation
- adds phosphates
what do phosphates do?
- catalyse dephosphorylation
- removes phosphates
what are ATPases?
enzyme that releases a phosphate from ATP
how to ATPases work?
by phosphorylating themselves
during muscle contraction, what forms the cross bridges?
binding of myosin head to actin
during muscle contraction, what does the binding of ATP cause?
causes a conformational change
during muscle contraction, what causes the third conformational change?
the myosin head rebinding to actin
during muscle contraction, when the ADP + Pi is released from myosin, what does the myosin do?
myosin head swings back dragging actin filament along
what are the two types of transmembrane proteins?
- channel proteins
- transporter proteins
what is the purpose of transmembrane proteins?
needed to allow movement of molecules into and out of the cell
is ATP required to move molecules through channel proteins?
no it is passive transport
what are aquaporins?
ungated channel proteins which allow the free movement of water molecules
what allows ions to move through a ligand gated channel?
when a protein or ligand attaches to the channel causing conformational change
when will a voltage-gated channel open?
opens if there is an ion concentration difference on the inside and outside of cell
if a transporter protein is active it requires what?
ATP
what are the functions of the sodium potassium pump?
- maintenance of osmotic balance in cells
- generates an ion gradient in kidney tubules and neurons
in the sodium potassium pump what changes the conformation to allow the Na ions to be released out of the cell?
a phosphate from hydrolysis of ATP binding to the pump
how many sodiums bind to the sodium potassium pump?
3 Na
how many potassiums bind to the sodium potassium pump?
2 K
is the sodium potassium pump active or facilitated?
active
what does the glucose symport do?
transports glucose from a low to high concentration
is the glucose symport active or facilitated?
facilitated
how many sodiums are transported in the glucose symport?
2 Na
what are receptor proteins?
proteins that have specific binding sites for extracellular hydrophilic signal molecules
what causes a conformational change in receptor proteins?
the binding of chemical signal which triggers a signal transduction pathway
when a signal transduction pathway is triggered what does this cause?
causes a specific intracellular response
what can a signal transduction pathway involve?
- activation of enzyme or G protein
- a change in uptake or secretion of molecules
- activation of proteins that regulate gene transcription
- rearrange the cell’s cytoskeleton
what is nerve transmission?
a wave of depolarisation of a resting potential
what is nerve transmission stimulated by?
stimulated by a signal molecule to open ligand gated channels at synapse
what does the opening of a ligand-gated channel in nerve transmission allow?
allows enough Na ions movement to undergo depolarisation
once depolarisation has passed, what makes the neuron’s membrane potential negative again?
- voltage-gated ions close
- stops Na moving in
- K moves out
what are the 5 changes in membrane potential as an impulse is passed along a neuron?
- resting potential
- depolarisation
- action potential
- repolarisation
- hyperpolarisation
